Subject: bug#34080: 27.0.50, 26.1; undocumented key bindings for *vc-diff*

From: Sean Whitton <[email-masked]>
Date: Sun, 18 May 2025 10:51:34 +0100

Hello,

On Thu 15 May 2025 at 07:54pm +03, Juri Linkov wrote:

>> Searching the code base, :advertised-binding is meant to affect
>> where-is-internal, and only that function, I think.
>> But it does seem to be broken:
>>
>>     (progn (put 'diff-hunk-next :advertised-binding "n") ; or '("n")
>>            (with-current-buffer "*vc-diff*"
>>              (mapcar #'key-description
>>                      (where-is-internal 'diff-hunk-next))))
>>
>>     => ("TAB" "n" "C-M-i" "M-n" "<menu-bar> <diff> <Next Hunk>")
>>
>> i.e. there is no prioritisation for the "n" binding.
>> Indeed, TAB comes first.
>>
>> Then it seems like a separate issue why the "TAB" binding is not
>> appearing in 'M-x describe-mode'.  So there are two problems here.
>
> There is no 'n' binding in 'diff-mode-map'.  'n' inherited
> from 'diff-mode-shared-map' becomes 'M-n' (via the ESC prefix).
> And its advertised-binding works correctly:
>
>   (put 'diff-hunk-next :advertised-binding "\M-n")
>   (substitute-command-keys "Type `\\<diff-mode-map>\\[diff-hunk-next]'.")
>   => #("Type ‘M-n’." 6 9 (font-lock-face help-key-binding face help-key-binding))

If you change "n" and "\M-n" in my example the return value of
where-is-internal does not change.  Therefore I think your example is
working accidentally and there is still a problem here.

-- 
Sean Whitton