bug#70010: 30.0.50; completion-preview-mode behaves mode-local, but is global

[Eshel Yaron]

Philip Kaludercic <philipk@posteo.net> writes:

> Eshel Yaron <me@eshelyaron.com> writes:
>
>> Hello Philip,
>>
>> Philip Kaludercic <philipk@posteo.net> writes:
>>
>>> I tried to enable `completion-preview-mode' by adding
>>>
>>>   (setopt completion-preview-mode t)
>>>
>>> in my init, but it had not effect.
>>
>> Indeed, it is a minor mode, so one normally enables it by calling the
>> function completion-preview-mode, perhaps interactively via M-x.
>
> I enable all minor modes as user options, so I'd disagree that using a
> function or invoking the command are the only ways to expect a minor
> mode to be enabled.

Fair enough :)

>>> When I check the implementation, I noticed that it modifies
>>> `post-command-hook' locally.  I think it would make sense to rename
>>> the current `completion-preview-mode' to
>>> `completion-preview-local-mode', and then use
>>> `define-globalized-minor-mode' to define `completion-preview-mode'.
>>
>> We can add a global variant, although IMO the natural scope for
>> completion-preview-mode is per major mode: for some kinds of content you
>> want to have completion preview, and for others you may want it off.
>> Note that a necessary condition for completion-preview-mode to be useful
>> in a certain context is that completion-at-point is useful in that
>> context, since otherwise there's nothing to preview.
>>
>> Therefore, I recommend enabling completion-preview-mode by adding it to
>> major mode hooks, such as prog-mode-hook or comint-mode-hook.
>> Admittedly, if you do want to enable it for all buffers, the major mode
>> hook approach would require adding it to four or five hooks, which is a
>> bit less elegant than enabling a global minor mode once.
>>
>> So I suggest we keep completion-preview-mode local and add a global
>> variant, say, completion-preview-global-mode, for enabling it globally.
>> WDYT?
>
> That seems fine as well.

All right, here's a patch that adds such a global variant.  I find the
:predicate argument of define-globalized-minor-mode pretty neat, it adds
a user option that lets users choose in which major modes the minor mode
should take effect, and we can provide a sane default:

0001-Add-global-minor-mode-completion-preview-global-mode.patch
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