GNU bug report logs - #12502
24.2.50; Debugger messes up current-buffer

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Helmut Eller <eller.helmut <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.2.50; Debugger messes up current-buffer
Date: Mon, 24 Sep 2012 10:31:04 +0200

The debugger now changes the current buffer in the following situation:

1. Create a file foo.el with this code:

(progn
  (require 'cl)
  (defun foo ()
    (with-current-buffer (get-buffer-create "test")
      (let ((b (current-buffer)))
	(debug)
	(assert (eq b (current-buffer)) t))))
  (foo))

2. In the foo.el buffer, evaluate the expression with C-x C-e

3. The debugger pops up with this message:
   Debugger entered: nil

4. Press c (i.e. debugger-continue)

5. The assertion fails with:
  Assertion failed: (eq b (current-buffer)), #<buffer test>, #<buffer foo.el>

This is a regression to older versions.


In GNU Emacs 24.2.50.1 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2012-09-22 on ix
Bzr revision: 110128 cyd <at> gnu.org-20120922032937-yf6yua64ed45tzap
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
Configured using:
 `configure '--with-jpeg=no' '--with-gif=no' '--with-tiff=no''

Message #8 received at 12502 <at> debbugs.gnu.org (full text, mbox):

From: martin rudalics <rudalics <at> gmx.at>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 12502 <at> debbugs.gnu.org
Subject: Re: bug#12502: 24.2.50; Debugger messes up current-buffer
Date: Mon, 24 Sep 2012 14:38:01 +0200

[Message part 1 (text/plain, inline)]

> The debugger now changes the current buffer in the following situation:
[...]
> This is a regression to older versions.

Thanks for the report.  Would the attached patch fix it?

BTW, I notice that you quite often run functions with a current buffer
different from that of the selected window.  In all these cases
`quit-window' might misbehave for you because it does not restore the
buffer that was current at the time the window's buffer was displayed.
So if you see any problems in this context, please tell me.  We then
could try to restore the current buffer (optionally at least) too.

martin

[debug-restore-current-buffer.diff (text/plain, inline)]

=== modified file 'lisp/emacs-lisp/debug.el'
--- lisp/emacs-lisp/debug.el	2012-09-20 13:35:13 +0000
+++ lisp/emacs-lisp/debug.el	2012-09-24 12:30:50 +0000
@@ -273,7 +273,8 @@
 	    (setq debugger-previous-window-height
 		  (window-total-size debugger-window))
 	    ;; Unshow debugger-buffer.
-	    (quit-restore-window debugger-window debugger-bury-or-kill))
+	    (quit-restore-window debugger-window debugger-bury-or-kill)
+	    (set-buffer debugger-old-buffer))
           ;; Restore previous state of debugger-buffer in case we were
           ;; in a recursive invocation of the debugger, otherwise just
           ;; erase the buffer and put it into fundamental mode.

Message #11 received at 12502 <at> debbugs.gnu.org (full text, mbox):

From: Helmut Eller <eller.helmut <at> gmail.com>
To: martin rudalics <rudalics <at> gmx.at>
Cc: 12502 <at> debbugs.gnu.org
Subject: Re: bug#12502: 24.2.50; Debugger messes up current-buffer
Date: Tue, 25 Sep 2012 17:36:19 +0200

On Mon, Sep 24 2012, martin rudalics wrote:

>> The debugger now changes the current buffer in the following situation:
> [...]
>> This is a regression to older versions.
>
> Thanks for the report.  Would the attached patch fix it?

Yes, that seems to fix the problem.  But the save-exursion in line 218
looks now supsisously irrelevant.

> BTW, I notice that you quite often run functions with a current buffer
> different from that of the selected window.  In all these cases
> `quit-window' might misbehave for you because it does not restore the
> buffer that was current at the time the window's buffer was displayed.
> So if you see any problems in this context, please tell me.  We then
> could try to restore the current buffer (optionally at least) too.

I'l look for problems, but I'm not sure what the correct/incorrect
behaviour regarding window management should be.  The old
save-window-excursion worked pretty well for me.

Helmut

Message #14 received at 12502 <at> debbugs.gnu.org (full text, mbox):

From: martin rudalics <rudalics <at> gmx.at>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 12502 <at> debbugs.gnu.org
Subject: Re: bug#12502: 24.2.50; Debugger messes up current-buffer
Date: Tue, 25 Sep 2012 18:45:27 +0200

> Yes, that seems to fix the problem.  But the save-exursion in line 218
> looks now supsisously irrelevant.

Maybe.  There's another one nested inside.  I know next to nothing about
the internals of the debugger.

> I'l look for problems, but I'm not sure what the correct/incorrect
> behaviour regarding window management should be.  The old
> save-window-excursion worked pretty well for me.

It didn't work at all for people showing the debugger in an extra frame.

martin

Message #19 received at 12502-done <at> debbugs.gnu.org (full text, mbox):

From: martin rudalics <rudalics <at> gmx.at>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 12502-done <at> debbugs.gnu.org
Subject: Re: bug#12502: 24.2.50; Debugger messes up current-buffer
Date: Wed, 03 Oct 2012 11:14:55 +0200

>> Thanks for the report.  Would the attached patch fix it?
>
> Yes, that seems to fix the problem.

Installed.  Bug closed.

> But the save-exursion in line 218
> looks now supsisously irrelevant.

I left it in because IIUC it can't do any harm.

martin

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