[jvmakine]

Tools that generate files from a fetched source, such as scaffolder templates, sometimes need the exact same source again later, for example to re-render an old version and diff it against the latest. Fetch doesn't say which revision it fetched, and Resolve can't know it: ref=main only turns into a commit once the clone happens.

This adds an optional interface, so Resolver and Fetch are unchanged:

type RevisionResolver interface {
	Resolver
	FetchRevision(ctx context.Context, source Source, dest string) (string, error)
	AtRevision(source Source, revision string) Source
}

Fetcher (and the package-level defaults) gain:

• FetchRevision(ctx, source, dest) (string, error): fetches like Fetch and also returns the revision.
• AtRevision(source, revision) (string, error): returns a source string pinned to that revision, to pass to Fetch.

Both return ErrNoRevisions when the source's resolver doesn't implement the interface.

Git implements it:

• The revision is the commit hash, read with git rev-parse HEAD after the clone.
• AtRevision replaces ref with commit=<hash>&depth=1, so only that commit is fetched.

Other resolvers can add it later. A tarball resolver, for example, could hash the archive while downloading it, which is why the revision comes from a fetch rather than from the unpacked files.

🤖 Generated with Claude Code