(stylua) lower max line length to 100

.github/workflows/ci.yaml

@@ -11,5 +11,6 @@ jobs:
       - uses: rhysd/action-setup-vim@v1
         with:
           neovim: true
-          version: v0.10.1
+          version: v0.11.0
+          arch: 'x86_64'
       - run: make test

.gitignore

@@ -1 +1,3 @@
+/.lux/
+lux.lock
 *.src.rock

.luacheckrc

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

Makefile

@@ -3,7 +3,8 @@ PLENARY_DIR=~/.local/share/nvim/site/pack/test/opt/plenary.nvim
 all: lint test
 
 lint:
-	selene .
+	lua-language-server --check=lua/u/ --checklevel=Hint
+	lux check
 
 fmt:
 	stylua .

README.md

@@ -2,10 +2,12 @@
 
 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.
 
-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.
+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).
 - **Code Writer**: Write code with automatic indentation and formatting.
 - **Operator Key Mapping**: Flexible key mapping that works with the selected text.
@@ -20,11 +22,215 @@ lazy.nvim:
 { 'jrop/u.nvim', lazy = true }
 ```
 
-## Usage
+## Signal and Rendering Usage
+
+### Overview
+
+The Signal and Rendering mechanisms are two subsystems of u.nvim, that, while
+simplistic, [compose](./examples/counter.lua) [together](./examples/filetree.lua)
+[powerfully](./examples/picker.lua) to create a system for interactive and
+responsive user interfaces. Here is a quick example that show-cases how easy it
+is to dive in to make any buffer an interactive UI:
+
+<details>
+<summary>Example Code: counter.lua</summary>
+
+```lua
+local tracker = require 'u.tracker'
+local Buffer = require 'u.buffer'
+local h = require('u.renderer').h
+
+-- Create an buffer for the UI
+vim.cmd.vnew()
+local ui_buf = Buffer.current()
+ui_buf:set_tmp_options()
+
+local s_count = tracker.create_signal(0)
+
+-- Effect: Render
+-- Setup the effect for rendering the UI whenever dependencies are updated
+tracker.create_effect(function()
+  -- Calling `Signal:get()` in an effect registers the given signal as a
+  -- dependency of the current effect. Whenever that signal (or any other
+  -- dependency) changes, the effect will rerun. In this particular case,
+  -- rendering the UI is an effect that depends on one signal.
+  local count = s_count:get()
+
+  -- Markup is hyperscript, which is just 1) text, and 2) tags (i.e.,
+  -- constructed with `h(...)` calls). To help organize the markup, text and
+  -- tags can be nested in tables at any depth. Line breaks must be specified
+  -- manually, with '\n'.
+  ui_buf:render {
+    'Reactive Counter Example\n',
+    '========================\n\n',
+
+    { 'Counter: ', tostring(count), '\n' },
+
+    '\n',
+
+    {
+      h('text', {
+        hl = 'DiffDelete',
+        nmap = {
+          ['<CR>'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            vim.schedule(function()
+              s_count:update(function(n) return n - 1 end)
+            end)
+            -- Also equivalent: s_count:set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Decrement '),
+      ' ',
+      h('text', {
+        hl = 'DiffAdd',
+        nmap = {
+          ['<CR>'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            vim.schedule(function()
+              s_count:update(function(n) return n + 1 end)
+            end)
+            -- Also equivalent: s_count:set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Increment '),
+    },
+
+    '\n',
+    '\n',
+    { 'Press <CR> on each "button" above to increment/decrement the counter.' },
+  }
+end)
+```
+
+</details>
+
+### `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.
+
+```lua
+local tracker = require('u.tracker')
+
+local s_number = tracker.Signal:new(0)
+-- auto-compute the double of the number each time it changes:
+local s_doubled = tracker.create_memo(function() return s_number:get() * 2 end)
+tracker.create_effect(function()
+  local n = s_doubled:get()
+  -- ...
+  -- whenever s_doubled changes, this function gets run
+end)
+```
+
+**Note**: circular dependencies are **not** supported.
+
+### `u.renderer`
+
+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:
+
+```lua
+local h = require('u.renderer').h
+-- Hyperscript can be organized into tables:
+{
+  "Hello, ",
+  {
+    "I am ", { "a" }, " nested table.",
+  },
+  '\n', -- newlines must be explicitly specified
+
+  -- booleans/nil are ignored:
+  some_conditional_flag and 'This text only shows when the flag is true',
+  -- e.g., use the above to show newlines in lists:
+  idx > 1 and '\n',
+
+  -- <text> tags are specified like so:
+  -- h('text', attributes, children)
+  h('text', {}, "I am a text node."),
+
+  -- <text> tags can be highlighted:
+  h('text', { hl = 'Comment' }, "I am highlighted."),
+
+  -- <text> tags can respond to key events:
+  h('text', {
+    hl = 'Keyword',
+    nmap = {
+      ["<CR>"] = function()
+        print("Hello World")
+        -- Return '' to swallow the event:
+        return ''
+      end,
+    },
+  }, "I am a text node."),
+}
+```
+
+Managing complex tables of hyperscript can be done more ergonomically using the
+`TreeBuilder` helper class:
+
+```lua
+local TreeBuilder = require('u.renderer').TreeBuilder
+
+-- ...
+renderer:render(
+  TreeBuilder.new()
+    -- text:
+    :put('some text')
+    -- hyperscript tables:
+    :put({ 'some text', 'more hyperscript' })
+    -- hyperscript tags:
+    :put_h('text', { --[[attributes]] }, { --[[children]] })
+    -- callbacks:
+    --- @param tb TreeBuilder
+    :nest(function(tb)
+      tb:put('some text')
+    end)
+    :tree()
+)
+```
+
+**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
+local renderer = Renderer:new(0 --[[buffer number]])
+renderer:render {
+  -- ...hyperscript...
+}
+
+-- or, if you already have a buffer:
+local Buffer = require('u.buffer')
+local buf = Buffer.current()
+buf:render {
+  -- ...hyperscript...
+}
+```
+
+## Range Usage
 
 ### A note on indices
 
+<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
 
@@ -32,8 +238,8 @@ The `Range` utility is the main feature upon which most other things in this lib
 
 ```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
@@ -43,15 +249,15 @@ This is usually not how you want to obtain a `Range`, however. Usually you want
 
 ```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
@@ -92,8 +298,8 @@ So far, that's a lot of ways to _get_ a `Range`. But what can you do with a rang
 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',
@@ -136,14 +342,15 @@ cw:write('}')
 
 #### Custom Text Objects
 
-Simply by returning a `Range` or a `Pos`, you can easily and quickly define your own text objects:
+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)
 ```
@@ -163,11 +370,11 @@ 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)

examples/counter.lua

@@ -0,0 +1,65 @@
+local tracker = require 'u.tracker'
+local Buffer = require 'u.buffer'
+local h = require('u.renderer').h
+
+-- Create an buffer for the UI
+vim.cmd.vnew()
+local ui_buf = Buffer.current()
+ui_buf:set_tmp_options()
+
+local s_count = tracker.create_signal(0, 'counter_signal')
+
+-- Effect: Render
+-- Setup the effect for rendering the UI whenever dependencies are updated
+tracker.create_effect(function()
+  -- Calling `Signal:get()` in an effect registers the given signal as a
+  -- dependency of the current effect. Whenever that signal (or any other
+  -- dependency) changes, the effect will rerun. In this particular case,
+  -- rendering the UI is an effect that depends on one signal.
+  local count = s_count:get()
+
+  -- Markup is hyperscript, which is just 1) text, and 2) tags (i.e.,
+  -- constructed with `h(...)` calls). To help organize the markup, text and
+  -- tags can be nested in tables at any depth. Line breaks must be specified
+  -- manually, with '\n'.
+  ui_buf:render {
+    'Reactive Counter Example\n',
+    '========================\n\n',
+
+    { 'Counter: ', tostring(count), '\n' },
+
+    '\n',
+
+    {
+      h('text', {
+        hl = 'DiffDelete',
+        nmap = {
+          ['<CR>'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            s_count:schedule_update(function(n) return n - 1 end)
+            -- Also equivalent: s_count:schedule_set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Decrement '),
+      ' ',
+      h('text', {
+        hl = 'DiffAdd',
+        nmap = {
+          ['<CR>'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            s_count:schedule_update(function(n) return n + 1 end)
+            -- Also equivalent: s_count:schedule_set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Increment '),
+    },
+
+    '\n',
+    '\n',
+    { 'Press <CR> on each "button" above to increment/decrement the counter.' },
+  }
+end)

