[PATCH 0/2] merging renames of empty files

From: Jeff King <peff@peff.net>
Date: Mar 22, 2012, 22:46 UTC
Message-ID: <20120322224651.GA14874@sigill.intra.peff.net>
In-Reply-To: <7vwr6cwiux.fsf@alter.siamese.dyndns.org>

On Thu, Mar 22, 2012 at 12:12:06PM -0700, Junio C Hamano wrote:

Show 10 quoted lines

> Jeff King <peff@peff.net> writes:
> 
> > That is a slight layering violation, in that we are making assumptions
> > about how the diffcore-rename subsystem works.
> 
> I do not think I have to say any more than that.  The special case we want
> to have is for the "empty to empty" case and nothing else, and I do not
> want to see people having to remember to look at the merge-recursive code
> if/when rename detection starts to treat "empty to small" as "rename with
> minor modification."

Here's a 2-patch series to replace the old 3/3 (they go on top of the first two cleanups from the previous iteration).

  [1/2]: teach diffcore-rename to optionally ignore empty content
  [2/2]: merge-recursive: don't detect renames of empty files

Thinking on this more, it is actually a more generic problem than just empty files. It is really a problem of having generic placeholder files with the same content. So a fully general solution would be something like a gitattribute for "don't do renames on this". However, in practice, these placeholder files are empty (since any non-empty file is likely to actually have different content). So I think just dropping the empty files as rename candidates is a pretty good heuristic, and it's nice and simple.

After responding to Jonathan, I'm on the fence about whether diff should follow the same heuristic. I left the diff behavior unchanged, but a 3/2 that turns it off by default would be a trivial one-liner.

-Peff