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

User · Accepted Answer

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.

User · Answer

Borealid s answer is correct  but suppose that you don t care about preserving the exact merging history of a branch and just want to cherry-pick a linearized version of it  Here s an easy and safe way to do that   Starting state  you are on branch X  and you want to cherry-pick the commits Y  Z    git checkout -b tempZ Z git rebase Y git checkout -b newX X git cherry-pick Y  tempZ  optional  git branch -D tempZ   What this does is to create a branch tempZ based on Z  but with the history from Y onward linearized  and then cherry-pick that onto a copy of X called newX   It s safer to do this on a new branch rather than to mutate X   Of course there might be conflicts in step 4  which you ll have to resolve in the usual way  cherry-pick works very much like rebase in that respect   Finally it deletes the temporary tempZ branch   If step 2 gives the message  Current branch tempZ is up to date   then Y  Z was already linear  so just ignore that message and proceed with steps 3 onward   Then review newX and see whether that did what you wanted    Note  this is not the same as a simple git rebase X when on branch Z  because it doesn t depend in any way on the relationship between X and Y  there may be commits between the common ancestor and Y that you didn t want

User · Answer

Simplify  Cherry-pick the commits  Don t cherry-pick the merge   Here s a rewrite of the accepted answer that ideally clarifies the advantages risks of possible approaches   You re trying to cherry pick fd9f578  which was a merge with two parents   Instead of cherry-picking a merge  the simplest thing is to cherry pick the commit s  you actually want from each branch in the merge   Since you ve already merged  it s likely all your desired commits are in your list  Cherry-pick them directly and you don t need to mess with the merge commit   explanation  The way a cherry-pick works is by taking the diff that a changeset represents  the difference between the working tree at that point and the working tree of its parent   and applying the changeset to your current branch    If a commit has two or more parents  as is the case with a merge  that commit also represents two or more diffs  The error occurs because of the uncertainty over which diff should apply   alternatives  If you determine you need to include the merge vs cherry-picking the related commits  you have two options     More complicated and obscure  also discards history  you can indicate which parent should apply    Use the -m option to do so  For example  git cherry-pick -m 1 fd9f578 will use the first parent listed in the merge as the base  Also consider that 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    Simpler and more familiar  preserves history  you can use git merge instead of git cherry-pick    As is usual with git merge  it will attempt to apply all commits that exist on the branch you are merging  and list them individually in your git log

User · Answer

-m means the parent number   From the git doc       Usually you cannot cherry-pick a merge because you do not know which side of the merge should be considered the mainline  This option specifies the parent number  starting from              1  of the mainline and allows cherry-pick to replay the change relative to the specified parent    For example  if your commit tree is like below   - A - D - E - F -   master                B - C           branch one   then git cherry-pick E will produce the issue you faced   git cherry-pick E -m 1 means using D-E  while git cherry-pick E -m 2 means using B-C-E

User · Answer

Simplification of  Daira Hopwood method good for picking one single commit  Need no temporary branches   In the case of the author    Z is wanted commit  fd9f578   Y is commit before it  X current working    branch   then do   git checkout Z     move HEAD to wanted commit git reset Y        have Z as changes in working tree git stash          save Z in stash git checkout X     return to working branch git stash pop      apply Z to current branch git commit -a      do commit

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

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