Re: [PATCH v2 04/29] log: add exhaustive tests for pattern style options & config

From: Junio C Hamano <gitster@pobox.com>
Date: May 16, 2017, 00:50 UTC
Message-ID: <xmqqy3tx4obg.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <CACBZZX4EfWCD3rwQbRJ1TokDkH=7EfoepMd_ipHr5NSv9kWOJg@mail.gmail.com>

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

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> On Mon, May 15, 2017 at 6:57 AM, Junio C Hamano <gitster@pobox.com> wrote:
>> Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:
>>> +             if test_have_prereq PCRE
>>> +             then
>>> +                     # Only PCRE would match [\d]\| with only
>>> +                     # "(1|2)" due to [\d]. POSIX basic would match
>>> +                     # both it and "1", and POSIX extended would
>>> +                     # match neither.
>>
>> OK.  BRE would match because the other side of "\|" is empty to
>> match anything?
>
> Yes. I'll clarify this. It's not just a POSIX basic feature. The same
> is true of extended and perl. E.g.:

Yes, but "\|" won't be taken as alternative in ERE or PCRE, and that is why "[\d]\|" would match everything with BRE (as opposed to others---PCRE matches "(1|2)" not because "\|" is an alternative but because the pattern looks for a digit followed by a literal vert-bar, and ERE does not match any because there is no 'd' followed by a literal vert-bar).

I was mostly reacting to "BRE would match both it and '1'", which singled out "1" as if "1" is special and gives a false impression that it wouldn't have matched if it were "7".

Show 12 quoted lines

>
>     git grep [-E|-P] 'foo|bar'
>
> Both match the same as:
>
>     git grep [-E|-P] '(foo|bar)'
>
>>> +                     git -c grep.patternType=perl log --pretty=tformat:%s \
>>> +                             --grep="[\d]\|" >actual.perl &&
>>> +                     test_cmp expect.perl actual.perl
>>> +             fi &&
>>