examples/filetree.lua

@@ -0,0 +1,445 @@
+--------------------------------------------------------------------------------
+-- File Tree Viewer Module
+--
+-- Future Enhancements:
+-- - Consider implementing additional features like searching for files,
+--   filtering displayed nodes, or adding support for more file types.
+-- - Improve user experience with customizable UI elements and enhanced
+--   navigation options.
+-- - Implement a file watcher to automatically update the file tree when files
+--   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 }
+
+local Buffer = require 'u.buffer'
+local Renderer = require('u.renderer').Renderer
+local TreeBuilder = require('u.renderer').TreeBuilder
+local h = require('u.renderer').h
+local tracker = require 'u.tracker'
+
+local logger = require('u.logger').Logger.new 'filetree'
+
+local M = {}
+local H = {}
+
+--------------------------------------------------------------------------------
+-- Helpers:
+--------------------------------------------------------------------------------
+
+--- Splits the given path into a list of path components.
+--- @param path string
+function H.split_path(path)
+  local parts = {}
+  local curr = path
+  while #curr > 0 and curr ~= '.' and curr ~= '/' do
+    table.insert(parts, 1, vim.fs.basename(curr))
+    curr = vim.fs.dirname(curr)
+  end
+  return parts
+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
+
+--- Computes the relative path from `base` to `path`.
+--- @param path string
+--- @param base string
+function H.relative(path, base)
+  path = H.normalize(path)
+  base = H.normalize(base)
+  if path:sub(1, #base) == base then path = path:sub(#base + 1) end
+  if vim.startswith(path, '/') then path = path:sub(2) end
+  return path
+end
+
+--- @param root_path string
+--- @return { tree: FsDir; path_to_node: table<string, FsNode> }
+function H.get_tree_inf(root_path)
+  logger:info { 'get_tree_inf', root_path }
+  --- @type table<string, FsNode>
+  local path_to_node = {}
+
+  --- @type FsDir
+  local tree = {
+    kind = 'dir',
+    path = H.normalize(root_path or '.'),
+    expanded = true,
+    children = {},
+  }
+  path_to_node[tree.path] = tree
+
+  H.populate_dir_children(tree, path_to_node)
+  return { tree = tree, path_to_node = path_to_node }
+end
+
+--- @param tree FsDir
+--- @param path_to_node table<string, FsNode>
+function H.populate_dir_children(tree, path_to_node)
+  tree.children = {}
+
+  for child_path, kind in vim.iter(vim.fs.dir(tree.path, { depth = 1 })) do
+    child_path = H.normalize(vim.fs.joinpath(tree.path, child_path))
+    local prev_node = path_to_node[child_path]
+
+    if kind == 'directory' then
+      local new_node = {
+        kind = 'dir',
+        path = child_path,
+        expanded = prev_node and prev_node.expanded or false,
+        children = prev_node and prev_node.children or {},
+      }
+      path_to_node[new_node.path] = new_node
+      table.insert(tree.children, new_node)
+    else
+      local new_node = {
+        kind = 'file',
+        path = child_path,
+      }
+      path_to_node[new_node.path] = new_node
+      table.insert(tree.children, new_node)
+    end
+  end
+
+  table.sort(tree.children, function(a, b)
+    -- directories first:
+    if a.kind ~= b.kind then return a.kind == 'dir' end
+    return a.path < b.path
+  end)
+end
+
+--- @param opts {
+---   bufnr: number;
+---   prev_winnr: number;
+---   root_path: string;
+---   focus_path?: string;
+--- }
+---
+--- @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 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))
+
+  tracker.create_effect(function()
+    local focused_path = s_focused_path:get()
+
+    s_tree_inf:update(function(tree_inf)
+      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 child_names string[]
+      local function expand_to(node, child_names)
+        if #child_names == 0 then return end
+        node.expanded = true
+
+        local next_child_name = table.remove(child_names, 1)
+        for _, child in ipairs(node.children) do
+          if child.kind == 'dir' and vim.fs.basename(child.path) == next_child_name then
+            H.populate_dir_children(child, path_to_node)
+            expand_to(child, child_names)
+          end
+        end
+      end
+      expand_to(tree_inf.tree, parts)
+      return tree_inf
+    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
+
+  local controller = {}
+
+  --- @param path string
+  function controller.focus_path(path) s_focused_path:set(H.normalize(path)) end
+
+  function controller.refresh() s_tree_inf:set(H.get_tree_inf(opts.root_path)) end
+
+  --- @param path string
+  function controller.expand(path)
+    path = H.normalize(path)
+    local path_to_node = s_tree_inf:get().path_to_node
+
+    local node = path_to_node[path]
+    if node == nil then return end
+
+    if node.kind == 'dir' then
+      s_tree_inf:update(function(tree_inf2)
+        H.populate_dir_children(node, path_to_node)
+        tree_inf2.path_to_node[node.path].expanded = true
+        return tree_inf2
+      end)
+      if #node.children == 0 then
+        s_focused_path:set(node.path)
+      else
+        s_focused_path:set(node.children[1].path)
+      end
+    else
+      if node.kind == 'file' then
+        -- open file:
+        vim.api.nvim_win_call(opts.prev_winnr, function() vim.cmd.edit(node.path) end)
+        vim.api.nvim_set_current_win(opts.prev_winnr)
+      end
+    end
+  end
+
+  --- @param path string
+  function controller.collapse(path)
+    path = H.normalize(path)
+    local path_to_node = s_tree_inf:get().path_to_node
+
+    local node = path_to_node[path]
+    if node == nil then return end
+
+    if node.kind == 'dir' then
+      if node.expanded then
+        -- collapse self/node:
+        s_focused_path:set(node.path)
+        s_tree_inf:update(function(tree_inf2)
+          tree_inf2.path_to_node[node.path].expanded = false
+          return tree_inf2
+        end)
+      else
+        -- collapse parent:
+        local parent_dir = path_to_node[vim.fs.dirname(node.path)]
+        if parent_dir ~= nil then
+          s_focused_path:set(parent_dir.path)
+          s_tree_inf:update(function(tree_inf2)
+            tree_inf2.path_to_node[parent_dir.path].expanded = false
+            return tree_inf2
+          end)
+        end
+      end
+    elseif node.kind == 'file' then
+      local parent_dir = path_to_node[vim.fs.dirname(node.path)]
+      if parent_dir ~= nil then
+        s_focused_path:set(parent_dir.path)
+        s_tree_inf:update(function(tree_inf2)
+          tree_inf2.path_to_node[parent_dir.path].expanded = false
+          return tree_inf2
+        end)
+      end
+    end
+  end
+
+  --- @param root_path string
+  function controller.new(root_path)
+    vim.ui.input({
+      prompt = 'New: ',
+      completion = 'file',
+    }, function(input)
+      if input == nil then return end
+      local new_path = vim.fs.joinpath(root_path, input)
+
+      if vim.endswith(input, '/') then
+        -- Create a directory:
+        vim.fn.mkdir(new_path, input, 'p')
+      else
+        -- Create a file:
+
+        -- First, make sure the parent directory exists:
+        vim.fn.mkdir(vim.fs.dirname(new_path), 'p')
+
+        -- Now create an empty file:
+        local uv = vim.loop or vim.uv
+        local fd = uv.fs_open(new_path, 'w', 438)
+        if fd then uv.fs_write(fd, '') end
+      end
+
+      controller.refresh()
+      controller.focus_path(new_path)
+    end)
+  end
+
+  --- @param path string
+  function controller.rename(path)
+    path = H.normalize(path)
+    local root_path = vim.fs.dirname(path)
+    vim.ui.input({
+      prompt = 'Rename: ',
+      default = vim.fs.basename(path),
+      completion = 'file',
+    }, function(input)
+      if input == nil then return end
+
+      local new_path = vim.fs.joinpath(root_path, input);
+      (vim.loop or vim.uv).fs_rename(path, new_path)
+      controller.refresh()
+      controller.focus_path(new_path)
+    end)
+  end
+
+  --
+  -- Render:
+  --
+  local renderer = Renderer.new(opts.bufnr)
+  tracker.create_effect(function()
+    --- @type { tree: FsDir; path_to_node: table<string, FsNode> }
+    local tree_inf = s_tree_inf:get()
+    local tree = tree_inf.tree
+
+    --- @type string
+    local focused_path = s_focused_path:get()
+
+    --- As we render the tree, keep track of what line each node is on, so that
+    --- we have an easy way to make the cursor jump to each node (i.e., line)
+    --- at will:
+    --- @type table<string, number>
+    local node_lines = {}
+    local current_line = 0
+
+    --- The UI is rendered as a list of hypserscript elements:
+    local tb = TreeBuilder.new()
+
+    --- 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 level number
+    local function render_node(node, level)
+      local name = vim.fs.basename(node.path)
+      current_line = current_line + 1
+      node_lines[node.path] = current_line
+
+      local nmaps = {
+        h = function()
+          vim.schedule(function() controller.collapse(node.path) end)
+          return ''
+        end,
+        l = function()
+          vim.schedule(function() controller.expand(node.path) end)
+          return ''
+        end,
+        n = function()
+          vim.schedule(function() controller.new(node.kind == 'file' and vim.fs.dirname(node.path) or node.path) end)
+          return ''
+        end,
+        r = function()
+          vim.schedule(function() controller.rename(node.path) end)
+          return ''
+        end,
+        y = function()
+          vim.fn.setreg([["]], H.relative(node.path, tree.path))
+          return ''
+        end,
+      }
+
+      if node.kind == 'dir' then
+        --
+        -- Render a directory node:
+        --
+        local icon = node.expanded and '' or ''
+        tb:put {
+          current_line > 1 and '\n',
+          h('text', { hl = 'Constant', nmap = nmaps }, { string.rep('  ', level), icon, ' ', name }),
+        }
+        if node.expanded then
+          for _, child in ipairs(node.children) do
+            render_node(child, level + 1)
+          end
+        end
+      elseif node.kind == 'file' then
+        tb:put {
+          current_line > 1 and '\n',
+          h('text', { nmap = nmaps }, { string.rep('  ', level), '󰈔 ', name }),
+        }
+      end
+    end
+    render_node(tree, 0)
+
+    -- The following modifies buffer contents, so it needs to be scheduled:
+    vim.schedule(function()
+      renderer:render(tb:tree())
+
+      local cpos = vim.api.nvim_win_get_cursor(winnr)
+      pcall(vim.api.nvim_win_set_cursor, winnr, { node_lines[focused_path], cpos[2] })
+    end)
+  end, 's:tree')
+
+  return controller
+end
+
+--------------------------------------------------------------------------------
+-- Public API functions:
+--------------------------------------------------------------------------------
+
+--- @type {
+---   bufnr: number;
+---   winnr: number;
+---   controller: { expand: fun(path: string), collapse: fun(path: string) };
+--- } | nil
+local current_inf = nil
+
+--- Show the filetree:
+--- @param opts? ShowOpts
+function M.show(opts)
+  if current_inf ~= nil then return current_inf.controller end
+  opts = opts or {}
+
+  local prev_winnr = vim.api.nvim_get_current_win()
+
+  vim.cmd 'vnew'
+  local buf = Buffer.from_nr(vim.api.nvim_get_current_buf())
+  buf:set_tmp_options()
+
+  local winnr = vim.api.nvim_get_current_win()
+  vim.api.nvim_feedkeys(vim.api.nvim_replace_termcodes('<C-w>H', true, true, true), 'x', false)
+  vim.api.nvim_win_set_width(0, opts.width or 30)
+  vim.api.nvim_create_autocmd('WinClosed', {
+    once = true,
+    pattern = tostring(winnr),
+    callback = M.hide,
+  })
+
+  vim.wo.number = false
+  vim.wo.relativenumber = false
+
+  local bufnr = vim.api.nvim_get_current_buf()
+
+  local controller = _render_in_buffer(vim.tbl_extend('force', opts, {
+    bufnr = bufnr,
+    prev_winnr = prev_winnr,
+    root_path = opts.root_path or H.normalize '.',
+  }))
+  current_inf = { bufnr = bufnr, winnr = winnr, controller = controller }
+  return controller
+end
+
+--- Hide the filetree:
+function M.hide()
+  if current_inf == nil then return end
+  pcall(vim.cmd.bdelete, current_inf.bufnr)
+  current_inf = nil
+end
+
+--- Toggle the filetree:
+--- @param opts? ShowOpts
+function M.toggle(opts)
+  if current_inf == nil then
+    M.show(opts)
+  else
+    M.hide()
+  end
+end
+
+return M

