Fix encoding of omitempty feature for the slice or interface type

encode_test.go

@@ -1806,6 +1806,52 @@ func TestIssue104(t *testing.T) {
 	}
 }
 
+func TestIssue179(t *testing.T) {
+	data := `
+{
+  "t": {
+    "t1": false,
+    "t2": 0,
+    "t3": "",
+    "t4": [],
+    "t5": null,
+    "t6": null
+  }
+}`
+	type T struct {
+		X struct {
+			T1 bool        `json:"t1,omitempty"`
+			T2 float64     `json:"t2,omitempty"`
+			T3 string      `json:"t3,omitempty"`
+			T4 []string    `json:"t4,omitempty"`
+			T5 *struct{}   `json:"t5,omitempty"`
+			T6 interface{} `json:"t6,omitempty"`
+		} `json:"x"`
+	}
+	var v T
+	if err := stdjson.Unmarshal([]byte(data), &v); err != nil {
+		t.Fatal(err)
+	}
+	var v2 T
+	if err := json.Unmarshal([]byte(data), &v2); err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(v, v2) {
+		t.Fatalf("failed to decode: expected %v got %v", v, v2)
+	}
+	b1, err := stdjson.Marshal(v)
+	if err != nil {
+		t.Fatal(err)
+	}
+	b2, err := json.Marshal(v2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(b1, b2) {
+		t.Fatalf("failed to equal encoded result: expected %q but got %q", b1, b2)
+	}
+}
+
 func TestIssue180(t *testing.T) {
 	v := struct {
 		T struct {

internal/encoder/compiler.go

@@ -1439,7 +1439,7 @@ func compileStruct(ctx *compileContext, isPtr bool) (*Opcode, error) {
 			Indirect:         indirect,
 			Nilcheck:         nilcheck,
 			AddrForMarshaler: addrForMarshaler,
-			IsNextOpPtrType:  strings.Contains(valueCode.Op.String(), "Ptr"),
+			IsNextOpPtrType:  strings.Contains(valueCode.Op.String(), "Ptr") || valueCode.Op == OpInterface,
 			IsNilableType:    isNilableType,
 		}
 		if fieldIdx == 0 {

internal/encoder/vm/vm.go

@@ -2451,7 +2451,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			}
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = append(b, code.Key...)
@@ -3780,7 +3780,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			p := load(ctxptr, code.HeadIdx)
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = append(b, code.Key...)

internal/encoder/vm_debug/vm.go

@@ -2464,7 +2464,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			}
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = append(b, code.Key...)
@@ -3793,7 +3793,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			p := load(ctxptr, code.HeadIdx)
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = append(b, code.Key...)

internal/encoder/vm_escaped/vm.go

@@ -2451,7 +2451,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			}
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = append(b, code.EscapedKey...)
@@ -3780,7 +3780,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			p := load(ctxptr, code.HeadIdx)
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = append(b, code.EscapedKey...)

internal/encoder/vm_escaped_indent/vm.go

@@ -2576,7 +2576,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			}
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = appendIndent(ctx, b, code.Indent+1)
@@ -4059,7 +4059,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			p := load(ctxptr, code.HeadIdx)
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = appendIndent(ctx, b, code.Indent)

internal/encoder/vm_indent/vm.go

@@ -2576,7 +2576,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			}
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = appendIndent(ctx, b, code.Indent+1)
@@ -4059,7 +4059,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			p := load(ctxptr, code.HeadIdx)
 			p += code.Offset
 			slice := ptrToSlice(p)
-			if slice.Data == nil {
+			if slice.Len == 0 {
 				code = code.NextField
 			} else {
 				b = appendIndent(ctx, b, code.Indent)