Add new code for resolving deps graphs in a phased build.

build/CHANGELOG.md

@@ -14,6 +14,7 @@
 - Refactor `BuildCacheReader` to `BuildCacheAssetPathProvider`.
 - Refactor `FileBasedAssetReader` and `FileBasedAssetWriter` to `ReaderWriter`.
 - Move `BuildStepImpl` to `build_runner_core`, use `SingleStepReader` directly.
+- Add `LibraryCycleGraphLoader` for loading transitive deps for analysis.
 
 ## 2.4.2
 

build/lib/src/internal.dart

@@ -6,6 +6,13 @@
 /// `build_runner_core` and `build_test` only.
 library;
 
+export 'library_cycle_graph/asset_deps.dart';
+export 'library_cycle_graph/asset_deps_loader.dart';
+export 'library_cycle_graph/library_cycle.dart';
+export 'library_cycle_graph/library_cycle_graph.dart';
+export 'library_cycle_graph/library_cycle_graph_loader.dart';
+export 'library_cycle_graph/phased_reader.dart';
+export 'library_cycle_graph/phased_value.dart';
 export 'state/asset_finder.dart';
 export 'state/asset_path_provider.dart';
 export 'state/filesystem.dart';

build/lib/src/library_cycle_graph/asset_deps.dart

@@ -0,0 +1,27 @@
+// 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 'package:built_collection/built_collection.dart';
+import 'package:built_value/built_value.dart';
+
+import '../../build.dart' hide Builder;
+
+part 'asset_deps.g.dart';
+
+/// Dependencies of a Dart source asset.
+///
+/// A "dependency" is another Dart source mentioned in `import`, `export`,
+/// `part` or `part of`.
+///
+/// Missing or not-yet-generated sources can be represented by this class: they
+/// have no deps.
+abstract class AssetDeps implements Built<AssetDeps, AssetDepsBuilder> {
+  static final AssetDeps empty = _$AssetDeps._(deps: BuiltSet());
+
+  BuiltSet<AssetId> get deps;
+
+  factory AssetDeps(Iterable<AssetId> deps) =>
+      _$AssetDeps._(deps: BuiltSet.of(deps));
+  AssetDeps._();
+}

build/lib/src/library_cycle_graph/asset_deps_loader.dart

@@ -0,0 +1,59 @@
+// 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 'package:analyzer/dart/analysis/utilities.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+
+import '../asset/id.dart';
+import 'asset_deps.dart';
+import 'phased_reader.dart';
+import 'phased_value.dart';
+
+/// Loads Dart source assets to [PhasedValue]s of [AssetDeps].
+class AssetDepsLoader {
+  static const _ignoredSchemes = ['dart', 'dart-ext'];
+
+  final PhasedReader _reader;
+
+  AssetDepsLoader(this._reader);
+
+  /// The phase that this loader is reading build state at.
+  int get phase => _reader.phase;
+
+  /// Reads [id]
+  ///
+  /// If [id] will be generated at a phase equal to or after [phase], the
+  /// result is incomplete, with an expirey phase.
+  Future<PhasedValue<AssetDeps>> load(AssetId id) async {
+    final content = await _reader.readPhased(id);
+
+    return PhasedValue((b) {
+      b.values.addAll(content.values.map((content) => _parse(id, content)));
+    });
+  }
+
+  /// Parses directives in [content] to return an [AssetDeps].
+  ExpiringValue<AssetDeps> _parse(AssetId id, ExpiringValue<String> content) {
+    final result =
+        ExpiringValueBuilder<AssetDeps>()..expiresAfter = content.expiresAfter;
+
+    final parsed =
+        parseString(content: content.value, throwIfDiagnostics: false).unit;
+
+    final depsNodeBuilder = AssetDepsBuilder();
+
+    for (final directive in parsed.directives) {
+      if (directive is! UriBasedDirective) continue;
+      final uri = directive.uri.stringValue;
+      if (uri == null) continue;
+      final parsedUri = Uri.parse(uri);
+      if (_ignoredSchemes.any(parsedUri.isScheme)) continue;
+      final assetId = AssetId.resolve(parsedUri, from: id);
+      depsNodeBuilder.deps.add(assetId);
+    }
+
+    result.value = depsNodeBuilder.build();
+    return result.build();
+  }
+}

build/lib/src/library_cycle_graph/library_cycle.dart

@@ -0,0 +1,22 @@
+// 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 'package:built_collection/built_collection.dart';
+import 'package:built_value/built_value.dart';
+
+import '../asset/id.dart';
+
+part 'library_cycle.g.dart';
+
+/// A set of Dart source assets that mutually depend on each other.
+///
+/// This means they have to be compiled as a single unit.
+abstract class LibraryCycle
+    implements Built<LibraryCycle, LibraryCycleBuilder> {
+  BuiltSet<AssetId> get ids;
+
+  factory LibraryCycle([void Function(LibraryCycleBuilder) updates]) =
+      _$LibraryCycle;
+  LibraryCycle._();
+}

build/lib/src/library_cycle_graph/library_cycle_graph.dart

@@ -0,0 +1,48 @@
+// 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 'package:built_collection/built_collection.dart';
+import 'package:built_value/built_value.dart';
+
+import '../asset/id.dart';
+import 'library_cycle.dart';
+
+part 'library_cycle_graph.g.dart';
+
+/// A directed acyclic graph of [LibraryCycle]s.
+abstract class LibraryCycleGraph
+    implements Built<LibraryCycleGraph, LibraryCycleGraphBuilder> {
+  LibraryCycle get root;
+  BuiltList<LibraryCycleGraph> get children;
+
+  factory LibraryCycleGraph([void Function(LibraryCycleGraphBuilder) updates]) =
+      _$LibraryCycleGraph;
+  LibraryCycleGraph._();
+
+  /// All subgraphs in the graph, including the root.
+  Iterable<LibraryCycleGraph> get transitiveGraphs {
+    final result = Set<LibraryCycleGraph>.identity();
+    final nextGraphs = [this];
+
+    while (nextGraphs.isNotEmpty) {
+      final graph = nextGraphs.removeLast();
+      if (result.add(graph)) {
+        nextGraphs.addAll(graph.children);
+      }
+    }
+
+    return result;
+  }
+
+  /// All assets in the graph, including the root.
+  // TODO(davidmorgan): for best performance the graph should usually stay as a
+  // graph rather than being expanded into an explicit set of nodes. So, remove
+  // uses of this. If in the end it's still needed, investigate if it needs to
+  // be optimized.
+  Iterable<AssetId> get transitiveDeps sync* {
+    for (final graph in transitiveGraphs) {
+      yield* graph.root.ids;
+    }
+  }
+}