bug#71419: 30.0.50; Completion does not always highlight the "common part" corresponding to suffix

[Dmitry Gutov <dmitry@gutov.dev>]

On 09/06/2024 16:52, Stefan Monnier wrote:
>> For example:
>>
>> 1. Type (fo|-function
>> 2. C-M-i
>>
>> You get 5 completions (the exact number is not important), where "fo" is
>> highlighted in all of them, but "function is not.
> 
> Looks like a bug in the `basic` completion style: it filters things that
> match the glob pattern `fo*-function` yet it only highlights the prefix.

Yes, thanks. Looks like this one-liner fixes it:

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index f62cb2566b2..144cda8cfdc 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -3816,7 +3816,7 @@ completion-basic-all-completions
                              'point
                              (substring afterpoint 0 (cdr bounds)))))
           (all (completion-pcm--all-completions prefix pattern table 
pred)))
-    (completion-hilit-commonality all point (car bounds))))
+    (completion-pcm--hilit-commonality pattern all)))

  ;;; Partial-completion-mode style completion.



>> Also, highlighting is information. If it was more uniform, we could use
>> it to e.g. address the FIXME in completion-all-completions.
> 
> I don't think it could be trusted to always provide the needed data (and
> even if it does, it would be sufficiently clunky to use that I'm not
> sure we'd want to rely on it).

You're probably right.

But it would have been nice to be able to use it in the "progressive 
improvement" kind of fashion: when the suffix and the other parts are 
highlighted correctly, we do the right thing; if the style missed the 
suffix highlighting, we do the other thing - and put the responsibility 
on the third party.