Re: git-submodule getting submodules from the parent repository

On 30. mars. 2008, at 19.48, Sam Vilain wrote:

Well, the point of "submodule push" was to avoid having to push in each submodule manually; not enforcing the requirement that commits in submodules must be publicly available before pushing from the main module is a recipe for disaster, or at least annoyance. And nobody likes an annoying git.

Pushing to a branch works except that I couldn't figure out what to do if the push doesn't succeed, ie, the branch has advanced on the remote end. That's a problem if more than one module references the submodule or there are multiple branches in the main module.

One solution that occurred to me was to have a branch in each submodule for every main module and branch. A branch name would be provided for each submodule in .gitmodules, used by "submodule push" but not "submodule update". In this case, if the push to the branch fails, the main module branch is probably behind too.

This seemed like a good idea, but it's racy. If two simultaneous "submodule push"es try to push to the same branch on a submodule, one of them will be rejected, but it might already have updated branches on other submodules. Ick.

I briefly toyed with creating tags named after the main module and its branch, with the submodule sha1 included for good measure, but that leaves a _real_ mess in refs/tags. Figuring out that I could use refs/ submodule-push instead seemed like an epiphany at the time.

As an aside, my mental model of what the submodule needs is a fetchable reflog for every main module and branch that uses it, containing the history of commits used by that module/branch.

It's a reflog, not a branch, because a submodule can be changed to a different branch, rewound, etc between commits in the main module; there's no requirement that the old commit is in the new commit's history. You actually don't want to fetch the whole thing, but you have to be able to fetch every sha1 contained in it, by sha1.

...so that's what refs/submodule-push is supposed to look like. You might need to squint a bit.

True :) I still have no idea how to figure out which submodules are dirty, though. Solving that will enable a safe "submodule update", which I think is more important than "submodule push".