range: extmarks/tsquery; renderer: text-change

It seems that closures are not interacting well with the global nature
of operatorfunc's. That is just a hunch, and this feels like a hack, but
it fixes the issue.

.busted

@@ -0,0 +1,13 @@
+return {
+  _all = {
+    coverage = false,
+    lpath = "lua/?.lua;lua/?/init.lua",
+    lua = "nvim -u NONE -i NONE -l",
+  },
+  default = {
+    verbose = true
+  },
+  tests = {
+    verbose = true
+  },
+}

.github/workflows/ci.yaml

@@ -2,14 +2,28 @@
 name: NeoVim tests
 on: [push]
 jobs:
-  plenary-tests:
+  code-quality:
     runs-on: ubuntu-latest
     env:
       XDG_CONFIG_HOME: ${{ github.workspace }}/.config/
     steps:
       - uses: actions/checkout@v4
-      - uses: rhysd/action-setup-vim@v1
+      - uses: cachix/install-nix-action@v31
         with:
-          neovim: true
-          version: v0.10.1
-      - run: make test
+          nix_path: nixpkgs=channel:nixos-unstable
+
+      - name: Populate Nix store
+        run:
+          nix-shell --pure --run 'true'
+
+      - name: Type-check with lua-language-server
+        run:
+          nix-shell --pure --run 'make lint'
+
+      - name: Check formatting with stylua
+        run:
+          nix-shell --pure --run 'make fmt-check'
+
+      - name: Run busted tests
+        run:
+          nix-shell --pure --run 'make test'

.gitignore

@@ -1 +1,3 @@
 *.src.rock
+*.aider*
+luacov.*.out

.luacheckrc

@@ -0,0 +1,2 @@
+-- :vim set ft=lua
+globals = { "vim" }

.luacov

@@ -0,0 +1,6 @@
+return {
+  include = {
+    'lua/u/',
+  },
+  tick = true,
+}

.woodpecker/ci.yaml

@@ -0,0 +1,10 @@
+when:
+  - event: push
+
+steps:
+  - name: build
+    image: nixos/nix
+    commands:
+      - nix-shell --pure --run 'make lint'
+      - nix-shell --pure --run 'make fmt-check'
+      - nix-shell --pure --run 'make test'

Makefile

@@ -1,15 +1,24 @@
-PLENARY_DIR=~/.local/share/nvim/site/pack/test/opt/plenary.nvim
-
-all: lint test
+all: lint fmt-check test
 
 lint:
-	selene .
+	@echo "## Typechecking"
+	@lua-language-server --check=lua/u/ --checklevel=Error
+
+fmt-check:
+	@echo "## Checking code format"
+	@stylua --check .
 
 fmt:
-	stylua .
+	@echo "## Formatting code"
+	@stylua .
 
-test: $(PLENARY_DIR)
-	NVIM_APPNAME=noplugstest nvim -u NORC --headless -c 'set packpath+=~/.local/share/nvim/site' -c 'packadd plenary.nvim' -c "PlenaryBustedDirectory spec/"
+test:
+	@rm -f luacov.*.out
+	@echo "## Running tests"
+	@busted --coverage --verbose
+	@echo "## Generating coverage report"
+	@luacov
+	@awk '/^Summary$$/{flag=1;next} flag{print}' luacov.report.out
 
-$(PLENARY_DIR):
-	git clone https://github.com/nvim-lua/plenary.nvim/ $(PLENARY_DIR)
+watch:
+	@watchexec -c -e lua make

README.md

@@ -1,26 +1,40 @@
 # u.nvim
 
-Welcome to **u.nvim** – a powerful Lua library designed to enhance your text manipulation experience in NeoVim, focusing primarily on a context-aware "Range" utility. This utility allows you to work efficiently with text selections based on various conditions, in a variety of contexts, making coding and editing more intuitive and productive.
+Welcome to **u.nvim** - a powerful Lua library designed to enhance your text
+manipulation experience in NeoVim, focusing on text-manipulation utilities.
+This includes a `Range` utility, allowing you to work efficiently with text
+selections based on various conditions, as well as a declarative `Render`-er,
+making coding and editing more intuitive and productive.
 
-This is meant to be used as a **library**, not a plugin. On its own, `u.nvim` does nothing. It is meant to be used by plugin authors, to make their lives easier based on the variety of utilities I found I needed while growing my NeoVim config. To get an idea of what a plugin built on top of `u.nvim` would look like, check out the [examples/](./examples/) directory.
+This is meant to be used as a **library**, not a plugin. On its own, `u.nvim`
+does nothing. It is meant to be used by plugin authors, to make their lives
+easier based on the variety of utilities I found I needed while growing my
+NeoVim config. To get an idea of what a plugin built on top of `u.nvim` would
+look like, check out the [examples/](./examples/) directory.
 
 ## Features
 
-- **Rendering System**: a utility that can declaratively render NeoVim-specific hyperscript into a buffer, supporting creating/managing extmarks, highlights, and key-event handling (requires NeoVim >0.11)
-- **Signals**: a simple dependency tracking system that pairs well with the rendering utilities for creating reactive/interactive UIs in NeoVim.
-- **Range Utility**: Get context-aware selections with ease. Replace regions with new text. Think of it as a programmatic way to work with visual selections (or regions of text).
+- **Rendering System**: a utility that can declaratively render NeoVim-specific
+  hyperscript into a buffer, supporting creating/managing extmarks, highlights,
+  and key-event handling (requires NeoVim >0.11)
+- **Signals**: a simple dependency tracking system that pairs well with the
+  rendering utilities for creating reactive/interactive UIs in NeoVim.
+- **Range Utility**: Get context-aware selections with ease. Replace regions
+  with new text. Think of it as a programmatic way to work with visual
+  selections (or regions of text).
 - **Code Writer**: Write code with automatic indentation and formatting.
-- **Operator Key Mapping**: Flexible key mapping that works with the selected text.
-- **Text and Position Utilities**: Convenient functions to manage text objects and cursor positions.
+- **Operator Key Mapping**: Flexible key mapping that works with the selected
+  text.
+- **Text and Position Utilities**: Convenient functions to manage text objects
+  and cursor positions.
 
 ### Installation
 
-lazy.nvim:
-```lua
--- Setting `lazy = true` ensures that the library is only loaded
--- when `require 'u.<utility>' is called.
-{ 'jrop/u.nvim', lazy = true }
-```
+This being a library, and not a proper plugin, it is recommended that you
+vendor the specific version of this library that you need, including it in your
+code. Package managers are a developing landscape for Lua in the context of
+NeoVim. Perhaps in the future, `lux` will eliminate the need to vendor this
+library in your application code.
 
 ## Signal and Rendering Usage
 
@@ -111,7 +125,9 @@ end)
 
 ### `u.tracker`
 
-The `u.tracker` module provides a simple API for creating reactive variables. These can be composed in Effects and Memos utilizing Execution Contexts that track what signals are used by effects/memos.
+The `u.tracker` module provides a simple API for creating reactive variables.
+These can be composed in Effects and Memos utilizing Execution Contexts that
+track what signals are used by effects/memos.
 
 ```lua
 local tracker = require('u.tracker')
@@ -134,7 +150,8 @@ The renderer library renders hyperscript into a buffer. Each render performs a
 minimal set of changes in order to transform the current buffer text into the
 desired state.
 
-**Hyperscript** is just 1) _text_ 2) `<text>` tags, which can be nested in 3) Lua tables for readability:
+**Hyperscript** is just 1) _text_ 2) `<text>` tags, which can be nested in 3)
+Lua tables for readability:
 
 ```lua
 local h = require('u.renderer').h
@@ -196,7 +213,8 @@ renderer:render(
 )
 ```
 
-**Rendering**: The renderer library provides a `render` function that takes hyperscript in, and converts it to formatted buffer text:
+**Rendering**: The renderer library provides a `render` function that takes
+hyperscript in, and converts it to formatted buffer text:
 
 ```lua
 local Renderer = require('u.renderer').Renderer
@@ -217,37 +235,68 @@ buf:render {
 
 ### A note on indices
 
-I love NeoVim. I am coming to love Lua. I don't like 1-based indices; perhaps I am too old. Perhaps I am too steeped in the history of loving the elegance of simple pointer arithmetic. Regardless, the way positions are addressed in NeoVim/Vim is (terrifyingly) mixed. Some methods return 1-based, others accept only 0-based. In order to stay sane, I had to make a choice to store everything in one, uniform representation in this library. I chose (what I humbly think is the only sane way) to stick with the tried-and-true 0-based index scheme. That abstraction leaks into the public API of this library.
+<blockquote>
+<del>
+I love NeoVim. I am coming to love Lua. I don't like 1-based indices; perhaps I
+am too old. Perhaps I am too steeped in the history of loving the elegance of
+simple pointer arithmetic. Regardless, the way positions are addressed in
+NeoVim/Vim is (terrifyingly) mixed. Some methods return 1-based, others accept
+only 0-based. In order to stay sane, I had to make a choice to store everything
+in one, uniform representation in this library. I chose (what I humbly think is
+the only sane way) to stick with the tried-and-true 0-based index scheme. That
+abstraction leaks into the public API of this library.
+</del>
+</blockquote>
+
+<br />
+<b>This has changed in v2</b>. After much thought, I realized that:
+
+1. The 0-based indexing in NeoVim is prevelant in the `:api`, which is designed
+   to be exposed to many languages. As such, it makes sense for this interface
+   to use 0-based indexing. However, many internal Vim functions use 1-based
+   indexing.
+2. This is a Lua library (surprise, surprise, duh) - the idioms of the language
+   should take precedence over my preference
+3. There were subtle bugs in the code where indices weren't being normalized to
+   0-based, anyways. Somehow it worked most of the time.
+
+As such, this library now uses 1-based indexing everywhere, doing the necessary
+interop conversions when calling `:api` functions.
 
 ### 1. Creating a Range
 
-The `Range` utility is the main feature upon which most other things in this library are built, aside from a few standalone utilities. Ranges can be constructed manually, or preferably, obtained based on a variety of contexts.
+The `Range` utility is the main feature upon which most other things in this
+library are built, aside from a few standalone utilities. Ranges can be
+constructed manually, or preferably, obtained based on a variety of contexts.
 
 ```lua
 local Range = require 'u.range'
-local start = Pos.new(0, 0, 0) -- Line 1, first column
-local stop = Pos.new(0, 2, 0) -- Line 3, first column
+local start = Pos.new(0, 1, 1) -- Line 1, first column
+local stop = Pos.new(0, 3, 1) -- Line 3, first column
 
 Range.new(start, stop, 'v') -- charwise selection
 Range.new(start, stop, 'V') -- linewise selection
 ```
 
-This is usually not how you want to obtain a `Range`, however. Usually you want to get the corresponding context of an edit operation and just "get me the current Range that represents this context".
+This is usually not how you want to obtain a `Range`, however. Usually you want
+to get the corresponding context of an edit operation and just "get me the
+current Range that represents this context".
 
 ```lua
 -- get the first line in a buffer:
-Range.from_line(0, 0)
+Range.from_line(bufnr, 1)
 
 -- Text Objects (any text object valid in your configuration is supported):
 -- get the word the cursor is on:
-Range.from_text_object('iw')
+Range.from_motion('iw')
 -- get the WORD the cursor is on:
-Range.from_text_object('iW')
+Range.from_motion('iW')
 -- get the "..." the cursor is within:
-Range.from_text_object('a"')
+Range.from_motion('a"')
 
 -- Get the currently visually selected text:
--- NOTE: this does NOT work within certain contexts; more specialized utilities are more appropriate in certain circumstances
+-- NOTE: this does NOT work within certain contexts; more specialized utilities
+-- are more appropriate in certain circumstances
 Range.from_vtext()
 
 --
@@ -259,7 +308,8 @@ function MyOpFunc(ty)
   local range = Range.from_op_func(ty)
   -- do something with the range
 end
--- Try invoking this with: `<Leader>toaw`, and the current word will be the context:
+-- Try invoking this with: `<Leader>toaw`, and the current word will be the
+-- context:
 vim.keymap.set('<Leader>to', function()
   vim.g.operatorfunc = 'v:lua.MyOpFunc'
   return 'g@'
@@ -268,7 +318,8 @@ end, { expr = true })
 --
 -- Commands:
 --
--- When executing commands in a visual context, getting the selected text has to be done differently:
+-- When executing commands in a visual context, getting the selected text has
+-- to be done differently:
 vim.api.nvim_create_user_command('MyCmd', function(args)
   local range = Range.from_cmd_args(args)
   if range == nil then
@@ -279,14 +330,15 @@ vim.api.nvim_create_user_command('MyCmd', function(args)
 end, { range = true })
 ```
 
-So far, that's a lot of ways to _get_ a `Range`. But what can you do with a range once you have one? Plenty, it turns out!
+So far, that's a lot of ways to _get_ a `Range`. But what can you do with a
+range once you have one? Plenty, it turns out!
 
 ```lua
 local range = ...
 range:lines() -- get the lines in the range's region
 range:text() -- get the text (i.e., string) in the range's region
-range:line0(0) -- get the first line within this range
-range:line0(-1) -- get the last line within this range
+range:line(1) -- get the first line within this range
+range:line(-1) -- get the last line within this range
 -- replace with new contents:
 range:replace {
   'replacement line 1',
@@ -333,11 +385,11 @@ Simply by returning a `Range` or a `Pos`, you can easily and quickly define
 your own text objects:
 
 ```lua
-local utils = require 'u.utils'
+local txtobj = require 'u.txtobj'
 local Range = require 'u.range'
 
