Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> So is the plan to add a completion metadata `eager-display' such that
>> completion tables can request immediate display? This completion
>> metadata can then be overridden by the user via
>> `completion-category-overrides'. The patch would include changes to tmm,
>> ffap-menu and imenu (obsoleting `imenu-eager-completion-buffer').
>
> That sounds good, except that in order for
> `completion-category-overrides` to work reliably, the `eager-display`
> should not be in the metadata but in `completion-category-defaults`.

Okay. Can you please clarify why you assume that overriding isn't
reliably possible if the metadata is specified directly? In
`completion-metadata-get' the `completion-category-defaults' and
`completion-category-overrides' take precedence over the completion
table metadata.

I attached a patch which adds a customization option
`completion-eager-display' and an `eager-display' completion table
metadata. The customization option can be set to nil (never), t (always)
or to auto, which means that the *Completions* buffer will only be shown
if the completion table requests eager display via the `eager-display'
metadata.

I updated ffap.el, tmm.el and imenu.el to take advantage of the new
`eager-display' metadata. I added completion categories where missing
such that overriding the metadata becomes possible. If desired, the
metadata can be moved to `completion-category-defaults' instead.

Daniel