Refactor FileBasedAssetReader and FileBasedAssetWriter to ReaderWriter.

Author: davidmorgan

_test_common/lib/in_memory_reader_writer.dart

@@ -5,20 +5,56 @@ import 'dart:async';
 import 'dart:convert';
 
 import 'package:build/build.dart';
+// ignore: implementation_imports
+import 'package:build/src/internal.dart';
 import 'package:build_runner_core/build_runner_core.dart';
 import 'package:build_test/build_test.dart';
 // ignore: implementation_imports
 import 'package:build_test/src/in_memory_reader_writer.dart';
 import 'package:path/path.dart' as p;
 import 'package:watcher/watcher.dart';
 
+// TODO(davidmorgan): refactor to remove this class.
 class InMemoryRunnerAssetReaderWriter extends InMemoryAssetReaderWriter
     implements AssetReader, RunnerAssetWriter {
   final _onCanReadController = StreamController<AssetId>.broadcast();
   Stream<AssetId> get onCanRead => _onCanReadController.stream;
   void Function(AssetId)? onDelete;
 
-  InMemoryRunnerAssetReaderWriter({super.rootPackage});
+  factory InMemoryRunnerAssetReaderWriter({String? rootPackage}) {
+    final filesystem = InMemoryFilesystem();
+    return InMemoryRunnerAssetReaderWriter.using(
+      rootPackage: rootPackage ?? 'unset',
+      assetFinder: InMemoryAssetFinder(filesystem, rootPackage),
+      assetPathProvider: const InMemoryAssetPathProvider(),
+      filesystem: filesystem,
+      cache: const PassthroughFilesystemCache(),
+      inputTracker: InputTracker(),
+    );
+  }
+
+  InMemoryRunnerAssetReaderWriter.using({
+    required super.rootPackage,
+    required super.assetFinder,
+    required super.assetPathProvider,
+    required super.filesystem,
+    required super.cache,
+    required super.inputTracker,
+  }) : super.using();
+
+  @override
+  InMemoryRunnerAssetReaderWriter copyWith({
+    AssetPathProvider? assetPathProvider,
+    FilesystemCache? cache,
+    InputTracker? inputTracker,
+  }) => InMemoryRunnerAssetReaderWriter.using(
+    rootPackage: rootPackage,
+    assetFinder: assetFinder,
+    assetPathProvider: assetPathProvider ?? this.assetPathProvider,
+    filesystem: filesystem,
+    cache: cache ?? this.cache,
+    inputTracker: inputTracker ?? this.inputTracker,
+  );
 
   @override
   Future<bool> canRead(AssetId id) {

build/CHANGELOG.md

@@ -11,6 +11,7 @@
   implementations.
 - Refactor `CachingAssetReader` to `FilesystemCache`.
 - Refactor `BuildCacheReader` to `BuildCacheAssetPathProvider`.
+- Refactor `FileBasedAssetReader` and `FileBasedAssetWriter` to `ReaderWriter`.
 
 ## 2.4.2
 

build_runner/CHANGELOG.md

@@ -6,6 +6,7 @@
 - Refactor `MultiPackageAssetReader` to internal `AssetFinder`.
 - `FinalizedReader` no longer implements `AssetReader`.
 - Refactor `CachingAssetReader` to `FilesystemCache`.
+- Refactor `FileBasedAssetReader` and `FileBasedAssetWriter` to `ReaderWriter`.
 
 ## 2.4.15
 

build_runner/lib/src/build_script_generate/build_script_generate.dart

@@ -103,7 +103,7 @@ Future<BuildScriptInfo> findBuildScriptOptions({
     equals: (a, b) => a.name == b.name,
     hashCode: (n) => n.name.hashCode,
   ).expand((c) => c);
-  var reader = FileBasedAssetReader(packageGraph);
+  var reader = ReaderWriter(packageGraph);
   var overrides =
       buildConfigOverrides ??= await findBuildConfigOverrides(
         packageGraph,

build_runner/lib/src/entrypoint/clean.dart

@@ -84,7 +84,7 @@ Future<void> _cleanUpSourceOutputs(
   AssetGraph assetGraph,
   PackageGraph packageGraph,
 ) async {
-  var writer = FileBasedAssetWriter(packageGraph);
+  var writer = ReaderWriter(packageGraph);
   for (var id in assetGraph.outputs) {
     if (id.package != packageGraph.root.name) continue;
     var node = assetGraph.get(id) as GeneratedAssetNode;

build_runner/lib/src/entrypoint/doctor.dart

@@ -63,7 +63,7 @@ class DoctorCommand extends BuildRunnerCommand {
     final packageGraph = await PackageGraph.forThisPackage();
     final buildConfigOverrides = await findBuildConfigOverrides(
       packageGraph,
-      FileBasedAssetReader(packageGraph),
+      ReaderWriter(packageGraph),
     );
     Future<BuildConfig> packageBuildConfig(PackageNode package) async {
       if (buildConfigOverrides.containsKey(package.name)) {

build_runner_core/CHANGELOG.md

@@ -11,6 +11,7 @@
   implementations.
 - Refactor `CachingAssetReader` to `FilesystemCache`.
 - Refactor `BuildCacheReader` to `BuildCacheAssetPathProvider`.
+- Refactor `FileBasedAssetReader` and `FileBasedAssetWriter` to `ReaderWriter`.
 