 -- Select whole file:
-utils.define_text_object('ag', function()
+txtobj.define('ag', function()
   return Range.from_buf_text()
 end)
 ```
@@ -349,27 +401,39 @@ Access and manipulate buffers easily:
 ```lua
 local Buffer = require 'u.buffer'
 local buf = Buffer.current()
+buf.b.<option>        -- get buffer-local variables
+buf.b.<option>  = ... -- set buffer-local variables
+buf.bo.<option>       -- get buffer options
+buf.bo.<option> = ... -- set buffer options
 buf:line_count()      -- the number of lines in the current buffer
-buf:get_option '...'
-buf:set_option('...', ...)
-buf:get_var '...'
-buf:set_var('...', ...)
 buf:all()             -- returns a Range representing the entire buffer
 buf:is_empty()        -- returns true if the buffer has no text
 buf:append_line '...'
-buf:line0(0) -- returns a Range representing the first line in the buffer
-buf:line0(-1) -- returns a Range representing the last line in the buffer
-buf:lines(0, 1) -- returns a Range representing the first two lines in the buffer
-buf:lines(1, -2) -- returns a Range representing all but the first and last lines of a buffer
-buf:text_object('iw') -- returns a Range representing the text object 'iw' in the give buffer
+buf:line(1)           -- returns a Range representing the first line in the buffer
+buf:line(-1)          -- returns a Range representing the last line in the buffer
+buf:lines(1, 2)       -- returns a Range representing the first two lines in the buffer
+buf:lines(2, -2)      -- returns a Range representing all but the first and last lines of a buffer
+buf:txtobj('iw')      -- returns a Range representing the text object 'iw' in the give buffer
 ```
 
 ## License (MIT)
 
 Copyright (c) 2024 jrapodaca@gmail.com
 
-Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
 
-The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

examples/counter.lua

@@ -1,5 +1,5 @@
-local tracker = require 'u.tracker'
 local Buffer = require 'u.buffer'
+local tracker = require 'u.tracker'
 local h = require('u.renderer').h
 
 -- Create an buffer for the UI

examples/filetree.lua

@@ -10,10 +10,10 @@
 --   change on the underlying filesystem.
 --------------------------------------------------------------------------------
 
---- @alias FsDir { kind: 'dir'; path: string; expanded: boolean; children: FsNode[] }
---- @alias FsFile { kind: 'file'; path: string }
---- @alias FsNode FsDir | FsFile
---- @alias ShowOpts { root_path?: string, width?: number, focus_path?: string }
+--- @alias u.examples.FsDir { kind: 'dir'; path: string; expanded: boolean; children: u.examples.FsNode[] }
+--- @alias u.examples.FsFile { kind: 'file'; path: string }
+--- @alias u.examples.FsNode u.examples.FsDir | u.examples.FsFile
+--- @alias u.examples.ShowOpts { root_path?: string, width?: number, focus_path?: string }
 
 local Buffer = require 'u.buffer'
 local Renderer = require('u.renderer').Renderer
@@ -44,11 +44,7 @@ end
 
 --- Normalizes the given path to an absolute path.
 --- @param path string
-function H.normalize(path)
-  path = vim.fs.normalize(path)
-  if path:sub(1, 1) ~= '/' then path = vim.fs.joinpath(vim.uv.cwd(), path) end
-  return vim.fs.normalize(path)
-end
+function H.normalize(path) return vim.fs.abspath(vim.fs.normalize(path)) end
 
 --- Computes the relative path from `base` to `path`.
 --- @param path string
@@ -62,13 +58,13 @@ function H.relative(path, base)
 end
 
 --- @param root_path string
---- @return { tree: FsDir; path_to_node: table<string, FsNode> }
+--- @return { tree: u.examples.FsDir; path_to_node: table<string, u.examples.FsNode> }
 function H.get_tree_inf(root_path)
   logger:info { 'get_tree_inf', root_path }
-  --- @type table<string, FsNode>
+  --- @type table<string, u.examples.FsNode>
   local path_to_node = {}
 
-  --- @type FsDir
+  --- @type u.examples.FsDir
   local tree = {
     kind = 'dir',
     path = H.normalize(root_path or '.'),
@@ -81,8 +77,8 @@ function H.get_tree_inf(root_path)
   return { tree = tree, path_to_node = path_to_node }
 end
 
---- @param tree FsDir
---- @param path_to_node table<string, FsNode>
+--- @param tree u.examples.FsDir
+--- @param path_to_node table<string, u.examples.FsNode>
 function H.populate_dir_children(tree, path_to_node)
   tree.children = {}
 
@@ -125,7 +121,10 @@ end
 ---
 --- @return { expand: fun(path: string), collapse: fun(path: string) }
 local function _render_in_buffer(opts)
-  local winnr = vim.api.nvim_buf_call(opts.bufnr, function() return vim.api.nvim_get_current_win() end)
+  local winnr = vim.api.nvim_buf_call(
+    opts.bufnr,
+    function() return vim.api.nvim_get_current_win() end
+  )
   local s_tree_inf = tracker.create_signal(H.get_tree_inf(opts.root_path))
   local s_focused_path = tracker.create_signal(H.normalize(opts.focus_path or opts.root_path))
 
@@ -136,7 +135,7 @@ local function _render_in_buffer(opts)
       local parts = H.split_path(H.relative(focused_path, tree_inf.tree.path))
       local path_to_node = tree_inf.path_to_node
 
-      --- @param node FsDir
+      --- @param node u.examples.FsDir
       --- @param child_names string[]
       local function expand_to(node, child_names)
         if #child_names == 0 then return end
@@ -155,19 +154,35 @@ local function _render_in_buffer(opts)
     end)
   end)
 
-  -- --
-  -- -- TODO: :help watch-file
-  -- --
-  -- local watcher = vim.uv.new_fs_event()
-  -- if watcher ~= nil then
-  --   watcher:start(root_path, { recursive = true }, function(err, fname, status)
-  --     -- TODO: more efficient update:
-  --     s_tree_inf:set(H.get_tree(root_path))
   --
-  --     -- TODO: proper disposal
-  --     watcher:stop()
-  --   end)
-  -- end
+  -- :help watch-file
+  --
+  local watcher = vim.uv.new_fs_event()
+  if watcher ~= nil then
+    --- @diagnostic disable-next-line: unused-local
+    watcher:start(opts.root_path, { recursive = true }, function(_err, fname, _status)
+      fname = H.normalize(fname)
+
+      local dir_path = vim.fs.dirname(fname)
+      local dir = s_tree_inf:get().path_to_node[dir_path]
+      if not dir then return end
+
+      s_tree_inf:schedule_update(function(tree_inf)
+        H.populate_dir_children(dir, tree_inf.path_to_node)
+        return tree_inf
+      end)
+    end)
+  end
+  vim.api.nvim_create_autocmd('WinClosed', {
+    once = true,
+    pattern = tostring(winnr),
+    callback = function()
+      if watcher == nil then return end
+
+      watcher:stop()
+      watcher = nil
+    end,
+  })
 
   local controller = {}
 
@@ -295,7 +310,7 @@ local function _render_in_buffer(opts)
   --
   local renderer = Renderer.new(opts.bufnr)
   tracker.create_effect(function()
-    --- @type { tree: FsDir; path_to_node: table<string, FsNode> }
+    --- @type { tree: u.examples.FsDir; path_to_node: table<string, u.examples.FsNode> }
     local tree_inf = s_tree_inf:get()
     local tree = tree_inf.tree
 
@@ -314,7 +329,7 @@ local function _render_in_buffer(opts)
 
     --- Since the filesystem is a recursive tree of nodes, we need to
     --- recursively render each node. This function does just that:
-    --- @param node FsNode
+    --- @param node u.examples.FsNode
     --- @param level number
     local function render_node(node, level)
       local name = vim.fs.basename(node.path)
@@ -331,7 +346,11 @@ local function _render_in_buffer(opts)
           return ''
         end,
         n = function()
-          vim.schedule(function() controller.new(node.kind == 'file' and vim.fs.dirname(node.path) or node.path) end)
+          vim.schedule(
+            function()
+              controller.new(node.kind == 'file' and vim.fs.dirname(node.path) or node.path)
+            end
+          )
           return ''
         end,
         r = function()
@@ -351,7 +370,11 @@ local function _render_in_buffer(opts)
         local icon = node.expanded and '' or ''
         tb:put {
           current_line > 1 and '\n',
-          h('text', { hl = 'Constant', nmap = nmaps }, { string.rep('  ', level), icon, ' ', name }),
+          h(
+            'text',
+            { hl = 'Constant', nmap = nmaps },
+            { string.rep('  ', level), icon, ' ', name }
+          ),
         }
         if node.expanded then
           for _, child in ipairs(node.children) do
@@ -391,7 +414,7 @@ end
 local current_inf = nil
 
 --- Show the filetree:
---- @param opts? ShowOpts
+--- @param opts? u.examples.ShowOpts
 function M.show(opts)
   if current_inf ~= nil then return current_inf.controller end
   opts = opts or {}
@@ -411,8 +434,8 @@ function M.show(opts)
     callback = M.hide,
   })
 
-  vim.wo.number = false
-  vim.wo.relativenumber = false
+  vim.wo[0][0].number = false
+  vim.wo[0][0].relativenumber = false
 
   local bufnr = vim.api.nvim_get_current_buf()
 
@@ -433,7 +456,7 @@ function M.hide()
 end
 
 --- Toggle the filetree:
---- @param opts? ShowOpts
+--- @param opts? u.examples.ShowOpts
 function M.toggle(opts)
   if current_inf == nil then
     M.show(opts)

examples/form.lua

@@ -0,0 +1,117 @@
+-- form.lua:
+--
+-- This is a runnable example of a form. Open this file in Neovim, and execute
+-- `:luafile %` to run it. It will create a new buffer to the side, and render
+-- an interactive form. Edit the "inputs" between the `[...]` brackets, and
+-- watch the buffer react immediately to your changes.
+--
+
+local Renderer = require('u.renderer').Renderer
+local h = require('u.renderer').h
+local tracker = require 'u.tracker'
+
+-- Create a new, temporary, buffer to the side:
+vim.cmd.vnew()
+vim.bo.buftype = 'nofile'
+vim.bo.bufhidden = 'wipe'
+vim.bo.buflisted = false
+local renderer = Renderer.new()
+
+-- Create two signals:
+local s_name = tracker.create_signal 'whoever-you-are'
+local s_age = tracker.create_signal 'ideally-a-number'
+
+-- We can create derived information from the signals above. Say we want to do
+-- some validation on the input for `age`: we can do that with a memo:
+local s_age_info = tracker.create_memo(function()
+  local age_raw = s_age:get()
+  local age_digits = age_raw:match '^%s*(%d+)%s*$'
+  local age_n = age_digits and tonumber(age_digits) or nil
+  return {
+    type = age_n and 'number' or 'string',
+    raw = age_raw,
+    n = age_n,
+    n1 = age_n and age_n + 1 or nil,
+  }
+end)
+
+-- This is the render effect that depends on the signals created above. This
+-- will re-run every time one of the signals changes.
+tracker.create_effect(function()
+  local name = s_name:get()
+  local age = s_age:get()
+  local age_info = s_age_info:get()
+
+  -- Each time the signals change, we re-render the buffer:
+  renderer:render {
+    h.Type({}, '# Form Example'),
+    '\n\n',
+
+    -- We can also listen for when specific locations in the buffer change, on
+    -- a tag-by-tag basis. This gives us two-way data-binding between the
+    -- buffer and the signals.
+    {
+      'Name: ',
+      h.Structure({
+        on_change = function(text) s_name:set(text) end,
+      }, name),
+    },
+    {
+      '\nAge: ',
+      h.Structure({
+        on_change = function(text) s_age:set(text) end,
+      }, age),
+    },
+
+    '\n\n',
+
+    -- Show the values of the signals here, too, so that we can see the
+    -- reactivity in action. If you change the values in the tags above, you
+    -- can see the changes reflected here immediately.
+    { 'Hello, "', name, '"!' },
+
+    --
+    -- A more complex example: we can do much more complex rendering, based on
+    -- the state. For example, if you type different values into the `age`
+    -- field, you can see not only the displayed information change, but also
+    -- the color of the highlights in this section will adapt to the type of
+    -- information that has been detected.
+    --
+    -- If string input is detected, values below are shown in the
+    -- `String`/`ErrorMsg` highlight groups.
+    --
+    -- If number input is detected, values below are shown in the `Number`
+    -- highlight group.
+    --
+    -- If a valid number is entered, then this section also displays how old
+    -- you willl be next year (`n + 1`).
+    --
+
+    '\n\n',
+    h.Type({}, '## Computed Information (derived from `age`)'),
+    '\n\n',
+    {
+      'Type: ',
+      h('text', {
+        hl = age_info.type == 'number' and 'Number' or 'String',
+      }, age_info.type),
+    },
+    { '\nRaw input: ', h.String({}, '"' .. age_info.raw .. '"') },
+    {
+      '\nCurrent age: ',
+      age_info.n
+          -- Show the age:
+          and h.Number({}, tostring(age_info.n))
+        -- Show an error-placeholder if the age is invalid:
+        or h.ErrorMsg({}, '(?)'),
+    },
+
+    -- This part is shown conditionally, i.e., only if the age next year can be
+    -- computed:
+    age_info.n1
+      and {
+        '\nAge next year: ',
+        h.Number({}, tostring(age_info.n1)),
+      },
+  }
+end)

examples/notify.lua

@@ -1,8 +1,7 @@
-local Buffer = require 'u.buffer'
+local Renderer = require('u.renderer').Renderer
 local TreeBuilder = require('u.renderer').TreeBuilder
 local tracker = require 'u.tracker'
 local utils = require 'u.utils'
-local Window = require 'my.window'
 
 local TIMEOUT = 4000
 local ICONS = {
@@ -14,15 +13,25 @@ local ICONS = {
 }
 local DEFAULT_ICON = { text = '', group = 'DiagnosticSignOk' }
 
---- @alias Notification {
+local S_EDITOR_DIMENSIONS =
+  tracker.create_signal(utils.get_editor_dimensions(), 's:editor_dimensions')
+vim.api.nvim_create_autocmd('VimResized', {
+  callback = function()
+    local new_dim = utils.get_editor_dimensions()
+    S_EDITOR_DIMENSIONS:set(new_dim)
+  end,
+})
+
+--- @alias u.examples.Notification {
 ---   kind: number;
 ---   id: number;
 ---   text: string;
+---   timer: uv.uv_timer_t;
 --- }
 
 local M = {}
 
---- @type Window | nil
+--- @type { win: integer, buf: integer, renderer: u.renderer.Renderer } | nil
 local notifs_w
 
 local s_notifications_raw = tracker.create_signal {}
@@ -30,44 +39,49 @@ local s_notifications = s_notifications_raw:debounce(50)
 
 -- Render effect:
 tracker.create_effect(function()
-  --- @type Notification[]
+  --- @type u.examples.Notification[]
   local notifs = s_notifications:get()
+  --- @type { width: integer, height: integer }
+  local editor_size = S_EDITOR_DIMENSIONS:get()
 
   if #notifs == 0 then
     if notifs_w then
-      notifs_w:close(true)
+      if vim.api.nvim_win_is_valid(notifs_w.win) then vim.api.nvim_win_close(notifs_w.win, true) end
       notifs_w = nil
     end
     return
   end
 
-  vim.schedule(function()
-    local editor_size = utils.get_editor_dimensions()
   local avail_width = editor_size.width
   local float_width = 40
+  local float_height = math.min(#notifs, editor_size.height - 3)
   local win_config = {
     relative = 'editor',
     anchor = 'NE',
     row = 0,
     col = avail_width,
     width = float_width,
-      height = math.min(#notifs, editor_size.height - 3),
+    height = float_height,
     border = 'single',
     focusable = false,
+    zindex = 900,
   }
+  vim.schedule(function()
     if not notifs_w or not vim.api.nvim_win_is_valid(notifs_w.win) then
-      notifs_w = Window.new(Buffer.create(false, true), win_config)
-      vim.wo[notifs_w.win].cursorline = false
-      vim.wo[notifs_w.win].list = false
-      vim.wo[notifs_w.win].listchars = ''
-      vim.wo[notifs_w.win].number = false
-      vim.wo[notifs_w.win].relativenumber = false
-      vim.wo[notifs_w.win].wrap = false
+      local b = vim.api.nvim_create_buf(false, true)
+      local w = vim.api.nvim_open_win(b, false, win_config)
+      vim.wo[w].cursorline = false
+      vim.wo[w].list = false
+      vim.wo[w].listchars = ''
+      vim.wo[w].number = false
+      vim.wo[w].relativenumber = false
+      vim.wo[w].wrap = false
+      notifs_w = { win = w, buf = b, renderer = Renderer.new(b) }
     else
-      notifs_w:set_config(win_config)
+      vim.api.nvim_win_set_config(notifs_w.win, win_config)
     end
 
-    notifs_w:render(TreeBuilder.new()
+    notifs_w.renderer:render(TreeBuilder.new()
       :nest(function(tb)
         for idx, notif in ipairs(notifs) do
           if idx > 1 then tb:put '\n' end
@@ -79,48 +93,81 @@ tracker.create_effect(function()
       end)
       :tree())
     vim.api.nvim_win_call(notifs_w.win, function()
-      -- scroll to bottom:
-      vim.cmd.normal 'G'
-      -- scroll all the way to the left:
-      vim.cmd.normal '9999zh'
+      vim.fn.winrestview {
+        -- scroll all the way left:
+        leftcol = 0,
+        -- set the bottom line to be at the bottom of the window:
+        topline = vim.api.nvim_buf_line_count(notifs_w.buf) - win_config.height + 1,
+      }
     end)
   end)
 end)
 
-local _orig_notify
-
---- @param msg string
---- @param level integer|nil
---- @param opts table|nil
-local function my_notify(msg, level, opts)
-  vim.schedule(function() _orig_notify(msg, level, opts) end)
-  if level == nil then level = vim.log.levels.INFO end
-  if level < vim.log.levels.INFO then return end
-
-  local id = math.random(math.huge)
-
-  --- @param notifs Notification[]
-  s_notifications_raw:schedule_update(function(notifs)
-    table.insert(notifs, { kind = level, id = id, text = msg })
-    return notifs
-  end)
-
-  vim.defer_fn(function()
-    --- @param notifs Notification[]
+--- @param id number
+local function _delete_notif(id)
+  --- @param notifs u.examples.Notification[]
   s_notifications_raw:schedule_update(function(notifs)
     for i, notif in ipairs(notifs) do
       if notif.id == id then
+        notif.timer:stop()
+        notif.timer:close()
         table.remove(notifs, i)
         break
       end
     end
     return notifs
   end)
-  end, TIMEOUT)
+end
+
+local _orig_notify
+
+--- @param msg string
+--- @param level integer|nil
+--- @param opts? { id: number }
+function M.notify(msg, level, opts)
+  if level == nil then level = vim.log.levels.INFO end
+
+  opts = opts or {}
+  local id = opts.id or math.random(999999999)
+
+  --- @type u.examples.Notification?
+  local notif = vim.iter(s_notifications_raw:get()):find(function(n) return n.id == id end)
+  if not notif then
+    -- Create a new notification (maybe):
+    if vim.trim(msg) == '' then return id end
+    if level < vim.log.levels.INFO then return id end
+
+    local timer = assert((vim.uv or vim.loop).new_timer(), 'could not create timer')
+    timer:start(TIMEOUT, 0, function() _delete_notif(id) end)
+    notif = {
+      id = id,
+      kind = level,
+      text = msg,
+      timer = timer,
+    }
+    --- @param notifs u.examples.Notification[]
+    s_notifications_raw:schedule_update(function(notifs)
+      table.insert(notifs, notif)
+      return notifs
+    end)
+  else
+    -- Update an existing notification:
+    s_notifications_raw:schedule_update(function(notifs)
+      -- We already have a copy-by-reference of the notif we want to modify:
+      notif.timer:stop()
+      notif.text = msg
+      notif.kind = level
+      notif.timer:start(TIMEOUT, 0, function() _delete_notif(id) end)
+
+      return notifs
+    end)
+  end
+
+  return id
 end
 
 local _once_msgs = {}
-local function my_notify_once(msg, level, opts)
+function M.notify_once(msg, level, opts)
   if vim.tbl_contains(_once_msgs, msg) then return false end
   table.insert(_once_msgs, msg)
   vim.notify(msg, level, opts)
@@ -130,8 +177,8 @@ end
 function M.setup()
   if _orig_notify == nil then _orig_notify = vim.notify end
 
-  vim.notify = my_notify
-  vim.notify_once = my_notify_once
+  vim.notify = M.notify
+  vim.notify_once = M.notify_once
 end
 
 return M

examples/picker.lua

@@ -1,5 +1,5 @@
-local utils = require 'u.utils'
 local Buffer = require 'u.buffer'
+local utils = require 'u.utils'
 local Renderer = require('u.renderer').Renderer
 local h = require('u.renderer').h
 local TreeBuilder = require('u.renderer').TreeBuilder
@@ -7,7 +7,8 @@ local tracker = require 'u.tracker'
 
 local M = {}
 
-local S_EDITOR_DIMENSIONS = tracker.create_signal(utils.get_editor_dimensions(), 's:editor_dimensions')
+local S_EDITOR_DIMENSIONS =
+  tracker.create_signal(utils.get_editor_dimensions(), 's:editor_dimensions')
 vim.api.nvim_create_autocmd('VimResized', {
   callback = function()
     local new_dim = utils.get_editor_dimensions()
@@ -43,7 +44,7 @@ local function shallow_copy_arr(arr) return vim.iter(arr):totable() end
 --    shortest portion of this function.
 --------------------------------------------------------------------------------
 
---- @alias SelectController {
+--- @alias u.examples.SelectController {
 ---   get_items: fun(): T[];
 ---   set_items: fun(items: T[]);
 ---   set_filter_text: fun(filter_text: string);
@@ -52,18 +53,18 @@ local function shallow_copy_arr(arr) return vim.iter(arr):totable() end
 ---   set_selected_indices: fun(indicies: number[], ephemeral?: boolean);
 ---   close: fun();
 --- }
---- @alias SelectOpts<T> {
+--- @alias u.examples.SelectOpts<T> {
 ---   items: `T`[];
 ---   multi?: boolean;
----   format_item?: fun(item: T): Tree;
+---   format_item?: fun(item: T): u.renderer.Tree;
 ---   on_finish?: fun(items: T[], indicies: number[]);
 ---   on_selection_changed?: fun(items: T[], indicies: number[]);
----   mappings?: table<string, fun(select: SelectController)>;
+---   mappings?: table<string, fun(select: u.examples.SelectController)>;
 --- }
 
 --- @generic T
---- @param opts SelectOpts<T>
-function M.create_picker(opts)
+--- @param opts u.examples.SelectOpts<T>
+function M.create_picker(opts) -- {{{
   local is_in_insert_mode = vim.api.nvim_get_mode().mode:sub(1, 1) == 'i'
   local stopinsert = not is_in_insert_mode
 
@@ -145,17 +146,19 @@ function M.create_picker(opts)
     col = s_w_input_coords:get().col,
     relative = 'editor',
     focusable = true,
-    border = 'rounded',
+    border = vim.o.winborder or 'rounded',
   }
   local w_input_buf = Buffer.create(false, true)
-  local w_input = vim.api.nvim_open_win(w_input_buf.buf, false, w_input_cfg)
-  vim.wo[w_input].number = false
-  vim.wo[w_input].relativenumber = false
+  local w_input = vim.api.nvim_open_win(w_input_buf.bufnr, false, w_input_cfg)
+  vim.wo[w_input][0].cursorline = false
+  vim.wo[w_input][0].list = false
+  vim.wo[w_input][0].number = false
+  vim.wo[w_input][0].relativenumber = false
 
   -- The following option is a signal to other plugins like 'cmp' to not mess
   -- with this buffer:
-  vim.bo[w_input_buf.buf].buftype = 'prompt'
-  vim.fn.prompt_setprompt(w_input_buf.buf, '')
+  vim.bo[w_input_buf.bufnr].buftype = 'prompt'
+  vim.fn.prompt_setprompt(w_input_buf.bufnr, '')
 
   vim.api.nvim_set_current_win(w_input)
   tracker.create_effect(safe_wrap(function()
@@ -174,10 +177,10 @@ function M.create_picker(opts)
     border = 'rounded',
   }
   local w_list_buf = Buffer.create(false, true)
-  local w_list = vim.api.nvim_open_win(w_list_buf.buf, false, w_list_cfg)
-  vim.wo[w_list].number = false
-  vim.wo[w_list].relativenumber = false
-  vim.wo[w_list].scrolloff = 0
+  local w_list = vim.api.nvim_open_win(w_list_buf.bufnr, false, w_list_cfg)
+  vim.wo[w_list][0].number = false
+  vim.wo[w_list][0].relativenumber = false
+  vim.wo[w_list][0].scrolloff = 0
   tracker.create_effect(safe_wrap(function()
     -- update window position/size every time the editor is resized:
     w_list_cfg = vim.tbl_deep_extend('force', w_list_cfg, s_w_list_coords:get())
@@ -200,7 +203,9 @@ function M.create_picker(opts)
 
   local s_filter_text_undebounced = tracker.create_signal('', 's:filter_text')
   w_input_buf:autocmd('TextChangedI', {
-    callback = safe_wrap(function() s_filter_text_undebounced:set(vim.api.nvim_get_current_line()) end),
+    callback = safe_wrap(
+      function() s_filter_text_undebounced:set(vim.api.nvim_get_current_line()) end
+    ),
   })
   local s_filter_text = s_filter_text_undebounced:debounce(50)
 
@@ -209,10 +214,15 @@ function M.create_picker(opts)
   --
 
   local s_formatted_items = tracker.create_memo(function()
-    local function _format_item(item) return opts.format_item and opts.format_item(item) or tostring(item) end
+    local function _format_item(item)
+      return opts.format_item and opts.format_item(item) or tostring(item)
+    end
 
     local items = s_items:get()
-    return vim.iter(items):map(function(item) return { item = item, formatted = _format_item(item) } end):totable()
+    return vim
+      .iter(items)
+      :map(function(item) return { item = item, formatted = _format_item(item) } end)
+      :totable()
   end)
 
   -- When the filter text changes, update the filtered items:
@@ -221,13 +231,21 @@ function M.create_picker(opts)
       local formatted_items = s_formatted_items:get()
       local filter_text = vim.trim(s_filter_text:get()):lower()
 
-      local filter_pattern = ''
+      --- @type string
+      local filter_pattern
+      --- @type boolean
+      local use_plain_pattern
       if #formatted_items > 250 and #filter_text <= 3 then
-        filter_pattern = filter_text:gsub('%.', '%%.')
+        filter_pattern = filter_text
+        use_plain_pattern = true
+      elseif #formatted_items > 1000 then
+        filter_pattern = filter_text
+        use_plain_pattern = true
       else
         filter_pattern = '('
           .. vim.iter(vim.split(filter_text, '')):map(function(c) return c .. '.*' end):join ''
           .. ')'
+        use_plain_pattern = false
       end
       filter_pattern = filter_pattern:lower()
 
@@ -239,13 +257,20 @@ function M.create_picker(opts)
       local new_filtered_items = vim
         .iter(formatted_items)
         :enumerate()
-        :map(function(i, inf) return { orig_idx = i, item = inf.item, formatted = inf.formatted } end)
+        :map(
+          function(i, inf) return { orig_idx = i, item = inf.item, formatted = inf.formatted } end
+        )
         :filter(function(inf)
           if filter_text == '' then return true end
           local formatted_as_string = Renderer.markup_to_string({ tree = inf.formatted }):lower()
 
           formatted_strings[inf.orig_idx] = formatted_as_string
+          if use_plain_pattern then
+            local x, y = formatted_as_string:find(filter_pattern, 1, true)
+            if x ~= nil and y ~= nil then matches[inf.orig_idx] = formatted_as_string:sub(x, y) end
+          else
             matches[inf.orig_idx] = string.match(formatted_as_string, filter_pattern)
+          end
 
           return matches[inf.orig_idx] ~= nil
         end)
@@ -305,7 +330,9 @@ function M.create_picker(opts)
       local filtered_items = s_filtered_items:get()
       local cursor_index = s_cursor_index:get()
       local indices = shallow_copy_arr(selected_indices)
-      if #indices == 0 and #filtered_items > 0 then indices = { filtered_items[cursor_index].orig_idx } end
+      if #indices == 0 and #filtered_items > 0 then
+        indices = { filtered_items[cursor_index].orig_idx }
+      end
       return {
         items = vim.iter(indices):map(function(i) return items[i] end):totable(),
         indices = indices,
@@ -329,7 +356,7 @@ function M.create_picker(opts)
     -- "invalid window ID" errors):
     H.unsubscribe_render_effect()
     -- buftype=prompt buffers are not "temporary", so delete the buffer manually:
-    vim.api.nvim_buf_delete(w_input_buf.buf, { force = true })
+    vim.api.nvim_buf_delete(w_input_buf.bufnr, { force = true })
     -- The following is not needed, since the buffer is deleted above:
     -- vim.api.nvim_win_close(w_input, false)
     vim.api.nvim_win_close(w_list, false)
@@ -370,9 +397,9 @@ function M.create_picker(opts)
   --
   -- Events
   --
-  vim.keymap.set('i', '<Esc>', function() H.finish(true) end, { buffer = w_input_buf.buf })
+  vim.keymap.set('i', '<Esc>', function() H.finish(true) end, { buffer = w_input_buf.bufnr })
 
-  vim.keymap.set('i', '<CR>', function() H.finish() end, { buffer = w_input_buf.buf })
+  vim.keymap.set('i', '<CR>', function() H.finish() end, { buffer = w_input_buf.bufnr })
 
   local function action_next_line()
     local max_line = #s_filtered_items:get()
@@ -382,8 +409,18 @@ function M.create_picker(opts)
     end
     s_cursor_index:set(next_cursor_index)
   end
-  vim.keymap.set('i', '<C-n>', safe_wrap(action_next_line), { buffer = w_input_buf.buf, desc = 'Picker: next' })
-  vim.keymap.set('i', '<Down>', safe_wrap(action_next_line), { buffer = w_input_buf.buf, desc = 'Picker: next' })
+  vim.keymap.set(
+    'i',
+    '<C-n>',
+    safe_wrap(action_next_line),
+    { buffer = w_input_buf.bufnr, desc = 'Picker: next' }
+  )
+  vim.keymap.set(
+    'i',
+    '<Down>',
+    safe_wrap(action_next_line),
+    { buffer = w_input_buf.bufnr, desc = 'Picker: next' }
+  )
 
   local function action_prev_line()
     local max_line = #s_filtered_items:get()
@@ -391,8 +428,18 @@ function M.create_picker(opts)
     if next_cursor_index - s_top_offset:get() < 1 then s_top_offset:set(s_top_offset:get() - 1) end
     s_cursor_index:set(next_cursor_index)
   end
-  vim.keymap.set('i', '<C-p>', safe_wrap(action_prev_line), { buffer = w_input_buf.buf, desc = 'Picker: previous' })
-  vim.keymap.set('i', '<Up>', safe_wrap(action_prev_line), { buffer = w_input_buf.buf, desc = 'Picker: previous' })
+  vim.keymap.set(
+    'i',
+    '<C-p>',
+    safe_wrap(action_prev_line),
+    { buffer = w_input_buf.bufnr, desc = 'Picker: previous' }
+  )
+  vim.keymap.set(
+    'i',
+    '<Up>',
+    safe_wrap(action_prev_line),
+    { buffer = w_input_buf.bufnr, desc = 'Picker: previous' }
+  )
 
   vim.keymap.set(
     'i',
@@ -402,7 +449,9 @@ function M.create_picker(opts)
 
       local index = s_filtered_items:get()[s_cursor_index:get()].orig_idx
       if vim.tbl_contains(s_selected_indices:get(), index) then
-        s_selected_indices:set(vim.iter(s_selected_indices:get()):filter(function(i) return i ~= index end):totable())
+        s_selected_indices:set(
+          vim.iter(s_selected_indices:get()):filter(function(i) return i ~= index end):totable()
+        )
       else
         local new_selected_indices = shallow_copy_arr(s_selected_indices:get())
         table.insert(new_selected_indices, index)
@@ -410,11 +459,16 @@ function M.create_picker(opts)
       end
       action_next_line()
     end),
-    { buffer = w_input_buf.buf }
+    { buffer = w_input_buf.bufnr }
   )
 
   for key, fn in pairs(opts.mappings or {}) do
-    vim.keymap.set('i', key, safe_wrap(function() return fn(controller) end), { buffer = w_input_buf.buf })
+    vim.keymap.set(
+      'i',
+      key,
+      safe_wrap(function() return fn(controller) end),
+      { buffer = w_input_buf.bufnr }
+    )
   end
 
   -- Render:
@@ -484,10 +538,9 @@ function M.create_picker(opts)
       if ephemeral == nil then ephemeral = false end
 
       if ephemeral and #indicies == 1 then
-        local matching_filtered_item_idx, _ = vim
-          .iter(s_filtered_items:get())
-          :enumerate()
-          :find(function(_idx, inf) return inf.orig_idx == indicies[1] end)
+        local matching_filtered_item_idx, _ = vim.iter(s_filtered_items:get()):enumerate():find(
