Include stderr on git failure.

utils/pub/version_solver.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.
 
 /**
  * Attempts to resolve a set of version constraints for a package dependency
  * graph and select an appropriate set of best specific versions for all
  * dependent packages. It works iteratively and tries to reach a stable
  * solution where the constraints of all dependencies are met. If it fails to
  * reach a solution after a certain number of iterations, it assumes the
@@ skipping 179 matching lines @@
     seen.add(dependency.name);
 
     for (var dependerName in dependency.dependers) {
       var depender = getDependency(dependerName);
       var locked = lockFile.packages[dependerName];
       if (locked != null && depender.version == locked.version) {
         enqueue(new UnlockPackage(depender));
         return true;
       }
     }
-    
+
     return dependency.dependers.map(getDependency).some((subdependency) =>
         tryUnlockDepender(subdependency, seen));
   }
 
   List<PackageId> buildResults() {
     return _packages.getValues().filter((dep) => dep.isDependedOn).map((dep) {
       var description = dep.description;
 
       // If the lockfile contains a fully-resolved description for the package,
       // use that. This allows e.g. Git to ensure that the same commit is used.
@@ skipping 110 matching lines @@
 }
 
 /**
  * A constraint that a depending package places on a dependent package has
  * changed.
  *
  * This is an abstract class that contains logic for updating the dependency
  * graph once a dependency has changed. Changing the dependency is the
  * responsibility of subclasses.
  */
-class ChangeConstraint implements WorkItem {
+abstract class ChangeConstraint implements WorkItem {
   abstract Future process(VersionSolver solver);
 
   abstract void undo(VersionSolver solver);
 
   Future _processChange(VersionSolver solver, Dependency oldDependency,
       Dependency newDependency) {
     var name = newDependency.name;
     var source = oldDependency.source != null ?
       oldDependency.source : newDependency.source;
     var description = oldDependency.description != null ?
@@ skipping 381 matching lines @@
   final description1;
   final description2;
 
   DescriptionMismatchException(this.package, this.description1,
       this.description2);
 
   // TODO(nweiz): Dump to YAML when that's supported
   String toString() => "Package '$package' has conflicting descriptions "
     "'${JSON.stringify(description1)}' and '${JSON.stringify(description2)}'";
 }