type Status struct {
	Revision    string    // Optional.
	CommitTime  time.Time // Optional.
	Uncommitted bool      // Required.
}

type VCS interface {
	// Root returns the root of the directory controlled by
	// the VCS (e.g. the directory containing .git).
	Root() string

	// ListFiles returns a list of all the files tracked by the VCS
	// under the given directory, relative to that directory, as
	// filepaths, in lexical order. It does not include directory
	// names.
	//
	// The directory should be within the VCS root.
	ListFiles(ctx context.Context, dir string) ([]string, error)

	// Status returns the current state of the repository holding
	// the given directory.
	Status(ctx context.Context) (Status, error)
}