GNU bug report logs - #69191
30.0.50; New var `major-mode-remap-defaults`, for packages

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: bug#69191: closed (Re: bug#69191: 30.0.50; New var
 `major-mode-remap-defaults`, for packages)
Date: Mon, 04 Mar 2024 05:00:03 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#69191: 30.0.50; New var `major-mode-remap-defaults`, for packages

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 69191 <at> debbugs.gnu.org.

-- 
69191: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=69191
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: "Basil L. Contovounesios" <basil <at> contovou.net>
Cc: 69191-done <at> debbugs.gnu.org
Subject: Re: bug#69191: 30.0.50; New var `major-mode-remap-defaults`, for
 packages
Date: Sun, 03 Mar 2024 23:59:16 -0500

Pushed with corresponding updates,


        Stefan

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.0.50; New var `major-mode-remap-defaults`, for packages
Date: Fri, 16 Feb 2024 10:45:13 -0500

[Message part 4 (text/plain, inline)]

Package: Emacs
Version: 30.0.50


While `major-mode-remap-alist` provides a way for users to indicate the
major mode of their choice, I think we need a similar variable for the
use of packages.

The package below accordingly adds a new `major-mode-remap-defaults`
and changes various packages to obey it or make use of it.
I think it nicely cleans the regexp duplication between CC-mode and
`c-ts-mode.el` and also makes it easier/cleaner for users to override
the changes made by `*-ts-mode.el`.

There are some FIXMEs that one might want to address, most importantly
whether we should use an indirection through `major-mode-remap-defaults`
for all TS modes or only for those for which we provide a non-TS mode.

And there's no doc update yet.


        Stefan

[major-mode-remap.patch (text/x-diff, inline)]

diff --git a/lisp/files.el b/lisp/files.el
index f67b650cb92..6b80175b157 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -3404,7 +3404,7 @@ set-auto-mode
 matches the buffer beginning against `magic-mode-alist',
 compares the file name against the entries in `auto-mode-alist',
 then matches the buffer beginning against `magic-fallback-mode-alist'.
-It also obeys `major-mode-remap-alist'.
+It also obeys `major-mode-remap-alist' and `major-mode-remap-defaults'.
 
 If `enable-local-variables' is nil, or if the file name matches
 `inhibit-local-variables-regexps', this function does not check
@@ -3550,9 +3550,22 @@ major-mode-remap-alist
 Every entry is of the form (MODE . FUNCTION) which means that in order
 to activate the major mode MODE (specified via something like
 `auto-mode-alist', file-local variables, ...) we should actually call
-FUNCTION instead."
+FUNCTION instead.
+FUNCTION can be nil to hide other entries (either in this var or in
+`major-mode-remap-defaults') and means that we should call MODE."
   :type '(alist (symbol) (function)))
 
