[merge] Fix merge of non-nullable slices (gogo#569)

proto/table_merge.go

@@ -530,6 +530,25 @@ func (mi *mergeInfo) computeMergeInfo() {
 			}
 		case reflect.Struct:
 			switch {
+			case isSlice && !isPointer: // E.g. []pb.T
+				mergeInfo := getMergeInfo(tf)
+				zero := reflect.Zero(tf)
+				mfi.merge = func(dst, src pointer) {
+					// TODO: Make this faster?
+					dstsp := dst.asPointerTo(f.Type)
+					dsts := dstsp.Elem()
+					srcs := src.asPointerTo(f.Type).Elem()
+					for i := 0; i < srcs.Len(); i++ {
+						dsts = reflect.Append(dsts, zero)
+						srcElement := srcs.Index(i).Addr()
+						dstElement := dsts.Index(dsts.Len() - 1).Addr()
+						mergeInfo.merge(valToPointer(dstElement), valToPointer(srcElement))
+					}
+					if dsts.IsNil() {
+						dsts = reflect.MakeSlice(f.Type, 0, 0)
+					}
+					dstsp.Elem().Set(dsts)
+				}
 			case !isPointer:
 				mergeInfo := getMergeInfo(tf)
 				mfi.merge = func(dst, src pointer) {

test/merge/merge.proto

@@ -5,8 +5,13 @@ import "github.com/gogo/protobuf/gogoproto/gogo.proto";
 
 message A {
   B B = 1 [(gogoproto.nullable) = false];
+  repeated C c = 2 [(gogoproto.nullable) = false];
 }
 
 message B {
   int64 c = 1;
-}
+}
+
+message C {
+  int64 d = 1;
+}

test/merge/merge_test.go

@@ -1,6 +1,8 @@
 package merge
 
 import (
+	"fmt"
+	"reflect"
 	"testing"
 
 	"github.com/gogo/protobuf/proto"
@@ -11,6 +13,17 @@ func TestClone1(t *testing.T) {
 	proto.Clone(f1)
 }
 
+func TestClone2(t *testing.T) {
+	f1 := &A{C: []C{{D: 1}, {D: 2}}}
+	f2 := proto.Clone(f1).(*A)
+	if !reflect.DeepEqual(f1.C, f2.C) {
+		t.Fatalf("got %v want %v", f2, f1)
+	}
+	if fmt.Sprintf("%p", f1.C) == fmt.Sprintf("%p", f2.C) {
+		t.Fatalf("slice is not deep copied")
+	}
+}
+
 func TestMerge1(t *testing.T) {
 	f1 := &A{}
 	f2 := &A{}
@@ -34,3 +47,22 @@ func TestMerge3(t *testing.T) {
 		t.Fatalf("got %d want %d", f1.B.C, 1)
 	}
 }
+
+func TestMerge4(t *testing.T) {
+	f1 := &A{}
+	f2 := &A{C: []C{}}
+	proto.Merge(f1, f2)
+	if f1.C == nil {
+		t.Fatalf("got %v want %v", f1, []C{})
+	}
+}
+
+func TestMerge5(t *testing.T) {
+	f1 := &A{C: []C{{D: 1}, {D: 2}}}
+	f2 := &A{C: []C{{D: 3}, {D: 4}}}
+	f3 := &A{C: []C{{D: 1}, {D: 2}, {D: 3}, {D: 4}}}
+	proto.Merge(f1, f2)
+	if !reflect.DeepEqual(f1, f3) {
+		t.Fatalf("got %v want %v", f1, f3)
+	}
+}