cmd/go: don't refuse to update a present package only because of its source configuration

If a package is checked out in the right place, but uses, for instance,
an unusual Git remote configuration, don't refuse to update just because
cmd/go can't parse it. In most cases, `git pull -ff-only` (or the
equivalent in other VCSes) works just fine.

Updates #25432.

Change-Id: I1952a0e6e03f185f34029b186e1756c9549689e1
Reviewed-on: https://go-review.googlesource.com/113456
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/go/go_test.go

@@ -3776,6 +3776,40 @@ func TestGoGetUpdateInsecure(t *testing.T) {
 	tg.run("get", "-d", "-u", "-f", "-insecure", pkg)
 }
 
+func TestGoGetUpdateUnknownProtocol(t *testing.T) {
+	testenv.MustHaveExternalNetwork(t)
+
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.makeTempdir()
+	tg.setenv("GOPATH", tg.path("."))
+
+	const repo = "github.com/golang/example"
+
+	// Clone the repo via HTTPS manually.
+	repoDir := tg.path("src/" + repo)
+	cmd := exec.Command("git", "clone", "-q", "https://"+repo, repoDir)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("cloning %v repo: %v\n%s", repo, err, out)
+	}
+
+	// Configure the repo to use a protocol unknown to cmd/go
+	// that still actually works.
+	cmd = exec.Command("git", "remote", "set-url", "origin", "xyz://"+repo)
+	cmd.Dir = repoDir
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("git remote set-url: %v\n%s", err, out)
+	}
+	cmd = exec.Command("git", "config", "--local", "url.https://github.com/.insteadOf", "xyz://github.com/")
+	cmd.Dir = repoDir
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("git config: %v\n%s", err, out)
+	}
+
+	// We need -f to ignore import comments.
+	tg.run("get", "-d", "-u", "-f", repo+"/hello")
+}
+
 func TestGoGetInsecureCustomDomain(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
 

src/cmd/go/internal/get/get.go

@@ -369,6 +369,7 @@ func downloadPackage(p *load.Package) error {
 		vcs            *vcsCmd
 		repo, rootPath string
 		err            error
+		blindRepo      bool // set if the repo has unusual configuration
 	)
 
 	security := web.Secure
@@ -389,10 +390,12 @@ func downloadPackage(p *load.Package) error {
 			dir := filepath.Join(p.Internal.Build.SrcRoot, filepath.FromSlash(rootPath))
 			remote, err := vcs.remoteRepo(vcs, dir)
 			if err != nil {
-				return err
+				// Proceed anyway. The package is present; we likely just don't understand
+				// the repo configuration (e.g. unusual remote protocol).
+				blindRepo = true
 			}
 			repo = remote
-			if !*getF {
+			if !*getF && err == nil {
 				if rr, err := repoRootForImportPath(p.ImportPath, security); err == nil {
 					repo := rr.repo
 					if rr.vcs.resolveRepo != nil {
@@ -416,7 +419,7 @@ func downloadPackage(p *load.Package) error {
 		}
 		vcs, repo, rootPath = rr.vcs, rr.repo, rr.root
 	}
-	if !vcs.isSecure(repo) && !*getInsecure {
+	if !blindRepo && !vcs.isSecure(repo) && !*getInsecure {
 		return fmt.Errorf("cannot download, %v uses insecure protocol", repo)
 	}