Look for major modes and extensions for grammar loading

See emacs-tree-sitter/tree-sitter-langs#116

Author: mattias

lisp/tree-sitter.el

@@ -150,7 +150,9 @@ OLD-LEN is the char length of the old text."
   "Enable `tree-sitter' in the current buffer."
   (unless tree-sitter-language
     ;; Determine the language symbol based on `major-mode' .
-    (let ((lang-symbol (alist-get major-mode tree-sitter-major-mode-language-alist)))
+    (let*
+        ((file-extension (if (eq major-mode 'tuareg-mode) (file-name-extension buffer-file-name) nil))
+         (lang-symbol (alist-get (list major-mode file-extension) tree-sitter-major-mode-language-alist nil nil 'equal)))
       (unless lang-symbol
         (error "No language registered for major mode `%s'" major-mode))
       (setq tree-sitter-language (tree-sitter-require lang-symbol))))