bug#34174: 27.0.50; Calling `par' via shell-command-on-region always errors out

[Kaushal Modi <kaushal.modi@gmail.com>]

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Hello,

I have found a regression in the behavior of shell-command-on-region,
though specifically for a third party binary `par'. par can be obtained
from http://www.nicemice.net/par/.

How to reproduce the error:

1. Install par and put it in PATH (sorry, I cannot reproduce this error
with any other utility).
2. Open emacs -Q.
3. Select the two lines that show up by default in the scratch buffer: ";;
This buffer is for text that is not saved, and for Lisp evaluation.
;; To create a file, visit it with C-x C-f and enter text in its buffer.
".
4. Call `M-| par'.

You will get this error on emacs master emacs -Q , but *not* on emacs 26.1:

===
ERROR in parse_header: buffer was ';; This buffer is for te'
error: client: reader got error Success
===

What's surprising is that I have selected the whole 2 lines to be sent to
par, but the error from par says:

    buffer was ';; This buffer is for te'

I cannot reproduce this error on 26.1.


I looked at the git revision history that affected shell-command-on-region
that affected in recent times, but I couldn't find any.

But I do see
https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=d1ec3a0a8e4d7d56ebc1e4fa743130b9974ac6a8
affecting callproc.c/call-process-region.

Can you please review if that change could have caused this regression?

Thanks.

In GNU Emacs 27.0.50 (build 11, x86_64-pc-linux-gnu, GTK+ Version 2.24.23)
 of 2019-01-22
Repository revision: 9eaf5e052a802a7b0560f983f2bb786e13ce2488
Repository branch: master
Windowing system distributor 'Open Text', version 11.0.11505
System Description: Red Hat Enterprise Linux Workstation release 6.8
(Santiago)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set
ERROR in parse_header: buffer was ';; This buffer is for te'
error: client: reader got error Success

Configured using:
 'configure --with-modules
 --prefix=/home/kmodi/usr_local/apps/6/emacs/master
 '--program-transform-name=s/^ctags$/ctags_emacs/' --with-harfbuzz
 --with-dumping=unexec 'CPPFLAGS=-I/home/kmodi/stowed/include
 -I/home/kmodi/usr_local/6/include -I/usr/include/freetype2
 -I/usr/include' 'CFLAGS=-O2 -march=native'
 'LDFLAGS=-L/home/kmodi/stowed/lib -L/home/kmodi/stowed/lib64
 -L/home/kmodi/usr_local/6/lib -L/home/kmodi/usr_local/6/lib64''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB
NOTIFY INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF
XFT ZLIB TOOLKIT_SCROLL_BARS GTK2 X11 XDBE XIM MODULES THREADS GMP

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

Major mode: Lisp Interaction

Minor modes in effect:
  shell-dirtrack-mode: t
  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
easymenu mml-sec password-cache epa derived epg epg-config gnus-util
rmail rmail-loaddefs time-date mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils shell pcomplete
comint ansi-color ring elec-pair mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd 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 dbusbind inotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 101350 8692)
 (symbols 48 20712 1)
 (strings 32 30382 2230)
 (string-bytes 1 841942)
 (vectors 16 15780)
 (vector-slots 8 517527 12352)
 (floats 8 43 74)
 (intervals 56 255 0)
 (buffers 992 12)
 (heap 1024 25874 879))


--
Kaushal Modi

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