bug#63754: 29.0.91; tmm breaks when tmm-completion-prompt is nil

[Juri Linkov <juri@linkov.net>]

>> > Should be fixed now on the emacs-29 branch.
>>
>> Cool.  I've tested, it's working nicely.  Thanks for the fix.
>
> Thanks for testing, I'm therefore closing this bug.

There is one remaining case where it fails:

  (setq completions-header-format nil)
  (setq tmm-completion-prompt nil)
  (tmm-menubar) ; or `tmm-prompt' with any menu/keymap

Then the first item is deleted.  The patch below fixes this.

>> Sorry if my comment is out of place, but I also gave a try to
>> `tmm-mid-prompt' = nil.  Since it disables the tmm shortcuts, maybe it
>> would be more intuitive to let users input keys and do completion at
>> the minibuffer in this situation? (unless I'm missing some unwanted
>> side effect here)
>>
>> With this little change, for example:
>
> I don't know.  The original completion works on the shortcuts, AFAIU,
> and thus makes no sense when tmm-mid-prompt is nil.  When that
> variable is nil, the user needs to use the arrow keys to select the
> menu items.  If someone wants to add a completion feature to that, I
> don't mind, but I don't know enough about tmm to tell, and such a
> change is definitely not for the release branch.
>
> If someone here has an opinion on this last suggestion, please speak
> up.

AFAICS, completion works without problems in tmm.  The artificial restriction
that removes self-inserting keys was needed to allow only character shortcuts
when tmm-mid-prompt is nil.

diff --git a/lisp/tmm.el b/lisp/tmm.el
index 88254f0d1b8..a4058594622 100644
--- a/lisp/tmm.el
+++ b/lisp/tmm.el
@@ -329,7 +329,8 @@ tmm-completion-delete-prompt
   (with-current-buffer standard-output
     (goto-char (point-min))
     (let* (;; First candidate: first string with mouse-face
-           (menu-start-1 (next-single-char-property-change (point) 'mouse-face))
+           (menu-start-1 (or (and (get-text-property (point) 'mouse-face) (point))
+                             (next-single-char-property-change (point) 'mouse-face)))
            ;; Second candidate: an inactive menu item with tmm-inactive face
            (tps-result (save-excursion
                          (text-property-search-forward 'face 'tmm-inactive t)))