bug#33510: 26.1.90; M-x man crashes if invoking man fails

bug#33510: 26.1.90; M-x man crashes if invoking man fails

[Richard Copley]

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If invoking 'man' fails, M-x man crashes, with errors:
  error in process sentinel: read-event: Buffer is read-only: #<buffer *Man
xyzzy*>
  error in process sentinel: Buffer is read-only: #<buffer *Man xyzzy*>

To reproduce from 'emacs -Q':
M-x man RET
xyzzy RET

In GNU Emacs 26.1.90 (build 1, x86_64-w64-mingw32)
 of 2018-11-22 built on [redacted]
Repository revision: 93242b14769ed40ae58e89d0ea45df8872f59869
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Invoking man xyzzy in the background
error in process sentinel: read-event: Buffer is read-only: #<buffer *Man
xyzzy*>
error in process sentinel: Buffer is read-only: #<buffer *Man xyzzy*>

Configured using:
 'configure --config-cache --with-modules --without-pop --without-dbus
 --without-gconf --without-gsettings 'CFLAGS=-O3 -ggdb3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS MODULES THREADS LCMS2

Important settings:
  value of $LANG: ENG
  locale-coding-system: cp1252

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
mml-sec password-cache epa derived epg epg-config gnus-util rmail
rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils imenu man easymenu cl-loaddefs cl-lib
ansi-color elec-pair time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp disp-table
term/w32-win w32-win w32-vars term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded 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 threads w32notify w32 lcms2 multi-tty make-network-process
emacs)

Memory information:
((conses 16 99435 9461)
 (symbols 48 20447 1)
 (miscs 40 40 95)
 (strings 32 30599 928)
 (string-bytes 1 792435)
 (vectors 16 14455)
 (vector-slots 8 505151 11586)
 (floats 8 56 218)
 (intervals 56 239 8)
 (buffers 992 12))

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bug#33510: 26.1.90; M-x man crashes if invoking man fails

[Eli Zaretskii]

> From: Richard Copley <rcopley@gmail.com>
> Date: Mon, 26 Nov 2018 12:34:41 +0000
> 
> If invoking 'man' fails, M-x man crashes, with errors:
>   error in process sentinel: read-event: Buffer is read-only: #<buffer *Man xyzzy*>
>   error in process sentinel: Buffer is read-only: #<buffer *Man xyzzy*>

Signaling an error is a far cry from a crash...

> To reproduce from 'emacs -Q':
> M-x man RET
> xyzzy RET

I cannot reproduce this, at least not on GNU/Linux: there, I get

  Can't find the xyzzy manpage

as expected.  On MS-Windows I get this instead:

  No manual entry for xyzzy.

So I think the problem is triggered by something done by the 'man'
port you have installed (an MSYS2 'man', perhaps?).  What does it say
if you invoke it from the shell prompt?

bug#33510: 26.1.90; M-x man crashes if invoking man fails

[Eli Zaretskii]

[Please use Reply All to have the discussion recorded by the tracker.]

> From: Richard Copley <rcopley@gmail.com>
> Date: Mon, 26 Nov 2018 17:02:33 +0000
> 
> On Mon, 26 Nov 2018 at 16:21, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>  > From: Richard Copley <rcopley@gmail.com>
>  > Date: Mon, 26 Nov 2018 12:34:41 +0000
>  > 
>  > If invoking 'man' fails, M-x man crashes, with errors:
>  >   error in process sentinel: read-event: Buffer is read-only: #<buffer *Man xyzzy*>
>  >   error in process sentinel: Buffer is read-only: #<buffer *Man xyzzy*>
> 
>  Signaling an error is a far cry from a crash...
> 
> Yes, sorry.
>  
>  > To reproduce from 'emacs -Q':
>  > M-x man RET
>  > xyzzy RET
> 
>  I cannot reproduce this, at least not on GNU/Linux: there, I get
> 
>    Can't find the xyzzy manpage
> 
>  as expected.  On MS-Windows I get this instead:
> 
>    No manual entry for xyzzy.
> 
>  So I think the problem is triggered by something done by the 'man'
>  port you have installed (an MSYS2 'man', perhaps?).  What does it say
>  if you invoke it from the shell prompt?
> 
> There was no "man" on the path. (Sorry, I didn't realize that at the time.)

Ah, okay.  With that, I _can_ reproduce the error.

bug#33510: 26.1.90; M-x man crashes if invoking man fails

[Eli Zaretskii]

> Date: Mon, 26 Nov 2018 19:18:48 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 33510@debbugs.gnu.org
> 
> > There was no "man" on the path. (Sorry, I didn't realize that at the time.)
> 
> Ah, okay.  With that, I _can_ reproduce the error.

Should be fixed no on the emacs-26 branch.