perf(ui): wrap treesitter.foldexpr and cache get_parser during a event loop tick. Fixes #1846

lua/lazyvim/config/options.lua

@@ -82,7 +82,7 @@ end
 -- HACK: causes freezes on <= 0.9, so only enable on >= 0.10 for now
 if vim.fn.has("nvim-0.10") == 1 then
   vim.opt.foldmethod = "expr"
-  vim.opt.foldexpr = "v:lua.vim.treesitter.foldexpr()"
+  vim.opt.foldexpr = "v:lua.require'lazyvim.util'.ui.foldexpr()"
 else
   vim.opt.foldmethod = "indent"
 end

lua/lazyvim/util/ui.lua

@@ -141,4 +141,42 @@ function M.fg(name)
   return fg and { fg = string.format("#%06x", fg) } or nil
 end
 
+M.skip_foldexpr = {} ---@type table<number,boolean>
+local skip_check = assert(vim.loop.new_check())
+
+function M.foldexpr()
+  local buf = vim.api.nvim_get_current_buf()
+
+  -- still in the same tick and no parser
+  if M.skip_foldexpr[buf] then
+    return "0"
+  end
+
+  -- don't use treesitter folds for non-file buffers
+  if vim.bo[buf].buftype ~= "" then
+    return "0"
+  end
+
+  -- as long as we don't have a filetype, don't bother
+  -- checking if treesitter is available (it won't)
+  if vim.bo[buf].filetype == "" then
+    return "0"
+  end
+
+  local ok = pcall(vim.treesitter.get_parser, buf)
+
+  if ok then
+    return vim.treesitter.foldexpr()
+  end
+
+  -- no parser available, so mark it as skip
+  -- in the next tick, all skip marks will be reset
+  M.skip_foldexpr[buf] = true
+  skip_check:start(function()
+    M.skip_foldexpr = {}
+    skip_check:stop()
+  end)
+  return "0"
+end
+
 return M