Use native async/await support in pub.

sdk/lib/_internal/pub_generated/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 '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);
-}