+          function(_idx, inf) return inf.orig_idx == indicies[1] end
+        )
         if matching_filtered_item_idx ~= nil then s_cursor_index:set(indicies[1]) end
       else
         if not opts.multi then
@@ -504,8 +557,8 @@ function M.create_picker(opts)
     return safe_run(function() H.finish(true) end)
   end
 
-  return controller --[[@as SelectController]]
-end
+  return controller --[[@as u.examples.SelectController]]
+end -- }}}
 
 --------------------------------------------------------------------------------
 -- END create_picker
@@ -522,6 +575,7 @@ function M.register_ui_select()
   --- @param items `T`[]
   --- @param opts { prompt?: string, kind?: any, format_item?: fun(item: T):string }
   --- @param cb fun(item: T|nil):any
+  --- @diagnostic disable-next-line: duplicate-set-field
   function vim.ui.select(items, opts, cb)
     M.create_picker {
       items = items,
@@ -552,7 +606,7 @@ end
 --------------------------------------------------------------------------------
 
 --- @param opts? { limit?: number }
-function M.files(opts)
+function M.files(opts) -- {{{
   opts = opts or {}
   opts.limit = opts.limit or 10000
 
@@ -705,7 +759,11 @@ function M.files(opts)
       -- fast laptop. Show a warning and truncate the list in this case.
       if #lines >= opts.limit then
         if not job_inf.notified_over_limit then
-          vim.notify('Picker list is too large (truncating list to ' .. opts.limit .. ' items)', vim.log.levels.WARN)
+          vim.notify(
+            'Picker list is too large (truncating list to ' .. opts.limit .. ' items)',
+            vim.log.levels.WARN
+          )
+          pcall(vim.fn.jobstop, job_inf.id)
           job_inf.notified_over_limit = true
         end
         return
@@ -726,10 +784,10 @@ function M.files(opts)
       set_lines_as_items_state()
     end),
   })
-end
+end -- }}}
 
-function M.buffers()
-  local cwd = vim.fn.getcwd(0, 0)
+function M.buffers() -- {{{
+  local cwd = vim.fn.getcwd()
   -- ensure that `cwd` ends with a trailing slash:
   if cwd[#cwd] ~= '/' then cwd = cwd .. '/' end
 
@@ -747,10 +805,7 @@ function M.buffers()
       -- trim leading `cwd` from the buffer name:
       if item_name:sub(1, #cwd) == cwd then item_name = item_name:sub(#cwd + 1) end
 
-      return TreeBuilder.new()
-        :put(item.changed == 1 and '[+] ' or '    ')
-        :put(item_name)
-        :tree()
+      return TreeBuilder.new():put(item.changed == 1 and '[+] ' or '    '):put(item_name):tree()
     end,
 
     --- @params items { bufnr: number }[]
@@ -831,10 +886,10 @@ function M.buffers()
       end,
     },
   }
-end
+end -- }}}
 
 local IS_CODE_SYMBOL_RUNNING = false
-function M.lsp_code_symbols()
+function M.lsp_code_symbols() -- {{{
   if IS_CODE_SYMBOL_RUNNING then return end
   IS_CODE_SYMBOL_RUNNING = true
 
@@ -863,7 +918,9 @@ function M.lsp_code_symbols()
     local item = items[1]
 
     -- Jump to the file/buffer:
-    local buf = vim.iter(vim.fn.getbufinfo { buflisted = 1 }):find(function(b) return b.name == item.filename end)
+    local buf = vim
+      .iter(vim.fn.getbufinfo { buflisted = 1 })
+      :find(function(b) return b.name == item.filename end)
     if buf ~= nil then
       vim.api.nvim_win_set_buf(0, buf.bufnr)
     else
@@ -881,13 +938,12 @@ function M.lsp_code_symbols()
 
   -- Kick off the async operation:
   vim.lsp.buf.document_symbol { on_list = STEPS._1_on_symbols }
-end
+end -- }}}
 
 function M.setup()
   utils.ucmd('Files', M.files)
   utils.ucmd('Buffers', M.buffers)
   utils.ucmd('Lspcodesymbols', M.lsp_code_symbols)
-  M.register_ui_select()
 end
 
 return M

examples/splitjoin.lua

@@ -1,10 +1,10 @@
-local vim_repeat = require 'u.repeat'
 local CodeWriter = require 'u.codewriter'
 local Range = require 'u.range'
+local vim_repeat = require 'u.repeat'
 
 local M = {}
 
----@param bracket_range Range
+--- @param bracket_range u.Range
 --- @param left string
 --- @param right string
 local function split(bracket_range, left, right)
@@ -52,17 +52,21 @@ local function split(bracket_range, left, right)
   bracket_range:replace(code.lines)
 end
 
----@param bracket_range Range
+--- @param bracket_range u.Range
 --- @param left string
 --- @param right string
 local function join(bracket_range, left, right)
-  local inner_range = Range.new(bracket_range.start:must_next(), bracket_range.stop:must_next(-1), bracket_range.mode)
+  local inner_range = bracket_range:shrink(1)
+  if inner_range then
     local newline = vim
       .iter(inner_range:lines())
       :map(function(l) return vim.trim(l) end)
       :filter(function(l) return l ~= '' end)
       :join ' '
     bracket_range:replace { left .. newline .. right }
+  else
+    bracket_range:replace { left .. right }
+  end
 end
 
 local function splitjoin()
@@ -80,7 +84,7 @@ local function splitjoin()
 end
 
 function M.setup()
-  vim.keymap.set('n', 'gS', function() vim_repeat.run(splitjoin) end)
+  vim.keymap.set('n', 'gS', function() vim_repeat.run_repeatable(splitjoin) end)
 end
 
 return M

examples/surround.lua

@@ -1,12 +1,12 @@
-local vim_repeat = require 'u.repeat'
-local opkeymap = require 'u.opkeymap'
-local Pos = require 'u.pos'
-local Range = require 'u.range'
 local Buffer = require 'u.buffer'
 local CodeWriter = require 'u.codewriter'
+local Range = require 'u.range'
+local vim_repeat = require 'u.repeat'
 
 local M = {}
 
+local ESC = vim.api.nvim_replace_termcodes('<Esc>', true, false, true)
+
 local surrounds = {
   [')'] = { left = '(', right = ')' },
   ['('] = { left = '( ', right = ' )' },
@@ -21,8 +21,17 @@ local surrounds = {
   ['`'] = { left = '`', right = '`' },
 }
 
+--- @type { left: string; right: string } | nil
+local CACHED_BOUNDS = nil
+
 --- @return { left: string; right: string }|nil
 local function prompt_for_bounds()
+  if vim_repeat.is_repeating() then
+    -- If we are repeating, we don't want to prompt for bounds, because
+    -- we want to reuse the last bounds:
+    return CACHED_BOUNDS
+  end
+
   local cn = vim.fn.getchar()
   -- Check for non-printable characters:
   if type(cn) ~= 'number' or cn < 32 or cn > 126 then return end
@@ -36,14 +45,16 @@ local function prompt_for_bounds()
     vim.keymap.del('c', '>')
     local endtag = '</' .. tag:sub(2):match '[^ >]*' .. '>'
     -- selene: allow(global_usage)
-    return { left = tag, right = endtag }
+    CACHED_BOUNDS = { left = tag, right = endtag }
+    return CACHED_BOUNDS
   else
     -- Default surround:
-    return (surrounds)[c] or { left = c, right = c }
+    CACHED_BOUNDS = (surrounds)[c] or { left = c, right = c }
+    return CACHED_BOUNDS
   end
 end
 
----@param range Range
+--- @param range u.Range
 --- @param bounds { left: string; right: string }
 local function do_surround(range, bounds)
   local left = bounds.left
@@ -59,7 +70,7 @@ local function do_surround(range, bounds)
     range:replace(left .. range:text() .. right)
   elseif range.mode == 'V' then
     local buf = Buffer.current()
-    local cw = CodeWriter.from_line(buf:line0(range.start.lnum):text(), buf.buf)
+    local cw = CodeWriter.from_line(range.start:line(), buf.bufnr)
 
     -- write the left bound at the current indent level:
     cw:write(left)
@@ -86,31 +97,51 @@ local function do_surround(range, bounds)
   range.start:save_to_pos '.'
 end
 
+-- Add surround:
+--- @param ty 'line' | 'char' | 'block'
+function _G.MySurroundOpFunc(ty)
+  if ty == 'block' then
+    -- We won't handle block-selection:
+    return
+  end
+
+  local range = Range.from_op_func(ty)
+  local hl
+  if not vim_repeat.is_repeating() then hl = range:highlight('IncSearch', { priority = 999 }) end
+
+  local bounds = prompt_for_bounds()
+  if hl then hl.clear() end
+  if bounds == nil then return end
+
+  do_surround(range, bounds)
+end
+
 function M.setup()
   require('u.repeat').setup()
 
   -- Visual
-  vim.keymap.set('v', 'S', function()
-    local c = vim.fn.getcharstr()
+  vim.keymap.set('x', 'S', function()
     local range = Range.from_vtext()
-    local bounds = surrounds[c] or { left = c, right = c }
-    vim_repeat.run(function()
+    local bounds = prompt_for_bounds()
+    if bounds == nil then return end
+
     do_surround(range, bounds)
     -- this is a visual mapping: end in normal mode:
-      vim.cmd { cmd = 'normal', args = { '' }, bang = true }
-    end)
+    vim.cmd.normal(ESC)
   end, { noremap = true, silent = true })
 
   -- Change
   vim.keymap.set('n', 'cs', function()
-    local from_cn = vim.fn.getchar()
+    local from_cn = vim.fn.getchar() --[[@as number]]
     -- Check for non-printable characters:
     if from_cn < 32 or from_cn > 126 then return end
+
+    vim_repeat.run_repeatable(function()
       local from_c = vim.fn.nr2char(from_cn)
       local from = surrounds[from_c] or { left = from_c, right = from_c }
       local function get_fresh_arange()
-      local arange = Range.from_text_object('a' .. from_c, { user_defined = true })
-      if arange == nil then return nil end
+        local arange = Range.from_motion('a' .. from_c, { user_defined = true })
+        if arange == nil then return end
         if from_c == 'q' then
           from.left = arange.start:char()
           from.right = arange.stop:char()
@@ -119,10 +150,12 @@ function M.setup()
       end
 
       local arange = get_fresh_arange()
-    if arange == nil then return nil end
+      if arange == nil then return end
 
-    local hl_info1 = Range.new(arange.start, arange.start, 'v'):highlight('IncSearch', { priority = 999 })
-    local hl_info2 = Range.new(arange.stop, arange.stop, 'v'):highlight('IncSearch', { priority = 999 })
+      local hl_info1 = vim_repeat.is_repeating() and nil
+        or Range.new(arange.start, arange.start, 'v'):highlight('IncSearch', { priority = 999 })
+      local hl_info2 = vim_repeat.is_repeating() and nil
+        or Range.new(arange.stop, arange.stop, 'v'):highlight('IncSearch', { priority = 999 })
       local hl_clear = function()
         if hl_info1 then hl_info1.clear() end
         if hl_info2 then hl_info2.clear() end
@@ -132,51 +165,39 @@ function M.setup()
       hl_clear()
       if to == nil then return end
 
-    vim_repeat.run(function()
-      -- Re-fetch the arange, just in case this action is being repeated:
-      arange = get_fresh_arange()
-      if arange == nil then return nil end
-
       if from_c == 't' then
         -- For tags, we want to replace the inner text, not the tag:
-        local irange = Range.from_text_object('i' .. from_c, { user_defined = true })
-        if arange == nil or irange == nil then return nil end
+        local irange = Range.from_motion('i' .. from_c, { user_defined = true })
+        if arange == nil or irange == nil then return end
 
-        local lrange = Range.new(arange.start, irange.start:must_next(-1))
-        local rrange = Range.new(irange.stop:must_next(1), arange.stop)
+        local lrange, rrange = arange:difference(irange)
+        if not lrange or not rrange then return end
 
         rrange:replace(to.right)
         lrange:replace(to.left)
       else
         -- replace `from.right` with `to.right`:
-        local last_line = arange:line0(-1).text() --[[@as string]]
-        local from_right_match = last_line:match(vim.pesc(from.right) .. '$')
-        if from_right_match then
-          local match_start = arange.stop:clone()
-          match_start.col = match_start.col - #from_right_match + 1
-          Range.new(match_start, arange.stop):replace(to.right)
-        end
+        local right_text = arange:sub(-1, -#from.right)
+        right_text:replace(to.right)
 
         -- replace `from.left` with `to.left`:
-        local first_line = arange:line0(0).text() --[[@as string]]
-        local from_left_match = first_line:match('^' .. vim.pesc(from.left))
-        if from_left_match then
-          local match_end = arange.start:clone()
-          match_end.col = match_end.col + #from_left_match - 1
-          Range.new(arange.start, match_end):replace(to.left)
-        end
+        local left_text = arange:sub(1, #from.left)
+        left_text:replace(to.left)
       end
     end)
   end, { noremap = true, silent = true })
 
   -- Delete
+  local CACHED_DELETE_FROM = nil
   vim.keymap.set('n', 'ds', function()
-    local txt_obj = vim.fn.getcharstr()
-    vim_repeat.run(function()
+    vim_repeat.run_repeatable(function()
+      local txt_obj = vim_repeat.is_repeating() and CACHED_DELETE_FROM or vim.fn.getcharstr()
+      CACHED_DELETE_FROM = txt_obj
+
       local buf = Buffer.current()
-      local irange = Range.from_text_object('i' .. txt_obj)
-      local arange = Range.from_text_object('a' .. txt_obj)
-      if arange == nil or irange == nil then return nil end
+      local irange = Range.from_motion('i' .. txt_obj)
+      local arange = Range.from_motion('a' .. txt_obj)
+      if arange == nil or irange == nil then return end
       local starting_cursor_pos = arange.start:clone()
 
       -- Now, replace `arange` with the content of `irange`.  If `arange` was multiple lines,
@@ -187,28 +208,19 @@ function M.setup()
         -- Dedenting moves the cursor, so we need to set the cursor to a consistent starting spot:
         arange.start:save_to_pos '.'
         -- Dedenting also changed the inner text, so re-acquire it:
-        arange = Range.from_text_object('a' .. txt_obj)
-        irange = Range.from_text_object('i' .. txt_obj)
+        arange = Range.from_motion('a' .. txt_obj)
+        irange = Range.from_motion('i' .. txt_obj)
         if arange == nil or irange == nil then return end -- should never be true
         arange:replace(irange:lines())
-
-        local final_range = Range.new(
-          arange.start,
-          Pos.new(
-            arange.stop.buf,
-            irange.start.lnum + (arange.stop.lnum + arange.start.lnum),
-            arange.stop.col,
-            arange.stop.off
-          ),
-          irange.mode
-        )
+        -- `arange:replace(..)` updates its own `stop` position, so we will use
+        -- `arange` as the final resulting range that holds the modified text
 
         -- delete last line, if it is empty:
-        local last = buf:line0(final_range.stop.lnum)
+        local last = buf:line(arange.stop.lnum)
         if last:text():match '^%s*$' then last:replace(nil) end
 
         -- delete first line, if it is empty:
-        local first = buf:line0(final_range.start.lnum)
+        local first = buf:line(arange.start.lnum)
         if first:text():match '^%s*$' then first:replace(nil) end
       else
         -- trim start:
@@ -220,35 +232,10 @@ function M.setup()
     end)
   end, { noremap = true, silent = true })
 
-  opkeymap('n', 'ys', function(range)
-    local hl_info = range:highlight('IncSearch', { priority = 999 })
-
-    ---@type { left: string; right: string }
-    local bounds
-    -- selene: allow(global_usage)
-    if _G.my_surround_bounds ~= nil then
-      -- This command was repeated with `.`, we don't need
-      -- to prompt for the bounds:
-      -- selene: allow(global_usage)
-      bounds = _G.my_surround_bounds
-    else
-      local prompted_bounds = prompt_for_bounds()
-      if prompted_bounds == nil and hl_info then return hl_info.clear() end
-      if prompted_bounds then bounds = prompted_bounds end
-    end
-
-    if hl_info then hl_info.clear() end
-    do_surround(range, bounds)
-    -- selene: allow(global_usage)
-    _G.my_surround_bounds = nil
-
-    -- return repeatable injection
-    return function()
-      -- on_repeat, we "stage" the bounds that we were originally called with:
-      -- selene: allow(global_usage)
-      _G.my_surround_bounds = bounds
-    end
-  end)
+  vim.keymap.set('n', 'ys', function()
+    vim.o.operatorfunc = 'v:lua.MySurroundOpFunc'
+    return 'g@'
+  end, { expr = true })
 end
 
 return M

examples/text-objects.lua

@@ -1,23 +1,20 @@
-local utils = require 'u.utils'
+local Buffer = require 'u.buffer'
 local Pos = require 'u.pos'
 local Range = require 'u.range'
-local Buffer = require 'u.buffer'
+local txtobj = require 'u.txtobj'
 
 local M = {}
 
 function M.setup()
   -- Select whole file:
-  utils.define_text_object('ag', function() return Buffer.current():all() end)
+  txtobj.define('ag', function() return Buffer.current():all() end)
 
   -- Select current line:
-  utils.define_text_object('a.', function()
-    local lnum = Pos.from_pos('.').lnum
-    return Buffer.current():line0(lnum)
-  end)
+  txtobj.define('a.', function() return Buffer.current():line(Pos.from_pos('.').lnum) end)
 
   -- Select the nearest quote:
-  utils.define_text_object('aq', function() return Range.find_nearest_quotes() end)
-  utils.define_text_object('iq', function()
+  txtobj.define('aq', function() return Range.find_nearest_quotes() end)
+  txtobj.define('iq', function()
     local range = Range.find_nearest_quotes()
     if range == nil then return end
     return range:shrink(1)
@@ -26,33 +23,17 @@ function M.setup()
   ---Selects the next quote object (searches forward)
   --- @param q string
   local function define_quote_obj(q)
-    local function select_around()
-      -- Operator mappings are effectively running in visual mode, the way
-      -- `define_text_object` is implemented, so feed the keys `a${q}` to vim
-      -- to select the appropriate text-object
-      vim.cmd { cmd = 'normal', args = { 'a' .. q }, bang = true }
+    local function select_around() return Range.from_motion('a' .. q) end
 
-      -- Now check on the visually selected text:
-      local range = Range.from_vtext()
-      if range:is_empty() then return range.start end
-      range.start = range.start:find_next(1, q) or range.start
-      range.stop = range.stop:find_next(-1, q) or range.stop
-      return range
-    end
+    txtobj.define('a' .. q, function() return select_around() end)
+    txtobj.define('i' .. q, function()
+      local range = select_around()
+      if range == nil or range:is_empty() then return range end
 
-    utils.define_text_object('a' .. q, function() return select_around() end)
-    utils.define_text_object('i' .. q, function()
-      local range_or_pos = select_around()
-      if Range.is(range_or_pos) then
-        local start_next = range_or_pos.start:next(1)
-        local stop_prev = range_or_pos.stop:next(-1)
-        if start_next > stop_prev then return start_next end
-
-        local range = range_or_pos:shrink(1)
-        return range
-      else
-        return range_or_pos
-      end
+      local start_next = range.start:next(1) or range.start
+      local stop_prev = range.stop:next(-1)
+      if start_next > stop_prev then return Range.new(start_next) end
+      return range:shrink(1) or range
     end)
   end
   define_quote_obj [["]]
@@ -66,30 +47,20 @@ function M.setup()
       local curr = Pos.from_pos('.'):find_next(-1, q)
       if not curr then return end
       -- Reset visual selection to current context:
-      Range.new(curr, curr):set_visual_selection()
-      vim.cmd.normal('a' .. q)
-      local range = Range.from_vtext()
-      if range:is_empty() then return range.start end
-      range.start = range.start:find_next(1, q) or range.start
-      range.stop = range.stop:find_next(-1, q) or range.stop
-      return range
+      curr:save_to_pos '.'
+      return Range.from_motion('a' .. q)
     end
 
-    utils.define_text_object('al' .. q, function() return select_around() end)
-    utils.define_text_object('il' .. q, function()
-      local range_or_pos = select_around()
-      if range_or_pos == nil then return end
+    txtobj.define('al' .. q, function() return select_around() end)
+    txtobj.define('il' .. q, function()
+      local range = select_around()
+      if range == nil or range:is_empty() then return range end
 
-      if Range.is(range_or_pos) then
-        local start_next = range_or_pos.start:next(1)
-        local stop_prev = range_or_pos.stop:next(-1)
-        if start_next > stop_prev then return start_next end
+      local start_next = range.start:next(1) or range.start
+      local stop_prev = range.stop:next(-1)
+      if start_next > stop_prev then return Range.new(start_next) end
 
-        local range = range_or_pos:shrink(1)
-        return range
-      else
-        return range_or_pos
-      end
+      return range:shrink(1) or range
     end)
   end
   define_last_quote_obj [["]]
@@ -111,8 +82,8 @@ function M.setup()
     local keybinds = { ... }
     table.insert(keybinds, b)
     for _, k in ipairs(keybinds) do
-      utils.define_text_object('al' .. k, function() return select_around() end)
-      utils.define_text_object('il' .. k, function()
+      txtobj.define('al' .. k, function() return select_around() end)
+      txtobj.define('il' .. k, function()
         local range = select_around()
         return range and range:shrink(1)
       end)

lua/u/.luarc.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "https://raw.githubusercontent.com/LuaLS/vscode-lua/master/setting/schema.json",
+  "diagnostics.globals": ["assert", "vim"],
+  "runtime.version": "LuaJIT"
+}

lua/u/buffer.lua

@@ -1,86 +1,131 @@
 local Range = require 'u.range'
-local Renderer = require 'u.renderer'.Renderer
+local Renderer = require('u.renderer').Renderer
 
----@class Buffer
----@field buf number
----@field private renderer Renderer
+--- @class u.Buffer
+--- @field bufnr integer
+--- @field b vim.var_accessor
+--- @field bo vim.bo
+--- @field renderer u.renderer.Renderer
 local Buffer = {}
+Buffer.__index = Buffer
 
----@param buf? number
----@return Buffer
-function Buffer.from_nr(buf)
-  if buf == nil or buf == 0 then buf = vim.api.nvim_get_current_buf() end
-
-  local renderer = Renderer.new(buf)
+--- @param bufnr? number
+--- @return u.Buffer
+function Buffer.from_nr(bufnr)
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
+  local renderer = Renderer.new(bufnr)
   return setmetatable({
-    buf = buf,
+    bufnr = bufnr,
+    b = vim.b[bufnr],
+    bo = vim.bo[bufnr],
     renderer = renderer,
-  }, { __index = Buffer })
+  }, Buffer)
 end
 
----@return Buffer
+--- @return u.Buffer
 function Buffer.current() return Buffer.from_nr(0) end
 
 --- @param listed boolean
 --- @param scratch boolean
----@return Buffer
-function Buffer.create(listed, scratch) return Buffer.from_nr(vim.api.nvim_create_buf(listed, scratch)) end
-
-function Buffer:set_tmp_options()
-  self:set_option('bufhidden', 'delete')
-  self:set_option('buflisted', false)
-  self:set_option('buftype', 'nowrite')
+--- @return u.Buffer
+function Buffer.create(listed, scratch)
+  return Buffer.from_nr(vim.api.nvim_create_buf(listed, scratch))
 end
 
----@param nm string
-function Buffer:get_option(nm) return vim.api.nvim_get_option_value(nm, { buf = self.buf }) end
+function Buffer:set_tmp_options()
+  self.bo.bufhidden = 'delete'
+  self.bo.buflisted = false
+  self.bo.buftype = 'nowrite'
+end
 
----@param nm string
-function Buffer:set_option(nm, val) return vim.api.nvim_set_option_value(nm, val, { buf = self.buf }) end
+function Buffer:line_count() return vim.api.nvim_buf_line_count(self.bufnr) end
 
----@param nm string
-function Buffer:get_var(nm) return vim.api.nvim_buf_get_var(self.buf, nm) end
+function Buffer:all() return Range.from_buf_text(self.bufnr) end
 
----@param nm string
-function Buffer:set_var(nm, val) return vim.api.nvim_buf_set_var(self.buf, nm, val) end
-
-function Buffer:line_count() return vim.api.nvim_buf_line_count(self.buf) end
-
-function Buffer:all() return Range.from_buf_text(self.buf) end
-
-function Buffer:is_empty() return self:line_count() == 1 and self:line0(0):text() == '' end
+function Buffer:is_empty() return self:line_count() == 1 and self:line(1):text() == '' end
 
 --- @param line string
 function Buffer:append_line(line)
   local start = -1
   if self:is_empty() then start = -2 end
-  vim.api.nvim_buf_set_lines(self.buf, start, -1, false, { line })
+  vim.api.nvim_buf_set_lines(self.bufnr, start, -1, false, { line })
 end
 
----@param num number 0-based line index
-function Buffer:line0(num)
-  if num < 0 then return self:line0(self:line_count() + num) end
-  return Range.from_line(self.buf, num)
+--- @param num number 1-based line index
+function Buffer:line(num)
+  if num < 0 then num = self:line_count() + num + 1 end
+  return Range.from_line(self.bufnr, num)
 end
 
----@param start number 0-based line index
----@param stop number 0-based line index
-function Buffer:lines(start, stop) return Range.from_lines(self.buf, start, stop) end
+--- @param start number 1-based line index
+--- @param stop number 1-based line index
+function Buffer:lines(start, stop) return Range.from_lines(self.bufnr, start, stop) end
 
----@param txt_obj string
----@param opts? { contains_cursor?: boolean; pos?: Pos }
-function Buffer:text_object(txt_obj, opts)
-  opts = vim.tbl_extend('force', opts or {}, { buf = self.buf })
-  return Range.from_text_object(txt_obj, opts)
+--- @param motion string
+--- @param opts? { contains_cursor?: boolean; pos?: u.Pos }
+function Buffer:motion(motion, opts)
+  opts = vim.tbl_extend('force', opts or {}, { bufnr = self.bufnr })
+  return Range.from_motion(motion, opts)
 end
 
---- @param event string|string[]
+--- @param event vim.api.keyset.events|vim.api.keyset.events[]
+--- @diagnostic disable-next-line: undefined-doc-name
 --- @param opts vim.api.keyset.create_autocmd
 function Buffer:autocmd(event, opts)
-  vim.api.nvim_create_autocmd(event, vim.tbl_extend('force', opts, { buffer = self.buf }))
+  vim.api.nvim_create_autocmd(event, vim.tbl_extend('force', opts, { buffer = self.bufnr }))
 end
 
---- @param tree Tree
+--- @param fn function
+function Buffer:call(fn) return vim.api.nvim_buf_call(self.bufnr, fn) end
+
+--- @param tree u.renderer.Tree
 function Buffer:render(tree) return self.renderer:render(tree) end
 
+--- Filter buffer content through an external command (like Vim's :%!)
+--- @param cmd string[] Command to run (with arguments)
+--- @param opts? {cwd?: string, preserve_cursor?: boolean}
+--- @return nil
+--- @throws string Error message if command fails
+--- @note Special placeholders in cmd:
+---   - $FILE: replaced with the buffer's filename (if any)
+---   - $DIR: replaced with the buffer's directory (if any)
+function Buffer:filter_cmd(cmd, opts)
+  opts = opts or {}
+  local cwd = opts.cwd or vim.uv.cwd()
+  local old_lines = self:all():lines()
+  -- Save cursor position if needed, defaulting to true
+  local save_pos = opts.preserve_cursor ~= false and vim.fn.winsaveview()
+
+  -- Run the command
+  local result = vim
+    .system(
+      -- Replace special placeholders in `cmd` with their values:
+      vim
+        .iter(cmd)
+        :map(function(x)
+          if x == '$FILE' then return vim.api.nvim_buf_get_name(self.bufnr) end
+          if x == '$DIR' then return vim.fs.dirname(vim.api.nvim_buf_get_name(self.bufnr)) end
+          return x
+        end)
+        :totable(),
+      {
+        cwd = cwd,
+        stdin = old_lines,
+        text = true,
+      }
+    )
+    :wait()
+
+  -- Check for command failure
+  if result.code ~= 0 then error('Command failed: ' .. (result.stderr or '')) end
+
+  -- Process and apply the result
+  local new_lines = vim.split(result.stdout, '\n')
+  if new_lines[#new_lines] == '' then table.remove(new_lines) end
+  Renderer.patch_lines(self.bufnr, old_lines, new_lines)
+
+  -- Restore cursor position if saved
+  if save_pos then vim.fn.winrestview(save_pos) end
+end
+
 return Buffer

lua/u/codewriter.lua

@@ -1,14 +1,15 @@
 local Buffer = require 'u.buffer'
 
----@class CodeWriter
+--- @class u.CodeWriter
 --- @field lines string[]
 --- @field indent_level number
 --- @field indent_str string
 local CodeWriter = {}
+CodeWriter.__index = CodeWriter
 
 --- @param indent_level? number
 --- @param indent_str? string
----@return CodeWriter
+--- @return u.CodeWriter
 function CodeWriter.new(indent_level, indent_str)
   if indent_level == nil then indent_level = 0 end
   if indent_str == nil then indent_str = '  ' end
@@ -18,26 +19,27 @@ function CodeWriter.new(indent_level, indent_str)
     indent_level = indent_level,
     indent_str = indent_str,
   }
-  setmetatable(cw, { __index = CodeWriter })
+  setmetatable(cw, CodeWriter)
   return cw
 end
 
----@param p Pos
+--- @param p u.Pos
 function CodeWriter.from_pos(p)
-  local line = Buffer.from_nr(p.buf):line0(p.lnum):text()
-  return CodeWriter.from_line(line, p.buf)
+  local line = Buffer.from_nr(p.bufnr):line(p.lnum):text()
+  return CodeWriter.from_line(line, p.bufnr)
 end
 
 --- @param line string
----@param buf? number
-function CodeWriter.from_line(line, buf)
-  if buf == nil then buf = vim.api.nvim_get_current_buf() end
+--- @param bufnr? number
+function CodeWriter.from_line(line, bufnr)
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
 
   local ws = line:match '^%s*'
-  local expandtab = vim.api.nvim_get_option_value('expandtab', { buf = buf })
-  local shiftwidth = vim.api.nvim_get_option_value('shiftwidth', { buf = buf })
+  local expandtab = vim.api.nvim_get_option_value('expandtab', { buf = bufnr })
+  local shiftwidth = vim.api.nvim_get_option_value('shiftwidth', { buf = bufnr })
 
-  local indent_level = 0
+  --- @type number
+  local indent_level
   local indent_str = ''
   if expandtab then
     while #indent_str < shiftwidth do
@@ -61,7 +63,7 @@ end
 --- @param line string
 function CodeWriter:write(line) self:write_raw(self.indent_str:rep(self.indent_level) .. line) end
 
----@param f? fun(cw: CodeWriter):any
+--- @param f? fun(cw: u.CodeWriter):any
 function CodeWriter:indent(f)
   local cw = {
     lines = self.lines,

lua/u/extmark.lua

@@ -0,0 +1,71 @@
+local Pos = require 'u.pos'
+
+---@class u.Extmark
+---@field bufnr integer
+---@field id integer
+---@field nsid integer
+local Extmark = {}
+Extmark.__index = Extmark
+
+--- @param bufnr integer
+--- @param nsid integer
+--- @param id integer
+function Extmark.new(bufnr, nsid, id)
+  return setmetatable({
+    bufnr = bufnr,
+    nsid = nsid,
+    id = id,
+  }, Extmark)
+end
+
+--- @param range u.Range
+--- @param nsid integer
+function Extmark.from_range(range, nsid)
+  local r = range:to_charwise()
+  local stop = r.stop or r.start
+  local end_row = stop.lnum - 1
+  local end_col = stop.col
+  if range.mode == 'V' then
+    end_row = end_row + 1
+    end_col = 0
+  end
+  local id = vim.api.nvim_buf_set_extmark(r.start.bufnr, nsid, r.start.lnum - 1, r.start.col - 1, {
+    right_gravity = false,
+    end_right_gravity = true,
+    end_row = end_row,
+    end_col = end_col,
+  })
+  return Extmark.new(r.start.bufnr, nsid, id)
+end
+
+function Extmark:range()
+  local Range = require 'u.range'
+
+  local raw_extmark =
+    vim.api.nvim_buf_get_extmark_by_id(self.bufnr, self.nsid, self.id, { details = true })
+  local start_row0, start_col0, details = unpack(raw_extmark)
+
+  --- @type u.Pos
+  local start = Pos.from00(self.bufnr, start_row0, start_col0)
+  --- @type u.Pos?
+  local stop = details
+    and details.end_row
