range: extmarks/tsquery; renderer: text-change

lua/u/buffer.lua

@@ -2,10 +2,10 @@ local Range = require 'u.range'
 local Renderer = require('u.renderer').Renderer
 
 --- @class u.Buffer
---- @field bufnr number
+--- @field bufnr integer
 --- @field b vim.var_accessor
 --- @field bo vim.bo
---- @field private renderer u.Renderer
+--- @field renderer u.renderer.Renderer
 local Buffer = {}
 Buffer.__index = Buffer
 
@@ -68,13 +68,16 @@ function Buffer:motion(motion, opts)
   return Range.from_motion(motion, opts)
 end
 
---- @param event string|string[]
+--- @param event vim.api.keyset.events|vim.api.keyset.events[]
 --- @diagnostic disable-next-line: undefined-doc-name
 --- @param opts vim.api.keyset.create_autocmd
 function Buffer:autocmd(event, opts)
   vim.api.nvim_create_autocmd(event, vim.tbl_extend('force', opts, { buffer = self.bufnr }))
 end
 
+--- @param fn function
+function Buffer:call(fn) return vim.api.nvim_buf_call(self.bufnr, fn) end
+
 --- @param tree u.renderer.Tree
 function Buffer:render(tree) return self.renderer:render(tree) end
 

lua/u/codewriter.lua

@@ -32,7 +32,7 @@ end
 --- @param line string
 --- @param bufnr? number
 function CodeWriter.from_line(line, bufnr)
-  if bufnr == nil then bufnr = vim.api.nvim_get_current_buf() end
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
 
   local ws = line:match '^%s*'
   local expandtab = vim.api.nvim_get_option_value('expandtab', { buf = bufnr })

lua/u/extmark.lua

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

lua/u/logger.lua

@@ -1,9 +1,9 @@
 local M = {}
 
+local LOG_ROOT = vim.fs.joinpath(vim.fn.stdpath 'cache', 'u.log')
+
 --- @params name string
-function M.file_for_name(name)
-  return vim.fs.joinpath(vim.fn.stdpath 'cache', 'u.log', name .. '.log.jsonl')
-end
+function M.file_for_name(name) return vim.fs.joinpath(LOG_ROOT, name .. '.log.jsonl') end
 
 --------------------------------------------------------------------------------
 -- Logger class
@@ -11,7 +11,6 @@ end
 
 --- @class u.Logger
 --- @field name string
---- @field private fd number
 local Logger = {}
 Logger.__index = Logger
 M.Logger = Logger
@@ -20,10 +19,7 @@ M.Logger = Logger
 function Logger.new(name)
   local file_path = M.file_for_name(name)
   vim.fn.mkdir(vim.fs.dirname(file_path), 'p')
-  local self = setmetatable({
-    name = name,
-    fd = (vim.uv or vim.loop).fs_open(file_path, 'a', tonumber('644', 8)),
-  }, Logger)
+  local self = setmetatable({ name = name }, Logger)
   return self
 end
 
@@ -32,10 +28,12 @@ end
 function Logger:write(level, ...)
   local data = { ... }
   if #data == 1 then data = data[1] end
-  (vim.uv or vim.loop).fs_write(
-    self.fd,
-    vim.json.encode { ts = os.date(), level = level, data = data } .. '\n'
+  local f = assert(io.open(M.file_for_name(self.name), 'a'), 'could not open file')
+  assert(
+    f:write(vim.json.encode { ts = os.date(), level = level, data = data } .. '\n'),
+    'could not write to file'
   )
+  f:close()
 end
 
 function Logger:trace(...) self:write('INFO', ...) end
@@ -64,6 +62,12 @@ function M.setup()
     vim.cmd.terminal('tail -f "' .. log_file_path .. '"')
     vim.cmd.startinsert()
   end, { nargs = '*' })
+
+  vim.api.nvim_create_user_command(
+    'Logroot',
+    function() vim.api.nvim_echo({ { LOG_ROOT } }, false, {}) end,
+    {}
+  )
 end
 
 return M

lua/u/pos.lua

@@ -7,9 +7,9 @@ local function line_text(bufnr, lnum)
 end
 
 --- @class u.Pos
---- @field bufnr number buffer number
---- @field lnum number 1-based line index
---- @field col number 1-based column index
+--- @field bufnr integer buffer number
+--- @field lnum integer 1-based line index
+--- @field col integer 1-based column index
 --- @field off number
 local Pos = {}
 Pos.__index = Pos
@@ -31,16 +31,33 @@ end
 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 = {
+  --- @type u.Pos
+  return setmetatable({
     bufnr = bufnr,
     lnum = lnum,
     col = col,
     off = off,
-  }
-  setmetatable(pos, Pos)
-  return pos
+  }, Pos)
 end
 
+--- @param bufnr? number
+--- @param lnum0 number 1-based
+--- @param col0 number 1-based
+--- @param off? number
+function Pos.from00(bufnr, lnum0, col0, off) return Pos.new(bufnr, lnum0 + 1, col0 + 1, off) end
+
+--- @param bufnr? number
+--- @param lnum0 number 1-based
+--- @param col1 number 1-based
+--- @param off? number
+function Pos.from01(bufnr, lnum0, col1, off) return Pos.new(bufnr, lnum0 + 1, col1, off) end
+
+--- @param bufnr? number
+--- @param lnum1 number 1-based
+--- @param col0 number 1-based
+--- @param off? number
+function Pos.from10(bufnr, lnum1, col0, off) return Pos.new(bufnr, lnum1, col0 + 1, off) end
+
 function Pos.invalid() return Pos.new(0, 0, 0, 0) end
 
 function Pos.__lt(a, b) return a.lnum < b.lnum or (a.lnum == b.lnum and a.col < b.col) end
@@ -67,6 +84,15 @@ function Pos.__sub(x, y)
   return x:next(-y)
 end
 
+--- @param bufnr number
+--- @param lnum number
+function Pos.from_eol(bufnr, lnum)
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
+  local pos = Pos.new(bufnr, lnum, 0)
+  pos.col = pos:line():len()
+  return pos
+end
+
 --- @param name string
 --- @return u.Pos
 function Pos.from_pos(name)
@@ -96,9 +122,16 @@ end
 
 function Pos:as_vim() return { self.bufnr, self.lnum, self.col, self.off } end
 
+function Pos:eol() return Pos.from_eol(self.bufnr, self.lnum) end
+
 --- @param pos string
 function Pos:save_to_pos(pos) vim.fn.setpos(pos, { self.bufnr, self.lnum, self.col, self.off }) end
 
