Fix some bugs related to the covariant keyword

[email protected]

Review-Url: https://codereview.chromium.org/2662433002 .

Author: bwilkerson

pkg/analyzer/lib/src/generated/parser.dart

@@ -3848,7 +3848,7 @@ class Parser {
           modifiers.constKeyword = getAndAdvance();
         }
       } else if (keyword == Keyword.COVARIANT) {
-        if (modifiers.constKeyword != null) {
+        if (modifiers.covariantKeyword != null) {
           _reportErrorForCurrentToken(
               ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
           _advance();
@@ -4152,6 +4152,11 @@ class Parser {
           _tokenMatchesIdentifier(next)) {
         covariantKeyword = getAndAdvance();
       }
+      while (_matchesKeyword(Keyword.COVARIANT)) {
+        _reportErrorForCurrentToken(
+            ParserErrorCode.DUPLICATED_MODIFIER, [_currentToken.lexeme]);
+        _advance();
+      }
     }
     FinalConstVarOrType holder = parseFinalConstVarOrType(!inFunctionType,
         inFunctionType: inFunctionType);

pkg/analyzer/test/generated/parser_test.dart

@@ -987,6 +987,14 @@ class ErrorParserTest extends ParserTestCase {
     listener.assertErrorsWithCodes([ParserErrorCode.DUPLICATED_MODIFIER]);
   }
 
+  void test_duplicatedModifier_covariant() {
+    createParser('covariant covariant m;');
+    FormalParameter parameter =
+        parser.parseFormalParameter(ParameterKind.REQUIRED);
+    expectNotNullIfNoErrors(parameter);
+    listener.assertErrorsWithCodes([ParserErrorCode.DUPLICATED_MODIFIER]);
+  }
+
   void test_duplicatedModifier_external() {
     createParser('external external f();');
     ClassMember member = parser.parseClassMember('C');
@@ -8991,7 +8999,7 @@ void''');
 
   void test_parseFormalParameter_covariant_type_normal() {
     ParameterKind kind = ParameterKind.REQUIRED;
-    createParser('covariant A a');
+    createParser('covariant A<B<C>> a');
     FormalParameter parameter = parser.parseFormalParameter(kind);
     expectNotNullIfNoErrors(parameter);
     listener.assertNoErrors();