Fix issue with typed union in record (hamba#5)

codec_union.go

@@ -163,6 +163,10 @@ type unionTypedDecoder struct {
 }
 
 func (d *unionTypedDecoder) Decode(ptr unsafe.Pointer, r *Reader) {
+	if *((*unsafe.Pointer)(ptr)) == nil {
+		newPtr := d.typ.UnsafeNew()
+		*((*unsafe.Pointer)(ptr)) = newPtr
+	}
 	union := d.typ.UnsafeIndirect(ptr).(UnionType)
 
 	schema := getUnionSchema(d.schema, r)

decoder_union_test.go

@@ -104,6 +104,26 @@ func TestDecoder_UnionTyped(t *testing.T) {
 	assert.Equal(t, 27, got.Val)
 }
 
+func TestDecoder_UnionTypedInRecord(t *testing.T) {
+	defer ConfigTeardown()
+
+	data := []byte{0x02, 0x36}
+	schema := `{
+	"type": "record",
+	"name": "test",
+	"fields" : [
+		{"name": "a", "type": ["null", "int"]}
+	]
+}`
+	dec, _ := avro.NewDecoder(schema, bytes.NewReader(data))
+
+	got := &TestUnionRecord{}
+	err := dec.Decode(&got)
+
+	assert.NoError(t, err)
+	assert.Equal(t, 27, got.A.Val)
+}
+
 func TestDecoder_UnionTypedNull(t *testing.T) {
 	defer ConfigTeardown()
 

types_test.go

@@ -28,6 +28,10 @@ type TestNestedRecord struct {
 	B TestRecord `avro:"b"`
 }
 
+type TestUnionRecord struct {
+	A *TestUnionType `avro:"a"`
+}
+
 type TestUnionType struct {
 	Val interface{}
 }