1 files changed, 75 insertions, 0 deletions
diff --git a/go/tools/fetch_repo/main.go b/go/tools/fetch_repo/main.go
new file mode 100644
index 00000000..d3993202
--- /dev/null
+++ b/go/tools/fetch_repo/main.go
@@ -0,0 +1,75 @@
+// Command fetch_repo is similar to "go get -d" but it works even if the given
+// repository path is not a buildable Go package and it checks out a specific
+// revision rather than the latest revision.
+//
+// The difference between fetch_repo and "git clone" or {new_,}git_repository is
+// that fetch_repo recognizes import redirection of Go and it supports other
+// version control systems than git.
+//
+// These differences help us to manage external Go repositories in the manner of
+// Bazel.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+
+	"golang.org/x/tools/go/vcs"
+)
+
+var (
+	remote     = flag.String("remote", "", "The URI of the remote repository. Must be used with the --vcs flag.")
+	cmd        = flag.String("vcs", "", "Version control system to use to fetch the repository. Should be one of: git,hg,svn,bzr. Must be used with the --remote flag.")
+	rev        = flag.String("rev", "", "target revision")
+	dest       = flag.String("dest", "", "destination directory")
+	importpath = flag.String("importpath", "", "Go importpath to the repository fetch")
+
+	// Used for overriding in tests to disable network calls.
+	repoRootForImportPath = vcs.RepoRootForImportPath
+)
+
+func getRepoRoot(remote, cmd, importpath string) (*vcs.RepoRoot, error) {
+	if (cmd == "") != (remote == "") {
+		return nil, fmt.Errorf("--remote should be used with the --vcs flag. If this is an import path, use --importpath instead.")
+	}
+
+	if cmd != "" && remote != "" {
+		v := vcs.ByCmd(cmd)
+		if v == nil {
+			return nil, fmt.Errorf("invalid VCS type: %s", cmd)
+		}
+		return &vcs.RepoRoot{
+			VCS:  v,
+			Repo: remote,
+			Root: importpath,
+		}, nil
+	}
+
+	// User did not give us complete information for VCS / Remote.
+	// Try to figure out the information from the import path.
+	r, err := repoRootForImportPath(importpath, true)
+	if err != nil {
+		return nil, err
+	}
+	if importpath != r.Root {
+		return nil, fmt.Errorf("not a root of a repository: %s", importpath)
+	}
+	return r, nil
+}
+
+func run() error {
+	r, err := getRepoRoot(*remote, *cmd, *importpath)
+	if err != nil {
+		return err
+	}
+	return r.VCS.CreateAtRev(*dest, r.Repo, *rev)
+}
+
+func main() {
+	flag.Parse()
+
+	if err := run(); err != nil {
+		log.Fatal(err)
+	}
+}