Correctly detecting modified paths in merge commits?

[Dun Peal <dunpealer@gmail.com>]

Hi.

We wrote a post-receive hook that alerts users (via email) when
specific paths are modified by their peers. The implementation is
pretty simple: whenever a new commit is made, we ask git for the full
list of files modified by that commit:

  git diff --name-only <COMMIT HASH>^!

This works well for regular commits, but breaks for merge commits.

For example, suppose we have the following basic merge scenario:

  B
 / \
A   D
 \ /
  C

Root A was branched to B and C, then merged into commit D.

Problem is, the diff for D^! will include all the changes introduced by C.

One obvious solution is to simply ignore merge commits, by parsing
`git cat-file commit D` and discarding all commits with parent count >
1. But merge commits may actually contain legitimate modified files if
there were any conflict resolutions.

So what's the best solution for this problem, oh wise Git wizards?

Thanks, D.