Subject: bug#50228: [PATCH] 'command-completion-using-modes-p' doesn't work with multiple modes

From: Johannes Maier <[email-masked]>
Date: Fri, 27 Aug 2021 12:38:38 +0200

Hello everyone,

I'm using an up-to-date build of Emacs on NixOS and on Ubuntu (M-x
emacs-version yields "GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu,
GTK+ Version 3.24.30, cairo version 1.16.0").

I tried writing a command that would only show up in M-x TAB in certain
modes, using the new MODES argument to 'interactive', like so:

(setq read-extended-command-predicate
      #'command-completion-default-include-p)

(defun my-foo ()
  (interactive nil haskell-mode emacs-lisp-mode)
  (message "foo"))

I would have expected the command 'my-foo' to be shown in an Elisp
buffer, but hidden in fundamental-mode.  But 'my-foo' never shows up (it
works in the case where the 'interactive' call only specifies one mode,
though).

I checked the code that is called and found that
'command-completion-using-modes-p' seems to be missing an 'or' around
the predicates in the alternative case.  Digging a little deeper I found
the predicate function 'command-completion-with-modes-p' that already
seems to do what's needed for the other predicate, but with slightly
different arguments.  In particular the single-mode case seems to be
handled correctly by the code in 'command-completion-with-modes-p' as
well.

I've attached a patch that removes the duplicated checks in these two
functions and simply calls 'command-completion-with-modes-p' from
'command-completion-using-modes-p'.  Now it works for me with one or
more (major or minor) modes in 'interactive'.

I'm very much looking forward to feedback on whether that's a "good"
solution and hope I gave all the information that's needed.

(I didn't see any tests for those functions, but I'm not sure how to go
about those yet.  Could probably have look into those, too.)

Thank you,
Johannes

>From 08d6f48b4f7a295d3fd590ad6e5723beb3f0eadf Mon Sep 17 00:00:00 2001
From: Johannes Maier <[email-masked]>
Date: Fri, 27 Aug 2021 09:40:08 +0200
Subject: [PATCH] Fix 'command-completion-using-modes-p' in case of multiple
 modes

* lisp/simple.el: Use `command-completion-with-modes-p' inside of
`command-completion-using-modes-p' instead of performing a faulty
check (`or' was missing) in the case where `command-modes' returns
multiple modes.
---
 lisp/simple.el | 21 +++------------------
 1 file changed, 3 insertions(+), 18 deletions(-)

diff --git a/lisp/simple.el b/lisp/simple.el
index db083cfc25..82ab8927a7 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2067,24 +2067,9 @@ read-extended-command
        t nil 'extended-command-history))))
 
 (defun command-completion-using-modes-p (symbol buffer)
-  "Say whether SYMBOL has been marked as a mode-specific command in BUFFER."
-  ;; Check the modes.
-  (let ((modes (command-modes symbol)))
-    ;; Common case: Just a single mode.
-    (if (null (cdr modes))
-        (or (provided-mode-derived-p
-             (buffer-local-value 'major-mode buffer) (car modes))
-            (memq (car modes)
-                  (buffer-local-value 'local-minor-modes buffer))
-            (memq (car modes) global-minor-modes))
-      ;; Uncommon case: Multiple modes.
-      (apply #'provided-mode-derived-p
-             (buffer-local-value 'major-mode buffer)
-             modes)
-      (seq-intersection modes
-                        (buffer-local-value 'local-minor-modes buffer)
-                        #'eq)
-      (seq-intersection modes global-minor-modes #'eq))))
+  "Say whether SYMBOL has been marked as a mode-specific command in
+BUFFER."
+  (command-completion-with-modes-p (command-modes symbol) buffer))
 
 (defun command-completion-default-include-p (symbol buffer)
   "Say whether SYMBOL should be offered as a completion.
-- 
2.32.0