examples/notify.lua

@@ -0,0 +1,137 @@
+local Buffer = require 'u.buffer'
+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 = {
+  [vim.log.levels.TRACE] = { text = '󰃤', group = 'DiagnosticSignOk' },
+  [vim.log.levels.DEBUG] = { text = '󰃤', group = 'DiagnosticSignOk' },
+  [vim.log.levels.INFO] = { text = '', group = 'DiagnosticSignInfo' },
+  [vim.log.levels.WARN] = { text = '', group = 'DiagnosticSignWarn' },
+  [vim.log.levels.ERROR] = { text = '', group = 'DiagnosticSignError' },
+}
+local DEFAULT_ICON = { text = '', group = 'DiagnosticSignOk' }
+
+--- @alias Notification {
+---   kind: number;
+---   id: number;
+---   text: string;
+--- }
+
+local M = {}
+
+--- @type Window | nil
+local notifs_w
+
+local s_notifications_raw = tracker.create_signal {}
+local s_notifications = s_notifications_raw:debounce(50)
+
+-- Render effect:
+tracker.create_effect(function()
+  --- @type Notification[]
+  local notifs = s_notifications:get()
+
+  if #notifs == 0 then
+    if notifs_w then
+      notifs_w:close(true)
+      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 win_config = {
+      relative = 'editor',
+      anchor = 'NE',
+      row = 0,
+      col = avail_width,
+      width = float_width,
+      height = math.min(#notifs, editor_size.height - 3),
+      border = 'single',
+      focusable = false,
+    }
+    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
+    else
+      notifs_w:set_config(win_config)
+    end
+
+    notifs_w:render(TreeBuilder.new()
+      :nest(function(tb)
+        for idx, notif in ipairs(notifs) do
+          if idx > 1 then tb:put '\n' end
+
+          local notif_icon = ICONS[notif.kind] or DEFAULT_ICON
+          tb:put_h('text', { hl = notif_icon.group }, notif_icon.text)
+          tb:put { '  ', notif.text }
+        end
+      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'
+    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[]
+    s_notifications_raw:schedule_update(function(notifs)
+      for i, notif in ipairs(notifs) do
+        if notif.id == id then
+          table.remove(notifs, i)
+          break
+        end
+      end
+      return notifs
+    end)
+  end, TIMEOUT)
+end
+
+local _once_msgs = {}
+local function my_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)
+  return true
+end
+
+function M.setup()
+  if _orig_notify == nil then _orig_notify = vim.notify end
+
+  vim.notify = my_notify
+  vim.notify_once = my_notify_once
+end
+
+return M