+    and details.end_col
+    and Pos.from01(self.bufnr, details.end_row, details.end_col)
+
+  local n_buf_lines = vim.api.nvim_buf_line_count(self.bufnr)
+  if stop and stop.lnum > n_buf_lines then
+    stop.lnum = n_buf_lines
+    stop = stop:eol()
+  end
+  if stop and stop.col == 0 then
+    stop.col = 1
+    stop = stop:next(-1)
+  end
+
+  return Range.new(start, stop, 'v')
+end
+
+function Extmark:delete() vim.api.nvim_buf_del_extmark(self.bufnr, self.nsid, self.id) end
+
+return Extmark

lua/u/logger.lua

@@ -1,15 +1,16 @@
 local M = {}
 
+local LOG_ROOT = vim.fs.joinpath(vim.fn.stdpath 'cache', 'u.log')
+
 --- @params name string
-function M.file_for_name(name) return vim.fs.joinpath(vim.fn.stdpath 'cache', 'my.log', name .. '.log.jsonl') end
+function M.file_for_name(name) return vim.fs.joinpath(LOG_ROOT, name .. '.log.jsonl') end
 
 --------------------------------------------------------------------------------
 -- Logger class
 --------------------------------------------------------------------------------
 
---- @class Logger
+--- @class u.Logger
 --- @field name string
---- @field private fd number
 local Logger = {}
 Logger.__index = Logger
 M.Logger = Logger
@@ -18,10 +19,7 @@ M.Logger = Logger
 function Logger.new(name)
   local file_path = M.file_for_name(name)
   vim.fn.mkdir(vim.fs.dirname(file_path), 'p')
-  local self = setmetatable({
-    name = name,
-    fd = (vim.uv or vim.loop).fs_open(file_path, 'a', tonumber('644', 8)),
-  }, Logger)
+  local self = setmetatable({ name = name }, Logger)
   return self
 end
 
@@ -30,7 +28,12 @@ end
 function Logger:write(level, ...)
   local data = { ... }
   if #data == 1 then data = data[1] end
-  (vim.uv or vim.loop).fs_write(self.fd, vim.json.encode { ts = os.date(), level = level, data = data } .. '\n')
+  local f = assert(io.open(M.file_for_name(self.name), 'a'), 'could not open file')
+  assert(
+    f:write(vim.json.encode { ts = os.date(), level = level, data = data } .. '\n'),
+    'could not write to file'
+  )
+  f:close()
 end
 
 function Logger:trace(...) self:write('INFO', ...) end
@@ -49,8 +52,22 @@ function M.setup()
     local log_file_path = M.file_for_name(args.fargs[1])
     vim.fn.mkdir(vim.fs.dirname(log_file_path), 'p')
     vim.system({ 'touch', log_file_path }):wait()
-    vim.cmd.Term('tail -f "' .. log_file_path .. '"')
+
+    vim.cmd.new()
+
+    local winnr = vim.api.nvim_get_current_win()
+    vim.wo[winnr][0].number = false
+    vim.wo[winnr][0].relativenumber = false
+
+    vim.cmd.terminal('tail -f "' .. log_file_path .. '"')
+    vim.cmd.startinsert()
   end, { nargs = '*' })
+
+  vim.api.nvim_create_user_command(
+    'Logroot',
+    function() vim.api.nvim_echo({ { LOG_ROOT } }, false, {}) end,
+    {}
+  )
 end
 
 return M

lua/u/opkeymap.lua

@@ -1,24 +1,17 @@
 local Range = require 'u.range'
-local vim_repeat = require 'u.repeat'
 
----@type fun(range: Range): nil|(fun():any)
+--- @type fun(range: u.Range): nil|(fun():any)
 local __U__OpKeymapOpFunc_rhs = nil
 
 --- This is the global utility function used for operatorfunc
 --- in opkeymap
----@type nil|fun(range: Range): fun():any|nil
+--- @type nil|fun(range: u.Range): fun():any|nil
 --- @param ty 'line'|'char'|'block'
 -- selene: allow(unused_variable)
-function __U__OpKeymapOpFunc(ty)
+function _G.__U__OpKeymapOpFunc(ty)
   if __U__OpKeymapOpFunc_rhs ~= nil then
     local range = Range.from_op_func(ty)
-    local repeat_inject = __U__OpKeymapOpFunc_rhs(range)
-
-    vim_repeat.set(function()
-      vim.o.operatorfunc = 'v:lua.__U__OpKeymapOpFunc'
-      if repeat_inject ~= nil and type(repeat_inject) == 'function' then repeat_inject() end
-      vim_repeat.native_repeat()
-    end)
+    __U__OpKeymapOpFunc_rhs(range)
   end
 end
 
@@ -30,10 +23,15 @@ end
 ---    then calls the original passed callback with said range.
 --- @param mode string|string[]
 --- @param lhs string
----@param rhs fun(range: Range): nil|(fun():any) This function may return another function, which is called whenever the operator is repeated
+--- @param rhs fun(range: u.Range): nil
+--- @diagnostic disable-next-line: undefined-doc-name
 --- @param opts? vim.keymap.set.Opts
 local function opkeymap(mode, lhs, rhs, opts)
   vim.keymap.set(mode, lhs, function()
+    -- We don't need to wrap the operation in a repeat, because expr mappings are
+    -- repeated seamlessly by Vim anyway. In addition, the u.repeat:`.` mapping will
+    -- set IS_REPEATING to true, so that callbacks can check if they should used cached
+    -- values.
     __U__OpKeymapOpFunc_rhs = rhs
     vim.o.operatorfunc = 'v:lua.__U__OpKeymapOpFunc'
     return 'g@'

lua/u/pos.lua

@@ -1,149 +1,190 @@
 local MAX_COL = vim.v.maxcol
 
----@param buf number
----@param lnum number
-local function line_text(buf, lnum) return vim.api.nvim_buf_get_lines(buf, lnum, lnum + 1, false)[1] end
+--- @param bufnr number
+--- @param lnum number 1-based
+local function line_text(bufnr, lnum)
+  return vim.api.nvim_buf_get_lines(bufnr, lnum - 1, lnum, false)[1]
+end
 
----@class Pos
----@field buf number buffer number
----@field lnum number 1-based line index
----@field col number 1-based column index
+--- @class u.Pos
+--- @field bufnr integer buffer number
+--- @field lnum integer 1-based line index
+--- @field col integer 1-based column index
 --- @field off number
 local Pos = {}
+Pos.__index = Pos
 Pos.MAX_COL = MAX_COL
 
----@param buf? number
----@param lnum number
----@param col number
+function Pos.__tostring(self)
+  if self.off ~= 0 then
+    return string.format('Pos(%d:%d){bufnr=%d, off=%d}', self.lnum, self.col, self.bufnr, self.off)
+  else
+    return string.format('Pos(%d:%d){bufnr=%d}', self.lnum, self.col, self.bufnr)
+  end
+end
+
+--- @param bufnr? number
+--- @param lnum number 1-based
+--- @param col number 1-based
 --- @param off? number
----@return Pos
-function Pos.new(buf, lnum, col, off)
-  if buf == nil or buf == 0 then buf = vim.api.nvim_get_current_buf() end
+--- @return u.Pos
+function Pos.new(bufnr, lnum, col, off)
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
   if off == nil then off = 0 end
-  local pos = {
-    buf = buf,
+  --- @type u.Pos
+  return setmetatable({
+    bufnr = bufnr,
     lnum = lnum,
     col = col,
     off = off,
-  }
-
-  local function str()
-    if pos.off ~= 0 then
-      return string.format('Pos(%d:%d){buf=%d, off=%d}', pos.lnum, pos.col, pos.buf, pos.off)
-    else
-      return string.format('Pos(%d:%d){buf=%d}', pos.lnum, pos.col, pos.buf)
-    end
-  end
-  setmetatable(pos, {
-    __index = Pos,
-    __tostring = str,
-    __lt = Pos.__lt,
-    __le = Pos.__le,
-    __eq = Pos.__eq,
-  })
-  return pos
+  }, Pos)
 end
 
-function Pos.is(x)
-  local mt = getmetatable(x)
-  return mt and mt.__index == Pos
-end
+--- @param bufnr? number
+--- @param lnum0 number 1-based
+--- @param col0 number 1-based
+--- @param off? number
+function Pos.from00(bufnr, lnum0, col0, off) return Pos.new(bufnr, lnum0 + 1, col0 + 1, off) end
+
+--- @param bufnr? number
+--- @param lnum0 number 1-based
+--- @param col1 number 1-based
+--- @param off? number
+function Pos.from01(bufnr, lnum0, col1, off) return Pos.new(bufnr, lnum0 + 1, col1, off) end
+
+--- @param bufnr? number
+--- @param lnum1 number 1-based
+--- @param col0 number 1-based
+--- @param off? number
+function Pos.from10(bufnr, lnum1, col0, off) return Pos.new(bufnr, lnum1, col0 + 1, off) end
+
+function Pos.invalid() return Pos.new(0, 0, 0, 0) end
 
 function Pos.__lt(a, b) return a.lnum < b.lnum or (a.lnum == b.lnum and a.col < b.col) end
 function Pos.__le(a, b) return a < b or a == b end
-function Pos.__eq(a, b) return a.lnum == b.lnum and a.col == b.col end
-
----@param name string
----@return Pos
-function Pos.from_pos(name)
-  local p = vim.fn.getpos(name)
-  local col = p[3]
-  if col ~= MAX_COL then col = col - 1 end
-  return Pos.new(p[1], p[2] - 1, col, p[4])
+function Pos.__eq(a, b)
+  return getmetatable(a) == Pos
+    and getmetatable(b) == Pos
+    and a.bufnr == b.bufnr
+    and a.lnum == b.lnum
+    and a.col == b.col
+end
+function Pos.__add(x, y)
+  if type(x) == 'number' then
+    x, y = y, x
+  end
+  if getmetatable(x) ~= Pos or type(y) ~= 'number' then return nil end
+  return x:next(y)
+end
+function Pos.__sub(x, y)
+  if type(x) == 'number' then
+    x, y = y, x
+  end
+  if getmetatable(x) ~= Pos or type(y) ~= 'number' then return nil end
+  return x:next(-y)
 end
 
-function Pos:clone() return Pos.new(self.buf, self.lnum, self.col, self.off) end
+--- @param bufnr number
+--- @param lnum number
+function Pos.from_eol(bufnr, lnum)
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
+  local pos = Pos.new(bufnr, lnum, 0)
+  pos.col = pos:line():len()
+  return pos
+end
+
+--- @param name string
+--- @return u.Pos
+function Pos.from_pos(name)
+  local p = vim.fn.getpos(name)
+  return Pos.new(p[1], p[2], p[3], p[4])
+end
+
+function Pos:is_invalid() return self.lnum == 0 and self.col == 0 and self.off == 0 end
+
+function Pos:clone() return Pos.new(self.bufnr, self.lnum, self.col, self.off) end
 
 --- @return boolean
 function Pos:is_col_max() return self.col == MAX_COL end
 
----@return number[]
-function Pos:as_vim() return { self.buf, self.lnum, self.col, self.off } end
-
 --- Normalize the position to a real position (take into account vim.v.maxcol).
 function Pos:as_real()
+  local maxlen = #line_text(self.bufnr, self.lnum)
   local col = self.col
-  if self:is_col_max() then
+  if col > maxlen then
     -- We could use utilities in this file to get the given line, but
     -- since this is a low-level function, we are going to optimize and
     -- use the API directly:
-    col = #line_text(self.buf, self.lnum) - 1
+    col = maxlen
   end
-  return Pos.new(self.buf, self.lnum, col, self.off)
+  return Pos.new(self.bufnr, self.lnum, col, self.off)
 end
 
+function Pos:as_vim() return { self.bufnr, self.lnum, self.col, self.off } end
+
+function Pos:eol() return Pos.from_eol(self.bufnr, self.lnum) end
+
 --- @param pos string
-function Pos:save_to_pos(pos)
-  if pos == '.' then
-    vim.api.nvim_win_set_cursor(0, { self.lnum + 1, self.col })
-    return
-  end
+function Pos:save_to_pos(pos) vim.fn.setpos(pos, { self.bufnr, self.lnum, self.col, self.off }) end
 
-  local p = self:as_real()
-  vim.fn.setpos(pos, { p.buf, p.lnum + 1, p.col + 1, p.off })
+--- @param winnr? integer
+function Pos:save_to_cursor(winnr)
+  vim.api.nvim_win_set_cursor(winnr or 0, { self.lnum, self.col - 1 })
 end
 
 --- @param mark string
 function Pos:save_to_mark(mark)
   local p = self:as_real()
-  vim.api.nvim_buf_set_mark(p.buf, mark, p.lnum + 1, p.col, {})
+  vim.api.nvim_buf_set_mark(p.bufnr, mark, p.lnum, p.col - 1, {})
 end
 
 --- @return string
 function Pos:char()
-  local line = line_text(self.buf, self.lnum)
+  local line = line_text(self.bufnr, self.lnum)
   if line == nil then return '' end
-  return line:sub(self.col + 1, self.col + 1)
+  return line:sub(self.col, self.col)
 end
 
+function Pos:line() return line_text(self.bufnr, self.lnum) end
+
 --- @param dir? -1|1
 --- @param must? boolean
----@return Pos|nil
+--- @return u.Pos|nil
 function Pos:next(dir, must)
   if must == nil then must = false end
 
   if dir == nil or dir == 1 then
     -- Next:
-    local num_lines = vim.api.nvim_buf_line_count(self.buf)
-    local last_line = line_text(self.buf, num_lines - 1) -- buf:line0(-1)
-    if self.lnum == num_lines - 1 and self.col == (#last_line - 1) then
+    local num_lines = vim.api.nvim_buf_line_count(self.bufnr)
+    local last_line = line_text(self.bufnr, num_lines)
+    if self.lnum == num_lines and self.col == #last_line then
       if must then error 'error in Pos:next(): Pos:next() returned nil' end
       return nil
     end
 
     local col = self.col + 1
     local line = self.lnum
-    local line_max_col = #line_text(self.buf, self.lnum) - 1
+    local line_max_col = #line_text(self.bufnr, self.lnum)
     if col > line_max_col then
-      col = 0
+      col = 1
       line = line + 1
     end
-    return Pos.new(self.buf, line, col, self.off)
+    return Pos.new(self.bufnr, line, col, self.off)
   else
     -- Previous:
-    if self.col == 0 and self.lnum == 0 then
+    if self.col == 1 and self.lnum == 1 then
       if must then error 'error in Pos:next(): Pos:next() returned nil' end
       return nil
     end
 
     local col = self.col - 1
     local line = self.lnum
-    local prev_line_max_col = #(line_text(self.buf, self.lnum - 1) or '') - 1
-    if col < 0 then
-      col = math.max(prev_line_max_col, 0)
+    local prev_line_max_col = #(line_text(self.bufnr, self.lnum - 1) or '')
+    if col < 1 then
+      col = math.max(prev_line_max_col, 1)
       line = line - 1
     end
-    return Pos.new(self.buf, line, col, self.off)
+    return Pos.new(self.bufnr, line, col, self.off)
   end
 end
 
@@ -155,7 +196,7 @@ function Pos:must_next(dir)
 end
 
 --- @param dir -1|1
----@param predicate fun(p: Pos): boolean
+--- @param predicate fun(p: u.Pos): boolean
 --- @param test_current? boolean
 function Pos:next_while(dir, predicate, test_current)
   if test_current and not predicate(self) then return end
@@ -169,14 +210,14 @@ function Pos:next_while(dir, predicate, test_current)
 end
 
 --- @param dir -1|1
----@param predicate string|fun(p: Pos): boolean
+--- @param predicate string|fun(p: u.Pos): boolean
 function Pos:find_next(dir, predicate)
   if type(predicate) == 'string' then
     local s = predicate
     predicate = function(p) return s == p:char() end
   end
 
-  ---@type Pos|nil
+  --- @type u.Pos|nil
   local curr = self
   while curr ~= nil do
     if predicate(curr) then return curr end
@@ -187,11 +228,13 @@ end
 
 --- Finds the matching bracket/paren for the current position.
 --- @param max_chars? number|nil
----@param invocations? Pos[]
----@return Pos|nil
+--- @param invocations? u.Pos[]
+--- @return u.Pos|nil
 function Pos:find_match(max_chars, invocations)
   if invocations == nil then invocations = {} end
-  if vim.tbl_contains(invocations, function(p) return self == p end, { predicate = true }) then return nil end
+  if vim.tbl_contains(invocations, function(p) return self == p end, { predicate = true }) then
+    return nil
+  end
   table.insert(invocations, self)
 
   local openers = { '{', '[', '(', '<' }
@@ -201,12 +244,20 @@ function Pos:find_match(max_chars, invocations)
   local is_closer = vim.tbl_contains(closers, c)
   if not is_opener and not is_closer then return nil end
 
-  local i, _ = vim.iter(is_opener and openers or closers):enumerate():find(function(_, c2) return c == c2 end)
+  local i, _ = vim
+    .iter(is_opener and openers or closers)
+    :enumerate()
+    :find(function(_, c2) return c == c2 end)
+  -- Store the character we will be looking for:
   local c_match = (is_opener and closers or openers)[i]
 
-  ---@type Pos|nil
+  --- @type u.Pos|nil
   local cur = self
-  ---@return Pos|nil
+  --- `adv` is a helper that moves the current position backward or forward,
+  --- depending on whether we are looking for an opener or a closer. It returns
+  --- nil if 1) the watch-dog `max_chars` falls bellow 0, or 2) if we have gone
+  --- beyond the beginning/end of the file.
+  --- @return u.Pos|nil
   local function adv()
     if cur == nil then return nil end
 
@@ -218,7 +269,7 @@ function Pos:find_match(max_chars, invocations)
     return cur:next(is_opener and 1 or -1)
   end
 
-  -- scan until we find a match:
+  -- scan until we find `c_match`:
   cur = adv()
   while cur ~= nil and cur:char() ~= c_match do
     cur = adv()
@@ -236,4 +287,17 @@ function Pos:find_match(max_chars, invocations)
   return cur
 end
 
+--- @param lines string|string[]
+function Pos:insert_before(lines)
+  if type(lines) == 'string' then lines = vim.split(lines, '\n') end
+  vim.api.nvim_buf_set_text(
+    self.bufnr,
+    self.lnum - 1,
+    self.col - 1,
+    self.lnum - 1,
+    self.col - 1,
+    lines
+  )
+end
+
 return Pos

lua/u/range.lua

@@ -1,31 +1,17 @@
+local Extmark = require 'u.extmark'
 local Pos = require 'u.pos'
-local State = require 'u.state'
 
-local orig_on_yank = (vim.hl or vim.highlight).on_yank
-local on_yank_enabled = true;
-((vim.hl or vim.highlight) --[[@as any]]).on_yank = function(opts)
-  if not on_yank_enabled then return end
-  return orig_on_yank(opts)
-end
+local ESC = vim.api.nvim_replace_termcodes('<Esc>', true, false, true)
+local NS = vim.api.nvim_create_namespace 'u.range'
 
----@class Range
----@field start Pos
----@field stop Pos|nil
+--- @class u.Range
+--- @field start u.Pos
+--- @field stop u.Pos|nil
 --- @field mode 'v'|'V'
 local Range = {}
-
----@param start Pos
----@param stop Pos|nil
----@param mode? 'v'|'V'
----@return Range
-function Range.new(start, stop, mode)
-  if stop ~= nil and stop < start then
-    start, stop = stop, start
-  end
-
-  local r = { start = start, stop = stop, mode = mode or 'v' }
-  local function str()
-    ---@param p Pos
+Range.__index = Range
+function Range.__tostring(self)
+  --- @param p u.Pos
   local function posstr(p)
     if p == nil then
       return 'nil'
@@ -36,22 +22,54 @@ function Range.new(start, stop, mode)
     end
   end
 
-    local _1 = posstr(r.start)
-    local _2 = posstr(r.stop)
-    return string.format('Range{buf=%d, mode=%s, start=%s, stop=%s}', r.start.buf, r.mode, _1, _2)
+  local _1 = posstr(self.start)
+  local _2 = posstr(self.stop)
+  return string.format(
+    'Range{bufnr=%d, mode=%s, start=%s, stop=%s}',
+    self.start.bufnr,
+    self.mode,
+    _1,
+    _2
+  )
 end
-  setmetatable(r, { __index = Range, __tostring = str })
+
+--------------------------------------------------------------------------------
+-- Range constructors:
+--------------------------------------------------------------------------------
+
+--- @param start u.Pos
+--- @param stop u.Pos|nil
+--- @param mode? 'v'|'V'
+--- @return u.Range
+function Range.new(start, stop, mode)
+  if stop ~= nil and stop < start then
+    start, stop = stop, start
+  end
+
+  local r = { start = start, stop = stop, mode = mode or 'v' }
+
+  setmetatable(r, Range)
   return r
 end
 
-function Range.is(x)
-  local mt = getmetatable(x)
-  return mt and mt.__index == Range
+--- @param ranges (u.Range|nil)[]
+function Range.smallest(ranges)
+  --- @type u.Range[]
+  ranges = vim.iter(ranges):filter(function(r) return r ~= nil and not r:is_empty() end):totable()
+  if #ranges == 0 then return nil end
+
+  -- find smallest match
+  local smallest = ranges[1]
+  for _, r in ipairs(ranges) do
+    local start, stop = r.start, r.stop
+    if start > smallest.start and stop < smallest.stop then smallest = r end
+  end
+  return smallest
 end
 
 --- @param lpos string
 --- @param rpos string
----@return Range
+--- @return u.Range
 function Range.from_marks(lpos, rpos)
   local start = Pos.from_pos(lpos)
   local stop = Pos.from_pos(rpos)
@@ -67,101 +85,137 @@ function Range.from_marks(lpos, rpos)
   return Range.new(start, stop, mode)
 end
 
----@param buf? number
-function Range.from_buf_text(buf)
-  if buf == nil or buf == 0 then buf = vim.api.nvim_get_current_buf() end
-  local num_lines = vim.api.nvim_buf_line_count(buf)
+--- @param bufnr? number
+function Range.from_buf_text(bufnr)
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
+  local num_lines = vim.api.nvim_buf_line_count(bufnr)
 
-  local start = Pos.new(buf, 0, 0)
-  local stop = Pos.new(buf, num_lines - 1, Pos.MAX_COL)
+  local start = Pos.new(bufnr, 1, 1)
+  local stop = Pos.new(bufnr, num_lines, Pos.MAX_COL)
   return Range.new(start, stop, 'V')
 end
 
----@param buf? number
----@param line number 0-based line index
-function Range.from_line(buf, line) return Range.from_lines(buf, line, line) end
+--- @param bufnr? number
+--- @param line number 1-based line index
+function Range.from_line(bufnr, line) return Range.from_lines(bufnr, line, line) end
 
----@param buf? number
----@param start_line number 0-based line index
----@param stop_line number 0-based line index
-function Range.from_lines(buf, start_line, stop_line)
-  if buf == nil or buf == 0 then buf = vim.api.nvim_get_current_buf() end
+--- @param bufnr? number
+--- @param start_line number based line index
+--- @param stop_line number based line index
+function Range.from_lines(bufnr, start_line, stop_line)
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
   if stop_line < 0 then
-    local num_lines = vim.api.nvim_buf_line_count(buf)
-    stop_line = num_lines + stop_line
+    local num_lines = vim.api.nvim_buf_line_count(bufnr)
+    stop_line = num_lines + stop_line + 1
   end
-  return Range.new(Pos.new(buf, start_line, 0), Pos.new(buf, stop_line, Pos.MAX_COL), 'V')
+  return Range.new(Pos.new(bufnr, start_line, 1), Pos.new(bufnr, stop_line, Pos.MAX_COL), 'V')
 end
 
----@param text_obj string
----@param opts? { buf?: number; contains_cursor?: boolean; pos?: Pos, user_defined?: boolean }
----@return Range|nil
-function Range.from_text_object(text_obj, opts)
+--- @param motion string
+--- @param opts? { bufnr?: number; contains_cursor?: boolean; pos?: u.Pos, user_defined?: boolean }
+--- @return u.Range|nil
+function Range.from_motion(motion, opts)
+  -- Options handling:
   opts = opts or {}
-  if opts.buf == nil then opts.buf = vim.api.nvim_get_current_buf() end
+  if opts.bufnr == nil or opts.bufnr == 0 then opts.bufnr = vim.api.nvim_get_current_buf() end
   if opts.contains_cursor == nil then opts.contains_cursor = false end
   if opts.user_defined == nil then opts.user_defined = false end
 
-  ---@type "a" | "i"
-  local selection_type = text_obj:sub(1, 1)
-  local obj_type = text_obj:sub(#text_obj, #text_obj)
-  local is_quote = vim.tbl_contains({ "'", '"', '`' }, obj_type)
-  local cursor = Pos.from_pos '.'
+  -- Extract some information from the motion:
+  --- @type 'a'|'i', string
+  local scope, motion_rest = motion:sub(1, 1), motion:sub(2)
+  local is_txtobj = scope == 'a' or scope == 'i'
+  local is_quote_txtobj = is_txtobj and vim.tbl_contains({ "'", '"', '`' }, motion_rest)
 
-  -- Yank, then read '[ and '] to know the bounds:
-  ---@type { start: Pos; stop: Pos }
-  local positions
-  vim.api.nvim_buf_call(opts.buf, function()
-    positions = State.run(0, function(s)
-      s:track_winview()
-      s:track_register '"'
-      s:track_pos '.'
-      s:track_pos "'["
-      s:track_pos "']"
+  -- Capture the original state of the buffer for restoration later.
+  local original_state = {
+    winview = vim.fn.winsaveview(),
+    regquote = vim.fn.getreg '"',
+    cursor = vim.fn.getpos '.',
+    pos_lbrack = vim.fn.getpos "'[",
+    pos_rbrack = vim.fn.getpos "']",
+    opfunc = vim.go.operatorfunc,
+    prev_captured_range = _G.Range__from_motion_opfunc_captured_range,
+    prev_mode = vim.fn.mode(),
+    vinf = Range.from_vtext(),
+  }
+  --- @type u.Range|nil
+  _G.Range__from_motion_opfunc_captured_range = nil
 
+  vim.api.nvim_buf_call(opts.bufnr, function()
     if opts.pos ~= nil then opts.pos:save_to_pos '.' end
 
-      local null_pos = Pos.new(0, 0, 0, 0)
-      null_pos:save_to_pos "'["
-      null_pos:save_to_pos "']"
-
-      local prev_on_yank_enabled = on_yank_enabled
-      on_yank_enabled = false
+    _G.Range__from_motion_opfunc = function(ty)
+      _G.Range__from_motion_opfunc_captured_range = Range.from_op_func(ty)
+    end
+    local old_eventignore = vim.o.eventignore
+    vim.o.eventignore = 'all'
+    vim.go.operatorfunc = 'v:lua.Range__from_motion_opfunc'
     vim.cmd {
       cmd = 'normal',
       bang = not opts.user_defined,
-        args = { '""y' .. text_obj },
+      args = { ESC .. 'g@' .. motion },
       mods = { silent = true },
     }
-      on_yank_enabled = prev_on_yank_enabled
+    vim.o.eventignore = old_eventignore
+  end)
+  local captured_range = _G.Range__from_motion_opfunc_captured_range
 
-      local start = Pos.from_pos "'["
-      local stop = Pos.from_pos "']"
+  -- Restore original state:
+  vim.fn.winrestview(original_state.winview)
+  vim.fn.setreg('"', original_state.regquote)
+  vim.fn.setpos('.', original_state.cursor)
+  vim.fn.setpos("'[", original_state.pos_lbrack)
+  vim.fn.setpos("']", original_state.pos_rbrack)
+  if original_state.prev_mode ~= 'n' then original_state.vinf:set_visual_selection() end
+  vim.go.operatorfunc = original_state.opfunc
+  _G.Range__from_motion_opfunc_captured_range = original_state.prev_captured_range
 
+  if not captured_range then return nil end
+
+  -- Fixup the bounds:
   if
     -- I have no idea why, but when yanking `i"`, the stop-mark is
     -- placed on the ending quote. For other text-objects, the stop-
     -- mark is placed before the closing character.
-        (is_quote and selection_type == 'i' and stop:char() == obj_type)
+    (is_quote_txtobj and scope == 'i' and captured_range.stop:char() == motion_rest)
     -- *Sigh*, this also sometimes happens for `it` as well.
-        or (text_obj == 'it' and stop:char() == '<')
+    or (motion == 'it' and captured_range.stop:char() == '<')
   then
-        stop = stop:next(-1) or stop
+    captured_range.stop = captured_range.stop:next(-1) or captured_range.stop
   end
-      return { start = start, stop = stop }
-    end)
-  end)
-  local start = positions.start
-  local stop = positions.stop
-  if start == stop and start.lnum == 0 and start.col == 0 and start.off == 0 then return nil end
-  if opts.contains_cursor and not Range.new(start, stop):contains(cursor) then return nil end
-
-  if is_quote and selection_type == 'a' then
-    start = start:find_next(1, obj_type) or start
-    stop = stop:find_next(-1, obj_type) or stop
+  if is_quote_txtobj and scope == 'a' then
+    captured_range.start = captured_range.start:find_next(1, motion_rest) or captured_range.start
+    captured_range.stop = captured_range.stop:find_next(-1, motion_rest) or captured_range.stop
   end
 
-  return Range.new(start, stop)
+  if
+    opts.contains_cursor and not captured_range:contains(Pos.new(unpack(original_state.cursor)))
+  then
+    return nil
+  end
+
+  return captured_range
+end
+
+--- @param opts? { contains_cursor?: boolean }
+function Range.from_tsquery_caps(bufnr, query, opts)
+  opts = opts or { contains_cursor = true }
+
+  local ranges = Range.from_buf_text(bufnr):tsquery(query)
+  if not ranges then return end
+  if not opts.contains_cursor then return ranges end
+
+  local cursor = Pos.from_pos '.'
+  return vim.tbl_map(function(cap_ranges)
+    return vim
+      .iter(cap_ranges)
+      :filter(
+        --- @param r u.Range
+        function(r) return r:contains(cursor) end
+      )
+      :totable()
+  end, ranges)
 end
 
 --- Get range information from the currently selected visual text.
@@ -189,90 +243,199 @@ end
 
 --- Get range information from command arguments.
 --- @param args unknown
----@return Range|nil
+--- @return u.Range|nil
 function Range.from_cmd_args(args)
-  ---@type 'v'|'V'
-  local mode
-  ---@type nil|Pos
-  local start
-  local stop
-  if args.range == 0 then
-    return nil
-  else
-    start = Pos.from_pos "'<"
-    stop = Pos.from_pos "'>"
-    if stop:is_col_max() then
-      mode = 'V'
-    else
-      mode = 'v'
-    end
-  end
-  return Range.new(start, stop, mode)
+  if args.range == 0 then return nil end
+
+  local bufnr = vim.api.nvim_get_current_buf()
+  if args.range == 1 then
+    return Range.new(Pos.new(bufnr, args.line1, 1), Pos.new(bufnr, args.line1, Pos.MAX_COL), 'V')
+  end
+
+  local is_visual = vim.fn.histget('cmd', -1):sub(1, 5) == [['<,'>]]
+  --- @type 'v'|'V'
+  local mode = is_visual and vim.fn.visualmode() or 'V'
+
+  if is_visual then
+    return Range.new(Pos.from_pos "'<", Pos.from_pos "'>", mode)
+  else
+    return Range.new(Pos.new(bufnr, args.line1, 1), Pos.new(bufnr, args.line2, Pos.MAX_COL), mode)
+  end
 end
 
----
 function Range.find_nearest_brackets()
-  local a = Range.from_text_object('a<', { contains_cursor = true })
-  local b = Range.from_text_object('a[', { contains_cursor = true })
-  local c = Range.from_text_object('a(', { contains_cursor = true })
-  local d = Range.from_text_object('a{', { contains_cursor = true })
-  return Range.smallest { a, b, c, d }
+  return Range.smallest {
+    Range.from_motion('a<', { contains_cursor = true }),
+    Range.from_motion('a[', { contains_cursor = true }),
+    Range.from_motion('a(', { contains_cursor = true }),
+    Range.from_motion('a{', { contains_cursor = true }),
+  }
 end
 
 function Range.find_nearest_quotes()
-  local a = Range.from_text_object([[a']], { contains_cursor = true })
-  if a ~= nil and a:is_empty() then a = nil end
-  local b = Range.from_text_object([[a"]], { contains_cursor = true })
-  if b ~= nil and b:is_empty() then b = nil end
-  local c = Range.from_text_object([[a`]], { contains_cursor = true })
-  if c ~= nil and c:is_empty() then c = nil end
-  return Range.smallest { a, b, c }
+  return Range.smallest {
+    Range.from_motion([[a']], { contains_cursor = true }),
+    Range.from_motion([[a"]], { contains_cursor = true }),
+    Range.from_motion([[a`]], { contains_cursor = true }),
+  }
 end
 
----@param ranges (Range|nil)[]
-function Range.smallest(ranges)
-  ---@type Range[]
-  local new_ranges = {}
-  for _, r in pairs(ranges) do
-    if r ~= nil then table.insert(new_ranges, r) end
-  end
-  ranges = new_ranges
-  if #ranges == 0 then return nil end
+--------------------------------------------------------------------------------
+-- Structural utilities:
+--------------------------------------------------------------------------------
 
-  -- find smallest match
-  local max_start = ranges[1].start
-  local min_stop = ranges[1].stop
-  local result = ranges[1]
-
-  for _, r in ipairs(ranges) do
-    local start, stop = r.start, r.stop
-    if start > max_start and stop < min_stop then
-      max_start = start
-      min_stop = stop
-      result = r
-    end
+function Range:clone()
+  return Range.new(self.start:clone(), self.stop ~= nil and self.stop:clone() or nil, self.mode)
 end
 
-  return result
-end
-
-function Range:clone() return Range.new(self.start:clone(), self.stop ~= nil and self.stop:clone() or nil, self.mode) end
-function Range:line_count()
-  if self:is_empty() then return 0 end
-  return self.stop.lnum - self.start.lnum + 1
-end
+function Range:is_empty() return self.stop == nil end
 
 function Range:to_linewise()
   local r = self:clone()
 
   r.mode = 'V'
-  r.start.col = 0
+  r.start.col = 1
   if r.stop ~= nil then r.stop.col = Pos.MAX_COL end
 
   return r
 end
 
-function Range:is_empty() return self.stop == nil end
+function Range:to_charwise()
+  local r = self:clone()
+  r.mode = 'v'
+  if r.stop:is_col_max() then r.stop = r.stop:as_real() end
+  return r
+end
+
+--- @param x u.Pos | u.Range
+function Range:contains(x)
+  if getmetatable(x) == Pos then
+    return not self:is_empty() and x >= self.start and x <= self.stop
+  elseif getmetatable(x) == Range then
+    return self:contains(x.start) and self:contains(x.stop)
+  end
+  return false
+end
