fix(json): improve handling of omitempty with embedded pointers

json/codec.go

@@ -677,7 +677,9 @@ func appendStructFields(fields []structField, t reflect.Type, offset uintptr, se
 
 		if embfield.pointer {
 			subfield.codec = constructEmbeddedStructPointerCodec(embfield.subtype.typ, embfield.unexported, subfield.offset, subfield.codec)
+			subfield.ptrOffset += subfield.offset
 			subfield.offset = embfield.offset
+			subfield.ptr = true
 		} else {
 			subfield.offset += embfield.offset
 		}
@@ -931,7 +933,6 @@ type structType struct {
 	fieldsIndex map[string]*structField
 	ficaseIndex map[string]*structField
 	typ         reflect.Type
-	inlined     bool
 }
 
 type structField struct {
@@ -946,6 +947,8 @@ type structField struct {
 	typ       reflect.Type
 	zero      reflect.Value
 	index     int
+	ptr       bool
+	ptrOffset uintptr
 }
 
 func unmarshalTypeError(b []byte, t reflect.Type) error {

json/encode.go

@@ -767,8 +767,17 @@ func (e encoder) encodeStruct(b []byte, p unsafe.Pointer, st *structType) ([]byt
 		f := &st.fields[i]
 		v := unsafe.Pointer(uintptr(p) + f.offset)
 
-		if f.omitempty && f.empty(v) {
-			continue
+		if f.omitempty {
+			if f.ptr {
+				v2 := *(*unsafe.Pointer)(v)
+				v3 := unsafe.Pointer(uintptr(v2) + f.ptrOffset)
+
+				if f.empty(v3) {
+					continue
+				}
+			} else if f.empty(v) {
+				continue
+			}
 		}
 
 		if escapeHTML {

json/json_test.go

@@ -1578,7 +1578,6 @@ func TestGithubIssue41(t *testing.T) {
 			"expected: ", expectedString,
 		)
 	}
-
 }
 
 func TestGithubIssue44(t *testing.T) {
@@ -1602,6 +1601,105 @@ func (r *rawJsonString) UnmarshalJSON(b []byte) error {
 	return nil
 }
 
+// See https://github.com/segmentio/encoding/issues/63
+// In short, embedding a struct pointer resulted in an incorrect memory address
+// as we were still looking to the parent struct to start and only using offsets
+// which resulted in the wrong values being extracted.
+func TestGithubIssue63(t *testing.T) {
+	spec := []struct {
+		description string
+		input       func() interface{}
+		expected    string
+	}{
+		{
+			description: "original",
+			expected:    `{"my_field":"test","code":0}`,
+			input: func() interface{} {
+				type MyStruct struct {
+					MyField string `json:"my_field,omitempty"`
+				}
+
+				type MyStruct2 struct {
+					*MyStruct
+					Code int `json:"code"`
+				}
+
+				return MyStruct2{
+					MyStruct: &MyStruct{
+						MyField: "test",
+					},
+					Code: 0,
+				}
+			},
+		},
+		{
+			description: "additional fields",
+			expected:    `{"my_field":"test","my_other_field":"testing","code":1}`,
+			input: func() interface{} {
+				type MyStruct struct {
+					MyField      string `json:"my_field,omitempty"`
+					MyOtherField string `json:"my_other_field"`
+					MyEmptyField string `json:"my_empty_field,omitempty"`
+				}
+
+				type MyStruct2 struct {
+					*MyStruct
+					Code int `json:"code"`
+				}
+
+				return MyStruct2{
+					MyStruct: &MyStruct{
+						MyField:      "test",
+						MyOtherField: "testing",
+					},
+					Code: 1,
+				}
+			},
+		},
+		{
+			description: "multiple embed levels",
+			expected:    `{"my_field":"test","my_other_field":"testing","code":1}`,
+			input: func() interface{} {
+				type MyStruct struct {
+					MyField      string `json:"my_field,omitempty"`
+					MyOtherField string `json:"my_other_field"`
+					MyEmptyField string `json:"my_empty_field,omitempty"`
+				}
+
+				type MyStruct2 struct {
+					*MyStruct
+					Code int `json:"code"`
+				}
+
+				type MyStruct3 struct {
+					*MyStruct2
+				}
+
+				return MyStruct3{
+					MyStruct2: &MyStruct2{
+						MyStruct: &MyStruct{
+							MyField:      "test",
+							MyOtherField: "testing",
+						},
+						Code: 1,
+					},
+				}
+			},
+		},
+	}
+
+	for _, test := range spec {
+		t.Run(test.description, func(t *testing.T) {
+			if b, err := Marshal(test.input()); err != nil {
+				t.Error(err)
+			} else if string(b) != test.expected {
+				t.Errorf("got:      %s", string(b))
+				t.Errorf("expected: %s", test.expected)
+			}
+		})
+	}
+}
+
 func TestSetTrustRawMessage(t *testing.T) {
 	buf := &bytes.Buffer{}
 	enc := NewEncoder(buf)