pkg/analyzer/lib/src/fasta/token_utils.dart

// Copyright (c) 2016, 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.

import 'package:front_end/src/scanner/token.dart' show CommentToken, Token;

/// Search for the token before [target] starting the search with [start].
/// Return `null` if [target] is a comment token
/// or the previous token cannot be found.
Token findPrevious(Token start, Token target) {
  if (start == target || target is CommentToken) {
    return null;
  }
  Token token = start is CommentToken ? start.parent : start;
  do {
    Token next = token.next;
    if (next == target) {
      return token;
    }
    token = next;
  } while (!token.isEof);
  return null;
}