bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Ian Kelling]

Repro steps:
emacs -Q
C-h b
click function name link
click back

expected:
go back to the C-h b keymap listing

acutal
in echo area: "Current buffer is not in Help mode"
the help buffer does no change.


The problem does not always happen, but it seems consistent on the first try in a
fresh emacs. Toggling debug on error, gives this trace:

Debugger entered--Lisp error: (error "Current buffer is not in Help mode")
  signal(error ("Current buffer is not in Help mode"))
  error("Current buffer is not in Help mode")
  help-buffer()
  describe-bindings-internal(nil nil)
  describe-bindings(nil #<buffer *scratch*>)
  apply(describe-bindings (nil #<buffer *scratch*>))
  help-xref-go-back(#<buffer *Help*>)
  apply(help-xref-go-back #<buffer *Help*>)
  help-do-xref(63 help-xref-go-back (#<buffer *Help*>))
  help-button-action(#<marker (moves after insertion) at 66 in *Help*>)
  button-activate(#<marker (moves after insertion) at 66 in *Help*> nil)
  push-button(66)
  push-button((mouse-2 (#<window 6 on *Help*> 66 (34 . 106) 107906261 nil 66 (3 .
5) nil (7 . 11) (9 . 19))))
  call-interactively(push-button nil nil)
  command-execute(push-button)



In GNU Emacs 24.3.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.4.2)
 of 2014-03-18 on treetowl
Repository revision: 116779 dgutov@yandex.ru-20140317064809-2mea5nujkyricpny
Windowing system distributor `The X.Org Foundation', version 11.0.11204000
System Description:	Debian GNU/Linux 7.4 (wheezy)

Configured using:
 `configure --enable-link-time-optimization 'CFLAGS=-std=gnu99 -g3 -O2''

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-h b <help-echo> <help-echo> <down-mouse-2> <mouse-1>
<help-echo> <down-mouse-2> <mouse-1> <help-echo> M-x
r e C-g M-x b u g <kp-add> <backspace> <tab> <tab>
<backspace> <backspace> <backspace> <backspace> <backspace>
<backspace> <backspace> <backspace> <backspace> <backspace>
<backspace> <backspace> <backspace> <backspace> r e
p o r t - b <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Type C-x 1 to delete the help window, C-M-v to scroll help.

help-buffer: Current buffer is not in Help mode
Quit
Making completion list...
call-interactively: End of buffer

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils help-fns kmacro two-column iso-transl help-mode
easymenu time-date tooltip electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process dbusbind
gfilenotify dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty emacs)

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[martin rudalics]

 > Repro steps:
 > emacs -Q
 > C-h b
 > click function name link
 > click back
 >
 > expected:
 > go back to the C-h b keymap listing
 >
 > acutal
 > in echo area: "Current buffer is not in Help mode"
 > the help buffer does no change.
 >
 >
 > The problem does not always happen, but it seems consistent on the first try in a
 > fresh emacs. Toggling debug on error, gives this trace:
 >
 > Debugger entered--Lisp error: (error "Current buffer is not in Help mode")
 >    signal(error ("Current buffer is not in Help mode"))
 >    error("Current buffer is not in Help mode")
 >    help-buffer()
 >    describe-bindings-internal(nil nil)
 >    describe-bindings(nil #<buffer *scratch*>)
 >    apply(describe-bindings (nil #<buffer *scratch*>))
 >    help-xref-go-back(#<buffer *Help*>)
 >    apply(help-xref-go-back #<buffer *Help*>)
 >    help-do-xref(63 help-xref-go-back (#<buffer *Help*>))
 >    help-button-action(#<marker (moves after insertion) at 66 in *Help*>)
 >    button-activate(#<marker (moves after insertion) at 66 in *Help*> nil)
 >    push-button(66)
 >    push-button((mouse-2 (#<window 6 on *Help*> 66 (34 . 106) 107906261 nil 66 (3 .
 > 5) nil (7 . 11) (9 . 19))))
 >    call-interactively(push-button nil nil)
 >    command-execute(push-button)

Confirmed.  Thanks for caring to provide a simple scenario.

