[PATCH STABLE] templater: strip single backslash before quotation mark in quoted template

[Augie Fackler]

On Fri, May 08, 2015 at 07:30:03PM +0900, Yuya Nishihara wrote:
> # HG changeset patch
> # User Yuya Nishihara <yuya at tcha.org>
> # Date 1431076286 -32400
> #      Fri May 08 18:11:26 2015 +0900
> # Branch stable
> # Node ID 0dae4fd11c554338c2f0083d259d996e45aa1536
> # Parent  169d2470d283f19f7c94112dc1eff1d355f29f40
> templater: strip single backslash before quotation mark in quoted template

This looks right to me, but I'm not taking it so that someone else can review.

>
> db7463aa080f fixed the issue of double escapes, but it made the following
> template fail with syntax error because of <\">. Strictly speaking, <\">
> appears to be invalid in non-string part, but we are likely to escape <">
> if surrounded by quotes, and we are used to write such templates by trial
> and error.
>
>   [templates]
>   sl = "{tags % \"{ifeq(tag,'tip','',label('log.tag', ' {tag}'))}\"}"
>
> So, for backward compatibility between 2.8.1 and 3.4, a single backslash
> before quotation mark is stripped only in quoted template. We don't care
> for <\"> in string literal in quoted template, which never worked as expected
> before.
>
>   template  result
>   --------- ------------------------
>   {\"\"}    parse error
>   "{""}"    {""} -> <>
>   "{\"\"}"  {""} -> <>
>   {"\""}    {"\""} -> <">
>   '{"\""}'  {"\""} -> <">
>   "{"\""}"  parse error (don't care)
>
> diff --git a/mercurial/templater.py b/mercurial/templater.py
> --- a/mercurial/templater.py
> +++ b/mercurial/templater.py
> @@ -623,7 +623,12 @@ def parsestring(s, quoted=True):
>      if quoted:
>          if len(s) < 2 or s[0] != s[-1]:
>              raise SyntaxError(_('unmatched quotes'))
> -        return s[1:-1]
> +        # de-backslash-ify only <\">. it is invalid syntax in non-string part of
> +        # template, but we are likely to escape <"> in quoted string and it was
> +        # accepted before, thanks to issue4290. <\\"> is unmodified because it
> +        # is ambiguous and it was processed as such before 2.8.1.
> +        q = s[0]
> +        return s[1:-1].replace('\\\\' + q, '\\\\\\' + q).replace('\\' + q, q)
>
>      return s
>
> diff --git a/tests/test-command-template.t b/tests/test-command-template.t
> --- a/tests/test-command-template.t
> +++ b/tests/test-command-template.t
> @@ -2273,6 +2273,25 @@ Test string escaping:
>    <>\n<]>
>    <>\n<
>
> +Test exception in quoted template. single backslash before quotation mark is
> +stripped before parsing:
> +
> +  $ cat <<'EOF' > escquotetmpl
> +  > changeset = "\" \\" \\\" \\\\" {files % \"{file}\"}\n"
> +  > EOF
> +  $ cd latesttag
> +  $ hg log -r 2 --style ../escquotetmpl
> +  " \" \" \\" head1
> +
> +  $ hg log -r 2 -T esc --config templates.esc='{\"invalid\"}\n'
> +  hg: parse error at 1: syntax error
> +  [255]
> +  $ hg log -r 2 -T esc --config templates.esc='"{\"valid\"}\n"'
> +  valid
> +  $ hg log -r 2 -T esc --config templates.esc="'"'{\'"'"'valid\'"'"'}\n'"'"
> +  valid
> +  $ cd ..
> +
>  Test leading backslashes:
>
>    $ cd latesttag
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