+--- @param winnr? integer
+function Pos:save_to_cursor(winnr)
+  vim.api.nvim_win_set_cursor(winnr or 0, { self.lnum, self.col - 1 })
+end
+
 --- @param mark string
 function Pos:save_to_mark(mark)
   local p = self:as_real()

lua/u/range.lua

@@ -1,6 +1,8 @@
+local Extmark = require 'u.extmark'
 local Pos = require 'u.pos'
 
 local ESC = vim.api.nvim_replace_termcodes('<Esc>', true, false, true)
+local NS = vim.api.nvim_create_namespace 'u.range'
 
 --- @class u.Range
 --- @field start u.Pos
@@ -115,7 +117,7 @@ end
 function Range.from_motion(motion, opts)
   -- Options handling:
   opts = opts or {}
-  if opts.bufnr == nil then opts.bufnr = vim.api.nvim_get_current_buf() end
+  if opts.bufnr == nil or opts.bufnr == 0 then opts.bufnr = vim.api.nvim_get_current_buf() end
   if opts.contains_cursor == nil then opts.contains_cursor = false end
   if opts.user_defined == nil then opts.user_defined = false end
 
@@ -146,6 +148,8 @@ function Range.from_motion(motion, opts)
     _G.Range__from_motion_opfunc = function(ty)
       _G.Range__from_motion_opfunc_captured_range = Range.from_op_func(ty)
     end
+    local old_eventignore = vim.o.eventignore
+    vim.o.eventignore = 'all'
     vim.go.operatorfunc = 'v:lua.Range__from_motion_opfunc'
     vim.cmd {
       cmd = 'normal',
@@ -153,6 +157,7 @@ function Range.from_motion(motion, opts)
       args = { ESC .. 'g@' .. motion },
       mods = { silent = true },
     }
+    vim.o.eventignore = old_eventignore
   end)
   local captured_range = _G.Range__from_motion_opfunc_captured_range
 
@@ -193,6 +198,26 @@ function Range.from_motion(motion, opts)
   return captured_range
 end
 
+--- @param opts? { contains_cursor?: boolean }
+function Range.from_tsquery_caps(bufnr, query, opts)
+  opts = opts or { contains_cursor = true }
+
+  local ranges = Range.from_buf_text(bufnr):tsquery(query)
+  if not ranges then return end
+  if not opts.contains_cursor then return ranges end
+
+  local cursor = Pos.from_pos '.'
+  return vim.tbl_map(function(cap_ranges)
+    return vim
+      .iter(cap_ranges)
+      :filter(
+        --- @param r u.Range
+        function(r) return r:contains(cursor) end
+      )
+      :totable()
+  end, ranges)
+end
+
 --- Get range information from the currently selected visual text.
 --- Note: from within a command mapping or an opfunc, use other specialized
 --- utilities, such as:
@@ -220,19 +245,22 @@ end
 --- @param args unknown
 --- @return u.Range|nil
 function Range.from_cmd_args(args)
-  --- @type 'v'|'V'
-  local mode
-  --- @type nil|u.Pos
-  local start
-  local stop
-  if args.range == 0 then
-    return nil
-  else
-    start = Pos.from_pos "'<"
-    stop = Pos.from_pos "'>"
-    mode = stop:is_col_max() and 'V' or 'v'
+  if args.range == 0 then return nil end
+
+  local bufnr = vim.api.nvim_get_current_buf()
+  if args.range == 1 then
+    return Range.new(Pos.new(bufnr, args.line1, 1), Pos.new(bufnr, args.line1, Pos.MAX_COL), 'V')
+  end
+
+  local is_visual = vim.fn.histget('cmd', -1):sub(1, 5) == [['<,'>]]
+  --- @type 'v'|'V'
+  local mode = is_visual and vim.fn.visualmode() or 'V'
+
+  if is_visual then
+    return Range.new(Pos.from_pos "'<", Pos.from_pos "'>", mode)
+  else
+    return Range.new(Pos.new(bufnr, args.line1, 1), Pos.new(bufnr, args.line2, Pos.MAX_COL), mode)
   end
-  return Range.new(start, stop, mode)
 end
 
 function Range.find_nearest_brackets()
@@ -272,6 +300,13 @@ function Range:to_linewise()
   return r
 end
 
+function Range:to_charwise()
+  local r = self:clone()
+  r.mode = 'v'
+  if r.stop:is_col_max() then r.stop = r.stop:as_real() end
+  return r
+end
+
 --- @param x u.Pos | u.Range
 function Range:contains(x)
   if getmetatable(x) == Pos then
@@ -313,27 +348,19 @@ end
 --- @param left string
 --- @param right string
 function Range:save_to_pos(left, right)
-  if self:is_empty() then
-    self.start:save_to_pos(left)
-    self.start:save_to_pos(right)
-  else
-    self.start:save_to_pos(left)
-    self.stop:save_to_pos(right)
-  end
+  self.start:save_to_pos(left);
+  (self:is_empty() and self.start or self.stop):save_to_pos(right)
 end
 
 --- @param left string
 --- @param right string
 function Range:save_to_marks(left, right)
-  if self:is_empty() then
-    self.start:save_to_mark(left)
-    self.start:save_to_mark(right)
-  else
-    self.start:save_to_mark(left)
-    self.stop:save_to_mark(right)
-  end
+  self.start:save_to_mark(left);
+  (self:is_empty() and self.start or self.stop):save_to_mark(right)
 end
 
+function Range:save_to_extmark() return Extmark.from_range(self, NS) end
+
 function Range:set_visual_selection()
   if self:is_empty() then return end
   if vim.api.nvim_get_current_buf() ~= self.start.bufnr then
@@ -348,14 +375,46 @@ function Range:set_visual_selection()
   self.stop:save_to_pos '.'
 end
 
---------------------------------------------------------------------------------
--- Range.from_* functions:
---------------------------------------------------------------------------------
-
 --------------------------------------------------------------------------------
 -- Text access/manipulation utilities:
 --------------------------------------------------------------------------------
 
