bug#52839: 29.0.50; The '(declare (modes MODE...))' NEWS entry is confusing

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Tue, 28 Dec 2021 03:49:33 +0200
> 
> It says these syntaxes "declare how completion should happen" or one of
> them "can be used as a general predicate to say whether the command
> should be present when completing with 'M-x TAB'", but neither have any
> effect unless the user customizes read-extended-command-predicate.
> 
> The previous entry (the one about (interactive "p" dired-mode)) doesn't
> mention the predicate user option either.
> 
> Should read-extended-command-predicate be set to
> #'command-completion-default-include-p by default? Otherwise the NEWS
> entries (at least one of them) should probably mention it.
> 
> When reading the manual (subsection "Specifying Modes For Commands"),
> I'm feeling a similar problem.
> command-completion-default-include-p *is* mentioned, but only somewhere
> in the middle. The intro gives the impression that "specifying modes"
> will have an effect by default.
> 
> The small two paragraphs saying
> 
>    Specifying modes _may_ affect completion in @kbd{M-x}
> 
>    ...when using the ... predicate ...
> 
> look kind of sneaky. Like, we have just described a way to set up a
> bunch of meaningful information, and that _may_ affect your Emacs's
> behavior if (...). That's weird, but I'm not sure how to resolve that
> best. Apart from changing the default value, that is.
> 
> Other options may be:
> 
>    * Change the 'M-x' binding to call execute-extended-command-for-buffer
>    instead. The behavior of execute-extended-command won't change, but
>    that probably isn't going to save anybody: the user who set up the
>    binding to call that command explicitly is probably rare.
> 
>    * Have the subsection be actually about the command
>    execute-extended-command-for-buffer. Mention its binding (M-X) and say
>    that (interactive nil dired-mode) affects its behavior. Then mention
>    that by customizing read-extended-command-predicate the user can have
>    'M-x' behaving like that as well. If they like.

Stefan, any comments?