cmd/go: reject relative paths that don't start with a dot (.)

Change-Id: Idc4a7fdb561ba5b3b52094d895deaf3fcdf475bf
Reviewed-on: https://go-review.googlesource.com/10716Reviewed-by: Andrew Gerrand <adg@golang.org>

src/cmd/go/go_test.go

@@ -1036,11 +1036,12 @@ func TestInstalls(t *testing.T) {
 	tg.wantExecutable(tg.path("bin/progname")+exeSuffix, "did not install progname to $GOPATH/bin/progname")
 }
 
-func TestRejectRelativePathsInGOPATHCommandLinePackage(t *testing.T) {
+func TestRejectRelativeDotPathInGOPATHCommandLinePackage(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()
 	tg.setenv("GOPATH", ".")
 	tg.runFail("build", "testdata/src/go-cmd-test/helloworld.go")
+	tg.grepStderr("GOPATH entry is relative", "expected an error message rejecting relative GOPATH entries")
 }
 
 func TestRejectRelativePathsInGOPATH(t *testing.T) {
@@ -1049,6 +1050,15 @@ func TestRejectRelativePathsInGOPATH(t *testing.T) {
 	sep := string(filepath.ListSeparator)
 	tg.setenv("GOPATH", sep+filepath.Join(tg.pwd(), "testdata")+sep+".")
 	tg.runFail("build", "go-cmd-test")
+	tg.grepStderr("GOPATH entry is relative", "expected an error message rejecting relative GOPATH entries")
+}
+
+func TestRejectRelativePathsInGOPATHCommandLinePackage(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.setenv("GOPATH", "testdata")
+	tg.runFail("build", "testdata/src/go-cmd-test/helloworld.go")
+	tg.grepStderr("GOPATH entry is relative", "expected an error message rejecting relative GOPATH entries")
 }
 
 // Issue 4104.

src/cmd/go/main.go

@@ -142,7 +142,7 @@ func main() {
 				fmt.Fprintf(os.Stderr, "go: GOPATH entry cannot start with shell metacharacter '~': %q\n", p)
 				os.Exit(2)
 			}
-			if build.IsLocalImport(p) {
+			if !filepath.IsAbs(p) {
 				fmt.Fprintf(os.Stderr, "go: GOPATH entry is relative; must be absolute path: %q.\nRun 'go help gopath' for usage.\n", p)
 				os.Exit(2)
 			}