Git: Merging and Submodules

Question

Lets say I have two branches in RepoX called BranchA and BranchB. RepoX also has a submodule called SubmoduleY. BranchA has SubmoduleY at revision 'abc', BranchB has SubmoduleY at revision 'def'. Say I want to merge BranchA into BranchB, but I want to leave BranchB's SubmoduleY pointing to its original revision of 'def'. I see a couple ways of doing this: Method 1: - Checkout BranchB. - Move SubmoduleY to revision 'abc' to make the actual merge painless (we don't want to do any merging at the submodule level right now). - Commit the new revision for SubmoduleY (we can't have it floating for the merge). - Merge BranchA into BranchB. Resolve any conflicts. - Move SubmoduleY back to revision 'def'. - Commit the new revision for SubmoduleY. - Push changes up to the main repo. Method 2: Same as method 1, but instead of doing step 6, rebase and get rid of the extra submodule commit from step 3. Both seem to have annoying drawbacks: Method 1 puts two extra commits into history. Method 2 forg…

Accepted Answer

You could do a variation on your method 1, but do the commit that introduces the change to the submodule version (in your step 6) with `--amend` so that it changes the state of the submodule in the merge commit. In other words, this would be:

```
$ git checkout b
$ git merge a
Merge made by recursive.
 example.txt |    1 +
 sY          |    2 +-
 2 files changed, 2 insertions(+), 1 deletions(-)
 create mode 100644 example.txt
$ cd sY
$ git checkout def
[... you get the "detached HEAD" warning ...]
$ cd ..
$ git add sY
$ git commit --amend
```

Note that I didn't bother trying to avoid having the submodules at different versions before merging, as you suggested in your question. If there's a conflict, you can just choose to add the submodule at `def` to resolve it. If there isn't a conflict, the steps I mentioned above should work fine.

Git: Merging and Submodules

Solution

Problem