add tool to verify dependency information

bin/verify_deps.dart

+// Copyright (c) 2015, 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.
+
+/// This tools verifies that all elements that are included in the output are
+/// reachable from the program entrypoint. If there are elements that are not
+/// reachable from the entrypoint, then this indicates that we are missing
+/// dependencies. If all functions are reachable from the entrypoint, this
+/// script will return with exitcode 0. Otherwise it will list the unreachable
+/// functions and return with exitcode 1.
+library dart2js_info.bin.verify_deps;
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:dart2js_info/info.dart';
+import 'package:dart2js_info/src/graph.dart';
+import 'package:dart2js_info/src/util.dart';
+
+Future main(List<String> args) async {
+  if (args.length > 1) {
+    printUsage();
+    exit(1);
+  }
+  var json = JSON.decode(await new File(args[0]).readAsString());
+  var info = new AllInfo.fromJson(json);
+  var graph = graphFromInfo(info);
+  var entrypoint = info.program.entrypoint;
+  var reachables = findReachable(graph, entrypoint);
+
+  var unreachables = info.functions.where((func) => !reachables.contains(func));
+  if (unreachables.isNotEmpty) {
+    unreachables.forEach(print);
+    exit(1);
+  } else {
+    print('all elements are reachable from the entrypoint');
+  }
+}
+
+/// Finds the set of nodes reachable from [start] in [graph].
+Set<Info> findReachable(Graph<Info> graph, Info start) {
+  var visited = new Set<Info>();
+  var stack = <Info>[start];
+  while (stack.isNotEmpty) {
+    var next = stack.removeLast();
+    visited.add(next);
+    stack.addAll(
+        graph.targetsOf(next).where((target) => !visited.contains(target)));
+  }
+  return visited;
+}
+
+void printUsage() {
+  print('usage: dart2js_info_verify_deps <info file>');
+}