Refactor MultiPackagesAssetReader to AssetFinder.

Author: davidmorgan

_test_common/lib/in_memory_reader_writer.dart

@@ -11,7 +11,7 @@ import 'package:path/path.dart' as p;
 import 'package:watcher/watcher.dart';
 
 class InMemoryRunnerAssetReaderWriter extends InMemoryAssetReaderWriter
-    implements RunnerAssetReader, RunnerAssetWriter {
+    implements AssetReader, RunnerAssetWriter {
   final _onCanReadController = StreamController<AssetId>.broadcast();
   Stream<AssetId> get onCanRead => _onCanReadController.stream;
   void Function(AssetId)? onDelete;

_test_common/lib/test_environment.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:build/build.dart';
 import 'package:build_runner_core/build_runner_core.dart';
 import 'package:logging/logging.dart';
 
@@ -21,7 +22,7 @@ class TestBuildEnvironment extends BuildEnvironment {
   final InMemoryRunnerAssetReaderWriter _readerWriter;
 
   @override
-  RunnerAssetReader get reader => _readerWriter;
+  AssetReader get reader => _readerWriter;
   @override
   RunnerAssetWriter get writer => _readerWriter;
 

build/lib/src/asset/reader.dart

@@ -56,17 +56,3 @@ abstract class AssetReader {
     return digestSink.events.first;
   }
 }
-
-/// The same as an `AssetReader`, except that `findAssets` takes an optional
-/// argument `package` which allows you to glob any package.
-///
-/// This should not be exposed to end users generally, but can be used by
-/// different build system implementations.
-abstract class MultiPackageAssetReader extends AssetReader {
-  /// Returns all readable assets matching [glob] under [package].
-  ///
-  /// Some implementations may require the [package] argument, while others
-  /// may have a sane default.
-  @override
-  Stream<AssetId> findAssets(Glob glob, {String? package});
-}

build/lib/src/builder/build_step_impl.dart

@@ -18,6 +18,7 @@ import '../asset/id.dart';
 import '../asset/reader.dart';
 import '../asset/writer.dart';
 import '../resource/resource.dart';
+import '../state/asset_finder.dart';
 import '../state/asset_path_provider.dart';
 import '../state/input_tracker.dart';
 import '../state/reader_state.dart';
@@ -81,6 +82,9 @@ class BuildStepImpl implements BuildStep, AssetReaderState {
         _stageTracker = stageTracker ?? NoOpStageTracker.instance,
         _reportUnusedAssets = reportUnusedAssets;
 
+  @override
+  AssetFinder get assetFinder => _reader.assetFinder;
+
   @override
   AssetPathProvider? get assetPathProvider => _reader.assetPathProvider;
 
@@ -135,11 +139,7 @@ class BuildStepImpl implements BuildStep, AssetReaderState {
   @override
   Stream<AssetId> findAssets(Glob glob) {
     if (_isComplete) throw BuildStepCompletedException();
-    if (_reader is MultiPackageAssetReader) {
-      return _reader.findAssets(glob, package: inputId.package);
-    } else {
-      return _reader.findAssets(glob);
-    }
+    return _reader.assetFinder.find(glob, package: inputId.package);
   }
 
   @override

build/lib/src/internal.dart

@@ -2,10 +2,11 @@
 // 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.
 
-/// Internal build state for `build_resolvers`, `build_runner_core` and
-/// `build_test` only.
+/// Internal build state for `build_resolvers`, `build_runner`,
+/// `build_runner_core` and `build_test` only.
 library;
 
