Simplify finding of .dart files in subpackage_relationships_test.

pkg/front_end/test/subpackage_relationships_test.dart

 // Copyright (c) 2017, 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:async';
 import 'dart:io';
 
 import 'package:front_end/compiler_options.dart';
 import 'package:front_end/dependency_grapher.dart';
 import 'package:path/path.dart' as pathos;
@@ skipping 32 matching lines @@
 
   /// Indicates which other subpackages a given subpackage may directly depend
   /// on.
   final List<String> allowedDependencies;
 
   SubpackageRules(
       {this.mayImportAnalyzer: false, this.allowedDependencies: const []});
 }
 
 class _SubpackageRelationshipsTest {
-  /// File uri of the root of the front_end package.
-  final frontEndRootUri = Platform.script.resolve('..');
+  /// File uri of the front_end package's "lib" directory.
+  final frontEndLibUri = Platform.script.resolve('../lib/');
 
   /// Indicates whether any problems have been reported yet.
   bool problemsReported = false;
 
   /// Check for problems resulting from URI [src] having a direct dependency on
   /// URI [dst].
   void checkDependency(Uri src, Uri dst) {
     if (dst.scheme == 'dart') return;
     if (dst.scheme != 'package') {
       problem('$src depends on $dst, which is neither a package: or dart: URI');
@@ skipping 16 matching lines @@
     if (dstSubPackage == null) return;
     if (dstSubPackage == srcSubpackage) return;
     if (!srcSubpackageRules.allowedDependencies.contains(dstSubPackage)) {
       problem('$src depends on $dst, but subpackage "$srcSubpackage" is not '
           'allowed to depend on subpackage "$dstSubPackage"');
     }
   }
 
   /// Finds all files in the front_end's "lib" directory and returns their Uris
   /// (as "package:" URIs).
-  Future<List<Uri>> findFrontEndUris() async {
+  List<Uri> findFrontEndUris() {
     var frontEndUris = <Uri>[];
-    var frontEndRootPath = pathos.fromUri(frontEndRootUri);
-    await for (var entity in new Directory(frontEndRootPath)
-        .list(recursive: true, followLinks: false)) {
+    var frontEndLibPath = pathos.fromUri(frontEndLibUri);
+    for (var entity in new Directory(frontEndLibPath)
+        .listSync(recursive: true, followLinks: false)) {
       if (entity is File && entity.path.endsWith('.dart')) {
-        var posixRelativePath = pathos
-            .relative(entity.path, from: frontEndRootPath)
-            .replaceAll(pathos.separator, '/');
-        if (!posixRelativePath.startsWith('lib/')) continue;
-        frontEndUris.add(Uri.parse(
-            posixRelativePath.replaceFirst('lib/', 'package:front_end/')));
+        var posixRelativePath = pathos.url.joinAll(
+            pathos.split(pathos.relative(entity.path, from: frontEndLibPath)));
+        frontEndUris.add(Uri.parse('package:front_end/$posixRelativePath'));
       }
     }
     return frontEndUris;
   }
 
   /// Reports a single problem.
   void problem(String description) {
     print(description);
     problemsReported = true;
   }
 
   /// Tests all subpackage relationships in the front end, and returns an
   /// appropriate exit code.
   Future<int> run() async {
     var frontEndUris = await findFrontEndUris();
-    var packagesFileUri = frontEndRootUri.resolve('../../.packages');
+    var packagesFileUri = frontEndLibUri.resolve('../../../.packages');
     var graph = await graphForProgram(
         frontEndUris,
         new CompilerOptions()
           ..packagesFileUri = packagesFileUri
           ..chaseDependencies = true);
     for (var i = 0; i < graph.topologicallySortedCycles.length; i++) {
       for (var library in graph.topologicallySortedCycles[i].libraries.values) {
         for (var dependency in library.dependencies) {
           checkDependency(library.uri, dependency.uri);
         }
       }
     }
     return problemsReported ? 1 : 0;
   }
 
   /// Determines which subpackage [src] is in.
   ///
   /// If [src] is not part of the front end, `null` is returned.
   String subpackageForUri(Uri src) {
     if (src.scheme != 'package') return null;
     if (src.pathSegments[0] != 'front_end') return null;
     if (src.pathSegments[1] != 'src') return 'lib';
     if (src.pathSegments.length == 3) return 'lib/src';
     return 'lib/src/${src.pathSegments[2]}';
   }
 }