I could fix this by restoring the code of `describe-bindings-internal'
from Emacs 24.3.  But the behavior of `help-xref-go-back' here is
erratic per se: It does not restore the earlier contents of the bindings
from the *scratch* buffer but IIUC those of the *Help* buffer and I'm
not sure whether that's what we want (I think we don't).

Juri, any opinions?

martin

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Eli Zaretskii]

> Date: Mon, 07 Apr 2014 09:48:43 +0200
> From: martin rudalics <rudalics@gmx.at>
> 
>  > Debugger entered--Lisp error: (error "Current buffer is not in Help mode")
>  >    signal(error ("Current buffer is not in Help mode"))
>  >    error("Current buffer is not in Help mode")
>  >    help-buffer()
>  >    describe-bindings-internal(nil nil)
>  >    describe-bindings(nil #<buffer *scratch*>)
>  >    apply(describe-bindings (nil #<buffer *scratch*>))
>  >    help-xref-go-back(#<buffer *Help*>)
>  >    apply(help-xref-go-back #<buffer *Help*>)
>  >    help-do-xref(63 help-xref-go-back (#<buffer *Help*>))
>  >    help-button-action(#<marker (moves after insertion) at 66 in *Help*>)
>  >    button-activate(#<marker (moves after insertion) at 66 in *Help*> nil)
>  >    push-button(66)
>  >    push-button((mouse-2 (#<window 6 on *Help*> 66 (34 . 106) 107906261 nil 66 (3 .
>  > 5) nil (7 . 11) (9 . 19))))
>  >    call-interactively(push-button nil nil)
>  >    command-execute(push-button)
> 
> Confirmed.  Thanks for caring to provide a simple scenario.
> 
> I could fix this by restoring the code of `describe-bindings-internal'
> from Emacs 24.3.  But the behavior of `help-xref-go-back' here is
> erratic per se: It does not restore the earlier contents of the bindings
> from the *scratch* buffer but IIUC those of the *Help* buffer and I'm
> not sure whether that's what we want (I think we don't).

Can you tell why you replaced a literal "*Help*" with a call to
help-buffer?  That change was part of your pixel-resizing changes, but
it doesn't sound related to me, and the ChangeLog entry doesn't
provide any explanations to convince me otherwise.

Also, describe-bindings-internal is only called from this single
place, so I see no reason to support some other help buffers.  Do you?

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Stefan Monnier]

> Can you tell why you replaced a literal "*Help*" with a call to
> help-buffer?

I think it's just generally preferable.

> That change was part of your pixel-resizing changes, but
> it doesn't sound related to me, and the ChangeLog entry doesn't
> provide any explanations to convince me otherwise.

> Also, describe-bindings-internal is only called from this single
> place, so I see no reason to support some other help buffers.  Do you?

You might have done M-x rename-uniquely.
Does the patch below help?


        Stefan


=== modified file 'lisp/help.el'
--- lisp/help.el	2014-04-05 18:33:55 +0000
+++ lisp/help.el	2014-04-07 18:16:00 +0000
@@ -485,8 +485,11 @@
   (or buffer (setq buffer (current-buffer)))
   (help-setup-xref (list #'describe-bindings prefix buffer)
 		   (called-interactively-p 'interactive))
-  (with-current-buffer buffer
-    (describe-bindings-internal nil prefix)))
+  (with-help-window (help-buffer)
+    ;; Be aware that `describe-buffer-bindings' puts its output into
+    ;; the current buffer.
+    (with-current-buffer (help-buffer)
+      (describe-buffer-bindings buffer prefix))))
 