 ## 8.0.0
 

build_runner_core/lib/build_runner_core.dart

@@ -4,8 +4,8 @@
 
 export 'package:build/build.dart' show PostProcessBuildStep, PostProcessBuilder;
 
-export 'src/asset/file_based.dart';
 export 'src/asset/finalized_reader.dart';
+export 'src/asset/reader_writer.dart';
 export 'src/asset/writer.dart';
 export 'src/environment/build_environment.dart';
 export 'src/environment/io_environment.dart';

build_runner_core/lib/src/asset/file_based.dart renamed to build_runner_core/lib/src/asset/reader_writer.dart

@@ -1,4 +1,4 @@
-// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// 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:async';
@@ -15,43 +15,63 @@ import 'package:path/path.dart' as path;
 import '../package_graph/package_graph.dart';
 import 'writer.dart';
 
-/// Basic [AssetReader] which uses a [PackageGraph] to look up where to read
-/// files from disk.
-class FileBasedAssetReader extends AssetReader implements AssetReaderState {
+/// Pluggable [AssetReader] and [AssetWriter].
+class ReaderWriter extends AssetReader
+    implements AssetReaderState, RunnerAssetWriter {
+  /// The package the generator is running for.
+  ///
+  /// Deletes are only allowed within this package.
+  final String rootPackage;
+
   @override
   final AssetPathProvider assetPathProvider;
   @override
   final Filesystem filesystem;
   @override
-  late final AssetFinder assetFinder = FunctionAssetFinder(_findAssets);
+  final AssetFinder assetFinder;
   @override
   final FilesystemCache cache;
+  @override
+  final InputTracker? inputTracker;
+
+  /// A [ReaderWriter] suitable for real builds.
+  ///
+  /// [packageGraph] is used for mapping paths and finding assets. The
+  /// `dart-io` filesystem is used with no cache.
+  ///
+  /// Use [copyWith] to change settings such as caching.
+  factory ReaderWriter(PackageGraph packageGraph) => ReaderWriter.using(
+    rootPackage: packageGraph.root.name,
+    assetFinder: PackageGraphAssetFinder(packageGraph),
+    assetPathProvider: packageGraph,
+    filesystem: IoFilesystem(),
+    cache: const PassthroughFilesystemCache(),
+    // In real builds input tracking is done per generator.
+    inputTracker: null,
+  );
 
-  final PackageGraph packageGraph;
-
-  FileBasedAssetReader(
-    this.packageGraph, {
-    AssetPathProvider? assetPathProvider,
-    Filesystem? filesystem,
-    FilesystemCache? cache,
-  }) : filesystem = filesystem ?? IoFilesystem(),
-       cache = cache ?? const PassthroughFilesystemCache(),
-       assetPathProvider = assetPathProvider ?? packageGraph;
+  ReaderWriter.using({
+    required this.rootPackage,
+    required this.assetFinder,
+    required this.assetPathProvider,
+    required this.filesystem,
+    required this.cache,
+    required this.inputTracker,
+  });
 
   @override
-  FileBasedAssetReader copyWith({
+  ReaderWriter copyWith({
     AssetPathProvider? assetPathProvider,
     FilesystemCache? cache,
-  }) => FileBasedAssetReader(
-    packageGraph,
+  }) => ReaderWriter.using(
+    rootPackage: rootPackage,
+    assetFinder: assetFinder,
     assetPathProvider: assetPathProvider ?? this.assetPathProvider,
     filesystem: filesystem,
     cache: cache ?? this.cache,
+    inputTracker: inputTracker,
   );
 
-  @override
-  InputTracker? get inputTracker => null;
-
   @override
   Future<bool> canRead(AssetId id) {
     return cache.exists(
@@ -96,44 +116,11 @@ class FileBasedAssetReader extends AssetReader implements AssetReaderState {
   @override
   Stream<AssetId> findAssets(Glob glob) => throw UnimplementedError();
 
-  Stream<AssetId> _findAssets(Glob glob, String? package) {
-    var packageNode =
-        package == null ? packageGraph.root : packageGraph[package];
-    if (packageNode == null) {
-      throw ArgumentError(
-        "Could not find package '$package' which was listed as "
-        'an input. Please ensure you have that package in your deps, or '
-        'remove it from your input sets.',
-      );
-    }
-    // TODO(davidmorgan): make this read via `filesystem`, currently it
-    // reads directly via `dart:io`.
-    return glob
-        .list(followLinks: true, root: packageNode.path)
-        .where((e) => e is File && !path.basename(e.path).startsWith('._'))
-        .cast<File>()
-        .map((file) => _fileToAssetId(file, packageNode));
-  }
-
-  /// Creates an [AssetId] for [file], which is a part of [packageNode].
-  AssetId _fileToAssetId(File file, PackageNode packageNode) {
-    var filePath = path.normalize(file.absolute.path);
-    var relativePath = path.relative(filePath, from: packageNode.path);
-    return AssetId(packageNode.name, relativePath);
-  }
-}
-
-/// Basic [AssetWriter] which uses a [PackageGraph] to look up where to write
-/// files to disk.
-class FileBasedAssetWriter implements RunnerAssetWriter {
-  final PackageGraph packageGraph;
-  final Filesystem filesystem;
-
-  FileBasedAssetWriter(this.packageGraph) : filesystem = IoFilesystem();
+  // [AssetWriter] methods.
 
