Tweak SDK constraint checking a bit.

utils/pub/system_cache.dart

Index: utils/pub/system_cache.dart
diff --git a/utils/pub/system_cache.dart b/utils/pub/system_cache.dart
index 634dc173257b0e9742a549f86e6903fae9b855be..cd151f4f7518f0791f70659e5d98678ea763dd65 100644
--- a/utils/pub/system_cache.dart
+++ b/utils/pub/system_cache.dart
@@ -62,17 +62,21 @@ class SystemCache {
 
   /// 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.

       });
     }