+export 'state/asset_finder.dart';
 export 'state/asset_path_provider.dart';
 export 'state/input_tracker.dart';
 export 'state/reader_state.dart';

build/lib/src/state/asset_finder.dart

@@ -0,0 +1,25 @@
+// 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';
+
+import 'package:glob/glob.dart';
+
+import '../asset/id.dart';
+
+abstract interface class AssetFinder {
+  /// Returns all readable assets matching [glob] under [package].
+  ///
+  /// `Reader.findAssets` exposes this funcionality without allowing controlling
+  /// [package].
+  Stream<AssetId> find(Glob glob, {String? package});
+}
+
+class FunctionAssetFinder implements AssetFinder {
+  final Stream<AssetId> Function(Glob, String?) function;
+
+  FunctionAssetFinder(this.function);
+
+  @override
+  Stream<AssetId> find(Glob glob, {String? package}) => function(glob, package);
+}

build/lib/src/state/reader_state.dart

@@ -3,11 +3,17 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../asset/reader.dart';
+import 'asset_finder.dart';
 import 'asset_path_provider.dart';
 import 'input_tracker.dart';
 
 /// Provides access to the state backing an [AssetReader].
 extension AssetReaderStateExtension on AssetReader {
+  AssetFinder get assetFinder {
+    _requireIsAssetReaderState();
+    return (this as AssetReaderState).assetFinder;
+  }
+
   InputTracker? get inputTracker =>
       this is AssetReaderState ? (this as AssetReaderState).inputTracker : null;
 
@@ -37,6 +43,12 @@ extension AssetReaderStateExtension on AssetReader {
 
 /// The state backing an [AssetReader].
 abstract interface class AssetReaderState {
+  /// The [AssetFinder] associated with this reader.
+  ///
+  /// All readers have an [AssetFinder], but the functionality it provides,
+  /// globbing in arbitrary packages, is hidden from generators.
+  AssetFinder get assetFinder;
+
   /// The [InputTracker] that this reader records reads to; or `null` if it does
   /// not have one.
   InputTracker? get inputTracker;

build_runner/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 2.4.16-wip
 
 - Use `build_test` 3.0.0.
+- Start using `package:build/src/internal.dart'.
 
 ## 2.4.15
 

build_runner/lib/src/generate/build.dart

@@ -53,7 +53,7 @@ Future<BuildResult> build(List<BuilderApplication> builders,
     bool? assumeTty,
     String? configKey,
     PackageGraph? packageGraph,
-    RunnerAssetReader? reader,
+    AssetReader? reader,
     RunnerAssetWriter? writer,
     Resolvers? resolvers,
     Level? logLevel,
@@ -148,7 +148,7 @@ Future<ServeHandler> watch(List<BuilderApplication> builders,
         bool? assumeTty,
         String? configKey,
         PackageGraph? packageGraph,
-        RunnerAssetReader? reader,
+        AssetReader? reader,
         RunnerAssetWriter? writer,
         Resolvers? resolvers,
         Level? logLevel,

build_runner/lib/src/generate/watch_impl.dart

@@ -36,7 +36,7 @@ Future<ServeHandler> watch(
   bool? assumeTty,
   String? configKey,
   PackageGraph? packageGraph,
-  RunnerAssetReader? reader,
+  AssetReader? reader,
   RunnerAssetWriter? writer,
   Resolvers? resolvers,
   Level? logLevel,

build_runner/lib/src/package_graph/build_config_overrides.dart

@@ -5,6 +5,8 @@
 import 'dart:async';
 
 import 'package:build/build.dart';
+// ignore: implementation_imports
+import 'package:build/src/internal.dart';
 import 'package:build_config/build_config.dart';
 import 'package:build_runner_core/build_runner_core.dart';
 import 'package:glob/glob.dart';
@@ -14,11 +16,11 @@ import 'package:path/path.dart' as p;
 final _log = Logger('BuildConfigOverrides');
 
 Future<Map<String, BuildConfig>> findBuildConfigOverrides(
-    PackageGraph packageGraph, RunnerAssetReader reader,
+    PackageGraph packageGraph, AssetReader reader,
     {String? configKey}) async {
   final configs = <String, BuildConfig>{};
-  final configFiles =
-      reader.findAssets(Glob('*.build.yaml'), package: packageGraph.root.name);
+  final configFiles = reader.assetFinder
+      .find(Glob('*.build.yaml'), package: packageGraph.root.name);
   await for (final id in configFiles) {
     final packageName = p.basename(id.path).split('.').first;
     final packageNode = packageGraph.allPackages[packageName];

