Re: [PATCH v2] t5510: replace 'origin' with URL more carefully (was Re: Test Failure t5510,t5562 - was RE: [ANNOUNCE] Git v2.37.0-rc1)

From: Jeff King <peff@peff.net>
To: "SZEDER Gábor" <szeder.dev@gmail.com>
Cc: Derrick Stolee <derrickstolee@github.com>,
	rsbecker@nexbridge.com, 'Junio C Hamano' <gitster@pobox.com>,
	git@vger.kernel.org, avarab@gmail.com
Subject: Re: [PATCH v2] t5510: replace 'origin' with URL more carefully (was Re: Test Failure t5510,t5562 - was RE: [ANNOUNCE] Git v2.37.0-rc1)
Date: Tue, 21 Jun 2022 06:07:34 -0400	[thread overview]
Message-ID: <YrGYZieKgm4z3mZh@coredump.intra.peff.net> (raw)
In-Reply-To: <20220621092915.GD1689@szeder.dev>

On Tue, Jun 21, 2022 at 11:29:15AM +0200, SZEDER Gábor wrote:

> > So perhaps something like:
> > 
> >   perl -e '
> >     my ($cmdline, $url) = @ARGV;
> >     $cmdline =~ s[origin(?!/)][quotemeta($url)]ge;
> 
> I don't like this "(?!/)" magic, because I haven't got the slightest
> idea of what it might do by merely looking at it, and these characters
> are not exactly easy to search for.

Yeah, I hadn't really dug into the rest of the thread and didn't
understand what that part was trying to do. So I left it untouched in my
examples as an exercise for the reader. :)

> The good old "add a space prefix and suffix" trick can help to easily
> match the "origin" word even when it stands alone, but, alas, the
> result is still not as simple as I'd like with the \s and the string
> concatenation:
> 
>   perl -e '
>     new_cmdline=$(perl -e '
>             my ($cmdline, $url) = @ARGV;
>             $cmdline =~ s[\sorigin\s][" " . quotemeta($url) . " "]ge;
>             print $cmdline;
>     ' -- " $cmdline " "$remote_url")

If you do:

  $url = quotemeta($url);

then you can drop the "e" from the regex, which gets rid of the gross
concatenation:

  $cmdline =~ s[\sorigin\s][ $url ];

I think "\b" for a word boundary would avoid the whitespace
prefix/suffix hackery, but it also matches non-alphabetics (like "/").
You could use alternation, though, like:

  $ cmdline='origin notorigin origin originnot origin/foo origin'
  $ remote_url=real_url
  $ perl -e '
      my ($cmdline, $url) = @ARGV;
      $url = quotemeta($url);
      $cmdline =~ s/(\s|^)origin(\s|$)/$1$url$2/g;
      print $cmdline;
    ' "$cmdline" "$remote_url"
  real_url notorigin real_url originnot origin/foo real_url

Negative lookbehind and lookahead get rid of the "$1" and "$2", but they
are magical-looking, as you noted above. Possibly "/x" and some
whitespace would make the whole thing more readable.

-Peff