+
+--- @param other u.Range
+--- @return u.Range|nil, u.Range|nil
+function Range:difference(other)
+  local outer, inner = self, other
+  if not outer:contains(inner) then
+    outer, inner = inner, outer
+  end
+  if not outer:contains(inner) then return nil, nil end
+
+  local left
+  if outer.start ~= inner.start then
+    local stop = inner.start:clone() - 1
+    left = Range.new(outer.start, stop)
+  else
+    left = Range.new(outer.start) -- empty range
+  end
+
+  local right
+  if inner.stop ~= outer.stop then
+    local start = inner.stop:clone() + 1
+    right = Range.new(start, outer.stop)
+  else
+    right = Range.new(inner.stop) -- empty range
+  end
+
+  return left, right
+end
+
+--- @param left string
+--- @param right string
+function Range:save_to_pos(left, right)
+  self.start:save_to_pos(left);
+  (self:is_empty() and self.start or self.stop):save_to_pos(right)
+end
+
+--- @param left string
+--- @param right string
+function Range:save_to_marks(left, right)
+  self.start:save_to_mark(left);
+  (self:is_empty() and self.start or self.stop):save_to_mark(right)
+end
+
+function Range:save_to_extmark() return Extmark.from_range(self, NS) end
+
+function Range:set_visual_selection()
+  if self:is_empty() then return end
+  if vim.api.nvim_get_current_buf() ~= self.start.bufnr then
+    error 'Range:set_visual_selection() called on a buffer other than the current buffer'
+  end
+
+  local curr_mode = vim.fn.mode()
+  if curr_mode ~= self.mode then vim.cmd.normal { args = { self.mode }, bang = true } end
+
+  self.start:save_to_pos '.'
+  vim.cmd.normal { args = { 'o' }, bang = true }
+  self.stop:save_to_pos '.'
+end
+
+--------------------------------------------------------------------------------
+-- Text access/manipulation utilities:
+--------------------------------------------------------------------------------
+
+--- @param query string
+function Range:tsquery(query)
+  local bufnr = self.start.bufnr
+
+  local lang = vim.treesitter.language.get_lang(vim.bo[bufnr].filetype)
+  if lang == nil then return end
+  local parser = vim.treesitter.get_parser(bufnr, lang)
+  if parser == nil then return end
+  local tree = parser:parse()[1]
+  if tree == nil then return end
+
+  local root = tree:root()
+  local q = vim.treesitter.query.parse(lang, query)
+  --- @type table<string, u.Range[]>
+  local ranges = {}
+  for id, match, _meta in
+    q:iter_captures(root, bufnr, self.start.lnum - 1, (self.stop or self.start).lnum)
+  do
+    local start_row0, start_col0, stop_row0, stop_col0 = match:range()
+    local range = Range.new(
+      Pos.new(bufnr, start_row0 + 1, start_col0 + 1),
+      Pos.new(bufnr, stop_row0 + 1, stop_col0),
+      'v'
+    )
+    if range.stop.lnum > vim.api.nvim_buf_line_count(bufnr) then
+      range.stop = range.stop:must_next(-1)
+    end
+
+    local capture_name = q.captures[id]
+    if not ranges[capture_name] then ranges[capture_name] = {} end
+    if self:contains(range) then table.insert(ranges[capture_name], range) end
+  end
+
+  return ranges
+end
+
+function Range:length()
+  if self:is_empty() then return 0 end
+
+  local line_positions =
+    vim.fn.getregionpos(self.start:as_real():as_vim(), self.stop:as_real():as_vim(), { type = 'v' })
+
+  local len = 0
+  for linenr, line in ipairs(line_positions) do
+    if linenr > 1 then len = len + 1 end -- each newline is counted as a char
+    local line_start_col = line[1][3]
+    local line_stop_col = line[2][3]
+    local line_len = line_stop_col - line_start_col + 1
+    len = len + line_len
+  end
+  return len
+end
+
+function Range:line_count()
+  if self:is_empty() then return 0 end
+  return self.stop.lnum - self.start.lnum + 1
+end
 
 function Range:trim_start()
   if self:is_empty() then return end
@@ -298,57 +461,70 @@ function Range:trim_stop()
   return r
 end
 
----@param p Pos
-function Range:contains(p) return not self:is_empty() and p >= self.start and p <= self.stop end
+--- @param i number 1-based
+--- @param j? number 1-based
+function Range:sub(i, j)
+  local line_positions =
+    vim.fn.getregionpos(self.start:as_real():as_vim(), self.stop:as_real():as_vim(), { type = 'v' })
+
+  --- @param idx number 1-based
+  --- @return u.Pos|nil
+  local function get_pos(idx)
+    if idx < 0 then return get_pos(self:length() + idx + 1) end
+
+    -- find the position of the first line that contains the i-th character:
+    local curr_len = 0
+    for linenr, line in ipairs(line_positions) do
+      if linenr > 1 then curr_len = curr_len + 1 end -- each newline is counted as a char
+      local line_start_col = line[1][3]
+      local line_stop_col = line[2][3]
+      local line_len = line_stop_col - line_start_col + 1
+
+      if curr_len + line_len >= idx then
+        return Pos.new(self.start.bufnr, line[1][2], line_start_col + (idx - curr_len) - 1)
+      end
+      curr_len = curr_len + line_len
+    end
+  end
+
+  local start = get_pos(i)
+  if not start then
+    -- start is inalid, so return an empty range:
+    return Range.new(self.start, nil, self.mode)
+  end
+
+  local stop
+  if j then stop = get_pos(j) end
+  if not stop then
+    -- stop is inalid, so return an empty range:
+    return Range.new(start, nil, self.mode)
+  end
+  return Range.new(start, stop, 'v')
+end
 
 --- @return string[]
 function Range:lines()
   if self:is_empty() then return {} end
-
-  local lines = {}
-  for i = 0, self.stop.lnum - self.start.lnum do
-    local line = self:line0(i)
-    if line ~= nil then table.insert(lines, line.text()) end
-  end
-  return lines
+  return vim.fn.getregion(self.start:as_vim(), self.stop:as_vim(), { type = self.mode })
 end
 
 --- @return string
 function Range:text() return vim.fn.join(self:lines(), '\n') end
 
----@param i number 1-based
----@param j? number 1-based
-function Range:sub(i, j) return self:text():sub(i, j) end
-
 --- @param l number
----@return { line: string; idx0: { start: number; stop: number; }; lnum: number; range: fun():Range; text: fun():string }|nil
-function Range:line0(l)
-  if l < 0 then return self:line0(self:line_count() + l) end
+-- luacheck: ignore
+--- @return { line: string; idx0: { start: number; stop: number; }; lnum: number; range: fun():u.Range; text: fun():string }|nil
+function Range:line(l)
+  if l < 0 then l = self:line_count() + l + 1 end
   if l > self:line_count() then return end
 
-  local line = vim.api.nvim_buf_get_lines(self.start.buf, self.start.lnum + l, self.start.lnum + l + 1, false)[1]
-  if line == nil then return end
+  local line_indices =
+    vim.fn.getregionpos(self.start:as_vim(), self.stop:as_vim(), { type = self.mode })
+  local line_bounds = line_indices[l]
 
-  local start = 0
-  local stop = #line - 1
-  if l == 0 then start = self.start.col end
-  if l == self.stop.lnum - self.start.lnum then stop = self.stop.col end
-  if stop == Pos.MAX_COL then stop = #line - 1 end
-  local lnum = self.start.lnum + l
-
-  return {
-    line = line,
-    idx0 = { start = start, stop = stop },
-    lnum = lnum,
-    range = function()
-      return Range.new(
-        Pos.new(self.start.buf, lnum, start, self.start.off),
-        Pos.new(self.start.buf, lnum, stop, self.stop.off),
-        'v'
-      )
-    end,
-    text = function() return line:sub(start + 1, stop + 1) end,
-  }
+  local start = Pos.new(unpack(line_bounds[1]))
+  local stop = Pos.new(unpack(line_bounds[2]))
+  return Range.new(start, stop)
 end
 
 --- @param replacement nil|string|string[]
@@ -356,52 +532,58 @@ function Range:replace(replacement)
   if replacement == nil then replacement = {} end
   if type(replacement) == 'string' then replacement = vim.fn.split(replacement, '\n') end
 
-  local buf = self.start.buf
-  -- convert to start-inclusive, stop-exclusive coordinates:
-  local start_lnum, stop_lnum = self.start.lnum, (self.stop and self.stop.lnum or self.start.lnum) + 1
-  local start_col, stop_col = self.start.col, (self.stop and self.stop.col or self.start.col) + 1
-
+  local bufnr = self.start.bufnr
   local replace_type = (self:is_empty() and 'insert') or (self.mode == 'v' and 'region') or 'lines'
 
-  ---@param alnum number
-  ---@param acol number
-  ---@param blnum number
-  ---@param bcol number
-  local function set_text(alnum, acol, blnum, bcol, repl)
-    -- row indices are end-inclusive, and column indices are end-exclusive.
-    vim.api.nvim_buf_set_text(buf, alnum, acol, blnum, bcol, repl)
-
+  local function update_stop_non_linewise()
     local new_last_line_num = self.start.lnum + #replacement - 1
     local new_last_col = #(replacement[#replacement] or '')
-    if new_last_line_num == start_lnum then new_last_col = new_last_col + start_col - 1 end
-
-    self.stop = Pos.new(buf, new_last_line_num, new_last_col)
+    if new_last_line_num == self.start.lnum then
+      new_last_col = new_last_col + self.start.col - 1
     end
-
-  ---@param alnum number
-  ---@param blnum number
-  local function set_lines(alnum, blnum, repl)
-    -- indexing is zero-based, end-exclusive
-    vim.api.nvim_buf_set_lines(buf, alnum, blnum, false, repl)
-
-    if #repl == 0 then
+    self.stop = Pos.new(bufnr, new_last_line_num, new_last_col)
+  end
+  local function update_stop_linewise()
+    if #replacement == 0 then
       self.stop = nil
     else
-      local new_last_line_num = start_lnum + #replacement - 1
-      self.stop = Pos.new(self.start.buf, new_last_line_num, Pos.MAX_COL, self.stop.off)
+      local new_last_line_num = self.start.lnum - 1 + #replacement - 1
+      self.stop = Pos.new(bufnr, new_last_line_num + 1, Pos.MAX_COL, self.stop.off)
     end
     self.mode = 'v'
   end
 
   if replace_type == 'insert' then
-    set_text(start_lnum, start_col, start_lnum, start_col, replacement)
+    -- To insert text at a given `(row, column)` location, use `start_row =
+    -- end_row = row` and `start_col = end_col = col`.
+    vim.api.nvim_buf_set_text(
+      bufnr,
+      self.start.lnum - 1,
+      self.start.col - 1,
+      self.start.lnum - 1,
+      self.start.col - 1,
+      replacement
+    )
+    update_stop_non_linewise()
   elseif replace_type == 'region' then
     -- Fixup the bounds:
-    local last_line = vim.api.nvim_buf_get_lines(buf, stop_lnum - 1, stop_lnum, false)[1] or ''
-    local max_col = #last_line
-    set_text(start_lnum, start_col, stop_lnum - 1, math.min(stop_col, max_col), replacement)
+    local max_col = #self.stop:line()
+
+    -- Indexing is zero-based. Row indices are end-inclusive, and column indices
+    -- are end-exclusive.
+    vim.api.nvim_buf_set_text(
+      bufnr,
+      self.start.lnum - 1,
+      self.start.col - 1,
+      self.stop.lnum - 1,
+      math.min(self.stop.col, max_col),
+      replacement
+    )
+    update_stop_non_linewise()
   elseif replace_type == 'lines' then
-    set_lines(start_lnum, stop_lnum, replacement)
+    -- Indexing is zero-based, end-exclusive.
+    vim.api.nvim_buf_set_lines(bufnr, self.start.lnum - 1, self.stop.lnum, true, replacement)
+    update_stop_linewise()
   else
     error 'unreachable'
   end
@@ -428,56 +610,12 @@ end
 --- @param amount number
 function Range:must_shrink(amount)
   local shrunk = self:shrink(amount)
-  if shrunk == nil or shrunk:is_empty() then error 'error in Range:must_shrink: Range:shrink() returned nil' end
+  if shrunk == nil or shrunk:is_empty() then
+    error 'error in Range:must_shrink: Range:shrink() returned nil'
+  end
   return shrunk
 end
 
----@param left string
----@param right string
-function Range:save_to_pos(left, right)
-  if self:is_empty() then
-    self.start:save_to_pos(left)
-    self.start:save_to_pos(right)
-  else
-    self.start:save_to_pos(left)
-    self.stop:save_to_pos(right)
-  end
-end
-
----@param left string
----@param right string
-function Range:save_to_marks(left, right)
-  if self:is_empty() then
-    self.start:save_to_mark(left)
-    self.start:save_to_mark(right)
-  else
-    self.start:save_to_mark(left)
-    self.stop:save_to_mark(right)
-  end
-end
-
-function Range:set_visual_selection()
-  if self:is_empty() then return end
-
-  if vim.api.nvim_get_current_buf() ~= self.start.buf then vim.api.nvim_set_current_buf(self.start.buf) end
-
-  State.run(self.start.buf, function(s)
-    s:track_mark 'a'
-    s:track_mark 'b'
-
-    self.start:save_to_mark 'a'
-    self.stop:save_to_mark 'b'
-    local mode = self.mode
-
-    local normal_cmd_args = ''
-    if vim.api.nvim_get_mode().mode == 'n' then normal_cmd_args = normal_cmd_args .. mode end
-    normal_cmd_args = normal_cmd_args .. '`ao`b'
-    vim.cmd { cmd = 'normal', args = { normal_cmd_args }, bang = true }
-
-    return nil
-  end)
-end
-
 --- @param group string
 --- @param opts? { timeout?: number, priority?: number, on_macro?: boolean }
 function Range:highlight(group, opts)
@@ -490,33 +628,31 @@ function Range:highlight(group, opts)
   if not opts.on_macro and in_macro then return { clear = function() end } end
 
   local ns = vim.api.nvim_create_namespace ''
-  State.run(self.start.buf, function(s)
-    if not in_macro then s:track_winview() end
 
-    (vim.hl or vim.highlight).range(
-      self.start.buf,
+  local winview = vim.fn.winsaveview()
+  vim.hl.range(
+    self.start.bufnr,
     ns,
     group,
-      { self.start.lnum, self.start.col },
-      { self.stop.lnum, self.stop.col },
+    { self.start.lnum - 1, self.start.col - 1 },
+    { self.stop.lnum - 1, self.stop.col - 1 },
     {
       inclusive = true,
       priority = opts.priority,
+      timeout = opts.timeout,
       regtype = self.mode,
     }
   )
-
-    return nil
-  end)
+  if not in_macro then vim.fn.winrestview(winview) end
   vim.cmd.redraw()
 
-  local function clear()
-    vim.api.nvim_buf_clear_namespace(self.start.buf, ns, self.start.lnum, self.stop.lnum + 1)
+  return {
+    ns = ns,
+    clear = function()
+      vim.api.nvim_buf_clear_namespace(self.start.bufnr, ns, self.start.lnum - 1, self.stop.lnum)
       vim.cmd.redraw()
-  end
-  if opts.timeout ~= nil then vim.defer_fn(clear, opts.timeout) end
-
-  return { ns = ns, clear = clear }
+    end,
+  }
 end
 
 return Range

lua/u/renderer.lua

@@ -1,44 +1,73 @@
-local utils = require 'u.utils'
+function _G.URendererOpFuncSwallow() end
+
+local ENABLE_LOG = false
+
+local function log(...)
+  if not ENABLE_LOG then return end
+
+  local f = assert(io.open(vim.fs.joinpath(vim.fn.stdpath 'log', 'u.renderer.log'), 'a+'))
+  f:write(os.date() .. '\t' .. vim.inspect { ... } .. '\n')
+  f:close()
+end
 
 local M = {}
+local H = {}
 
---- @alias Tag { kind: 'tag'; name: string, attributes: table<string, unknown>, children: Tree }
---- @alias Node nil | boolean | string | Tag
---- @alias Tree Node | Node[]
-local TagMetaTable = {}
+--- @alias u.renderer.TagEventHandler fun(tag: u.renderer.Tag, mode: string, lhs: string): string
 
---- @param name string
---- @param attributes? table<string, any>
---- @param children? Node | Node[]
---- @return Tag
-function M.h(name, attributes, children)
+--- @alias u.renderer.TagAttributes { [string]?: unknown; imap?: table<string, u.renderer.TagEventHandler>; nmap?: table<string, u.renderer.TagEventHandler>; vmap?: table<string, u.renderer.TagEventHandler>; xmap?: table<string, u.renderer.TagEventHandler>; omap?: table<string, u.renderer.TagEventHandler>, on_change?: fun(text: string): unknown }
+
+--- @class u.renderer.Tag
+--- @field kind 'tag'
+--- @field name string
+--- @field attributes u.renderer.TagAttributes
+--- @field children u.renderer.Tree
+
+--- @alias u.renderer.Node nil | boolean | string | u.renderer.Tag
+--- @alias u.renderer.Tree u.renderer.Node | u.renderer.Node[]
+
+-- luacheck: ignore
+--- @type table<string, fun(attributes: u.renderer.TagAttributes, children: u.renderer.Tree): u.renderer.Tag> & fun(name: string, attributes: u.renderer.TagAttributes, children: u.renderer.Tree): u.renderer.Tag>
+M.h = setmetatable({}, {
+  __call = function(_, name, attributes, children)
     return {
       kind = 'tag',
       name = name,
       attributes = attributes or {},
       children = children,
     }
+  end,
+  __index = function(_, name)
+    return function(attributes, children)
+      return M.h('text', vim.tbl_deep_extend('force', { hl = name }, attributes), children)
     end
+  end,
+})
 
---------------------------------------------------------------------------------
--- Renderer class
---------------------------------------------------------------------------------
---- @alias RendererExtmark { id?: number; start: [number, number]; stop: [number, number]; opts: any; tag: any }
+-- Renderer {{{
+--- @class u.renderer.RendererExtmark
+--- @field id? number
+--- @field start [number, number]
+--- @field stop [number, number]
+--- @field opts vim.api.keyset.set_extmark
+--- @field tag u.renderer.Tag
 
---- @class Renderer
+--- @class u.renderer.Renderer
 --- @field bufnr number
 --- @field ns number
 --- @field changedtick number
---- @field old { lines: string[]; extmarks: RendererExtmark[] }
---- @field curr { lines: string[]; extmarks: RendererExtmark[] }
+--- @field old { lines: string[]; extmarks: u.renderer.RendererExtmark[] }
+--- @field curr { lines: string[]; extmarks: u.renderer.RendererExtmark[] }
 local Renderer = {}
 Renderer.__index = Renderer
 M.Renderer = Renderer
 
+--- @private
 --- @param x any
 --- @return boolean
 function Renderer.is_tag(x) return type(x) == 'table' and x.kind == 'tag' end
 
+--- @private
 --- @param x any
 --- @return boolean
 function Renderer.is_tag_arr(x)
@@ -46,8 +75,8 @@ function Renderer.is_tag_arr(x)
   return #x == 0 or not Renderer.is_tag(x)
 end
 --- @param bufnr number|nil
-function Renderer.new(bufnr)
-  if bufnr == nil then bufnr = vim.api.nvim_get_current_buf() end
+function Renderer.new(bufnr) -- {{{
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
 
   if vim.b[bufnr]._renderer_ns == nil then
     vim.b[bufnr]._renderer_ns = vim.api.nvim_create_namespace('my.renderer:' .. tostring(bufnr))
@@ -60,14 +89,20 @@ function Renderer.new(bufnr)
     old = { lines = {}, extmarks = {} },
     curr = { lines = {}, extmarks = {} },
   }, Renderer)
+
+  vim.api.nvim_create_autocmd({ 'TextChanged', 'TextChangedI', 'TextChangedP' }, {
+    buffer = bufnr,
+    callback = function() self:_on_text_changed() end,
+  })
+
   return self
-end
+end -- }}}
 
 --- @param opts {
----   tree: Tree;
----   on_tag?: fun(tag: Tag, start0: [number, number], stop0: [number, number]): any;
+---   tree: u.renderer.Tree;
+---   on_tag?: fun(tag: u.renderer.Tag, start0: [number, number], stop0: [number, number]): any;
 --- }
-function Renderer.markup_to_lines(opts)
+function Renderer.markup_to_lines(opts) -- {{{
   --- @type string[]
   local lines = {}
 
@@ -84,8 +119,8 @@ function Renderer.markup_to_lines(opts)
     curr_col1 = 1
   end
 
-  --- @param node Node
-  local function visit(node)
+  --- @param node u.renderer.Node
+  local function visit(node) -- {{{
     if node == nil or type(node) == 'boolean' then return end
 
     if type(node) == 'string' then
@@ -99,11 +134,13 @@ function Renderer.markup_to_lines(opts)
 
       -- visit the children:
       if Renderer.is_tag_arr(node.children) then
-        for _, child in ipairs(node.children) do
+        for _, child in
+          ipairs(node.children --[[@as u.renderer.Node[] ]])
+        do
           -- newlines are not controlled by array entries, do NOT output a line here:
           visit(child)
         end
-      else
+      else -- luacheck: ignore
         visit(node.children)
       end
 
@@ -115,34 +152,92 @@ function Renderer.markup_to_lines(opts)
         visit(child)
       end
     end
-  end
+  end -- }}}
   visit(opts.tree)
 
   return lines
-end
+end -- }}}
 
 --- @param opts {
----   tree: string;
----   format_tag?: fun(tag: Tag): string;
+---   tree: u.renderer.Tree;
+---   format_tag?: fun(tag: u.renderer.Tag): string;
 --- }
 function Renderer.markup_to_string(opts) return table.concat(Renderer.markup_to_lines(opts), '\n') end
 
---- @param tree Tree
-function Renderer:render(tree)
+--- @param bufnr number
+--- @param old_lines string[] | nil
+--- @param new_lines string[]
+function Renderer.patch_lines(bufnr, old_lines, new_lines) -- {{{
+  --
+  -- Helpers:
+  --
+
+  --- @param start integer
+  --- @param end_ integer
+  --- @param strict_indexing boolean
+  --- @param replacement string[]
+  local function _set_lines(start, end_, strict_indexing, replacement)
+    vim.api.nvim_buf_set_lines(bufnr, start, end_, strict_indexing, replacement)
+  end
+
+  --- @param start_row integer
+  --- @param start_col integer
+  --- @param end_row integer
+  --- @param end_col integer
+  --- @param replacement string[]
+  local function _set_text(start_row, start_col, end_row, end_col, replacement)
+    vim.api.nvim_buf_set_text(bufnr, start_row, start_col, end_row, end_col, replacement)
+  end
+
+  -- Morph the text to the desired state:
+  local line_changes =
+    H.levenshtein(old_lines or vim.api.nvim_buf_get_lines(bufnr, 0, -1, false), new_lines)
+  for _, line_change in ipairs(line_changes) do
+    local lnum0 = line_change.index - 1
+
+    if line_change.kind == 'add' then
+      _set_lines(lnum0, lnum0, true, { line_change.item })
+    elseif line_change.kind == 'change' then
+      -- Compute inter-line diff, and apply:
+      local col_changes =
+        H.levenshtein(vim.split(line_change.from, ''), vim.split(line_change.to, ''))
+
+      for _, col_change in ipairs(col_changes) do
+        local cnum0 = col_change.index - 1
+        if col_change.kind == 'add' then
+          _set_text(lnum0, cnum0, lnum0, cnum0, { col_change.item })
+        elseif col_change.kind == 'change' then
+          _set_text(lnum0, cnum0, lnum0, cnum0 + 1, { col_change.to })
+        elseif col_change.kind == 'delete' then
+          _set_text(lnum0, cnum0, lnum0, cnum0 + 1, {})
+        else -- luacheck: ignore
+          -- No change
+        end
+      end
+    elseif line_change.kind == 'delete' then
+      _set_lines(lnum0, lnum0 + 1, true, {})
+    else -- luacheck: ignore
+      -- No change
+    end
+  end
+end -- }}}
+
+--- @param tree u.renderer.Tree
+function Renderer:render(tree) -- {{{
   local changedtick = vim.b[self.bufnr].changedtick
   if changedtick ~= self.changedtick then
     self.curr = { lines = vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
     self.changedtick = changedtick
   end
 
-  --- @type RendererExtmark[]
+  --- @type u.renderer.RendererExtmark[]
   local extmarks = {}
 
   --- @type string[]
   local lines = Renderer.markup_to_lines {
     tree = tree,
 
-    on_tag = function(tag, start0, stop0)
+    on_tag = function(tag, start0, stop0) -- {{{
       if tag.name == 'text' then
         local hl = tag.attributes.hl
         if type(hl) == 'string' then
@@ -150,116 +245,69 @@ function Renderer:render(tree)
           tag.attributes.extmark.hl_group = tag.attributes.extmark.hl_group or hl
         end
 
-        local extmark = tag.attributes.extmark
+        local extmark_opts = tag.attributes.extmark or {}
 
         -- Set any necessary keymaps:
         for _, mode in ipairs { 'i', 'n', 'v', 'x', 'o' } do
           for lhs, _ in pairs(tag.attributes[mode .. 'map'] or {}) do
             -- Force creating an extmark if there are key handlers. To accurately
             -- sense the bounds of the text, we need an extmark:
-            extmark = extmark or {}
-            vim.keymap.set(
-              'n',
-              lhs,
-              function() return self:_on_expr_map('n', lhs) end,
-              { buffer = self.bufnr, expr = true, replace_keycodes = true }
-            )
+            vim.keymap.set(mode, lhs, function()
+              local result = self:_expr_map_callback(mode, lhs)
+              -- If the handler indicates that it wants to swallow the event,
+              -- we have to convert that intention into something compatible
+              -- with expr-mappings, which don't support '<Nop>' (they try to
+              -- execute the literal characters). We'll use the 'g@' operator
+              -- to do that, forwarding the event to an operatorfunc that does
+              -- nothing:
+              if result == '' then
+                if mode == 'i' then
+                  return ''
+                else
+                  vim.go.operatorfunc = 'v:lua.URendererOpFuncSwallow'
+                  return 'g@ '
+                end
+              end
+              return result
+            end, { buffer = self.bufnr, expr = true, replace_keycodes = true })
           end
         end
 
-        if extmark then
         table.insert(extmarks, {
           start = start0,
           stop = stop0,
-            opts = extmark,
+          opts = extmark_opts,
           tag = tag,
         })
       end
-      end
-    end,
+    end, -- }}}
   }
 
   self.old = self.curr
   self.curr = { lines = lines, extmarks = extmarks }
   self:_reconcile()
-end
+  vim.cmd.doautocmd { args = { 'User', 'Renderer:' .. tostring(self.bufnr) .. ':render' } }
+end -- }}}
 
 --- @private
---- @param info string
---- @param start integer
---- @param end_ integer
---- @param strict_indexing boolean
---- @param replacement string[]
-function Renderer:_set_lines(info, start, end_, strict_indexing, replacement)
-  self:_log { 'set_lines', self.bufnr, start, end_, strict_indexing, replacement }
-  vim.api.nvim_buf_set_lines(self.bufnr, start, end_, strict_indexing, replacement)
-  self:_log { 'after(' .. info .. ')', vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
-end
-
---- @private
---- @param info string
---- @param start_row integer
---- @param start_col integer
---- @param end_row integer
---- @param end_col integer
---- @param replacement string[]
-function Renderer:_set_text(info, start_row, start_col, end_row, end_col, replacement)
-  self:_log { 'set_text', self.bufnr, start_row, start_col, end_row, end_col, replacement }
-  vim.api.nvim_buf_set_text(self.bufnr, start_row, start_col, end_row, end_col, replacement)
-  self:_log { 'after(' .. info .. ')', vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
-end
-
---- @private
-function Renderer:_log(...)
-  --
-  -- vim.print(...)
-end
-
---- @private
-function Renderer:_reconcile()
-  local line_changes = utils.levenshtein(self.old.lines, self.curr.lines)
-  self.old = self.curr
-
+function Renderer:_reconcile() -- {{{
   --
   -- Step 1: morph the text to the desired state:
   --
-  self:_log { line_changes = line_changes }
-  for _, line_change in ipairs(line_changes) do
-    local lnum0 = line_change.index - 1
-
-    if line_change.kind == 'add' then
-      self:_set_lines('add-line', lnum0, lnum0, true, { line_change.item })
-    elseif line_change.kind == 'change' then
-      -- Compute inter-line diff, and apply:
-      self:_log '--------------------------------------------------------------------------------'
-      local col_changes = utils.levenshtein(vim.split(line_change.from, ''), vim.split(line_change.to, ''))
-
-      for _, col_change in ipairs(col_changes) do
-        local cnum0 = col_change.index - 1
-        self:_log { line_change = col_change, cnum = cnum0, lnum = lnum0 }
-        if col_change.kind == 'add' then
-          self:_set_text('add-char', lnum0, cnum0, lnum0, cnum0, { col_change.item })
-        elseif col_change.kind == 'change' then
-          self:_set_text('change-char', lnum0, cnum0, lnum0, cnum0 + 1, { col_change.to })
-        elseif col_change.kind == 'delete' then
-          self:_set_text('del-char', lnum0, cnum0, lnum0, cnum0 + 1, {})
-        else
-          -- No change
-        end
-      end
-    elseif line_change.kind == 'delete' then
-      self:_set_lines('del-line', lnum0, lnum0 + 1, true, {})
-    else
-      -- No change
-    end
-  end
+  Renderer.patch_lines(self.bufnr, self.old.lines, self.curr.lines)
   self.changedtick = vim.b[self.bufnr].changedtick
 
   --
   -- Step 2: reconcile extmarks:
+  -- You may be tempted to try to keep track of which extmarks are needed, and
+  -- only delete those that are not needed. However, each time a tree is
+  -- rendered, brand new extmarks are created. For simplicity, it is better to
+  -- just delete all extmarks, and recreate them.
   --
+
   -- Clear current extmarks:
   vim.api.nvim_buf_clear_namespace(self.bufnr, self.ns, 0, -1)
+
   -- Set current extmarks:
   for _, extmark in ipairs(self.curr.extmarks) do
     extmark.id = vim.api.nvim_buf_set_extmark(
@@ -271,19 +319,30 @@ function Renderer:_reconcile()
         id = extmark.id,
         end_row = extmark.stop[1],
         end_col = extmark.stop[2],
+        -- If we change the text starting from the beginning (where the extmark
+        -- is), we don't want the extmark to move to the right.
+        right_gravity = false,
+        -- If we change the text starting from the end (where the end extmark
+        -- is), we don't want the extmark to stay stationary: we want it to
+        -- move to the right.
+        end_right_gravity = true,
       }, extmark.opts)
     )
   end
-end
+
+  self.old = self.curr
+end -- }}}
 
 --- @private
 --- @param mode string
 --- @param lhs string
-function Renderer:_on_expr_map(mode, lhs)
+function Renderer:_expr_map_callback(mode, lhs) -- {{{
   -- find the tag with the smallest intersection that contains the cursor:
   local pos0 = vim.api.nvim_win_get_cursor(0)
   pos0[1] = pos0[1] - 1 -- make it actually 0-based
-  local pos_infos = self:get_pos_infos(pos0)
+  log('_expr_map_callback: pos0:', pos0)
+  local pos_infos = self:get_tags_at(pos0)
+  log('_expr_map_callback: pos_infos:', pos_infos)
 
   if #pos_infos == 0 then return lhs end
 
@@ -293,9 +352,10 @@ function Renderer:_on_expr_map(mode, lhs)
     local tag = pos_info.tag
 
     -- is the tag listening?
+    --- @type u.renderer.TagEventHandler?
     local f = vim.tbl_get(tag.attributes, mode .. 'map', lhs)
     if type(f) == 'function' then
-      local result = f()
+      local result = f(tag, mode, lhs)
       if result == '' then
         -- bubble-up to the next tag, but set cancel to true, in case there are
         -- no more tags to bubble up to:
@@ -308,25 +368,199 @@ function Renderer:_on_expr_map(mode, lhs)
 
   -- Resort to default behavior:
   return cancel and '' or lhs
+end -- }}}
+
+function Renderer:_on_text_changed() -- {{{
+  -- Reset changedtick, so that the reconciler knows to refresh its cached
+  -- buffer-content before computing the diff:
+  self.changedtick = 0
+
+  --- @type integer, integer
+  local l, c = unpack(vim.api.nvim_win_get_cursor(0))
+  l = l - 1 -- make it actually 0-based
+  local pos_infos = self:get_tags_at({ l, c }, 'i')
+  log('_on_text_changed', { cursor_0_0 = { l, c }, pos_infos = pos_infos })
+  for _, pos_info in ipairs(pos_infos) do
+    local extmark_inf = pos_info.extmark
+    local tag = pos_info.tag
+
+    local on_change = tag.attributes.on_change
+    if on_change and type(on_change) == 'function' then
+      local extmark =
