cmd/go: create executable when installing to working directory

Fixes #11065.

Change-Id: Idd854facd5fa78c0334f86740f351d404f9a5b2d
Reviewed-on: https://go-review.googlesource.com/11511Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/build.go

@@ -559,12 +559,14 @@ func runInstall(cmd *Command, args []string) {
 		// If it exists and is an executable file, remove it.
 		_, targ := filepath.Split(pkgs[0].ImportPath)
 		targ += exeSuffix
-		fi, err := os.Stat(targ)
-		if err == nil {
-			m := fi.Mode()
-			if m.IsRegular() {
-				if m&0111 != 0 || goos == "windows" { // windows never sets executable bit
-					os.Remove(targ)
+		if filepath.Join(pkgs[0].Dir, targ) != pkgs[0].Target { // maybe $GOBIN is the current directory
+			fi, err := os.Stat(targ)
+			if err == nil {
+				m := fi.Mode()
+				if m.IsRegular() {
+					if m&0111 != 0 || goos == "windows" { // windows never sets executable bit
+						os.Remove(targ)
+					}
 				}
 			}
 		}

src/cmd/go/go_test.go

@@ -439,7 +439,7 @@ func (tg *testgoData) grepCountBoth(match string) int {
 // removed if it exists.
 func (tg *testgoData) creatingTemp(path string) {
 	if filepath.IsAbs(path) && !strings.HasPrefix(path, tg.tempdir) {
-		tg.t.Fatal("internal testsuite error: creatingTemp(%q) with absolute path not in temporary directory")
+		tg.t.Fatal("internal testsuite error: creatingTemp(%q) with absolute path not in temporary directory", path)
 	}
 	// If we have changed the working directory, make sure we have
 	// an absolute path, because we are going to change directory
@@ -1109,6 +1109,19 @@ func TestInstallIntoGOBIN(t *testing.T) {
 	tg.wantExecutable("testdata/bin1/go-cmd-test"+exeSuffix, "go install go-cmd-test did not write to testdata/bin1/go-cmd-test")
 }
 
+// Issue 11065
+func TestInstallToCurrentDirectoryCreatesExecutable(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	pkg := filepath.Join(tg.pwd(), "testdata", "src", "go-cmd-test")
+	tg.creatingTemp(filepath.Join(pkg, "go-cmd-test"+exeSuffix))
+	tg.setenv("GOBIN", pkg)
+	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
+	tg.cd(pkg)
+	tg.run("install")
+	tg.wantExecutable("go-cmd-test"+exeSuffix, "go install did not write to current directory")
+}
+
 // Without $GOBIN set, installing a program outside $GOPATH should fail
 // (there is nowhere to install it).
 func TestInstallWithoutDestinationFails(t *testing.T) {