From: Jeff King <peff@peff.net>
Date: Thu, 04 Aug 2016 20:01:58 GMT
Subject: Re: [PATCH 0/8] Better heuristics make prettier diffs
Message-ID: <20160804200157.6xq67ceulwyvl7mv@sigill.intra.peff.net>
In-Reply-To: <xmqqy44c1f90.fsf@gitster.mtv.corp.google.com>

On Thu, Aug 04, 2016 at 12:54:51PM -0700, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > Not that you probably need more random cases of C code, but I happened
> > to be looking at a diff in git.git today, b333d0d6, which is another
> > regression for the compaction heuristic.
> 
> Wow, that one is _really_ bad.  Does it have something to do with
> the removal being at the very end of the file?

I think so. If it were:

  func1() {
     ... unique stuff ...
     ... shared ending ...
  }

  func2() {
     ... more unique stuff ...
     ... shared ending ...
  }

  unrelated_func() {
  }

and we dropped func2, then I think the blank line between func2() and
unrelated_func() would cause the compaction heuristic to stop shifting.

OTOH, if it were:

  func2() {
     ...
  }
  unrelated_func() {
  }

with no newline, you get a similar badly-shifted diff (which is not
surprising, as we were given no syntactic hint that "func2" is a
separate unit from "unrelated_func").

-Peff