How does git merge after cherry-pick work?

Question

Let's imagine that we have a master branch.

Then we create a newbranch

git checkout -b newbranch

and make two new commits to newbranch: commit1 and commit2

Then we switch to master and make cherry-pick

git checkout master
git cherry-pick hash_of_commit1

Looking into gitk we see that commit1 and its cherry-picked version have different hashes, so technically they are two different commits.

Finally we merge newbranch into master:

git merge newbranch

and see that these two commits with different hashes were merged without problems although they imply that the same changes should be applied twice, so one of them should fail.

Does git really do a smart analysis of commit's content while merging and decide that changes shouldn't be applied twice or these commits are marked internally as linked together?

Answer 1

Short answer

Don't worry, Git will handle it.

Long answer

Unlike e.g. SVN¹, Git does not store commits in delta format, but is snapshot-based^2,3. While SVN would naively try to apply each merged commit as a patch (and fail, for the exact reason you described), Git is generally able to handle this scenario.

When merging, Git will try to combine the snapshots of both HEAD commits into a new snapshot. If a portion of code or a file is identical in both snapshots (i.e. because a commit was already cherry-picked), Git won't touch it.

Sources

¹ Skip-Deltas in Subversion
² Git Basics
³ The Git object model