+--- @param query string
+function Range:tsquery(query)
+  local bufnr = self.start.bufnr
+
+  local lang = vim.treesitter.language.get_lang(vim.bo[bufnr].filetype)
+  if lang == nil then return end
+  local parser = vim.treesitter.get_parser(bufnr, lang)
+  if parser == nil then return end
+  local tree = parser:parse()[1]
+  if tree == nil then return end
+
+  local root = tree:root()
+  local q = vim.treesitter.query.parse(lang, query)
+  --- @type table<string, u.Range[]>
+  local ranges = {}
+  for id, match, _meta in
+    q:iter_captures(root, bufnr, self.start.lnum - 1, (self.stop or self.start).lnum)
+  do
+    local start_row0, start_col0, stop_row0, stop_col0 = match:range()
+    local range = Range.new(
+      Pos.new(bufnr, start_row0 + 1, start_col0 + 1),
+      Pos.new(bufnr, stop_row0 + 1, stop_col0),
+      'v'
+    )
+    if range.stop.lnum > vim.api.nvim_buf_line_count(bufnr) then
+      range.stop = range.stop:must_next(-1)
+    end
+
+    local capture_name = q.captures[id]
+    if not ranges[capture_name] then ranges[capture_name] = {} end
+    if self:contains(range) then table.insert(ranges[capture_name], range) end
+  end
+
+  return ranges
+end
+
 function Range:length()
   if self:is_empty() then return 0 end
 

lua/u/renderer.lua

@@ -1,12 +1,33 @@
+function _G.URendererOpFuncSwallow() end
+
+local ENABLE_LOG = false
+
+local function log(...)
+  if not ENABLE_LOG then return end
+
+  local f = assert(io.open(vim.fs.joinpath(vim.fn.stdpath 'log', 'u.renderer.log'), 'a+'))
+  f:write(os.date() .. '\t' .. vim.inspect { ... } .. '\n')
+  f:close()
+end
+
 local M = {}
 local H = {}
 
---- @alias u.renderer.Tag { kind: 'tag'; name: string, attributes: table<string, unknown>, children: u.renderer.Tree }
+--- @alias u.renderer.TagEventHandler fun(tag: u.renderer.Tag, mode: string, lhs: string): string
+
+--- @alias u.renderer.TagAttributes { [string]?: unknown; imap?: table<string, u.renderer.TagEventHandler>; nmap?: table<string, u.renderer.TagEventHandler>; vmap?: table<string, u.renderer.TagEventHandler>; xmap?: table<string, u.renderer.TagEventHandler>; omap?: table<string, u.renderer.TagEventHandler>, on_change?: fun(text: string): unknown }
+
+--- @class u.renderer.Tag
+--- @field kind 'tag'
+--- @field name string
+--- @field attributes u.renderer.TagAttributes
+--- @field children u.renderer.Tree
+
 --- @alias u.renderer.Node nil | boolean | string | u.renderer.Tag
 --- @alias u.renderer.Tree u.renderer.Node | u.renderer.Node[]
 
 -- luacheck: ignore
---- @type table<string, fun(attributes: table<string, any>, children: u.renderer.Tree): u.renderer.Tag> & fun(name: string, attributes: table<string, any>, children: u.renderer.Tree): u.renderer.Tag>
+--- @type table<string, fun(attributes: u.renderer.TagAttributes, children: u.renderer.Tree): u.renderer.Tag> & fun(name: string, attributes: u.renderer.TagAttributes, children: u.renderer.Tree): u.renderer.Tag>
 M.h = setmetatable({}, {
   __call = function(_, name, attributes, children)
     return {
@@ -17,7 +38,6 @@ M.h = setmetatable({}, {
     }
   end,
   __index = function(_, name)
-    -- vim.print('dynamic hl ' .. name)
     return function(attributes, children)
       return M.h('text', vim.tbl_deep_extend('force', { hl = name }, attributes), children)
     end
@@ -25,14 +45,19 @@ M.h = setmetatable({}, {
 })
 
 -- Renderer {{{
---- @alias RendererExtmark { id?: number; start: [number, number]; stop: [number, number]; opts: any; tag: any }
+--- @class u.renderer.RendererExtmark
+--- @field id? number
+--- @field start [number, number]
+--- @field stop [number, number]
+--- @field opts vim.api.keyset.set_extmark
+--- @field tag u.renderer.Tag
 
---- @class u.Renderer
+--- @class u.renderer.Renderer
 --- @field bufnr number
 --- @field ns number
 --- @field changedtick number
---- @field old { lines: string[]; extmarks: RendererExtmark[] }
---- @field curr { lines: string[]; extmarks: RendererExtmark[] }
+--- @field old { lines: string[]; extmarks: u.renderer.RendererExtmark[] }
+--- @field curr { lines: string[]; extmarks: u.renderer.RendererExtmark[] }
 local Renderer = {}
 Renderer.__index = Renderer
 M.Renderer = Renderer
@@ -51,7 +76,7 @@ function Renderer.is_tag_arr(x)
 end
 --- @param bufnr number|nil
 function Renderer.new(bufnr) -- {{{
-  if bufnr == nil then bufnr = vim.api.nvim_get_current_buf() end
+  if bufnr == nil or bufnr == 0 then bufnr = vim.api.nvim_get_current_buf() end
 
   if vim.b[bufnr]._renderer_ns == nil then
     vim.b[bufnr]._renderer_ns = vim.api.nvim_create_namespace('my.renderer:' .. tostring(bufnr))
@@ -64,6 +89,12 @@ function Renderer.new(bufnr) -- {{{
     old = { lines = {}, extmarks = {} },
     curr = { lines = {}, extmarks = {} },
   }, Renderer)
+
+  vim.api.nvim_create_autocmd({ 'TextChanged', 'TextChangedI', 'TextChangedP' }, {
+    buffer = bufnr,
+    callback = function() self:_on_text_changed() end,
+  })
+
   return self
 end -- }}}
 
@@ -128,7 +159,7 @@ function Renderer.markup_to_lines(opts) -- {{{
 end -- }}}
 
 --- @param opts {
----   tree: string;
+---   tree: u.renderer.Tree;
 ---   format_tag?: fun(tag: u.renderer.Tag): string;
 --- }
 function Renderer.markup_to_string(opts) return table.concat(Renderer.markup_to_lines(opts), '\n') end
@@ -136,7 +167,7 @@ function Renderer.markup_to_string(opts) return table.concat(Renderer.markup_to_
 --- @param bufnr number
 --- @param old_lines string[] | nil
 --- @param new_lines string[]
-function Renderer.patch_lines(bufnr, old_lines, new_lines)
+function Renderer.patch_lines(bufnr, old_lines, new_lines) -- {{{
   --
   -- Helpers:
   --
@@ -189,7 +220,7 @@ function Renderer.patch_lines(bufnr, old_lines, new_lines)
       -- No change
     end
   end
-end
+end -- }}}
 
 --- @param tree u.renderer.Tree
 function Renderer:render(tree) -- {{{
@@ -199,7 +230,7 @@ function Renderer:render(tree) -- {{{
     self.changedtick = changedtick
   end
 