 ;; This function used to be in keymap.c.
 (defun describe-bindings-internal (&optional menus prefix)
@@ -497,6 +500,7 @@
 \(Ordinarily these are omitted from the output.)
 The optional argument PREFIX, if non-nil, should be a key sequence;
 then we display only bindings that start with that prefix."
+  (declare (obsolete describe-buffer-bindings "24.4"))
   (let ((buf (current-buffer)))
     (with-help-window (help-buffer)
       ;; Be aware that `describe-buffer-bindings' puts its output into

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[martin rudalics]

 > Can you tell why you replaced a literal "*Help*" with a call to
 > help-buffer?  That change was part of your pixel-resizing changes, but
 > it doesn't sound related to me, and the ChangeLog entry doesn't
 > provide any explanations to convince me otherwise.

I tested `window-text-pixel-size' mostly by switching forward and
backward between help buffers because these are the only ones here whose
text size is not an integral multiple of the nominal character size.  In
the course of testing I found some problems with help buffers and fixed
them on the fly.

Later, when I installed the pixelwise changes, I was afraid to back out
some related ones like the one we talk about here.  But note that the
bug which is the subject of the current thread was implicitly caused by
reverting a behavior erroneously introduced in Emacs 24.3 (see the
threads of bug#16816 and bug#17007 for details).

 > Also, describe-bindings-internal is only called from this single
 > place, so I see no reason to support some other help buffers.  Do you?

I think Stefan explained that meanwhile.

martin

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[martin rudalics]

 > Does the patch below help?

It fixes the OP's problem so please check it in.  But when hitting the
back button you don't get the previous contents.  I suppose we have to
add the original buffer to the `help-args' of that button, but I leave
that to Juri.  In any case, the behavior is broken since Emacs 24.3 at
least (but I suppose it's broken ever since).

martin

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Juri Linkov]

> It fixes the OP's problem so please check it in.  But when hitting the
> back button you don't get the previous contents.  I suppose we have to
> add the original buffer to the `help-args' of that button, but I leave
> that to Juri.

In the recent discussion at http://thread.gmane.org/gmane.emacs.devel/168353
the idea was to store the previous content in hidden Help buffers
(buffer names starting with a space).

> In any case, the behavior is broken since Emacs 24.3 at least
> (but I suppose it's broken ever since).

For `C-h b' it was broken by design because after killing the initial buffer:

1. C-h b
2. click function name link
3. kill *scratch*
4. click back

clicking on [back] fails with the error "Selecting deleted buffer".

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[martin rudalics]

 > For `C-h b' it was broken by design because after killing the initial buffer:
 >
 > 1. C-h b
 > 2. click function name link
 > 3. kill *scratch*
 > 4. click back
 >
 > clicking on [back] fails with the error "Selecting deleted buffer".

Well, we could handle that more smoothly.  But the principal problem
remains - namely that going back all of a sudden describes different
bindings.

martin

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Eli Zaretskii]

> Date: Tue, 08 Apr 2014 09:13:56 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: ian@iankelling.org, 17210@debbugs.gnu.org
> 
> note that the bug which is the subject of the current thread was
> implicitly caused by reverting a behavior erroneously introduced in
> Emacs 24.3 (see the threads of bug#16816 and bug#17007 for details).

Only by side effect, because all that stuff had nothing to do with
which buffer is current when describe-bindings-internal is called.

>  > Also, describe-bindings-internal is only called from this single
>  > place, so I see no reason to support some other help buffers.  Do you?
> 
> I think Stefan explained that meanwhile.

As long as describe-bindings invokes describe-bindings-internal with
the current buffer set to the buffer whose keybindings we want to
describe, I don't understand how the multitude of Help buffer can be
relevant to the issue at hand.

My problem with help-buffer is that calling it requires intimate
understanding of its internal logic, because the caller doesn't
necessarily know whether help-xref-following is bound to nil or not.
Without knowing that, whoever calls help-buffer can easily trip on
this problem.  So it sounds like help-buffer is only suitable for
callers who bind help-xref-following themselves, or have tight
relationships with functions that do.  describe-bindings-internal
doesn't, so I don't see how it can be clean for it to call that
function.

