Serialize AssetId by identity.

build_runner_core/lib/src/asset_graph/graph.dart

@@ -70,7 +70,7 @@ class AssetGraph implements GeneratedAssetHider {
 
   /// Deserializes this graph.
   factory AssetGraph.deserialize(List<int> serializedGraph) =>
-      _AssetGraphDeserializer(serializedGraph).deserialize();
+      deserializeAssetGraph(serializedGraph);
 
   static Future<AssetGraph> build(
     BuildPhases buildPhases,
@@ -106,7 +106,7 @@ class AssetGraph implements GeneratedAssetHider {
     return graph;
   }
 
-  List<int> serialize() => _AssetGraphSerializer(this).serialize();
+  List<int> serialize() => serializeAssetGraph(this);
 
   @visibleForTesting
   Map<String, Map<PostProcessBuildStepId, Set<AssetId>>>

build_runner_core/lib/src/asset_graph/identity_serializer.dart

@@ -0,0 +1,91 @@
+// 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_value/serializer.dart';
+
+/// Wraps another `built_value` serializer to add serializing by identity.
+///
+/// Integer IDs are created as new values are encountered, and a mapping to
+/// objects and serialized object values is maintained.
+///
+/// The serialized data does not contain the object values, only IDs. This might
+/// not matter if this `IdentitySerializer` will stay in memory and be used to
+/// deserialize. Or, the serialized object values must be serialized separately:
+/// they can be obtained from [serializedObjects], and set via
+/// [deserializeWithObjects].
+///
+/// TODO(davidmorgan): consider upstreaming to `built_value`.
+class IdentitySerializer<T> implements PrimitiveSerializer<T> {
+  final Serializer<T> delegate;
+  final PrimitiveSerializer<T>? _primitiveDelegate;
+  final StructuredSerializer<T>? _structuredDelegate;
+
+  final Map<T, int> _ids = Map.identity();
+  final List<T> _objects = [];
+  List<Object?> _serializedObjects = [];
+
+  /// A serializer wrapping [delegate] to deduplicate by identity.
+  IdentitySerializer(this.delegate)
+    : _primitiveDelegate = delegate is PrimitiveSerializer<T> ? delegate : null,
+      _structuredDelegate =
+          delegate is StructuredSerializer<T> ? delegate : null;
+
+  /// Sets the stored object values to [objects].
+  ///
+  /// Serialized values are indices into this list.
+  void deserializeWithObjects(Iterable<T> objects) {
+    _ids.clear();
+    _objects.clear();
+    _serializedObjects.clear();
+    for (final object in objects) {
+      _objects.add(object);
+      _ids[object] = _objects.length - 1;
+    }
+  }
+
+  /// The list of unique objects encountered since the most recent [reset].
+  List<Object?> get serializedObjects => _serializedObjects;
+
+  /// Clears the ID to object and serialized object mappings.
+  ///
+  /// Call this after serializing or deserializing to avoid retaining objects in
+  /// memory; or, don't call it to continue using the same IDs and objects.
+  void reset() {
+    _ids.clear();
+    _objects.clear();
+    _serializedObjects = [];
+  }
+
+  @override
+  Iterable<Type> get types => delegate.types;
+
+  @override
+  String get wireName => delegate.wireName;
+
+  @override
+  T deserialize(
+    Serializers serializers,
+    Object serialized, {
+    FullType specifiedType = FullType.unspecified,
+  }) => _objects[serialized as int];
+
+  @override
+  Object serialize(
+    Serializers serializers,
+    T object, {
+    FullType specifiedType = FullType.unspecified,
+  }) {
+    // If it has already been seen, return the ID.
+    return _ids.putIfAbsent(object, () {
+      // Otherwise, serialize it, store the value and serialized value, and
+      // return the index of the last of `_objects` as the ID.
+      final serialized =
+          _primitiveDelegate == null
+              ? _structuredDelegate!.serialize(serializers, object)
+              : _primitiveDelegate.serialize(serializers, object);
+      _serializedObjects.add(serialized);
+      return (_objects..add(object)).length - 1;
+    });
+  }
+}

build_runner_core/lib/src/asset_graph/serialization.dart

@@ -8,148 +8,95 @@ part of 'graph.dart';
 ///
 /// This should be incremented any time the serialize/deserialize formats
 /// change.
-const _version = 27;
+const _version = 28;
 
