This makes it possible to evaluate crane in a nixos test without network
as well as allow to backup all fetched input derivations properly in a
binary cache, whereas fetchGit will fallback to downloading from a
repository, which also requires a `git` binary to be present.
Co-authored-by: Ivan Petkov <ivanppetkov@gmail.com>
* When Nix fetches a git repo it will only look for the specified
revision only starting from the main branch (apparently fetching
arbitrary revisions from a repository has some security implications)
* If a ref (i.e. branch or tag) is not specified, Nix will only fetch
the repo's main branch
* To remedy this we will supply Nix with the branch or tag (if specified
in the Cargo.lock) to help it find the specified revision
* If cargo does not specify a branch or tag for us, we'll set `allRefs =
true` so that Nix can try fetching all possible branches and tags
before trying to check out the locked revision
