Re: Stop frames stealing eachothers' minibuffers!

[Eli Zaretskii]

> Date: Sat, 14 Nov 2020 15:36:43 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: enometh@meer.net, monnier@iro.umontreal.ca, andreyk.mad@gmail.com,
>  emacs-devel@gnu.org
> 
> > Date: Wed, 11 Nov 2020 20:37:16 +0000
> > Cc: Andrii Kolomoiets <andreyk.mad@gmail.com>, monnier@iro.umontreal.ca,
> >   enometh@meer.net, emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>
> > 
> > > > C-x 5 2
> > > > M-x
> > > > C-x 5 o
> > > > M-x
> > 
> > > > With the default setting of `enable-recursive-minibuffers`, the
> > > > minibuffer is moved to active frame, but the error message is displayed
> > > > in the other frame.
> > 
> > > Arguably a bug.  Alan, could you please look into this?
> > 
> > I think this is a bug, too.
> > 
> > I've been looking at the C sources for some while but haven't found
> > anything useful.  I've tried setting echo_area_window during the frame
> > change, but this doesn't have any visible effect.
> > 
> > I'll carry on with the diagnosis.  Any quick tips would be welcome.
> 
> My guess is that this is somehow related to the fact that error
> messages are displayed as part of handling an error signal, which
> causes a throw to top level.

Specifically, read-from-minibuffer (called when we type the first M-x)
binds some variables, then enters recursive-edit.  When the error
unwinds the stack, it restores the original window configuration,
which includes the frame which was selected back then.  And that
undoes the effect of "C-x 5 o", so the error message is displayed on
the original frame.