os/user: fake Current on Android

On Android devices where the stub fallback for Current fails to
extract a User from the environment, return a dummy fallback instead
of failing.

While we're here, use / instead of /home/nacl for the NaCL fallback.

Hopefully fixes the Android builder.

Change-Id: Ia29304fbc224ee5f9c0f4e706d1756f765a7eae5
Reviewed-on: https://go-review.googlesource.com/37960
Run-TryBot: Elias Naur <elias.naur@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/os/user/lookup_stubs.go

@@ -26,7 +26,9 @@ func current() (*User, error) {
 		Name:     "", // ignored
 		HomeDir:  os.Getenv("HOME"),
 	}
-	if runtime.GOOS == "nacl" {
+	// On NaCL and Android, return a dummy user instead of failing.
+	switch runtime.GOOS {
+	case "nacl":
 		if u.Uid == "" {
 			u.Uid = "1"
 		}
@@ -34,7 +36,17 @@ func current() (*User, error) {
 			u.Username = "nacl"
 		}
 		if u.HomeDir == "" {
-			u.HomeDir = "/home/nacl"
+			u.HomeDir = "/"
+		}
+	case "android":
+		if u.Uid == "" {
+			u.Uid = "1"
+		}
+		if u.Username == "" {
+			u.Username = "android"
+		}
+		if u.HomeDir == "" {
+			u.HomeDir = "/sdcard"
 		}
 	}
 	// cgo isn't available, but if we found the minimum information

src/os/user/user_test.go

@@ -16,9 +16,6 @@ func checkUser(t *testing.T) {
 }
 
 func TestCurrent(t *testing.T) {
-	if runtime.GOOS == "android" {
-		t.Skipf("skipping on %s", runtime.GOOS)
-	}
 	u, err := Current()
 	if err != nil {
 		t.Fatalf("Current: %v (got %#v)", err, u)