Re: Navigating completions from minibuffer

[Juri Linkov <juri@linkov.net>]

> OK, how about this?  It's an adapted version of my
> completions-auto-update patch, which provides (for now) only the feature
> of deselecting the completion when point moves or the minibuffer
> changes.  The infrastructure for doing this turns out to be basically
> identical, which is interesting.

Indeed, it's easier to start with a simpler case, and then gradually
to add handling of more cases to the same option.

> It sets completions-auto-update to 'deselect by default, which I think
> is reasonable?

Isn't deselection needed only when minibuffer-visible-completions is enabled?

> minibuffer-visible-completions makes RET submit the selected
> completion candidate, if any, ignoring the contents of the minibuffer.
> But a user might select a completion candidate and then want to type
> something else in the minibuffer and submit what they typed.
>
> * lisp/minibuffer.el (completion--insert): Add a space before each
> candidate.

I don't think anyone would like such a space shifting the whole layout
to the right.  Rather I'd recommend to use a space after each candidate.
There is already a space between candidates.  Only at the end a space is
missing.

Or without adding a space at the end we could change `choose-completion`
to not select the candidate when point is at the end (`choose-completion`
needs fixing anyway since currently it raises an error at the end
of the first completion in case of no header.)

This still won't solve the case of no header.  So in this case
for the initial position we could add a narrow line at the top:

  (propertize "\n" 'face '(:height 0))

This solves a lot of problems, and will help to remove the complicated
special-handling of the 'first-completion' text property in many places.