feat(editor): :source can run Lua codeblock / ts injection #36799

Problem:
Can't use `:source` to run a Lua codeblock (treesitter injection) in
a help (vimdoc) file.

Solution:
Use treesitter to parse the range and treat it as Lua if detected as
such.

runtime/doc/news.txt

@@ -215,6 +215,8 @@ EDITOR
   "(v)iew" then run `:trust`.
 • |gx| in help buffers opens the online documentation for the tag under the
   cursor.
+• |:source| with a range in non-Lua files (e.g., vimdoc) now detects Lua
+  codeblocks via treesitter and executes them as Lua instead of Vimscript.
 • |:Undotree| for visually navigating the |undo-tree|
 • |:wall| permits a |++p| option for creating parent directories when writing
   changed buffers.

runtime/lua/vim/_core/util.lua

@@ -63,4 +63,22 @@ function M.read_chunk(file, size)
   return tostring(chunk)
 end
 
+--- Check if a range in a buffer is inside a Lua codeblock via treesitter injection.
+--- Used by :source to detect Lua code in non-Lua files (e.g., vimdoc).
+--- @param bufnr integer Buffer number
+--- @param line1 integer Start line (1-indexed)
+--- @param line2 integer End line (1-indexed)
+--- @return boolean True if the range is in a Lua injection
+function M.source_is_lua(bufnr, line1, line2)
+  local ok, parser = pcall(vim.treesitter.get_parser, bufnr)
+  if not ok or not parser then
+    return false
+  end
+  -- Parse from buffer start through one line past line2 to include injection closing markers
+  local range = { line1 - 1, 0, line2 - 1, -1 }
+  parser:parse({ 0, 0, line2, -1 })
+  local lang_tree = parser:language_for_range(range)
+  return lang_tree:lang() == 'lua'
+end
+
 return M

src/nvim/runtime.c

@@ -2275,8 +2275,26 @@ static int do_source_ext(char *const fname, const bool check_other, const int is
 
   cookie.conv.vc_type = CONV_NONE;              // no conversion
 
+  // Check if treesitter detects this range as Lua (for injections like vimdoc codeblocks)
+  bool ts_lua = false;
+  if (fname == NULL && eap != NULL && !ex_lua
+      && !strequal(curbuf->b_p_ft, "lua")
+      && !(curbuf->b_fname && path_with_extension(curbuf->b_fname, "lua"))) {
+    MAXSIZE_TEMP_ARRAY(args, 3);
+    ADD_C(args, INTEGER_OBJ(curbuf->handle));
+    ADD_C(args, INTEGER_OBJ(eap->line1));
+    ADD_C(args, INTEGER_OBJ(eap->line2));
+    Error err = ERROR_INIT;
+    Object result = NLUA_EXEC_STATIC("return require('vim._core.util').source_is_lua(...)",
+                                     args, kRetNilBool, NULL, &err);
+    if (!ERROR_SET(&err) && LUARET_TRUTHY(result)) {
+      ts_lua = true;
+    }
+    api_clear_error(&err);
+  }
+
   if (fname == NULL
-      && (ex_lua || strequal(curbuf->b_p_ft, "lua")
+      && (ex_lua || ts_lua || strequal(curbuf->b_p_ft, "lua")
           || (curbuf->b_fname && path_with_extension(curbuf->b_fname, "lua")))) {
     // Source lines from the current buffer as lua
     nlua_exec_ga(&cookie.buflines, fname_exp);

test/functional/ex_cmds/source_spec.lua

@@ -296,6 +296,35 @@ describe(':source', function()
     eq(nil, result:find('E484'))
     os.remove(test_file)
   end)
+
+  it('sources Lua/Vimscript codeblocks based on treesitter injection', function()
+    insert([[
+      *test.txt*  Test help file
+
+      Lua example: >lua
+        vim.g.test_lua = 42
+      <
+
+      Vim example: >vim
+        let g:test_vim = 99
+      <]])
+    command('setlocal filetype=help')
+
+    -- Source Lua codeblock (line 4 contains the Lua code)
+    command(':4source')
+    eq(42, eval('g:test_lua'))
+
+    -- Source Vimscript codeblock (line 8 contains the Vim code)
+    command(':8source')
+    eq(99, eval('g:test_vim'))
+
+    -- Test fallback without treesitter
+    command('enew')
+    insert([[let g:test_no_ts = 123]])
+    command('setlocal filetype=')
+    command('source')
+    eq(123, eval('g:test_no_ts'))
+  end)
 end)
 
 it('$HOME is not shortened in filepath in v:stacktrace from sourced file', function()