Skeleton code for running the forthcoming async/await compiler on pub.

sdk/lib/_internal/pub/bin/async_compile.dart

+// 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.
+
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+
+/// The path to pub's root directory (sdk/lib/_internal/pub) in the Dart repo.
+///
+/// This assumes this script is itself being run from within the repo.
+final sourceDir = p.dirname(p.dirname(p.fromUri(Platform.script)));
+
+/// The [sourceDir] as a URL, for use in import strings.
+final sourceUrl = p.toUri(sourceDir).toString();
+
+/// The directory that compiler output should be written to.
+String buildDir;
+
+/// This runs the async/await compiler on all of the pub source code.
+///
+/// It reads from the repo and writes the compiled output into the given build
+/// directory (using the same file names and relative layout). Does not
+/// compile files that haven't changed since the last time they were compiled.
+// TODO(rnystrom): Remove this when #104 is fixed.
+void main(List<String> arguments) {
+  _validate(arguments.isNotEmpty, "Missing build directory.");
+  _validate(arguments.length <= 2, "Unexpected arguments.");
+  if (arguments.length == 2) {
+    _validate(arguments[1] == "--silent",
+        "Invalid argument '${arguments[1]}");
+  }
+
+  // Create the build output directory if it's not already there.
+  buildDir = p.join(p.normalize(arguments[0]), "pub_async");
+  new Directory(buildDir).createSync(recursive: true);
+
+  var silent = arguments.length == 2 && arguments[1] == "--silent";
+  var numFiles = 0;
+  var numCompiled = 0;
+
+  // Compile any modified or missing files.
+  for (var entry in new Directory(sourceDir).listSync(recursive: true)) {
+    if (p.extension(entry.path) != ".dart") continue;
+
+    // Skip tests.
+    // TODO(rnystrom): Do we want to use this for tests too?
+    if (p.isWithin(p.join(sourceDir, "test"), entry.path)) continue;
+
+    numFiles++;
+    var relative = p.relative(entry.path, from: sourceDir);
+
+    var sourceFile = entry as File;
+    var destPath = p.join(buildDir, relative);
+    var destFile = new File(destPath);
+    if (!destFile.existsSync() ||
+        entry.lastModifiedSync().isAfter(destFile.lastModifiedSync())) {
+      compile(sourceFile.path, sourceFile.readAsStringSync(), destPath);
+      numCompiled++;
+      if (!silent) print("Compiled ${sourceFile.path}.");
+    }
+  }
+
+  if (!silent) print("Compiled $numCompiled out of $numFiles files.");
+}
+
+final _compilerPattern = new RegExp(r"import '(\.\./)+compiler");
+
+void compile(String sourcePath, String source, String destPath) {
+  var destDir = new Directory(p.dirname(destPath));
+  destDir.createSync(recursive: true);
+
+  // TODO(rnystrom): Do real async/await transformation here!
+  source = source.replaceAll("ASYNC!", "");
+
+  // Pub imports dart2js using relative imports that reach outside of pub's
+  // source tree. Since the build directory is in a different location, we need
+  // to fix those to be valid relative imports from the build directory.
+  var compilerDir = p.url.join(sourceUrl, "../compiler");
+  var relative = p.url.relative(compilerDir, from: destDir.path);
+  source = source.replaceAll(_compilerPattern, "import '$relative");
+
+  try {
+    new File(destPath).writeAsStringSync(source);
+  } on IOException catch (ex) {
+    // Do nothing. This may happen if two instances of the compiler are running
+    // concurrently and compile the same file. The second one to try to write
+    // the output may fail if the file is still open. Since they are producing
+    // the same output anyway, just ignore it when the second one fails.
+  }
+}
+
+/// Validates command-line argument usage and exits with [message] if [valid]
+/// is `false`.
+void _validate(bool valid, String message) {
+  if (valid) return;
+
+  stderr.writeln(message);
+  stderr.writeln();
+  stderr.writeln("Usage: dart async_compile.dart <build dir> [--silent]");
+  exit(64);
+}