git cherry-pick says "...38c74d is a merge but no -m option was given"

Question

I made some changes in my master branch and want to bring those upstream. When I cherry-pick the following commits. However, I get stuck on fd9f578 where git says:

$ git cherry-pick fd9f578 fatal: Commit fd9f57850f6b94b7906e5bbe51a0d75bf638c74d is a merge but no -m option was given. 

What is git trying to tell me and is cherry-pick the right thing to be using here? The master branch does include changes to files which have been modified in the upstream branch, so I'm sure there will be some merge conflicts but those aren't too bad to straighten out. I know which changes are needed where.

These are the commits I want to bring upstream.

e7d4cff added some comments... 23e6d2a moved static strings... 44cc65a incorporated test ... 40b83d5 whoops delete whitspace... 24f8a50 implemented global.c... 43651c3 cleaned up ... 068b2fe cleaned up version.c ... fd9f578 Merge branch 'master' of ssh://extgit/git/sessions_common 4172caa cleaned up comments in sessions.c ... 

Answer 1

The way a cherry-pick works is by taking the diff a changeset represents (the difference between the working tree at that point and the working tree of its parent), and applying it to your current branch.

So, if a commit has two or more parents, it also represents two or more diffs - which one should be applied?

You're trying to cherry pick fd9f578, which was a merge with two parents. So you need to tell the cherry-pick command which one against which the diff should be calculated, by using the -m option. For example, git cherry-pick -m 1 fd9f578 to use parent 1 as the base.

I can't say for sure for your particular situation, but using git merge instead of git cherry-pick is generally advisable. When you cherry-pick a merge commit, it collapses all the changes made in the parent you didn't specify to -m into that one commit. You lose all their history, and glom together all their diffs. Your call.