+        vim.api.nvim_buf_get_extmark_by_id(self.bufnr, self.ns, extmark_inf.id, { details = true })
+
+      --- @type integer, integer, vim.api.keyset.extmark_details
+      local start_row0, start_col0, details = unpack(extmark)
+      local end_row0, end_col0 = details.end_row, details.end_col
+      log('_on_text_changed: fetched current extmark for pos_info', {
+        pos_info = pos_info,
+        curr_extmark = {
+          start_row0 = start_row0,
+          start_col0 = start_col0,
+          end_row0 = end_row0,
+          end_col0 = end_col0,
+          details = details,
+        },
+      })
+
+      if start_row0 == end_row0 and start_col0 == end_col0 then
+        on_change ''
+        return
       end
 
+      local buf_max_line0 = math.max(1, vim.api.nvim_buf_line_count(self.bufnr) - 1)
+      if end_row0 > buf_max_line0 then
+        end_row0 = buf_max_line0
+        local last_line = vim.api.nvim_buf_get_lines(self.bufnr, end_row0, end_row0 + 1, false)[1]
+          or ''
+        end_col0 = last_line:len()
+      end
+      if end_col0 == 0 then
+        end_row0 = end_row0 - 1
+        local last_line = vim.api.nvim_buf_get_lines(self.bufnr, end_row0, end_row0 + 1, false)[1]
+          or ''
+        end_col0 = last_line:len()
+      end
+      log('_on_text_changed: after position correction', {
+        curr_extmark = {
+          start_row0 = start_row0,
+          start_col0 = start_col0,
+          end_row0 = end_row0,
+          end_col0 = end_col0,
+        },
+      })
+
+      if start_row0 == end_row0 and start_col0 == end_col0 then
+        on_change ''
+        return
+      end
+
+      local pos1 = { self.bufnr, start_row0 + 1, start_col0 + 1 }
+      local pos2 = { self.bufnr, end_row0 + 1, end_col0 }
+      local ok, lines = pcall(vim.fn.getregion, pos1, pos2, { type = 'v' })
+      if not ok then
+        log('_on_text_changed: getregion: invalid-pos ', {
+          { pos1, pos2 },
+        })
+        vim.api.nvim_echo({
+          { '(u.nvim:getregion:invalid-pos) ', 'ErrorMsg' },
+          {
+            '{ start, end } = ' .. vim.inspect({ pos1, pos2 }, { newline = ' ', indent = '' }),
+          },
+        }, true, {})
+        error(lines)
+      end
+      local text = table.concat(lines, '\n')
+      on_change(text)
+    end
+  end
+end -- }}}
+
+--- @private
+function Renderer:_debug() -- {{{
+  local prev_w = vim.api.nvim_get_current_win()
+  vim.cmd.vnew()
+  local info_bufnr = vim.api.nvim_get_current_buf()
+  vim.bo.bufhidden = 'delete'
+  vim.bo.buflisted = false
+  vim.bo.buftype = 'nowrite'
+
+  local ids = {}
+  local function cleanup()
+    for _, id in ipairs(ids) do
+      vim.api.nvim_del_autocmd(id)
+    end
+    vim.api.nvim_buf_delete(info_bufnr, { force = true })
+  end
+
+  local function autocmd_callback()
+    if vim.api.nvim_get_current_win() ~= prev_w then return end
+
+    local l, c = unpack(vim.api.nvim_win_get_cursor(0))
+    l = l - 1 -- make it actually 0-based
+
+    local info = {
+      cursor = {
+        pos = { l, c },
+        tags = self:get_tags_at { l, c },
+        extmarks = vim.api.nvim_buf_get_extmarks(
+          self.bufnr,
+          self.ns,
+          { l, c },
+          { l, c },
+          { details = true, overlap = true }
+        ),
+      },
+      computed = {
+        extmarks = self.curr.extmarks,
+      },
+    }
+    vim.api.nvim_buf_set_lines(info_bufnr, 0, -1, true, vim.split(vim.inspect(info), '\n'))
+  end
+
+  table.insert(
+    ids,
+    vim.api.nvim_create_autocmd({ 'CursorMoved', 'CursorMovedI' }, {
+      callback = autocmd_callback,
+    })
+  )
+  table.insert(
+    ids,
+    vim.api.nvim_create_autocmd({ 'User' }, {
+      pattern = 'Renderer:' .. tostring(self.bufnr) .. ':render',
+      callback = autocmd_callback,
+    })
+  )
+  table.insert(
+    ids,
+    vim.api.nvim_create_autocmd('WinClosed', {
+      pattern = tostring(vim.api.nvim_get_current_win()),
+      callback = cleanup,
+    })
+  )
+  table.insert(
+    ids,
+    vim.api.nvim_create_autocmd('WinClosed', {
+      pattern = tostring(prev_w),
+      callback = cleanup,
+    })
+  )
+
+  vim.api.nvim_set_current_win(prev_w)
+end -- }}}
+
 --- Returns pairs of extmarks and tags associate with said extmarks. The
 --- returned tags/extmarks are sorted smallest (innermost) to largest
 --- (outermost).
 ---
 --- @private (private for now)
 --- @param pos0 [number; number]
---- @return { extmark: RendererExtmark; tag: Tag; }[]
-function Renderer:get_pos_infos(pos0)
+--- @param mode string?
+--- @return { extmark: u.renderer.RendererExtmark; tag: u.renderer.Tag; }[]
+function Renderer:get_tags_at(pos0, mode) -- {{{
   local cursor_line0, cursor_col0 = pos0[1], pos0[2]
+  if not mode then mode = vim.api.nvim_get_mode().mode end
+  mode = mode:sub(1, 1) -- we don't care about sub-modes
+
+  local raw_overlapping_extmarks = vim.api.nvim_buf_get_extmarks(
+    self.bufnr,
+    self.ns,
+    pos0,
+    pos0,
+    { details = true, overlap = true }
+  )
+  log(
+    'get_tags_at: context:',
+    { pos0 = pos0, mode = mode, raw_overlapping_extmarks = raw_overlapping_extmarks }
+  )
 
   -- The cursor (block) occupies **two** extmark spaces: one for it's left
   -- edge, and one for it's right. We need to do our own intersection test,
   -- because the NeoVim API is over-inclusive in what it returns:
-  --- @type RendererExtmark[]
-  local intersecting_extmarks = vim
-    .iter(vim.api.nvim_buf_get_extmarks(self.bufnr, self.ns, pos0, pos0, { details = true, overlap = true }))
-    --- @return RendererExtmark
+  --- @type u.renderer.RendererExtmark[]
+  local mapped_extmarks = vim
+    .iter(raw_overlapping_extmarks)
+    --- @return u.renderer.RendererExtmark
     :map(function(ext)
       --- @type number, number, number, { end_row?: number; end_col?: number }|nil
       local id, line0, col0, details = unpack(ext)
@@ -337,13 +571,43 @@ function Renderer:get_pos_infos(pos0)
       end
       return { id = id, start = start, stop = stop, opts = details }
     end)
-    --- @param ext RendererExtmark
+    :totable()
+
+  local intersecting_extmarks = vim
+    .iter(mapped_extmarks)
+    --- @param ext u.renderer.RendererExtmark
     :filter(function(ext)
       if ext.stop[1] ~= nil and ext.stop[2] ~= nil then
-        return cursor_line0 >= ext.start[1]
-          and cursor_col0 >= ext.start[2]
+        -- If we've "ciw" and "collapsed" an extmark onto the cursor,
+        -- the cursor pos will equal the exmark's start AND end. In this
+        -- case, we want to include the extmark.
+        if
+          cursor_line0 == ext.start[1]
+          and cursor_col0 == ext.start[2]
+          and cursor_line0 == ext.stop[1]
+          and cursor_col0 == ext.stop[2]
+        then
+          return true
+        end
+
+        return
+          -- START: line check
+          cursor_line0 >= ext.start[1]
+            -- START: column check
+            and (cursor_line0 ~= ext.start[1] or cursor_col0 >= ext.start[2])
+            -- STOP: line check
             and cursor_line0 <= ext.stop[1]
-          and cursor_col0 < ext.stop[2]
+            -- STOP: column check
+            and (
+              cursor_line0 ~= ext.stop[1]
+              or (
+                mode == 'i'
+                  -- In insert mode, the cursor is "thin", so <= to compensate:
+                  and cursor_col0 <= ext.stop[2]
+                -- In normal mode, the cursor is "wide", so < to compensate:
+                or cursor_col0 < ext.stop[2]
+              )
+            )
       else
         return true
       end
@@ -353,8 +617,8 @@ function Renderer:get_pos_infos(pos0)
   -- Sort the tags into smallest (inner) to largest (outer):
   table.sort(
     intersecting_extmarks,
-    --- @param x1 RendererExtmark
-    --- @param x2 RendererExtmark
+    --- @param x1 u.renderer.RendererExtmark
+    --- @param x2 u.renderer.RendererExtmark
     function(x1, x2)
       if
         x1.start[1] == x2.start[1]
@@ -376,10 +640,10 @@ function Renderer:get_pos_infos(pos0)
   -- created extmarks in self.curr.extmarks, which also has which tag each
   -- extmark is associated with. Cross-reference with that list to get a list
   -- of tags that we need to fire events for:
-  --- @type { extmark: RendererExtmark; tag: Tag }[]
+  --- @type { extmark: u.renderer.RendererExtmark; tag: u.renderer.Tag }[]
   local matching_tags = vim
     .iter(intersecting_extmarks)
-    --- @param ext RendererExtmark
+    --- @param ext u.renderer.RendererExtmark
     :map(function(ext)
       for _, extmark_cache in ipairs(self.curr.extmarks) do
         if extmark_cache.id == ext.id then return { extmark = ext, tag = extmark_cache.tag } end
@@ -388,14 +652,25 @@ function Renderer:get_pos_infos(pos0)
     :totable()
 
   return matching_tags
+end -- }}}
+
+--- @private
+--- @param tag_or_id string | u.renderer.Tag
+--- @return { start: [number, number]; stop: [number, number] } | nil
+function Renderer:get_tag_bounds(tag_or_id) -- {{{
+  for _, x in ipairs(self.curr.extmarks) do
+    local pos = { start = x.start, stop = x.stop }
+    local does_tag_match = type(tag_or_id) == 'string' and x.tag.attributes.id == tag_or_id
+      or x.tag == tag_or_id
+    if does_tag_match then return pos end
   end
+end -- }}}
 
---------------------------------------------------------------------------------
--- TreeBuilder class
---------------------------------------------------------------------------------
+-- }}}
 
---- @class TreeBuilder
---- @field private nodes Node[]
+-- TreeBuilder {{{
+--- @class u.renderer.TreeBuilder
+--- @field private nodes u.renderer.Node[]
 local TreeBuilder = {}
 TreeBuilder.__index = TreeBuilder
 M.TreeBuilder = TreeBuilder
@@ -405,8 +680,8 @@ function TreeBuilder.new()
   return self
 end
 
---- @param nodes Tree
---- @return TreeBuilder
+--- @param nodes u.renderer.Tree
+--- @return u.renderer.TreeBuilder
 function TreeBuilder:put(nodes)
   table.insert(self.nodes, nodes)
   return self
@@ -414,16 +689,16 @@ end
 
 --- @param name string
 --- @param attributes? table<string, any>
---- @param children? Node | Node[]
---- @return TreeBuilder
+--- @param children? u.renderer.Node | u.renderer.Node[]
+--- @return u.renderer.TreeBuilder
 function TreeBuilder:put_h(name, attributes, children)
   local tag = M.h(name, attributes, children)
   table.insert(self.nodes, tag)
   return self
 end
 
---- @param fn fun(TreeBuilder): any
---- @return TreeBuilder
+--- @param fn fun(tb: u.renderer.TreeBuilder): any
+--- @return u.renderer.TreeBuilder
 function TreeBuilder:nest(fn)
   local nested_writer = TreeBuilder.new()
   fn(nested_writer)
@@ -431,7 +706,132 @@ function TreeBuilder:nest(fn)
   return self
 end
 
---- @return Tree
+--- @generic T
+--- @param arr T[]
+--- @param f fun(tb: u.renderer.TreeBuilder, item: T, idx: number): any
+function TreeBuilder:ipairs(arr, f)
+  return self:nest(function(tb)
+    for idx, item in ipairs(arr) do
+      f(tb, item, idx)
+    end
+  end)
+end
+
+--- @param tab table
+--- @param f fun(tb: u.renderer.TreeBuilder, key: any, value: any): any
+function TreeBuilder:pairs(tab, f)
+  return self:nest(function(tb)
+    for k, v in pairs(tab) do
+      f(tb, k, v)
+    end
+  end)
+end
+
+--- @return u.renderer.Tree
 function TreeBuilder:tree() return self.nodes end
+-- }}}
+
+-- Levenshtein utility {{{
+-- luacheck: ignore
+--- @alias u.renderer.LevenshteinChange<T> ({ kind: 'add'; item: T; index: number; } | { kind: 'delete'; item: T; index: number; } | { kind: 'change'; from: T; to: T; index: number; })
+--- @private
+--- @generic T
+--- @param x `T`[]
+--- @param y T[]
+--- @param cost? { of_delete?: fun(x: T): number; of_add?: fun(x: T): number; of_change?: fun(x: T, y: T): number; }
+--- @return u.renderer.LevenshteinChange<T>[] The changes, from last (greatest index) to first (smallest index).
+function H.levenshtein(x, y, cost)
+  -- At the moment, this whole `cost` plumbing is not used. Deletes have the
+  -- same cost as Adds or Changes. I can imagine a future, however, where
+  -- fudging with the costs of operations produces a more optimized change-set
+  -- that is tailored to working better with how NeoVim manipulates text. I've
+  -- done no further investigation in this area, however, so it's impossible to
+  -- tell if such tuning would produce real benefit. For now, I'm leaving this
+  -- in here even though it's not actively used. Hopefully having this
+  -- callback-based plumbing does not cause too much of a performance hit to
+  -- the renderer.
+  cost = cost or {}
+  local cost_of_delete_f = cost.of_delete or function() return 1 end
+  local cost_of_add_f = cost.of_add or function() return 1 end
+  local cost_of_change_f = cost.of_change or function() return 1 end
+
+  local m, n = #x, #y
+  -- Initialize the distance matrix
+  local dp = {}
+  for i = 0, m do
+    dp[i] = {}
+    for j = 0, n do
+      dp[i][j] = 0
+    end
+  end
+
+  -- Fill the base cases
+  for i = 0, m do
+    dp[i][0] = i
+  end
+  for j = 0, n do
+    dp[0][j] = j
+  end
+
+  -- Compute the Levenshtein distance dynamically
+  for i = 1, m do
+    for j = 1, n do
+      if x[i] == y[j] then
+        dp[i][j] = dp[i - 1][j - 1] -- no cost if items are the same
+      else
+        local cost_delete = dp[i - 1][j] + cost_of_delete_f(x[i])
+        local cost_add = dp[i][j - 1] + cost_of_add_f(y[j])
+        local cost_change = dp[i - 1][j - 1] + cost_of_change_f(x[i], y[j])
+        dp[i][j] = math.min(cost_delete, cost_add, cost_change)
+      end
+    end
+  end
+
+  -- Backtrack to find the changes
+  local i = m
+  local j = n
+  --- @type u.renderer.LevenshteinChange[]
+  local changes = {}
+
+  while i > 0 or j > 0 do
+    local default_cost = dp[i][j]
+    local cost_of_change = (i > 0 and j > 0) and dp[i - 1][j - 1] or default_cost
+    local cost_of_add = j > 0 and dp[i][j - 1] or default_cost
+    local cost_of_delete = i > 0 and dp[i - 1][j] or default_cost
+
+    --- @param u number
+    --- @param v number
+    --- @param w number
+    local function is_first_min(u, v, w) return u <= v and u <= w end
+
+    if is_first_min(cost_of_change, cost_of_add, cost_of_delete) then
+      -- potential change
+      if x[i] ~= y[j] then
+        --- @type u.renderer.LevenshteinChange
+        local change = { kind = 'change', from = x[i], index = i, to = y[j] }
+        table.insert(changes, change)
+      end
+      i = i - 1
+      j = j - 1
+    elseif is_first_min(cost_of_add, cost_of_change, cost_of_delete) then
+      -- addition
+      --- @type u.renderer.LevenshteinChange
+      local change = { kind = 'add', item = y[j], index = i + 1 }
+      table.insert(changes, change)
+      j = j - 1
+    elseif is_first_min(cost_of_delete, cost_of_change, cost_of_add) then
+      -- deletion
+      --- @type u.renderer.LevenshteinChange
+      local change = { kind = 'delete', item = x[i], index = i }
+      table.insert(changes, change)
+      i = i - 1
+    else
+      error 'unreachable'
+    end
+  end
+
+  return changes
+end
+-- }}}
 
 return M

lua/u/repeat.lua

@@ -1,61 +1,39 @@
 local M = {}
 
-local function _normal(cmd) vim.cmd { cmd = 'normal', args = { cmd }, bang = true } end
+local IS_REPEATING = false
+--- @type function
+local REPEAT_ACTION = nil
 
-M.native_repeat = function() _normal '.' end
-M.native_undo = function() _normal 'u' end
+local function is_repeatable_last_mutator() return vim.b.changedtick <= (vim.b.my_changedtick or 0) end
 
-local function update_ts() vim.b.tt_changedtick = vim.b.changedtick end
-
----@param cmd? string|fun():unknown
-function M.set(cmd)
-  update_ts()
-  if cmd ~= nil then vim.b.tt_repeatcmd = cmd end
+--- @param f fun()
+function M.run_repeatable(f)
+  REPEAT_ACTION = f
+  REPEAT_ACTION()
+  vim.b.my_changedtick = vim.b.changedtick
 end
 
-local function tt_was_last_repeatable()
-  local ts, tt_ts = vim.b.changedtick, vim.b.tt_changedtick
-  return tt_ts ~= nil and ts <= tt_ts
-end
-
----@generic T
----@param cmd string|fun():T
----@return T
-function M.run(cmd)
-  M.set(cmd)
-  local result = cmd()
-  update_ts()
-  return result
-end
-
-function M.do_repeat()
-  local tt_cmd = vim.b.tt_repeatcmd
-  if not tt_was_last_repeatable() or (type(tt_cmd) ~= 'function' and type(tt_cmd) ~= 'string') then
-    return M.native_repeat()
-  end
-
-  -- execute the cached command:
-  local count = vim.api.nvim_get_vvar 'count1'
-  if type(tt_cmd) == 'string' then
-    _normal(count .. tt_cmd --[[@as string]])
-  else
-    local last_return
-    for _ = 1, count do
-      last_return = M.run(tt_cmd --[[@as fun():any]])
-    end
-    return last_return
-  end
-end
-
-function M.undo()
-  local tt_was_last_repeatable_before_undo = tt_was_last_repeatable()
-  M.native_undo()
-  if tt_was_last_repeatable_before_undo then update_ts() end
-end
+function M.is_repeating() return IS_REPEATING end
 
 function M.setup()
-  vim.keymap.set('n', '.', M.do_repeat)
-  vim.keymap.set('n', 'u', M.undo)
+  vim.keymap.set('n', '.', function()
+    IS_REPEATING = true
+    for _ = 1, vim.v.count1 do
+      if is_repeatable_last_mutator() and type(REPEAT_ACTION) == 'function' then
+        M.run_repeatable(REPEAT_ACTION)
+      else
+        vim.cmd { cmd = 'normal', args = { '.' }, bang = true }
+      end
+    end
+    IS_REPEATING = false
+  end)
+  vim.keymap.set('n', 'u', function()
+    local was_repeatable_last_mutator = is_repeatable_last_mutator()
+    for _ = 1, vim.v.count1 do
+      vim.cmd { cmd = 'normal', args = { 'u' }, bang = true }
+    end
+    if was_repeatable_last_mutator then vim.b.my_changedtick = vim.b.changedtick end
+  end)
 end
 
 return M

lua/u/state.lua

@@ -1,90 +0,0 @@
----@class State
----@field buf number
----@field registers table
----@field marks table
----@field positions table
----@field keymaps { mode: string; lhs: any, rhs: any, buffer?: number }[]
----@field global_options table<string, any>
----@field win_view vim.fn.winsaveview.ret|nil
-local State = {}
-
----@param buf number
----@return State
-function State.new(buf)
-  if buf == 0 then buf = vim.api.nvim_get_current_buf() end
-  local s = { buf = buf, registers = {}, marks = {}, positions = {}, keymaps = {}, global_options = {} }
-  setmetatable(s, { __index = State })
-  return s
-end
-
----@generic T
----@param buf number
----@param f fun(s: State):T
----@return T
-function State.run(buf, f)
-  local s = State.new(buf)
-  local ok, result = pcall(f, s)
-  s:restore()
-  if not ok then error(result) end
-  return result
-end
-
----@param buf number
----@param f fun(s: State, callback: fun(): any):any
----@param callback fun():any
-function State.run_async(buf, f, callback)
-  local s = State.new(buf)
-  f(s, function()
-    s:restore()
-    callback()
-  end)
-end
-
-function State:track_keymap(mode, lhs)
-  local old =
-    -- Look up the mapping in buffer-local maps:
-    vim.iter(vim.api.nvim_buf_get_keymap(self.buf, mode)):find(function(map) return map.lhs == lhs end)
-    -- Look up the mapping in global maps:
-    or vim.iter(vim.api.nvim_get_keymap(mode)):find(function(map) return map.lhs == lhs end)
-
-  -- Did we find a mapping?
-  if old == nil then return end
-
-  -- Track it:
-  table.insert(self.keymaps, { mode = mode, lhs = lhs, rhs = old.rhs or old.callback, buffer = old.buffer })
-end
-
----@param reg string
-function State:track_register(reg) self.registers[reg] = vim.fn.getreg(reg) end
-
----@param mark string
-function State:track_mark(mark) self.marks[mark] = vim.api.nvim_buf_get_mark(self.buf, mark) end
-
----@param pos string
-function State:track_pos(pos) self.positions[pos] = vim.fn.getpos(pos) end
-
----@param nm string
-function State:track_global_option(nm) self.global_options[nm] = vim.g[nm] end
-
-function State:track_winview() self.win_view = vim.fn.winsaveview() end
-
-function State:restore()
-  for reg, val in pairs(self.registers) do
-    vim.fn.setreg(reg, val)
-  end
-  for mark, val in pairs(self.marks) do
-    vim.api.nvim_buf_set_mark(self.buf, mark, val[1], val[2], {})
-  end
-  for pos, val in pairs(self.positions) do
-    vim.fn.setpos(pos, val)
-  end
-  for _, map in ipairs(self.keymaps) do
-    vim.keymap.set(map.mode, map.lhs, map.rhs, { buffer = map.buffer })
-  end
-  for nm, val in pairs(self.global_options) do
-    vim.g[nm] = val
-  end
-  if self.win_view ~= nil then vim.fn.winrestview(self.win_view) end
-end
-
-return State

lua/u/tracker.lua

@@ -6,19 +6,19 @@ M.debug = false
 -- class Signal
 --------------------------------------------------------------------------------
 
---- @class Signal
+--- @class u.Signal<T>
 --- @field name? string
 --- @field private changing boolean
---- @field private value any
+--- @field private value T
 --- @field private subscribers table<function, boolean>
 --- @field private on_dispose_callbacks function[]
 local Signal = {}
 M.Signal = Signal
 Signal.__index = Signal
 
---- @param value any
+--- @param value `T`
 --- @param name? string
---- @return Signal
+--- @return u.Signal<T>
 function Signal:new(value, name)
   local obj = setmetatable({
     name = name,
@@ -30,14 +30,17 @@ function Signal:new(value, name)
   return obj
 end
 
---- @param value any
+--- @param value T
 function Signal:set(value)
   self.value = value
 
   -- We don't handle cyclic updates:
   if self.changing then
     if M.debug then
-      vim.notify('circular dependency detected' .. (self.name and (' in ' .. self.name) or ''), vim.log.levels.WARN)
+      vim.notify(
+        'circular dependency detected' .. (self.name and (' in ' .. self.name) or ''),
+        vim.log.levels.WARN
+      )
     end
     return
   end
@@ -64,11 +67,12 @@ function Signal:set(value)
   end
 end
 
+--- @param value T
 function Signal:schedule_set(value)
   vim.schedule(function() self:set(value) end)
 end
 
---- @return any
+--- @return T
 function Signal:get()
   local ctx = M.ExecutionContext.current()
   if ctx then ctx:track(self) end
@@ -82,8 +86,8 @@ function Signal:update(fn) self:set(fn(self.value)) end
 function Signal:schedule_update(fn) self:schedule_set(fn(self.value)) end
 
 --- @generic U
---- @param fn fun(value: T): U
---- @return Signal --<U>
+--- @param fn fun(value: T): `U`
+--- @return u.Signal<U>
 function Signal:map(fn)
   local mapped_signal = M.create_memo(function()
     local value = self:get()
@@ -92,13 +96,13 @@ function Signal:map(fn)
   return mapped_signal
 end
 
---- @return Signal
+--- @return u.Signal<T>
 function Signal:clone()
   return self:map(function(x) return x end)
 end
 
 --- @param fn fun(value: T): boolean
---- @return Signal -- <T>
+--- @return u.Signal<T>
 function Signal:filter(fn)
   local filtered_signal = M.create_signal(nil, self.name and self.name .. ':filtered' or nil)
   local unsubscribe_from_self = self:subscribe(function(value)
@@ -109,10 +113,10 @@ function Signal:filter(fn)
 end
 
 --- @param ms number
---- @return Signal -- <T>
+--- @return u.Signal<T>
 function Signal:debounce(ms)
   local function set_timeout(timeout, callback)
-    local timer = (vim.uv or vim.loop).new_timer()
+    local timer = assert((vim.uv or vim.loop).new_timer(), 'could not create new timer')
     timer:start(timeout, 0, function()
       timer:stop()
       timer:close()
@@ -123,15 +127,15 @@ function Signal:debounce(ms)
 
   local filtered = M.create_signal(self.value, self.name and self.name .. ':debounced' or nil)
 
-  --- @type {
-  --   queued: { value: T, ts: number }[]
-  --   timer?: uv_timer_t
-  -- }
+  --- @diagnostic disable-next-line: undefined-doc-name
+  --- @type { queued: { value: T, ts: number }[], timer?: uv.uv_timer_t }
   local state = { queued = {}, timer = nil }
   local function clear_timeout()
     if state.timer == nil then return end
     pcall(function()
+      --- @diagnostic disable-next-line: undefined-field
       state.timer:stop()
+      --- @diagnostic disable-next-line: undefined-field
       state.timer:close()
     end)
     state.timer = nil
@@ -143,7 +147,10 @@ function Signal:debounce(ms)
     local now_ms = (vim.uv or vim.loop).hrtime() / 1e6
 
     -- If there is anything older than `ms` in our queue, emit it:
-    local older_than_ms = vim.iter(state.queued):filter(function(item) return now_ms - item.ts > ms end):totable()
+    local older_than_ms = vim
+      .iter(state.queued)
+      :filter(function(item) return now_ms - item.ts > ms end)
+      :totable()
     local last_older_than_ms = older_than_ms[#older_than_ms]
     if last_older_than_ms then
       filtered:set(last_older_than_ms.value)
@@ -196,16 +203,17 @@ end
 -- class ExecutionContext
 --------------------------------------------------------------------------------
 
-CURRENT_CONTEXT = nil
+--- @type u.ExecutionContext|nil
+local CURRENT_CONTEXT = nil
 
---- @class ExecutionContext
---- @field signals table<Signal, boolean>
+--- @class u.ExecutionContext
+--- @field signals table<u.Signal, boolean>
 local ExecutionContext = {}
 M.ExecutionContext = ExecutionContext
 ExecutionContext.__index = ExecutionContext
 
---- @return ExecutionContext
-function ExecutionContext:new()
+--- @return u.ExecutionContext
+function ExecutionContext.new()
   return setmetatable({
     signals = {},
     subscribers = {},
@@ -215,8 +223,8 @@ end
 function ExecutionContext.current() return CURRENT_CONTEXT end
 
 --- @param fn function
---- @param ctx ExecutionContext
-function ExecutionContext:run(fn, ctx)
+--- @param ctx u.ExecutionContext
+function ExecutionContext.run(fn, ctx)
   local oldCtx = CURRENT_CONTEXT
   CURRENT_CONTEXT = ctx
   local result
@@ -256,16 +264,18 @@ end
 -- Helpers
 --------------------------------------------------------------------------------
 
---- @param value any
+--- @generic T
+--- @param value `T`
 --- @param name? string
---- @return Signal
+--- @return u.Signal<T>
 function M.create_signal(value, name) return Signal:new(value, name) end
 
---- @param fn function
+--- @generic T
+--- @param fn fun(): `T`
 --- @param name? string
---- @return Signal
+--- @return u.Signal
 function M.create_memo(fn, name)
-  --- @type Signal
+  --- @type u.Signal<T> | nil
   local result
   local unsubscribe = M.create_effect(function()
     local value = fn()
@@ -276,15 +286,15 @@ function M.create_memo(fn, name)
       result = M.create_signal(value, name and ('m.s:' .. name) or nil)
     end
   end, name)
-  result:on_dispose(unsubscribe)
-  return result
+  assert(result):on_dispose(unsubscribe)
+  return assert(result)
 end
 
 --- @param fn function
 --- @param name? string
 function M.create_effect(fn, name)
-  local ctx = M.ExecutionContext:new()
-  M.ExecutionContext:run(fn, ctx)
+  local ctx = M.ExecutionContext.new()
+  M.ExecutionContext.run(fn, ctx)
   return ctx:subscribe(function()
     if name and M.debug then
       local deps = vim

lua/u/txtobj.lua

@@ -0,0 +1,45 @@
+local Range = require 'u.range'
+
+local M = {}
+
+local ESC = vim.api.nvim_replace_termcodes('<Esc>', true, false, true)
+
+--- @param key_seq string
+--- @param fn fun(key_seq: string):u.Range|nil
+--- @param opts? { buffer: number|nil }
+function M.define(key_seq, fn, opts)
+  if opts ~= nil and opts.buffer == 0 then opts.buffer = vim.api.nvim_get_current_buf() end
+
+  local function handle_visual()
+    local range = fn(key_seq)
+    if range == nil or range:is_empty() then
+      vim.cmd.normal(ESC)
+      return
+    end
+    range:set_visual_selection()
+  end
+  vim.keymap.set({ 'x' }, key_seq, handle_visual, opts and { buffer = opts.buffer } or nil)
+
+  local function handle_normal()
+    local range = fn(key_seq)
+    if range == nil then return end
+
+    if not range:is_empty() then
+      range:set_visual_selection()
+    else
+      local original_eventignore = vim.go.eventignore
+      vim.go.eventignore = 'all'
+
+      -- insert a single space, so we can select it:
+      local p = range.start
+      p:insert_before ' '
+      vim.go.eventignore = original_eventignore
+
+      -- select the space:
+      Range.new(p, p, 'v'):set_visual_selection()
+    end
+  end
+  vim.keymap.set({ 'o' }, key_seq, handle_normal, opts and { buffer = opts.buffer } or nil)
+end
+
+return M

lua/u/utils.lua

@@ -4,14 +4,63 @@ local M = {}
 -- Types
 --
 
----@alias QfItem { col: number, filename: string, kind: string, lnum: number, text: string }
----@alias KeyMaps table<string, fun(): any | string> }
----@alias CmdArgs { args: string; bang: boolean; count: number; fargs: string[]; line1: number; line2: number; mods: string; name: string; range: 0|1|2; reg: string; smods: any; info: Range|nil }
+--- @class u.utils.QfItem
+--- @field col number
+--- @field filename string
+--- @field kind string
+--- @field lnum number
+--- @field text string
 
+--- @class u.utils.RawCmdArgs
+--- @field args string
+--- @field bang boolean
+--- @field count number
+--- @field fargs string[]
+--- @field line1 number
+--- @field line2 number
+--- @field mods string
+--- @field name string
+--- @field range 0|1|2
+--- @field reg string
+--- @field smods any
+
+--- @class u.utils.CmdArgs: u.utils.RawCmdArgs
+--- @field info u.Range|nil
+
+--- @class u.utils.UcmdArgs
+--- @field nargs? 0|1|'*'|'?'|'+'
+--- @field range? boolean|'%'|number
+--- @field count? boolean|number
+--- @field addr? string
+--- @field completion? string
+--- @field force? boolean
+--- @field preview? fun(opts: u.utils.UcmdArgs, ns: integer, buf: integer):0|1|2
+
+--
+-- Functions
+--
+
+--- Debug utility that prints a value and returns it unchanged.
+--- Useful for debugging in the middle of expressions or function chains.
+---
 --- @generic T
---- @param x `T`
---- @param message? string
---- @return T
+--- @param x `T` The value to debug print
+--- @param message? string Optional message to print alongside the value
+--- @return T The original value, unchanged
+---
+--- @usage
+--- ```lua
+--- -- Debug a value in the middle of a chain:
+--- local result = some_function()
+---   :map(utils.dbg)  -- prints the intermediate value
+---   :filter(predicate)
+---
+--- -- Debug with a custom message:
+--- local config = utils.dbg(get_config(), "Current config:")
+---
+--- -- Debug return values:
+--- return utils.dbg(calculate_result(), "Final result")
+--- ```
 function M.dbg(x, message)
   local t = {}
   if message ~= nil then table.insert(t, message) end
@@ -20,21 +69,37 @@ function M.dbg(x, message)
   return x
 end
 
---- A utility for creating user commands that also pre-computes useful information
---- and attaches it to the arguments.
+--- Creates a user command with enhanced argument processing.
+--- Automatically computes range information and attaches it as `args.info`.
 ---
+--- @param name string The command name (without the leading colon)
+--- @param cmd string | fun(args: u.utils.CmdArgs): any Command implementation
+--- @param opts? u.utils.UcmdArgs Command options (nargs, range, etc.)
+---
+--- @usage
 --- ```lua
---- -- Example:
---- ucmd('MyCmd', function(args)
----   -- print the visually selected text:
