Show implicit pub dependency on barback in errors.

sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart

Index: sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart
diff --git a/sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart b/sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart
index d1f687ee9beaf0ad59ae48bc4c6fe73df592e10d..e80db88465f295c627f17a4a2941514ea3dc6426 100644
--- a/sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart
+++ b/sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart
@@ -509,6 +509,26 @@ class Traverser {
         var dependencies = _getDependencies(dep.name);
         dependencies.add(new Dependency(depender, dep));
 
+        // If the package is barback, pub has an implicit version constraint on it
+        // since pub itself uses barback too. Note that we don't check for the
+        // hosted source here because we still want to do this even when people on
+        // the Dart team are on the bleeding edge and have a path dependency on the

[nweiz, 2013/12/13 23:15:21]

Long lines.

[Bob Nystrom, 2013/12/14 00:07:35]

Done.

+        // tip version of barback in the Dart repo.
+        if (dep.name == "barback" && dependencies.length == 1) {

[nweiz, 2013/12/13 23:15:21]

Document why you're checking [dependencies.length] here. I assume it's because
you don't want to add the dependency from pub if it's already there?

[Bob Nystrom, 2013/12/14 00:07:35]

Yup. Done.

+          var range = new VersionRange(
+              min: barback.supportedVersion, includeMin: true,
+              max: barback.supportedVersion.nextMinor, includeMax: false);
+          _solver.logSolve('add implicit $range pub dependency on barback');
+
+          // Use the same source and description as the explicit dependency.
+          // That way, this doesn't fail with a source/desc conflict if users
+          // (like Dart team members) use things like a path dependency to
+          // find barback.
+          var barbackDep = new PackageDep(dep.name, dep.source, range,
+              dep.description);
+          dependencies.add(new Dependency("pub", barbackDep));

[nweiz, 2013/12/13 23:15:21]

Just using the string "pub" here worries me. If we ever release a package named
pub (which seems likely at some point), that could wreak some serious havoc.

We have pretty stringent rules on what package names can appear in a pubspec, so
we should be able to create a "special" name that avoids conflict by having it
contain spaces or start with "*" or something.

[Bob Nystrom, 2013/12/14 00:07:35]

Changed it to "pub itself" and then tweaked SolveFailure to not quote that name.
Looks like:

Incompatible version constraints on 'barback':
- 'myapp' depends on version $previous
- pub itself depends on version >=0.11.0 <0.12.0

+        }
+
         var constraint = _getConstraint(dep.name);
 
         // See if it's possible for a package to match that constraint.
@@ -639,19 +659,6 @@ class Traverser {
         .map((dep) => dep.dep.constraint)
         .fold(VersionConstraint.any, (a, b) => a.intersect(b));
 
-    // If the package is barback, pub has an implicit version constraint on it
-    // since pub itself uses barback too. Note that we don't check for the
-    // hosted source here because we still want to do this even when people on
-    // the Dart team are on the bleeding edge and have a path dependency on the
-    // tip version of barback in the Dart repo.
-    if (name == "barback") {
-      var range = new VersionRange(
-          min: barback.supportedVersion, includeMin: true,
-          max: barback.supportedVersion.nextMinor, includeMax: false);
-      constraint = constraint.intersect(range);
-      _solver.logSolve('add implicit $range constraint to barback');
-    }
-
     return constraint;
   }