bug#74617: 30.0.92; ffap-menu always displays the *Completions* buffer

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

Juri Linkov <juri@linkov.net> writes:

>> The pattern where completion commands want to display candidates
>> immediately is not uncommon. There are ffap, tmm and multiple
>> third-party packages which have such a requirement. So I suggest to not
>> necessarily treat "immediate candidate display" as a bug report, but
>> rather as a feature request for `completing-read'.
>
> And imenu.el calls minibuffer-completion-help conditionally
> unless imenu-eager-completion-buffer is not nil.

Thanks, I wasn't aware of this option. It seems the behavior is
inverted? The completion buffer pops up if imenu-eager-completion-buffer
is nil.

(defcustom imenu-eager-completion-buffer t
  "If non-nil, eagerly pop up the completion buffer."
  :type 'boolean
  :version "22.1")

It is likely that there are more such uses in the Emacs code and other
packages. One possible solution would be a display-eager metadata:

(completing-read "Test: "
 (lambda (string pred action)
   (if (eq action 'metadata)
       '(metadata (display-eager . t))
     (complete-with-action action #'read-file-name-internal string pred))))

This pushes the responsibility of displaying the candidates to
`completing-read'. In `completing-read-default' the following code
would have to be added to the `minibuffer-with-setup-hook':
                
(when (completion-metadata-get
       (completion-metadata "" minibuffer-completion-table nil)
       'display-eager)
  (minibuffer-completion-help))

Daniel