bug#20333: 24.3; Add warning about shell quoting to documentation of combine-and-quote-strings

[Eli Zaretskii <eliz@gnu.org>]

> From: npostavs@users.sourceforge.net
> Date: Sun, 03 Jul 2016 10:03:55 -0400
> Cc: 20333@debbugs.gnu.org
> 
> >From 5a1d23231bcf3c279fd3b09654fb132513748e6c Mon Sep 17 00:00:00 2001
> From: Noam Postavsky <npostavs@gmail.com>
> Date: Sun, 3 Jul 2016 09:56:36 -0400
> Subject: [PATCH v1] Note combine-and-quote-strings doesn't shell quote
> 
> * doc/lispref/processes.texi (Shell Arguments):
> * lisp/subr.el (combine-and-quote-strings): Add a note that
> combine-and-quote-strings doesn't protect arguments against shell
> evaluation (Bug #20333).
> ---
>  doc/lispref/processes.texi | 5 +++++
>  lisp/subr.el               | 5 ++++-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/lispref/processes.texi b/doc/lispref/processes.texi
> index 5bd0b11..b4542f6 100644
> --- a/doc/lispref/processes.texi
> +++ b/doc/lispref/processes.texi
> @@ -215,6 +215,11 @@ Shell Arguments
>  string arguments to be passed to @code{call-process} or
>  @code{start-process}, or for converting such lists of arguments into
>  a single Lisp string to be presented in the minibuffer or echo area.
> +Note that if a shell is involved (e.g., if using
> +@code{call-process-shell-command}), arguments should still be
> +protected by @code{shell-quote-argument};
> +@code{combine-and-quote-strings} is @emph{not} intended to protect
> +special characters from shell evaluation.
>  
>  @defun split-string-and-unquote string &optional separators
>  This function splits @var{string} into substrings at matches for the
> diff --git a/lisp/subr.el b/lisp/subr.el
> index ed2166a..e9e19d3 100644
> --- a/lisp/subr.el
> +++ b/lisp/subr.el
> @@ -3706,7 +3706,10 @@ combine-and-quote-strings
>    "Concatenate the STRINGS, adding the SEPARATOR (default \" \").
>  This tries to quote the strings to avoid ambiguity such that
>    (split-string-and-unquote (combine-and-quote-strings strs)) == strs
> -Only some SEPARATORs will work properly."
> +Only some SEPARATORs will work properly.
> +
> +Note that this is not intended to protect STRINGS from
> +interpretation by shells, use `shell-quote-argument' for that."
>    (let* ((sep (or separator " "))
>           (re (concat "[\\\"]" "\\|" (regexp-quote sep))))
>      (mapconcat
> -- 
> 2.8.0

LGTM, thanks.  This is good for emacs-25.