lib/src/barback/transformer_id.dart

// Copyright (c) 2013, 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 'dart:async';

import 'package:barback/barback.dart';
import 'package:source_span/source_span.dart';

import '../utils.dart';

/// A list of the names of all built-in transformers that pub exposes.
const _BUILT_IN_TRANSFORMERS = const ['\$dart2js'];

/// An identifier that indicates the library that contains a transformer.
///
/// It's possible that the library identified by [this] defines multiple
/// transformers. If so, they're all always loaded in the same phase.
class TransformerId {
  /// The package containing the library where the transformer is defined.
  final String package;

  /// The `/`-separated path to the library that contains this transformer.
  ///
  /// This is relative to the `lib/` directory in [package], and doesn't end in
  /// `.dart`.
  ///
  /// This can be null; if so, it indicates that the transformer(s) should be
  /// loaded from `lib/transformer.dart` if that exists, and `lib/$package.dart`
  /// otherwise.
  final String path;

  /// The source span from which this id was parsed.
  final SourceSpan span;

  /// Whether this ID points to a built-in transformer exposed by pub.
  bool get isBuiltInTransformer => package.startsWith('\$');

  /// Parses a transformer identifier.
  ///
  /// A transformer identifier is a string of the form "package_name" or
  /// "package_name/path/to/library". It does not have a trailing extension. If
  /// it just has a package name, it expands to lib/transformer.dart if that
  /// exists, or lib/${package}.dart otherwise. Otherwise, it expands to
  /// lib/${path}.dart. In either case it's located in the given package.
  factory TransformerId.parse(String identifier, SourceSpan span) {
    if (identifier.isEmpty) {
      throw new FormatException('Invalid library identifier: "".');
    }

    var parts = split1(identifier, "/");
    if (parts.length == 1) {
      return new TransformerId(parts.single, null, span);
    }

    return new TransformerId(parts.first, parts.last, span);
  }

  TransformerId(this.package, this.path, this.span) {
    if (!package.startsWith('\$')) return;
    if (_BUILT_IN_TRANSFORMERS.contains(package)) return;
    throw new SourceSpanFormatException(
        'Unsupported built-in transformer $package.', span);
  }

  bool operator ==(other) =>
      other is TransformerId && other.package == package && other.path == path;

  int get hashCode => package.hashCode ^ path.hashCode;

  /// Returns a serialized form of [this] that can be passed to
  /// [new TransformerId.parse].
  String serialize() => path == null ? package : '$package/$path';

  String toString() => serialize();

  /// Returns the asset id for the library identified by this transformer id.
  ///
  /// If `path` is null, this will determine which library to load. Unlike
  /// [getAssetId], this doesn't take generated assets into account; it's used
  /// to determine transformers' dependencies, which requires looking at files
  /// on disk.
  Future<AssetId> getAssetId(Barback barback) async {
    if (path != null) {
      return new AssetId(package, 'lib/$path.dart');
    }

    var transformerAsset = new AssetId(package, 'lib/transformer.dart');
    try {
      await barback.getAssetById(transformerAsset);
      return transformerAsset;
    } on AssetNotFoundException catch (_) {
      return new AssetId(package, 'lib/$package.dart');
    }
  }
}