Start using FileState/FileSystemState to provide consistent view.

pkg/front_end/lib/src/incremental_kernel_generator_impl.dart

Index: pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
diff --git a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
index 9739aa4473dbc6bc7c6ddf15c5d5c9ad2075c9ff..780852dfcb62b80e3885e65c1718588d0996fb9e 100644
--- a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
+++ b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
@@ -12,7 +12,9 @@ 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.
@@ -34,9 +36,16 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
   /// 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;
 
@@ -45,13 +54,18 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
   @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.
@@ -66,11 +80,25 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
   }
 
   @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 {
@@ -86,6 +114,24 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
     }
     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.