Frequently asked questions

What does the name subpatch mean?

The name subpatch consists of two parts: sub and patch

The term sub is inspired by git submodules and git subtree. Both use the prefix sub, because the act on subdirectories. subpatch does the same. Third party dependencies (=subprojects) are added as subdirectories to the superproject.

The second term patch stands for patching the source code. subpatch allows to maintain a linear patch stack on top of the subproject. As far as I know, this is a unique feature for multi repository management tools like subpatch.

Subpatch is just another wrapper around git, right?

No, subpatch is not another wrapper around git. Like git submodules or git subtree, subpatch is an extension to git.

Refere to the learning (L1) on Pre-subpatch history: The solution to the multi repository problem is inside of git (or generally inside any version control system).

E.g., look at two common operations for SCM tools: tagging and switches branches. For subpatch git switch and git tag just work as before. When tagging a release, all source code files and all subprojects are tagged with a single command and a single tag. Same for git switch. With the same command, all source code files and all subprojects are switched to a different branch.

Now look at the repo tool, which I call a wrapper around git. How does tagging work? There is no single command to tag the whole superproject. You have to perform multiple steps

$ repo forall git tag -a ... # tag all subprojects individually
$ repo forall git push <remote name> <tagname>

# Now continue in the manifest repository
$ cd ../manifest-repo
$ vim manifest.xml  # replace default revision with newly create tag
$ git commit -a -m "add tag in release manifest"
$ git push origin HEAD:refs/heads/release-xy

So just making a release, consists of multiple steps. And the whole process is error prone and not atomic. If you make a error somewhere, there is no easy way to roll back everything.

It's the same issue apply when switching branches. The repo tool does not support an easy way to checkout the branches of pull request/merged. For that some of my coworkers and I coded our own tool. See repoload.

That's why I call repo and other tools "a wrapper around git", because existing features of a SCM tool are reimplemented or need to be reimplemented. And subpatch is carefully designed to not be a wrapper around git.