Re: Stop frames stealing eachothers' minibuffers!

[Gregory Heytings]

> > Note that this patch and discussion started with the following 
> > observation (on Oct 13):
> >
> > > (i) Have two frames open displaying buffers.
> > > (ii) On frame F1 do C-x b.  This leaves a minibuffer open there.
> > > (iii) Move to F2.
> > > (iv) Do C-x 8 RET <enter some character>.
> > > F1's minibuffer is now on F2.  This is bad.
>
> But I see the same with Emacs 27.  After moving to F2, the minibuffer of 
> F1 appears there.

Are you sure?  You see the minibuffer moving from frame F1 to frame F2, 
without doing anything?  With Emacs 27?  I have Emacs 27.1, and do not see 
this, neither with graphical nor with terminal Emacs.

> > It is indeed not possible to replicate the behavior of Emacs 27 and
> > earlier.  What we have is, for example:
> >
> >   | Emacs 21-27 | Emacs 28 with (setq m-f-s-f t) | Emacs 28 with (setq m-f-s-f 
> > nil)
> > A | MB1 on F1   | MB1 on F2                      | MB1 on F1
> > B | MB1+2 on F2 | MB1+2 on F2                    | MB1 on F1, MB2 on F2 [1]
> >
> > A: type C-x C-f on frame F1, switch to frame F2
> > B: type C-x C-f on frame F1, switch to frame F2, type M-:
>
> Right.  Needs 'enable-recursive-minibuffers' non-nil to replicate.

Or using a command which temporarily sets enable-recursive-minibuffers, 
like C-x 8 RET or C-h f or C-h w or...  But without 
enable-recursive-minibuffers this patch and discussion would not take 
place, you simply get a "Command attempted to use minibuffer while in 
minibuffer".  In any case, it is not possible to replicate the behavior of 
Emacs 21-27, which is IMO not a good thing, especially for something as 
central to Emacs as the minibuffer.

> > [1] There is also a severe regression in this case.  Type C-x C-f on 
> > frame F1, switch to frame F2, type M-:.  "Find file" is still visible 
> > in the miniwindow on frame F1; switch to frame F1.
> >
> > Experiment 1: Type the name of a file and RET.  You'll get the error 
> > message "End of file during parsing", and MB2 on frame F2 will be left. 
> > MB1 is now unuseable, and impossible to leave, it will stay on F1 
> > whatever you do.
>
> 'keyboard-escape-quit' gets me out.  While this should be the last 
> resort only, it happened to me occasionally before Alan's changes. Yet, 
> your scenario must be fixed.

Indeed, 'abort-recursive-edit' also works.  But as you write these 
commands should be used in last resort, especially as they are not known 
to newcomers.

> > Experiment 2: Type C-g.  MB2 on frame F2 will be left, and "Find file" 
> > will stay in MB1 on frame F1.  However you cannot use it anymore, the 
> > keymap of MB1 is now minibuffer-inactive-mode-map.  And like in 
> > experiment 1, you cannot leave it.
>
> Bad indeed.  Must be fixed too.

IMO "fixing" in this case should be going back to the earlier state (the 
Emacs 21-27 behavior), and first trying to _precisely_ define the desired 
new behavior.