Handle single string=>string flags without quotes (#179)

OK: --f1 "a=5,6" --f2 b=3,4 --f3 "c=5,6",d=7
Not OK: --f4 c="5,6"

string_to_string.go

@@ -22,11 +22,22 @@ func newStringToStringValue(val map[string]string, p *map[string]string) *string
 
 // Format: a=1,b=2
 func (s *stringToStringValue) Set(val string) error {
-	r := csv.NewReader(strings.NewReader(val))
-	ss, err := r.Read()
-	if err != nil {
-		return err
+	var ss []string
+	n := strings.Count(val, "=")
+	switch n {
+	case 0:
+		return fmt.Errorf("%s must be formatted as key=value", val)
+	case 1:
+		ss = append(ss, strings.Trim(val, `"`))
+	default:
+		r := csv.NewReader(strings.NewReader(val))
+		var err error
+		ss, err = r.Read()
+		if err != nil {
+			return err
+		}
 	}
+
 	out := make(map[string]string, len(ss))
 	for _, pair := range ss {
 		kv := strings.SplitN(pair, "=", 2)

string_to_string_test.go

@@ -140,16 +140,20 @@ func TestS2SCalledTwice(t *testing.T) {
 	var s2s map[string]string
 	f := setUpS2SFlagSet(&s2s)
 
-	in := []string{"a=1,b=2", "b=3", `"e=5,6"`, `f="7,8"`}
+	in := []string{"a=1,b=2", "b=3", `"e=5,6"`, `f=7,8`}
 	expected := map[string]string{"a": "1", "b": "3", "e": "5,6", "f": "7,8"}
 	argfmt := "--s2s=%s"
-	arg1 := fmt.Sprintf(argfmt, in[0])
-	arg2 := fmt.Sprintf(argfmt, in[1])
-	arg3 := fmt.Sprintf(argfmt, in[2])
-	err := f.Parse([]string{arg1, arg2, arg3})
+	arg0 := fmt.Sprintf(argfmt, in[0])
+	arg1 := fmt.Sprintf(argfmt, in[1])
+	arg2 := fmt.Sprintf(argfmt, in[2])
+	arg3 := fmt.Sprintf(argfmt, in[3])
+	err := f.Parse([]string{arg0, arg1, arg2, arg3})
 	if err != nil {
 		t.Fatal("expected no error; got", err)
 	}
+	if len(s2s) != len(expected) {
+		t.Fatalf("expected %d flags; got %d flags", len(expected), len(s2s))
+	}
 	for i, v := range s2s {
 		if expected[i] != v {
 			t.Fatalf("expected s2s[%s] to be %s but got: %s", i, expected[i], v)