Tweak SDK constraint checking a bit.

utils/pub/entrypoint.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 entrypoint;
 
 import 'dart:async';
 import 'io.dart';
 import 'lock_file.dart';
 import 'log.dart' as log;
 import 'package.dart';
+import 'pubspec.dart';
 import 'sdk.dart' as sdk;
 import 'system_cache.dart';
 import 'utils.dart';
 import 'version.dart';
 import 'version_solver.dart';
 
 /// Pub operates over a directed graph of dependencies that starts at a root
 /// "entrypoint" package. This is typically the package where the current
 /// working directory is located. An entrypoint knows the [root] package it is
 /// associated with and is responsible for managing the "packages" directory
@@ skipping 114 matching lines @@
         return install(id);
       }));
     }).then(_saveLockFile)
       .then(_installSelfReference)
       .then(_linkSecondaryPackageDirs);
   }
 
   /// Traverses the root's package dependency graph and loads each of the
   /// reached packages. This should only be called after the lockfile has been
   /// successfully generated.
-  Future<List<Package>> walkDependencies() {
+  Future<List<Pubspec>> walkDependencies() {
     return loadLockFile().then((lockFile) {
-      var group = new FutureGroup<Package>();
+      var group = new FutureGroup<Pubspec>();
       var visited = new Set<String>();
 
       // Include the root package in the results.
-      group.add(new Future.immediate(root));
+      group.add(new Future.immediate(root.pubspec));
 
-      visitPackage(Package package) {
-        for (var ref in package.dependencies) {
+      visitPackage(Pubspec pubspec) {
+        for (var ref in pubspec.dependencies) {
           if (visited.contains(ref.name)) continue;
 
           // Look up the concrete version.
           var id = lockFile.packages[ref.name];
 
           visited.add(ref.name);
           var future = cache.describe(id);
           group.add(future.then(visitPackage));
         }
 
-        return package;
+        return pubspec;
       }
 
-      visitPackage(root);
+      visitPackage(root.pubspec);
       return group.future;
     });
   }
 
   /// Validates that the current Dart SDK version matches the SDK constraints
   /// of every package in the dependency graph. If a package's constraint does
   /// not match, prints an error.
   Future validateSdkConstraints() {
-    return walkDependencies().then((packages) {
+    return walkDependencies().then((pubspecs) {
       var errors = [];
 
-      for (var package in packages) {
-        var sdkConstraint = package.pubspec.environment.sdkVersion;
+      for (var pubspec in pubspecs) {
+        var sdkConstraint = pubspec.environment.sdkVersion;
         if (!sdkConstraint.allows(sdk.version)) {
-          errors.add("- '${package.name}' requires ${sdkConstraint}");
+          errors.add("- '${pubspec.name}' requires ${sdkConstraint}");
         }
       }
 
       if (errors.length > 0) {
         log.error("Some packages are not compatible with your SDK version "
                 "${sdk.version}:\n"
             "${errors.join('\n')}\n\n"
             "You may be able to resolve this by upgrading to the latest Dart "
                 "SDK\n"
             "or adding a version constraint to use an older version of a "
@@ skipping 101 matching lines @@
 
   /// Creates a symlink to the `packages` directory in [dir] if none exists.
   Future _linkSecondaryPackageDir(String dir) {
     var to = join(dir, 'packages');
     return exists(to).then((exists) {
       if (exists) return;
       return createSymlink(path, to);
     });
   }
 }