Honor major-mode-remap-alist in php-mode-maybe

Emacs's built-in php-ts-mode registers

    (add-to-list 'treesit-major-mode-remap-alist '(php-mode . php-ts-mode))

with the comment "To be able to toggle between an external package and
core ts-mode", and `treesit-enabled-modes' copies that entry into
`major-mode-remap-alist' when the user opts in.  So a user who installs
this package and enables php-ts-mode is asking for php-ts-mode.

They did not get it for .php files.  `set-auto-mode' applies the
remapping to whatever `auto-mode-alist' names, so entries pointing
straight at `php-mode' honored it, but ".php"/".phtml" go through
`php-mode-maybe', which is not itself a remap target and called the
derived mode directly.  The same buffer therefore opened in different
modes depending on the extension:

    a.stub   auto-mode-alist=php-mode        -> php-ts-mode   (remapped)
    a.php    auto-mode-alist=php-mode-maybe  -> php-mode      (not remapped)

Resolve the derived mode through `major-mode-remap' so `php-mode-maybe'
behaves as if `auto-mode-alist' had named the mode directly.  The
function is Emacs 30 or later, hence the `fboundp' guard; on older
Emacs the mode is used unchanged, as before.

Note that no adjustment is needed for `php-base-mode': php-ts-mode
declares `php-mode' as an extra parent via `derived-mode-add-parents',
and `php-mode' derives from `php-base-mode', so once this package is
loaded `derived-mode-all-parents' of php-ts-mode already resolves to
(php-ts-mode php-mode php-base-mode prog-mode).

Author: zonuexe

lisp/php.el

@@ -646,10 +646,17 @@ indentation."
 
 ;;;###autoload
 (defun php-mode-maybe ()
-  "Select PHP mode or other major mode."
+  "Select PHP mode or other major mode.
+
+The selected mode is resolved through `major-mode-remap-alist' the way
+`set-auto-mode' would have done had `auto-mode-alist' named it directly,
+so that a remapping the user asked for still applies.  Emacs's built-in
+`php-ts-mode' registers (php-mode . php-ts-mode) for exactly this
+purpose, and `treesit-enabled-modes' installs it when the user opts in."
   (interactive)
   (run-hooks php-mode-maybe-hook)
-  (funcall (php-derivation-major-mode)))
+  (let ((mode (php-derivation-major-mode)))
+    (funcall (if (fboundp 'major-mode-remap) (major-mode-remap mode) mode))))
 
 ;;;###autoload
 (defun php-current-class ()

tests/php-mode-test.el

@@ -699,6 +699,41 @@ than depending on `poly-php', because that package pulls in a released
         (set-buffer-modified-p nil)
         (setq buffer-file-name nil)))))
 
+(define-derived-mode php-mode-test--stub-ts-mode prog-mode "PHP/stub-ts"
+  "Stand-in for `php-ts-mode' in `php-mode-test-mode-remap'.
+Using a stub keeps the test independent of whether the PHP tree-sitter
+grammar is installed.")
+
+(ert-deftest php-mode-test-mode-remap ()
+  "`php-mode-maybe' must honor `major-mode-remap-alist'.
+
+Emacs's built-in `php-ts-mode' registers (php-mode . php-ts-mode) in
+`treesit-major-mode-remap-alist' so that users can toggle between this
+package and the core tree-sitter mode; `treesit-enabled-modes' copies
+that entry into `major-mode-remap-alist' when they opt in.
+
+`set-auto-mode' applies the remapping to whatever `auto-mode-alist'
+names, so file patterns pointing straight at `php-mode' honored it while
+those going through `php-mode-maybe' did not: the same buffer became
+`php-mode' for \".php\" but the remapped mode for \".stub\"."
+  (skip-unless (fboundp 'major-mode-remap))
+  (dolist (probe '((((php-mode . php-mode-test--stub-ts-mode))
+                    . php-mode-test--stub-ts-mode)
+                   ;; Without a remapping the derived mode is used as-is.
+                   (nil . php-mode)))
+    (let ((major-mode-remap-alist (car probe)))
+      (with-temp-buffer
+        ;; `php-derivation-major-mode' consults `buffer-file-name'.
+        (setq buffer-file-name (expand-file-name "remap.php" temporary-file-directory))
+        (unwind-protect
+            (progn
+              (insert "<?php\necho 'hi';\n")
+              (php-mode-maybe)
+              (should (equal (cons (car probe) (cdr probe))
+                             (cons (car probe) major-mode))))
+          (set-buffer-modified-p nil)
+          (setq buffer-file-name nil))))))
+
 (ert-deftest php-mode-test-php74 ()
   "Test highlighting language constructs added in PHP 7.4."
   (with-php-mode-test ("7.4/arrow-function.php" :faces t))