   @override
   Future<void> writeAsBytes(AssetId id, List<int> bytes) async {
-    final path = packageGraph.pathFor(id);
+    final path = assetPathProvider.pathFor(id);
     await filesystem.writeAsBytes(path, bytes);
   }
 
@@ -143,19 +130,19 @@ class FileBasedAssetWriter implements RunnerAssetWriter {
     String contents, {
     Encoding encoding = utf8,
   }) async {
-    final path = packageGraph.pathFor(id);
+    final path = assetPathProvider.pathFor(id);
     await filesystem.writeAsString(path, contents, encoding: encoding);
   }
 
   @override
   Future delete(AssetId id) async {
-    if (id.package != packageGraph.root.name) {
+    if (id.package != rootPackage) {
       throw InvalidOutputException(
         id,
-        'Should not delete assets outside of ${packageGraph.root.name}',
+        'Should not delete assets outside of $rootPackage',
       );
     }
-    final path = packageGraph.pathFor(id);
+    final path = assetPathProvider.pathFor(id);
     await filesystem.delete(path);
   }
 
@@ -164,3 +151,38 @@ class FileBasedAssetWriter implements RunnerAssetWriter {
     // TODO(davidmorgan): add back write caching, "batching".
   }
 }
+
+/// [AssetFinder] that uses [PackageGraph] to map packages to paths, then
+/// uses the `dart:io` filesystem to find files.
+///
+/// TODO(davidmorgan): read via `Filesystem` instead of `dart-io`.
+class PackageGraphAssetFinder implements AssetFinder {
+  final PackageGraph packageGraph;
+
+  PackageGraphAssetFinder(this.packageGraph);
+
+  @override
+  Stream<AssetId> find(Glob glob, {String? package}) {
+    var packageNode =
+        package == null ? packageGraph.root : packageGraph[package];
+    if (packageNode == null) {
+      throw ArgumentError(
+        "Could not find package '$package' which was listed as "
+        'an input. Please ensure you have that package in your deps, or '
+        'remove it from your input sets.',
+      );
+    }
+    return glob
+        .list(followLinks: true, root: packageNode.path)
+        .where((e) => e is File && !path.basename(e.path).startsWith('._'))
+        .cast<File>()
+        .map((file) => _fileToAssetId(file, packageNode));
+  }
+
+  /// Creates an [AssetId] for [file], which is a part of [packageNode].
+  static AssetId _fileToAssetId(File file, PackageNode packageNode) {
+    var filePath = path.normalize(file.absolute.path);
+    var relativePath = path.relative(filePath, from: packageNode.path);
+    return AssetId(packageNode.name, relativePath);
+  }
+}

build_runner_core/lib/src/environment/io_environment.dart

@@ -8,7 +8,7 @@ import 'dart:io';
 import 'package:build/build.dart';
 import 'package:logging/logging.dart';
 
-import '../asset/file_based.dart';
+import '../asset/reader_writer.dart';
 import '../asset/writer.dart';
 import '../generate/build_directory.dart';
 import '../generate/build_result.dart';
@@ -22,7 +22,7 @@ final _logger = Logger('IOEnvironment');
 /// A [BuildEnvironment] writing to disk and stdout.
 class IOEnvironment implements BuildEnvironment {
   @override
-  final AssetReader reader;
+  final ReaderWriter reader;
 
   @override
   final RunnerAssetWriter writer;
@@ -54,9 +54,11 @@ class IOEnvironment implements BuildEnvironment {
       );
     }
 
+    final readerWriter = ReaderWriter(packageGraph);
+
     return IOEnvironment._(
-      FileBasedAssetReader(packageGraph),
-      FileBasedAssetWriter(packageGraph),
+      readerWriter,
+      readerWriter,
       assumeTty == true || _canPrompt(),
       outputSymlinksOnly,
       packageGraph,

build_runner_core/test/asset/batch_test.dart

@@ -21,10 +21,9 @@ void main() {
 
   setUp(() async {
     packageGraph = await _createTestPackage();
-    final fileReader = FileBasedAssetReader(packageGraph);
-    final fileWriter = FileBasedAssetWriter(packageGraph);
+    final readerWriter = ReaderWriter(packageGraph);
 
-    (reader, writer) = wrapInBatch(reader: fileReader, writer: fileWriter);
+    (reader, writer) = wrapInBatch(reader: readerWriter, writer: readerWriter);
   });
 
   test('delays writes until end', () async {