build_runner/lib/src/server/server.dart

@@ -381,7 +381,7 @@ class AssetHandler {
     var directoryPath = p.url.dirname(from.path);
     var glob = p.url.join(directoryPath, '*');
     var result =
-        await _reader.findAssets(Glob(glob)).map((a) => a.path).toList();
+        await _reader.assetFinder.find(Glob(glob)).map((a) => a.path).toList();
     var message = StringBuffer('Could not find ${from.path}');
     if (result.isEmpty) {
       message.write(' or any files in $directoryPath. ');

build_runner/pubspec.yaml

@@ -16,7 +16,7 @@ dependencies:
   analyzer: '>=4.4.0 <8.0.0'
   args: ^2.0.0
   async: ^2.5.0
-  build: ">=2.1.0 <2.5.0"
+  build: ^2.3.4-wip
   build_config: ">=1.1.0 <1.2.0"
   build_daemon: ^4.0.0
   build_resolvers: ^2.4.4

build_runner_core/lib/build_runner_core.dart

@@ -7,7 +7,6 @@ export 'package:build/build.dart' show PostProcessBuildStep, PostProcessBuilder;
 export 'src/asset/batch.dart' show wrapInBatch;
 export 'src/asset/file_based.dart';
 export 'src/asset/finalized_reader.dart';
-export 'src/asset/reader.dart' show RunnerAssetReader;
 export 'src/asset/writer.dart';
 export 'src/environment/build_environment.dart';
 export 'src/environment/io_environment.dart';

build_runner_core/lib/src/asset/batch.dart

@@ -12,7 +12,6 @@ import 'package:glob/glob.dart';
 import 'package:meta/meta.dart';
 
 import '../environment/io_environment.dart';
-import 'reader.dart';
 import 'writer.dart';
 
 /// A batch of file system writes that should be committed at once instead of
@@ -46,15 +45,15 @@ final class _FileSystemWriteBatch {
   }
 }
 
-/// Wraps a pair of a [RunnerAssetReader] with path-prividing capabilities and
+/// Wraps a pair of a [AssetReader] with path-providing capabilities and
 /// a [RunnerAssetWriter] into a pair of readers and writers that will
 /// internally buffer writes and only flush them in
 /// [RunnerAssetWriter.completeBuild].
 ///
 /// The returned reader will see pending writes by the returned writer before
 /// they are flushed to the file system.
-(RunnerAssetReader, RunnerAssetWriter) wrapInBatch({
-  required RunnerAssetReader reader,
+(AssetReader, RunnerAssetWriter) wrapInBatch({
+  required AssetReader reader,
   required RunnerAssetWriter writer,
 }) {
   final batch = _FileSystemWriteBatch._();
@@ -74,9 +73,10 @@ final class _PendingFileState {
 }
 
 @internal
-final class BatchReader extends AssetReader
-    implements AssetReaderState, RunnerAssetReader {
-  final RunnerAssetReader _inner;
+final class BatchReader extends AssetReader implements AssetReaderState {
+  @override
+  late final AssetFinder assetFinder = FunctionAssetFinder(_findAssets);
+  final AssetReader _inner;
   final _FileSystemWriteBatch _batch;
 
   BatchReader(this._inner, this._batch);
@@ -87,6 +87,12 @@ final class BatchReader extends AssetReader
   @override
   InputTracker? get inputTracker => _inner.inputTracker;
 
+  @override
+  AssetPathProvider? get assetPathProvider => _inner.assetPathProvider;
+
+  @override
+  InputTracker? get inputTracker => _inner.inputTracker;
+
   _PendingFileState? _stateFor(AssetId id) {
     return _batch._pendingWrites[id];
   }
@@ -100,10 +106,13 @@ final class BatchReader extends AssetReader
     }
   }
 