examples/picker.lua

@@ -0,0 +1,909 @@
+local utils = require 'u.utils'
+local Buffer = require 'u.buffer'
+local Renderer = require('u.renderer').Renderer
+local h = require('u.renderer').h
+local TreeBuilder = require('u.renderer').TreeBuilder
+local tracker = require 'u.tracker'
+
+local M = {}
+
+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,
+})
+
+--- @param low number
+--- @param x number
+--- @param high number
+local function clamp(low, x, high)
+  x = math.max(low, x)
+  x = math.min(x, high)
+  return x
+end
+
+--- @generic T
+--- @param arr `T`[]
+--- @return T[]
+local function shallow_copy_arr(arr) return vim.iter(arr):totable() end
+
+--------------------------------------------------------------------------------
+-- BEGIN create_picker
+--
+-- This is the star of the show (in this file, anyway).
+-- In summary, the outline of this function is:
+-- 1. Setup signals/memos for computing the picker size, and window positions
+-- 2. Create the two windows:
+--   a. The picker input. This is where the filter is typed
+--   b. The picker list. This is where the items are displayed
+-- 3. Setup event handlers that respond to user input
+-- 4. Render the list. After all the prework above, this is probably the
+--    shortest portion of this function.
+--------------------------------------------------------------------------------
+
+--- @alias SelectController {
+---   get_items: fun(): T[];
+---   set_items: fun(items: T[]);
+---   set_filter_text: fun(filter_text: string);
+---   get_selected_indices: fun(): number[];
+---   get_selected_items: fun(): T[];
+---   set_selected_indices: fun(indicies: number[], ephemeral?: boolean);
+---   close: fun();
+--- }
+--- @alias SelectOpts<T> {
+---   items: `T`[];
+---   multi?: boolean;
+---   format_item?: fun(item: T): Tree;
+---   on_finish?: fun(items: T[], indicies: number[]);
+---   on_selection_changed?: fun(items: T[], indicies: number[]);
+---   mappings?: table<string, fun(select: SelectController)>;
+--- }
+
+--- @generic T
+--- @param opts 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
+
+  if opts.multi == nil then opts.multi = false end
+
+  local H = {}
+
+  --- Runs a function `fn`, and if it fails, cleans up the UI by calling
+  --- `H.finish`
+  ---
+  --- @generic T
+  --- @param fn fun(): `T`
+  --- @return T
+  local function safe_run(fn, ...)
+    local ok, result_or_error = pcall(fn, ...)
+    if not ok then
+      pcall(H.finish, true, result_or_error)
+      error(result_or_error .. '\n' .. debug.traceback())
+    end
+    return result_or_error
+  end
+
+  --- Creates a function that safely calls the given function, cleaning up the
+  --- UI if it ever fails
+  ---
+  --- @generic T
+  --- @param fn `T`
+  --- @return T
+  local function safe_wrap(fn)
+    return function(...) return safe_run(fn, ...) end
+  end
+
+  --
+  -- Compute the positions of the input bar and the list:
+  --
+
+  -- Reactively compute the space available for the picker based on the size of
+  -- the editor
+  local s_editor_dimensions = S_EDITOR_DIMENSIONS:clone()
+  local s_picker_space_available = tracker.create_memo(safe_wrap(function()
+    local editor_dim = s_editor_dimensions:get()
+    local width = math.floor(editor_dim.width * 0.75)
+    local height = math.floor(editor_dim.height * 0.75)
+    local row = math.floor((editor_dim.height - height) / 2)
+    local col = math.floor((editor_dim.width - width) / 2)
+    return { width = width, height = height, row = row, col = col }
+  end))
+
+  -- Reactively compute the size of the prompt (input) bar
+  local s_w_input_coords = tracker.create_memo(safe_wrap(function()
+    local picker_coords = s_picker_space_available:get()
+    return {
+      width = picker_coords.width,
+      height = 1,
+      row = picker_coords.row,
+      col = picker_coords.col,
+    }
+  end))
+
+  -- Reactively compute the size of the list view
+  local s_w_list_coords = tracker.create_memo(safe_wrap(function()
+    local picker_coords = s_picker_space_available:get()
+    return {
+      width = picker_coords.width,
+      height = picker_coords.height - 3,
+      row = picker_coords.row + 3,
+      col = picker_coords.col,
+    }
+  end))
+
+  --
+  -- Create resources (i.e., windows):
+  --
+
+  local w_input_cfg = {
+    width = s_w_input_coords:get().width,
+    height = s_w_input_coords:get().height,
+    row = s_w_input_coords:get().row,
+    col = s_w_input_coords:get().col,
+    relative = 'editor',
+    focusable = true,
+    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.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.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()
+    -- update window position/size every time the editor is resized:
+    w_input_cfg = vim.tbl_deep_extend('force', w_input_cfg, s_w_input_coords:get())
+    vim.api.nvim_win_set_config(w_input, w_input_cfg)
+  end))
+
+  local w_list_cfg = {
+    width = s_w_list_coords:get().width,
+    height = s_w_list_coords:get().height,
+    row = s_w_list_coords:get().row,
+    col = s_w_list_coords:get().col,
+    relative = 'editor',
+    focusable = true,
+    border = 'rounded',
+  }
+  local w_list_buf = Buffer.create(false, true)
+  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())
+    vim.api.nvim_win_set_config(w_list, w_list_cfg)
+  end))
+
+  -- Now that we have created the window with the prompt in it, start insert
+  -- mode so that the user can type immediately:
+  vim.cmd.startinsert()
+
+  --
+  -- State:
+  --
+
+  local s_items_raw = tracker.create_signal(opts.items, 's:items')
+  local s_items = s_items_raw:debounce(100)
+  local s_selected_indices = tracker.create_signal({}, 's:selected_indices')
+  local s_top_offset = tracker.create_signal(0, 's:top_offset')
+  local s_cursor_index = tracker.create_signal(1, 's:cursor_index')
+
+  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),
+  })
+  local s_filter_text = s_filter_text_undebounced:debounce(50)
+
+  --
+  -- Derived State:
+  --
+
+  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 items = s_items:get()
+    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:
+  local s_filtered_items = tracker.create_memo(
+    safe_wrap(function()
+      local formatted_items = s_formatted_items:get()
+      local filter_text = vim.trim(s_filter_text:get()):lower()
+
+      local filter_pattern = ''
+      local use_plain_pattern = false
+      if #formatted_items > 250 and #filter_text <= 3 then
+        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()
+
+      --- @type table<integer, string>
+      local formatted_strings = {}
+      --- @type table<integer, string>
+      local matches = {}
+
+      local new_filtered_items = vim
+        .iter(formatted_items)
+        :enumerate()
+        :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)
+        :totable()
+
+      -- Don't sort if there are over 500 items:
+      if #new_filtered_items <= 500 then
+        table.sort(new_filtered_items, function(a_inf, b_inf)
+          local a = formatted_strings[a_inf.orig_idx]
+          local b = formatted_strings[b_inf.orig_idx]
+          if a == b then return false end
+
+          local a_match = matches[a_inf.orig_idx]
+          local b_match = matches[b_inf.orig_idx]
+          return #a_match < #b_match
+        end)
+      end
+
+      s_top_offset:set(0)
+      s_cursor_index:set(1)
+      return new_filtered_items
+    end),
+    'e:(filter_text=>filtered_items)'
+  )
+
+  -- Visible items, are _just_ the items that fit into the current viewport.
+  -- This is an optimization so that we are not rendering thousands of lines of
+  -- items on each state-change.
+  local s_visible_items = tracker.create_memo(
+    safe_wrap(function()
+      return vim
+        .iter(s_filtered_items:get())
+        :enumerate()
+        :skip(s_top_offset:get())
+        :take(s_w_list_coords:get().height)
+        :map(
+          function(i, inf)
+            return {
+              filtered_idx = i,
+              orig_idx = inf.orig_idx,
+              item = inf.item,
+              formatted = inf.formatted,
+            }
+          end
+        )
+        :totable()
+    end),
+    'm:visible_items'
+  )
+
+  -- Track selection information:
+  local s_selection_info = tracker.create_memo(
+    safe_wrap(function()
+      local items = s_items:get()
+      local selected_indices = s_selected_indices:get()
+      --- @type { orig_idx: number; item: T }[]
+      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
+      return {
+        items = vim.iter(indices):map(function(i) return items[i] end):totable(),
+        indices = indices,
+      }
+    end),
+    'm:selection_info'
+  )
+
+  --- When it is time to close the picker, this is the main cleanup routine
+  --- that runs in all cases:
+  ---
+  --- @param esc? boolean Whether the user pressed <Esc> or not
+  --- @param err? any Any error that occurred
+  function H.finish(esc, err)
+    -- s_editor_dimensions is the only signal that is cloned from a global,
+    -- one. It is therefore the only one that needs to be manually disposed.
+    -- The other ones should get cleaned up by the GC
+    s_editor_dimensions:dispose()
+    -- If we happen to have any async state-changes coming down the pipeline,
+    -- we can say right now that we are done rendering new UI (to avoid
+    -- "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.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)
+    if stopinsert then vim.cmd.stopinsert() end
+    local inf = s_selection_info:get()
+    if not err and opts.on_finish then
+      -- If on_finish opens another picker, the closing of this one can happen
+      -- in _too_ quick succession, so put a small delay in there.
+      --
+      -- TODO: figure out _why_ this is actually happening, and then a better
+      -- way to handle this.
+      vim.defer_fn(function()
+        if esc then
+          opts.on_finish({}, {})
+        else
+          opts.on_finish(inf.items, inf.indices)
+        end
+      end, 100)
+    end
+  end
+
+  -- On selection info changed:
+  tracker.create_effect(
+    safe_wrap(function()
+      local inf = s_selection_info:get()
+      if opts.on_selection_changed then opts.on_selection_changed(inf.items, inf.indices) end
+    end),
+    'e:selection_changed'
+  )
+
+  --
+  -- Public API (i.e., `controller`):
+  -- We will fill in the methods further down, but we need this variable in scope so that it can be
+  -- closed over by some of the event handlers:
+  --
+  local controller = {}
+
+  --
+  -- Events
+  --
+  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.bufnr })
+
+  local function action_next_line()
+    local max_line = #s_filtered_items:get()
+    local next_cursor_index = clamp(1, s_cursor_index:get() + 1, max_line)
+    if next_cursor_index - s_top_offset:get() > s_w_list_coords:get().height then
+      s_top_offset:set(s_top_offset:get() + 1)
+    end
+    s_cursor_index:set(next_cursor_index)
+  end
+  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()
+    local next_cursor_index = clamp(1, s_cursor_index:get() - 1, max_line)
+    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.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',
+    '<Tab>',
+    safe_wrap(function()
+      if not opts.multi then return end
+
+      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())
+      else
+        local new_selected_indices = shallow_copy_arr(s_selected_indices:get())
+        table.insert(new_selected_indices, index)
+        s_selected_indices:set(new_selected_indices)
+      end
+      action_next_line()
+    end),
+    { 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.bufnr })
+  end
+
+  -- Render:
+  H.unsubscribe_render_effect = tracker.create_effect(
+    safe_wrap(function()
+      local selected_indices = s_selected_indices:get()
+      local top_offset = s_top_offset:get()
+      local cursor_index = s_cursor_index:get()
+      --- @type { filtered_idx: number; orig_idx: number; item: T; formatted: string }[]
+      local visible_items = s_visible_items:get()
+
+      -- The above has to run in the execution context for the signaling to work, but
+      -- the following cannot run in a NeoVim loop-callback:
+      vim.schedule(function()
+        w_list_buf:render(TreeBuilder.new()
+          :nest(function(tb)
+            for loop_idx, inf in ipairs(visible_items) do
+              local is_cur_line = inf.filtered_idx == cursor_index
+              local is_selected = vim.tbl_contains(selected_indices, inf.orig_idx)
+
+              tb:put(loop_idx > 1 and '\n')
+              tb:put(is_cur_line and h('text', { hl = 'Structure' }, '❯') or ' ')
+              tb:put(is_selected and h('text', { hl = 'Comment' }, '* ') or '  ')
+              tb:put(inf.formatted)
+            end
+          end)
+          :tree())
+
+        -- set the window viewport to have the first line in view:
+        pcall(vim.api.nvim_win_call, w_list, function() vim.fn.winrestview { topline = 1 } end)
+        pcall(vim.api.nvim_win_set_cursor, w_list, { cursor_index - top_offset, 0 })
+      end)
+    end),
+    'e:render'
+  )
+
+  --
+  -- Populate the public API:
+  --
+  function controller.get_items()
+    return safe_run(function() return s_items_raw:get() end)
+  end
+
+  --- @param items T[]
+  function controller.set_items(items)
+    return safe_run(function() s_items_raw:set(items) end)
+  end
+
+  function controller.set_filter_text(filter_text)
+    return safe_run(function()
+      vim.api.nvim_win_call(w_input, function() vim.api.nvim_set_current_line(filter_text) end)
+    end)
+  end
+
+  function controller.get_selected_indices()
+    return safe_run(function() return s_selection_info:get().indices end)
+  end
+
+  function controller.get_selected_items()
+    return safe_run(function() return s_selection_info:get().items end)
+  end
+
+  --- @param indicies number[]
+  --- @param ephemeral? boolean
+  function controller.set_selected_indices(indicies, ephemeral)
+    return safe_run(function()
+      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)
+        if matching_filtered_item_idx ~= nil then s_cursor_index:set(indicies[1]) end
+      else
+        if not opts.multi then
+          local err = 'Cannot set multiple selected indices on a single-select picker'
+          H.finish(true, err)
+          error(err)
+        end
+        s_selected_indices:set(indicies)
+      end
+    end)
+  end
+
+  function controller.close()
+    return safe_run(function() H.finish(true) end)
+  end
+
+  return controller --[[@as SelectController]]
+end -- }}}
+
+--------------------------------------------------------------------------------
+-- END create_picker
+--------------------------------------------------------------------------------
+
+--------------------------------------------------------------------------------
+-- vim.ui.select override
+--------------------------------------------------------------------------------
+
+local ORIGINAL_UI_SELECT
+function M.register_ui_select()
+  ORIGINAL_UI_SELECT = vim.ui.select
+  --- @generic T
+  --- @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,
+      format_item = function(item)
+        local s = opts.format_item and opts.format_item(item) or tostring(item)
+        s = s:gsub('<', '&lt;')
+        return s
+      end,
+      on_finish = function(sel_items)
+        if #sel_items == 0 then cb(nil) end
+        cb(sel_items[#sel_items])
+      end,
+    }
+  end
+end
+function M.unregister_ui_select()
+  if not ORIGINAL_UI_SELECT then return end
+
+  vim.ui.select = ORIGINAL_UI_SELECT
+  ORIGINAL_UI_SELECT = nil
+end
+
+--------------------------------------------------------------------------------
+-- Built-in pickers
+-- 1. files
+-- 2. buffers
+-- 3. code-symbols
+--------------------------------------------------------------------------------
+
+--- @param opts? { limit?: number }
+function M.files(opts) -- {{{
+  opts = opts or {}
+  opts.limit = opts.limit or 10000
+
+  local cmd = {}
+  if vim.fn.executable 'rg' then
+    cmd = {
+      'rg',
+      '--color=never',
+      '--files',
+      '--hidden',
+      '--follow',
+      '-g',
+      '!.git',
+      '-g',
+      '!node_modules',
+      '-g',
+      '!target',
+    }
+  elseif vim.fn.executable 'fd' then
+    cmd = {
+      'fd',
+      '--color=never',
+      '--type',
+      'f',
+      '--hidden',
+      '--follow',
+      '--exclude',
+      '.git',
+      '--exclude',
+      'node_modules',
+      '--exclude',
+      'target',
+    }
+  elseif vim.fn.executable 'find' then
+    cmd = {
+      'find',
+      '-type',
+      'f',
+      '-not',
+      '-path',
+      "'*/.git/*'",
+      '-not',
+      '-path',
+      "'*/node_modules/*'",
+      '-not',
+      '-path',
+      "'*/target/*'",
+      '-printf',
+      "'%P\n'",
+    }
+  end
+
+  if #cmd == 0 then
+    vim.notify('rg/fd/find executable not found: cannot list files', vim.log.levels.ERROR)
+    return
+  end
+
+  -- Keep track of the job that will list files independent from the picker. We
+  -- will stream lines from this process to the picker as they come in:
+  local job_inf = { id = 0, proc_lines = {}, notified_over_limit = false }
+
+  -- Initially, create the picker with no items:
+  local picker = M.create_picker {
+    multi = true,
+    items = {},
+
+    --- @params items string[]
+    on_finish = function(items)
+      pcall(vim.fn.jobstop, job_inf.id)
+
+      if #items == 0 then return end
+      if #items == 1 then
+        vim.cmd.edit(items[1])
+      else
+        -- populate quickfix:
+        vim.fn.setqflist(vim
+          .iter(items)
+          :map(
+            function(item)
+              return {
+                filename = item,
+                lnum = 1,
+                col = 1,
+              }
+            end
+          )
+          :totable())
+        vim.cmd.copen()
+      end
+    end,
+
+    mappings = {
+      ['<C-t>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in new tab:
+        for _, item in ipairs(items) do
+          vim.cmd.tabnew(item)
+        end
+      end,
+
+      ['<C-v>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in vertical split:
+        for _, item in ipairs(items) do
+          vim.cmd.vsplit(item)
+        end
+      end,
+
+      ['<C-s>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in horizontal split:
+        for _, item in ipairs(items) do
+          vim.cmd.split(item)
+        end
+      end,
+    },
+  }
+
+  -- Kick off the process that lists the files. As lines come in, send them to
+  -- the picker:
+  job_inf.id = vim.fn.jobstart(cmd, {
+    --- @param data string[]
+    on_stdout = vim.schedule_wrap(function(_chanid, data, _name)
+      local lines = job_inf.proc_lines
+      local function set_lines_as_items_state()
+        picker.set_items(vim
+          .iter(lines)
+          :enumerate()
+          :filter(function(idx, item)
+            -- Filter out an incomplete last line:
+            local is_last_line = idx == #lines
+            if is_last_line and item == '' then return false end
+            return true
+          end)
+          :map(function(_, item) return item end)
+          :totable())
+      end
+
+      -- It's just not a good idea to process large lists with Lua. The default
+      -- limit is 10,000 items, and even crunching through this is iffy on a
+      -- 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)
+          pcall(vim.fn.jobstop, job_inf.id)
+          job_inf.notified_over_limit = true
+        end
+        return
+      end
+
+      -- :help channel-lines
+
+      local eof = #data == 1 and data[1] == ''
+      if eof then set_lines_as_items_state() end
+
+      -- Complete the previous line:
+      if #lines > 0 then lines[#lines] = lines[#lines] .. table.remove(data, 1) end
+
+      for _, l in ipairs(data) do
+        table.insert(lines, l)
+      end
+
+      set_lines_as_items_state()
+    end),
+  })
+end -- }}}
+
+function M.buffers() -- {{{
+  local cwd = vim.fn.getcwd()
+  -- ensure that `cwd` ends with a trailing slash:
+  if cwd[#cwd] ~= '/' then cwd = cwd .. '/' end
+
+  --- @type { name: string; changed: number; bufnr: number }[]
+  local bufs = vim.fn.getbufinfo { buflisted = 1 }
+
+  M.create_picker {
+    multi = true,
+    items = bufs,
+
+    --- @param item { name: string; changed: number; bufnr: number }
+    format_item = function(item)
+      local item_name = item.name
+      if item_name == '' then item_name = '[No Name]' end
+      -- 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()
+    end,
+
+    --- @params items { bufnr: number }[]
+    on_finish = function(items)
+      if #items == 0 then return end
+      if #items == 1 then
+        vim.cmd.buffer(items[1].bufnr)
+      else
+        -- populate quickfix:
+        vim.fn.setqflist(vim
+          .iter(items)
+          :map(
+            function(item)
+              return {
+                bufnr = item.bufnr,
+                filename = item.name,
+                lnum = 1,
+                col = 1,
+              }
+            end
+          )
+          :totable())
+        vim.cmd.copen()
+      end
+    end,
+
+    mappings = {
+      ['<C-t>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in new tab:
+        for _, item in ipairs(items) do
+          vim.cmd.tabnew()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-v>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in new vertial split:
+        for _, item in ipairs(items) do
+          vim.cmd.vsplit()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-s>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in horizontal split:
+        for _, item in ipairs(items) do
+          vim.cmd.split()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-x>'] = function(sel)
+        local selected_items = sel.get_selected_items()
+        for _, item in ipairs(selected_items) do
+          -- delete the buffer
+          vim.cmd.bdelete(item.bufnr)
+        end
+
+        sel.set_selected_indices {}
+        sel.set_items(
+          vim
+            .iter(sel.get_items())
+            :filter(function(item) return not vim.tbl_contains(selected_items, item) end)
+            :totable()
+        )
+      end,
+    },
+  }
+end -- }}}
+
+local IS_CODE_SYMBOL_RUNNING = false
+function M.lsp_code_symbols() -- {{{
+  if IS_CODE_SYMBOL_RUNNING then return end
+  IS_CODE_SYMBOL_RUNNING = true
+
+  -- Avoid callback-hell with a wizard-based "steps"-system. Define each "step"
+  -- sequentially in the code, and wire up the callbacks to call the next step:
+  -- a simple, yet powerful, and easy to understand pattern/approach.
+  local STEPS = {}
+
+  --- @param info vim.lsp.LocationOpts.OnList
+  function STEPS._1_on_symbols(info)
+    M.create_picker {
+      items = info.items,
+      --- @param item { text: string }
+      format_item = function(item)
+        local s = item.text:gsub('<', '&lt;')
+        return s
+      end,
+      on_finish = STEPS._2_on_symbol_picked,
+    }
+  end
+
+  --- @param items { filename: string, lnum: integer, col: integer }[]
+  function STEPS._2_on_symbol_picked(items)
+    if #items == 0 then return STEPS._finally() end
+
+    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)
+    if buf ~= nil then
+      vim.api.nvim_win_set_buf(0, buf.bufnr)
+    else
+      vim.cmd.edit(item.filename)
+    end
+
+    -- Jump to the specific location:
+    vim.api.nvim_win_set_cursor(0, { item.lnum, item.col - 1 })
+    vim.cmd.normal 'zz'
+
+    STEPS._finally()
+  end
+
+  function STEPS._finally() IS_CODE_SYMBOL_RUNNING = false end
+
+  -- Kick off the async operation:
+  vim.lsp.buf.document_symbol { on_list = STEPS._1_on_symbols }
+end -- }}}
+
+function M.setup()
+  utils.ucmd('Files', M.files)
+  utils.ucmd('Buffers', M.buffers)
+  utils.ucmd('Lspcodesymbols', M.lsp_code_symbols)
+end
+
+return M

