Revert "Revert "Use native async/await support in pub.""

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

Index: sdk/lib/_internal/pub_generated/lib/src/preprocess.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/preprocess.dart b/sdk/lib/_internal/pub_generated/lib/src/preprocess.dart
deleted file mode 100644
index bf05f89fae1cdd0e320db0f7379a006b4987c423..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/lib/src/preprocess.dart
+++ /dev/null
@@ -1,144 +0,0 @@
-// Copyright (c) 2014, 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.preprocess;
-
-import 'package:pub_semver/pub_semver.dart';
-import 'package:string_scanner/string_scanner.dart';
-
-/// Runs a simple preprocessor over [input] to remove sections that are
-/// incompatible with the available barback version.
-///
-/// [versions] are the available versions of each installed package, and
-/// [sourceUrl] is a [String] or [Uri] indicating where [input] came from. It's
-/// used for error reporting.
-///
-/// For the most part, the preprocessor leaves text in the source document
-/// alone. However, it handles two types of lines specially. Lines that begin
-/// with `//>` are uncommented by the preprocessor, and lines that begin with
-/// `//#` are operators.
-///
-/// The preprocessor currently supports one top-level operator, "if":
-///
-///     //# if barback >=0.14.1
-///       ...
-///     //# else
-///       ...
-///     //# end
-///
-/// If can check against any package installed in the current package. It can
-/// check the version of the package, as above, or (if the version range is
-/// omitted) whether the package exists at all. If the condition is true,
-/// everything within the first block is included in the output and everything
-/// within the second block is removed; otherwise, the first block is removed
-/// and the second block is included. The `else` block is optional.
-///
-/// It's important that the preprocessor syntax also be valid Dart code, because
-/// pub loads the source files before preprocessing and runs them against the
-/// version of barback that was compiled into pub. This is why the `//>` syntax
-/// exists: so that code can be hidden from the running pub process but still be
-/// visible to the barback isolate. For example:
-///
-///     //# if barback >= 0.14.1
-///       ClassMirror get aggregateClass => reflectClass(AggregateTransformer);
-///     //# else
-///     //>   ClassMirror get aggregateClass => null;
-///     //# end
-String preprocess(String input, Map<String, Version> versions, sourceUrl) {
-  // Short-circuit if there are no preprocessor directives in the file.
-  if (!input.contains(new RegExp(r"^//[>#]", multiLine: true))) return input;
-  return new _Preprocessor(input, versions, sourceUrl).run();
-}
-
-/// The preprocessor class.
-class _Preprocessor {
-  /// The scanner over the input string.
-  final StringScanner _scanner;
-
-  final Map<String, Version> _versions;
-
-  /// The buffer to which the output is written.
-  final _buffer = new StringBuffer();
-
-  _Preprocessor(String input, this._versions, sourceUrl)
-      : _scanner = new StringScanner(input, sourceUrl: sourceUrl);
-
-  /// Run the preprocessor and return the processed output.
-  String run() {
-    while (!_scanner.isDone) {
-      if (_scanner.scan(new RegExp(r"//#[ \t]*"))) {
-        _if();
-      } else {
-        _emitText();
-      }
-    }
-
-    _scanner.expectDone();
-    return _buffer.toString();
-  }
-
-  /// Emit lines of the input document directly until an operator is
-  /// encountered.
-  void _emitText() {
-    while (!_scanner.isDone && !_scanner.matches("//#")) {
-      if (_scanner.scan("//>")) {
-        if (!_scanner.matches("\n")) _scanner.expect(" ");
-      }
-
-      _scanner.scan(new RegExp(r"[^\n]*\n?"));
-      _buffer.write(_scanner.lastMatch[0]);
-    }
-  }
-
-  /// Move through lines of the input document without emitting them until an
-  /// operator is encountered.
-  void _ignoreText() {
-    while (!_scanner.isDone && !_scanner.matches("//#")) {
-      _scanner.scan(new RegExp(r"[^\n]*\n?"));
-    }
-  }
-
-  /// Handle an `if` operator.
-  void _if() {
-    _scanner.expect(new RegExp(r"if[ \t]+"), name: "if statement");
-    _scanner.expect(new RegExp(r"[a-zA-Z0-9_]+"), name: "package name");
-    var package = _scanner.lastMatch[0];
-
-    _scanner.scan(new RegExp(r"[ \t]*"));
-    var constraint = VersionConstraint.any;
-    if (_scanner.scan(new RegExp(r"[^\n]+"))) {
-      try {
-        constraint = new VersionConstraint.parse(_scanner.lastMatch[0]);
-      } on FormatException catch (error) {
-        _scanner.error("Invalid version constraint: ${error.message}");
-      }
-    }
-    _scanner.expect("\n");
-
-    var allowed =
-        _versions.containsKey(package) &&
-        constraint.allows(_versions[package]);
-    if (allowed) {
-      _emitText();
-    } else {
-      _ignoreText();
-    }
-
-    _scanner.expect("//#");
-    _scanner.scan(new RegExp(r"[ \t]*"));
-    if (_scanner.scan("else")) {
-      _scanner.expect("\n");
-      if (allowed) {
-        _ignoreText();
-      } else {
-        _emitText();
-      }
-      _scanner.expect("//#");
-      _scanner.scan(new RegExp(r"[ \t]*"));
-    }
-
-    _scanner.expect("end");
-    if (!_scanner.isDone) _scanner.expect("\n");
-  }
-}