Add implicit constraints from pub onto stack_trace and source_maps.

sdk/lib/_internal/pub/lib/src/barback.dart

 // Copyright (c) 2013, 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 pub.barback;
 
 import 'package:barback/barback.dart';
 import 'package:path/path.dart' as p;
 
 import 'version.dart';
 
-/// The currently supported versions of the Barback package that this version of
-/// pub works with.
+/// The currently supported versions of packages that this version of pub works
+/// with.
 ///
-/// Pub implicitly constrains barback to these versions.
+/// Pub implicitly constrains these packages to these versions as long as
+/// barback is a dependency.
 ///
-/// Barback is in a unique position. Pub imports it, so a copy of Barback is
-/// physically included in the SDK. Packages also depend on Barback (from
-/// pub.dartlang.org) when they implement their own transformers. Pub's plug-in
-/// API dynamically loads transformers into their own isolate.
+/// Users' transformers are loaded in an isolate that uses the entrypoint
+/// package's dependency versions. However, that isolate also loads code
+/// provided by pub (`asset/dart/transformer_isolate.dart` and associated
+/// files). This code uses these packages as well, so these constraints exist to
+/// ensure that its usage of the packages remains valid.
 ///
-/// This includes a Dart file (`asset/dart/transformer_isolate.dart`) which
-/// imports "package:barback/barback.dart". This file is included in the SDK,
-/// but that import is resolved using the application’s version of Barback. That
-/// means pub must tightly control which version of Barback the application is
-/// using so that it's one that pub supports.
+/// Most constraints here are like normal version constraints in that their
+/// upper bound is the next major version of the package (or minor version for
+/// pre-1.0.0 packages). If a new major version of the package is released,
+/// these *must* be incremented to synchronize with that.
+///
+/// The constraint on barback is different. Its upper bound is the next *patch*
+/// version of barback—that is, the next version with new features. This is
+/// because most barback features need additional serialization code to be fully
+/// supported in pub, even if they're otherwise backwards-compatible.
 ///
 /// Whenever a new minor or patch version of barback is published, this *must*
 /// be incremented to synchronize with that. See the barback [compatibility
 /// documentation][compat] for details on the relationship between this
 /// constraint and barback's version.
 ///
 /// [compat]: https://gist.github.com/nex3/10942218
-final supportedVersions = new VersionConstraint.parse(">=0.13.0 <0.14.2");
+final pubConstraints = {
+  "barback": new VersionConstraint.parse(">=0.13.0 <0.14.2"),
+  "source_maps": new VersionConstraint.parse(">=0.9.0 <0.10.0"),
+  "stack_trace": new VersionConstraint.parse(">=0.9.1 <2.0.0")
+};
 
 /// Converts [id] to a "package:" URI.
 ///
 /// This will throw an [ArgumentError] if [id] doesn't represent a library in
 /// `lib/`.
 Uri idToPackageUri(AssetId id) {
   if (!id.path.startsWith('lib/')) {
     throw new ArgumentError("Asset id $id doesn't identify a library.");
   }
 
@@ skipping 26 matching lines @@
   if (parts.length <= index + 1) {
     throw new FormatException(
         'Invalid URL path "${url.path}". Expected package name '
         'after "packages".');
   }
 
   var package = parts[index + 1];
   var assetPath = p.url.join("lib", p.url.joinAll(parts.skip(index + 2)));
   return new AssetId(package, assetPath);
 }