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Date: Fri, 16 Mar 2012 16:56:44 +0000
To: perl6-compi...@perl.org
Subject: Re: [perl #111796] Rakudo regex regression
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References: <RT-Ticket-111796@perl.org> <4F635375.9000706@faui2k3.org> <rt-3.6.HEAD-4610-1331909504-115.111796-82-0@perl.org>
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From: n...@ccl4.org (Nicholas Clark)
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On Fri, Mar 16, 2012 at 07:51:44AM -0700, Moritz Lenz wrote:

> Somwhere between the 2012.02 release and 2012.02-180-g16bf0f4, test 253 
> in S05-mass/rx.t started to fail:
> 
> eval_dies_ok '/a|&b/', 'alternation and conjunction (|&) - parse error';
> 
> I have no idea what might caused it, but the proper fix probably 
> involves detecting Null Patterns.

Isn't this were a git bisect is a routine way to find out the cause?

(In that, it's proving a very powerful way to find the cause of regressions
in Perl 5 with minimal human effort, a fast machine, and a cup of tea*

And if git bisect on its own isn't easy enough, write a wrapper to automate
as much as possible. I wrote one for perl 5:

https://metacpan.org/module/CORION/perl-5.15.8/Porting/bisect-runner.pl

which tries to make it as easy as taking your failing 1 liner:

perl -e '... stuff that regressed ...'

and changing that to

.../Porting/bisect.pl -e '... stuff that regressed ...'


and off it goes.

No messing with git bisect start, git bisect run, having to make a wrapper
script, getting the build to build at that revision, getting the test case
round the wrong way, etc ...)


Nicholas Clark

* Or other source of amusement whilst the bisect runs for 15 to 30 minutes