examples/splitjoin.lua

@@ -4,7 +4,7 @@ local Range = require 'u.range'
 
 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

@@ -1,5 +1,4 @@
 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'
@@ -21,8 +20,17 @@ 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 +44,16 @@ 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 +69,7 @@ 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 +96,51 @@ 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)
   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 +149,12 @@ 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
@@ -132,15 +164,10 @@ 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)
@@ -149,7 +176,7 @@ function M.setup()
         lrange:replace(to.left)
       else
         -- replace `from.right` with `to.right`:
-        local last_line = arange:line0(-1).text() --[[@as string]]
+        local last_line = arange:line(-1):text()
         local from_right_match = last_line:match(vim.pesc(from.right) .. '$')
         if from_right_match then
           local match_start = arange.stop:clone()
@@ -158,7 +185,7 @@ function M.setup()
         end
 
         -- replace `from.left` with `to.left`:
-        local first_line = arange:line0(0).text() --[[@as string]]
+        local first_line = arange:line(1):text()
         local from_left_match = first_line:match('^' .. vim.pesc(from.left))
         if from_left_match then
           local match_end = arange.start:clone()
@@ -170,13 +197,16 @@ function M.setup()
   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 +217,19 @@ 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 +241,10 @@ 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

@@ -1,4 +1,4 @@
-local utils = require 'u.utils'
+local txtobj = require 'u.txtobj'
 local Pos = require 'u.pos'
 local Range = require 'u.range'
 local Buffer = require 'u.buffer'
@@ -7,17 +7,14 @@ 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

@@ -1,25 +1,32 @@
 local Range = require 'u.range'
+local Renderer = require('u.renderer').Renderer
 
----@class Buffer
----@field buf number
+--- @class u.Buffer
+--- @field bufnr number
+--- @field private renderer u.Renderer
 local 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 b = { buf = buf }
-  setmetatable(b, { __index = Buffer })
-  return b
+--- @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({
+    bufnr = bufnr,
+    renderer = renderer,
+  }, { __index = 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
+--- @return u.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')
@@ -28,45 +35,57 @@ function Buffer:set_tmp_options()
 end
 
 --- @param nm string
-function Buffer:get_option(nm) return vim.api.nvim_get_option_value(nm, { buf = self.buf }) end
+function Buffer:get_option(nm) return vim.api.nvim_get_option_value(nm, { buf = self.bufnr }) 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:set_option(nm, val)
+  return vim.api.nvim_set_option_value(nm, val, { buf = self.bufnr })
+end
 
 --- @param nm string
-function Buffer:get_var(nm) return vim.api.nvim_buf_get_var(self.buf, nm) end
+function Buffer:get_var(nm) return vim.api.nvim_buf_get_var(self.bufnr, nm) end
 
 --- @param nm string
-function Buffer:set_var(nm, val) return vim.api.nvim_buf_set_var(self.buf, nm, val) end
+function Buffer:set_var(nm, val) return vim.api.nvim_buf_set_var(self.bufnr, nm, val) end
 
-function Buffer:line_count() return vim.api.nvim_buf_line_count(self.buf) end
+function Buffer:line_count() return vim.api.nvim_buf_line_count(self.bufnr) end
 
-function Buffer:all() return Range.from_buf_text(self.buf) end
+function Buffer:all() return Range.from_buf_text(self.bufnr) 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[]
+--- @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.bufnr }))
+end
+
+--- @param tree Tree
+function Buffer:render(tree) return self.renderer:render(tree) end
+
 return Buffer

lua/u/codewriter.lua

@@ -1,6 +1,6 @@
 local Buffer = require 'u.buffer'
 
----@class CodeWriter
+--- @class u.CodeWriter
 --- @field lines string[]
 --- @field indent_level number
 --- @field indent_str string
@@ -8,7 +8,7 @@ local 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
@@ -22,20 +22,20 @@ function CodeWriter.new(indent_level, indent_str)
   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 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
   local indent_str = ''
@@ -61,7 +61,7 @@ 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/logger.lua

@@ -0,0 +1,69 @@
+local M = {}
+
+--- @params name string
+function M.file_for_name(name)
+  return vim.fs.joinpath(vim.fn.stdpath 'cache', 'u.log', name .. '.log.jsonl')
+end
+
+--------------------------------------------------------------------------------
+-- Logger class
+--------------------------------------------------------------------------------
+
+--- @class u.Logger
+--- @field name string
+--- @field private fd number
+local Logger = {}
+Logger.__index = Logger
+M.Logger = Logger
+
+--- @param name string
+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)
+  return self
+end
+
+--- @private
+--- @param level string
+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'
+  )
+end
+
+function Logger:trace(...) self:write('INFO', ...) end
+function Logger:debug(...) self:write('DEBUG', ...) end
+function Logger:info(...) self:write('INFO', ...) end
+function Logger:warn(...) self:write('WARN', ...) end
+function Logger:error(...) self:write('ERROR', ...) end
+
+function M.setup()
+  vim.api.nvim_create_user_command('Logfollow', function(args)
+    if #args.fargs == 0 then
+      vim.print 'expected log name'
+      return
+    end
+
+    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.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 = '*' })
+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)
   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

@@ -1,27 +1,29 @@
 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
+--- @class u.Pos
+--- @field bufnr number buffer number
 --- @field lnum number 1-based line index
 --- @field col number 1-based column index
 --- @field off number
 local Pos = {}
 Pos.MAX_COL = MAX_COL
 
----@param buf? number
----@param lnum number
----@param col number
+--- @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,
+    bufnr = bufnr,
     lnum = lnum,
     col = col,
     off = off,
@@ -29,9 +31,9 @@ function Pos.new(buf, lnum, col, 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)
+      return string.format('Pos(%d:%d){bufnr=%d, off=%d}', pos.lnum, pos.col, pos.bufnr, pos.off)
     else
-      return string.format('Pos(%d:%d){buf=%d}', pos.lnum, pos.col, pos.buf)
+      return string.format('Pos(%d:%d){bufnr=%d}', pos.lnum, pos.col, pos.bufnr)
     end
   end
   setmetatable(pos, {
@@ -44,106 +46,119 @@ function Pos.new(buf, lnum, col, off)
   return pos
 end
 
