Fix proto.Equal handling of proto3 bytes fields.

proto3 specifies that non-message scalar fields don't have a "has" bit,
and so []byte{} and []byte(nil) are considered equivalent.

proto/equal.go

@@ -50,7 +50,9 @@ Equality is defined in this way:
     are equal, and extensions sets are equal.
   - Two set scalar fields are equal iff their values are equal.
     If the fields are of a floating-point type, remember that
-    NaN != x for all x, including NaN.
+    NaN != x for all x, including NaN. If the message is defined
+    in a proto3 .proto file, fields are not "set"; specifically,
+    zero length proto3 "bytes" fields are equal (nil == {}).
   - Two repeated fields are equal iff their lengths are the same,
     and their corresponding elements are equal (a "bytes" field,
     although represented by []byte, is not a repeated field)
@@ -88,6 +90,7 @@ func Equal(a, b Message) bool {
 
 // v1 and v2 are known to have the same type.
 func equalStruct(v1, v2 reflect.Value) bool {
+	sprop := GetProperties(v1.Type())
 	for i := 0; i < v1.NumField(); i++ {
 		f := v1.Type().Field(i)
 		if strings.HasPrefix(f.Name, "XXX_") {
@@ -113,7 +116,7 @@ func equalStruct(v1, v2 reflect.Value) bool {
 			}
 			f1, f2 = f1.Elem(), f2.Elem()
 		}
-		if !equalAny(f1, f2) {
+		if !equalAny(f1, f2, sprop.Prop[i]) {
 			return false
 		}
 	}
@@ -140,7 +143,8 @@ func equalStruct(v1, v2 reflect.Value) bool {
 }
 
 // v1 and v2 are known to have the same type.
-func equalAny(v1, v2 reflect.Value) bool {
+// prop may be nil.
+func equalAny(v1, v2 reflect.Value, prop *Properties) bool {
 	if v1.Type() == protoMessageType {
 		m1, _ := v1.Interface().(Message)
 		m2, _ := v2.Interface().(Message)
@@ -163,7 +167,7 @@ func equalAny(v1, v2 reflect.Value) bool {
 		if e1.Type() != e2.Type() {
 			return false
 		}
-		return equalAny(e1, e2)
+		return equalAny(e1, e2, nil)
 	case reflect.Map:
 		if v1.Len() != v2.Len() {
 			return false
@@ -174,16 +178,22 @@ func equalAny(v1, v2 reflect.Value) bool {
 				// This key was not found in the second map.
 				return false
 			}
-			if !equalAny(v1.MapIndex(key), val2) {
+			if !equalAny(v1.MapIndex(key), val2, nil) {
 				return false
 			}
 		}
 		return true
 	case reflect.Ptr:
-		return equalAny(v1.Elem(), v2.Elem())
+		return equalAny(v1.Elem(), v2.Elem(), prop)
 	case reflect.Slice:
 		if v1.Type().Elem().Kind() == reflect.Uint8 {
 			// short circuit: []byte
+
+			// Edge case: if this is in a proto3 message, a zero length
+			// bytes field is considered the zero value.
+			if prop != nil && prop.proto3 && v1.Len() == 0 && v2.Len() == 0 {
+				return true
+			}
 			if v1.IsNil() != v2.IsNil() {
 				return false
 			}
@@ -194,7 +204,7 @@ func equalAny(v1, v2 reflect.Value) bool {
 			return false
 		}
 		for i := 0; i < v1.Len(); i++ {
-			if !equalAny(v1.Index(i), v2.Index(i)) {
+			if !equalAny(v1.Index(i), v2.Index(i), prop) {
 				return false
 			}
 		}
@@ -229,7 +239,7 @@ func equalExtensions(base reflect.Type, em1, em2 map[int32]Extension) bool {
 
 		if m1 != nil && m2 != nil {
 			// Both are unencoded.
-			if !equalAny(reflect.ValueOf(m1), reflect.ValueOf(m2)) {
+			if !equalAny(reflect.ValueOf(m1), reflect.ValueOf(m2), nil) {
 				return false
 			}
 			continue
@@ -257,7 +267,7 @@ func equalExtensions(base reflect.Type, em1, em2 map[int32]Extension) bool {
 			log.Printf("proto: badly encoded extension %d of %v: %v", extNum, base, err)
 			return false
 		}
-		if !equalAny(reflect.ValueOf(m1), reflect.ValueOf(m2)) {
+		if !equalAny(reflect.ValueOf(m1), reflect.ValueOf(m2), nil) {
 			return false
 		}
 	}

proto/equal_test.go

@@ -35,6 +35,7 @@ import (
 	"testing"
 
 	. "github.com/golang/protobuf/proto"
+	proto3pb "github.com/golang/protobuf/proto/proto3_proto"
 	pb "github.com/golang/protobuf/proto/testdata"
 )
 
@@ -131,6 +132,8 @@ var EqualTests = []struct {
 		&pb.MyMessage{RepBytes: [][]byte{[]byte("sham"), []byte("wow")}},
 		true,
 	},
+	// In proto3, []byte{} and []byte(nil) are equal.
+	{"proto3 bytes, empty vs nil", &proto3pb.Message{Data: []byte{}}, &proto3pb.Message{Data: nil}, true},
 
 	{"extension vs. no extension", messageWithoutExtension, messageWithExtension1a, false},
 	{"extension vs. same extension", messageWithExtension1a, messageWithExtension1b, true},