dart-sass/tool/grind/synchronize.dart

// Copyright 2017 Google Inc. Use of this source code is governed by an
// MIT-style license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT.

import 'dart:io';

import 'package:analyzer/analyzer.dart';
import 'package:analyzer/dart/ast/token.dart';
import 'package:crypto/crypto.dart';
import 'package:dart2_constant/convert.dart' as convert;
import 'package:dart_style/dart_style.dart';
import 'package:grinder/grinder.dart';
import 'package:path/path.dart' as p;

/// The files to compile to synchronous versions.
final _sources = {
  'lib/src/visitor/async_evaluate.dart': 'lib/src/visitor/evaluate.dart',
  'lib/src/async_environment.dart': 'lib/src/environment.dart'
};

/// This is how we support both synchronous and asynchronous compilation modes.
///
/// Both modes are necessary. Synchronous mode is faster, works in sync-only
/// contexts, and allows us to support Node Sass's renderSync() method.
/// Asynchronous mode allows users to write async importers and functions in
/// both Dart and JS.
///
/// The logic for synchronous and asynchronous mode is identical, but the async
/// code needs to await every statement and expression evaluation in case they
/// do asynchronous work. To avoid duplicating logic, we hand-write asynchronous
/// code for the evaluator and the environment and use this task to compile it
/// to a synchronous equivalent.
@Task('Compile async code to synchronous code.')
synchronize() {
  _sources.forEach((source, target) {
    var visitor = new _Visitor(new File(source).readAsStringSync(), source);
    parseDartFile(source).accept(visitor);
    var formatted = new DartFormatter().format(visitor.result);
    new File(target).writeAsStringSync(formatted);
  });
}

/// The visitor that traverses the asynchronous parse tree and converts it to
/// synchronous code.
///
/// To preserve the original whitespace and comments, this copies text from the
/// original source where possible. It tracks the [_position] at the end of the
/// text that's been written, and writes from that position to the new position
/// whenever text needs to be emitted.
class _Visitor extends RecursiveAstVisitor {
  /// The source of the original asynchronous file.
  final String _source;

  /// The current position in [_source].
  var _position = 0;

  /// The buffer in which the text of the synchronous file is built up.
  final _buffer = new StringBuffer();

  /// The synchronous text.
  String get result {
    _buffer.write(_source.substring(_position));
    _position = _source.length;
    return _buffer.toString();
  }

  _Visitor(this._source, String path) {
    var afterHeader = "\n".allMatches(_source).skip(3).first.end;
    _buffer.writeln(_source.substring(0, afterHeader));
    _buffer.writeln("""
// DO NOT EDIT. This file was generated from ${p.basename(path)}.
// See tool/synchronize.dart for details.
//
// Checksum: ${sha1.convert(convert.utf8.encode(_source))}
""");

    if (p.basename(path) == 'async_evaluate.dart') {
      _buffer.writeln();
      _buffer.writeln("import 'async_evaluate.dart' show EvaluateResult;");
      _buffer.writeln("export 'async_evaluate.dart' show EvaluateResult;");
      _buffer.writeln();
    }

    _position = afterHeader;
  }

  void visitAwaitExpression(AwaitExpression node) {
    _skip(node.awaitKeyword);

    // Skip the space after "await" to work around dart-lang/dart_style#226.
    _position++;
    node.expression.accept(this);
  }

  void visitParenthesizedExpression(ParenthesizedExpression node) {
    if (node.expression is AwaitExpression) {
      _skip(node.leftParenthesis);
      node.expression.accept(this);
      _skip(node.rightParenthesis);
    } else {
      node.expression.accept(this);
    }
  }

  void visitBlockFunctionBody(BlockFunctionBody node) {
    _skip(node.keyword);
    node.visitChildren(this);
  }

  void visitClassDeclaration(ClassDeclaration node) {
    if (node.name.name == 'EvaluateResult') {
      _skipNode(node);
    } else {
      super.visitClassDeclaration(node);
    }
  }

  void visitExpressionFunctionBody(ExpressionFunctionBody node) {
    _skip(node.keyword);
    node.visitChildren(this);
  }

  void visitMethodDeclaration(MethodDeclaration node) {
    if (_synchronizeName(node.name.name) != node.name.name) {
      // If the file defines any asynchronous versions of synchronous functions,
      // remove them.
      _skipNode(node);
    } else {
      super.visitMethodDeclaration(node);
    }
  }

  void visitImportDirective(ImportDirective node) {
    _skipNode(node);
    var text = node.toString();
    if (!text.contains("dart:async")) {
      _buffer.write(text.replaceAll("async_", ""));
    }
  }

  void visitMethodInvocation(MethodInvocation node) {
    // Convert async utility methods to their synchronous equivalents.
    if (node.target == null &&
        ["mapAsync", "putIfAbsentAsync"].contains(node.methodName.name)) {
      _writeTo(node);
      var arguments = node.argumentList.arguments;
      _write(arguments.first);

      _buffer.write(".${_synchronizeName(node.methodName.name)}");
      if (node.typeArguments != null) _write(node.typeArguments);
      _buffer.write("(");

      _position = arguments[1].beginToken.offset;
      for (var argument in arguments.skip(1)) {
        argument.accept(this);
      }
    } else {
      super.visitMethodInvocation(node);
    }
  }

  void visitSimpleIdentifier(SimpleIdentifier node) {
    _skip(node.token);
    _buffer.write(_synchronizeName(node.name));
  }

  void visitTypeName(TypeName node) {
    if (["Future", "FutureOr"].contains(node.name.name)) {
      _skip(node.name.beginToken);
      if (node.typeArguments != null) {
        _skip(node.typeArguments.leftBracket);
        node.typeArguments.arguments.first.accept(this);
        _skip(node.typeArguments.rightBracket);
      } else {
        _buffer.write("void");
      }
    } else {
      super.visitTypeName(node);
    }
  }

  /// Writes [_source] to [_buffer] up to the beginning of [token], then puts
  /// [_position] after [token] so it doesn't get written.
  void _skip(Token token) {
    if (token == null) return;
    _buffer.write(_source.substring(_position, token.offset));
    _position = token.end;
  }

  /// Writes [_source] to [_buffer] up to the beginning of [node], then puts
  /// [_position] after [node] so it doesn't get written.
  void _skipNode(AstNode node) {
    if (node == null) return;
    _writeTo(node);
    _position = node.endToken.end;
  }

  /// Writes [_source] to [_buffer] up to the beginning of [node].
  void _writeTo(AstNode node) {
    _buffer.write(_source.substring(_position, node.beginToken.offset));
    _position = node.beginToken.offset;
  }

  /// Writes the contents of [node] to [_buffer].
  ///
  /// This leaves [_position] at the end of [node].
  void _write(AstNode node) {
    _position = node.beginToken.offset;
    node.accept(this);
    _buffer.write(_source.substring(_position, node.endToken.end));
    _position = node.endToken.end;
  }

  /// Strips an "async" prefix or suffix from [name].
  String _synchronizeName(String name) {
    if (name.toLowerCase().startsWith('async')) {
      return name.substring('async'.length);
    } else if (name.toLowerCase().endsWith('async')) {
      return name.substring(0, name.length - 'async'.length);
    } else {
      return name;
    }
  }
}