+function Pos.invalid() return Pos.new(0, 0, 0, 0) end
+
 function Pos.is(x)
+  if not type(x) == 'table' then return false end
   local mt = getmetatable(x)
   return mt and mt.__index == Pos
 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 Pos.is(a) and Pos.is(b) 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 not Pos.is(x) 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 not Pos.is(x) 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 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
+
 --- @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
-
-  local p = self:as_real()
-  vim.fn.setpos(pos, { p.buf, p.lnum + 1, p.col + 1, p.off })
-end
+function Pos:save_to_pos(pos) vim.fn.setpos(pos, { self.bufnr, self.lnum, self.col, self.off }) 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 +170,7 @@ 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 +184,14 @@ 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 +202,13 @@ 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 +218,20 @@ 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 +243,7 @@ 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 +261,17 @@ 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

@@ -1,23 +1,22 @@
 local Pos = require 'u.pos'
-local State = require 'u.state'
 
-local orig_on_yank = vim.highlight.on_yank
+local orig_on_yank = (vim.hl or vim.highlight).on_yank
 local on_yank_enabled = true;
-(vim.highlight --[[@as any]]).on_yank = function(opts)
+((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
 
----@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 start u.Pos
+--- @param stop u.Pos|nil
 --- @param mode? 'v'|'V'
----@return Range
+--- @return u.Range
 function Range.new(start, stop, mode)
   if stop ~= nil and stop < start then
     start, stop = stop, start
@@ -25,7 +24,7 @@ function Range.new(start, stop, mode)
 
   local r = { start = start, stop = stop, mode = mode or 'v' }
   local function str()
-    ---@param p Pos
+    --- @param p u.Pos
     local function posstr(p)
       if p == nil then
         return 'nil'
@@ -38,7 +37,13 @@ function Range.new(start, stop, mode)
 
     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)
+    return string.format(
+      'Range{bufnr=%d, mode=%s, start=%s, stop=%s}',
+      r.start.bufnr,
+      r.mode,
+      _1,
+      _2
+    )
   end
   setmetatable(r, { __index = Range, __tostring = str })
   return r
@@ -51,7 +56,7 @@ 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)
@@ -67,98 +72,109 @@ 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 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 '.'
-
-  -- 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 "']"
+  -- 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)
 
+  --- @type u.Pos
+  local start
+  --- @type u.Pos
+  local stop
+  -- 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 "']",
+  }
+  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 "']"
+    Pos.invalid():save_to_pos "'["
+    Pos.invalid():save_to_pos "']"
 
     local prev_on_yank_enabled = on_yank_enabled
     on_yank_enabled = false
     vim.cmd {
       cmd = 'normal',
       bang = not opts.user_defined,
-        args = { '""y' .. text_obj },
+      args = { '""y' .. motion },
       mods = { silent = true },
     }
     on_yank_enabled = prev_on_yank_enabled
 
-      local start = Pos.from_pos "'["
-      local stop = Pos.from_pos "']"
+    start = Pos.from_pos "'["
+    stop = Pos.from_pos "']"
+  end)
+  -- 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 start == stop and start:is_invalid() 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 stop:char() == motion_rest)
     -- *Sigh*, this also sometimes happens for `it` as well.
-        or (text_obj == 'it' and stop:char() == '<')
+    or (motion == 'it' and stop:char() == '<')
   then
     stop = stop:next(-1) or 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_txtobj and scope == 'a' then
+    start = start:find_next(1, motion_rest) or start
+    stop = stop:find_next(-1, motion_rest) or stop
+  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
+    opts.contains_cursor
+    and not Range.new(start, stop):contains(Pos.new(unpack(original_state.cursor)))
+  then
+    return nil
   end
 
   return Range.new(start, stop)
@@ -189,11 +205,11 @@ 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
+  --- @type nil|u.Pos
   local start
   local stop
   if args.range == 0 then
@@ -201,62 +217,47 @@ function Range.from_cmd_args(args)
   else
     start = Pos.from_pos "'<"
     stop = Pos.from_pos "'>"
-    if stop:is_col_max() then
-      mode = 'V'
-    else
-      mode = 'v'
-    end
+    mode = stop:is_col_max() and 'V' or 'v'
   end
   return Range.new(start, stop, mode)
 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)[]
+--- @param ranges (u.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
+  --- @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 max_start = ranges[1].start
-  local min_stop = ranges[1].stop
-  local result = ranges[1]
-
+  local smallest = 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
+    if start > smallest.start and stop < smallest.stop then smallest = r end
   end
+  return smallest
 end
 
-  return result
+function Range:clone()
+  return Range.new(self.start:clone(), self.stop ~= nil and self.stop:clone() or nil, self.mode)
 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
@@ -266,7 +267,7 @@ 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
@@ -298,19 +299,13 @@ function Range:trim_stop()
   return r
 end
 
----@param p Pos
+--- @param p u.Pos
 function Range:contains(p) return not self:is_empty() and p >= self.start and p <= self.stop 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
@@ -321,34 +316,18 @@ function Range:text() return vim.fn.join(self:lines(), '\n') end
 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
+--- @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 +335,58 @@ 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
@@ -428,7 +413,9 @@ 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
 
@@ -458,24 +445,16 @@ 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
 
-  if vim.api.nvim_get_current_buf() ~= self.start.buf then vim.api.nvim_set_current_buf(self.start.buf) end
+  local curr_mode = vim.fn.mode()
+  if curr_mode ~= self.mode then vim.cmd.normal { args = { self.mode }, bang = true } 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)
+  self.start:save_to_pos '.'
+  vim.cmd.normal { args = { 'o' }, bang = true }
+  self.stop:save_to_pos '.'
 end
 
 --- @param group string
@@ -490,33 +469,31 @@ 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.highlight.range(
-      self.start.buf,
+  local winview = vim.fn.winsaveview();
+  (vim.hl or vim.highlight).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

