cmd/go: fix test for moved package in go get -u

What matters during go get -u is not whether there is an import comment
but whether we resolved the path by an HTML <meta> tag.

Fixes #16471.

Change-Id: I6b194a3f73a7962a0170b4d5cf51cfed74e02c00
Reviewed-on: https://go-review.googlesource.com/31658
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Quentin Smith <quentin@golang.org>

src/cmd/go/get.go

@@ -388,7 +388,7 @@ func downloadPackage(p *Package) error {
 							repo = resolved
 						}
 					}
-					if remote != repo && p.ImportComment != "" {
+					if remote != repo && rr.isCustom {
 						return fmt.Errorf("%s is a custom import path for %s, but %s is checked out from %s", rr.root, repo, dir, remote)
 					}
 				}

src/cmd/go/go_test.go

@@ -1180,6 +1180,23 @@ func TestIssue10952(t *testing.T) {
 	tg.run("get", "-d", "-u", importPath)
 }
 
+func TestIssue16471(t *testing.T) {
+	testenv.MustHaveExternalNetwork(t)
+	if _, err := exec.LookPath("git"); err != nil {
+		t.Skip("skipping because git binary not found")
+	}
+
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+	tg.tempDir("src")
+	tg.setenv("GOPATH", tg.path("."))
+	tg.must(os.MkdirAll(tg.path("src/rsc.io/go-get-issue-10952"), 0755))
+	tg.runGit(tg.path("src/rsc.io"), "clone", "https://github.com/zombiezen/go-get-issue-10952")
+	tg.runFail("get", "-u", "rsc.io/go-get-issue-10952")
+	tg.grepStderr("rsc.io/go-get-issue-10952 is a custom import path for https://github.com/rsc/go-get-issue-10952, but .* is checked out from https://github.com/zombiezen/go-get-issue-10952", "did not detect updated import path")
+}
+
 // Test git clone URL that uses SCP-like syntax and custom import path checking.
 func TestIssue11457(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)

src/cmd/go/vcs.go

@@ -528,6 +528,9 @@ type repoRoot struct {
 	// root is the import path corresponding to the root of the
 	// repository
 	root string
+
+	// isCustom is true for custom import paths (those defined by HTML meta tags)
+	isCustom bool
 }
 
 var httpPrefixRE = regexp.MustCompile(`^https?:`)
@@ -713,9 +716,10 @@ func repoRootForImportDynamic(importPath string, security securityMode) (*repoRo
 		return nil, fmt.Errorf("%s: invalid repo root %q; no scheme", urlStr, mmi.RepoRoot)
 	}
 	rr := &repoRoot{
-		vcs:  vcsByCmd(mmi.VCS),
-		repo: mmi.RepoRoot,
-		root: mmi.Prefix,
+		vcs:      vcsByCmd(mmi.VCS),
+		repo:     mmi.RepoRoot,
+		root:     mmi.Prefix,
+		isCustom: true,
 	}
 	if rr.vcs == nil {
 		return nil, fmt.Errorf("%s: unknown vcs %q", urlStr, mmi.VCS)