Re: [BUG-ish] diff compaction heuristic false positive

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> On Fri, Jun 10, 2016 at 03:50:43AM -0400, Jeff King wrote:
>
>> I found a false positive with the new compaction heuristic in v2.9:
>> [...]
>
> And by the way, this is less "hey neat, I found a case" and more "wow,
> this is a lot worse than I thought".
>
> I diffed the old and new output for the top 10,000 commits in this
> particular ruby code base. There were 45 commits with changed diffs.
> Spot-checking them manually, a little over 1/3 of them featured this bad
> pattern. The others looked like strict improvements.
>
> That's a lot worse than the outcomes we saw on other code bases earlier.
> 1/3 bad is still a net improvement, so I dunno. Is this worth worrying
> about? Should we bring back the documentation for the knob to disable
> it? Should we consider making it tunable via gitattributes?
>
> I don't think that last one really helps; the good cases _and_ the bad
> ones are both in ruby code (though certainly the C code we looked at
> earlier was all good).
>
> It may also be possible to make it Just Work by using extra information
> like indentation. I haven't thought hard enough about that to say.
>
> -Peff

I recall saying "we'd end up being better in some and worse in
others" at the very beginning.  How about toggling the default back
for the upcoming release, keeping the experimentation knob in the
code, and try different heuristics like the "indentation" during the
next cycle?