From: Junio C Hamano <gitster@pobox.com>
Date: Wed, 05 Nov 2008 01:30:20 GMT
Subject: Re: git log -S doesn't find some commits
Message-ID: <7vy6zzm02b.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <877i7jrp67.fsf@gollum.intra.norang.ca>

Bernt Hansen <bernt@norang.ca> writes:

> Junio C Hamano <gitster@pobox.com> writes:
> ...
>> There seems to be a misconception on what -S<foo> does.  It does *NOT*
>> grep for string <foo> in the patch text.  It counts number of <foo> in
>> preimage and postimage and decides that the commit is worth showing iff
>> they differ.
>>
>> If you look at, for example (B):
>>
>>     http://repo.or.cz/w/org-mode.git?a=commitdiff;h=837c81ce51
>>
>> You can see that in org-publish.el, org-publish-validate-link appears once
>> as removed and once as added, so the total number of the appearance of the
>> symbol in preimage and postimage are the same.
>
> Now I get it :)
>
> Thanks both of you!

By the way, I would not be opposed to a new feature, perhaps triggered
with -G<foo>, that acts as if it is grepping inside the patch text.

The reason behind -S<foo>'s behaviour is because it was designed as a part
ofa "incremetal digging" tool before the current "git-blame" that allows
to track even line-movements.

That is, you could write a tool to help the following interactively:

 (1) get interested in a block of text in a recent version;

 (2) feed that to 'git log' like this:

 	git log -1 -p -S"$potentially_multi_line_text" $rev

     this will find an old rev R whose parent R^ did not have the lines
     in the exact form you fed with -S.

 (3) inspect the output, and decide what to do next:

     (3-a) you may want to adjust the text you look for, taking into
     account how the neighbouring lines used to look like in R^, and run
     another "git log -S" starting at R^; and/or

     (3-b) you may want to run "git grep" for the text in the entire
     tree in R^, to see if this was a code refactoring that consolidates
     multiple copies of the same thing into a single place.

     and go back to step (2).


cf. http://thread.gmane.org/gmane.comp.version-control.git/27/focus=217