+// This is only for generators, so only `BuildStep` needs to implement it.
   @override
-  Stream<AssetId> findAssets(Glob glob, {String? package}) {
-    return _inner
-        .findAssets(glob, package: package)
+  Stream<AssetId> findAssets(Glob glob) => throw UnimplementedError();
+
+  Stream<AssetId> _findAssets(Glob glob, String? package) {
+    return _inner.assetFinder
+        .find(glob, package: package)
         .where((asset) => _stateFor(asset)?.isDeleted != true);
   }
 

build_runner_core/lib/src/asset/build_cache.dart

@@ -33,6 +33,9 @@ class BuildCacheReader implements AssetReader, AssetReaderState {
                 delegate: delegate.assetPathProvider!,
                 overlay: (id) => _cacheLocation(id, assetGraph, rootPackage));
 
+  @override
+  AssetFinder get assetFinder => _delegate.assetFinder;
+
   @override
   InputTracker? get inputTracker => _delegate.inputTracker;
 

build_runner_core/lib/src/asset/cache.dart

@@ -17,8 +17,6 @@ import 'lru_cache.dart';
 /// An [AssetReader] that caches all results from the delegate.
 ///
 /// Assets are cached until [invalidate] is invoked.
-///
-/// Does not implement [findAssets].
 class CachingAssetReader implements AssetReader, AssetReaderState {
   /// Cached results of [readAsBytes].
   final _bytesContentCache = LruCache<AssetId, List<int>>(
@@ -55,16 +53,25 @@ class CachingAssetReader implements AssetReader, AssetReaderState {
   @override
   InputTracker? get inputTracker => _delegate.inputTracker;
 
+  @override
+  AssetFinder get assetFinder => _delegate.assetFinder;
+
+  @override
+  AssetPathProvider? get assetPathProvider => _delegate.assetPathProvider;
+
+  @override
+  InputTracker? get inputTracker => _delegate.inputTracker;
+
   @override
   Future<bool> canRead(AssetId id) =>
       _canReadCache.putIfAbsent(id, () => _delegate.canRead(id));
 
   @override
   Future<Digest> digest(AssetId id) => _delegate.digest(id);
 
+  // This is only for generators, so only `BuildStep` needs to implement it.
   @override
-  Stream<AssetId> findAssets(Glob glob) =>
-      throw UnimplementedError('unimplemented!');
+  Stream<AssetId> findAssets(Glob glob) => throw UnimplementedError();
 
   @override
   Future<List<int>> readAsBytes(AssetId id, {bool cache = true}) {

build_runner_core/lib/src/asset/file_based.dart

@@ -14,16 +14,17 @@ import 'package:path/path.dart' as path;
 import 'package:pool/pool.dart';
 
 import '../package_graph/package_graph.dart';
-import 'reader.dart';
 import 'writer.dart';
 
 /// Pool for async file operations, we don't want to use too many file handles.
 final _descriptorPool = Pool(32);
 
 /// Basic [AssetReader] which uses a [PackageGraph] to look up where to read
 /// files from disk.
-class FileBasedAssetReader extends AssetReader
-    implements AssetReaderState, RunnerAssetReader {
+class FileBasedAssetReader extends AssetReader implements AssetReaderState {
+  @override
+  late final AssetFinder assetFinder = FunctionAssetFinder(_findAssets);
+
   final PackageGraph packageGraph;
 
   FileBasedAssetReader(this.packageGraph);
@@ -34,6 +35,13 @@ class FileBasedAssetReader extends AssetReader
   @override
   InputTracker? get inputTracker => null;
 
+  @override
+  AssetPathProvider get assetPathProvider => packageGraph;
+
+  @override
+  // TODO: implement inputTracker
+  InputTracker? get inputTracker => throw UnimplementedError();
+
   @override
   Future<bool> canRead(AssetId id) =>
       _descriptorPool.withResource(() => _fileFor(id, packageGraph).exists());
@@ -47,8 +55,11 @@ class FileBasedAssetReader extends AssetReader
       _fileForOrThrow(id, packageGraph).then((file) => _descriptorPool
           .withResource(() => file.readAsString(encoding: encoding)));
 
+// This is only for generators, so only `BuildStep` needs to implement it.
   @override
-  Stream<AssetId> findAssets(Glob glob, {String? package}) {
+  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) {