bug#70381: [PATCH] New command 'completion-preview-complete'

[Eli Zaretskii <eliz@gnu.org>]

> Cc: Ergus <spacibba@aol.com>
> Date: Sun, 14 Apr 2024 13:21:54 +0200
> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Following a recent discussion on emacs-devel[0], this patch adds a new
> command for Completion Preview mode that completes the symbol at point up
> to the longest common prefix of all completion candidates.  This patch
> also adds a visual indication for the longest common prefix when showing
> it as part of the completion preview, so the user can tell how far the new
> 'completion-preview-complete' will complete before invoking this command.
> For example, if the symbol at point is "foo", and the completion
> candidates are "foobar" and "foobaz", then the preview shows "bar" with
> the common prefix "ba" highlighted in face 'completion-preview-common'.

Thanks.

> * lisp/completion-preview.el (completion-preview--try-table):
> Return longest common prefix and list of suffixes instead of
> list of full candidates.  Add illustrative comment.
> (completion-preview--capf-wrapper, completion-preview--update)
> (completion-preview--show, completion-preview-insert)
> (completion-preview-next-candidate): Adjust.
> (completion-preview-common): New face.
> (completion-preview-exact): Distinguish from 'c-p-common'.
> (completion-preview-complete): New command.   ^^^^^^^^^^
> (completion-preview-active-mode-map): Bind it.
> (completion-preview-mode): Mention it in docstring.
> (completion-preview-commands): Add 'c-p-complete'.
                                      ^^^^^^^^^^^^
Please don't abbreviate symbols in the log entries.  Those are
frequently used to search for changes of functions/variables, and such
abbreviations defeat those searches.

If you are annoyed by the need to type long strings, I usually find
M-/ instrumental in reducing that annoyance considerably.

> +(defface completion-preview-common
>    '((((supports :underline t))
>       :underline t :inherit completion-preview)
>      (((supports :weight bold))
>       :weight bold :inherit completion-preview)
>      (t :background "gray"))
> -  "Face for exact completion preview overlay."
> +  "Face for completions longest common prefix in the completion preview."
               ^^^^^^^^^^^
This word is redundant here.  I'd replace it with "the".

> +(defvar-local completion-preview--inhibit-update-p nil
> +  "Whether to inhibit updateing the completion preview following this command.")
                         ^^^^^^^^^
"updating"

> +      (set-text-properties 0 (length suffix)
> +                           `(face ,(if (cdr suffixes)
> +                                       'completion-preview
> +                                     'completion-preview-exact))
> +                           suffix)
> +      (set-text-properties 0 (length common)
> +                           `(face ,(if (cdr suffixes)
> +                                       'completion-preview-common
> +                                     'completion-preview-exact))
> +                           common)

Is the use of back-ticks really necessary here?

> +      (set-text-properties 0 (length suffix)
> +                           `(face ,(if (cdr sufs)
> +                                       'completion-preview
> +                                     'completion-preview-exact))
> +                           suffix)

Likewise here (and in few other places).