fix(ci): fix treesitter parser installation in headless CI

TSUpdateSync does not exist in this nvim-treesitter version. Replace with
a Lua script (test/install_parsers.lua) that calls TSInstall! per parser
and polls parser .so files via vim.wait() until compiled or timeout.
Also fix validate_treesitter.lua to handle nil return from get_parser
(parser not installed) in addition to pcall errors.

Author: Venkata Subramani Renduchintala

.github/workflows/validate.yml

@@ -79,7 +79,9 @@ jobs:
             -v "${{ github.workspace }}:/home/dev/.config/nvim:ro" \
             -v "$HOME/.local/share/nvim-ci:/home/dev/.local/share/nvim" \
             nvim-config:ci \
-            nvim --headless -c "TSUpdateSync" -c "qall"
+            nvim --headless \
+              -c "luafile /home/dev/.config/nvim/test/install_parsers.lua" \
+              -c "qall"
         timeout-minutes: 10
 
       - name: Test Go and Terraform treesitter parsers

test/install_parsers.lua

@@ -0,0 +1,38 @@
+-- Headless treesitter parser installer for CI.
+-- Uses TSInstall! + vim.wait() polling parser .so files on disk.
+-- Exit code 1 on timeout so the CI step fails visibly.
+local langs = { 'go', 'terraform', 'hcl' }
+local parser_dir = vim.fn.stdpath('data') .. '/lazy/nvim-treesitter/parser/'
+
+local function installed(lang)
+  return vim.fn.filereadable(parser_dir .. lang .. '.so') == 1
+end
+
+for _, lang in ipairs(langs) do
+  if installed(lang) then
+    print('SKIP [' .. lang .. ']: already compiled')
+  else
+    print('INST [' .. lang .. ']: installing...')
+    pcall(vim.cmd, 'TSInstall! ' .. lang)
+  end
+end
+
+local ok = vim.wait(300000, function()
+  for _, lang in ipairs(langs) do
+    if not installed(lang) then return false end
+  end
+  return true
+end, 2000)
+
+if not ok then
+  for _, lang in ipairs(langs) do
+    if not installed(lang) then
+      io.stderr:write('FAIL [' .. lang .. ']: compile timed out\n')
+    end
+  end
+  vim.cmd('cquit 1')
+else
+  for _, lang in ipairs(langs) do
+    print('OK   [' .. lang .. ']: parser ready')
+  end
+end

test/validate_treesitter.lua

@@ -13,7 +13,7 @@ local function test_parser(lang, filepath)
   vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)
 
   local ok, result = pcall(vim.treesitter.get_parser, buf, lang)
-  if not ok then
+  if not ok or result == nil then
     table.insert(errors, string.format('[%s] parser load failed: %s', lang, tostring(result)))
     vim.api.nvim_buf_delete(buf, { force = true })
     return