Eli Zaretskii <eliz@gnu.org> writes:
> I'm okay with adding a new style, per B, but why do we need to
> deprecate emacs22 at the same time?  Let users who want this new
> behavior customize their completion styles to use this new style
> instead of emacs22.  That'd be fully backward compatible, and will
> solve the problem for those who don't like the current behavior.

That's fair enough, we don't need to deprecate emacs22 at the same time,
we can wait until the new style has been battle-tested.

I think a new style should replace emacs22 in the default
completion-styles eventually, but that can wait.

And after working on this bug for a while, I now am convinced that the
new style approach is straightforward, and is the best way.  (Although
it would also work to make these changes in the emacs22 style)

Attached is a patch which adds a new ignore-after-point style.  The fix
for this bug is entirely contained in the differences between
completion-ignore-after-point-all-completions (c-iap-a-c) and
completion-emacs22-all-completions (c-e22-a-c).

c-e22-a-c always omits the text after point, which means
choose-completion always deletes that text, causing this bug.

c-iap-a-c includes the text after point in some cases.  Whenever the
text after point is included, it's grayed out with a new
completions-ignored face to indicate it was ignored.

The cases where c-iap-a-c includes the text after point are those where
the user will have further chances to edit or complete with that text:

- When we're doing minibuffer completion and choose-completion will
  immediately exit the minibuffer, the text after point is not included,
  since the user won't get any further changes to use it, and it's
  probably garbage.

- When we're doing completion-at-point (or certain kinds of minibuffer
  completion, e.g. completing a directory in filename completion), the
  text after point is included.  In such cases, the user can always
  delete it themselves later, or might want to actually use it.

To make this work consistently with completion-try-completion (which
keeps point before the ignored suffix in both the ignore-after-point and
emacs22 styles), choose-completion-string now checks a new
'completion-position-after-insert text property, and moves point to that
position.

(There are two other changes which are general improvements unrelated to
this bug:

- The behavior of keeping point before the ignored suffix is more
  consistent.

- Instead of hardcoding try-completion and all-completion,
  ignore-after-point uses the configured completion styles.)

Stefan, Dmitry, any comments?