Simpler in memory filesystem

build_resolvers/CHANGELOG.md

@@ -1,7 +1,7 @@
 ## 2.4.4-wip
 
 - Refactor `BuildAssetUriResolver` into `AnalysisDriverModel` and
-  `AnalysisDriverModelUriResolver`. Add new implementation of
+  `AnalysisDriverFilesystem`. Add new implementation of
   `AnalysisDriverModel`.
 
 ## 2.4.3

build_resolvers/lib/src/analysis_driver.dart

@@ -13,7 +13,6 @@ import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 
 import 'analysis_driver_model.dart';
-import 'analysis_driver_model_uri_resolver.dart';
 import 'build_asset_uri_resolver.dart';
 
 /// Builds an [AnalysisDriverForPackageBuild] backed by a summary SDK.
@@ -29,12 +28,12 @@ Future<AnalysisDriverForPackageBuild> analysisDriver(
     analysisOptions: analysisOptions,
     packages: _buildAnalyzerPackages(
       packageConfig,
-      analysisDriverModel.resourceProvider,
+      analysisDriverModel.filesystem,
     ),
-    resourceProvider: analysisDriverModel.resourceProvider,
+    resourceProvider: analysisDriverModel.filesystem,
     sdkSummaryBytes: File(sdkSummaryPath).readAsBytesSync(),
     uriResolvers: [
-      AnalysisDriverModelUriResolver(analysisDriverModel),
+      analysisDriverModel.filesystem,
     ],
   );
 }

