Algorithm to find when a set of git projects was broken?

Question

Let's assume I have N git projects, which combined together define a release/ repository R.

When R pass a sanity test, T, we name it a good R and if it fails we name it a bad R.

I want to come up with a script, and in the future push it to google repo, which generalizes the git bisect mechanism for a repository R defined by N git projects.

The aim is to find the latest good R named best R. VonC suggested a solution with submodules which is great but I am looking for a solution/algorithm for a repo-google based repository contains N git projects (e.g. Android).

Answer 1

I don't think a special script is necessary at first:

If those N git repos are referenced together in a parent repo as submodules, you can go back in the history of that parent repo and get back all N repos as they were versioned at the time.

Apply your git-bisect on your parent repo, and make sure your test T take advantage of the sources of the N repos in N sub-directories of that main repo.

That won't be as precise as a bisect done directly in the faulty submodule, but it can certainly help narrowing the search.
As in this blog post, your test T might have to run a sub-git bisect in each submodules.