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

pkg/front_end/lib/src/incremental/file_state.dart

Index: pkg/front_end/lib/src/incremental/file_state.dart
diff --git a/pkg/front_end/lib/src/incremental/file_state.dart b/pkg/front_end/lib/src/incremental/file_state.dart
new file mode 100644
index 0000000000000000000000000000000000000000..fec7c17940977ef7b681a9df3f08231f8a15ab41
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+++ b/pkg/front_end/lib/src/incremental/file_state.dart
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+// 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:convert';
+import 'dart:typed_data';
+
+import 'package:front_end/file_system.dart';
+import 'package:front_end/src/fasta/parser/top_level_parser.dart';
+import 'package:front_end/src/fasta/scanner.dart';
+import 'package:front_end/src/fasta/source/directive_listener.dart';
+import 'package:front_end/src/fasta/translate_uri.dart';
+
+/// Information about a file being compiled, explicitly or implicitly.
+///
+/// It provides a consistent view on its properties.
+///
+/// The properties are not guaranteed to represent the most recent state
+/// of the file system. To update the file to the most recent state, [refresh]
+/// should be called.
+class FileState {
+  final FileSystemState _fsState;
+
+  /// The resolved URI of the file in the file system.
+  final Uri fileUri;
+
+  bool _exists;
+  List<int> _contentBytes;
+  String _content;
+
+  List<FileState> _importedFiles;
+  List<FileState> _exportedFiles;
+  List<FileState> _partFiles;
+
+  Set<FileState> _directReferencedFiles = new Set<FileState>();
+
+  FileState._(this._fsState, this.fileUri);
+
+  /// The content of the file.
+  String get content => _content;
+
+  /// The content bytes of the file.
+  List<int> get contentBytes => _contentBytes;
+
+  /// Whether the file exists.
+  bool get exists => _exists;
+
+  @override
+  int get hashCode => fileUri.hashCode;
+
+  /// Return the set of transitive files - the file itself and all of the
+  /// directly or indirectly referenced files.
+  Set<FileState> get transitiveFiles {
+    // TODO(scheglov) add caching.
+    var transitiveFiles = new Set<FileState>();
+
+    void appendReferenced(FileState file) {
+      if (transitiveFiles.add(file)) {
+        file._directReferencedFiles.forEach(appendReferenced);
+      }
+    }
+
+    appendReferenced(this);
+    return transitiveFiles;
+  }
+
+  @override
+  bool operator ==(Object other) {
+    return other is FileState && other.fileUri == fileUri;
+  }
+
+  /// Read the file content and ensure that all of the file properties are
+  /// consistent with the read content, including all its dependencies.
+  Future<Null> refresh() async {
+    // Read the content.
+    try {
+      FileSystemEntity entry = _fsState.fileSystem.entityForUri(fileUri);
+      _contentBytes = await entry.readAsBytes();
+      _content = UTF8.decode(_contentBytes);
+      _exists = true;
+    } catch (_) {
+      _contentBytes = new Uint8List(0);
+      _content = '';
+      _exists = false;
+    }
+
+    // Parse directives.
+    ScannerResult scannerResults = scanString(_content);
+    var listener = new DirectiveListener();
+    new TopLevelParser(listener).parseUnit(scannerResults.tokens);
+
+    // Build the graph.
+    _importedFiles = <FileState>[];
+    _exportedFiles = <FileState>[];
+    _partFiles = <FileState>[];
+    await _addFileForRelativeUri(_importedFiles, 'dart:core');
+    for (String uri in listener.imports) {
+      await _addFileForRelativeUri(_importedFiles, uri);
+    }
+    for (String uri in listener.exports) {
+      await _addFileForRelativeUri(_exportedFiles, uri);
+    }
+    for (String uri in listener.parts) {
+      await _addFileForRelativeUri(_partFiles, uri);
+    }
+
+    // Compute referenced files.
+    _directReferencedFiles = new Set<FileState>()
+      ..addAll(_importedFiles)
+      ..addAll(_exportedFiles)
+      ..addAll(_partFiles);
+  }
+
+  /// Add the [FileState] for the given [relativeUri] to the [files].
+  /// Do nothing if the URI cannot be parsed, cannot correspond any file, etc.
+  Future<Null> _addFileForRelativeUri(
+      List<FileState> files, String relativeUri) async {
+    if (relativeUri.isEmpty) return;
+
+    // Resolve the relative URI into absolute.
+    // The result is either:
+    //   1) The absolute file URI.
+    //   2) The absolute non-file URI, e.g. `package:foo/foo.dart`.
+    Uri absoluteUri;
+    try {
+      absoluteUri = fileUri.resolve(relativeUri);
+    } on FormatException {
+      return;
+    }
+
+    // Resolve the absolute URI into the absolute file URI.
+    Uri resolvedUri = _fsState.uriTranslator.translate(absoluteUri);
+    if (resolvedUri == null) return;
+
+    FileState file = await _fsState.getFile(resolvedUri);
+    files.add(file);
+  }
+}
+
+/// Information about known file system state.
+class FileSystemState {
+  final FileSystem fileSystem;
+  final TranslateUri uriTranslator;
+
+  _FileSystemView _fileSystemView;
+
+  /// Mapping from file URIs to corresponding [FileState]s.
+  final Map<Uri, FileState> _fileUriToFile = {};
+
+  FileSystemState(this.fileSystem, this.uriTranslator);
+
+  /// Return the [FileSystem] that is backed by this [FileSystemState].  The
+  /// files in this [FileSystem] always have the same content as the
+  /// corresponding [FileState]s, thus avoiding race conditions when a file
+  /// is updated on the actual file system.
+  FileSystem get fileSystemView {
+    return _fileSystemView ??= new _FileSystemView(this);
+  }
+
+  /// Return the [FileState] for the given resolved file [fileUri].
+  /// The returned file has the last known state since it was last refreshed.
+  Future<FileState> getFile(Uri fileUri) async {
+    FileState file = _fileUriToFile[fileUri];
+    if (file == null) {
+      file = new FileState._(this, fileUri);
+      _fileUriToFile[fileUri] = file;
+
+      // Build the sub-graph of the file.
+      await file.refresh();
+    }
+    return file;
+  }
+}
+
+/// [FileSystemState] based implementation of [FileSystem].
+/// It provides a consistent view on the known file system state.
+class _FileSystemView implements FileSystem {
+  final FileSystemState fsState;
+
+  _FileSystemView(this.fsState);
+
+  @override
+  FileSystemEntity entityForUri(Uri uri) {
+    FileState file = fsState._fileUriToFile[uri];
+    return new _FileSystemViewEntry(uri, file);
+  }
+}
+
+/// [FileSystemState] based implementation of [FileSystemEntity].
+class _FileSystemViewEntry implements FileSystemEntity {
+  @override
+  final Uri uri;
+
+  final FileState file;
+
+  _FileSystemViewEntry(this.uri, this.file);
+
+  @override
+  Future<bool> exists() async => file?.exists ?? false;
+
+  @override
+  Future<DateTime> lastModified() async {
+    throw new StateError(
+        'FileSystemViewEntry modification stamp should not be queried');
+  }
+
+  @override
+  Future<List<int>> readAsBytes() async {
+    _throwIfDoesNotExist();
+    return file.contentBytes;
+  }
+
+  @override
+  Future<String> readAsString() async {
+    _throwIfDoesNotExist();
+    return file.content;
+  }
+
+  void _throwIfDoesNotExist() {
+    if (file == null) {
+      throw new FileSystemException(uri, 'File $uri does not exist.');
+    }
+  }
+}