Fixed omitempty for non-comparable structs.

Problem reported by Andrew Bonventre.

Author: niemeyer

bson/bson_test.go

@@ -957,7 +957,7 @@ type condTime struct {
 	V time.Time ",omitempty"
 }
 type condStruct struct {
-	V struct { A int } ",omitempty"
+	V struct { A []int } ",omitempty"
 }
 
 type shortInt struct {
@@ -1157,8 +1157,8 @@ var twoWayCrossItems = []crossTypeItem{
 	{&condTime{time.Unix(123456789, 123e6)}, map[string]time.Time{"v": time.Unix(123456789, 123e6)}},
 	{&condTime{}, map[string]string{}},
 
-	{&condStruct{struct{A int}{1}}, bson.M{"v": bson.M{"a": 1}}},
-	{&condStruct{struct{A int}{}}, bson.M{}},
+	{&condStruct{struct{A []int}{[]int{1}}}, bson.M{"v": bson.M{"a": []interface{}{1}}}},
+	{&condStruct{struct{A []int}{}}, bson.M{}},
 
 	{&namedCondStr{"yo"}, map[string]string{"myv": "yo"}},
 	{&namedCondStr{}, map[string]string{}},

bson/encode.go

@@ -179,11 +179,12 @@ func isZero(v reflect.Value) bool {
 		if v.Type() == typeTime {
 			return v.Interface().(time.Time).IsZero()
 		}
-		info, err := getStructInfo(v.Type())
-		if err != nil {
-			panic("should never happen here: " + err.Error())
+		for i := v.NumField()-1; i >= 0; i-- {
+			if !isZero(v.Field(i)) {
+				return false
+			}
 		}
-		return info.Zero.Interface() == v.Interface()
+		return true
 	}
 	return false
 }