Re: *Completions* in minibuffer-only frames

[martin rudalics]

> How old is this problem?

It's with us at least since Emacs 25.

> It doesn't sound too serious to me, FWIW
> (but then I never use minibuffer-only frames).

As a rule I don't use minibuffer-only frames either so I only recently
bumped into a number of problems while looking at them a bit harder.

The behavior I describe is a direct consequence of our idiosyncrasy to
consider the minibuffer window of a minibuffer-only frame as the root
window of its frame's window tree while we do not consider the
minibuffer window of a "normal" frame as part of that frame's window
tree.  This confuses ‘walk-window-tree’ which may not interpret its
MINIBUF argument as intended when "walking" a minibuffer-only frame.

> I'd really like to release Emacs 26.2 VSN; the bug reports about
> recent regressions or serious bugs all but ceased to arrive, so I
> think we have a stable branch.  Installing non-trivial (by their
> effect) changes is something I'd like to avoid if possible.

Since nobody ever complained I have no problems with postponing the
fix to Emacs 27.

martin