Fix encoding of primitive pointer with string tag

encode_compile.go

@@ -542,8 +542,10 @@ func (e *Encoder) structHeader(fieldCode *structFieldCode, valueCode *opcode, ta
 	switch op {
 	case opStructFieldHead,
 		opStructFieldHeadOmitEmpty,
+		opStructFieldHeadStringTag,
 		opStructFieldHeadIndent,
-		opStructFieldHeadOmitEmptyIndent:
+		opStructFieldHeadOmitEmptyIndent,
+		opStructFieldHeadStringTagIndent:
 		return valueCode.beforeLastCode()
 	}
 	return (*opcode)(unsafe.Pointer(fieldCode))
@@ -556,8 +558,10 @@ func (e *Encoder) structField(fieldCode *structFieldCode, valueCode *opcode, tag
 	switch op {
 	case opStructField,
 		opStructFieldOmitEmpty,
+		opStructFieldStringTag,
 		opStructFieldIndent,
-		opStructFieldOmitEmptyIndent:
+		opStructFieldOmitEmptyIndent,
+		opStructFieldStringTagIndent:
 		return valueCode.beforeLastCode()
 	}
 	return code
@@ -617,6 +621,16 @@ func (e *Encoder) compileStruct(typ *rtype, isPtr, root, withIndent bool) (*opco
 				f = f.nextField.toStructFieldCode()
 			}
 		}
+		if fieldNum == 1 && valueCode.op == opPtr {
+			// if field number is one and primitive pointer type,
+			// it should encode as **not** pointer .
+			switch valueCode.next.op {
+			case opInt, opInt8, opInt16, opInt32, opInt64,
+				opUint, opUint8, opUint16, opUint32, opUint64,
+				opFloat32, opFloat64, opBool, opString, opBytes:
+				valueCode = valueCode.next
+			}
+		}
 		key := fmt.Sprintf(`"%s":`, tag.key)
 		fieldCode := &structFieldCode{
 			opcodeHeader: &opcodeHeader{

encode_test.go

@@ -1132,3 +1132,29 @@ func TestEncodeBytekind(t *testing.T) {
 		}
 	}
 }
+
+// golang.org/issue/8582
+func TestEncodePointerString(t *testing.T) {
+	type stringPointer struct {
+		N *int64 `json:"n,string"`
+	}
+	var n int64 = 42
+	b, err := json.Marshal(stringPointer{N: &n})
+	if err != nil {
+		t.Fatalf("Marshal: %v", err)
+	}
+	if got, want := string(b), `{"n":"42"}`; got != want {
+		t.Errorf("Marshal = %s, want %s", got, want)
+	}
+	var back stringPointer
+	err = json.Unmarshal(b, &back)
+	if err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	if back.N == nil {
+		t.Fatalf("Unmarshaled nil N field")
+	}
+	if *back.N != 42 {
+		t.Fatalf("*N = %d; want 42", *back.N)
+	}
+}