fix #25739, incorrectly expanding a generic comment multiple times

pkg/analyzer/test/generated/parser_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.generated.parser_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 1513 matching lines @@
           ParserErrorCode.EXPECTED_TOKEN /*>*/,
           ParserErrorCode.MISSING_IDENTIFIER,
           ParserErrorCode.EXPECTED_TOKEN /*(*/,
           ParserErrorCode.EXPECTED_TOKEN /*)*/,
           ParserErrorCode.MISSING_FUNCTION_BODY
         ]);
     expect(method.typeParameters.toString(), '<E, hello>',
         reason: 'parser recovers what it can');
   }
 
+  void test_method_invalidTypeParameterExtends() {
+    // Regression test for https://github.com/dart-lang/sdk/issues/25739.
+
+    // TODO(jmesserly): ideally we'd be better at parser recovery here.
+    enableGenericMethods = true;
+    MethodDeclaration method = parse3(
+        "parseClassMember",
+        <Object>["C"],
+        "f<E>(E extends num p);",
+        [
+          ParserErrorCode.MISSING_IDENTIFIER, // `extends` is a keyword
+          ParserErrorCode.EXPECTED_TOKEN, // comma
+          ParserErrorCode.EXPECTED_TOKEN, // close paren
+          ParserErrorCode.MISSING_FUNCTION_BODY
+        ]);
+    expect(method.parameters.toString(), '(E, extends)',
+        reason: 'parser recovers what it can');
+  }
+
+
+  void test_method_invalidTypeParameterExtendsComment() {
+    // Regression test for https://github.com/dart-lang/sdk/issues/25739.
+
+    // TODO(jmesserly): ideally we'd be better at parser recovery here.
+    // Also, this behavior is slightly different from how we would parse a
+    // normal generic method, because we "discover" the comment at a different
+    // point in the parser. This has a slight effect on the AST that results
+    // from error recovery.
+    enableGenericMethodComments = true;
+    MethodDeclaration method = parse3(
+        "parseClassMember",
+        <Object>["C"],
+        "f/*<E>*/(dynamic/*=E extends num*/p);",
+        [
+          ParserErrorCode.MISSING_IDENTIFIER, // `extends` is a keyword
+          ParserErrorCode.EXPECTED_TOKEN, // comma
+          ParserErrorCode.MISSING_IDENTIFIER, // `extends` is a keyword
+          ParserErrorCode.EXPECTED_TOKEN, // close paren
+          ParserErrorCode.MISSING_FUNCTION_BODY
+        ]);
+    expect(method.parameters.toString(), '(E extends, extends)',
+        reason: 'parser recovers what it can');
+  }
+
   void test_missingAssignableSelector_identifiersAssigned() {
     parseExpression("x.y = y;");
   }
 
   void test_missingAssignableSelector_prefix_minusMinus_literal() {
     parseExpression("--0", [ParserErrorCode.MISSING_ASSIGNABLE_SELECTOR]);
   }
 
   void test_missingAssignableSelector_prefix_plusPlus_literal() {
     parseExpression("++0", [ParserErrorCode.MISSING_ASSIGNABLE_SELECTOR]);
@@ skipping 9995 matching lines @@
         new Scanner(null, new CharSequenceReader(source), listener);
     Token tokenStream = scanner.tokenize();
     //
     // Parse the source.
     //
     Parser parser = new Parser(null, listener);
     return invokeParserMethodImpl(
         parser, methodName, <Object>[tokenStream], tokenStream) as Token;
   }
 }