Improve selecting mode when editting code blocks

CHANGES.md

@@ -23,6 +23,7 @@
     - Don't hide backslashes in code blocks when using `markdown-hide-markup`
       and `markdown-fontify-code-blocks-natively` together [GH-766][]
     - Fix `markdown-fontify-whole-heading-line` regression [GH-848][]
+    - Fix using fundamental-mode issue when editting code block [GH-868][]
 
 *   Improvements:
     - Apply url-unescape against URL in an inline link [GH-805][]
@@ -45,6 +46,7 @@
   [gh-845]: https://github.com/jrblevin/markdown-mode/issues/845
   [gh-848]: https://github.com/jrblevin/markdown-mode/issues/848
   [gh-855]: https://github.com/jrblevin/markdown-mode/issues/855
+  [gh-868]: https://github.com/jrblevin/markdown-mode/issues/868
   [gh-870]: https://github.com/jrblevin/markdown-mode/issues/870
 
 # Markdown Mode 2.6

markdown-mode.el

@@ -9099,6 +9099,10 @@ LANG is a string, and the returned major mode is a symbol."
   (and mode
        (fboundp mode)
        (or
+        (not (string-match-p "ts-mode\\'" (symbol-name mode)))
+        ;; Don't load tree-sitter mode if the mode is in neither auto-mode-alist nor major-mode-remap-alist
+        ;; Because some ts-mode overwrites auto-mode-alist and it might break user configurations
+
         ;; https://github.com/jrblevin/markdown-mode/issues/787
         ;; major-mode-remap-alist was introduced at Emacs 29.1
         (cl-loop for pair in (bound-and-true-p major-mode-remap-alist)

tests/markdown-test.el

@@ -4379,12 +4379,17 @@ x: x
 
 (ert-deftest test-markdown-parsing/get-lang-mode ()
   "Test `markdown-get-lang-mode'.
-Do not load major-mode function if it isn't in auto-mode-alist.
-Details: https://github.com/jrblevin/markdown-mode/issues/761"
+Do not load tree-sitter-mode function if it is in neither auto-mode-alist nor major-mode-remap-alist.
+Details:
+- https://github.com/jrblevin/markdown-mode/issues/761
+- https://github.com/jrblevin/markdown-mode/issues/868"
   (should (eq (markdown-get-lang-mode "emacs-lisp") 'emacs-lisp-mode))
 
-  (let ((auto-mode-alist nil))
-    (should (null (markdown-get-lang-mode "emacs-lisp")))))
+  (when (and (fboundp 'treesit-language-available-p)
+             (funcall 'treesit-language-available-p 'python))
+    (let ((auto-mode-alist nil)
+          (major-mode-remap-alist nil))
+      (should (null (markdown--lang-mode-predicate 'python-ts-mode))))))
 
 (ert-deftest test-markdown-parsing/get-lang-mode-from-remap-alist ()
   "Test `markdown-get-lang-mode' from major-mode-remap-alist.