Store a file state in the incremental resolved AST generator.

pkg/front_end/lib/src/incremental_resolved_ast_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:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
@@ skipping 34 matching lines @@
 class IncrementalResolvedAstGeneratorImpl
     implements IncrementalResolvedAstGenerator {
   driver.AnalysisDriverScheduler _scheduler;
   final _fileRepository = new FileRepository();
   _ResourceProviderProxy _resourceProvider;
   driver.AnalysisDriver _driver;
   bool _isInitialized = false;
   final ProcessedOptions _options;
   final Uri _source;
   bool _schedulerStarted = false;
+  final _fileState = <Uri, String>{};
 
   IncrementalResolvedAstGeneratorImpl(this._source, this._options);
 
   @override
   Future<DeltaLibraries> computeDelta() async {
     if (!_isInitialized) {
       await init();
     }
     // The analysis driver doesn't currently support an asynchronous file API,
     // so we have to find all the files first to read their contents.
     // TODO(paulberry): this is an unnecessary source of duplicate work and
     // should be eliminated ASAP.
-    var graph = await graphForProgram([_source], _options);
+    var graph =
+        await graphForProgram([_source], _options, fileReader: _fileReader);
+    // TODO(paulberry): collect no-longer-referenced files from _fileState and
+    // _fileRepository.
     var libraries = <Uri, ResolvedLibrary>{};
     if (!_schedulerStarted) {
       _scheduler.start();
       _schedulerStarted = true;
     }
     // The driver will request files from dart:, even though it actually uses
     // the data from the summary.  TODO(paulberry): fix this.
     _fileRepository.store(Uri.parse('dart:core'), '');
     for (var libraryCycle in graph.topologicallySortedCycles) {
       for (var libraryUri in libraryCycle.libraries.keys) {
         var libraryNode = libraryCycle.libraries[libraryUri];
-        var libraryContents =
-            await _options.fileSystem.entityForUri(libraryUri).readAsString();
-        _fileRepository.store(libraryUri, libraryContents);
         for (var partUri in libraryNode.parts) {
-          var partContents =
-              await _options.fileSystem.entityForUri(partUri).readAsString();
-          _fileRepository.store(partUri, partContents);
+          // TODO(paulberry): resolve the part URI.
+          _fileReader(partUri, partUri);
         }
       }
       for (var libraryUri in libraryCycle.libraries.keys) {
         var libraryNode = libraryCycle.libraries[libraryUri];
         var result =
             await _driver.getResult(_fileRepository.pathForUri(libraryUri));
         // TODO(paulberry): handle errors.
         var definingCompilationUnit = result.unit;
         var partUnits = <Uri, CompilationUnit>{};
         for (var partUri in libraryNode.parts) {
@@ skipping 47 matching lines @@
     _isInitialized = true;
   }
 
   @override
   void invalidate(String path) {
     throw new UnimplementedError();
   }
 
   @override
   void invalidateAll() {
+    _fileState.clear();
+    _fileRepository.clearContents();
     // TODO(paulberry): verify that this has an effect (requires a multi-file
     // test).
     if (_isInitialized) {
       _driver.knownFiles.forEach(_driver.changeFile);
     }
   }
+
+  Future<String> _fileReader(Uri originalUri, Uri resolvedUri) async {
+    String contents = _fileState[resolvedUri] ??=
+        await _options.fileSystem.entityForUri(resolvedUri).readAsString();
+    _fileRepository.store(originalUri, contents);
+    return contents;
+  }
 }
 
 class _DartSdkProxy implements DartSdk {
   final PackageBundle summary;
 
   final AnalysisContext context;
 
   _DartSdkProxy(this.summary, this.context);
 
   @override
@@ skipping 112 matching lines @@
 class _SourceProxy extends BasicSource {
   @override
   final String fullName;
 
   _SourceProxy(Uri uri, this.fullName) : super(uri);
 
   int get modificationStamp => 0;
 
   noSuchMethod(Invocation invocation) => unimplemented();
 }