improve parser recovery for incomplete prefixed identifier in method/function parameter list

pkg/analyzer/lib/src/generated/parser.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.parser;
 
 import "dart:math" as math;
@@ skipping 7845 matching lines @@
    *     prefixedIdentifier ::=
    *         identifier ('.' identifier)?
    */
   Token _skipPrefixedIdentifier(Token startToken) {
     Token token = _skipSimpleIdentifier(startToken);
     if (token == null) {
       return null;
     } else if (!_tokenMatches(token, TokenType.PERIOD)) {
       return token;
     }
-    return _skipSimpleIdentifier(token.next);
+    token = token.next;
+    Token nextToken = _skipSimpleIdentifier(token);
+    if (nextToken != null) {
+      return nextToken;
+    } else if (_tokenMatches(token, TokenType.CLOSE_PAREN)
+            || _tokenMatches(token, TokenType.COMMA)) {
+      // If the `id.` is followed by something that cannot produce a valid
+      // structure then assume this is a prefixed identifier but missing the
+      // trailing identifier
+      return token;
+    }
+    return null;
   }
 
   /**
    * Parse a return type, starting at the [startToken], without actually
    * creating a return type or changing the current token. Return the token
    * following the return type that was parsed, or `null` if the given token is
    * not the first token in a valid return type.
    *
    * This method must be kept in sync with [parseReturnType].
    *
@@ skipping 2700 matching lines @@
   }
 
   /**
    * Copy resolution data from the [fromNode] to the [toNode].
    */
   static void copyResolutionData(AstNode fromNode, AstNode toNode) {
     ResolutionCopier copier = new ResolutionCopier();
     copier._isEqualNodes(fromNode, toNode);
   }
 }