bug#24803: Redirection problem with separate minibuffer frame

bug#24803: Redirection problem with separate minibuffer frame

[Stefan Monnier]

Package: Emacs
Version: 26.0.50


I'm seeing redirection problems in my Emacs setup (with separate
minibuffer-only frame).  I suspect it comes from

    commit 421c0512f76683e0b85ea5e1362291c2da4149ba
    Author: Martin Rudalics <rudalics@gmx.at>
    Date:   Mon Oct 17 10:52:01 2016 +0200
    
      Fix frame focus redirection with shared minibuffer windows (Bug#24500)
      
      * src/frame.c (do_switch_frame): Redirect frame focus also when
      the frame switched to has its minibuffer window on the selected
      frame.
      * src/window.c (candidate_window_p): To qualify as candidate
      it's not sufficient for the window's frame to just share the
      minibuffer window - it must be active as well.

I just managed to reliably reproduce one of the symptoms of the problem:

    % emacs -Q --eval "(setq default-frame-alist '((minibuffer)))"
    ... place the minibuffer frame so that half of it covers the main frame ...
    ... now from the minibuffer frame, do
    C-h f car RET

at this point, the stacking order has been changed: the main frame is above
the minibuffer-only frame.  Then I move the mouse into the part of the
minibuffer frame still visible and I type

    ffff

The first `f` should call `find-file` (according to
minibuffer-inactive-mode-map), but instead the `ffff` text gets inserted
into the *scratch* buffer because of some inappropriate focus redirection.
[ This recipe depends on using a window-manager with
  focus-follows-mouse and it might also depend on other aspects of the
  window manager's behavior.  ]

A few years back, I had a problem with focus redirection which I tracked
with the patch below.  I never removed the patch after fixing the bug,
so the first symptom of the new problem was that I started to see "Left
over focus redirection!" messages all the time.  At first I thought it
was my patch at fault, so I disabled it, but since then I started to see
various odd behaviors, which I think all get down to the left over
redirection reproduced in the above recipe.

This said, I also noticed something else: ever since this redirection
problem appeared, I often see my cursor furiously blinking very rapidly
for a very short amount of time, every time I select another frame
(which happens all the time with my focus-follows-mouse WM).  I used to
see this also back when I was tracking that old redirection problem, so
I suspect that we have a redisplay bug/inefficiency that's only
triggered when some redirection is in place.


        Stefan


diff --git a/src/minibuf.c b/src/minibuf.c
index 57eea05..dcafc77 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -338,6 +338,18 @@ If the current buffer is not a minibuffer, return its entire contents.  */)
   return make_buffer_string (prompt_end, PT, 1);
 }
 
+static void
+check_no_redirected_focus (void)
+{
+  Lisp_Object tail, frame;
+  FOR_EACH_FRAME (tail, frame)
+    {
+      if (!NILP (FRAME_FOCUS_FRAME (XFRAME (frame)))
+          && !EQ (FRAME_FOCUS_FRAME (XFRAME (frame)), frame))
+	message ("Left over focus redirection!");
+    }
+}
+
 \f
 /* Read from the minibuffer using keymap MAP and initial contents INITIAL,
    putting point minus BACKUP_N bytes from the end of INITIAL,
@@ -380,6 +392,10 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
   Lisp_Object empty_minibuf;
   Lisp_Object dummy, frame;
 
+
+  if (minibuf_level == 0)
+    record_unwind_protect_void (check_no_redirected_focus);
+
   specbind (Qminibuffer_default, defalt);
   specbind (Qinhibit_read_only, Qnil);
 

bug#24803: Redirection problem with separate minibuffer frame

[martin rudalics]

 > I'm seeing redirection problems in my Emacs setup (with separate
 > minibuffer-only frame).  I suspect it comes from
 >
 >      commit 421c0512f76683e0b85ea5e1362291c2da4149ba
 >      Author: Martin Rudalics <rudalics@gmx.at>
 >      Date:   Mon Oct 17 10:52:01 2016 +0200
 >
 >        Fix frame focus redirection with shared minibuffer windows (Bug#24500)
 >
 >        * src/frame.c (do_switch_frame): Redirect frame focus also when
 >        the frame switched to has its minibuffer window on the selected
 >        frame.
 >        * src/window.c (candidate_window_p): To qualify as candidate
 >        it's not sufficient for the window's frame to just share the
 >        minibuffer window - it must be active as well.

Please revert the frame.c change so we can be sure which of the two is
the real culprit.

