Making moreflag.Parse safe to call repeatedly. (bazelbuild#75)

go/pkg/moreflag/moreflag.go

@@ -13,10 +13,13 @@ import (
 // Parse parses flags which are set in environment variables using the FLAG_ prefix. That is
 // for a flag named x, x=$FLAG_x if $FLAG_x is set. If the flag is set in the command line, the
 // command line value of the flag takes precedence over the environment variable value.
-// It also calls flag.Parse() to parse flags sent directly as arguments.
+// It also calls flag.Parse() to parse flags sent directly as arguments, unless flag.Parse
+// has been previously called.
 func Parse() {
 	ParseFromEnv()
-	flag.Parse()
+	if !flag.Parsed() {
+		flag.Parse()
+	}
 }
 
 // ParseFromEnv parses flags which are set in environment variables using the FLAG_ prefix. That is

go/pkg/moreflag/moreflag_test.go

@@ -8,17 +8,17 @@ import (
 	"github.com/google/go-cmp/cmp"
 )
 
-func TestParseFromEnv(t *testing.T) {
+func TestParse(t *testing.T) {
 	f := flag.String("value", "", "Some value")
 
-	ParseFromEnv()
+	Parse()
 	if *f != "" {
 		t.Errorf("Flag has wrong value, want '', got %q", *f)
 	}
 
 	os.Setenv("FLAG_value", "test")
 	defer os.Setenv("FLAG_value", "")
-	ParseFromEnv()
+	Parse()
 	if *f != "test" {
 		t.Errorf("Flag has wrong value, want 'test', got %q", *f)
 	}