fix(treesitter): get_node_text() inconsistent trailing newline #39409

Problem:
`get_node_text()` returned inconsistent results between buffer and
string sources when a node's range ends at `end_col == 0` (i.e. the node
ends with a newline). The buffer path dropped the trailing newline; the
string path included it correctly.

Solution:
Append `'\n'` in `buf_range_get_text()` when `end_col == 0` and
`start_row ~= end_row`. The `start_row ~= end_row` guard excludes
zero-width nodes at column 0, which should return `""`.

Remove the workaround in the `#trim!` directive that manually
compensated for the missing newline.

Strip whitespace in `resolve_lang()` so injection language nodes ending
at `end_col == 0` (e.g. `">lua\n"`) still resolve correctly.

(cherry picked from commit 7ed5609439)

runtime/lua/vim/treesitter.lua

@@ -201,6 +201,8 @@ end
 ---@returns string
 local function buf_range_get_text(buf, range)
   local start_row, start_col, end_row, end_col = M._range.unpack4(range)
+  local append_newline = end_col == 0 and start_row ~= end_row
+
   if end_col == 0 then
     if start_row == end_row then
       start_col = -1
@@ -209,7 +211,12 @@ local function buf_range_get_text(buf, range)
     end_col = -1
     end_row = end_row - 1
   end
+
   local lines = api.nvim_buf_get_text(buf, start_row, start_col, end_row, end_col, {})
+  if append_newline then
+    table.insert(lines, '')
+  end
+
   return table.concat(lines, '\n')
 end
 

runtime/lua/vim/treesitter/languagetree.lua

@@ -1023,7 +1023,9 @@ end)
 ---@return string? # resolved parser name
 local function resolve_lang(alias)
   -- normalize: treesitter language names are always lower case and use underscores
-  alias = alias and alias:lower():gsub('%-', '_')
+  -- Language name (from `get_text_node`) may end with "\n".
+  alias = alias and alias:gsub('%s+', ''):lower():gsub('%-', '_')
+
   -- validate that `alias` is a legal language
   if not (alias and alias:match('[%w_]+') == alias) then
     return

runtime/lua/vim/treesitter/query.lua

@@ -706,10 +706,6 @@ local directive_handlers = {
     local start_row, start_col, end_row, end_col = node:range()
 
     local node_text = vim.split(vim.treesitter.get_node_text(node, bufnr), '\n')
-    if end_col == 0 then
-      -- get_node_text() will ignore the last line if the node ends at column 0
-      node_text[#node_text + 1] = ''
-    end
 
     local end_idx = #node_text
     local start_idx = 1

test/functional/treesitter/node_spec.lua

@@ -227,6 +227,32 @@ describe('treesitter node API', function()
     eq({ 0, 0, 2, 3 }, lua_eval('range'))
   end)
 
+  it(
+    'get_node_text() includes trailing newline for buffer source when node end_col == 0',
+    function()
+      insert('local x = 1')
+
+      exec_lua(function()
+        _G.node = vim.treesitter.get_parser(0, 'lua'):parse()[1]:root()
+      end)
+
+      eq('local x = 1\n', lua_eval('vim.treesitter.get_node_text(_G.node, 0)'))
+    end
+  )
+
+  it(
+    'get_node_text() includes trailing newline for string source when node end_col == 0',
+    function()
+      exec_lua(function()
+        local source = 'local x = 1\n'
+        _G.source = source
+        _G.node = vim.treesitter.get_string_parser(source, 'lua'):parse()[1]:root()
+      end)
+
+      eq('local x = 1\n', lua_eval('vim.treesitter.get_node_text(_G.node, _G.source)'))
+    end
+  )
+
   it('tree:root() is idempotent', function()
     insert([[
       function x()

test/functional/treesitter/parser_spec.lua

@@ -441,7 +441,7 @@ describe('treesitter parser API', function()
       local tree = parser:parse()[1]
       return vim.treesitter.get_node_text(tree:root(), 0)
     end)
-    eq(t.dedent(test_text), res)
+    eq(t.dedent(test_text) .. '\n', res)
 
     local res2 = exec_lua(function()
       local parser = vim.treesitter.get_parser(0, 'c')