Regenerate pub sources.

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

Index: sdk/lib/_internal/pub_generated/lib/src/barback.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/barback.dart b/sdk/lib/_internal/pub_generated/lib/src/barback.dart
index 3a26b723dc3b0899252a0dae1033dfb0a1f56d97..ea7e650557dd98a7c5cb9a20e52422a2364ca1ca 100644
--- a/sdk/lib/_internal/pub_generated/lib/src/barback.dart
+++ b/sdk/lib/_internal/pub_generated/lib/src/barback.dart
@@ -1,30 +1,88 @@
+// 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 'package:pub_semver/pub_semver.dart';
+
+/// The currently supported versions of packages that this version of pub works
+/// with.
+///
+/// Pub implicitly constrains these packages to these versions as long as
+/// barback is a dependency.
+///
+/// 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.
+///
+/// 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 pubConstraints = {
   "barback": new VersionConstraint.parse(">=0.13.0 <0.15.3"),
   "source_span": new VersionConstraint.parse(">=1.0.0 <2.0.0"),
   "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 $id doesn't identify a library.");
   }
+
   return new Uri(
       scheme: 'package',
       path: p.url.join(id.package, id.path.replaceFirst('lib/', '')));
 }
+
+/// Converts [uri] into an [AssetId] if its path is within "packages".
+///
+/// If the URL contains a special directory, but lacks a following package name,
+/// throws a [FormatException].
+///
+/// If the URI doesn't contain one of those special directories, returns null.
 AssetId packagesUrlToId(Uri url) {
   var parts = p.url.split(url.path);
+
+  // Strip the leading "/" from the URL.
   if (parts.isNotEmpty && parts.first == "/") parts = parts.skip(1).toList();
+
   if (parts.isEmpty) return null;
+
+  // Check for "packages" in the URL.
+  // TODO(rnystrom): If we rewrite "package:" imports to relative imports that
+  // point to a canonical "packages" directory, we can limit "packages" to the
+  // root of the URL as well. See: #16649.
   var index = parts.indexOf("packages");
   if (index == -1) return null;
+
+  // There should be a package name after "packages".
   if (parts.length <= index + 1) {
     throw new FormatException(
         'Invalid URL path "${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);