avoid treesitter races in netrw previews

lua/netrw-preview.lua

@@ -2,10 +2,12 @@ local M = {}
 
 local uv = vim.uv
 local states = {}
+local preview_buffers = {}
 local preview_group = vim.api.nvim_create_augroup('netrw_live_preview', { clear = true })
 
 local DEBOUNCE_MS = 90
 local MAX_ENTRIES = 200
+local PREVIEW_BUFFER_CLEANUP_MS = 2000
 
 local function is_valid_buffer(buf)
   return type(buf) == 'number' and buf > 0 and vim.api.nvim_buf_is_valid(buf)
@@ -53,6 +55,46 @@ local function close_timer(state, key)
   state[key] = nil
 end
 
+local function restore_preview_buffer(buf, for_editing)
+  local metadata = preview_buffers[buf]
+  if not metadata or not is_valid_buffer(buf) then
+    return
+  end
+
+  vim.b[buf].netrw_live_preview_buffer = nil
+  vim.bo[buf].bufhidden = metadata.bufhidden
+  vim.bo[buf].buflisted = for_editing or metadata.buflisted
+  vim.bo[buf].syntax = metadata.syntax
+  if metadata.treesitter_active then
+    pcall(vim.treesitter.start, buf)
+  end
+  preview_buffers[buf] = nil
+end
+
+local function schedule_preview_buffer_cleanup(state)
+  if not state or state.preview_cleanup_scheduled then
+    return
+  end
+
+  state.preview_cleanup_scheduled = true
+  vim.defer_fn(function()
+    state.preview_cleanup_scheduled = false
+
+    for buf, metadata in pairs(preview_buffers) do
+      local is_preview = is_valid_buffer(buf) and vim.b[buf].netrw_live_preview_buffer == true
+      local is_visible = is_valid_buffer(buf) and #vim.fn.win_findbuf(buf) > 0
+      if not is_preview or not is_visible then
+        if is_preview and metadata.loaded then
+          restore_preview_buffer(buf, false)
+        end
+        if not is_preview then
+          preview_buffers[buf] = nil
+        end
+      end
+    end
+  end, PREVIEW_BUFFER_CLEANUP_MS)
+end
+
 local function close_preview(state)
   if not state then
     return
@@ -61,6 +103,7 @@ local function close_preview(state)
   local preview = find_preview_window(state.tab)
   if preview then
     pcall(vim.api.nvim_win_close, preview, false)
+    schedule_preview_buffer_cleanup(state)
   end
 end
 
@@ -395,7 +438,48 @@ end
 
 local function show_native_preview(state, entry)
   state.native_preview_active = true
+
+  local existing_buf = entry.path and vim.fn.bufnr(entry.path) or -1
+  local existing = is_valid_buffer(existing_buf) and {
+    buf = existing_buf,
+    loaded = vim.api.nvim_buf_is_loaded(existing_buf),
+    buflisted = vim.bo[existing_buf].buflisted,
+    bufhidden = vim.bo[existing_buf].bufhidden,
+    syntax = vim.bo[existing_buf].syntax,
+    treesitter_active = vim.treesitter.highlighter.active[existing_buf] ~= nil,
+  } or nil
+
   local ok, shown = pcall(native_preview, entry)
+
+  local preview = find_preview_window(state.tab)
+  if preview then
+    local preview_buf = vim.api.nvim_win_get_buf(preview)
+    local preview_only = #vim.fn.win_findbuf(preview_buf) == 1
+    if vim.bo[preview_buf].buftype == '' and preview_only then
+      preview_buffers[preview_buf] = preview_buffers[preview_buf] or {
+        loaded = existing ~= nil and existing.buf == preview_buf and existing.loaded,
+        buflisted = existing ~= nil and existing.buf == preview_buf and existing.buflisted or false,
+        bufhidden = existing ~= nil and existing.buf == preview_buf and existing.bufhidden or '',
+        syntax = existing ~= nil and existing.buf == preview_buf and existing.syntax or '',
+        treesitter_active = existing ~= nil
+            and existing.buf == preview_buf
+            and existing.loaded
+            and existing.treesitter_active
+          or vim.treesitter.highlighter.active[preview_buf] ~= nil,
+      }
+
+      vim.bo[preview_buf].bufhidden = 'hide'
+      vim.bo[preview_buf].buflisted = preview_buffers[preview_buf].buflisted
+      vim.b[preview_buf].netrw_live_preview_buffer = true
+      pcall(vim.treesitter.stop, preview_buf)
+
+      local filetype = vim.bo[preview_buf].filetype
+      if filetype ~= '' then
+        vim.bo[preview_buf].syntax = filetype
+      end
+    end
+  end
+
   if is_valid_window(state.win) then
     pcall(vim.api.nvim_set_current_win, state.win)
   end
@@ -445,7 +529,12 @@ local function preview_selected(state, allow_create)
 end
 
 local function schedule_preview(state)
-  if not state or not find_preview_window(state.tab) then
+  if not state then
+    return
+  end
+
+  if not find_preview_window(state.tab) then
+    schedule_preview_buffer_cleanup(state)
     return
   end
 
@@ -459,6 +548,26 @@ local function schedule_preview(state)
   end))
 end
 
+vim.api.nvim_create_autocmd('BufEnter', {
+  group = preview_group,
+  desc = 'Restore normal editing behavior for a file previously used as a netrw preview',
+  callback = function(args)
+    local buf = args.buf
+    if not is_valid_buffer(buf) or vim.b[buf].netrw_live_preview_buffer ~= true then
+      return
+    end
+
+    local win = vim.api.nvim_get_current_win()
+    if is_valid_window(win) and vim.wo[win].previewwindow then
+      return
+    end
+
+    if preview_buffers[buf] then
+      restore_preview_buffer(buf, true)
+    end
+  end,
+})
+
 local function state_for(buf)
   local state = states[buf]
   if not state then