support resolving .packages in FE

utils/kernel-service/kernel-service.dart

 // Copyright (c) 2016, 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 is an interface to the Dart Kernel parser and Kernel binary generator.
 ///
 /// It is used by the kernel-isolate to load Dart source code and generate
 /// Kernel binary format.
 ///
 /// This is either invoked as the root script of the Kernel isolate when used
 /// as a part of
 ///
 ///         dart --dfe=utils/kernel-service/kernel-service.dart ...
 ///
 /// invocation or it is invoked as a standalone script to perform training for
 /// the app-jit snapshot
 ///
 ///         dart utils/kernel-service/kernel-service.dart --train <source-file>
 ///
 ///
 library runtime.tools.kernel_service;
 
 import 'dart:async' show Future;
-import 'dart:io' show File, Platform hide FileSystemEntity;
+import 'dart:io' show Platform hide FileSystemEntity;
 import 'dart:isolate';
 import 'dart:typed_data' show Uint8List;
 
 import 'package:front_end/file_system.dart';
 import 'package:front_end/front_end.dart';
 import 'package:front_end/memory_file_system.dart';
 import 'package:front_end/physical_file_system.dart';
 import 'package:front_end/src/fasta/kernel/utils.dart';
 import 'package:front_end/src/testing/hybrid_file_system.dart';
 import 'package:kernel/kernel.dart' show Program;
 import 'package:kernel/target/targets.dart' show TargetFlags;
 import 'package:kernel/target/vm_fasta.dart' show VmFastaTarget;
 
 const bool verbose = const bool.fromEnvironment('DFE_VERBOSE');
 
 const bool strongMode = const bool.fromEnvironment('DFE_STRONG_MODE');
 
 Future<CompilationResult> _parseScriptInFileSystem(
     Uri script, FileSystem fileSystem,
     {bool verbose: false, bool strongMode: false}) async {
   final Uri packagesUri = (Platform.packageConfig != null)
       ? Uri.parse(Platform.packageConfig)
-      : await _findPackagesFile(fileSystem, script);
-  if (packagesUri == null) {
-    throw "Could not find .packages";
-  }
+      : null;
 
   final Uri patchedSdk = Uri.base
       .resolveUri(new Uri.file(Platform.resolvedExecutable))
       .resolveUri(new Uri.directory("patched_sdk"));
 
   if (verbose) {
     print("""DFE: Requesting compilation {
   scriptUri: ${script}
   packagesUri: ${packagesUri}
   patchedSdk: ${patchedSdk}
@@ skipping 20 matching lines @@
     // marked `external`, so we can use that bit to decide what to excluce.
     // TODO(sigmund): remove the following line (Issue #30111)
     program.libraries.forEach((e) => e.isExternal = false);
     return new CompilationResult.ok(
         serializeProgram(program, filter: (lib) => !lib.isExternal));
   } catch (err, stack) {
     return new CompilationResult.crash(err, stack);
   }
 }
 
-/// This duplicates functionality from the Loader which we can't easily
-/// access from here.
-// TODO(sigmund): delete, this should be supported by the default options in
-// package:front_end.
-Future<Uri> _findPackagesFile(FileSystem fileSystem, Uri base) async {
-  var dir = new File.fromUri(base).parent;
-  while (true) {
-    final packagesFile = dir.uri.resolve(".packages");
-    if (await fileSystem.entityForUri(packagesFile).exists()) {
-      return packagesFile;
-    }
-    if (dir.parent.path == dir.path) {
-      break;
-    }
-    dir = dir.parent;
-  }
-  return null;
-}
-
 Future<CompilationResult> _processLoadRequestImpl(
     String inputFilePathOrUri, FileSystem fileSystem) {
   Uri scriptUri = Uri.parse(inputFilePathOrUri);
 
   // Because we serve both Loader and bootstrapping requests we need to
   // duplicate the logic from _resolveScriptUri(...) here and attempt to
   // resolve schemaless uris using current working directory.
   if (!scriptUri.hasScheme) {
     // Script does not have a scheme, assume that it is a path,
     // resolve it against the working directory.
@@ skipping 176 matching lines @@
   _CompilationCrash(this.exception, this.stack);
 
   @override
   Status get status => Status.crash;
 
   @override
   String get errorString => "${exception}\n${stack}";
 
   String toString() => "_CompilationCrash(${errorString})";
 }