bug#74616: 30.0.92; tmm always displays the *Completions* buffer

[Eli Zaretskii <eliz@gnu.org>]

> Cc: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Sat, 30 Nov 2024 07:42:33 +0100
> From:  Daniel Mendler via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> The `tmm-add-prompt' function of tmm.el automatically displays the
> *Completions* buffer by calling `minibuffer-completion-help'. If an
> alternative minibuffer completion system like Icomplete or Vertico is
> used, the *Completions* buffer is not needed since the candidates are
> already displayed in the minibuffer. I propose to either detect these
> alternative completion systems (e.g., by checking the value of the
> completing-read-function and/or the mode variables) or to provide a new
> customization variable `tmm-display-completions' which defaults to t but
> can be set to nil to disable the call to `minibuffer-completion-help'. I
> am happy to provide a patch for either of these approaches.

I think the automatic detection is a better default behavior, but
maybe we could have a variable (not necessarily a defcustom) for users
who would like to have the old behavior.

Stefan, WDYT?