How do I determine if a commit descends from another commit?

[Lon Ingram]

We would like to reject merge commits on a branch A unless they are

1. from some branch B to A or
2. on branch B

In other words, a merge commit is ok if it merges B into A, or if it is an ancestor of the head of B.

The first condition is easy to check. I am a bit stymied with the second. I would like to ask, "does the head of B descend from the merge commit in question."

You would think that it would be a matter of repeatedly calling Commit.getParents, but that method returns a MinimalCommit, which is not very useful. Is there a more reasonable way to walk the ancestors of a commit than this?

I've also considered using CommitsBetweenRequest, but without a more clear definition of the "between" relation for two commits, I'm not sure that will work in all cases. Should I use that instead?

[JamieA]

It's a bit confusing what you mean by 2), taken as a whole it reads:

"like to reject merge commits on a branch A unless they are on branch B"

Have a look at the docn for getCommitsBetween: it will let you see if a commit is reachable from another, which I think is what you want.