Tag omitzero respects IsZero()

Author: lzap

encode.go

@@ -663,7 +663,34 @@ func getOptions(tag reflect.StructTag) tagOptions {
 	return opts
 }
 
+func callIsZero(rv reflect.Value) (bool, bool) {
+	if !rv.IsValid() {
+		return false, false
+	}
+
+	isZeroMethod := rv.MethodByName("IsZero")
+	if !isZeroMethod.IsValid() {
+		return false, false
+	}
+
+	methodType := isZeroMethod.Type()
+	if methodType.NumIn() != 0 || methodType.NumOut() != 1 || methodType.Out(0) != reflect.TypeOf(true) {
+		return false, false
+	}
+
+	returnValues := isZeroMethod.Call(nil)
+	if len(returnValues) == 1 && returnValues[0].Kind() == reflect.Bool {
+		return returnValues[0].Bool(), true
+	}
+
+	return false, false
+}
+
 func isZero(rv reflect.Value) bool {
+	if zero, ok := callIsZero(rv); ok {
+		return zero
+	}
+
 	switch rv.Kind() {
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 		return rv.Int() == 0

encode_test.go

@@ -274,24 +274,34 @@ slice = ["XXX"]
 	})
 }
 
+// a test type that is zero when its value is 42
+type int42 int
+
+func (i int42) IsZero() bool {
+	return i == 42
+}
+
 func TestEncodeOmitZero(t *testing.T) {
 	type simple struct {
 		Number   int     `toml:"number,omitzero"`
 		Real     float64 `toml:"real,omitzero"`
 		Unsigned uint    `toml:"unsigned,omitzero"`
+		Int42    int42   `toml:"int42,omitzero"`
 	}
 
-	value := simple{0, 0.0, uint(0)}
+	value := simple{0, 0.0, uint(0), int42(42)}
 	expected := ""
 
 	encodeExpected(t, "simple with omitzero, all zero", value, expected, nil)
 
 	value.Number = 10
 	value.Real = 20
 	value.Unsigned = 5
+	value.Int42 = int42(13) // this is zero for our custom type
 	expected = `number = 10
 real = 20.0
 unsigned = 5
+int42 = 13
 `
 	encodeExpected(t, "simple with omitzero, non-zero", value, expected, nil)
 }