-  --- @type RendererExtmark[]
+  --- @type u.renderer.RendererExtmark[]
   local extmarks = {}
 
   --- @type string[]
@@ -214,31 +245,40 @@ function Renderer:render(tree) -- {{{
           tag.attributes.extmark.hl_group = tag.attributes.extmark.hl_group or hl
         end
 
-        local extmark = tag.attributes.extmark
+        local extmark_opts = tag.attributes.extmark or {}
 
         -- Set any necessary keymaps:
         for _, mode in ipairs { 'i', 'n', 'v', 'x', 'o' } do
           for lhs, _ in pairs(tag.attributes[mode .. 'map'] or {}) do
             -- Force creating an extmark if there are key handlers. To accurately
             -- sense the bounds of the text, we need an extmark:
-            extmark = extmark or {}
-            vim.keymap.set(
-              'n',
-              lhs,
-              function() return self:_expr_map_callback('n', lhs) end,
-              { buffer = self.bufnr, expr = true, replace_keycodes = true }
-            )
+            vim.keymap.set(mode, lhs, function()
+              local result = self:_expr_map_callback(mode, lhs)
+              -- If the handler indicates that it wants to swallow the event,
+              -- we have to convert that intention into something compatible
+              -- with expr-mappings, which don't support '<Nop>' (they try to
+              -- execute the literal characters). We'll use the 'g@' operator
+              -- to do that, forwarding the event to an operatorfunc that does
+              -- nothing:
+              if result == '' then
+                if mode == 'i' then
+                  return ''
+                else
+                  vim.go.operatorfunc = 'v:lua.URendererOpFuncSwallow'
+                  return 'g@ '
+                end
+              end
+              return result
+            end, { buffer = self.bufnr, expr = true, replace_keycodes = true })
           end
         end
 
-        if extmark then
-          table.insert(extmarks, {
-            start = start0,
-            stop = stop0,
-            opts = extmark,
-            tag = tag,
-          })
-        end
+        table.insert(extmarks, {
+          start = start0,
+          stop = stop0,
+          opts = extmark_opts,
+          tag = tag,
+        })
       end
     end, -- }}}
   }
@@ -246,27 +286,9 @@ function Renderer:render(tree) -- {{{
   self.old = self.curr
   self.curr = { lines = lines, extmarks = extmarks }
   self:_reconcile()
+  vim.cmd.doautocmd { args = { 'User', 'Renderer:' .. tostring(self.bufnr) .. ':render' } }
 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() -- {{{
   --
@@ -277,10 +299,15 @@ function Renderer:_reconcile() -- {{{
 
   --
   -- Step 2: reconcile extmarks:
+  -- You may be tempted to try to keep track of which extmarks are needed, and
+  -- only delete those that are not needed. However, each time a tree is
+  -- rendered, brand new extmarks are created. For simplicity, it is better to
+  -- just delete all extmarks, and recreate them.
   --
 
   -- Clear current extmarks:
   vim.api.nvim_buf_clear_namespace(self.bufnr, self.ns, 0, -1)
+
   -- Set current extmarks:
   for _, extmark in ipairs(self.curr.extmarks) do
     extmark.id = vim.api.nvim_buf_set_extmark(
@@ -292,6 +319,13 @@ function Renderer:_reconcile() -- {{{
         id = extmark.id,
         end_row = extmark.stop[1],
         end_col = extmark.stop[2],
+        -- If we change the text starting from the beginning (where the extmark
+        -- is), we don't want the extmark to move to the right.
+        right_gravity = false,
+        -- If we change the text starting from the end (where the end extmark
+        -- is), we don't want the extmark to stay stationary: we want it to
+        -- move to the right.
+        end_right_gravity = true,
       }, extmark.opts)
     )
   end
@@ -306,7 +340,9 @@ function Renderer:_expr_map_callback(mode, lhs) -- {{{
   -- find the tag with the smallest intersection that contains the cursor:
   local pos0 = vim.api.nvim_win_get_cursor(0)
   pos0[1] = pos0[1] - 1 -- make it actually 0-based
-  local pos_infos = self:get_pos_infos(pos0)
+  log('_expr_map_callback: pos0:', pos0)
+  local pos_infos = self:get_tags_at(pos0)
+  log('_expr_map_callback: pos_infos:', pos_infos)
 
   if #pos_infos == 0 then return lhs end
 
@@ -316,9 +352,10 @@ function Renderer:_expr_map_callback(mode, lhs) -- {{{
     local tag = pos_info.tag
 
     -- is the tag listening?
+    --- @type u.renderer.TagEventHandler?
     local f = vim.tbl_get(tag.attributes, mode .. 'map', lhs)
     if type(f) == 'function' then
-      local result = f()
+      local result = f(tag, mode, lhs)
       if result == '' then
         -- bubble-up to the next tag, but set cancel to true, in case there are
         -- no more tags to bubble up to:
@@ -333,31 +370,197 @@ function Renderer:_expr_map_callback(mode, lhs) -- {{{
   return cancel and '' or lhs
 end -- }}}
 