+--- -- Create a command that works with visual selections:
+--- utils.ucmd('MyCmd', function(args)
+---   -- Print the visually selected text:
 ---   vim.print(args.info:text())
----   -- or get the vtext as an array of lines:
+---   -- Or get the selection as an array of lines:
 ---   vim.print(args.info:lines())
 --- end, { nargs = '*', range = true })
+---
+--- -- Create a command that processes the current line:
+--- utils.ucmd('ProcessLine', function(args)
+---   local line_text = args.info:text()
+---   -- Process the line...
+--- end, { range = '%' })
+---
+--- -- Create a command with arguments:
+--- utils.ucmd('SearchReplace', function(args)
+---   local pattern, replacement = args.fargs[1], args.fargs[2]
+---   local text = args.info:text()
+---   -- Perform search and replace...
+--- end, { nargs = 2, range = true })
 --- ```
----@param name string
----@param cmd string | fun(args: CmdArgs): any
----@param opts? { nargs?: 0|1|'*'|'?'|'+'; range?: boolean|'%'|number; count?: boolean|number, addr?: string; completion?: string }
+-- luacheck: ignore
 function M.ucmd(name, cmd, opts)
   local Range = require 'u.range'
 
@@ -46,170 +111,81 @@ function M.ucmd(name, cmd, opts)
       return cmd(args)
     end
   end
-  vim.api.nvim_create_user_command(name, cmd2, opts or {})
+  vim.api.nvim_create_user_command(name, cmd2, opts or {} --[[@as any]])
 end
 
----@param key_seq string
----@param fn fun(key_seq: string):Range|Pos|nil
----@param opts? { buffer: number|nil }
-function M.define_text_object(key_seq, fn, opts)
-  local Range = require 'u.range'
-  local Pos = require 'u.pos'
-
-  if opts ~= nil and opts.buffer == 0 then opts.buffer = vim.api.nvim_get_current_buf() end
-
-  local function handle_visual()
-    local range_or_pos = fn(key_seq)
-    if range_or_pos == nil then return end
-    if Range.is(range_or_pos) and range_or_pos:is_empty() then range_or_pos = range_or_pos.start end
-
-    if Range.is(range_or_pos) then
-      local range = range_or_pos --[[@as Range]]
-      range:set_visual_selection()
-    else
-      vim.cmd { cmd = 'normal', args = { '<Esc>' }, bang = true }
-    end
-  end
-  vim.keymap.set({ 'x' }, key_seq, handle_visual, opts and { buffer = opts.buffer } or nil)
-
-  local function handle_normal()
-    local State = require 'u.state'
-
-    -- enter visual mode:
-    vim.cmd { cmd = 'normal', args = { 'v' }, bang = true }
-
-    local range_or_pos = fn(key_seq)
-    if range_or_pos == nil then return end
-    if Range.is(range_or_pos) and range_or_pos:is_empty() then range_or_pos = range_or_pos.start end
-
-    if Range.is(range_or_pos) then
-      range_or_pos:set_visual_selection()
-    elseif Pos.is(range_or_pos) then
-      local p = range_or_pos --[[@as Pos]]
-      State.run(0, function(s)
-        s:track_global_option 'eventignore'
-        vim.opt_global.eventignore = 'all'
-
-        -- insert a single space, so we can select it:
-        vim.api.nvim_buf_set_text(0, p.lnum, p.col, p.lnum, p.col, { ' ' })
-        -- select the space:
-        Range.new(p, p, 'v'):set_visual_selection()
-      end)
-    end
-  end
-  vim.keymap.set({ 'o' }, key_seq, handle_normal, opts and { buffer = opts.buffer } or nil)
-end
-
----@type fun(): nil|(fun():any)
-local __U__RepeatableOpFunc_rhs = nil
-
---- This is the global utility function used for operatorfunc
---- in repeatablemap
----@type nil|fun(range: Range): fun():any|nil
--- selene: allow(unused_variable)
-function __U__RepeatableOpFunc()
-  if __U__RepeatableOpFunc_rhs ~= nil then __U__RepeatableOpFunc_rhs() end
-end
-
-function M.repeatablemap(mode, lhs, rhs, opts)
-  vim.keymap.set(mode, lhs, function()
-    __U__RepeatableOpFunc_rhs = rhs
-    vim.o.operatorfunc = 'v:lua.__U__RepeatableOpFunc'
-    return 'g@ '
-  end, vim.tbl_extend('force', opts or {}, { expr = true }))
+--- Creates command arguments for delegating from one command to another.
+--- Preserves all relevant context (range, modifiers, bang, etc.) when
+--- implementing a derived command in terms of a base command.
+---
+--- @param current_args vim.api.keyset.create_user_command.command_args|u.utils.RawCmdArgs The arguments from the current command
+--- @return vim.api.keyset.cmd Arguments suitable for vim.cmd() calls
+---
+--- @usage
+--- ```lua
+--- -- Implement :MyEdit in terms of :edit, preserving all context:
+--- utils.ucmd('MyEdit', function(args)
+---   local delegated_args = utils.create_delegated_cmd_args(args)
+---   -- Add custom logic here...
+---   vim.cmd.edit(delegated_args)
+--- end, { nargs = '*', range = true, bang = true })
+---
+--- -- Implement :MySubstitute that delegates to :substitute:
+--- utils.ucmd('MySubstitute', function(args)
+---   -- Pre-process arguments
+---   local pattern = preprocess_pattern(args.fargs[1])
+---
+---   local delegated_args = utils.create_delegated_cmd_args(args)
+---   delegated_args.args = { pattern, args.fargs[2] }
+---
+---   vim.cmd.substitute(delegated_args)
+--- end, { nargs = 2, range = true, bang = true })
+--- ```
+function M.create_delegated_cmd_args(current_args)
+  --- @type vim.api.keyset.cmd
+  local args = {
+    range = current_args.range == 1 and { current_args.line1 }
+      or current_args.range == 2 and { current_args.line1, current_args.line2 }
+      or nil,
+    count = (current_args.count ~= -1 and current_args.range == 0) and current_args.count or nil,
+    reg = current_args.reg ~= '' and current_args.reg or nil,
+    bang = current_args.bang or nil,
+    args = #current_args.fargs > 0 and current_args.fargs or nil,
+    mods = current_args.smods,
+  }
+  return args
 end
 
+--- Gets the current editor dimensions.
+--- Useful for positioning floating windows or calculating layout sizes.
+---
+--- @return { width: number, height: number } The editor dimensions in columns and lines
+---
+--- @usage
+--- ```lua
+--- -- Center a floating window:
+--- local dims = utils.get_editor_dimensions()
+--- local win_width = 80
+--- local win_height = 20
+--- local col = math.floor((dims.width - win_width) / 2)
+--- local row = math.floor((dims.height - win_height) / 2)
+---
+--- vim.api.nvim_open_win(bufnr, true, {
+---   relative = 'editor',
+---   width = win_width,
+---   height = win_height,
+---   col = col,
+---   row = row,
+--- })
+---
+--- -- Check if editor is wide enough for side-by-side layout:
+--- local dims = utils.get_editor_dimensions()
+--- if dims.width >= 160 then
+---   -- Use side-by-side layout
+--- else
+---   -- Use stacked layout
+--- end
+--- ```
 function M.get_editor_dimensions() return { width = vim.go.columns, height = vim.go.lines } end
 
---- @alias LevenshteinChange<T> ({ kind: 'add'; item: T; index: number; } | { kind: 'delete'; item: T; index: number; } | { kind: 'change'; from: T; to: T; index: number; })
---- @private
---- @generic T
---- @param x `T`[]
---- @param y T[]
---- @param cost? { of_delete?: fun(x: T): number; of_add?: fun(x: T): number; of_change?: fun(x: T, y: T): number; }
---- @return LevenshteinChange<T>[]
-function M.levenshtein(x, y, cost)
-  cost = cost or {}
-  local cost_of_delete_f = cost.of_delete or function() return 1 end
-  local cost_of_add_f = cost.of_add or function() return 1 end
-  local cost_of_change_f = cost.of_change or function() return 1 end
-
-  local m, n = #x, #y
-  -- Initialize the distance matrix
-  local dp = {}
-  for i = 0, m do
-    dp[i] = {}
-    for j = 0, n do
-      dp[i][j] = 0
-    end
-  end
-
-  -- Fill the base cases
-  for i = 0, m do
-    dp[i][0] = i
-  end
-  for j = 0, n do
-    dp[0][j] = j
-  end
-
-  -- Compute the Levenshtein distance dynamically
-  for i = 1, m do
-    for j = 1, n do
-      if x[i] == y[j] then
-        dp[i][j] = dp[i - 1][j - 1] -- no cost if items are the same
-      else
-        local costDelete = dp[i - 1][j] + cost_of_delete_f(x[i])
-        local costAdd = dp[i][j - 1] + cost_of_add_f(y[j])
-        local costChange = dp[i - 1][j - 1] + cost_of_change_f(x[i], y[j])
-        dp[i][j] = math.min(costDelete, costAdd, costChange)
-      end
-    end
-  end
-
-  -- Backtrack to find the changes
-  local i = m
-  local j = n
-  --- @type LevenshteinChange[]
-  local changes = {}
-
-  while i > 0 or j > 0 do
-    local default_cost = dp[i][j]
-    local cost_of_change = (i > 0 and j > 0) and dp[i - 1][j - 1] or default_cost
-    local cost_of_add = j > 0 and dp[i][j - 1] or default_cost
-    local cost_of_delete = i > 0 and dp[i - 1][j] or default_cost
-
-    --- @param u number
-    --- @param v number
-    --- @param w number
-    local function is_first_min(u, v, w) return u <= v and u <= w end
-
-    if is_first_min(cost_of_change, cost_of_add, cost_of_delete) then
-      -- potential change
-      if x[i] ~= y[j] then
-        --- @type LevenshteinChange
-        local change = { kind = 'change', from = x[i], index = i, to = y[j] }
-        table.insert(changes, change)
-      end
-      i = i - 1
-      j = j - 1
-    elseif is_first_min(cost_of_add, cost_of_change, cost_of_delete) then
-      -- addition
-      --- @type LevenshteinChange
-      local change = { kind = 'add', item = y[j], index = i + 1 }
-      table.insert(changes, change)
-      j = j - 1
-    elseif is_first_min(cost_of_delete, cost_of_change, cost_of_add) then
-      -- deletion
-      --- @type LevenshteinChange
-      local change = { kind = 'delete', item = x[i], index = i }
-      table.insert(changes, change)
-      i = i - 1
-    else
-      error 'unreachable'
-    end
-  end
-
-  return changes
-end
-
 return M

selene.toml

@@ -1,4 +0,0 @@
-std = "vim"
-
-[lints]
-multiple_statements = "allow"

shell.nix

@@ -0,0 +1,23 @@
+{
+  pkgs ?
+    import
+      # nixos-25.05 (neovim@0.11.2):
+      (fetchTarball {
+        url = "https://github.com/nixos/nixpkgs/archive/1c1c9b3f5ec0421eaa0f22746295466ee6a8d48f.tar.gz";
+        sha256 = "0szvq1swpzyjmyyw929ngxy1khdnd9ba96qds2bm6l6kg4iq3cq0";
+      })
+      { },
+}:
+pkgs.mkShell {
+  packages = [
+    pkgs.git
+    pkgs.gnumake
+    pkgs.lua-language-server
+    pkgs.lua51Packages.busted
+    pkgs.lua51Packages.luacov
+    pkgs.lua51Packages.luarocks
+    pkgs.neovim
+    pkgs.stylua
+    pkgs.watchexec
+  ];
+}

spec/buffer_spec.lua

@@ -6,7 +6,7 @@ describe('Buffer', function()
     withbuf({}, function()
       local buf = Buffer.from_nr()
       buf:all():replace 'bleh'
-      local actual_lines = vim.api.nvim_buf_get_lines(buf.buf, 0, -1, false)
+      local actual_lines = vim.api.nvim_buf_get_lines(buf.bufnr, 0, -1, false)
       assert.are.same({ 'bleh' }, actual_lines)
     end)
   end)
@@ -18,8 +18,8 @@ describe('Buffer', function()
       'three',
     }, function()
       local buf = Buffer.from_nr()
-      buf:lines(1, -2):replace 'too'
-      local actual_lines = vim.api.nvim_buf_get_lines(buf.buf, 0, -1, false)
+      buf:lines(2, -2):replace 'too'
+      local actual_lines = vim.api.nvim_buf_get_lines(buf.bufnr, 0, -1, false)
       assert.are.same({
         'one',
         'too',

spec/pos_spec.lua

@@ -4,12 +4,12 @@ local withbuf = loadfile './spec/withbuf.lua'()
 describe('Pos', function()
   it('get a char from a given position', function()
     withbuf({ 'asdf', 'bleh', 'a', '', 'goo' }, function()
-      assert.are.same('a', Pos.new(nil, 0, 0):char())
-      assert.are.same('d', Pos.new(nil, 0, 2):char())
-      assert.are.same('f', Pos.new(nil, 0, 3):char())
-      assert.are.same('a', Pos.new(nil, 2, 0):char())
-      assert.are.same('', Pos.new(nil, 3, 0):char())
-      assert.are.same('o', Pos.new(nil, 4, 2):char())
+      assert.are.same('a', Pos.new(nil, 1, 1):char())
+      assert.are.same('d', Pos.new(nil, 1, 3):char())
+      assert.are.same('f', Pos.new(nil, 1, 4):char())
+      assert.are.same('a', Pos.new(nil, 3, 1):char())
+      assert.are.same('', Pos.new(nil, 4, 1):char())
+      assert.are.same('o', Pos.new(nil, 5, 3):char())
     end)
   end)
 
@@ -23,47 +23,47 @@ describe('Pos', function()
   it('get the next position', function()
     withbuf({ 'asdf', 'bleh', 'a', '', 'goo' }, function()
       -- line 1: a => s
-      assert.are.same(Pos.new(nil, 0, 1), Pos.new(nil, 0, 0):next())
+      assert.are.same(Pos.new(nil, 1, 2), Pos.new(nil, 1, 1):next())
       -- line 1: d => f
-      assert.are.same(Pos.new(nil, 0, 3), Pos.new(nil, 0, 2):next())
+      assert.are.same(Pos.new(nil, 1, 4), Pos.new(nil, 1, 3):next())
       -- line 1 => 2
-      assert.are.same(Pos.new(nil, 1, 0), Pos.new(nil, 0, 3):next())
+      assert.are.same(Pos.new(nil, 2, 1), Pos.new(nil, 1, 4):next())
       -- line 3 => 4
-      assert.are.same(Pos.new(nil, 3, 0), Pos.new(nil, 2, 0):next())
+      assert.are.same(Pos.new(nil, 4, 1), Pos.new(nil, 3, 1):next())
       -- line 4 => 5
-      assert.are.same(Pos.new(nil, 4, 0), Pos.new(nil, 3, 0):next())
+      assert.are.same(Pos.new(nil, 5, 1), Pos.new(nil, 4, 1):next())
       -- end returns nil
-      assert.are.same(nil, Pos.new(nil, 4, 2):next())
+      assert.are.same(nil, Pos.new(nil, 5, 3):next())
     end)
   end)
 
   it('get the previous position', function()
     withbuf({ 'asdf', 'bleh', 'a', '', 'goo' }, function()
       -- line 1: s => a
-      assert.are.same(Pos.new(nil, 0, 0), Pos.new(nil, 0, 1):next(-1))
+      assert.are.same(Pos.new(nil, 1, 1), Pos.new(nil, 1, 2):next(-1))
       -- line 1: f => d
-      assert.are.same(Pos.new(nil, 0, 2), Pos.new(nil, 0, 3):next(-1))
+      assert.are.same(Pos.new(nil, 1, 3), Pos.new(nil, 1, 4):next(-1))
       -- line 2 => 1
-      assert.are.same(Pos.new(nil, 0, 3), Pos.new(nil, 1, 0):next(-1))
+      assert.are.same(Pos.new(nil, 1, 4), Pos.new(nil, 2, 1):next(-1))
       -- line 4 => 3
-      assert.are.same(Pos.new(nil, 2, 0), Pos.new(nil, 3, 0):next(-1))
+      assert.are.same(Pos.new(nil, 3, 1), Pos.new(nil, 4, 1):next(-1))
       -- line 5 => 4
-      assert.are.same(Pos.new(nil, 3, 0), Pos.new(nil, 4, 0):next(-1))
+      assert.are.same(Pos.new(nil, 4, 1), Pos.new(nil, 5, 1):next(-1))
       -- beginning returns nil
-      assert.are.same(nil, Pos.new(nil, 0, 0):next(-1))
+      assert.are.same(nil, Pos.new(nil, 1, 1):next(-1))
     end)
   end)
 
   it('find matching brackets', function()
     withbuf({ 'asdf ({} def <[{}]>) ;lkj' }, function()
       -- outer parens are matched:
-      assert.are.same(Pos.new(nil, 0, 19), Pos.new(nil, 0, 5):find_match())
+      assert.are.same(Pos.new(nil, 1, 20), Pos.new(nil, 1, 6):find_match())
       -- outer parens are matched (backward):
-      assert.are.same(Pos.new(nil, 0, 5), Pos.new(nil, 0, 19):find_match())
+      assert.are.same(Pos.new(nil, 1, 6), Pos.new(nil, 1, 20):find_match())
       -- no potential match returns nil
-      assert.are.same(nil, Pos.new(nil, 0, 0):find_match())
+      assert.are.same(nil, Pos.new(nil, 1, 1):find_match())
       -- watchdog expires before an otherwise valid match is found:
-      assert.are.same(nil, Pos.new(nil, 0, 5):find_match(2))
+      assert.are.same(nil, Pos.new(nil, 1, 6):find_match(2))
     end)
   end)
 end)

spec/range_spec.lua

@@ -1,5 +1,5 @@
-local Range = require 'u.range'
 local Pos = require 'u.pos'
+local Range = require 'u.range'
 local withbuf = loadfile './spec/withbuf.lua'()
 
 describe('Range', function()
@@ -28,7 +28,7 @@ describe('Range', function()
 
   it('get from positions: v in single line', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 0, 3), 'v')
+      local range = Range.new(Pos.new(nil, 1, 2), Pos.new(nil, 1, 4), 'v')
       local lines = range:lines()
       assert.are.same({ 'ine' }, lines)
 
@@ -39,7 +39,7 @@ describe('Range', function()
 
   it('get from positions: v across multiple lines', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 2, 4), 'v')
+      local range = Range.new(Pos.new(nil, 2, 5), Pos.new(nil, 3, 5), 'v')
       local lines = range:lines()
       assert.are.same({ 'quick brown fox', 'jumps' }, lines)
     end)
@@ -47,7 +47,7 @@ describe('Range', function()
 
   it('get from positions: V', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, Pos.MAX_COL), 'V')
+      local range = Range.new(Pos.new(nil, 1, 1), Pos.new(nil, 1, Pos.MAX_COL), 'V')
       local lines = range:lines()
       assert.are.same({ 'line one' }, lines)
 
@@ -58,7 +58,7 @@ describe('Range', function()
 
   it('get from positions: V across multiple lines', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.new(Pos.new(nil, 1, 0), Pos.new(nil, 2, Pos.MAX_COL), 'V')
+      local range = Range.new(Pos.new(nil, 2, 1), Pos.new(nil, 3, Pos.MAX_COL), 'V')
       local lines = range:lines()
       assert.are.same({ 'the quick brown fox', 'jumps over a lazy dog' }, lines)
     end)
@@ -66,7 +66,7 @@ describe('Range', function()
 
   it('get from line', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.from_line(nil, 0)
+      local range = Range.from_line(nil, 1)
       local lines = range:lines()
       assert.are.same({ 'line one' }, lines)
 
@@ -77,7 +77,7 @@ describe('Range', function()
 
   it('get from lines', function()
     withbuf({ 'line one', 'and line two', 'and line 3' }, function()
-      local range = Range.from_lines(nil, 0, 1)
+      local range = Range.from_lines(nil, 1, 2)
       local lines = range:lines()
       assert.are.same({ 'line one', 'and line two' }, lines)
 
@@ -88,35 +88,35 @@ describe('Range', function()
 
   it('replace within line', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 1, 8), 'v')
+      local range = Range.new(Pos.new(nil, 2, 5), Pos.new(nil, 2, 9), 'v')
       range:replace 'quack'
 
-      local text = Range.from_line(nil, 1):text()
+      local text = Range.from_line(nil, 2):text()
       assert.are.same('the quack brown fox', text)
     end)
   end)
 
   it('delete within line', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 1, 9), 'v')
+      local range = Range.new(Pos.new(nil, 2, 5), Pos.new(nil, 2, 10), 'v')
       range:replace ''
 
-      local text = Range.from_line(nil, 1):text()
+      local text = Range.from_line(nil, 2):text()
       assert.are.same('the brown fox', text)
     end)
 
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 1, 9), 'v')
+      local range = Range.new(Pos.new(nil, 2, 5), Pos.new(nil, 2, 10), 'v')
       range:replace(nil)
 
-      local text = Range.from_line(nil, 1):text()
+      local text = Range.from_line(nil, 2):text()
       assert.are.same('the brown fox', text)
     end)
   end)
 
   it('replace across multiple lines: v', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 2, 4), 'v')
+      local range = Range.new(Pos.new(nil, 2, 5), Pos.new(nil, 3, 5), 'v')
       range:replace 'plane flew'
 
       local lines = Range.from_buf_text():lines()
@@ -130,7 +130,7 @@ describe('Range', function()
 
   it('replace a line', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.from_line(nil, 1)
+      local range = Range.from_line(nil, 2)
       range:replace 'the rabbit'
 
       local lines = Range.from_buf_text():lines()
@@ -145,7 +145,7 @@ describe('Range', function()
 
   it('replace multiple lines', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.from_lines(nil, 1, 2)
+      local range = Range.from_lines(nil, 2, 3)
       range:replace 'the rabbit'
 
       local lines = Range.from_buf_text():lines()
@@ -159,7 +159,7 @@ describe('Range', function()
 
   it('delete single line', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.from_line(nil, 1)
+      local range = Range.from_line(nil, 2)
       range:replace(nil) -- delete lines
 
       local lines = Range.from_buf_text():lines()
@@ -173,7 +173,7 @@ describe('Range', function()
 
   it('delete multiple lines', function()
     withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
-      local range = Range.from_lines(nil, 1, 2)
+      local range = Range.from_lines(nil, 2, 3)
       range:replace(nil) -- delete lines
 
       local lines = Range.from_buf_text():lines()
@@ -187,57 +187,179 @@ describe('Range', function()
   it('text object: word', function()
     withbuf({ 'the quick brown fox' }, function()
       vim.fn.setpos('.', { 0, 1, 5, 0 })
-      assert.are.same('quick ', Range.from_text_object('aw'):text())
+      assert.are.same('quick ', Range.from_motion('aw'):text())
 
       vim.fn.setpos('.', { 0, 1, 5, 0 })
-      assert.are.same('quick', Range.from_text_object('iw'):text())
+      assert.are.same('quick', Range.from_motion('iw'):text())
     end)
   end)
 
   it('text object: quote', function()
     withbuf({ [[the "quick" brown fox]] }, function()
       vim.fn.setpos('.', { 0, 1, 5, 0 })
-      assert.are.same('"quick"', Range.from_text_object('a"'):text())
+      assert.are.same('"quick"', Range.from_motion('a"'):text())
 
       vim.fn.setpos('.', { 0, 1, 6, 0 })
-      assert.are.same('quick', Range.from_text_object('i"'):text())
+      assert.are.same('quick', Range.from_motion('i"'):text())
     end)
 
     withbuf({ [[the 'quick' brown fox]] }, function()
       vim.fn.setpos('.', { 0, 1, 5, 0 })
-      assert.are.same("'quick'", Range.from_text_object([[a']]):text())
+      assert.are.same("'quick'", Range.from_motion([[a']]):text())
 
       vim.fn.setpos('.', { 0, 1, 6, 0 })
-      assert.are.same('quick', Range.from_text_object([[i']]):text())
+      assert.are.same('quick', Range.from_motion([[i']]):text())
     end)
 
     withbuf({ [[the `quick` brown fox]] }, function()
       vim.fn.setpos('.', { 0, 1, 5, 0 })
-      assert.are.same('`quick`', Range.from_text_object([[a`]]):text())
+      assert.are.same('`quick`', Range.from_motion([[a`]]):text())
 
       vim.fn.setpos('.', { 0, 1, 6, 0 })
-      assert.are.same('quick', Range.from_text_object([[i`]]):text())
+      assert.are.same('quick', Range.from_motion([[i`]]):text())
     end)
   end)
 
   it('text object: block', function()
     withbuf({ 'this is a {', 'block', '} here' }, function()
       vim.fn.setpos('.', { 0, 2, 1, 0 })
-      assert.are.same('{\nblock\n}', Range.from_text_object('a{'):text())
+      assert.are.same('{\nblock\n}', Range.from_motion('a{'):text())
 
       vim.fn.setpos('.', { 0, 2, 1, 0 })
-      assert.are.same('block', Range.from_text_object('i{'):text())
+      assert.are.same('block', Range.from_motion('i{'):text())
     end)
   end)
 
   it('text object: restores cursor position', function()
     withbuf({ 'this is a {block} here' }, function()
       vim.fn.setpos('.', { 0, 1, 13, 0 })
-      assert.are.same('{block}', Range.from_text_object('a{'):text())
+      assert.are.same('{block}', Range.from_motion('a{'):text())
       assert.are.same(vim.api.nvim_win_get_cursor(0), { 1, 12 })
     end)
   end)
 
+  it('from_tsquery_caps', function()
+    withbuf({
+      '-- a comment',
+      '',
+      'function foo(bar) end',
+      '',
+      '-- a middle comment',
+      '',
+      'function bar(baz) end',
+      '',
+      '-- another comment',
+    }, function()
+      vim.cmd.setfiletype 'lua'
+
+      --- @param contains_cursor? boolean
+      local function get_caps(contains_cursor)
+        if contains_cursor == nil then contains_cursor = true end
+        return (Range.from_tsquery_caps(
+          0,
+          '(function_declaration) @f',
+          { contains_cursor = contains_cursor }
+        )).f or {}
+      end
+
+      local caps = get_caps(false)
+      assert.are.same(#caps, 2)
+      assert.are.same(vim.iter(caps):map(function(c) return c:text() end):totable(), {
+        'function foo(bar) end',
+        'function bar(baz) end',
+      })
+
+      Pos.new(0, 1, 1):save_to_pos '.'
+      caps = get_caps()
+      assert.are.same(#caps, 0)
+
+      Pos.new(0, 3, 18):save_to_pos '.'
+      caps = get_caps()
+      assert.are.same(#caps, 1)
+      assert.are.same(caps[1]:text(), 'function foo(bar) end')
+
+      Pos.new(0, 5, 1):save_to_pos '.'
+      caps = get_caps()
+      assert.are.same(#caps, 0)
+
+      Pos.new(0, 7, 1):save_to_pos '.'
+      caps = get_caps()
+      assert.are.same(#caps, 1)
+      assert.are.same(caps[1]:text(), 'function bar(baz) end')
+    end)
+  end)
+
+  it('from_tsquery_caps with string array filter', function()
+    withbuf({
+      '{',
+      '  sample_key1 = "sample-value1",',
+      '  sample_key2 = "sample-value2",',
+      '}',
+    }, function()
+      vim.cmd.setfiletype 'lua'
+
+      -- Place cursor in "sample-value1"
+      Pos.new(0, 2, 25):save_to_pos '.'
+
+      -- Query that captures both keys and values in pairs
+      local query = [[
+        (field
+          name: _ @key
+          value: _ @value)
+      ]]
+
+      local ranges = Range.from_line(0, 2):tsquery(query)
+
+      -- Should have both @key and @value captures for the first pair only
+      -- (since cursor is in sample-value1)
+      assert(ranges, 'Range should not be nil')
+      assert(ranges.key, 'Range.key should not be nil')
+      assert(ranges.value, 'Range.value should not be nil')
+
+      -- Should have exactly one key and one value
+      assert.are.same(#ranges.key, 1)
+      assert.are.same(#ranges.value, 1)
+
+      -- Check that we got sample-key1 and sample-value1
+      assert.are.same(ranges.key[1]:text(), 'sample_key1')
+      assert.are.same(ranges.value[1]:text(), '"sample-value1"')
+    end)
+
+    -- Make sure this works when the match is on the last line:
+    withbuf({
+      '{sample_key1= "sample-value1",',
+      'sample_key2= "sample-value2"}',
+    }, function()
+      vim.cmd.setfiletype 'lua'
+
+      -- Place cursor in "sample-value1"
+      Pos.new(0, 2, 25):save_to_pos '.'
+
+      -- Query that captures both keys and values in pairs
+      local query = [[
+        (field
+          name: _ @key
+          value: _ @value)
+      ]]
+
+      local ranges = Range.from_line(0, 2):tsquery(query)
+
+      -- Should have both @key and @value captures for the first pair only
+      -- (since cursor is in sample-value1)
+      assert(ranges, 'Range should not be nil')
+      assert(ranges.key, 'Range.key should not be nil')
+      assert(ranges.value, 'Range.value should not be nil')
+
+      -- Should have exactly one key and one value
+      assert.are.same(#ranges.key, 1)
+      assert.are.same(#ranges.value, 1)
+
+      -- Check that we got sample-key2 and sample-value2
+      assert.are.same(ranges.key[1]:text(), 'sample_key2')
+      assert.are.same(ranges.value[1]:text(), '"sample-value2"')
+    end)
+  end)
+
   it('should get nearest block', function()
     withbuf({
       'this is a {',
@@ -258,22 +380,18 @@ describe('Range', function()
     end)
   end)
 
-  it('line0', function()
+  it('line', function()
     withbuf({
       'this is a {',
       'block',
       '} here',
     }, function()
-      local range = Range.new(Pos.new(0, 0, 5), Pos.new(0, 1, 4), 'v')
-      local lfirst = range:line0(0)
-      assert.are.same(5, lfirst.idx0.start)
-      assert.are.same(10, lfirst.idx0.stop)
-      assert.are.same(0, lfirst.lnum)
-      assert.are.same('is a {', lfirst.text())
-      assert.are.same('is a {', lfirst.range():text())
-      assert.are.same(Pos.new(0, 0, 5), lfirst.range().start)
-      assert.are.same(Pos.new(0, 0, 10), lfirst.range().stop)
-      assert.are.same('block', range:line0(1).text())
+      local range = Range.new(Pos.new(0, 1, 6), Pos.new(0, 2, 5), 'v')
+      local lfirst = assert(range:line(1), 'lfirst null')
+      assert.are.same('is a {', lfirst:text())
+      assert.are.same(Pos.new(0, 1, 6), lfirst.start)
+      assert.are.same(Pos.new(0, 1, 11), lfirst.stop)
+      assert.are.same('block', range:line(2):text())
     end)
   end)
 
@@ -297,16 +415,16 @@ describe('Range', function()
       vim.cmd.normal 'v' -- enter visual mode
       vim.cmd.normal 'l' -- select one character to the right
       local range = Range.from_vtext()
-      assert.are.same(range.start, Pos.new(nil, 0, 2))
-      assert.are.same(range.stop, Pos.new(nil, 0, 3))
+      assert.are.same(range.start, Pos.new(nil, 1, 3))
+      assert.are.same(range.stop, Pos.new(nil, 1, 4))
       assert.are.same(range.mode, 'v')
     end)
   end)
 
   it('from_op_func', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local a = Pos.new(nil, 0, 0)
-      local b = Pos.new(nil, 1, 1)
+      local a = Pos.new(nil, 1, 1)
+      local b = Pos.new(nil, 2, 2)
       a:save_to_pos "'["
       b:save_to_pos "']"
 
@@ -317,23 +435,94 @@ describe('Range', function()
 
       range = Range.from_op_func 'line'
       assert.are.same(range.start, a)
-      assert.are.same(range.stop, Pos.new(nil, 1, Pos.MAX_COL))
+      assert.are.same(range.stop, Pos.new(nil, 2, Pos.MAX_COL))
       assert.are.same(range.mode, 'V')
     end)
   end)
 
-  it('from_cmd_args', function()
-    local args = { range = 1 }
+  it('from_cmd_args: range=0', function()
+    local args = { range = 0 }
+    withbuf(
+      { 'line one', 'and line two' },
+      function() assert.are.same(Range.from_cmd_args(args), nil) end
+    )
+  end)
+
+  it('from_cmd_args: range=1', function()
+    local args = { range = 1, line1 = 1 }
     withbuf({ 'line one', 'and line two' }, function()
-      local a = Pos.new(nil, 0, 0)
-      local b = Pos.new(nil, 1, 1)
+      local a = Pos.new(nil, 1, 1)
+      local b = Pos.new(nil, 1, Pos.MAX_COL)
+
+      local range = Range.from_cmd_args(args) --[[@as u.Range]]
+      assert.are.same(range.start, a)
+      assert.are.same(range.stop, b)
+      assert.are.same(range.mode, 'V')
+      assert.are.same(range:text(), 'line one')
+    end)
+  end)
+
+  it('from_cmd_args: range=2: no-visual', function()
+    local args = { range = 2, line1 = 1, line2 = 2 }
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.from_cmd_args(args) --[[@as u.Range]]
+      assert.are.same(range.start, Pos.new(nil, 1, 1))
+      assert.are.same(range.stop, Pos.new(nil, 2, Pos.MAX_COL))
+      assert.are.same(range.mode, 'V')
+      assert.are.same(range:text(), 'line one\nand line two')
+    end)
+  end)
+
+  it('from_cmd_args: range=2: visual: linewise', function()
+    local args = { range = 2, line1 = 1, line2 = 2 }
+    withbuf({ 'line one', 'and line two' }, function()
+      local a = Pos.new(nil, 1, 1)
+      local b = Pos.new(nil, 2, Pos.MAX_COL)
       a:save_to_pos "'<"
       b:save_to_pos "'>"
+      local range = Range.from_cmd_args(args) --[[@as u.Range]]
+      assert.are.same(range.start, a)
+      assert.are.same(range.stop, b)
+      assert.are.same(range.mode, 'V')
+      assert.are.same(range:text(), 'line one\nand line two')
+    end)
+  end)
 
-      local range = Range.from_cmd_args(args)
+  it('from_cmd_args: range=2: visual: charwise', function()
+    local args = { range = 2, line1 = 1, line2 = 1 }
+    withbuf({ 'line one', 'and line two' }, function()
+      -- Simulate a visual selection:
+      local a = Pos.new(nil, 1, 1)
+      local b = Pos.new(nil, 1, 4)
+      a:save_to_pos "'<"
+      b:save_to_pos "'>"
+      Range.new(a, b, 'v'):set_visual_selection()
+      assert.are.same(vim.fn.mode(), 'v')
+
+      -- In this simulated setup, we need to force visualmode() to return
+      -- 'v' and histget() to return [['<,'>]]:
+
+      -- visualmode()
+      local orig_visualmode = vim.fn.visualmode
