Select packages that match SDK constraints.

utils/pub/solver/version_solver.dart

Index: utils/pub/solver/version_solver.dart
diff --git a/utils/pub/solver/version_solver.dart b/utils/pub/solver/version_solver.dart
index 1169ae20f988533cf46d1e81eb4e6ce33402d69b..fbf996ee4a5ed50d9689e982625d85ae8cf38faa 100644
--- a/utils/pub/solver/version_solver.dart
+++ b/utils/pub/solver/version_solver.dart
@@ -11,6 +11,7 @@ import '../lock_file.dart';
 import '../log.dart' as log;
 import '../package.dart';
 import '../pubspec.dart';
+import '../sdk.dart' as sdk;
 import '../source.dart';
 import '../source_registry.dart';
 import '../version.dart';
@@ -46,6 +47,17 @@ Future<SolveResult> resolveVersions(SourceRegistry sources, Package root,
   return solver.solve();
 }
 
+/// Ensures that if [pubspec] has an SDK constraint, then it is compatible
+/// with the current SDK. Throws a [SolverFailure] if not.
+void validateSdkConstraint(Pubspec pubspec) {

[nweiz, 2013/04/16 23:52:32]

It seems really weird that this is a top-level, public function in this library.
It's just used by the two solvers, right? Not by any clients of this library? It
seems like it belongs in a utils library.

[Bob Nystrom, 2013/04/17 17:28:44]

It was being used by both VersionSolver and BacktrackingSolver. But to keep the
old SDK constraint stuff still working, I moved it so that only
BacktrackingSolver uses it, so I just moved this into that library.

+  if (pubspec.environment.sdkVersion.allows(sdk.version)) return;
+
+  throw new CouldNotSolveException(
+      'Package "{pubspec.name} requires SDK version '
+      '${pubspec.environment.sdkVersion} but the current SDK is '
+      '${sdk.version}.');
+}
+
 /// Base class for an implementation of the version constraint solver.
 class VersionSolver {
   final SourceRegistry sources;
@@ -73,12 +85,16 @@ class VersionSolver {
   /// successful or an error if it failed to find a solution.
   Future<SolveResult> solve() {
     var stopwatch = new Stopwatch();
-    stopwatch.start();
 
-    // Pre-cache the root package's known pubspec.
-    cache.cache(new PackageId.root(root), root.pubspec);
+    return new Future(() {
+      stopwatch.start();
 
-    return runSolver().then((packages) {
+      // Pre-cache the root package's known pubspec.
+      cache.cache(new PackageId.root(root), root.pubspec);
+
+      validateSdkConstraint(root.pubspec);
+      return runSolver();
+    }).then((packages) {
       return new SolveResult(packages, null, attemptedSolutions);
     }).catchError((error) {
       if (error is! SolveFailure) throw error;
@@ -304,12 +320,13 @@ class SolveFailure implements Exception {
 /// Exception thrown when the [VersionSolver] fails to find a solution after a
 /// certain number of iterations.
 class CouldNotSolveException extends SolveFailure {
-  CouldNotSolveException()
-      : super(null, null);
+  CouldNotSolveException([String message])
+      : super(null, null),
+        _message = (message != null) ? message :
+            "Could not find a solution that met all constraints.";
 
   /// A message describing the specific kind of solve failure.
-  String get _message =>
-      "Could not find a solution that met all constraints.";
+  final String _message;
 }
 
 /// Exception thrown when the [VersionConstraint] used to match a package is