How to fix error: commit abc1234 is a merge but no -m option was given in Git

First, verify that the commit you're trying to cherry-pick is indeed a merge commit:

git show --pretty=raw <commit-hash>

Look for a line starting with Merge: which shows the parent commit hashes. For example:

commit abc1234...
Merge: def5678 ghi9012

If you see two or more parent hashes, it's a merge commit and requires the -m option.

The parent number determines which changes get applied:

- Parent 1 (-m 1): Usually the branch being merged INTO (e.g., main/master)
- Parent 2 (-m 2): Usually the branch being merged FROM (e.g., feature branch)

To see what each parent represents:

git log --oneline -1 <parent1-hash>
git log --oneline -1 <parent2-hash>

In most cases, you want -m 1 because you want to apply the changes that were introduced by the feature branch (the diff between parent 1 and the merge).

Run the cherry-pick with the appropriate parent number:

git cherry-pick -m 1 <merge-commit-hash>

This tells Git to use the first parent as the base and apply the changes from the merged branch.

If you want the opposite (apply changes from the first parent's perspective):

git cherry-pick -m 2 <merge-commit-hash>

If conflicts occur during the cherry-pick, resolve them as usual:

# See which files have conflicts
git status

# Edit conflicted files to resolve
# Then mark them as resolved
git add <resolved-file>

# Continue the cherry-pick
git cherry-pick --continue

Or abort if needed:

git cherry-pick --abort

Often a better approach is to cherry-pick the individual commits from the merged branch rather than the merge commit itself:

# Find commits in the merged branch
git log --oneline <parent1>..<parent2>

# Cherry-pick each commit individually
git cherry-pick <commit1> <commit2> <commit3>

Or cherry-pick a range:

git cherry-pick <oldest-commit>^..<newest-commit>

This preserves the original commit structure and history.

The same -m option applies when reverting merge commits:

git revert -m 1 <merge-commit-hash>

This creates a new commit that undoes the changes introduced by the merge. Use -m 1 to revert the changes that came from the merged branch while keeping the mainline changes.

After a successful cherry-pick, verify the changes are correct:

# View the new commit
git log -1 --stat

# Compare with expected changes
git diff HEAD~1

# Run tests to ensure the cherry-picked changes work

Note that cherry-picking a merge commit creates a single commit containing all the squashed changes, losing the individual commit history from the original branch.