Add support for specifying SDK version constraints in pubspecs.

utils/pub/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.
 
 library pubspec;
 
 import 'package.dart';
 import 'source.dart';
 import 'source_registry.dart';
 import 'utils.dart';
 import 'version.dart';
 import 'yaml/yaml.dart';
 
 /// The parsed and validated contents of a pubspec file.
 class Pubspec {
   /// This package's name.
   final String name;
 
   /// This package's version.
   final Version version;
 
   /// The packages this package depends on.
   final List<PackageRef> dependencies;
 
+  /// The environment-related metadata.
+  final PubspecEnvironment environment;
+
   /// All pubspec fields. This includes the fields from which other properties
   /// are derived.
   final Map<String, Object> fields;
 
-  Pubspec(this.name, this.version, this.dependencies,
+  Pubspec(this.name, this.version, this.dependencies, this.environment,
       [Map<String, Object> fields])
     : this.fields = fields == null ? {} : fields;
 
   Pubspec.empty()
     : name = null,
       version = Version.none,
       dependencies = <PackageRef>[],
+      environment = new PubspecEnvironment(),
       fields = {};
 
-  /// Whether or not the pubspec has no contents. 
+  /// Whether or not the pubspec has no contents.
   bool get isEmpty =>
     name == null && version == Version.none && dependencies.isEmpty;
 
   /// Parses the pubspec whose text is [contents]. If the pubspec doesn't define
   /// version for itself, it defaults to [Version.none].
   factory Pubspec.parse(String contents, SourceRegistry sources) {
     var name = null;
     var version = Version.none;
 
     if (contents.trim() == '') return new Pubspec.empty();
@@ skipping 13 matching lines @@
       }
     }
 
     if (parsedPubspec.containsKey('version')) {
       version = new Version.parse(parsedPubspec['version']);
     }
 
     var dependencies = _parseDependencies(sources,
         parsedPubspec['dependencies']);
 
+    var environmentYaml = parsedPubspec['environment'];
+    var sdkConstraint = VersionConstraint.any;
+    if (environmentYaml != null) {
+      if (environmentYaml is! Map) {
+        throw new FormatException(
+            'The pubspec "environment" field should be a map, but was '
+            '"$environmentYaml".');
+      }
+
+      var sdkYaml = environmentYaml['sdk'];
+      if (sdkYaml is! String) {
+        throw new FormatException(
+            'The "sdk" field of "environment" should be a string, but was '
+            '"$sdkYaml".');
+      }
+
+      sdkConstraint = new VersionConstraint.parse(sdkYaml);
+    }
+    var environment = new PubspecEnvironment(sdkConstraint);
+
     // Even though the pub app itself doesn't use these fields, we validate
     // them here so that users find errors early before they try to upload to
     // the server:
     // TODO(rnystrom): We should split this validation into separate layers:
     // 1. Stuff that is required in any pubspec to perform any command. Things
     //    like "must have a name". That should go here.
     // 2. Stuff that is required to upload a package. Things like "homepage
     //    must use a valid scheme". That should go elsewhere. pub upload should
     //    call it, and we should provide a separate command to show the user,
     //    and also expose it to the editor in some way.
@@ skipping 33 matching lines @@
         throw new FormatException('The pubspec "authors" field should be a '
             'string or a list of strings, but was "$authors".');
       }
 
       if (parsedPubspec.containsKey('author')) {
         throw new FormatException('A pubspec should not have both an "author" '
             'and an "authors" field.');
       }
     }
 
-    return new Pubspec(name, version, dependencies, parsedPubspec);
+    return new Pubspec(name, version, dependencies, environment, parsedPubspec);
   }
 }
 
 List<PackageRef> _parseDependencies(SourceRegistry sources, yaml) {
   var dependencies = <PackageRef>[];
 
   // Allow an empty dependencies key.
   if (yaml == null) return dependencies;
 
   if (yaml is! Map || yaml.keys.any((e) => e is! String)) {
@@ skipping 37 matching lines @@
     }
 
     source.validateDescription(description, fromLockFile: false);
 
     dependencies.add(new PackageRef(
         name, source, versionConstraint, description));
   });
 
   return dependencies;
 }
+
+/// 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;
+}