use one hash to monitor a collection of revision hash changes?

Question

excuse me for the vague title, let me explain:

I have a collection of git repos, and I need to come up with a "synthetic" hash which is generated by the revision hashes from these repos, so it can be used to differentiate which repo has new commits:

E.g. if I have two repos with latest hashes:

• repo A: 90d4b6
• repo B: fa880b
• synthetic hash is e0ea5a

Next time repo A has new commits:

• repo A': ac9561
• repo B': fa880b
• synthetic hash' now becomes 12fc92

Is there a way/hash function to construct the synthetic hash so I can tell from the change (from e0ea5a to 12fc92) that this is caused by repo A changes?

I know the information about all repos's current revision hash, however I only know the "synthetic" hash from last time

Answer 1

You can do the following:

1. Use no-ff merge which will create a "side" graph for the merge. your merge will have 2 parents and using git show <SHA-1> you will be able to view the origin