Why is git log --cherry-pick not removing equivalent commits?

Question

I have been trying to use

git log --no-merges --cherry-pick --right-only master...my-branch

to generate a list of commits that are in the my-branch, but not in master (as per the git-log documentation). However, there are still many equivalent commits that are coming up in the list. If I show them and their patches, there is no difference apart from the commit id.

git show 16cbd0e47406a4f7acbd6dc13f02d74d0b6a7621 >patcha
git show c53c7c32dcd84bfa7096a50b27738458e84536d5 >patchb

diff patcha patchb
1c1
< commit 16cbd0e47406a4f7acbd6dc13f02d74d0b6a7621
---
> commit c53c7c32dcd84bfa7096a50b27738458e84536d5

And even git patch-id shows them as being equivalent:

git show c53c7c32dcd84bfa7096a50b27738458e84536d5 | git patch-id
2b5504fb9a8622b4326195d88c7a20f29701e62b c53c7c32dcd84bfa7096a50b27738458e84536d5
git show 16cbd0e47406a4f7acbd6dc13f02d74d0b6a7621 | git patch-id
2b5504fb9a8622b4326195d88c7a20f29701e62b 16cbd0e47406a4f7acbd6dc13f02d74d0b6a7621

How does git log --cherry-pick not pick these up as duplicates?

Answer 1

Have you merged master into your branch since doing the cherry picks? --cherry-pick works first by matching the commit id, and then if that fails, looking for the patch id. If you've merged master into your branch, then you'll now have the actual commit on your branch and the cherry-picked version. So it'll find the commit id, and then proceed to report the cherry-picked version.

I've often wondered if git should always check both, but that's probably a considerable performance hit.