git describe/contains for submodule commits

Hi,

I've had a few times where I was curious of when a submodule got set to a specific commit.

I noticed that git describe has "blob" support, which outputs something like

<commit>:/path/to/file

using the revision walking machinery.

I'm curious if anyone knows if that sort of revision walk could be expected to find the first treeish that had a submodule commit instead of a blob.

I'm not that familiar with the revision walking, so I was hoping to get some pointers of whre to look before I began implementing.

Ultimately, I'd like to have some sort of command like:

  git submodule contains <submodule> <commit id>

and have it try to figure out the most recent commit htat has a submodule change for which the submodule is a child of the specified submodule commit.

I can sort of reverse engineer this through git log, but it's slow and tedious, so I was hoping to be able to implement it into a revision walk that did this.

Once I know the commit that introduces the submodule change, I could feed that to git describe --contains to find the tag/version which included the change easily enough.

Thanks, Jake