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// 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 dart_style.src.dart_formatter;
import 'dart:math' as math;
import 'package:analyzer/dart/analysis/features.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/token.dart';
import 'package:analyzer/error/error.dart';
import 'package:analyzer/src/dart/scanner/reader.dart';
import 'package:analyzer/src/dart/scanner/scanner.dart';
import 'package:analyzer/src/generated/parser.dart';
import 'package:analyzer/src/generated/source.dart';
import 'package:analyzer/src/string_source.dart';
import 'error_listener.dart';
import 'exceptions.dart';
import 'source_code.dart';
import 'source_visitor.dart';
import 'string_compare.dart' as string_compare;
import 'style_fix.dart';
/// Dart source code formatter.
class DartFormatter {
/// The string that newlines should use.
/// If not explicitly provided, this is inferred from the source text. If the
/// first newline is `\r\n` (Windows), it will use that. Otherwise, it uses
/// Unix-style line endings (`\n`).
String lineEnding;
/// The number of characters allowed in a single line.
final int pageWidth;
/// The number of characters of indentation to prefix the output lines with.
final int indent;
final Set<StyleFix> fixes = Set();
/// Creates a new formatter for Dart code.
/// If [lineEnding] is given, that will be used for any newlines in the
/// output. Otherwise, the line separator will be inferred from the line
/// endings in the source file.
/// If [indent] is given, that many levels of indentation will be prefixed
/// before each resulting line in the output.
/// While formatting, also applies any of the given [fixes].
{this.lineEnding, int pageWidth, int indent, Iterable<StyleFix> fixes})
: pageWidth = pageWidth ?? 80,
indent = indent ?? 0 {
if (fixes != null) this.fixes.addAll(fixes);
/// Formats the given [source] string containing an entire Dart compilation
/// unit.
/// If [uri] is given, it is a [String] or [Uri] used to identify the file
/// being formatted in error messages.
String format(String source, {uri}) {
if (uri == null) {
// Do nothing.
} else if (uri is Uri) {
uri = uri.toString();
} else if (uri is String) {
// Do nothing.
} else {
throw ArgumentError("uri must be `null`, a Uri, or a String.");
return formatSource(SourceCode(source, uri: uri, isCompilationUnit: true))
/// Formats the given [source] string containing a single Dart statement.
String formatStatement(String source) {
return formatSource(SourceCode(source, isCompilationUnit: false)).text;
/// Formats the given [source].
/// Returns a new [SourceCode] containing the formatted code and the resulting
/// selection, if any.
SourceCode formatSource(SourceCode source) {
var errorListener = ErrorListener();
// Enable all features that are enabled by default in the current analyzer
// version.
// TODO(paulberry): consider plumbing in experiment enable flags from the
// command line.
var featureSet = FeatureSet.fromEnableFlags([
// Tokenize the source.
var reader = CharSequenceReader(source.text);
var stringSource = StringSource(source.text, source.uri);
var scanner = Scanner(stringSource, reader, errorListener);
var startToken = scanner.tokenize();
var lineInfo = LineInfo(scanner.lineStarts);
// Infer the line ending if not given one. Do it here since now we know
// where the lines start.
if (lineEnding == null) {
// If the first newline is "\r\n", use that. Otherwise, use "\n".
if (scanner.lineStarts.length > 1 &&
scanner.lineStarts[1] >= 2 &&
source.text[scanner.lineStarts[1] - 2] == '\r') {
lineEnding = "\r\n";
} else {
lineEnding = "\n";
// Parse it.
var parser = Parser(stringSource, errorListener, featureSet: featureSet);
parser.enableOptionalNewAndConst = true;
parser.enableSetLiterals = true;
AstNode node;
if (source.isCompilationUnit) {
node = parser.parseCompilationUnit(startToken);
} else {
node = parser.parseStatement(startToken);
// Make sure we consumed all of the source.
var token =;
if (token.type != TokenType.EOF) {
var error = AnalysisError(
math.max(token.length, 1),
throw FormatterException([error]);
// Format it.
var visitor = SourceVisitor(this, lineInfo, source);
var output =;
// Sanity check that only whitespace was changed if that's all we expect.
if (fixes.isEmpty &&
!string_compare.equalIgnoringWhitespace(source.text, output.text)) {
throw UnexpectedOutputException(source.text, output.text);
return output;