build_resolvers/lib/src/analysis_driver_filesystem.dart

@@ -0,0 +1,191 @@
+// Copyright (c) 2025, 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:convert';
+import 'dart:typed_data';
+
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/source/file_source.dart';
+// ignore: implementation_imports
+import 'package:analyzer/src/clients/build_resolvers/build_resolvers.dart';
+import 'package:build/build.dart' hide Resource;
+import 'package:path/path.dart' as p;
+
+/// The in-memory filesystem that is the analyzer's view of the build.
+///
+/// Tracks modified paths, which should be passed to
+/// `AnalysisDriver.changeFile` to update the analyzer state.
+class AnalysisDriverFilesystem implements UriResolver, ResourceProvider {
+  final Map<String, String> _data = {};
+  final Set<String> _changedPaths = {};
+
+  // Methods for use by `AnalysisDriverModel`.
+
+  /// Whether [path] exists.
+  bool exists(String path) => _data.containsKey(path);
+
+  /// Reads the data previously written to [path].
+  ///
+  /// Throws if ![exists].
+  String read(String path) => _data[path]!;
+
+  /// Deletes the data previously written to [path].
+  ///
+  /// Records the change in [changedPaths].
+  ///
+  /// Or, if it's missing, does nothing.
+  void deleteFile(String path) {
+    if (_data.remove(path) != null) _changedPaths.add(path);
+  }
+
+  /// Writes [content] to [path].
+  ///
+  /// Records the change in [changedPaths], only if the content actually
+  /// changed.
+  void writeFile(String path, String content) {
+    final oldContent = _data[path];
+    _data[path] = content;
+    if (content != oldContent) _changedPaths.add(path);
+  }
+
+  /// Paths that were modified by [deleteFile] or [writeFile] since the last
+  /// call to [clearChangedPaths].
+  Iterable<String> get changedPaths => _changedPaths;
+
+  /// Clears [changedPaths].
+  void clearChangedPaths() => _changedPaths.clear();
+
+  // `UriResolver` methods.
+
+  /// Converts [path] to [Uri].
+  ///
+  /// [path] must be absolute and matches one of two formats:
+  ///
+  /// ```
+  /// /<package>/lib/<rest> --> package:<package>/<rest>
+  /// /<package>/<rest> --> asset:<package>/<rest>
+  /// ```
+  @override
+  Uri pathToUri(String path) {
+    if (!path.startsWith('/')) {
+      throw ArgumentError.value('path', path, 'Must start with "/". ');
+    }
+    final pathSegments = path.split('/');
+    // First segment is empty because of the starting `/`.
+    final packageName = pathSegments[1];
+    if (pathSegments[2] == 'lib') {
+      return Uri(
+        scheme: 'package',
+        pathSegments: [packageName].followedBy(pathSegments.skip(3)),
+      );
+    } else {
+      return Uri(
+        scheme: 'asset',
+        pathSegments: [packageName].followedBy(pathSegments.skip(2)),
+      );
+    }
+  }
+
+  @override
+  Source? resolveAbsolute(Uri uri, [Uri? actualUri]) {
+    final assetId = parseAsset(uri);
+    if (assetId == null) return null;
+
+    var file = getFile(assetPath(assetId));
+    return FileSource(file, assetId.uri);
+  }
+
+  /// Path of [assetId] for the in-memory filesystem.
+  static String assetPath(AssetId assetId) =>
+      '/${assetId.package}/${assetId.path}';
+
+  /// Attempts to parse [uri] into an [AssetId].
+  ///
+  /// Handles 'package:' or 'asset:' URIs, as well as 'file:' URIs that have the
+  /// same pattern used by [assetPath].
+  ///
+  /// Returns null if the Uri cannot be parsed.
+  static AssetId? parseAsset(Uri uri) {
+    if (uri.isScheme('package') || uri.isScheme('asset')) {
+      return AssetId.resolve(uri);
+    }
+    if (uri.isScheme('file')) {
+      if (!uri.path.startsWith('/')) {
+        throw ArgumentError.value(
+            'uri.path', uri.path, 'Must start with "/". ');
+      }
+      final parts = uri.path.split('/');
+      // First part is empty because of the starting `/`, second is package,
+      // remainder is path in package.
+      return AssetId(parts[1], parts.skip(2).join('/'));
+    }
+    return null;
+  }
+
+  // `ResourceProvider` methods.
+
+  @override
+  p.Context get pathContext => p.posix;
+
+  @override
+  File getFile(String path) => _Resource(this, path);
+
+  @override
+  Folder getFolder(String path) => _Resource(this, path);
+
+  // `ResourceProvider` methods that are not needed.
+
+  @override
+  Link getLink(String path) => throw UnimplementedError();
+
+  @override
+  Resource getResource(String path) => throw UnimplementedError();
+
+  @override
+  Folder? getStateLocation(String pluginId) => throw UnimplementedError();
+}
+
+/// Minimal implementation of [File] and [Folder].
+///
+/// Provides only what the analyzer actually uses during analysis.
+class _Resource implements File, Folder {
+  final AnalysisDriverFilesystem filesystem;
+  @override
+  final String path;
+
+  _Resource(this.filesystem, this.path);
+
+  @override
+  bool get exists => filesystem.exists(path);
+
+  @override
+  String get shortName => filesystem.pathContext.basename(path);
+
+  @override
+  Uint8List readAsBytesSync() {
+    // TODO(davidmorgan): the analyzer reads as bytes in `FileContentCache`
+    // then converts back to `String` and hashes. It should be possible to save
+    // that work, for example by injecting a custom `FileContentCache`.
+    return utf8.encode(filesystem.read(path));
+  }
+
+  @override
+  String readAsStringSync() => filesystem.read(path);
+
+  // `Folder` methods.
+
+  @override
+  bool contains(String path) =>
+      filesystem.pathContext.isWithin(this.path, path);
+
+  // Most `File` and/or `Folder` methods are not needed.
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
+
+  // Needs an explicit override to satisfy both `File.copyTo` and
+  // `Folder.copyTo`.
+  @override
+  _Resource copyTo(Folder _) => throw UnimplementedError();
+}

build_resolvers/lib/src/analysis_driver_model.dart

@@ -7,13 +7,11 @@ import 'dart:collection';
 
 import 'package:analyzer/dart/analysis/utilities.dart';
 import 'package:analyzer/dart/ast/ast.dart';
-import 'package:analyzer/file_system/memory_file_system.dart';
 // ignore: implementation_imports
 import 'package:analyzer/src/clients/build_resolvers/build_resolvers.dart';
 import 'package:build/build.dart';
-import 'package:path/path.dart' as p;
 
-import 'analysis_driver_model_uri_resolver.dart';
+import 'analysis_driver_filesystem.dart';
 
 /// Manages analysis driver and related build state.
 ///
@@ -31,15 +29,14 @@ import 'analysis_driver_model_uri_resolver.dart';
 /// implementation.
 class AnalysisDriverModel {
   /// In-memory filesystem for the analyzer.
-  final MemoryResourceProvider resourceProvider =
-      MemoryResourceProvider(context: p.posix);
+  final AnalysisDriverFilesystem filesystem = AnalysisDriverFilesystem();
 
   /// The import graph of all sources needed for analysis.
   final _graph = _Graph();
 
   /// Assets that have been synced into the in-memory filesystem
-  /// [resourceProvider].
-  final _syncedOntoResourceProvider = <AssetId>{};
+  /// [filesystem].
+  final _syncedOntoFilesystem = <AssetId>{};
 
