Validate packages against their SDK constraints.

utils/pub/source.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 source;
 
 import 'dart:async';
 import 'io.dart';
 import 'package.dart';
 import 'pubspec.dart';
@@ skipping 86 matching lines @@
   Future<bool> install(PackageId id, String path) {
     throw "Either install or installToSystemCache must be implemented for "
         "source $name.";
   }
 
   /// Installs the package identified by [id] to the system cache. This is only
   /// called for sources with [shouldCache] set to true.
   ///
   /// By default, this uses [systemCacheDirectory] and [install].
   Future<Package> installToSystemCache(PackageId id) {
-    var path = systemCacheDirectory(id);
-    return exists(path).then((exists) {
-      if (exists) return new Future<bool>.immediate(true);
-      return ensureDir(dirname(path)).then((_) => install(id, path));
-    }).then((found) {
-      if (!found) throw 'Package $id not found.';
-      return Package.load(id.name, path, systemCache.sources);
+    return systemCacheDirectory(id).then((path) {
+      return exists(path).then((exists) {
+        if (exists) return new Future<bool>.immediate(true);
+        return ensureDir(dirname(path)).then((_) => install(id, path));
+      }).then((found) {
+        if (!found) throw 'Package $id not found.';
+        return Package.load(id.name, path, systemCache.sources);
+      });
     });
   }
 
   /// Returns the directory in the system cache that the package identified by
   /// [id] should be installed to. This should return a path to a subdirectory
   /// of [systemCacheRoot].
   ///
-  /// This doesn't need to be implemented if [shouldCache] is false, or if
-  /// [installToSystemCache] is implemented.
-  String systemCacheDirectory(PackageId id) {
-    throw 'Source.systemCacheDirectory must be implemented if shouldCache is '
-        'true and installToSystemCache is not implemented.';
+  /// This doesn't need to be implemented if [shouldCache] is false.
+  Future<String> systemCacheDirectory(PackageId id) {
+    return new Future.immediateError(
+        "systemCacheDirectory() must be implemented if shouldCache is true.");
   }
 
   /// When a [Pubspec] or [LockFile] is parsed, it reads in the description for
   /// each dependency. It is up to the dependency's [Source] to determine how
   /// that should be interpreted. This will be called during parsing to validate
   /// that the given [description] is well-formed according to this source. It
   /// should return if the description is valid, or throw a [FormatException] if
   /// not.
   ///
   /// [fromLockFile] is true when the description comes from a [LockFile], to
@@ skipping 25 matching lines @@
   /// according to [validateDescription], although it must still be serializable
   /// to JSON and YAML. It must also be equal to [id] according to
   /// [descriptionsEqual].
   ///
   /// By default, this just returns [id].
   Future<PackageId> resolveId(PackageId id) => new Future.immediate(id);
 
   /// Returns the source's name.
   String toString() => name;
 }