+(defvar major-mode-remap-defaults nil
+  "Alist mapping file-specified mode to actual mode.
+This works like `major-mode-remap-alist' except it has lower priority
+and it is meant to be modified by packages rather than users.")
+
+(defun major-mode-remap (mode)
+  "Return the function to use to enable MODE."
+  (or (cdr (or (assq mode major-mode-remap-alist)
+               (assq mode major-mode-remap-defaults)))
+      mode))
+
 ;; When `keep-mode-if-same' is set, we are working on behalf of
 ;; set-visited-file-name.  In that case, if the major mode specified is the
 ;; same one we already have, don't actually reset it.  We don't want to lose
@@ -3569,7 +3582,7 @@ set-auto-mode-0
 		        (eq mode (car set-auto-mode--last))
 		        (eq major-mode (cdr set-auto-mode--last)))))
     (when mode
-      (funcall (alist-get mode major-mode-remap-alist mode))
+      (funcall (major-mode-remap mode))
       (unless (eq mode major-mode)
         (setq set-auto-mode--last (cons mode major-mode)))
       mode)))
diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index 4ef17daf876..b9064d689cf 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -1439,36 +1439,33 @@ c-or-c++-ts-mode
 This function attempts to use file contents to determine whether
 the code is C or C++ and based on that chooses whether to enable
 `c-ts-mode' or `c++-ts-mode'."
+  ;; FIXME: (declare (obsolete c-or-c++-mode "30.1"))?
   (interactive)
-  (if (save-excursion
-        (save-restriction
-          (save-match-data ; Why `save-match-data'?
-            (widen)
-            (goto-char (point-min))
-            (re-search-forward c-ts-mode--c-or-c++-regexp nil t))))
-      (c++-ts-mode)
-    (c-ts-mode)))
+  (let ((mode
+         (if (save-excursion
+               (save-restriction
+                 (save-match-data       ; Why `save-match-data'?
+                   (widen)
+                   (goto-char (point-min))
+                   (re-search-forward c-ts-mode--c-or-c++-regexp nil t))))
+             'c++-ts-mode)
+         'c-ts-mode))
+    (funcall (major-mode-remap mode))))
+
 ;; The entries for C++ must come first to prevent *.c files be taken
 ;; as C++ on case-insensitive filesystems, since *.C files are C++,
 ;; not C.
 (if (treesit-ready-p 'cpp)
-    (add-to-list 'auto-mode-alist
-                 '("\\(\\.ii\\|\\.\\(CC?\\|HH?\\)\\|\\.[ch]\\(pp\\|xx\\|\\+\\+\\)\\|\\.\\(cc\\|hh\\)\\)\\'"
-                   . c++-ts-mode)))
+    (add-to-list 'major-mode-remap-defaults
+                 '(c++-mode . c++-ts-mode)))
 
 (when (treesit-ready-p 'c)
-  (add-to-list 'auto-mode-alist
-               '("\\(\\.[chi]\\|\\.lex\\|\\.y\\(acc\\)?\\)\\'" . c-ts-mode))
-  (add-to-list 'auto-mode-alist '("\\.x[pb]m\\'" . c-ts-mode))
-  ;; image-mode's association must be before the C mode, otherwise XPM
-  ;; images will be initially visited as C files.  Also note that the
-  ;; regexp must be different from what files.el does, or else
-  ;; add-to-list will not add the association where we want it.
-  (add-to-list 'auto-mode-alist '("\\.x[pb]m\\'" . image-mode)))
-
-(if (and (treesit-ready-p 'cpp)
-         (treesit-ready-p 'c))
-    (add-to-list 'auto-mode-alist '("\\.h\\'" . c-or-c++-ts-mode)))
+  (add-to-list 'major-mode-remap-defaults '(c++-mode . c++-ts-mode))
+  (add-to-list 'major-mode-remap-defaults '(c-mode . c-ts-mode)))
+
+(when (and (treesit-ready-p 'cpp)
+           (treesit-ready-p 'c))
+  (add-to-list 'major-mode-remap-defaults '(c-or-c++-mode . c-or-c++-ts-mode)))
 
 (provide 'c-ts-mode)
 (provide 'c++-ts-mode)
diff --git a/lisp/progmodes/cc-mode.el b/lisp/progmodes/cc-mode.el
index 64a679eacc7..6e98ce047c3 100644
--- a/lisp/progmodes/cc-mode.el
+++ b/lisp/progmodes/cc-mode.el
@@ -2902,15 +2902,19 @@ c-or-c++-mode
 the code is C or C++ and based on that chooses whether to enable
 `c-mode' or `c++-mode'."
   (interactive)
-  (if (save-excursion
-        (save-restriction
-          (save-match-data
-            (widen)
-            (goto-char (point-min))
-            (re-search-forward c-or-c++-mode--regexp
-                               (+ (point) c-guess-region-max) t))))
-      (c++-mode)
-    (c-mode)))
+  (let ((mode
+         (if (save-excursion
+               (save-restriction
+        	 (save-match-data
+        	   (widen)
+        	   (goto-char (point-min))
+        	   (re-search-forward c-or-c++-mode--regexp
+        			      (+ (point) c-guess-region-max) t))))
+             'c++-mode)
+         'c-mode))
+    (funcall (if (fboundp 'major-mode-remap)
+		 (major-mode-remap mode)
+	       mode))))
 