 > I just managed to reliably reproduce one of the symptoms of the problem:
 >
 >      % emacs -Q --eval "(setq default-frame-alist '((minibuffer)))"
 >      ... place the minibuffer frame so that half of it covers the main frame ...
 >      ... now from the minibuffer frame, do
 >      C-h f car RET
 >
 > at this point, the stacking order has been changed: the main frame is above
 > the minibuffer-only frame.  Then I move the mouse into the part of the
 > minibuffer frame still visible and I type
 >
 >      ffff
 >
 > The first `f` should call `find-file` (according to
 > minibuffer-inactive-mode-map), but instead the `ffff` text gets inserted
 > into the *scratch* buffer because of some inappropriate focus redirection.
 > [ This recipe depends on using a window-manager with
 >    focus-follows-mouse and it might also depend on other aspects of the
 >    window manager's behavior.  ]

Works as intended on both Windows XP and a GTK+ build with XFCE on
Debian.  I use focus-follows-mouse plus auto-raise-frame though the
minibuffer does _not_ get autoraised when moving the mouse there.
Actually, that's what I would call a misbehavior here ;-)

 > +      if (!NILP (FRAME_FOCUS_FRAME (XFRAME (frame)))
 > +          && !EQ (FRAME_FOCUS_FRAME (XFRAME (frame)), frame))
[...]
 > +  if (minibuf_level == 0)

Hmm... This seems to indicate that I do not remove the redirection when
exiting the minibuffer.  Could you try to augment in read_minibuf_unwind

   if (minibuf_level == 0)
     resize_mini_window (XWINDOW (window), 0);

to something that for each frame redirects focus to itself?  Obviously,
this might fail with recursive minibuffer invocations from two different
frames ...

martin

bug#24803: Redirection problem with separate minibuffer frame

[Stefan Monnier]

> Please revert the frame.c change so we can be sure which of the two is
> the real culprit.

Reverting the frame.c change seems to fix the problem.

BTW I also just noticed that the bogus (the one I get at the end of my
recipe) focus is "mutual":
- when the mouse points at the minibuffer window, the focus is in the
  *scratch* buffer.
- when the mouse points in the *scratch* window, the focus is in the
  minibuffer!

> Works as intended on both Windows XP and a GTK+ build with XFCE on
> Debian.  I use focus-follows-mouse plus auto-raise-frame though the
> minibuffer does _not_ get autoraised when moving the mouse there.
> Actually, that's what I would call a misbehavior here ;-)

I don't use auto-raise of any kind.  But yes, it's probably dependent on
some aspect of the window manager event sequences.

> Hmm... This seems to indicate that I do not remove the redirection when
> exiting the minibuffer.  Could you try to augment in read_minibuf_unwind
>
>   if (minibuf_level == 0)
>     resize_mini_window (XWINDOW (window), 0);
>
> to something that for each frame redirects focus to itself?

Still haven't found the time to try this, but I just want to mention
that until recently, the focus redirection was usually nil rather than
"redirected to itself".

I'm not sure if there should be a difference between these two states,
but I have the suspicion that not all the C code handles those two
states in the same way (then again, last time I looked at the
redirection code, I concluded that I just don't understand how it's
supposed to work, so maybe it's just my misunderstanding).


        Stefan

bug#24803: Redirection problem with separate minibuffer frame

[martin rudalics]

 > Reverting the frame.c change seems to fix the problem.

As expected.  Please keep it this way for the moment.  If we don't find
a better solution, I'll do the revert on master.  Currently, I'd be more
interested if someone else sees the same or a similar problem.

 > BTW I also just noticed that the bogus (the one I get at the end of my
 > recipe) focus is "mutual":
 > - when the mouse points at the minibuffer window, the focus is in the
 >    *scratch* buffer.
 > - when the mouse points in the *scratch* window, the focus is in the
 >    minibuffer!

With emacs -Q and just ‘display-buffer-alist’ customized and no
minibuffer dialogue in process?  Queer.

 >> Hmm... This seems to indicate that I do not remove the redirection when
 >> exiting the minibuffer.  Could you try to augment in read_minibuf_unwind
 >>
 >>    if (minibuf_level == 0)
 >>      resize_mini_window (XWINDOW (window), 0);
 >>
 >> to something that for each frame redirects focus to itself?
 >
 > Still haven't found the time to try this, but I just want to mention
 > that until recently, the focus redirection was usually nil rather than
 > "redirected to itself".

Indeed you would have to set it to nil.  And obviously my proposal is
not a solution anyway since someone might want to redirect focus without
any minibuffers being involved in the first place.

 > I'm not sure if there should be a difference between these two states,
 > but I have the suspicion that not all the C code handles those two
 > states in the same way (then again, last time I looked at the
 > redirection code, I concluded that I just don't understand how it's
 > supposed to work, so maybe it's just my misunderstanding).

I'm currently struggling with focus redirection in various contexts -
for example, when redirecting focus from a parent to a child frame and
back again.  So far it's a lost battle :-(

martin

bug#24803: Redirection problem with separate minibuffer frame

[martin rudalics]

 >  > Reverting the frame.c change seems to fix the problem.
 >
 > As expected.  Please keep it this way for the moment.  If we don't find
 > a better solution, I'll do the revert on master.

I reverted the change now for Emacs 27.2.  Please consider closing this
bug if there are no further complications.

Thanks, martin

bug#24803: Redirection problem with separate minibuffer frame

[martin rudalics]

tags 24803 fixed
close 24803 27.2
quit
> I reverted the change now for Emacs 27.2.  Please consider closing this > bug if there are no further complications.
Bug marked as done now.

martin