+      --- @diagnostic disable-next-line: duplicate-set-field
+      function vim.fn.visualmode() return 'v' end
+      assert.are.same(vim.fn.visualmode(), 'v')
+
+      -- histget()
+      local orig_histget = vim.fn.histget
+      --- @diagnostic disable-next-line: duplicate-set-field
+      function vim.fn.histget(x, y) return [['<,'>]] end
+
+      -- Now run the test:
+      local range = Range.from_cmd_args(args) --[[@as u.Range]]
       assert.are.same(range.start, a)
       assert.are.same(range.stop, b)
       assert.are.same(range.mode, 'v')
+      assert.are.same(range:text(), 'line')
+
+      -- Reset visualmode() and histget():
+      vim.fn.visualmode = orig_visualmode
+      vim.fn.histget = orig_histget
     end)
   end)
 
@@ -341,25 +530,25 @@ describe('Range', function()
     withbuf({ [[the "quick" brown fox]] }, function()
       vim.fn.setpos('.', { 0, 1, 5, 0 })
       local range = Range.find_nearest_quotes()
-      assert.are.same(range.start, Pos.new(nil, 0, 4))
-      assert.are.same(range.stop, Pos.new(nil, 0, 10))
+      assert.are.same(range.start, Pos.new(nil, 1, 5))
+      assert.are.same(range.stop, Pos.new(nil, 1, 11))
     end)
 
     withbuf({ [[the 'quick' brown fox]] }, function()
       vim.fn.setpos('.', { 0, 1, 5, 0 })
       local range = Range.find_nearest_quotes()
-      assert.are.same(range.start, Pos.new(nil, 0, 4))
-      assert.are.same(range.stop, Pos.new(nil, 0, 10))
+      assert.are.same(range.start, Pos.new(nil, 1, 5))
+      assert.are.same(range.stop, Pos.new(nil, 1, 11))
     end)
   end)
 
   it('smallest', function()
-    local r1 = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 0, 3), 'v')
-    local r2 = Range.new(Pos.new(nil, 0, 2), Pos.new(nil, 0, 4), 'v')
-    local r3 = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, 5), 'v')
+    local r1 = Range.new(Pos.new(nil, 1, 2), Pos.new(nil, 1, 4), 'v')
+    local r2 = Range.new(Pos.new(nil, 1, 3), Pos.new(nil, 1, 5), 'v')
+    local r3 = Range.new(Pos.new(nil, 1, 1), Pos.new(nil, 1, 6), 'v')
     local smallest = Range.smallest { r1, r2, r3 }
-    assert.are.same(smallest.start, Pos.new(nil, 0, 1))
-    assert.are.same(smallest.stop, Pos.new(nil, 0, 3))
+    assert.are.same(smallest.start, Pos.new(nil, 1, 2))
+    assert.are.same(smallest.stop, Pos.new(nil, 1, 4))
   end)
 
   it('clone', function()
@@ -381,9 +570,9 @@ describe('Range', function()
 
   it('to_linewise()', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 1, 3), 'v')
+      local range = Range.new(Pos.new(nil, 1, 2), Pos.new(nil, 2, 4), 'v')
       local linewise_range = range:to_linewise()
-      assert.are.same(linewise_range.start.col, 0)
+      assert.are.same(linewise_range.start.col, 1)
       assert.are.same(linewise_range.stop.col, Pos.MAX_COL)
       assert.are.same(linewise_range.mode, 'V')
     end)
@@ -391,82 +580,133 @@ describe('Range', function()
 
   it('is_empty', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 0), nil, 'v')
+      local range = Range.new(Pos.new(nil, 1, 1), nil, 'v')
       assert.is_true(range:is_empty())
 
-      local range2 = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, 1), 'v')
+      local range2 = Range.new(Pos.new(nil, 1, 1), Pos.new(nil, 1, 2), 'v')
       assert.is_false(range2:is_empty())
     end)
   end)
 
   it('trim_start', function()
     withbuf({ '   line one', 'line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, 9), 'v')
+      local range = Range.new(Pos.new(nil, 1, 1), Pos.new(nil, 1, 10), 'v')
       local trimmed = range:trim_start()
-      assert.are.same(trimmed.start, Pos.new(nil, 0, 3)) -- should be after the spaces
+      assert.are.same(trimmed.start, Pos.new(nil, 1, 4)) -- should be after the spaces
     end)
   end)
 
   it('trim_stop', function()
     withbuf({ 'line one   ', 'line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, 9), 'v')
+      local range = Range.new(Pos.new(nil, 1, 1), Pos.new(nil, 1, 10), 'v')
       local trimmed = range:trim_stop()
-      assert.are.same(trimmed.stop, Pos.new(nil, 0, 7)) -- should be before the spaces
+      assert.are.same(trimmed.stop, Pos.new(nil, 1, 8)) -- should be before the spaces
     end)
   end)
 
   it('contains', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 0, 3), 'v')
-      local pos = Pos.new(nil, 0, 2)
+      local range = Range.new(Pos.new(nil, 1, 2), Pos.new(nil, 1, 4), 'v')
+      local pos = Pos.new(nil, 1, 3)
       assert.is_true(range:contains(pos))
 
-      pos = Pos.new(nil, 0, 4) -- outside of range
+      pos = Pos.new(nil, 1, 5) -- outside of range
       assert.is_false(range:contains(pos))
     end)
   end)
 
+  it('difference', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range_outer = Range.new(Pos.new(nil, 2, 1), Pos.new(nil, 2, 12), 'v')
+      local range_inner = Range.new(Pos.new(nil, 2, 5), Pos.new(nil, 2, 8), 'v')
+
+      assert.are.same(range_outer:text(), 'and line two')
+      assert.are.same(range_inner:text(), 'line')
+
+      local left, right = range_outer:difference(range_inner)
+      assert.are.same(left:text(), 'and ')
+      assert.are.same(right:text(), ' two')
+
+      left, right = range_inner:difference(range_outer)
+      assert.are.same(left:text(), 'and ')
+      assert.are.same(right:text(), ' two')
+
+      left, right = range_outer:difference(range_outer)
+      assert.are.same(left:is_empty(), true)
+      assert.are.same(left:text(), '')
+      assert.are.same(right:is_empty(), true)
+      assert.are.same(right:text(), '')
+    end)
+  end)
+
+  it('length', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 2, 4), Pos.new(nil, 2, 9), 'v')
+      assert.are.same(range:length(), #range:text())
+
+      range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 2, 9), 'v')
+      assert.are.same(range:length(), #range:text())
+    end)
+  end)
+
+  it('sub', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 2, 4), Pos.new(nil, 2, 9), 'v')
+      assert.are.same(range:text(), ' line ')
+      assert.are.same(range:sub(1, -1):text(), ' line ')
+      assert.are.same(range:sub(2, -2):text(), 'line')
+      assert.are.same(range:sub(1, 5):text(), ' line')
+      assert.are.same(range:sub(2, 5):text(), 'line')
+      assert.are.same(range:sub(20, 25):text(), '')
+    end)
+  end)
+
   it('shrink', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 1, 3), 'v')
+      local range = Range.new(Pos.new(nil, 2, 3), Pos.new(nil, 3, 5), 'v')
       local shrunk = range:shrink(1)
-      assert.are.same(shrunk.start, Pos.new(nil, 0, 2))
-      assert.are.same(shrunk.stop, Pos.new(nil, 1, 2))
+      assert.are.same(shrunk.start, Pos.new(nil, 2, 4))
+      assert.are.same(shrunk.stop, Pos.new(nil, 3, 4))
     end)
   end)
 
   it('must_shrink', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 1, 3), 'v')
+      local range = Range.new(Pos.new(nil, 2, 3), Pos.new(nil, 3, 5), 'v')
       local shrunk = range:must_shrink(1)
-      assert.are.same(shrunk.start, Pos.new(nil, 0, 2))
-      assert.are.same(shrunk.stop, Pos.new(nil, 1, 2))
+      assert.are.same(shrunk.start, Pos.new(nil, 2, 4))
+      assert.are.same(shrunk.stop, Pos.new(nil, 3, 4))
 
-      assert.has.error(function() range:must_shrink(100) end, 'error in Range:must_shrink: Range:shrink() returned nil')
+      assert.has.error(
+        function() range:must_shrink(100) end,
+        'error in Range:must_shrink: Range:shrink() returned nil'
+      )
     end)
   end)
 
   it('set_visual_selection', function()
     withbuf({ 'line one', 'and line two' }, function()
-      local range = Range.from_lines(nil, 0, 1)
+      local range = Range.from_lines(nil, 1, 2)
       range:set_visual_selection()
 
-      assert.are.same(Pos.from_pos 'v', Pos.new(nil, 0, 0))
-      assert.are.same(Pos.from_pos '.', Pos.new(nil, 1, 11))
+      assert.are.same(Pos.from_pos 'v', Pos.new(nil, 1, 1))
+      -- Since the selection is 'V' (instead of 'v'), the end
+      -- selects one character past the end:
+      assert.are.same(Pos.from_pos '.', Pos.new(nil, 2, 13))
     end)
   end)
 
   it('selections set to past the EOL should not error', function()
     withbuf({ 'Rg SET NAMES' }, function()
       local b = vim.api.nvim_get_current_buf()
-      local r = Range.new(Pos.new(b, 0, 3), Pos.new(b, 0, 12), 'v')
+      local r = Range.new(Pos.new(b, 1, 4), Pos.new(b, 1, 13), 'v')
       r:replace 'bleh'
       assert.are.same({ 'Rg bleh' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
     end)
 
     withbuf({ 'Rg SET NAMES' }, function()
       local b = vim.api.nvim_get_current_buf()
-      local r = Range.new(Pos.new(b, 0, 3), Pos.new(b, 0, 11), 'v')
+      local r = Range.new(Pos.new(b, 1, 4), Pos.new(b, 1, 12), 'v')
       r:replace 'bleh'
       assert.are.same({ 'Rg bleh' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
     end)
@@ -475,13 +715,19 @@ describe('Range', function()
   it('replace updates Range.stop: same line', function()
     withbuf({ 'The quick brown fox jumps over the lazy dog' }, function()
       local b = vim.api.nvim_get_current_buf()
-      local r = Range.new(Pos.new(b, 0, 4), Pos.new(b, 0, 8), 'v')
+      local r = Range.new(Pos.new(b, 1, 5), Pos.new(b, 1, 9), 'v')
 
       r:replace 'bleh1'
-      assert.are.same({ 'The bleh1 brown fox jumps over the lazy dog' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+      assert.are.same(
+        { 'The bleh1 brown fox jumps over the lazy dog' },
+        vim.api.nvim_buf_get_lines(b, 0, -1, false)
+      )
 
       r:replace 'bleh2'
-      assert.are.same({ 'The bleh2 brown fox jumps over the lazy dog' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+      assert.are.same(
+        { 'The bleh2 brown fox jumps over the lazy dog' },
+        vim.api.nvim_buf_get_lines(b, 0, -1, false)
+      )
     end)
   end)
 
@@ -491,14 +737,21 @@ describe('Range', function()
       'over the lazy dog',
     }, function()
       local b = vim.api.nvim_get_current_buf()
-      local r = Range.new(Pos.new(b, 0, 20), Pos.new(b, 1, 3), 'v')
+      local r = Range.new(Pos.new(b, 1, 21), Pos.new(b, 2, 4), 'v')
       assert.are.same({ 'jumps', 'over' }, r:lines())
 
       r:replace 'bleh1'
-      assert.are.same({ 'The quick brown fox bleh1 the lazy dog' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+      assert.are.same(
+        { 'The quick brown fox bleh1 the lazy dog' },
+        vim.api.nvim_buf_get_lines(b, 0, -1, false)
+      )
+      assert.are.same({ 'bleh1' }, r:lines())
 
       r:replace 'blehGoo2'
-      assert.are.same({ 'The quick brown fox blehGoo2 the lazy dog' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+      assert.are.same(
+        { 'The quick brown fox blehGoo2 the lazy dog' },
+        vim.api.nvim_buf_get_lines(b, 0, -1, false)
+      )
     end)
   end)
 
@@ -511,7 +764,7 @@ describe('Range', function()
       'the lazy dog',
     }, function()
       local b = vim.api.nvim_get_current_buf()
-      local r = Range.new(Pos.new(b, 1, 0), Pos.new(b, 3, Pos.MAX_COL), 'V')
+      local r = Range.new(Pos.new(b, 2, 1), Pos.new(b, 4, Pos.MAX_COL), 'V')
       assert.are.same({ 'fox', 'jumps', 'over' }, r:lines())
 
       r:replace { 'bleh1', 'bleh2' }
@@ -540,7 +793,7 @@ describe('Range', function()
       'the lazy dog',
     }, function()
       local b = vim.api.nvim_get_current_buf()
-      local r = Range.new(Pos.new(b, 1, 0), Pos.new(b, 3, Pos.MAX_COL), 'V')
+      local r = Range.new(Pos.new(b, 2, 1), Pos.new(b, 4, Pos.MAX_COL), 'V')
       assert.are.same({ 'fox', 'jumps', 'over' }, r:lines())
 
       r:replace(nil)
@@ -557,4 +810,86 @@ describe('Range', function()
       }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
     end)
   end)
+
+  it('can save to extmark', function()
+    withbuf({
+      'The quick brown',
+      'fox',
+      'jumps',
+      'over',
+      'the lazy dog',
+    }, function()
+      -- Construct a range over 'fox jumps'
+      local r = Range.new(Pos.new(nil, 2, 1), Pos.new(nil, 3, 5), 'v')
+      local extrange = r:save_to_extmark()
+      assert.are.same({ 'fox', 'jumps' }, extrange:range():lines())
+      -- change 'jumps' to 'leaps':
+      vim.api.nvim_buf_set_text(extrange.bufnr, 2, 0, 2, 4, { 'leap' })
+      assert.are.same({
+        'The quick brown',
+        'fox',
+        'leaps',
+        'over',
+        'the lazy dog',
+      }, vim.api.nvim_buf_get_lines(extrange.bufnr, 0, -1, false))
+      assert.are.same({ 'fox', 'leaps' }, extrange:range():lines())
+    end)
+  end)
+
+  it('can save linewise extmark', function()
+    withbuf({
+      'The quick brown',
+      'fox',
+      'jumps',
+      'over',
+      'the lazy dog',
+    }, function()
+      -- Construct a range over 'fox jumps'
+      local r = Range.new(Pos.new(nil, 2, 1), Pos.new(nil, 3, Pos.MAX_COL), 'V')
+      local extrange = r:save_to_extmark()
+      assert.are.same({ 'fox', 'jumps' }, extrange:range():lines())
+
+      local extmark = vim.api.nvim_buf_get_extmark_by_id(
+        extrange.bufnr,
+        vim.api.nvim_create_namespace 'u.range',
+        extrange.id,
+        { details = true }
+      )
+      local row0, col0, details = unpack(extmark)
+      assert.are.same({ 1, 0 }, { row0, col0 })
+      assert.are.same({ 3, 0 }, { details.end_row, details.end_col })
+    end)
+  end)
+
+  it('discerns range bounds from extmarks beyond the end of the buffer', function()
+    local Buffer = require 'u.buffer'
+
+    vim.cmd.vnew()
+    local left = Buffer.current()
+    left:set_tmp_options()
+    vim.cmd.vnew()
+    local right = Buffer.current()
+    right:set_tmp_options()
+
+    left:all():replace {
+      'one',
+      'two',
+      'three',
+    }
+    local left_all_ext = left:all():save_to_extmark()
+
+    right:all():replace {
+      'foo',
+      'bar',
+    }
+
+    vim.api.nvim_set_current_buf(right.bufnr)
+    vim.cmd [[normal! ggyG]]
+    vim.api.nvim_set_current_buf(left.bufnr)
+    vim.cmd [[normal! ggVGp]]
+
+    assert.are.same({ 'foo', 'bar' }, left_all_ext:range():lines())
+    vim.api.nvim_buf_delete(left.bufnr, { force = true })
+    vim.api.nvim_buf_delete(right.bufnr, { force = true })
+  end)
 end)

spec/renderer_spec.lua

@@ -0,0 +1,297 @@
+local R = require 'u.renderer'
+local withbuf = loadfile './spec/withbuf.lua'()
+
+local function getlines() return vim.api.nvim_buf_get_lines(0, 0, -1, true) end
+
+describe('Renderer', function()
+  it('should render text in an empty buffer', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render { 'hello', ' ', 'world' }
+      assert.are.same(getlines(), { 'hello world' })
+    end)
+  end)
+
+  it('should result in the correct text after repeated renders', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render { 'hello', ' ', 'world' }
+      assert.are.same(getlines(), { 'hello world' })
+
+      r:render { 'goodbye', ' ', 'world' }
+      assert.are.same(getlines(), { 'goodbye world' })
+
+      r:render { 'hello', ' ', 'universe' }
+      assert.are.same(getlines(), { 'hello universe' })
+    end)
+  end)
+
+  it('should handle tags correctly', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render {
+        R.h('text', { hl = 'HighlightGroup' }, 'hello '),
+        R.h('text', { hl = 'HighlightGroup' }, 'world'),
+      }
+      assert.are.same(getlines(), { 'hello world' })
+    end)
+  end)
+
+  it('should reconcile added lines', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render { 'line 1', '\n', 'line 2' }
+      assert.are.same(getlines(), { 'line 1', 'line 2' })
+
+      -- Add a new line:
+      r:render { 'line 1', '\n', 'line 2\n', 'line 3' }
+      assert.are.same(getlines(), { 'line 1', 'line 2', 'line 3' })
+    end)
+  end)
+
+  it('should reconcile deleted lines', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render { 'line 1', '\nline 2', '\nline 3' }
+      assert.are.same(getlines(), { 'line 1', 'line 2', 'line 3' })
+
+      -- Remove a line:
+      r:render { 'line 1', '\nline 3' }
+      assert.are.same(getlines(), { 'line 1', 'line 3' })
+    end)
+  end)
+
+  it('should handle multiple nested elements', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render {
+        R.h('text', {}, {
+          'first line',
+        }),
+        '\n',
+        R.h('text', {}, 'second line'),
+      }
+      assert.are.same(getlines(), { 'first line', 'second line' })
+
+      r:render {
+        R.h('text', {}, 'updated first line'),
+        '\n',
+        R.h('text', {}, 'third line'),
+      }
+      assert.are.same(getlines(), { 'updated first line', 'third line' })
+    end)
+  end)
+
+  --
+  -- get_tags_at
+  --
+
+  it('should return no extmarks for an empty buffer', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      local pos_infos = r:get_tags_at { 0, 0 }
+      assert.are.same(pos_infos, {})
+    end)
+  end)
+
+  it('should return correct extmark for a given position', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render {
+        R.h('text', { hl = 'HighlightGroup1' }, 'Hello'),
+        R.h('text', { hl = 'HighlightGroup2' }, ' World'),
+      }
+
+      local pos_infos = r:get_tags_at { 0, 2 }
+      assert.are.same(#pos_infos, 1)
+      assert.are.same(pos_infos[1].tag.attributes.hl, 'HighlightGroup1')
+      assert.are.same(pos_infos[1].extmark.start, { 0, 0 })
+      assert.are.same(pos_infos[1].extmark.stop, { 0, 5 })
+      pos_infos = r:get_tags_at { 0, 4 }
+      assert.are.same(#pos_infos, 1)
+      assert.are.same(pos_infos[1].tag.attributes.hl, 'HighlightGroup1')
+      assert.are.same(pos_infos[1].extmark.start, { 0, 0 })
+      assert.are.same(pos_infos[1].extmark.stop, { 0, 5 })
+
+      pos_infos = r:get_tags_at { 0, 5 }
+      assert.are.same(#pos_infos, 1)
+      assert.are.same(pos_infos[1].tag.attributes.hl, 'HighlightGroup2')
+      assert.are.same(pos_infos[1].extmark.start, { 0, 5 })
+      assert.are.same(pos_infos[1].extmark.stop, { 0, 11 })
+
+      -- In insert mode, bounds are eagerly included:
+      pos_infos = r:get_tags_at({ 0, 5 }, 'i')
+      assert.are.same(#pos_infos, 2)
+      assert.are.same(pos_infos[1].tag.attributes.hl, 'HighlightGroup1')
+      assert.are.same(pos_infos[2].tag.attributes.hl, 'HighlightGroup2')
+    end)
+  end)
+
+  it('should return multiple extmarks for overlapping text', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render {
+        R.h('text', { hl = 'HighlightGroup1' }, {
+          'Hello',
+          R.h(
+            'text',
+            { hl = 'HighlightGroup2', extmark = { hl_group = 'HighlightGroup2' } },
+            ' World'
+          ),
+        }),
+      }
+
+      local pos_infos = r:get_tags_at { 0, 5 }
+
+      assert.are.same(#pos_infos, 2)
+      assert.are.same(pos_infos[1].tag.attributes.hl, 'HighlightGroup2')
+      assert.are.same(pos_infos[2].tag.attributes.hl, 'HighlightGroup1')
+    end)
+  end)
+
+  it('repeated patch_lines calls should not change the buffer content', function()
+    local lines = {
+      [[{ {]],
+      [[    bounds = {]],
+      [[      start1 = { 1, 1 },]],
+      [[      stop1 = { 4, 1 }]],
+      [[    },]],
+      [[    end_right_gravity = true,]],
+      [[    id = 1,]],
+      [[    ns_id = 623,]],
+      [[    ns_name = "my.renderer:91",]],
+      [[    right_gravity = false]],
+      [[  } }]],
+      [[]],
+    }
+    withbuf(lines, function()
+      local Buffer = require 'u.buffer'
+      R.Renderer.patch_lines(0, nil, lines)
+      assert.are.same(Buffer.current():all():lines(), lines)
+
+      R.Renderer.patch_lines(0, lines, lines)
+      assert.are.same(Buffer.current():all():lines(), lines)
+
+      R.Renderer.patch_lines(0, lines, lines)
+      assert.are.same(Buffer.current():all():lines(), lines)
+    end)
+  end)
+
+  it('should fire text-changed events', function()
+    withbuf({}, function()
+      local Buffer = require 'u.buffer'
+      local buf = Buffer.current()
+      local r = R.Renderer.new(0)
+      local captured_changed_text = ''
+      r:render {
+        R.h('text', {
+          on_change = function(txt) captured_changed_text = txt end,
+        }, {
+          'one\n',
+          'two\n',
+          'three\n',
+        }),
+      }
+
+      vim.fn.setreg('"', 'bleh')
+      vim.cmd [[normal! ggVGp]]
+      -- For some reason, the autocmd does not fire in the busted environment.
+      -- We'll call the handler ourselves:
+      r:_on_text_changed()
+
+      assert.are.same(buf:all():text(), 'bleh')
+      assert.are.same(captured_changed_text, 'bleh')
+
+      vim.fn.setreg('"', '')
+      vim.cmd [[normal! ggdG]]
+      -- We'll call the handler ourselves:
+      r:_on_text_changed()
+
+      assert.are.same(buf:all():text(), '')
+      assert.are.same(captured_changed_text, '')
+    end)
+
+    withbuf({}, function()
+      local Buffer = require 'u.buffer'
+      local buf = Buffer.current()
+      local r = R.Renderer.new(0)
+      --- @type string?
+      local captured_changed_text = nil
+      r:render {
+        'prefix:',
+        R.h('text', {
+          on_change = function(txt) captured_changed_text = txt end,
+        }, {
+          'one',
+        }),
+        'suffix',
+      }
+
+      vim.fn.setreg('"', 'bleh')
+      vim.api.nvim_win_set_cursor(0, { 1, 9 })
+      vim.cmd [[normal! vhhd]]
+      -- For some reason, the autocmd does not fire in the busted environment.
+      -- We'll call the handler ourselves:
+      r:_on_text_changed()
+
+      assert.are.same(buf:all():text(), 'prefix:suffix')
+      assert.are.same(captured_changed_text, '')
+    end)
+  end)
+
+  it('should find tags by position', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render {
+        'pre',
+        R.h('text', {
+          id = 'outer',
+        }, {
+          'inner-pre',
+          R.h('text', {
+            id = 'inner',
+          }, {
+            'inner-text',
+          }),
+          'inner-post',
+        }),
+        'post',
+      }
+
+      local tags = r:get_tags_at { 0, 11 }
+      assert.are.same(#tags, 1)
+      assert.are.same(tags[1].tag.attributes.id, 'outer')
+
+      tags = r:get_tags_at { 0, 12 }
+      assert.are.same(#tags, 2)
+      assert.are.same(tags[1].tag.attributes.id, 'inner')
+      assert.are.same(tags[2].tag.attributes.id, 'outer')
+    end)
+  end)
+
+  it('should find tags by id', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      r:render {
+        R.h('text', {
+          id = 'outer',
+        }, {
+          'inner-pre',
+          R.h('text', {
+            id = 'inner',
+          }, {
+            'inner-text',
+          }),
+          'inner-post',
+        }),
+        'post',
+      }
+
+      local bounds = r:get_tag_bounds 'outer'
+      assert.are.same(bounds, { start = { 0, 0 }, stop = { 0, 29 } })
+
+      bounds = r:get_tag_bounds 'inner'
+      assert.are.same(bounds, { start = { 0, 9 }, stop = { 0, 19 } })
+    end)
+  end)
+end)

spec/tracker_spec.lua

@@ -58,66 +58,66 @@ describe('Signal', function()
 
   describe('Signal:map', function()
     it('should transform the signal value', function()
-      local signal = Signal:new(5)
-      local mapped_signal = signal:map(function(value) return value * 2 end)
+      local test_signal = Signal:new(5)
+      local mapped_signal = test_signal:map(function(value) return value * 2 end)
 
       assert.is.equal(mapped_signal:get(), 10) -- Initial transformation
-      signal:set(10)
+      test_signal:set(10)
       assert.is.equal(mapped_signal:get(), 20) -- Updated transformation
     end)
 
     it('should handle empty transformations', function()
-      local signal = Signal:new(nil)
-      local mapped_signal = signal:map(function(value) return value or 'default' end)
+      local test_signal = Signal:new(nil)
+      local mapped_signal = test_signal:map(function(value) return value or 'default' end)
 
       assert.is.equal(mapped_signal:get(), 'default') -- Return default
-      signal:set 'new value'
+      test_signal:set 'new value'
       assert.is.equal(mapped_signal:get(), 'new value') -- Return new value
     end)
   end)
 
   describe('Signal:filter', function()
     it('should only emit values that pass the filter', function()
-      local signal = Signal:new(5)
-      local filtered_signal = signal:filter(function(value) return value > 10 end)
+      local test_signal = Signal:new(5)
+      local filtered_signal = test_signal:filter(function(value) return value > 10 end)
 
       assert.is.equal(filtered_signal:get(), nil) -- Initial value should not pass
-      signal:set(15)
+      test_signal:set(15)
       assert.is.equal(filtered_signal:get(), 15) -- Now filtered
-      signal:set(8)
+      test_signal:set(8)
       assert.is.equal(filtered_signal:get(), 15) -- Does not pass the filter
     end)
 
     it('should handle empty initial values', function()
-      local signal = Signal:new(nil)
-      local filtered_signal = signal:filter(function(value) return value ~= nil end)
+      local test_signal = Signal:new(nil)
+      local filtered_signal = test_signal:filter(function(value) return value ~= nil end)
 
       assert.is.equal(filtered_signal:get(), nil) -- Should be nil
-      signal:set(10)
+      test_signal:set(10)
       assert.is.equal(filtered_signal:get(), 10) -- Should pass now
     end)
   end)
 
   describe('create_memo', function()
     it('should compute a derived value and update when dependencies change', function()
-      local signal = Signal:new(2)
-      local memoized_signal = tracker.create_memo(function() return signal:get() * 2 end)
+      local test_signal = Signal:new(2)
+      local memoized_signal = tracker.create_memo(function() return test_signal:get() * 2 end)
 
       assert.is.equal(memoized_signal:get(), 4) -- Initially compute 2 * 2
 
-      signal:set(3)
+      test_signal:set(3)
       assert.is.equal(memoized_signal:get(), 6) -- Update to 3 * 2 = 6
 
-      signal:set(5)
+      test_signal:set(5)
       assert.is.equal(memoized_signal:get(), 10) -- Update to 5 * 2 = 10
     end)
 
     it('should not recompute if the dependencies do not change', function()
       local call_count = 0
-      local signal = Signal:new(10)
+      local test_signal = Signal:new(10)
       local memoized_signal = tracker.create_memo(function()
         call_count = call_count + 1
-        return signal:get() + 1
+        return test_signal:get() + 1
       end)
 
       assert.is.equal(memoized_signal:get(), 11) -- Compute first value
@@ -126,11 +126,11 @@ describe('Signal', function()
       memoized_signal:get() -- Call again, should use memoized value
       assert.is.equal(call_count, 1) -- Still should only be one call
 
-      signal:set(10) -- Set the same value
+      test_signal:set(10) -- Set the same value
       assert.is.equal(memoized_signal:get(), 11)
       assert.is.equal(call_count, 2)
 
-      signal:set(20)
+      test_signal:set(20)
       assert.is.equal(memoized_signal:get(), 21)
       assert.is.equal(call_count, 3)
     end)
@@ -138,31 +138,31 @@ describe('Signal', function()
 
   describe('create_effect', function()
     it('should track changes and execute callback', function()
-      local signal = Signal:new(5)
+      local test_signal = Signal:new(5)
       local call_count = 0
 
       tracker.create_effect(function()
-        signal:get() -- track as a dependency
+        test_signal:get() -- track as a dependency
         call_count = call_count + 1
       end)
 
       assert.is.equal(call_count, 1)
-      signal:set(10)
+      test_signal:set(10)
       assert.is.equal(call_count, 2)
     end)
 
     it('should clean up signals and not call after dispose', function()
-      local signal = Signal:new(5)
+      local test_signal = Signal:new(5)
       local call_count = 0
 
       local unsubscribe = tracker.create_effect(function()
         call_count = call_count + 1
-        return signal:get() * 2
+        return test_signal:get() * 2
       end)
 
       assert.is.equal(call_count, 1) -- Initially calls
       unsubscribe() -- Unsubscribe the effect
-      signal:set(10) -- Update signal value
+      test_signal:set(10) -- Update signal value
       assert.is.equal(call_count, 1) -- Callback should not be called again
     end)
   end)

spec/utils_spec.lua

@@ -1,70 +0,0 @@
-local utils = require 'u.utils'
-
---- @param s string
-local function split(s) return vim.split(s, '') end
-
---- @param original string
---- @param changes LevenshteinChange[]
-local function morph(original, changes)
-  local t = split(original)
-  for _, change in ipairs(changes) do
-    if change.kind == 'add' then
-      table.insert(t, change.index, change.item)
-    elseif change.kind == 'delete' then
-      table.remove(t, change.index)
-    elseif change.kind == 'change' then
-      t[change.index] = change.to
-    end
-  end
-  return vim.iter(t):join ''
-end
-
-describe('utils', function()
-  it('levenshtein', function()
-    local original = 'abc'
-    local result = 'absece'
-    local changes = utils.levenshtein(split(original), split(result))
-    assert.are.same(changes, {
-      {
-        item = 'e',
-        kind = 'add',
-        index = 4,
-      },
-      {
-        item = 'e',
-        kind = 'add',
-        index = 3,
-      },
-      {
-        item = 's',
-        kind = 'add',
-        index = 3,
-      },
-    })
-    assert.are.same(morph(original, changes), result)
-
-    original = 'jonathan'
-    result = 'ajoanthan'
-    changes = utils.levenshtein(split(original), split(result))
-    assert.are.same(changes, {
-      {
-        from = 'a',
-        index = 4,
-        kind = 'change',
-        to = 'n',
-      },
-      {
-        from = 'n',
-        index = 3,
-        kind = 'change',
-        to = 'a',
-      },
-      {
-        index = 1,
-        item = 'a',
-        kind = 'add',
-      },
-    })
-    assert.are.same(morph(original, changes), result)
-  end)
-end)

spec/withbuf.lua

@@ -1,5 +1,6 @@
+require 'luacov'
 local function withbuf(lines, f)
-  vim.opt_global.swapfile = false
+  vim.go.swapfile = false
 
   vim.cmd.new()
   vim.api.nvim_buf_set_lines(0, 0, -1, false, lines)

stylua.toml

@@ -1,6 +1,10 @@
+syntax = "LuaJIT"
 call_parentheses = "None"
 collapse_simple_statement = "Always"
-column_width = 120
+column_width = 100
 indent_type = "Spaces"
 indent_width = 2
 quote_style = "AutoPreferSingle"
+
+[sort_requires]
+enabled = true

vim.yml

@@ -1,36 +0,0 @@
----
-base: lua51
-globals:
-  vim:
-    any: true
-  assert.are.same:
-    args:
-      - type: any
-      - type: any
-  assert.are_not.same:
-    args:
-      - type: any
-      - type: any
-  assert.has.error:
-    args:
-      - type: any
-      - type: any
-  assert.is_true:
-    args:
-      - type: any
-      - type: any
-  assert.is_false:
-    args:
-      - type: any
-      - type: any
-  describe:
-    args:
-      - type: string
-      - type: function
-  it:
-    args:
-      - type: string
-      - type: function
-  before_each:
-    args:
-      - type: function