 
 ;; Support for C++
diff --git a/lisp/progmodes/go-ts-mode.el b/lisp/progmodes/go-ts-mode.el
index 65adc1c55ea..296e4d0037d 100644
--- a/lisp/progmodes/go-ts-mode.el
+++ b/lisp/progmodes/go-ts-mode.el
@@ -262,6 +262,8 @@ go-ts-mode
     (treesit-major-mode-setup)))
 
 (if (treesit-ready-p 'go)
+    ;; FIXME: Should we instead put `go-mode' in `auto-mode-alist'
+    ;; and then use `major-mode-remap-defaults' to map it to `go-ts-mode'?
     (add-to-list 'auto-mode-alist '("\\.go\\'" . go-ts-mode)))
 
 (defun go-ts-mode--defun-name (node &optional skip-prefix)
diff --git a/lisp/progmodes/ruby-ts-mode.el b/lisp/progmodes/ruby-ts-mode.el
index 426ae248cac..cdfa3dca498 100644
--- a/lisp/progmodes/ruby-ts-mode.el
+++ b/lisp/progmodes/ruby-ts-mode.el
@@ -1211,18 +1211,8 @@ ruby-ts-mode
   (setq-local syntax-propertize-function #'ruby-ts--syntax-propertize))
 
 (if (treesit-ready-p 'ruby)
-    ;; Copied from ruby-mode.el.
-    (add-to-list 'auto-mode-alist
-                 (cons (concat "\\(?:\\.\\(?:"
-                               "rbw?\\|ru\\|rake\\|thor"
-                               "\\|jbuilder\\|rabl\\|gemspec\\|podspec"
-                               "\\)"
-                               "\\|/"
-                               "\\(?:Gem\\|Rake\\|Cap\\|Thor"
-                               "\\|Puppet\\|Berks\\|Brew"
-                               "\\|Vagrant\\|Guard\\|Pod\\)file"
-                               "\\)\\'")
-                       'ruby-ts-mode)))
+    (add-to-list 'major-mode-remap-defaults
+                 '(ruby-mode . ruby-ts-mode)))
 
 (provide 'ruby-ts-mode)
 
diff --git a/lisp/textmodes/tex-mode.el b/lisp/textmodes/tex-mode.el
index 5c5ca573f38..d14953ef1c7 100644
--- a/lisp/textmodes/tex-mode.el
+++ b/lisp/textmodes/tex-mode.el
@@ -1032,17 +1032,13 @@ tex--redirect-to-submode
                  ;; `tex--guess-mode' really tries to guess the *type* of file,
                  ;; so we still need to consult `major-mode-remap-alist'
                  ;; to see which mode to use for that type.
-                 (alist-get mode major-mode-remap-alist mode))))))
+                 (major-mode-remap mode))))))
 
-;; The following three autoloaded aliases appear to conflict with
-;; AUCTeX.  We keep those confusing aliases for those users who may
-;; have files annotated with -*- LaTeX -*- (e.g. because they received
+;; Support files annotated with -*- LaTeX -*- (e.g. because they received
 ;; them from someone using AUCTeX).
-;; FIXME: Turn them into autoloads so that AUCTeX can override them
-;; with its own autoloads?  Or maybe rely on `major-mode-remap-alist'?
-;;;###autoload (defalias 'TeX-mode #'tex-mode)
-;;;###autoload (defalias 'plain-TeX-mode #'plain-tex-mode)
-;;;###autoload (defalias 'LaTeX-mode #'latex-mode)
+;;;###autoload (add-to-list 'major-mode-remap-defaults '(TeX-mode . tex-mode))
+;;;###autoload (add-to-list 'major-mode-remap-defaults '(plain-TeX-mode . plain-tex-mode))
+;;;###autoload (add-to-list 'major-mode-remap-defaults '(LaTeX-mode . latex-mode))
 
 ;;;###autoload
 (define-derived-mode plain-tex-mode tex-mode "TeX"

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