fix(treesitter): normalize language aliases

Hyphenated language names are silently dropped when used as injections
(see #38132).

This combines the normalization of language aliases into `resolve_lang`,
and also adds the normalization of hyphens to underscores, which allows
for handling of injected language tags with hyphens in their names.

Fixes #38132.

runtime/lua/vim/treesitter/languagetree.lua

@@ -1022,6 +1022,8 @@ end)
 ---@param alias string language or filetype name
 ---@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('-', '_')
   -- validate that `alias` is a legal language
   if not (alias and alias:match('[%w_]+') == alias) then
     return
@@ -1058,7 +1060,7 @@ function LanguageTree:_get_injection(match, metadata)
       -- Lang should override any other language tag
       if name == 'injection.language' then
         local text = vim.treesitter.get_node_text(node, self._source, { metadata = metadata[id] })
-        lang = resolve_lang(text:lower()) -- language names are always lower case
+        lang = resolve_lang(text)
       elseif name == 'injection.filename' then
         local text = vim.treesitter.get_node_text(node, self._source, { metadata = metadata[id] })
         local ft = vim.filetype.match({ filename = text })

test/functional/treesitter/parser_spec.lua

@@ -938,6 +938,23 @@ int x = INT_MAX;
         eq({ 'gsub!', 'offset!', 'set!', 'trim!' }, res_list)
       end)
     end)
+
+    it('normalizes hyphens to underscores in injection.language', function()
+      exec_lua(function()
+        -- register "c" as the parser for "shell_session" (normalized form of "shell-session")
+        vim.treesitter.language.register('c', 'shell_session')
+        _G.parser = vim.treesitter.get_parser(0, 'c', {
+          injections = {
+            c = '(preproc_def (preproc_arg) @injection.content (#set! injection.language "shell-session"))',
+          },
+        })
+        _G.parser:parse(true)
+      end)
+
+      -- injection.language "shell-session" should normalize to "shell_session",
+      -- which resolves via the registered alias to the "c" parser
+      eq('table', exec_lua('return type(parser:children().c)'))
+    end)
   end)
 
   it('clips nested injections #34098', function()