bug#73234: 30.0.91; completion-preview-mode doesn't trigger for case-insensitive capf

[Eshel Yaron via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Hi,

Morgan Willcock <morgan@ice9.digital> writes:

> Eshel Yaron <me@eshelyaron.com> writes:
>
>> FYI, I've added a new user option completion-preview-ignore-case on the
>> master branch (commit f1794a17b62), which controls case sensitivity for
>> Completion Preview mode specifically.  This is definitely safe to set
>> buffer-locally.  The docstring of this new variable should hopefully
>> also explain exactly what's the expected behavior in this regard.
>
> Thanks for adding the new option.  For my use case I don't think I would
> be able to use it because the case mismatch between the text already
> typed and the completion will effectively be generating a completion
> which may not actually exist.
>
> e.g. If a valid completion was "FooBar", and I typed "foo", having the
> final result as "fooBar" wouldn't be ideal.

Fair enough, although earlier you mentioned that your use case was
completing symbols in a case-insensitive language, so I wonder what's
wrong with "fooBar", or "foobar" for that matter.  They are all the same
as the completion candidate, "FooBar", ignoring case differences, no?

> I've been trying to think of a way to get it to work without disturbing
> the user interface that already exists.  Maybe it would be possible
> fixup the result in a post-insertion hook if one existed - such a hook
> might be generally useful anyway.

We have the :exit-function (which your capf can provide as an extra
property alongside the completion table it returns), and indeed you
could use that to "fix" the case of your prefix after completing it.
That's an interesting solution, I think.  Or do you have some other kind
of hook in mind?


Best,

Eshel