 /// Deserializes an [AssetGraph] from a [Map].
-class _AssetGraphDeserializer {
-  // Iteration order does not matter
-  final _idToAssetId = HashMap<int, AssetId>();
-  final Map _serializedGraph;
-
-  _AssetGraphDeserializer._(this._serializedGraph);
-
-  factory _AssetGraphDeserializer(List<int> bytes) {
-    dynamic decoded;
-    try {
-      decoded = jsonDecode(utf8.decode(bytes));
-    } on FormatException {
-      throw AssetGraphCorruptedException();
-    }
-    if (decoded is! Map) throw AssetGraphCorruptedException();
-    if (decoded['version'] != _version) {
-      throw AssetGraphCorruptedException();
-    }
-    return _AssetGraphDeserializer._(decoded);
+AssetGraph deserializeAssetGraph(List<int> bytes) {
+  dynamic serializedGraph;
+  try {
+    serializedGraph = jsonDecode(utf8.decode(bytes));
+  } on FormatException {
+    throw AssetGraphCorruptedException();
+  }
+  if (serializedGraph is! Map) throw AssetGraphCorruptedException();
+  if (serializedGraph['version'] != _version) {
+    throw AssetGraphCorruptedException();
   }
 
-  /// Perform the deserialization, should only be called once.
-  AssetGraph deserialize() {
-    var packageLanguageVersions = {
-      for (var entry
-          in (_serializedGraph['packageLanguageVersions']
-                  as Map<String, dynamic>)
-              .entries)
-        entry.key:
-            entry.value != null
-                ? LanguageVersion.parse(entry.value as String)
-                : null,
-    };
-    var graph = AssetGraph._(
-      _deserializeDigest(_serializedGraph['buildActionsDigest'] as String)!,
-      _serializedGraph['dart_version'] as String,
-      packageLanguageVersions.build(),
-      BuiltList<String>.from(_serializedGraph['enabledExperiments'] as List),
-    );
-
-    var packageNames = _serializedGraph['packages'] as List;
-
-    // Read in the id => AssetId map from the graph first.
-    var assetPaths = _serializedGraph['assetPaths'] as List;
-    for (var i = 0; i < assetPaths.length; i += 2) {
-      var packageName = packageNames[assetPaths[i + 1] as int] as String;
-      _idToAssetId[i ~/ 2] = AssetId(packageName, assetPaths[i] as String);
-    }
-
-    // Read in all the nodes and their outputs.
-    //
-    // Note that this does not read in the inputs of generated nodes.
-    for (var serializedItem in _serializedGraph['nodes'] as Iterable) {
-      graph._add(_deserializeAssetNode(serializedItem as List));
-    }
+  identityAssetIdSerializer.deserializeWithObjects(
+    (serializedGraph['ids'] as List).map(
+      (id) => assetIdSerializer.deserialize(serializers, id as Object),
+    ),
+  );
+
+  var packageLanguageVersions = {
+    for (var entry
+        in (serializedGraph['packageLanguageVersions'] as Map<String, dynamic>)
+            .entries)
+      entry.key:
+          entry.value != null
+              ? LanguageVersion.parse(entry.value as String)
+              : null,
+  };
+  var graph = AssetGraph._(
+    _deserializeDigest(serializedGraph['buildActionsDigest'] as String)!,
+    serializedGraph['dart_version'] as String,
+    packageLanguageVersions.build(),
+    BuiltList<String>.from(serializedGraph['enabledExperiments'] as List),
+  );
+
+  for (var serializedItem in serializedGraph['nodes'] as Iterable) {
+    graph._add(_deserializeAssetNode(serializedItem as List));
+  }
 
-    final postProcessOutputs =
-        serializers.deserialize(
-              _serializedGraph['postProcessOutputs'],
-              specifiedType: postProcessBuildStepOutputsFullType,
-            )
-            as Map<String, Map<PostProcessBuildStepId, Set<AssetId>>>;
+  final postProcessOutputs =
+      serializers.deserialize(
+            serializedGraph['postProcessOutputs'],
+            specifiedType: postProcessBuildStepOutputsFullType,
+          )
+          as Map<String, Map<PostProcessBuildStepId, Set<AssetId>>>;
 
-    for (final postProcessOutputsForPackage in postProcessOutputs.values) {
-      for (final entry in postProcessOutputsForPackage.entries) {
-        graph.updatePostProcessBuildStep(entry.key, outputs: entry.value);
-      }
+  for (final postProcessOutputsForPackage in postProcessOutputs.values) {
+    for (final entry in postProcessOutputsForPackage.entries) {
+      graph.updatePostProcessBuildStep(entry.key, outputs: entry.value);
     }
-
-    return graph;
   }
 
-  AssetNode _deserializeAssetNode(List serializedNode) =>
-      serializers.deserializeWith(AssetNode.serializer, serializedNode)
-          as AssetNode;
+  identityAssetIdSerializer.reset();
+  return graph;
 }
 
