(Reland) Start using FileState/FileSystemState to provide consistent view.

pkg/front_end/lib/src/incremental_kernel_generator_impl.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 'package:front_end/file_system.dart';
 import 'package:front_end/incremental_kernel_generator.dart';
 import 'package:front_end/incremental_resolved_ast_generator.dart';
 import 'package:front_end/src/base/processed_options.dart';
 import 'package:front_end/src/fasta/dill/dill_target.dart';
 import 'package:front_end/src/fasta/kernel/kernel_target.dart';
 import 'package:front_end/src/fasta/ticker.dart';
 import 'package:front_end/src/fasta/translate_uri.dart';
+import 'package:front_end/src/incremental/file_state.dart';
 import 'package:kernel/kernel.dart' hide Source;
+import 'package:kernel/target/vm.dart';
 
 dynamic unimplemented() {
   // TODO(paulberry): get rid of this.
   throw new UnimplementedError();
 }
 
 /// Implementation of [IncrementalKernelGenerator].
 ///
 /// TODO(scheglov) Update the documentation.
 ///
 /// Theory of operation: an instance of [IncrementalResolvedAstGenerator] is
 /// used to obtain resolved ASTs, and these are fed into kernel code generation
 /// logic.
 class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
   /// The URI of the program entry point.
   final Uri _entryPoint;
 
   /// The compiler options, such as the [FileSystem], the SDK dill location,
   /// etc.
   final ProcessedOptions _options;
 
+  /// The set of absolute file URIs that were reported through [invalidate]
+  /// and not checked for actual changes yet.
+  final Set<Uri> _invalidatedFiles = new Set<Uri>();
+
   /// The object that knows how to resolve "package:" and "dart:" URIs.
   TranslateUri _uriTranslator;
 
+  /// The current file system state.
+  FileSystemState _fsState;
+
   /// The cached SDK kernel.
   DillTarget _sdkDillTarget;
 
   IncrementalKernelGeneratorImpl(this._entryPoint, this._options);
 
   @override
   Future<DeltaProgram> computeDelta(
       {Future<Null> watch(Uri uri, bool used)}) async {
-    _uriTranslator ??= await _options.getUriTranslator();
+    await _initialize();
+    await _ensureVmLibrariesLoaded();
+    await _refreshInvalidatedFiles();
+
+    // Ensure that the graph starting at the entry point is ready.
+    await _fsState.getFile(_entryPoint);
 
     DillTarget sdkTarget = await _getSdkDillTarget();
     // TODO(scheglov) Use it to also serve other package kernels.
 
-    KernelTarget kernelTarget = new KernelTarget(_options.fileSystem, sdkTarget,
-        _uriTranslator, _options.strongMode, null);
+    KernelTarget kernelTarget = new KernelTarget(_fsState.fileSystemView,
+        sdkTarget, _uriTranslator, _options.strongMode, null);
     kernelTarget.read(_entryPoint);
 
     // TODO(scheglov) Replace with a better API.
     // Firstly, we don't "write" anything here.
     // Secondly, it catches all the exceptions and write them to `stderr`.
     // This is too interactive and not API-clients friendly.
     await kernelTarget.writeOutline(null);
 
     // TODO(scheglov) Replace with a better API.
     Program program = await kernelTarget.writeProgram(null);
     return new DeltaProgram(program);
   }
 
   @override
-  void invalidate(String path) => unimplemented();
+  void invalidate(Uri uri) {
+    _invalidatedFiles.add(uri);
+  }
 
   @override
   void invalidateAll() => unimplemented();
 
+  /// Fasta unconditionally loads all VM libraries.  In order to be able to
+  /// serve them using the file system view, we need to ask [_fsState] for
+  /// the corresponding files.
+  Future<Null> _ensureVmLibrariesLoaded() async {
+    List<String> extraLibraries = new VmTarget(null).extraRequiredLibraries;
+    for (String absoluteUriStr in extraLibraries) {
+      Uri absoluteUri = Uri.parse(absoluteUriStr);
+      Uri fileUri = _uriTranslator.translate(absoluteUri);
+      await _fsState.getFile(fileUri);
+    }
+  }
+
   /// Return the [DillTarget] that is used inside of [KernelTarget] to
   /// resynthesize SDK libraries.
   Future<DillTarget> _getSdkDillTarget() async {
     if (_sdkDillTarget == null) {
       _sdkDillTarget =
           new DillTarget(new Ticker(isVerbose: false), _uriTranslator);
       // TODO(scheglov) Read the SDK kernel.
 //      _sdkDillTarget.read(options.sdkSummary);
 //      await _sdkDillTarget.writeOutline(null);
     } else {
 //      Program sdkProgram = _sdkDillTarget.loader.program;
 //      sdkProgram.visitChildren(new _ClearCanonicalNamesVisitor());
     }
     return _sdkDillTarget;
   }
+
+  /// Ensure that asynchronous data from options is ready.
+  ///
+  /// Ideally this data should be prepared in the constructor, but constructors
+  /// cannot be asynchronous.
+  Future<Null> _initialize() async {
+    _uriTranslator ??= await _options.getUriTranslator();
+    _fsState ??= new FileSystemState(_options.fileSystem, _uriTranslator);
+  }
+
+  /// Refresh all the invalidated files and update dependencies.
+  Future<Null> _refreshInvalidatedFiles() async {
+    for (Uri fileUri in _invalidatedFiles) {
+      FileState file = await _fsState.getFile(fileUri);
+      await file.refresh();
+    }
+    _invalidatedFiles.clear();
+  }
 }
 
 ///// Clears canonical names of [NamedNode] references.
 //class _ClearCanonicalNamesVisitor extends Visitor {
 //  defaultNode(Node node) {
 //    if (node is NamedNode) {
 //      node.reference.canonicalName = null;
 //    }
 //    node.visitChildren(this);
 //  }
 //}