Only force hash calculation on interface containing struct

hash/structhash/structhash.go

@@ -102,7 +102,7 @@ func write(buf *bytes.Buffer, v reflect.Value) *bytes.Buffer {
 			// NOTE: structhash will allow to process all interface types.
 			// gogo/protobuf is not able to set tags for directly oneof interface.
 			// see: https://github.com/gogo/protobuf/issues/623
-			if to.name == "" && reflect.Zero(sf.Type).Kind() == reflect.Interface {
+			if to.name == "" && reflect.Zero(sf.Type).Kind() == reflect.Interface && (v.Field(i).Elem().Kind() == reflect.Struct || (v.Field(i).Elem().Kind() == reflect.Ptr && v.Field(i).Elem().Elem().Kind() == reflect.Struct)) {
 				to.skip = false
 				to.name = sf.Name
 			}

hash/structhash/structhash_test.go

@@ -22,6 +22,7 @@ func TestMd5(t *testing.T) {
 
 //nolint:megacheck
 func TestDump(t *testing.T) {
+	int1 := int(1)
 	tests := []struct {
 		v interface{}
 		s string
@@ -139,6 +140,68 @@ func TestDump(t *testing.T) {
 			}{b: false}},
 			"{a:{b:false}}",
 		},
+		{
+			struct {
+				a interface{}
+			}{
+				struct {
+					b int
+					c interface{}
+				}{
+					b: 1,
+					c: 2,
+				},
+			},
+			"{a:{}}",
+		},
+		{
+			struct {
+				a interface{}
+			}{
+				&struct {
+					b int         `hash:"name:b"`
+					c interface{} `hash:"name:c"`
+				}{
+					b: 1,
+					c: 2,
+				},
+			},
+			"{a:{b:1,c:2}}",
+		},
+		{
+			struct {
+				a interface{}
+			}{
+				&struct {
+					b *int
+					c interface{}
+				}{
+					b: &int1,
+					c: &int1,
+				},
+			},
+			"{a:{}}",
+		},
+		{
+			struct {
+				a interface{}
+			}{
+				&struct {
+					b *int
+					c interface{}
+				}{
+					b: nil,
+					c: nil,
+				},
+			},
+			"{a:{}}",
+		},
+		{
+			struct {
+				a interface{}
+			}{nil},
+			"{}",
+		},
 	}
 
 	for _, tt := range tests {