bug#49104: [PATCH] 28.0.50; Handle remapped commands for M-TAB in `flyspell-prog-mode'

[Jim Porter <jporterbugs@gmail.com>]

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`flyspell-prog-mode' uses the original M-TAB binding outside of
comments, which is nice (see bug#18533). However, it doesn't account
for remapped commands. For example, I remap `completion-at-point' to
`company-complete' when `company-mode' is active. If I hit M-TAB while
`company-mode' and `flyspell-prog-mode' are active, I get
`completion-at-point', which isn't what I want.

To reproduce this issue, you can do the following:

  emacs -Q
  (global-set-key [remap completion-at-point]
                  (lambda () (interactive) (message "remapped")))
  M-x flyspell-prog-mode
  M-TAB ;; Or C-M-i

I've attached a patch that fixes the issue (hopefully it works in all
cases; it works for me).

[-- Attachment #2: 0001-Handle-remapped-commands-for-original-M-TAB-binding-.patch --]
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From 734890adff84cf8fbec9cff0a5bb6ad620877216 Mon Sep 17 00:00:00 2001
From: Jim Porter <jporterbugs@gmail.com>
Date: Fri, 18 Jun 2021 16:02:07 -0700
Subject: [PATCH] Handle remapped commands for original M-TAB binding in
 'flyspell-prog-mode'

* lisp/textmodes/flyspell.el (flyspell-prog-mode): Get the remapped
command for the original M-TAB binding if necessary.
---
 lisp/textmodes/flyspell.el | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lisp/textmodes/flyspell.el b/lisp/textmodes/flyspell.el
index ba48e5de21..eb4c5cde28 100644
--- a/lisp/textmodes/flyspell.el
+++ b/lisp/textmodes/flyspell.el
@@ -410,9 +410,11 @@ flyspell-prog-mode
   (interactive)
   (setq flyspell-generic-check-word-predicate
         #'flyspell-generic-progmode-verify)
-  (setq-local flyspell--prev-meta-tab-binding
-              (or (local-key-binding "\M-\t" t)
-                  (global-key-binding "\M-\t" t)))
+  (let ((prev-meta-tab-binding (or (local-key-binding "\M-\t" t)
+                                   (global-key-binding "\M-\t" t))))
+    (setq-local flyspell--prev-meta-tab-binding
+                (or (command-remapping prev-meta-tab-binding)
+                    prev-meta-tab-binding)))
   (flyspell-mode 1)
   (run-hooks 'flyspell-prog-mode-hook))
 
-- 
2.25.1