I built a source that uses git-fetch - by default (recursive? #f) - and the package failed to build, then I remembered it uses submodules, so I set (recursive? #t) but it failed with the same error. The problem is that the store path of the source is the same for both, so it didn't try to rebuild the git checkout with submodules checked out.
After garbage collecting the source so it rebuilds it, I can build the package.
