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.

library fasta.analyzer.token_utils;

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

import 'package:front_end/src/fasta/scanner/token_constants.dart';

import 'package:front_end/src/scanner/errors.dart' show translateErrorToken;

import 'package:front_end/src/scanner/errors.dart' as analyzer
    show ScannerErrorCode;

/// Class capable of converting a stream of Fasta tokens to a stream of analyzer
/// tokens.
///
/// This is a class rather than an ordinary method so that it can be subclassed
/// in tests.
class ToAnalyzerTokenStreamConverter {
  /// Converts a stream of Fasta tokens (starting with [token] and continuing to
  /// EOF) to a stream of analyzer tokens. This modifies the fasta token stream
  /// to be an analyzer token stream by removing error tokens and reporting
  /// those errors to the associated error listener.
  Token convertTokens(Token firstToken) {
    Token token = new Token.eof(-1)..setNext(firstToken);
    Token next = firstToken;
    while (!next.isEof) {
      if (next.type.kind == BAD_INPUT_TOKEN) {
        translateErrorToken(next, reportError);
        token.setNext(next.next);
      } else {
        token = next;
      }
      next = token.next;
    }
    return firstToken;
  }

  /// Handles an error found during [convertTokens].
  ///
  /// Intended to be overridden by derived classes; by default, does nothing.
  void reportError(analyzer.ScannerErrorCode errorCode, int offset,
      List<Object> arguments) {}
}

/// 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;
}