Select packages that match SDK constraints.

utils/pub/solver/backtracking_solver.dart

Index: utils/pub/solver/backtracking_solver.dart
diff --git a/utils/pub/solver/backtracking_solver.dart b/utils/pub/solver/backtracking_solver.dart
index 0a583e2f6077cac765d207b3bf92181ea04d19de..94487920b6486d06026319334dd852335471a97d 100644
--- a/utils/pub/solver/backtracking_solver.dart
+++ b/utils/pub/solver/backtracking_solver.dart
@@ -74,7 +74,7 @@ class BacktrackingVersionSolver extends VersionSolver {
 
   /// The number of possible solutions that have been attempted.
   int get attemptedSolutions => _attemptedSolutions;
-  var _attemptedSolutions = 0;
+  var _attemptedSolutions = 1;
 
   BacktrackingVersionSolver(SourceRegistry sources, Package root,
       LockFile lockFile, List<String> useLatest)
@@ -122,12 +122,13 @@ class BacktrackingVersionSolver extends VersionSolver {
   /// previous selections, and so on. If there is nothing left to backtrack to,
   /// completes to the last failure that occurred.
   Future<List<PackageId>> _traverseSolution() {
-    _attemptedSolutions++;
-
     return new Traverser(this).traverse().catchError((error) {
       if (error is! SolveFailure) throw error;
 
-      if (_backtrack(error)) return _traverseSolution();
+      if (_backtrack(error)) {
+        _attemptedSolutions++;

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

Why is this moving in here? Won't this just decrement the reported number of
solutions by 1? It doesn't look like you've adjusted the maxTries flags on the
tests accordingly.

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

This handles a weird little corner case. If the root package's SDK constraint
does not match the current SDK, then VersionSolver will report an error before
ever calling _traverseSolution(). This meant that in that case, it would return
a SolveResult with 0 attempted solutions instead of 1.

So this change ensures the attempted solutions always start at 1.
It would except the initializer for _attemptedSolutions now starts it at 1.
The end result is the same.

+        return _traverseSolution();
+      }
 
       // All out of solutions, so fail.
       throw error;
@@ -307,6 +308,8 @@ class Traverser {
     _visited.add(id);
 
     return _solver.cache.getPubspec(id).then((pubspec) {
+      validateSdkConstraint(pubspec);
+
       var refs = pubspec.dependencies.toList();
 
       // Include dev dependencies of the root package.