@@ -0,0 +1,532 @@
+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[]
+
+--- @param name string
+--- @param attributes? table<string, any>
+--- @param children? Node | Node[]
+--- @return Tag
+function M.h(name, attributes, children)
+  return {
+    kind = 'tag',
+    name = name,
+    attributes = attributes or {},
+    children = children,
+  }
+end
+
+-- Renderer {{{
+--- @alias RendererExtmark { id?: number; start: [number, number]; stop: [number, number]; opts: any; tag: any }
+
+--- @class u.Renderer
+--- @field bufnr number
+--- @field ns number
+--- @field changedtick number
+--- @field old { lines: string[]; extmarks: RendererExtmark[] }
+--- @field curr { lines: string[]; extmarks: 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)
+  if type(x) ~= 'table' then return false end
+  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
+
+  if vim.b[bufnr]._renderer_ns == nil then
+    vim.b[bufnr]._renderer_ns = vim.api.nvim_create_namespace('my.renderer:' .. tostring(bufnr))
+  end
+
+  local self = setmetatable({
+    bufnr = bufnr,
+    ns = vim.b[bufnr]._renderer_ns,
+    changedtick = 0,
+    old = { lines = {}, extmarks = {} },
+    curr = { lines = {}, extmarks = {} },
+  }, Renderer)
+  return self
+end -- }}}
+
+--- @param opts {
+---   tree: Tree;
+---   on_tag?: fun(tag: Tag, start0: [number, number], stop0: [number, number]): any;
+--- }
+function Renderer.markup_to_lines(opts) -- {{{
+  --- @type string[]
+  local lines = {}
+
+  local curr_line1 = 1
+  local curr_col1 = 1 -- exclusive: sits one position **beyond** the last inserted text
+  --- @param s string
+  local function put(s)
+    lines[curr_line1] = (lines[curr_line1] or '') .. s
+    curr_col1 = #lines[curr_line1] + 1
+  end
+  local function put_line()
+    table.insert(lines, '')
+    curr_line1 = curr_line1 + 1
+    curr_col1 = 1
+  end
+
+  --- @param node Node
+  local function visit(node) -- {{{
+    if node == nil or type(node) == 'boolean' then return end
+
+    if type(node) == 'string' then
+      local node_lines = vim.split(node, '\n')
+      for lnum, s in ipairs(node_lines) do
+        if lnum > 1 then put_line() end
+        put(s)
+      end
+    elseif Renderer.is_tag(node) then
+      local start0 = { curr_line1 - 1, curr_col1 - 1 }
+
+      -- visit the children:
+      if Renderer.is_tag_arr(node.children) then
+        for _, child in
+          ipairs(node.children --[[@as Node[] ]])
+        do
+          -- newlines are not controlled by array entries, do NOT output a line here:
+          visit(child)
+        end
+      else
+        visit(node.children)
+      end
+
+      local stop0 = { curr_line1 - 1, curr_col1 - 1 }
+      if opts.on_tag then opts.on_tag(node, start0, stop0) end
+    elseif Renderer.is_tag_arr(node) then
+      for _, child in ipairs(node) do
+        -- newlines are not controlled by array entries, do NOT output a line here:
+        visit(child)
+      end
+    end
+  end -- }}}
+  visit(opts.tree)
+
+  return lines
+end -- }}}
+
+--- @param opts {
+---   tree: string;
+---   format_tag?: fun(tag: 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) -- {{{
+  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[]
+  local extmarks = {}
+
+  --- @type string[]
+  local lines = Renderer.markup_to_lines {
+    tree = tree,
+
+    on_tag = function(tag, start0, stop0) -- {{{
+      if tag.name == 'text' then
+        local hl = tag.attributes.hl
+        if type(hl) == 'string' then
+          tag.attributes.extmark = tag.attributes.extmark or {}
+          tag.attributes.extmark.hl_group = tag.attributes.extmark.hl_group or hl
+        end
+
+        local extmark = tag.attributes.extmark
+
+        -- 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:_expr_map_callback('n', lhs) end,
+              { buffer = self.bufnr, expr = true, replace_keycodes = true }
+            )
+          end
+        end
+
+        if extmark then
+          table.insert(extmarks, {
+            start = start0,
+            stop = stop0,
+            opts = extmark,
+            tag = tag,
+          })
+        end
+      end
+    end, -- }}}
+  }
+
+  self.old = self.curr
+  self.curr = { lines = lines, extmarks = extmarks }
+  self:_reconcile()
+end -- }}}
+
+--- @private
+--- @param start integer
+--- @param end_ integer
+--- @param strict_indexing boolean
+--- @param replacement string[]
+function Renderer:_set_lines(start, end_, strict_indexing, replacement)
+  vim.api.nvim_buf_set_lines(self.bufnr, start, end_, strict_indexing, replacement)
+end
+
+--- @private
+--- @param start_row integer
+--- @param start_col integer
+--- @param end_row integer
+--- @param end_col integer
+--- @param replacement string[]
+function Renderer:_set_text(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)
+end
+
+--- @private
+function Renderer:_reconcile() -- {{{
+  local line_changes = H.levenshtein(self.old.lines, self.curr.lines)
+  self.old = self.curr
+
+  --
+  -- Step 1: morph the text to the desired state:
+  --
+  for _, line_change in ipairs(line_changes) do
+    local lnum0 = line_change.index - 1
+
+    if line_change.kind == 'add' then
+      self:_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
+          self:_set_text(lnum0, cnum0, lnum0, cnum0, { col_change.item })
+        elseif col_change.kind == 'change' then
+          self:_set_text(lnum0, cnum0, lnum0, cnum0 + 1, { col_change.to })
+        elseif col_change.kind == 'delete' then
+          self:_set_text(lnum0, cnum0, lnum0, cnum0 + 1, {})
+        else
+          -- No change
+        end
+      end
+    elseif line_change.kind == 'delete' then
+      self:_set_lines(lnum0, lnum0 + 1, true, {})
+    else
+      -- No change
+    end
+  end
+  self.changedtick = vim.b[self.bufnr].changedtick
+
+  --
+  -- Step 2: reconcile extmarks:
+  --
+  -- 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(
+      self.bufnr,
+      self.ns,
+      extmark.start[1],
+      extmark.start[2],
+      vim.tbl_extend('force', {
+        id = extmark.id,
+        end_row = extmark.stop[1],
+        end_col = extmark.stop[2],
+      }, extmark.opts)
+    )
+  end
+end -- }}}
+
+--- @private
+--- @param mode string
+--- @param lhs string
+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)
+
+  if #pos_infos == 0 then return lhs end
+
+  -- Find the first tag that is listening for this event:
+  local cancel = false
+  for _, pos_info in ipairs(pos_infos) do
+    local tag = pos_info.tag
+
+    -- is the tag listening?
+    local f = vim.tbl_get(tag.attributes, mode .. 'map', lhs)
+    if type(f) == 'function' then
+      local result = f()
+      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:
+        cancel = true
+      else
+        return result
+      end
+    end
+  end
+
+  -- Resort to default behavior:
+  return cancel and '' or lhs
+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) -- {{{
+  local cursor_line0, cursor_col0 = pos0[1], pos0[2]
+
+  -- 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
+    :map(function(ext)
+      --- @type number, number, number, { end_row?: number; end_col?: number }|nil
+      local id, line0, col0, details = unpack(ext)
+      local start = { line0, col0 }
+      local stop = { line0, col0 }
+      if details and details.end_row ~= nil and details.end_col ~= nil then
+        stop = { details.end_row, details.end_col }
+      end
+      return { id = id, start = start, stop = stop, opts = details }
+    end)
+    --- @param ext 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]
+          and cursor_line0 <= ext.stop[1]
+          and cursor_col0 < ext.stop[2]
+      else
+        return true
+      end
+    end)
+    :totable()
+
+  -- Sort the tags into smallest (inner) to largest (outer):
+  table.sort(
+    intersecting_extmarks,
+    --- @param x1 RendererExtmark
+    --- @param x2 RendererExtmark
+    function(x1, x2)
+      if
+        x1.start[1] == x2.start[1]
+        and x1.start[2] == x2.start[2]
+        and x1.stop[1] == x2.stop[1]
+        and x1.stop[2] == x2.stop[2]
+      then
+        return x1.id < x2.id
+      end
+
+      return x1.start[1] >= x2.start[1]
+        and x1.start[2] >= x2.start[2]
+        and x1.stop[1] <= x2.stop[1]
+        and x1.stop[2] <= x2.stop[2]
+    end
+  )
+
+  -- When we set the extmarks in the step above, we captured the IDs of the
+  -- 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 }[]
+  local matching_tags = vim
+    .iter(intersecting_extmarks)
+    --- @param ext 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
+      end
+    end)
+    :totable()
+
+  return matching_tags
+end -- }}}
+-- }}}
+
+-- TreeBuilder {{{
+--- @class u.TreeBuilder
+--- @field private nodes Node[]
+local TreeBuilder = {}
+TreeBuilder.__index = TreeBuilder
+M.TreeBuilder = TreeBuilder
+
+function TreeBuilder.new()
+  local self = setmetatable({ nodes = {} }, TreeBuilder)
+  return self
+end
+
+--- @param nodes Tree
+--- @return u.TreeBuilder
+function TreeBuilder:put(nodes)
+  table.insert(self.nodes, nodes)
+  return self
+end
+
+--- @param name string
+--- @param attributes? table<string, any>
+--- @param children? Node | Node[]
+--- @return u.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 u.TreeBuilder
+function TreeBuilder:nest(fn)
+  local nested_writer = TreeBuilder.new()
+  fn(nested_writer)
+  table.insert(self.nodes, nested_writer.nodes)
+  return self
+end
+
+--- @return Tree
+function TreeBuilder:tree() return self.nodes end
+-- }}}
+
+-- Levenshtein utility {{{
+--- @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 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 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

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.go[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.go[nm] = val
-  end
-  if self.win_view ~= nil then vim.fn.winrestview(self.win_view) end
-end
-
-return State

lua/u/tracker.lua

@@ -0,0 +1,307 @@
+local M = {}
+
+M.debug = false
+
+--------------------------------------------------------------------------------
+-- class Signal
+--------------------------------------------------------------------------------
+
+--- @class u.Signal
+--- @field name? string
+--- @field private changing boolean
+--- @field private value any
+--- @field private subscribers table<function, boolean>
+--- @field private on_dispose_callbacks function[]
+local Signal = {}
+M.Signal = Signal
+Signal.__index = Signal
+
+--- @param value any
+--- @param name? string
+--- @return u.Signal
+function Signal:new(value, name)
+  local obj = setmetatable({
+    name = name,
+    changing = false,
+    value = value,
+    subscribers = {},
+    on_dispose_callbacks = {},
+  }, self)
+  return obj
+end
+
+--- @param value any
+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
+      )
+    end
+    return
+  end
+
+  local prev_changing = self.changing
+  self.changing = true
+  local ok = true
+  local err = nil
+  for _, cb in ipairs(self.subscribers) do
+    local ok2, err2 = pcall(cb, value)
+    if not ok2 then
+      ok = false
+      err = err or err2
+    end
+  end
+  self.changing = prev_changing
+
+  if not ok then
+    vim.notify(
+      'error notifying' .. (self.name and (' in ' .. self.name) or '') .. ': ' .. tostring(err),
+      vim.log.levels.WARN
+    )
+    error(err)
+  end
+end
+
+function Signal:schedule_set(value)
+  vim.schedule(function() self:set(value) end)
+end
+
+--- @return any
+function Signal:get()
+  local ctx = M.ExecutionContext.current()
+  if ctx then ctx:track(self) end
+  return self.value
+end
+
+--- @param fn function
+function Signal:update(fn) self:set(fn(self.value)) end
+
+--- @param fn function
+function Signal:schedule_update(fn) self:schedule_set(fn(self.value)) end
+
+--- @generic 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()
+    return fn(value)
+  end, self.name and self.name .. ':mapped' or nil)
+  return mapped_signal
+end
+
+--- @return u.Signal
+function Signal:clone()
+  return self:map(function(x) return x end)
+end
+
+--- @param fn fun(value: T): boolean
+--- @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)
+    if fn(value) then filtered_signal:set(value) end
+  end)
+  filtered_signal:on_dispose(unsubscribe_from_self)
+  return filtered_signal
+end
+
+--- @param ms number
+--- @return u.Signal -- <T>
+function Signal:debounce(ms)
+  local function set_timeout(timeout, callback)
+    local timer = (vim.uv or vim.loop).new_timer()
+    timer:start(timeout, 0, function()
+      timer:stop()
+      timer:close()
+      callback()
+    end)
+    return timer
+  end
+
+  local filtered = M.create_signal(self.value, self.name and self.name .. ':debounced' or nil)
+
+  --- @diagnostic disable-next-line: undefined-doc-name
+  --- @type { queued: { value: T, ts: number }[]; timer?: 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
+  end
+
+  local unsubscribe_from_self = self:subscribe(function(value)
+    -- Stop any previously running timer:
+    if state.timer then clear_timeout() end
+    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 last_older_than_ms = older_than_ms[#older_than_ms]
+    if last_older_than_ms then
+      filtered:set(last_older_than_ms.value)
+      state.queued = {}
+    end
+
+    -- overwrite anything young enough
+    table.insert(state.queued, { value = value, ts = now_ms })
+    state.timer = set_timeout(ms, function()
+      vim.schedule(function() filtered:set(value) end)
+      -- If a timer was allowed to run to completion, that means that no other
+      -- item has been queued, since the timer is reset every time a new item
+      -- comes in. This means we can reset the queue
+      clear_timeout()
+      state.queued = {}
+    end)
+  end)
+  filtered:on_dispose(unsubscribe_from_self)
+
+  return filtered
+end
+
+--- @param callback function
+function Signal:subscribe(callback)
+  table.insert(self.subscribers, callback)
+  return function() self:unsubscribe(callback) end
+end
+
+--- @param callback function
+function Signal:on_dispose(callback) table.insert(self.on_dispose_callbacks, callback) end
+
+--- @param callback function
+function Signal:unsubscribe(callback)
+  for i, cb in ipairs(self.subscribers) do
+    if cb == callback then
+      table.remove(self.subscribers, i)
+      break
+    end
+  end
+end
+
+function Signal:dispose()
+  self.subscribers = {}
+  for _, callback in ipairs(self.on_dispose_callbacks) do
+    callback()
+  end
+end
+
+--------------------------------------------------------------------------------
+-- class ExecutionContext
+--------------------------------------------------------------------------------
+
+CURRENT_CONTEXT = nil
+
+--- @class u.ExecutionContext
+--- @field signals table<u.Signal, boolean>
+local ExecutionContext = {}
+M.ExecutionContext = ExecutionContext
+ExecutionContext.__index = ExecutionContext
+
+--- @return u.ExecutionContext
+function ExecutionContext:new()
+  return setmetatable({
+    signals = {},
+    subscribers = {},
+  }, ExecutionContext)
+end
+
+function ExecutionContext.current() return CURRENT_CONTEXT end
+
+--- @param fn function
+--- @param ctx u.ExecutionContext
+function ExecutionContext:run(fn, ctx)
+  local oldCtx = CURRENT_CONTEXT
+  CURRENT_CONTEXT = ctx
+  local result
+  local success, err = pcall(function() result = fn() end)
+
+  CURRENT_CONTEXT = oldCtx
+
+  if not success then error(err) end
+
+  return result
+end
+
+function ExecutionContext:track(signal) self.signals[signal] = true end
+
+--- @param callback function
+function ExecutionContext:subscribe(callback)
+  local wrapped_callback = function() callback() end
+  for signal in pairs(self.signals) do
+    signal:subscribe(wrapped_callback)
+  end
+
+  return function()
+    for signal in pairs(self.signals) do
+      signal:unsubscribe(wrapped_callback)
+    end
+  end
+end
+
+function ExecutionContext:dispose()
+  for signal, _ in pairs(self.signals) do
+    signal:dispose()
+  end
+  self.signals = {}
+end
+
+--------------------------------------------------------------------------------
+-- Helpers
+--------------------------------------------------------------------------------
+
+--- @param value any
+--- @param name? string
+--- @return u.Signal
+function M.create_signal(value, name) return Signal:new(value, name) end
+
+--- @param fn function
+--- @param name? string
+--- @return u.Signal
+function M.create_memo(fn, name)
+  --- @type u.Signal
+  local result
+  local unsubscribe = M.create_effect(function()
+    local value = fn()
+    if name and M.debug then vim.notify(name) end
+    if result then
+      result:set(value)
+    else
+      result = M.create_signal(value, name and ('m.s:' .. name) or nil)
+    end
+  end, name)
+  result:on_dispose(unsubscribe)
+  return result
+end
+
+--- @param fn function
+--- @param name? string
+function M.create_effect(fn, name)
+  local ctx = M.ExecutionContext:new()
+  M.ExecutionContext:run(fn, ctx)
+  return ctx:subscribe(function()
+    if name and M.debug then
+      local deps = vim
+        .iter(vim.tbl_keys(ctx.signals))
+        :map(function(s) return s.name end)
+        :filter(function(nm) return nm ~= nil end)
+        :join ','
+      vim.notify(name .. '(deps=' .. deps .. ')')
+    end
+    fn()
+  end)
+end
+
+return M

