merge: non nullable struct

Makefile

@@ -120,6 +120,7 @@ regenerate:
 	make -C test/issue322 regenerate
 	make -C test/issue330 regenerate
 	make -C test/importcustom-issue389 regenerate
+	make -C test/merge regenerate
 	make gofmt
 
 tests:

proto/table_merge.go

@@ -531,7 +531,10 @@ func (mi *mergeInfo) computeMergeInfo() {
 		case reflect.Struct:
 			switch {
 			case !isPointer:
-				panic(fmt.Sprintf("message field %s without pointer", tf))
+				mergeInfo := getMergeInfo(tf)
+				mfi.merge = func(dst, src pointer) {
+					mergeInfo.merge(dst, src)
+				}
 			case isSlice: // E.g., []*pb.T
 				mergeInfo := getMergeInfo(tf)
 				mfi.merge = func(dst, src pointer) {

test/merge/Makefile

@@ -0,0 +1,5 @@
+regenerate:
+	go install github.com/gogo/protobuf/protoc-min-version
+	go install github.com/gogo/protobuf/protoc-gen-gogo
+	protoc-min-version --version="3.0.0" --gogo_out=. \
+	--proto_path=../../../../../:../../protobuf/:. merge.proto

test/merge/merge.proto

@@ -0,0 +1,12 @@
+syntax = "proto3";
+package merge;
+
+import "github.com/gogo/protobuf/gogoproto/gogo.proto";
+
+message A {
+  B B = 1 [(gogoproto.nullable) = false];
+}
+
+message B {
+  int64 c = 1;
+}

test/merge/merge_test.go

@@ -0,0 +1,36 @@
+package merge
+
+import (
+	"testing"
+
+	"github.com/gogo/protobuf/proto"
+)
+
+func TestClone1(t *testing.T) {
+	f1 := &A{}
+	proto.Clone(f1)
+}
+
+func TestMerge1(t *testing.T) {
+	f1 := &A{}
+	f2 := &A{}
+	proto.Merge(f1, f2)
+}
+
+func TestMerge2(t *testing.T) {
+	f1 := &A{B: B{C: 1}}
+	f2 := &A{}
+	proto.Merge(f1, f2)
+	if f1.B.C != 1 {
+		t.Fatalf("got %d want %d", f1.B.C, 1)
+	}
+}
+
+func TestMerge3(t *testing.T) {
+	f1 := &A{}
+	f2 := &A{B: B{C: 1}}
+	proto.Merge(f1, f2)
+	if f1.B.C != 1 {
+		t.Fatalf("got %d want %d", f1.B.C, 1)
+	}
+}