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// Copyright (c) 2017, 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:collection';
import 'package:collection/collection.dart';
import 'package:pub_semver/pub_semver.dart';
import 'package_name.dart';
/// A feature declared by a package.
/// Features are collections of optional dependencies. Dependers can choose
/// which features to require from packages they depend on.
class Feature {
/// The name of this feature.
final String name;
/// Whether this feature is enabled by default.
final bool onByDefault;
/// The additional dependencies added by this feature.
final List<PackageRange> dependencies;
/// Other features that this feature requires.
final List<String> requires;
/// A map from SDK identifiers to this feature's constraints on those SDKs.
final Map<String, VersionConstraint> sdkConstraints;
/// Returns the set of features in [features] that are enabled by
/// [dependencies].
static Set<Feature> featuresEnabledBy(Map<String, Feature> features,
Map<String, FeatureDependency> dependencies) {
if (features.isEmpty) return const UnmodifiableSetView.empty();
// [enableFeature] adds a feature to [features], along with any other
// features it requires.
var enabledFeatures = <Feature>{};
void enableFeature(Feature feature) {
if (!enabledFeatures.add(feature)) return;
for (var require in feature.requires) {
// Enable all features that are explicitly enabled by dependencies, or on by
// default and not disabled by dependencies.
for (var feature in features.values) {
if (dependencies[]?.isEnabled ?? feature.onByDefault) {
return enabledFeatures;
Feature(, Iterable<PackageRange> dependencies,
{Iterable<String> requires,
Map<String, VersionConstraint> sdkConstraints,
this.onByDefault = true})
: dependencies = UnmodifiableListView(dependencies.toList()),
requires = requires == null
? const []
: UnmodifiableListView(requires.toList()),
sdkConstraints = UnmodifiableMapView(
sdkConstraints ?? {'dart': VersionConstraint.any});
String toString() => name;