GODRIVER-1502 Fix variable shadowing in parsing

Author: Divjot Arora

bson/bsonrw/extjson_parser.go

@@ -118,16 +118,16 @@ func (ejp *extJSONParser) peekType() (bsontype.Type, error) {
 			switch t {
 			case bsontype.JavaScript:
 				// just saw $code, need to check for $scope at same level
-				_, err := ejp.readValue(bsontype.JavaScript)
-
-				if err != nil {
+				_, tempErr := ejp.readValue(bsontype.JavaScript)
+				if tempErr != nil {
 					break
 				}
 
 				switch ejp.s {
 				case jpsSawEndObject: // type is TypeJavaScript
 				case jpsSawComma:
 					ejp.advanceState()
+
 					if ejp.s == jpsSawKey && ejp.k == "$scope" {
 						t = bsontype.CodeWithScope
 					} else {

bson/bsonrw/extjson_parser_test.go

@@ -148,6 +148,8 @@ func TestExtJSONParserPeekType(t *testing.T) {
 			errFs: []expectedErrorFunc{expectNoError, expectError},
 		},
 		makeInvalidTestCase("lone $scope", `{"$scope": {}}`, expectError),
+		makeInvalidTestCase("empty code with unknown extra key", `{"$code":"", "0":""}`, expectError),
+		makeInvalidTestCase("non-empty code with unknown extra key", `{"$code":"foobar", "0":""}`, expectError),
 	}
 
 	for _, tc := range cases {