fix: checked if a interface is empty by its value field instead of ty…

…pe field (#540)

internal/encoder/compiler.go

@@ -831,7 +831,7 @@ func (self *_Compiler) compileStructFieldZero(p *_Program, vt reflect.Type) {
         case reflect.Float32   : p.add(_OP_is_zero_4)
         case reflect.Float64   : p.add(_OP_is_zero_8)
         case reflect.String    : p.add(_OP_is_nil_p1)
-        case reflect.Interface : p.add(_OP_is_nil_p1)
+        case reflect.Interface : p.add(_OP_is_nil)
         case reflect.Map       : p.add(_OP_is_zero_map)
         case reflect.Ptr       : p.add(_OP_is_nil)
         case reflect.Slice     : p.add(_OP_is_nil_p1)

issue_test/issue539_test.go

@@ -0,0 +1,51 @@
+// Copyright 2023 CloudWeGo Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package issue_test
+
+import (
+   `encoding/json`
+   `testing`
+
+   `github.com/bytedance/sonic`
+   `github.com/stretchr/testify/require`
+)
+
+type OmitEmptyInterface struct {
+    ErrCode int32       `json:"code"`
+    Data    interface{} `json:"data,omitempty"`
+}
+
+func TestOmitEmptyInterface(t *testing.T) {
+    // non-enmpty type
+    var data *string
+        resp := &OmitEmptyInterface{
+        ErrCode: 123,
+        Data:    data,
+        }
+    eout, eerr := json.Marshal(resp)
+    sout, serr := sonic.Marshal(resp)
+    require.Equal(t, eerr == nil, serr == nil)
+    require.Equal(t, string(eout), string(sout))
+
+    // empty type and value
+    resp = &OmitEmptyInterface{
+        ErrCode: 123,
+        Data:    nil,
+        }
+        eout, eerr = json.Marshal(resp)
+        sout, serr = sonic.Marshal(resp)
+        require.Equal(t, eerr == nil, serr == nil)
+        require.Equal(t, string(eout), string(sout))
+}