-/// Serializes an [AssetGraph] into a [Map].
-class _AssetGraphSerializer {
-  // Iteration order does not matter
-  final _assetIdToId = HashMap<AssetId, int>();
-
-  final AssetGraph _graph;
-
-  _AssetGraphSerializer(this._graph);
-
-  /// Perform the serialization, should only be called once.
-  List<int> serialize() {
-    var pathId = 0;
-    // [path0, packageId0, path1, packageId1, ...]
-    var assetPaths = <dynamic>[];
-    var packages = _graph._nodesByPackage.keys.toList(growable: false);
-    for (var node in _graph.allNodes) {
-      _assetIdToId[node.id] = pathId;
-      pathId++;
-      assetPaths
-        ..add(node.id.path)
-        ..add(packages.indexOf(node.id.package));
-    }
+AssetNode _deserializeAssetNode(List serializedNode) =>
+    serializers.deserializeWith(AssetNode.serializer, serializedNode)
+        as AssetNode;
 
-    var result = <String, dynamic>{
-      'version': _version,
-      'dart_version': _graph.dartVersion,
-      'nodes': _graph.allNodes
-          .map((node) => serializers.serializeWith(AssetNode.serializer, node))
-          .toList(growable: false),
-      'buildActionsDigest': _serializeDigest(_graph.buildPhasesDigest),
-      'packages': packages,
-      'assetPaths': assetPaths,
-      'packageLanguageVersions':
-          _graph.packageLanguageVersions
-              .map((pkg, version) => MapEntry(pkg, version?.toString()))
-              .toMap(),
-      'enabledExperiments': _graph.enabledExperiments.toList(),
-      'postProcessOutputs': serializers.serialize(
-        _graph._postProcessBuildStepOutputs,
-        specifiedType: postProcessBuildStepOutputsFullType,
-      ),
-    };
-    return utf8.encode(json.encode(result));
-  }
-
-  int findAssetIndex(
-    AssetId id, {
-    required AssetId from,
-    required String field,
-  }) {
-    final index = _assetIdToId[id];
-    if (index == null) {
-      log.severe(
-        'The $field field in $from references a non-existent asset '
-        '$id and will corrupt the asset graph. '
-        'If you encounter this error please copy '
-        'the details from this message and add them to '
-        'https://github.com/dart-lang/build/issues/1804.',
-      );
-    }
-    return index!;
-  }
+/// Serializes an [AssetGraph] into a [Map].
+List<int> serializeAssetGraph(AssetGraph graph) {
+  // Serialize nodes first so all `AssetId` instances are seen by
+  // `identityAssetIdSeralizer`.
+  final nodes = graph.allNodes
+      .map((node) => serializers.serializeWith(AssetNode.serializer, node))
+      .toList(growable: false);
+
+  var result = <String, dynamic>{
+    'version': _version,
+    'ids': identityAssetIdSerializer.serializedObjects,
+    'dart_version': graph.dartVersion,
+    'nodes': nodes,
+    'buildActionsDigest': _serializeDigest(graph.buildPhasesDigest),
+    'packageLanguageVersions':
+        graph.packageLanguageVersions
+            .map((pkg, version) => MapEntry(pkg, version?.toString()))
+            .toMap(),
+    'enabledExperiments': graph.enabledExperiments.toList(),
+    'postProcessOutputs': serializers.serialize(
+      graph._postProcessBuildStepOutputs,
+      specifiedType: postProcessBuildStepOutputsFullType,
+    ),
+  };
+
+  identityAssetIdSerializer.reset();
+  return utf8.encode(json.encode(result));
 }
 
 Digest? _deserializeDigest(String? serializedDigest) =>

build_runner_core/lib/src/asset_graph/serializers.dart

@@ -9,6 +9,7 @@ import 'package:built_collection/built_collection.dart';
 import 'package:built_value/serializer.dart';
 import 'package:crypto/crypto.dart';
 
+import 'identity_serializer.dart';
 import 'node.dart';
 import 'post_process_build_step_id.dart';
 
@@ -24,10 +25,15 @@ final postProcessBuildStepOutputsFullType = FullType(Map, [
   postProcessBuildStepOutputsInnerFullType,
 ]);
 
+final assetIdSerializer = AssetIdSerializer();
+final identityAssetIdSerializer = IdentitySerializer<AssetId>(
+  assetIdSerializer,
+);
+
 @SerializersFor([AssetNode])
 final Serializers serializers =
     (_$serializers.toBuilder()
-          ..add(AssetIdSerializer())
+          ..add(identityAssetIdSerializer)
           ..add(DigestSerializer())
           ..add(MapSerializer())
           ..add(SetSerializer())