GNU bug report logs - #23779
25.0.95; consing "SHELLVAR" onto process-environment doesn't remove it from subprocess env

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#23779: closed (25.0.95; consing "SHELLVAR" onto
 process-environment doesn't remove it from subprocess env)
Date: Mon, 20 Jun 2016 14:23:02 +0000

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Your message dated Mon, 20 Jun 2016 17:21:03 +0300
with message-id <83fus87xgw.fsf <at> gnu.org>
and subject line Re: bug#23779: 25.0.95; consing "SHELLVAR" onto process-environment doesn't remove it from subprocess env
has caused the debbugs.gnu.org bug report #23779,
regarding 25.0.95; consing "SHELLVAR" onto process-environment doesn't remove it from subprocess env
to be marked as done.

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23779: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23779
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From: Noam Postavsky <npostavs <at> users.sourceforge.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.0.95; consing "SHELLVAR" onto process-environment doesn't remove
 it from subprocess env
Date: Thu, 16 Jun 2016 23:33:02 -0400

Start emacs -Q, evaluate the following lisp code (I wrote the return
values after ;=>)

(defun check-env-var (var)
  (catch 'ret
    (dolist (var=val (process-lines "env"))
      (when (string-prefix-p var var=val)
        (throw 'ret var=val)))))

(check-env-var "SHELL");=>"SHELL=/bin/bash"
(let ((process-environment (copy-sequence process-environment)))
  (setenv "SHELL" nil)
  (check-env-var "SHELL"));=>nil
(let ((process-environment (cons "SHELL" process-environment)))
  (check-env-var "SHELL"));=>"SHELL=/bin/bash"
(let ((process-environment (cons "SHELL=" process-environment)))
  (check-env-var "SHELL"));=>"SHELL="

As you can see from the 3rd expression, contrary to its docstring,
consing the env variable "SHELL" onto process-environment has no
effect at all.

process-environment is a variable defined in ‘C source code’.
Its value is
[...]
Documentation:
List of overridden environment variables for subprocesses to inherit.
Each element should be a string of the form ENVVARNAME=VALUE.

Entries in this list take precedence to those in the frame-local
environments.  Therefore, let-binding ‘process-environment’ is an easy
way to temporarily change the value of an environment variable,
irrespective of where it comes from.  To use ‘process-environment’ to
remove an environment variable, include only its name in the list,
without "=VALUE".

[Message part 3 (message/rfc822, inline)]

From: Eli Zaretskii <eliz <at> gnu.org>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: npostavs <at> users.sourceforge.net, schwab <at> linux-m68k.org,
 23779-done <at> debbugs.gnu.org, dgutov <at> yandex.ru
Subject: Re: bug#23779: 25.0.95; consing "SHELLVAR" onto process-environment
 doesn't remove it from subprocess env
Date: Mon, 20 Jun 2016 17:21:03 +0300

> Cc: dgutov <at> yandex.ru, schwab <at> linux-m68k.org, npostavs <at> users.sourceforge.net,
>  23779 <at> debbugs.gnu.org
> From: Paul Eggert <eggert <at> cs.ucla.edu>
> Date: Mon, 20 Jun 2016 00:53:21 +0200
> 
> On 06/19/2016 05:01 PM, Eli Zaretskii wrote:
> >> >I resisted the temptation of cleaning up the surrounding code to
> >> >make it more readable.
> > Feel free to do that on master; I can mark the emacs-25 fix "not to be
> > merged".
> 
> Please don't bother.

OK, thanks.  Pushed as 5f37572 on the emacs-25 branch, and closing.

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