How to show diff of changes made in a merge commit?

Question

I didn't realize I was in the middle of a merge when I wrote a bunch of code. Now git log -p will not show me the diff of this change (which got auto-committed as a merge commit).

How can I get it to show up in my log diff history?

Answer 1

It's a bit disappointing that Git doesn't show you a patch for merges with -p. Part of the reason is that the patch produced by -p is a unified diff, and it's created from one base and one target revision. A merge has two bases, so a unified diff isn't representative of the change that needs to be made.

So there are two ways to get what you want. git log -p -c will show you N diffs in a merge commit, where N is the number of merge parents. Or, you can use git log -p --cc and see a more compacted form of the diff. It looks a lot like a unified diff, but can handle the fact that merges have multiple parents. FWIW, --cc stands for "compact combined". Compact combined output is what you would see if you ran git show SHA1 for the commit in question.

One more small note: if there were no edits where made in a merge commit, then you will not see a diff in the git log -p --cc output. Also, there's current no way to make a diff show up merge commits by default. You're best bet is to use an alias if you need something short and memorable.