Update submodule after rewriting commit history

Question

So here's what you need to know:

• Repo A was a large legacy repo used in several other projects as a submodule on GitHub Enterprise.
• While migrating Repo A to GitLab, we found that some commits deep in the history had their data corrupted and were causing the migration to fail.
• In order to remove these corrupted files, we had to rewrite the git history around the corrupted commit.
• Repo B uses Repo A as a submodule.

I have been attempting to update Repo B by doing the following:

1. Clone Repo B from GitLab
2. Update the path in .gitmodules to point to the new (GitLab) location of Repo A
3. git submodule init
4. Confirm that Repo A's url is correct and pointing to the new (GitLab) Repo A
5. cd repo-b/repo-a
6. git checkout $hash where $hash is the exact same commit in Repo A that we used to point to, but with the new hash because history was rewritten.

I keep getting this error:

fatal: reference is not a tree: 01b517847508dd5942887950e4a5ab1468bb21b4

I can't figure out what I'm doing wrong, every answer I've seen seems to imply that I should be able to checkout a specific hash in the submodule and then commit that change to the repo.

Also, just for clarification, I did confirm that my hash is correct and exists by checking it out in the new (GitLab) Repo A, so it's there.

Answer 1

I found a solution! I can't explain why it works, but it fix the error.

I had previously tried this with a git submodule update between step 3 and step 5, and that didn't seem to work. However:

git submodule init
git submodule update --checkout

Did in fact allow the hash checkout to succeed in the submodule.