perf(foldtext): cache fold highlights by state (#1077)

* perf(fold): cache fold highlights by state

Navigation over folded sections in larger org files felt sluggish due to
repeated treesitter queries on every cursor move.

Check fold state before using cached highlights - cache hit when
unchanged, full recompute only when folds toggle.

* test(fold): implement several fold tests

Author: seflue

lua/orgmode/colors/highlighter/foldtext.lua

@@ -1,5 +1,4 @@
 local config = require('orgmode.config')
-local utils = require('orgmode.utils')
 
 ---@alias OrgFoldtextLineValue false | { col: number, hl_group: string }
 
@@ -32,26 +31,56 @@ function OrgFoldtext:_highlight(bufnr, line, value)
     hl_mode = 'combine',
     virt_text = { { config.org_ellipsis, value.hl_group } },
     virt_text_pos = 'overlay',
-    ephemeral = true,
+    ephemeral = self.highlighter._ephemeral,
   })
 end
 
-function OrgFoldtext:on_line(bufnr, line)
-  local is_current_buf = bufnr == vim.api.nvim_get_current_buf()
+function OrgFoldtext:on_line(bufnr, line, winid)
+  if not config.ui.folds.colored then
+    return
+  end
+
+  -- Use provided winid for correct window context (foldclosed and col are window-local)
+  local lnum = line + 1
+  local is_fold_open, line_end
 
-  if not is_current_buf then
-    return self:_highlight(bufnr, line, self.cache[bufnr] and self.cache[bufnr][line])
+  if winid and winid ~= vim.api.nvim_get_current_win() then
+    -- foldclosed() and col() are window-local, so execute in the correct window
+    vim.api.nvim_win_call(winid, function()
+      is_fold_open = vim.fn.foldclosed(lnum) == -1
+      line_end = vim.fn.col({ lnum, '$' }) or 0
+    end)
+  else
+    is_fold_open = vim.fn.foldclosed(lnum) == -1
+    line_end = vim.fn.col({ lnum, '$' }) or 0
   end
 
+  local cache_entry = self.cache[bufnr] and self.cache[bufnr][line]
+
+  -- Cache: nil = unprocessed, false = open, {col, hl_group} = closed
+  if cache_entry ~= nil then
+    local was_open = cache_entry == false
+    if was_open == is_fold_open then
+      if cache_entry and cache_entry.col then
+        if cache_entry.col == line_end - 1 then
+          return self:_highlight(bufnr, line, cache_entry)
+        end
+        -- Line length changed, need full update
+      else
+        return self:_highlight(bufnr, line, cache_entry)
+      end
+    end
+  end
+
+  -- Full update: query treesitter
   self.cache[bufnr] = self.cache[bufnr] or {}
-  local is_fold_closed = vim.fn.foldclosed(line + 1) > -1
 
-  if not is_fold_closed then
+  if is_fold_open then
     self.cache[bufnr][line] = false
-    return
+    return -- No ellipsis to highlight
   end
 
-  local col = vim.fn.col({ line + 1, '$' }) or 0
+  local col = line_end
 
   local hl_group = 'Comment'
   local captures_at_pos = vim.treesitter.get_captures_at_pos(bufnr, line, col - 2)

lua/orgmode/colors/highlighter/init.lua

@@ -81,25 +81,25 @@ function OrgHighlighter:_on_win(_, win, bufnr, topline, botline)
     self:_parse_tree(bufnr, win, { topline, botline + 1 })
     if self.parsing[win] then
       for line = topline, botline do
-        self:_on_line_impl(bufnr, line, true)
+        self:_on_line_impl(bufnr, line, true, win)
       end
       return false
     end
   end
 end
 
-function OrgHighlighter:_on_line(_, _, bufnr, line)
-  self:_on_line_impl(bufnr, line)
+function OrgHighlighter:_on_line(_, winid, bufnr, line)
+  self:_on_line_impl(bufnr, line, false, winid)
 end
 
 ---@param bufnr number
 ---@param line number
 ---@param use_cache? boolean
-function OrgHighlighter:_on_line_impl(bufnr, line, use_cache)
+function OrgHighlighter:_on_line_impl(bufnr, line, use_cache, winid)
   if self.buffers[bufnr].tree then
     self.markup:on_line(bufnr, line, self.buffers[bufnr].tree, use_cache)
     self.stars:on_line(bufnr, line)
-    self.foldtext:on_line(bufnr, line)
+    self.foldtext:on_line(bufnr, line, winid)
   end
 end