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Eli Zaretskii]

> Date: Tue, 08 Apr 2014 09:14:04 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: ian@iankelling.org, 17210@debbugs.gnu.org, 
>  Juri Linkov <juri@jurta.org>
> 
>  > Does the patch below help?
> 
> It fixes the OP's problem so please check it in.  But when hitting the
> back button you don't get the previous contents.

If "back" doesn't get you back, then it isn't really a solution, is
it?

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[martin rudalics]

 > If "back" doesn't get you back, then it isn't really a solution, is
 > it?

My first conclusion was wrong.  "back" gets me the right buffer but it
gives me different contents.  After C-h b my first 12 lines of the
*Help* buffer are


Key translations:
key             binding
---             -------

C-x		Prefix Command
<double-down-mouse-1> mouse--down-1-maybe-follows-link
<down-mouse-1>	mouse--down-1-maybe-follows-link

C-x 8		iso-transl-ctl-x-8-map

C-x 8 SPC	
...


and *Help* has 1050 lines while after going to some function and hitting
"back" these lines are


Key translations:
key             binding
---             -------

C-x		Prefix Command
A-SPC		
A-!		¡
A-"		Prefix Command
A-$		¤
A-'		Prefix Command
A-*		Prefix Command
A-+		±
...


and *Help* has 1637 lines.  Confusing.  I think I'll have to debug
`describe-buffer-bindings' to find out what happens.

martin

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Eli Zaretskii]

> Date: Tue, 08 Apr 2014 18:34:38 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: monnier@IRO.UMontreal.CA, ian@iankelling.org, 17210@debbugs.gnu.org, 
>  juri@jurta.org
> 
>  > If "back" doesn't get you back, then it isn't really a solution, is
>  > it?
> 
> My first conclusion was wrong.  "back" gets me the right buffer but it
> gives me different contents.

That is a different problem, and AFAIK it is not new: try the same in
Emacs from before your pixelwise resize changes, and I think you will
see the same behavior.

> and *Help* has 1637 lines.  Confusing.  I think I'll have to debug
> `describe-buffer-bindings' to find out what happens.

I think it simply describes bindings in another buffer (*Help* instead
of *scratch*).

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[martin rudalics]

 >> My first conclusion was wrong.  "back" gets me the right buffer but it
 >> gives me different contents.
 >
 > That is a different problem, and AFAIK it is not new: try the same in
 > Emacs from before your pixelwise resize changes, and I think you will
 > see the same behavior.

I know.

 > I think it simply describes bindings in another buffer (*Help* instead
 > of *scratch*).

That's what I thought.  But the same buffer (e.g. *scratch*) is passed
to `describe-buffer-bindings' in both cases.  I'm sure that following
the links forward and backward is responsible but why has that such
drastic consequences?

martin

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[martin rudalics]

 > That's what I thought.  But the same buffer (e.g. *scratch*) is passed
 > to `describe-buffer-bindings' in both cases.  I'm sure that following
 > the links forward and backward is responsible but why has that such
 > drastic consequences?

It's `describe-bindings' itself, some sort of Heisenbug.

martin

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Andreas Schwab]

martin rudalics <rudalics@gmx.at> writes:

> and *Help* has 1050 lines while after going to some function and hitting
> "back" these lines are
>
>
> Key translations:
> key             binding
> ---             -------
>
> C-x		Prefix Command
> A-SPC		
> A-!		¡
> A-"		Prefix Command
> A-$		¤
> A-'		Prefix Command
> A-*		Prefix Command
> A-+		±
> ...
>
>
> and *Help* has 1637 lines.

This is normal.  Listing the key translations autoloads iso-transl which
installs more bindings as a side effect.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

bug#17210: 24.3.50; help mode [back] link to a C-h b keybind listing fails with message "Current buffer is not in Help mode"

[Stefan Monnier]

> It fixes the OP's problem so please check it in.

Thanks, installed.


        Stefan