+function Renderer:_on_text_changed() -- {{{
+  -- Reset changedtick, so that the reconciler knows to refresh its cached
+  -- buffer-content before computing the diff:
+  self.changedtick = 0
+
+  --- @type integer, integer
+  local l, c = unpack(vim.api.nvim_win_get_cursor(0))
+  l = l - 1 -- make it actually 0-based
+  local pos_infos = self:get_tags_at({ l, c }, 'i')
+  log('_on_text_changed', { cursor_0_0 = { l, c }, pos_infos = pos_infos })
+  for _, pos_info in ipairs(pos_infos) do
+    local extmark_inf = pos_info.extmark
+    local tag = pos_info.tag
+
+    local on_change = tag.attributes.on_change
+    if on_change and type(on_change) == 'function' then
+      local extmark =
+        vim.api.nvim_buf_get_extmark_by_id(self.bufnr, self.ns, extmark_inf.id, { details = true })
+
+      --- @type integer, integer, vim.api.keyset.extmark_details
+      local start_row0, start_col0, details = unpack(extmark)
+      local end_row0, end_col0 = details.end_row, details.end_col
+      log('_on_text_changed: fetched current extmark for pos_info', {
+        pos_info = pos_info,
+        curr_extmark = {
+          start_row0 = start_row0,
+          start_col0 = start_col0,
+          end_row0 = end_row0,
+          end_col0 = end_col0,
+          details = details,
+        },
+      })
+
+      if start_row0 == end_row0 and start_col0 == end_col0 then
+        on_change ''
+        return
+      end
+
+      local buf_max_line0 = math.max(1, vim.api.nvim_buf_line_count(self.bufnr) - 1)
+      if end_row0 > buf_max_line0 then
+        end_row0 = buf_max_line0
+        local last_line = vim.api.nvim_buf_get_lines(self.bufnr, end_row0, end_row0 + 1, false)[1]
+          or ''
+        end_col0 = last_line:len()
+      end
+      if end_col0 == 0 then
+        end_row0 = end_row0 - 1
+        local last_line = vim.api.nvim_buf_get_lines(self.bufnr, end_row0, end_row0 + 1, false)[1]
+          or ''
+        end_col0 = last_line:len()
+      end
+      log('_on_text_changed: after position correction', {
+        curr_extmark = {
+          start_row0 = start_row0,
+          start_col0 = start_col0,
+          end_row0 = end_row0,
+          end_col0 = end_col0,
+        },
+      })
+
+      if start_row0 == end_row0 and start_col0 == end_col0 then
+        on_change ''
+        return
+      end
+
+      local pos1 = { self.bufnr, start_row0 + 1, start_col0 + 1 }
+      local pos2 = { self.bufnr, end_row0 + 1, end_col0 }
+      local ok, lines = pcall(vim.fn.getregion, pos1, pos2, { type = 'v' })
+      if not ok then
+        log('_on_text_changed: getregion: invalid-pos ', {
+          { pos1, pos2 },
+        })
+        vim.api.nvim_echo({
+          { '(u.nvim:getregion:invalid-pos) ', 'ErrorMsg' },
+          {
+            '{ start, end } = ' .. vim.inspect({ pos1, pos2 }, { newline = ' ', indent = '' }),
+          },
+        }, true, {})
+        error(lines)
+      end
+      local text = table.concat(lines, '\n')
+      on_change(text)
+    end
+  end
+end -- }}}
+
+--- @private
+function Renderer:_debug() -- {{{
+  local prev_w = vim.api.nvim_get_current_win()
+  vim.cmd.vnew()
+  local info_bufnr = vim.api.nvim_get_current_buf()
+  vim.bo.bufhidden = 'delete'
+  vim.bo.buflisted = false
+  vim.bo.buftype = 'nowrite'
+
+  local ids = {}
+  local function cleanup()
+    for _, id in ipairs(ids) do
+      vim.api.nvim_del_autocmd(id)
+    end
+    vim.api.nvim_buf_delete(info_bufnr, { force = true })
+  end
+
+  local function autocmd_callback()
+    if vim.api.nvim_get_current_win() ~= prev_w then return end
+
+    local l, c = unpack(vim.api.nvim_win_get_cursor(0))
+    l = l - 1 -- make it actually 0-based
+
+    local info = {
+      cursor = {
+        pos = { l, c },
+        tags = self:get_tags_at { l, c },
+        extmarks = vim.api.nvim_buf_get_extmarks(
+          self.bufnr,
+          self.ns,
+          { l, c },
+          { l, c },
+          { details = true, overlap = true }
+        ),
+      },
+      computed = {
+        extmarks = self.curr.extmarks,
+      },
+    }
+    vim.api.nvim_buf_set_lines(info_bufnr, 0, -1, true, vim.split(vim.inspect(info), '\n'))
+  end
+
+  table.insert(
+    ids,
+    vim.api.nvim_create_autocmd({ 'CursorMoved', 'CursorMovedI' }, {
+      callback = autocmd_callback,
+    })
+  )
+  table.insert(
+    ids,
+    vim.api.nvim_create_autocmd({ 'User' }, {
+      pattern = 'Renderer:' .. tostring(self.bufnr) .. ':render',
+      callback = autocmd_callback,
+    })
+  )
+  table.insert(
+    ids,
+    vim.api.nvim_create_autocmd('WinClosed', {
+      pattern = tostring(vim.api.nvim_get_current_win()),
+      callback = cleanup,
+    })
+  )
+  table.insert(
+    ids,
+    vim.api.nvim_create_autocmd('WinClosed', {
+      pattern = tostring(prev_w),
+      callback = cleanup,
+    })
+  )
+
+  vim.api.nvim_set_current_win(prev_w)
+end -- }}}
+
 --- Returns pairs of extmarks and tags associate with said extmarks. The
 --- returned tags/extmarks are sorted smallest (innermost) to largest
 --- (outermost).
 ---
 --- @private (private for now)
 --- @param pos0 [number; number]
---- @return { extmark: RendererExtmark; tag: u.renderer.Tag; }[]
-function Renderer:get_pos_infos(pos0) -- {{{
+--- @param mode string?
+--- @return { extmark: u.renderer.RendererExtmark; tag: u.renderer.Tag; }[]
+function Renderer:get_tags_at(pos0, mode) -- {{{
   local cursor_line0, cursor_col0 = pos0[1], pos0[2]
+  if not mode then mode = vim.api.nvim_get_mode().mode end
+  mode = mode:sub(1, 1) -- we don't care about sub-modes
+
+  local raw_overlapping_extmarks = vim.api.nvim_buf_get_extmarks(
+    self.bufnr,
+    self.ns,
+    pos0,
+    pos0,
+    { details = true, overlap = true }
+  )
+  log(
+    'get_tags_at: context:',
+    { pos0 = pos0, mode = mode, raw_overlapping_extmarks = raw_overlapping_extmarks }
+  )
 
