Add support for Flutter SDK constraints.

lib/src/pubspec.dart

 // Copyright (c) 2012, 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 'package:path/path.dart' as path;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
 
 import 'barback/transformer_config.dart';
@@ skipping 204 matching lines @@
       if (map == null) return false;
 
       if (map is! Map) {
         _error('"$field" field must be a map.', fields.nodes[field].span);
       }
 
       return map.containsKey(package);
     });
   }
 
-  /// The environment-related metadata.
-  PubspecEnvironment get environment {
-    if (_environment != null) return _environment;
+  /// The constraint on the Dart SDK, or [VersionConstraint.any] if none is
+  /// specified.
+  VersionConstraint get dartSdkConstraint {
+    _parseEnvironment();
+    return _dartSdkConstraint;
+  }
+  VersionConstraint _dartSdkConstraint;
+
+  /// The constraint on the Flutter SDK, or `null` if none is specified.
+  VersionConstraint get flutterSdkConstraint {
+    _parseEnvironment();
+    return _flutterSdkConstraint;
+  }
+  VersionConstraint _flutterSdkConstraint;
+
+  /// Parses the "environment" field and sets [_dartSdkConstraint] and
+  /// [_flutterSdkConstraint] accordingly.
+  void _parseEnvironment() {
+    if (_dartSdkConstraint != null) return;
 
     var yaml = fields['environment'];
     if (yaml == null) {
-      _environment = new PubspecEnvironment(VersionConstraint.any);
-      return _environment;
+      _dartSdkConstraint = VersionConstraint.any;
+      return;
     }
 
     if (yaml is! Map) {
       _error('"environment" field must be a map.',
              fields.nodes['environment'].span);
     }
 
-    _environment = new PubspecEnvironment(
-        _parseVersionConstraint(yaml.nodes['sdk']));
-    return _environment;
+    _dartSdkConstraint = _parseVersionConstraint(yaml.nodes['sdk']);
+    _flutterSdkConstraint = yaml.containsKey('flutter')
+        ? _parseVersionConstraint(yaml.nodes['flutter'])
+        : null;
   }
-  PubspecEnvironment _environment;
 
   /// The URL of the server that the package should default to being published
   /// to, "none" if the package should not be published, or `null` if it should
   /// be published to the default server.
   ///
   /// If this does return a URL string, it will be a valid parseable URL.
   String get publishTo {
     if (_parsedPublishTo) return _publishTo;
 
     var publishTo = fields['publish_to'];
@@ skipping 95 matching lines @@
           pubspecPath);
     }
 
     return new Pubspec.parse(readTextFile(pubspecPath), sources,
         expectedName: expectedName, location: pubspecUri);
   }
 
   Pubspec(this._name, {Version version, Iterable<PackageDep> dependencies,
           Iterable<PackageDep> devDependencies,
           Iterable<PackageDep> dependencyOverrides,
-          VersionConstraint sdkConstraint,
+          VersionConstraint dartSdkConstraint,
+          VersionConstraint flutterSdkConstraint,
           Iterable<Iterable<TransformerConfig>> transformers,
           Map fields, SourceRegistry sources})
       : _version = version,
         _dependencies = dependencies == null ? null : dependencies.toList(),
         _devDependencies = devDependencies == null ? null :
             devDependencies.toList(),
         _dependencyOverrides = dependencyOverrides == null ? null :
             dependencyOverrides.toList(),
-        _environment = new PubspecEnvironment(sdkConstraint),
+        _dartSdkConstraint = dartSdkConstraint ?? VersionConstraint.any,
+        _flutterSdkConstraint = flutterSdkConstraint,
         _transformers = transformers == null ? [] :
             transformers.map((phase) => phase.toSet()).toList(),
         fields = fields == null ? new YamlMap() : new YamlMap.wrap(fields),
         _sources = sources;
 
   Pubspec.empty()
     : _sources = null,
       _name = null,
       _version = Version.none,
       _dependencies = <PackageDep>[],
       _devDependencies = <PackageDep>[],
-      _environment = new PubspecEnvironment(),
+      _dartSdkConstraint = VersionConstraint.any,
+      _flutterSdkConstraint = null,
       _transformers = <Set<TransformerConfig>>[],
       fields = new YamlMap();
 
   /// Returns a Pubspec object for an already-parsed map representing its
   /// contents.
   ///
   /// If [expectedName] is passed and the pubspec doesn't have a matching name
   /// field, this will throw a [PubspecError].
   ///
   /// [location] is the location from which this pubspec was loaded.
@@ skipping 39 matching lines @@
       } on PubspecException catch (e) {
         errors.add(e);
       }
     }
 
     _getError(() => this.name);
     _getError(() => this.version);
     _getError(() => this.dependencies);
     _getError(() => this.devDependencies);
     _getError(() => this.transformers);
-    _getError(() => this.environment);
     _getError(() => this.publishTo);
+    _getError(() => this._parseEnvironment());
     return errors;
   }
 
   /// Parses the dependency field named [field], and returns the corresponding
   /// list of dependencies.
   List<PackageDep> _parseDependencies(String field) {
     var dependencies = <PackageDep>[];
 
     var yaml = fields[field];
     // Allow an empty dependencies key.
@@ skipping 69 matching lines @@
       });
 
       dependencies.add(ref.withConstraint(versionConstraint));
     });
 
     return dependencies;
   }
 
   /// Parses [node] to a [VersionConstraint].
   VersionConstraint _parseVersionConstraint(YamlNode node) {
-    if (node.value == null) return VersionConstraint.any;
+    if (node?.value == null) return VersionConstraint.any;
     if (node.value is! String) {
       _error('A version constraint must be a string.', node.span);
     }
 
     return _wrapFormatException('version constraint', node.span,
         () => new VersionConstraint.parse(node.value));
   }
 
   /// Makes sure the same package doesn't appear as both a regular and dev
   /// dependency.
@@ skipping 39 matching lines @@
       _error('Invalid $description: ${e.message}', e.span);
     }
   }
 
   /// Throws a [PubspecException] with the given message.
   void _error(String message, SourceSpan span) {
     throw new PubspecException(message, span);
   }
 }
 
-/// The environment-related metadata in the pubspec.
-///
-/// Corresponds to the data under the "environment:" key in the pubspec.
-class PubspecEnvironment {
-  /// The version constraint specifying which SDK versions this package works
-  /// with.
-  final VersionConstraint sdkVersion;
-
-  PubspecEnvironment([VersionConstraint sdk])
-      : sdkVersion = sdk != null ? sdk : VersionConstraint.any;
-}
-
 /// An exception thrown when parsing a pubspec.
 ///
 /// These exceptions are often thrown lazily while accessing pubspec properties.
 class PubspecException extends SourceSpanFormatException
     implements ApplicationException {
   PubspecException(String message, SourceSpan span)
       : super(message, span);
 }
 
 /// Returns whether [uri] is a file URI.
 ///
 /// This is slightly more complicated than just checking if the scheme is
 /// 'file', since relative URIs also refer to the filesystem on the VM.
 bool _isFileUri(Uri uri) => uri.scheme == 'file' || uri.scheme == '';