fix: change isPtr to true on listElemCode

fix #370

encode_test.go

@@ -2424,3 +2424,32 @@ func TestIssue376(t *testing.T) {
 		t.Errorf("unexpected result: %v != %v", got, expected)
 	}
 }
+
+type Issue370 struct {
+	String string
+	Valid  bool
+}
+
+func (i *Issue370) MarshalJSON() ([]byte, error) {
+	if !i.Valid {
+		return json.Marshal(nil)
+	}
+	return json.Marshal(i.String)
+}
+
+func TestIssue370(t *testing.T) {
+	v := []struct {
+		V Issue370
+	}{
+		{V: Issue370{String: "test", Valid: true}},
+	}
+	b, err := json.Marshal(v)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := string(b)
+	expected := `[{"V":"test"}]`
+	if got != expected {
+		t.Errorf("unexpected result: %v != %v", got, expected)
+	}
+}

internal/encoder/compiler.go

@@ -487,7 +487,8 @@ func (c *Compiler) listElemCode(typ *runtime.Type) (Code, error) {
 	case typ.Kind() == reflect.Map:
 		return c.ptrCode(runtime.PtrTo(typ))
 	default:
-		code, err := c.typeToCodeWithPtr(typ, false)
+		// Strictly not isPtr == true, but reflect.ValueOf().Index() is canAddr, so set isPtr == true.
+		code, err := c.typeToCodeWithPtr(typ, true)
 		if err != nil {
 			return nil, err
 		}