   -- The cursor (block) occupies **two** extmark spaces: one for it's left
   -- edge, and one for it's right. We need to do our own intersection test,
   -- because the NeoVim API is over-inclusive in what it returns:
-  --- @type RendererExtmark[]
-  local intersecting_extmarks = vim
-    .iter(
-      vim.api.nvim_buf_get_extmarks(
-        self.bufnr,
-        self.ns,
-        pos0,
-        pos0,
-        { details = true, overlap = true }
-      )
-    )
-    --- @return RendererExtmark
+  --- @type u.renderer.RendererExtmark[]
+  local mapped_extmarks = vim
+    .iter(raw_overlapping_extmarks)
+    --- @return u.renderer.RendererExtmark
     :map(function(ext)
       --- @type number, number, number, { end_row?: number; end_col?: number }|nil
       local id, line0, col0, details = unpack(ext)
@@ -368,13 +571,43 @@ function Renderer:get_pos_infos(pos0) -- {{{
       end
       return { id = id, start = start, stop = stop, opts = details }
     end)
-    --- @param ext RendererExtmark
+    :totable()
+
+  local intersecting_extmarks = vim
+    .iter(mapped_extmarks)
+    --- @param ext u.renderer.RendererExtmark
     :filter(function(ext)
       if ext.stop[1] ~= nil and ext.stop[2] ~= nil then
-        return cursor_line0 >= ext.start[1]
-          and cursor_col0 >= ext.start[2]
-          and cursor_line0 <= ext.stop[1]
-          and cursor_col0 < ext.stop[2]
+        -- If we've "ciw" and "collapsed" an extmark onto the cursor,
+        -- the cursor pos will equal the exmark's start AND end. In this
+        -- case, we want to include the extmark.
+        if
+          cursor_line0 == ext.start[1]
+          and cursor_col0 == ext.start[2]
+          and cursor_line0 == ext.stop[1]
+          and cursor_col0 == ext.stop[2]
+        then
+          return true
+        end
+
+        return
+          -- START: line check
+          cursor_line0 >= ext.start[1]
+            -- START: column check
+            and (cursor_line0 ~= ext.start[1] or cursor_col0 >= ext.start[2])
+            -- STOP: line check
+            and cursor_line0 <= ext.stop[1]
+            -- STOP: column check
+            and (
+              cursor_line0 ~= ext.stop[1]
+              or (
+                mode == 'i'
+                  -- In insert mode, the cursor is "thin", so <= to compensate:
+                  and cursor_col0 <= ext.stop[2]
+                -- In normal mode, the cursor is "wide", so < to compensate:
+                or cursor_col0 < ext.stop[2]
+              )
+            )
       else
         return true
       end
@@ -384,8 +617,8 @@ function Renderer:get_pos_infos(pos0) -- {{{
   -- Sort the tags into smallest (inner) to largest (outer):
   table.sort(
     intersecting_extmarks,
-    --- @param x1 RendererExtmark
-    --- @param x2 RendererExtmark
+    --- @param x1 u.renderer.RendererExtmark
+    --- @param x2 u.renderer.RendererExtmark
     function(x1, x2)
       if
         x1.start[1] == x2.start[1]
@@ -407,10 +640,10 @@ function Renderer:get_pos_infos(pos0) -- {{{
   -- created extmarks in self.curr.extmarks, which also has which tag each
   -- extmark is associated with. Cross-reference with that list to get a list
   -- of tags that we need to fire events for:
-  --- @type { extmark: RendererExtmark; tag: u.renderer.Tag }[]
+  --- @type { extmark: u.renderer.RendererExtmark; tag: u.renderer.Tag }[]
   local matching_tags = vim
     .iter(intersecting_extmarks)
-    --- @param ext RendererExtmark
+    --- @param ext u.renderer.RendererExtmark
     :map(function(ext)
       for _, extmark_cache in ipairs(self.curr.extmarks) do
         if extmark_cache.id == ext.id then return { extmark = ext, tag = extmark_cache.tag } end
@@ -420,10 +653,23 @@ function Renderer:get_pos_infos(pos0) -- {{{
 
   return matching_tags
 end -- }}}
+
+--- @private
+--- @param tag_or_id string | u.renderer.Tag
+--- @return { start: [number, number]; stop: [number, number] } | nil
+function Renderer:get_tag_bounds(tag_or_id) -- {{{
+  for _, x in ipairs(self.curr.extmarks) do
+    local pos = { start = x.start, stop = x.stop }
+    local does_tag_match = type(tag_or_id) == 'string' and x.tag.attributes.id == tag_or_id
+      or x.tag == tag_or_id
+    if does_tag_match then return pos end
+  end
+end -- }}}
+
 -- }}}
 
 -- TreeBuilder {{{
---- @class u.TreeBuilder
+--- @class u.renderer.TreeBuilder
 --- @field private nodes u.renderer.Node[]
 local TreeBuilder = {}
 TreeBuilder.__index = TreeBuilder
@@ -435,7 +681,7 @@ function TreeBuilder.new()
 end
 
 --- @param nodes u.renderer.Tree
---- @return u.TreeBuilder
+--- @return u.renderer.TreeBuilder
 function TreeBuilder:put(nodes)
   table.insert(self.nodes, nodes)
   return self
@@ -444,15 +690,15 @@ end
 --- @param name string
 --- @param attributes? table<string, any>
 --- @param children? u.renderer.Node | u.renderer.Node[]
---- @return u.TreeBuilder
+--- @return u.renderer.TreeBuilder
 function TreeBuilder:put_h(name, attributes, children)
   local tag = M.h(name, attributes, children)
   table.insert(self.nodes, tag)
   return self
 end
 
---- @param fn fun(TreeBuilder): any
---- @return u.TreeBuilder
+--- @param fn fun(tb: u.renderer.TreeBuilder): any
+--- @return u.renderer.TreeBuilder
 function TreeBuilder:nest(fn)
   local nested_writer = TreeBuilder.new()
   fn(nested_writer)
@@ -460,19 +706,40 @@ function TreeBuilder:nest(fn)
   return self
 end
 
+--- @generic T
+--- @param arr T[]
+--- @param f fun(tb: u.renderer.TreeBuilder, item: T, idx: number): any
+function TreeBuilder:ipairs(arr, f)
+  return self:nest(function(tb)
+    for idx, item in ipairs(arr) do
+      f(tb, item, idx)
+    end
+  end)
+end
+
+--- @param tab table
+--- @param f fun(tb: u.renderer.TreeBuilder, key: any, value: any): any
+function TreeBuilder:pairs(tab, f)
+  return self:nest(function(tb)
+    for k, v in pairs(tab) do
+      f(tb, k, v)
+    end
+  end)
+end
+
 --- @return u.renderer.Tree
 function TreeBuilder:tree() return self.nodes end
 -- }}}
 
