cmd/go: ignore volume name case when checking vendor path

Fixes #11409

Change-Id: Ic1610e124b2d8b2b12310fc9538d5078cc7302a0
Reviewed-on: https://go-review.googlesource.com/11316Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/main.go

@@ -474,6 +474,28 @@ func hasPathPrefix(s, prefix string) bool {
 	}
 }
 
+// hasFilePathPrefix reports whether the filesystem path s begins with the
+// elements in prefix.
+func hasFilePathPrefix(s, prefix string) bool {
+	sv := strings.ToUpper(filepath.VolumeName(s))
+	pv := strings.ToUpper(filepath.VolumeName(prefix))
+	s = s[len(sv):]
+	prefix = prefix[len(pv):]
+	switch {
+	default:
+		return false
+	case sv != pv:
+		return false
+	case len(s) == len(prefix):
+		return s == prefix
+	case len(s) > len(prefix):
+		if prefix != "" && prefix[len(prefix)-1] == filepath.Separator {
+			return strings.HasPrefix(s, prefix)
+		}
+		return s[len(prefix)] == filepath.Separator && s[:len(prefix)] == prefix
+	}
+}
+
 // treeCanMatchPattern(pattern)(name) reports whether
 // name or children of name can possibly match pattern.
 // Pattern is the same limited glob accepted by matchPattern.

src/cmd/go/pkg.go

@@ -360,7 +360,7 @@ func vendoredImportPath(parent *Package, path string) (found string, searched []
 	}
 	dir := filepath.Clean(parent.Dir)
 	root := filepath.Clean(parent.Root)
-	if !strings.HasPrefix(dir, root) || len(dir) <= len(root) || dir[len(root)] != filepath.Separator {
+	if !hasFilePathPrefix(dir, root) || len(dir) <= len(root) || dir[len(root)] != filepath.Separator {
 		fatalf("invalid vendoredImportPath: dir=%q root=%q separator=%q", dir, root, string(filepath.Separator))
 	}
 	vpath := "vendor/" + path

src/cmd/go/vendor_test.go

@@ -54,6 +54,22 @@ func TestVendorRun(t *testing.T) {
 	tg.grepStdout("hello, world", "missing hello world output")
 }
 
+func TestVendorGOPATH(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	changeVolume := func(s string, f func(s string) string) string {
+		vol := filepath.VolumeName(s)
+		return f(vol) + s[len(vol):]
+	}
+	gopath := changeVolume(filepath.Join(tg.pwd(), "testdata"), strings.ToLower)
+	tg.setenv("GOPATH", gopath)
+	tg.setenv("GO15VENDOREXPERIMENT", "1")
+	cd := changeVolume(filepath.Join(tg.pwd(), "testdata/src/vend/hello"), strings.ToUpper)
+	tg.cd(cd)
+	tg.run("run", "hello.go")
+	tg.grepStdout("hello, world", "missing hello world output")
+}
+
 func TestVendorTest(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()