bug#43519: 28.0.50; Overlay at end of minibuf hides minibuf's real content

[Eli Zaretskii]

> Date: Mon, 21 Sep 2020 15:44:16 +0000
> From: Gregory Heytings <ghe@sdf.org>
> cc: monnier@iro.umontreal.ca, 43519@debbugs.gnu.org
> 
> Perhaps I misunderstood something, but for me "start the display at the 
> beginning of the screen line where we end up after 
> move_it_vertically_backward" would mean that if the prompt and the user 
> input so far needs more than one line, only the last line would be 
> displayed.  So instead of having, say,
> 
> Find file: <user input>
> <user input>|
> <completion candidates>
> 
> (where | represents the cursor) we would only have:
> 
> <user input>|
> <completion candidates>

Yes.

This bug was filed to request that Emacs behaves with overlay-string in
the minibuffer prompt the same as with regular buffer text.  What I
propose will do that, or as close as possible to it.  By contrast, you
seem to suggest a change in the current behavior for buffer text as
well.  That may or may not be a good idea, but it's a separate issue,
so should be discussed separately (and in that separate discussion I
will generally be opposed to the change you are proposing, because we
had the current behavior for many years, and so changes like the one
you propose run serious risk of breaking expectations of some package
out there).