 -- Levenshtein utility {{{
 -- luacheck: ignore
---- @alias LevenshteinChange<T> ({ kind: 'add'; item: T; index: number; } | { kind: 'delete'; item: T; index: number; } | { kind: 'change'; from: T; to: T; index: number; })
+--- @alias u.renderer.LevenshteinChange<T> ({ kind: 'add'; item: T; index: number; } | { kind: 'delete'; item: T; index: number; } | { kind: 'change'; from: T; to: T; index: number; })
 --- @private
 --- @generic T
 --- @param x `T`[]
 --- @param y T[]
 --- @param cost? { of_delete?: fun(x: T): number; of_add?: fun(x: T): number; of_change?: fun(x: T, y: T): number; }
---- @return LevenshteinChange<T>[] The changes, from last (greatest index) to first (smallest index).
+--- @return u.renderer.LevenshteinChange<T>[] The changes, from last (greatest index) to first (smallest index).
 function H.levenshtein(x, y, cost)
   -- At the moment, this whole `cost` plumbing is not used. Deletes have the
   -- same cost as Adds or Changes. I can imagine a future, however, where
@@ -523,7 +790,7 @@ function H.levenshtein(x, y, cost)
   -- Backtrack to find the changes
   local i = m
   local j = n
-  --- @type LevenshteinChange[]
+  --- @type u.renderer.LevenshteinChange[]
   local changes = {}
 
   while i > 0 or j > 0 do
@@ -540,7 +807,7 @@ function H.levenshtein(x, y, cost)
     if is_first_min(cost_of_change, cost_of_add, cost_of_delete) then
       -- potential change
       if x[i] ~= y[j] then
-        --- @type LevenshteinChange
+        --- @type u.renderer.LevenshteinChange
         local change = { kind = 'change', from = x[i], index = i, to = y[j] }
         table.insert(changes, change)
       end
@@ -548,13 +815,13 @@ function H.levenshtein(x, y, cost)
       j = j - 1
     elseif is_first_min(cost_of_add, cost_of_change, cost_of_delete) then
       -- addition
-      --- @type LevenshteinChange
+      --- @type u.renderer.LevenshteinChange
       local change = { kind = 'add', item = y[j], index = i + 1 }
       table.insert(changes, change)
       j = j - 1
     elseif is_first_min(cost_of_delete, cost_of_change, cost_of_add) then
       -- deletion
-      --- @type LevenshteinChange
+      --- @type u.renderer.LevenshteinChange
       local change = { kind = 'delete', item = x[i], index = i }
       table.insert(changes, change)
       i = i - 1

lua/u/tracker.lua

@@ -6,19 +6,19 @@ M.debug = false
 -- class Signal
 --------------------------------------------------------------------------------
 
---- @class u.Signal
+--- @class u.Signal<T>
 --- @field name? string
 --- @field private changing boolean
---- @field private value any
+--- @field private value T
 --- @field private subscribers table<function, boolean>
 --- @field private on_dispose_callbacks function[]
 local Signal = {}
 M.Signal = Signal
 Signal.__index = Signal
 
---- @param value any
+--- @param value `T`
 --- @param name? string
---- @return u.Signal
+--- @return u.Signal<T>
 function Signal:new(value, name)
   local obj = setmetatable({
     name = name,
@@ -30,7 +30,7 @@ function Signal:new(value, name)
   return obj
 end
 
---- @param value any
+--- @param value T
 function Signal:set(value)
   self.value = value
 
@@ -67,11 +67,12 @@ function Signal:set(value)
   end
 end
 
+--- @param value T
 function Signal:schedule_set(value)
   vim.schedule(function() self:set(value) end)
 end
 
---- @return any
+--- @return T
 function Signal:get()
   local ctx = M.ExecutionContext.current()
   if ctx then ctx:track(self) end
@@ -85,8 +86,8 @@ function Signal:update(fn) self:set(fn(self.value)) end
 function Signal:schedule_update(fn) self:schedule_set(fn(self.value)) end
 
 --- @generic U
---- @param fn fun(value: T): U
---- @return u.Signal --<U>
+--- @param fn fun(value: T): `U`
+--- @return u.Signal<U>
 function Signal:map(fn)
   local mapped_signal = M.create_memo(function()
     local value = self:get()
@@ -95,13 +96,13 @@ function Signal:map(fn)
   return mapped_signal
 end
 
---- @return u.Signal
+--- @return u.Signal<T>
 function Signal:clone()
   return self:map(function(x) return x end)
 end
 
 --- @param fn fun(value: T): boolean
---- @return u.Signal -- <T>
+--- @return u.Signal<T>
 function Signal:filter(fn)
   local filtered_signal = M.create_signal(nil, self.name and self.name .. ':filtered' or nil)
   local unsubscribe_from_self = self:subscribe(function(value)
@@ -112,10 +113,10 @@ function Signal:filter(fn)
 end
 
 --- @param ms number
---- @return u.Signal -- <T>
+--- @return u.Signal<T>
 function Signal:debounce(ms)
   local function set_timeout(timeout, callback)
-    local timer = (vim.uv or vim.loop).new_timer()
+    local timer = assert((vim.uv or vim.loop).new_timer(), 'could not create new timer')
     timer:start(timeout, 0, function()
       timer:stop()
       timer:close()
@@ -127,7 +128,7 @@ function Signal:debounce(ms)
   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; }
+  --- @type { queued: { value: T, ts: number }[], timer?: uv.uv_timer_t }
   local state = { queued = {}, timer = nil }
   local function clear_timeout()
     if state.timer == nil then return end
@@ -202,6 +203,7 @@ end
 -- class ExecutionContext
 --------------------------------------------------------------------------------
 
+--- @type u.ExecutionContext|nil
 local CURRENT_CONTEXT = nil
 
 --- @class u.ExecutionContext
@@ -262,16 +264,18 @@ end
 -- Helpers
 --------------------------------------------------------------------------------
 
---- @param value any
+--- @generic T
+--- @param value `T`
 --- @param name? string
---- @return u.Signal
+--- @return u.Signal<T>
 function M.create_signal(value, name) return Signal:new(value, name) end
 
---- @param fn function
+--- @generic T
+--- @param fn fun(): `T`
 --- @param name? string
 --- @return u.Signal
 function M.create_memo(fn, name)
-  --- @type u.Signal
+  --- @type u.Signal<T> | nil
   local result
   local unsubscribe = M.create_effect(function()
     local value = fn()
@@ -282,8 +286,8 @@ function M.create_memo(fn, name)
       result = M.create_signal(value, name and ('m.s:' .. name) or nil)
     end
   end, name)
-  result:on_dispose(unsubscribe)
-  return result
+  assert(result):on_dispose(unsubscribe)
+  return assert(result)
 end
 
 --- @param fn function

lua/u/utils.lua

@@ -4,15 +4,63 @@ local M = {}
 -- Types
 --
 
---- @alias QfItem { col: number, filename: string, kind: string, lnum: number, text: string }
---- @alias KeyMaps table<string, fun(): any | string> }
--- luacheck: ignore
---- @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 }
+--- @class u.utils.QfItem
+--- @field col number
+--- @field filename string
+--- @field kind string
+--- @field lnum number
+--- @field text string
 
