fix #25739, incorrectly expanding a generic comment multiple times

pkg/analyzer/lib/src/dart/ast/token.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.src.dart.ast.token;
 
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 
 /**
@@ skipping 17 matching lines @@
         type == TokenType.STRING_INTERPOLATION_EXPRESSION);
   }
 
   @override
   Token copy() => new BeginToken(type, offset);
 }
 
 /**
  * A begin token that is preceded by comments.
  */
-class BeginTokenWithComment extends BeginToken {
+class BeginTokenWithComment extends BeginToken implements TokenWithComment {
   /**
    * The first comment in the list of comments that precede this token.
    */
   CommentToken _precedingComment;
 
   /**
    * Initialize a newly created token to have the given [type] at the given
    * [offset] and to be preceded by the comments reachable from the given
    * [comment].
    */
@@ skipping 23 matching lines @@
   @override
   Token copy() =>
       new BeginTokenWithComment(type, offset, copyComments(precedingComments));
 }
 
 /**
  * A token representing a comment.
  */
 class CommentToken extends StringToken {
   /**
-   * The [Token] that contains this comment.
+   * The token that contains this comment.
    */
-  Token parent;
+  TokenWithComment parent;
 
   /**
    * Initialize a newly created token to represent a token of the given [type]
    * with the given [value] at the given [offset].
    */
   CommentToken(TokenType type, String value, int offset)
       : super(type, value, offset);
 
   @override
   CommentToken copy() => new CommentToken(type, _value, offset);
+
+  /**
+   * Remove this comment token from the list.
+   *
+   * This is used when we decide to interpret the comment as syntax.
+   */
+  void remove() {
+    if (previous != null) {
+      previous.setNextWithoutSettingPrevious(next);
+      next?.previous = previous;
+    } else {
+      assert(parent.precedingComments == this);
+      parent.precedingComments = next;
+    }
+  }
 }
 
 /**
  * A documentation comment token.
  */
 class DocumentationCommentToken extends CommentToken {
   /**
    * The references embedded within the documentation comment.
    * This list will be empty unless this is a documentation comment that has
    * references embedded within it.
@@ skipping 37 matching lines @@
   @override
   Token copy() => new KeywordToken(keyword, offset);
 
   @override
   Keyword value() => keyword;
 }
 
 /**
  * A keyword token that is preceded by comments.
  */
-class KeywordTokenWithComment extends KeywordToken {
+class KeywordTokenWithComment extends KeywordToken implements TokenWithComment {
   /**
    * The first comment in the list of comments that precede this token.
    */
   CommentToken _precedingComment;
 
   /**
    * Initialize a newly created token to to represent the given [keyword] at the
    * given [offset] and to be preceded by the comments reachable from the given
    * [comment].
    */
@@ skipping 170 matching lines @@
   @override
   Token copy() => new StringToken(type, _value, offset);
 
   @override
   String value() => _value;
 }
 
 /**
  * A string token that is preceded by comments.
  */
-class StringTokenWithComment extends StringToken {
+class StringTokenWithComment extends StringToken implements TokenWithComment {
   /**
    * The first comment in the list of comments that precede this token.
    */
   CommentToken _precedingComment;
 
   /**
    * Initialize a newly created token to have the given [type] at the given
    * [offset] and to be preceded by the comments reachable from the given
    * [comment].
    */
@@ skipping 191 matching lines @@
   CommentToken get precedingComments => _precedingComment;
 
   void set precedingComments(CommentToken comment) {
     _precedingComment = comment;
     _setCommentParent(_precedingComment);
   }
 
   @override
   Token copy() => new TokenWithComment(type, offset, precedingComments);
 }