Tweak SDK constraint checking a bit.

utils/pub/system_cache.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 system_cache;
 
 import 'dart:io';
 import 'dart:async';
 
 import 'git_source.dart';
@@ skipping 44 matching lines @@
 
   /// Registers a new source. This source must not have the same name as a
   /// source that's already been registered.
   void register(Source source) {
     source.bind(this);
     sources.register(source);
   }
 
   /// Gets the package identified by [id]. If the package is already cached,
   /// reads it from the cache. Otherwise, requests it from the source.
-  Future<Package> describe(PackageId id) {
-    Future<Package> getUncached() {
+  Future<Pubspec> describe(PackageId id) {
+    Future<Pubspec> getUncached() {

[nweiz, 2013/02/02 00:15:29]

This probably doesn't need to be a separate function anymore.

[Bob Nystrom, 2013/02/02 00:47:10]

Done.

       // Not cached, so get it from the source.
-      return id.describe().then((pubspec) => new Package.inMemory(pubspec));
+      return id.describe();
     }
 
     // Try to get it from the system cache first.
     if (id.source.shouldCache) {
       return id.systemCacheDirectory.then((packageDir) {
         if (!dirExistsSync(packageDir)) return getUncached();
-        return Package.load(id.name, packageDir, sources);
+        // TODO(rnystrom): Going through Package for this is a bit weird.
+        // Once Package loading is synchronous, should give Pubspec itself a
+        // constructor that loads the file.
+        return Package.load(id.name, packageDir, sources)
+            .then((package) => package.pubspec);;

[nweiz, 2013/02/02 00:15:29]

Style nit: extra semicolon

[Bob Nystrom, 2013/02/02 00:47:10]

Done.

       });
     }
 
     // Not cached, so get it from the source.
     return getUncached();
   }
 
   /// Ensures that the package identified by [id] is installed to the cache,
   /// loads it, and returns it.
   ///
@@ skipping 26 matching lines @@
 
   /// Delete's the system cache's internal temp directory.
   Future deleteTempDir() {
     log.fine('Clean up system cache temp directory $tempDir.');
     return dirExists(tempDir).then((exists) {
       if (!exists) return;
       return deleteDir(tempDir);
     });
   }
 }