+--- @class u.utils.RawCmdArgs
+--- @field args string
+--- @field bang boolean
+--- @field count number
+--- @field fargs string[]
+--- @field line1 number
+--- @field line2 number
+--- @field mods string
+--- @field name string
+--- @field range 0|1|2
+--- @field reg string
+--- @field smods any
+
+--- @class u.utils.CmdArgs: u.utils.RawCmdArgs
+--- @field info u.Range|nil
+
+--- @class u.utils.UcmdArgs
+--- @field nargs? 0|1|'*'|'?'|'+'
+--- @field range? boolean|'%'|number
+--- @field count? boolean|number
+--- @field addr? string
+--- @field completion? string
+--- @field force? boolean
+--- @field preview? fun(opts: u.utils.UcmdArgs, ns: integer, buf: integer):0|1|2
+
+--
+-- Functions
+--
+
+--- Debug utility that prints a value and returns it unchanged.
+--- Useful for debugging in the middle of expressions or function chains.
+---
 --- @generic T
---- @param x `T`
---- @param message? string
---- @return T
+--- @param x `T` The value to debug print
+--- @param message? string Optional message to print alongside the value
+--- @return T The original value, unchanged
+---
+--- @usage
+--- ```lua
+--- -- Debug a value in the middle of a chain:
+--- local result = some_function()
+---   :map(utils.dbg)  -- prints the intermediate value
+---   :filter(predicate)
+---
+--- -- Debug with a custom message:
+--- local config = utils.dbg(get_config(), "Current config:")
+---
+--- -- Debug return values:
+--- return utils.dbg(calculate_result(), "Final result")
+--- ```
 function M.dbg(x, message)
   local t = {}
   if message ~= nil then table.insert(t, message) end
@@ -21,22 +69,37 @@ function M.dbg(x, message)
   return x
 end
 
---- A utility for creating user commands that also pre-computes useful information
---- and attaches it to the arguments.
+--- Creates a user command with enhanced argument processing.
+--- Automatically computes range information and attaches it as `args.info`.
 ---
+--- @param name string The command name (without the leading colon)
+--- @param cmd string | fun(args: u.utils.CmdArgs): any Command implementation
+--- @param opts? u.utils.UcmdArgs Command options (nargs, range, etc.)
+---
+--- @usage
 --- ```lua
---- -- Example:
---- ucmd('MyCmd', function(args)
----   -- print the visually selected text:
+--- -- Create a command that works with visual selections:
+--- utils.ucmd('MyCmd', function(args)
+---   -- Print the visually selected text:
 ---   vim.print(args.info:text())
----   -- or get the vtext as an array of lines:
+---   -- Or get the selection as an array of lines:
 ---   vim.print(args.info:lines())
 --- end, { nargs = '*', range = true })
+---
+--- -- Create a command that processes the current line:
+--- utils.ucmd('ProcessLine', function(args)
+---   local line_text = args.info:text()
+---   -- Process the line...
+--- end, { range = '%' })
+---
+--- -- Create a command with arguments:
+--- utils.ucmd('SearchReplace', function(args)
+---   local pattern, replacement = args.fargs[1], args.fargs[2]
+---   local text = args.info:text()
+---   -- Perform search and replace...
+--- end, { nargs = 2, range = true })
 --- ```
---- @param name string
---- @param cmd string | fun(args: CmdArgs): any
 -- luacheck: ignore
---- @param opts? { nargs?: 0|1|'*'|'?'|'+'; range?: boolean|'%'|number; count?: boolean|number, addr?: string; completion?: string }
 function M.ucmd(name, cmd, opts)
   local Range = require 'u.range'
 
@@ -48,9 +111,81 @@ function M.ucmd(name, cmd, opts)
       return cmd(args)
     end
   end
-  vim.api.nvim_create_user_command(name, cmd2, opts or {})
+  vim.api.nvim_create_user_command(name, cmd2, opts or {} --[[@as any]])
 end
 
+--- Creates command arguments for delegating from one command to another.
+--- Preserves all relevant context (range, modifiers, bang, etc.) when
+--- implementing a derived command in terms of a base command.
+---
+--- @param current_args vim.api.keyset.create_user_command.command_args|u.utils.RawCmdArgs The arguments from the current command
+--- @return vim.api.keyset.cmd Arguments suitable for vim.cmd() calls
+---
+--- @usage
+--- ```lua
+--- -- Implement :MyEdit in terms of :edit, preserving all context:
+--- utils.ucmd('MyEdit', function(args)
+---   local delegated_args = utils.create_delegated_cmd_args(args)
+---   -- Add custom logic here...
+---   vim.cmd.edit(delegated_args)
+--- end, { nargs = '*', range = true, bang = true })
+---
+--- -- Implement :MySubstitute that delegates to :substitute:
+--- utils.ucmd('MySubstitute', function(args)
+---   -- Pre-process arguments
+---   local pattern = preprocess_pattern(args.fargs[1])
+---
+---   local delegated_args = utils.create_delegated_cmd_args(args)
+---   delegated_args.args = { pattern, args.fargs[2] }
+---
+---   vim.cmd.substitute(delegated_args)
+--- end, { nargs = 2, range = true, bang = true })
+--- ```
+function M.create_delegated_cmd_args(current_args)
+  --- @type vim.api.keyset.cmd
+  local args = {
+    range = current_args.range == 1 and { current_args.line1 }
+      or current_args.range == 2 and { current_args.line1, current_args.line2 }
+      or nil,
+    count = (current_args.count ~= -1 and current_args.range == 0) and current_args.count or nil,
+    reg = current_args.reg ~= '' and current_args.reg or nil,
+    bang = current_args.bang or nil,
+    args = #current_args.fargs > 0 and current_args.fargs or nil,
+    mods = current_args.smods,
+  }
+  return args
+end
+
+--- Gets the current editor dimensions.
+--- Useful for positioning floating windows or calculating layout sizes.
+---
+--- @return { width: number, height: number } The editor dimensions in columns and lines
+---
+--- @usage
+--- ```lua
+--- -- Center a floating window:
+--- local dims = utils.get_editor_dimensions()
+--- local win_width = 80
+--- local win_height = 20
+--- local col = math.floor((dims.width - win_width) / 2)
+--- local row = math.floor((dims.height - win_height) / 2)
+---
+--- vim.api.nvim_open_win(bufnr, true, {
+---   relative = 'editor',
+---   width = win_width,
+---   height = win_height,
+---   col = col,
+---   row = row,
+--- })
+---
+--- -- Check if editor is wide enough for side-by-side layout:
+--- local dims = utils.get_editor_dimensions()
+--- if dims.width >= 160 then
+---   -- Use side-by-side layout
+--- else
+---   -- Use stacked layout
+--- end
+--- ```
 function M.get_editor_dimensions() return { width = vim.go.columns, height = vim.go.lines } end
 
 return M