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bug#58343: 29.0.50; ELisp code run in "inconsitent" selected-window stat
From: |
Alan Mackenzie |
Subject: |
bug#58343: 29.0.50; ELisp code run in "inconsitent" selected-window state |
Date: |
Wed, 12 Oct 2022 18:08:47 +0000 |
Hello, Stefan.
On Thu, Oct 06, 2022 at 20:06:25 -0400, Stefan Monnier wrote:
> Package: Emacs
> Version: 29.0.50
> Hi Alan and friends,
> In commit dfa3e6f424b20fe27d9041b2ce7d69811df5d8cd, Alan added the
> following code to do_switch_frame:
> diff --git a/src/frame.c b/src/frame.c
> index ccac18d23c2..dc8045f41e6 100644
> --- a/src/frame.c
> +++ b/src/frame.c
> @@ -1564,6 +1564,13 @@ do_switch_frame (Lisp_Object frame, int track, int
> for_deletion, Lisp_Object nor
> if (! FRAME_MINIBUF_ONLY_P (XFRAME (selected_frame)))
> last_nonminibuf_frame = XFRAME (selected_frame);
> + /* If the selected window in the target frame is its mini-window, we
> move
> + to a different window, the most recently used one, unless there is a
> + valid active minibuffer in the mini-window. */
> + if (EQ (f->selected_window, f->minibuffer_window)
> + && NILP (Fminibufferp (XWINDOW (f->minibuffer_window)->contents,
> Qt)))
> + Fset_frame_selected_window (frame, call1 (Qget_mru_window, frame),
> Qnil);
> +
> Fselect_window (f->selected_window, norecord);
> /* We want to make sure that the next event generates a frame-switch
> the problem with this is that it calls `Qget_mru_window` which is ELisp
> code, and that we're in the very middle of changing the selected frame,
> so we have already changed the `selected-frame` variable a few lines
> earlier, but the select-window has not yet been adjusted accordingly.
> Running ELisp code in a state where (selected-window) and
> (frame-selected-window) aren't equal is a recipe for problems. I have
> already wasted many hours in the past tracking down bugs linked to this
> kind of situation (back when the mode-line was processed in such an
> inconsistent state, for example), and I really don't want to go there.
> So we should arrange to run this `get-mru-window` function at some other
> time, for example a few lines earlier before we set `selected-frame`.
> I don't understand this code nearly enough to know how to move the code,
> because it probably interacts with the other statements in non-trivial
> ways, so the patch below is just a naive suggestion (it seems to work
> here without triggering my many sprinkled assertions checking that
> `EQ (XFRAME (selected_frame)->selected_window, selected_window)`,
> but it's a far cry from a confirmation that it's right).
> Hopefully someone here is aware of some of the potential pitfalls.
One minor problem I see at the moment is that the call to
move_minibuffers_onto_frame wasn't moved together with the surrounding
code. With its current calling convention, it needs to be called
_after_ selected_frame has been set, because it uses selected_frame.
Is there any reason this function call was left where it was? Or could
it just be moved, too? Otherwise, its calling convention will need to
be adapted.
Other than that, I haven't seen any problems as yet, though I admit I
haven't tried it out.
> Stefan
[ .... ]
--
Alan Mackenzie (Nuremberg, Germany).