   /// Notifies that [step] has completed.
   ///
@@ -51,7 +48,7 @@ class AnalysisDriverModel {
   /// Clear cached information specific to an individual build.
   void reset() {
     _graph.clear();
-    _syncedOntoResourceProvider.clear();
+    _syncedOntoFilesystem.clear();
   }
 
   /// Attempts to parse [uri] into an [AssetId] and returns it if it is cached.
@@ -61,16 +58,16 @@ class AnalysisDriverModel {
   ///
   /// Returns null if the `Uri` cannot be parsed or is not cached.
   AssetId? lookupCachedAsset(Uri uri) {
-    final assetId = AnalysisDriverModelUriResolver.parseAsset(uri);
+    final assetId = AnalysisDriverFilesystem.parseAsset(uri);
     // TODO(davidmorgan): not clear if this is the right "exists" check.
-    if (assetId == null || !resourceProvider.getFile(assetId.asPath).exists) {
+    if (assetId == null || !filesystem.getFile(assetId.asPath).exists) {
       return null;
     }
 
     return assetId;
   }
 
-  /// Updates [resourceProvider] and the analysis driver given by
+  /// Updates [filesystem] and the analysis driver given by
   /// `withDriverResource`  with updated versions of [entryPoints].
   ///
   /// If [transitive], then all the transitive imports from [entryPoints] are
@@ -107,14 +104,14 @@ class AnalysisDriverModel {
               FutureOr<void> Function(AnalysisDriverForPackageBuild))
           withDriverResource,
       {required bool transitive}) async {
-    var idsToSyncOntoResourceProvider = entryPoints;
+    var idsToSyncOntoFilesystem = entryPoints;
     Iterable<AssetId> inputIds = entryPoints;
 
     // If requested, find transitive imports.
     if (transitive) {
       final previouslyMissingFiles = await _graph.load(buildStep, entryPoints);
-      _syncedOntoResourceProvider.removeAll(previouslyMissingFiles);
-      idsToSyncOntoResourceProvider = _graph.nodes.keys.toList();
+      _syncedOntoFilesystem.removeAll(previouslyMissingFiles);
+      idsToSyncOntoFilesystem = _graph.nodes.keys.toList();
       inputIds = _graph.inputsFor(entryPoints);
     }
 
@@ -124,39 +121,23 @@ class AnalysisDriverModel {
     }
 
     // Sync changes onto the "URI resolver", the in-memory filesystem.
-    final changedIds = <AssetId>[];
-    for (final id in idsToSyncOntoResourceProvider) {
-      if (!_syncedOntoResourceProvider.add(id)) continue;
+    for (final id in idsToSyncOntoFilesystem) {
+      if (!_syncedOntoFilesystem.add(id)) continue;
       final content =
           await buildStep.canRead(id) ? await buildStep.readAsString(id) : null;
-      final inMemoryFile = resourceProvider.getFile(id.asPath);
-      final inMemoryContent =
-          inMemoryFile.exists ? inMemoryFile.readAsStringSync() : null;
-
-      if (content != inMemoryContent) {
-        if (content == null) {
-          // TODO(davidmorgan): per "globallySeenAssets" in
-          // BuildAssetUriResolver, deletes should only be applied at the end
-          // of the build, in case the file is actually there but not visible
-          // to the current reader.
-          resourceProvider.deleteFile(id.asPath);
-          changedIds.add(id);
-        } else {
-          if (inMemoryContent == null) {
-            resourceProvider.newFile(id.asPath, content);
-          } else {
-            resourceProvider.modifyFile(id.asPath, content);
-          }
-          changedIds.add(id);
-        }
+      if (content == null) {
+        filesystem.deleteFile(id.asPath);
+      } else {
+        filesystem.writeFile(id.asPath, content);
       }
     }
 
     // Notify the analyzer of changes and wait for it to update its internal
     // state.
-    for (final id in changedIds) {
-      driver.changeFile(id.asPath);
+    for (final path in filesystem.changedPaths) {
+      driver.changeFile(path);
     }
+    filesystem.clearChangedPaths();
     await driver.applyPendingFileChanges();
   }
 }
@@ -181,7 +162,7 @@ List<AssetId> _parseDependencies(String content, AssetId from) =>
 
 extension _AssetIdExtensions on AssetId {
   /// Asset path for the in-memory filesystem.
-  String get asPath => AnalysisDriverModelUriResolver.assetPath(this);
+  String get asPath => AnalysisDriverFilesystem.assetPath(this);
 }
 
 /// The directive graph of all known sources.