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

@@ -6,7 +6,19 @@ local M = {}
 
 --- @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 }
+--- @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: u.Range|nil }
+
+--- @generic T
+--- @param x `T`
+--- @param message? string
+--- @return T
+function M.dbg(x, message)
+  local t = {}
+  if message ~= nil then table.insert(t, message) end
+  table.insert(t, x)
+  vim.print(t)
+  return x
+end
 
 --- A utility for creating user commands that also pre-computes useful information
 --- and attaches it to the arguments.
@@ -37,98 +49,6 @@ function M.ucmd(name, cmd, opts)
   vim.api.nvim_create_user_command(name, cmd2, opts or {})
 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.go.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 }))
-end
-
-function M.get_editor_dimensions()
-  local w = 0
-  local h = 0
-  local tabnr = vim.api.nvim_get_current_tabpage()
-  for _, winid in ipairs(vim.api.nvim_list_wins()) do
-    local tabpage = vim.api.nvim_win_get_tabpage(winid)
-    if tabpage == tabnr then
-      local pos = vim.api.nvim_win_get_position(winid)
-      local r, c = pos[1], pos[2]
-      local win_w = vim.api.nvim_win_get_width(winid)
-      local win_h = vim.api.nvim_win_get_height(winid)
-      local right = c + win_w
-      local bottom = r + win_h
-      if right > w then w = right end
-      if bottom > h then h = bottom end
-    end
-  end
-  if w == 0 or h == 0 then
-    w = vim.api.nvim_win_get_width(0)
-    h = vim.api.nvim_win_get_height(0)
-  end
-  return { width = w, height = h }
-end
+function M.get_editor_dimensions() return { width = vim.go.columns, height = vim.go.lines } end
 
 return M

lux.toml

@@ -0,0 +1,19 @@
+package = "u.nvim"
+version = "0.2.0"
+lua = ">=5.1"
+
+[description]
+summary = ""
+maintainer = "jrop"
+labels = [ "library", "neovim", "neovim-plugin", "range", "utility" ]
+
+
+[dependencies]
+# Add your dependencies here
+# `busted = ">=2.0"`
+
+[run]
+args = [ "src/main.lua" ]
+
+[build]
+type = "builtin"

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

@@ -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()
@@ -187,53 +187,53 @@ 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)
@@ -258,22 +258,18 @@ 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 +293,16 @@ 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 "']"
 
@@ -317,7 +313,7 @@ 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)
@@ -325,8 +321,8 @@ describe('Range', function()
   it('from_cmd_args', function()
     local args = { range = 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, 2, 2)
       a:save_to_pos "'<"
       b:save_to_pos "'>"
 
@@ -341,25 +337,25 @@ 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 +377,9 @@ 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)
@@ -391,56 +387,56 @@ 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('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')
     end)
@@ -448,25 +444,27 @@ describe('Range', function()
 
   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)
@@ -475,7 +473,7 @@ 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))
@@ -491,11 +489,12 @@ 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({ '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))
@@ -511,7 +510,7 @@ 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 +539,7 @@ 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)

spec/renderer_spec.lua

@@ -0,0 +1,131 @@
+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_pos_infos
+  --
+
+  it('should return no extmarks for an empty buffer', function()
+    withbuf({}, function()
+      local r = R.Renderer.new(0)
+      local pos_infos = r:get_pos_infos { 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_pos_infos { 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 })
+    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_pos_infos { 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)
+end)

spec/tracker_spec.lua

@@ -0,0 +1,206 @@
+local tracker = require 'u.tracker'
+local Signal = tracker.Signal
+local ExecutionContext = tracker.ExecutionContext
+
+describe('Signal', function()
+  local signal
+
+  before_each(function() signal = Signal:new(0, 'testSignal') end)
+
+  it('should initialize with correct parameters', function()
+    assert.is.equal(signal.value, 0)
+    assert.is.equal(signal.name, 'testSignal')
+    assert.is.not_nil(signal.subscribers)
+    assert.is.equal(#signal.subscribers, 0)
+    assert.is.equal(signal.changing, false)
+  end)
+
+  it('should set new value and notify subscribers', function()
+    local called = false
+    signal:subscribe(function(value)
+      called = true
+      assert.is.equal(value, 42)
+    end)
+
+    signal:set(42)
+    assert.is.equal(called, true)
+  end)
+
+  it('should not notify subscribers during circular dependency', function()
+    signal.changing = true
+    local notified = false
+
+    signal:subscribe(function() notified = true end)
+
+    signal:set(42)
+    assert.is.equal(notified, false) -- No notification should occur
+  end)
+
+  it('should get current value', function()
+    signal:set(100)
+    assert.is.equal(signal:get(), 100)
+  end)
+
+  it('should update value with function', function()
+    signal:set(10)
+    signal:update(function(value) return value * 2 end)
+    assert.is.equal(signal:get(), 20)
+  end)
+
+  it('should dispose subscribers', function()
+    local called = false
+    local unsubscribe = signal:subscribe(function() called = true end)
+
+    unsubscribe()
+    signal:set(10)
+    assert.is.equal(called, false) -- Should not be notified
+  end)
+
+  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)
+
+      assert.is.equal(mapped_signal:get(), 10) -- Initial transformation
+      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)
+
+      assert.is.equal(mapped_signal:get(), 'default') -- Return default
+      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)
+
+      assert.is.equal(filtered_signal:get(), nil) -- Initial value should not pass
+      signal:set(15)
+      assert.is.equal(filtered_signal:get(), 15) -- Now filtered
+      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)
+
+      assert.is.equal(filtered_signal:get(), nil) -- Should be nil
+      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)
+
+      assert.is.equal(memoized_signal:get(), 4) -- Initially compute 2 * 2
+
+      signal:set(3)
+      assert.is.equal(memoized_signal:get(), 6) -- Update to 3 * 2 = 6
+
+      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 memoized_signal = tracker.create_memo(function()
+        call_count = call_count + 1
+        return signal:get() + 1
+      end)
+
+      assert.is.equal(memoized_signal:get(), 11) -- Compute first value
+      assert.is.equal(call_count, 1) -- Should compute once
+
+      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
+      assert.is.equal(memoized_signal:get(), 11)
+      assert.is.equal(call_count, 2)
+
+      signal:set(20)
+      assert.is.equal(memoized_signal:get(), 21)
+      assert.is.equal(call_count, 3)
+    end)
+  end)
+
+  describe('create_effect', function()
+    it('should track changes and execute callback', function()
+      local signal = Signal:new(5)
+      local call_count = 0
+
+      tracker.create_effect(function()
+        signal:get() -- track as a dependency
+        call_count = call_count + 1
+      end)
+
+      assert.is.equal(call_count, 1)
+      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 call_count = 0
+
+      local unsubscribe = tracker.create_effect(function()
+        call_count = call_count + 1
+        return signal:get() * 2
+      end)
+
+      assert.is.equal(call_count, 1) -- Initially calls
+      unsubscribe() -- Unsubscribe the effect
+      signal:set(10) -- Update signal value
+      assert.is.equal(call_count, 1) -- Callback should not be called again
+    end)
+  end)
+end)
+
+describe('ExecutionContext', function()
+  local context
+
+  before_each(function() context = ExecutionContext:new() end)
+
+  it('should initialize a new context', function()
+    assert.is.table(context.signals)
+    assert.is.table(context.subscribers)
+  end)
+
+  it('should track signals', function()
+    local signal = Signal:new(0)
+    context:track(signal)
+
+    assert.is.equal(next(context.signals), signal) -- Check if signal is tracked
+  end)
+
+  it('should subscribe to signals', function()
+    local signal = Signal:new(0)
+    local callback_called = false
+
+    context:track(signal)
+    context:subscribe(function() callback_called = true end)
+
+    signal:set(100)
+    assert.is.equal(callback_called, true) -- Callback should be called
+  end)
+
+  it('should dispose tracked signals', function()
+    local signal = Signal:new(0)
+    context:track(signal)
+
+    context:dispose()
+    assert.is.falsy(next(context.signals)) -- Should not have any tracked signals
+  end)
+end)

stylua.toml

@@ -1,6 +1,6 @@
 call_parentheses = "None"
 collapse_simple_statement = "Always"
-column_width = 120
+column_width = 100
 indent_type = "Spaces"
 indent_width = 2
 quote_style = "AutoPreferSingle"