Implement deepCopy as copying, instead of merge (#742)

Currently `deepCopy` and `clone` create an empty message, and then merge the
cloned message into the empty message.

This is slow as merge needs to validate each element added to the message.

In this PR we instead directly copy the field set, and deeply copy map, list,
and message fields.

deepCopy benchmark results:

|                  | Before  | After   | Diff   |
|------------------|---------|---------|--------|
| AOT              | 238 us  | 151 us  | -36%   |
| dart2js -O4      | 242 us  | 140 us  | -42%   |
| dart2wasm -O2    | 230 us  | 123 us  | -46%   |
| JIT              | 189 us  | 104 us  | -44%   |

This CL is tested internally in cl/794080754.

Fixes #60.

Author: osa1

benchmarks/bin/deep_copy.dart

@@ -9,6 +9,11 @@ import 'package:protobuf_benchmarks/generated/google_message1_proto3.pb.dart'
     as p3;
 import 'package:protobuf_benchmarks/generated/google_message2.pb.dart';
 import 'package:protobuf_benchmarks/readfile.dart';
+import 'package:protobuf/protobuf.dart';
+
+GeneratedMessage? sink1;
+GeneratedMessage? sink2;
+GeneratedMessage? sink3;
 
 class Benchmark extends BenchmarkBase {
   final p2.GoogleMessage1 _message1Proto2;
@@ -26,12 +31,9 @@ class Benchmark extends BenchmarkBase {
 
   @override
   void run() {
-    // ignore: unused_result
-    _message1Proto2.deepCopy();
-    // ignore: unused_result
-    _message1Proto3.deepCopy();
-    // ignore: unused_result
-    _message2.deepCopy();
+    sink1 = _message1Proto2.deepCopy();
+    sink2 = _message1Proto3.deepCopy();
+    sink3 = _message2.deepCopy();
   }
 }
 
@@ -49,4 +51,10 @@ void main() {
     message1Proto3Input,
     message2Input,
   ).report();
+
+  if (int.parse('1') == 0) {
+    print(sink1);
+    print(sink2);
+    print(sink3);
+  }
 }

protobuf/CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 5.0.0-wip
 
+* Improve performance of `GeneratedMessage.deepCopy`. ([#742])
+
+[#742]: https://github.com/google/protobuf.dart/pull/742
+
 ## 4.2.0
 
 * Internal refactoring to split the package into libraries. This allows

protobuf/lib/src/protobuf/extension_field_set.dart

@@ -6,11 +6,15 @@ part of 'internal.dart';
 
 class ExtensionFieldSet {
   final FieldSet _parent;
-  final Map<int, Extension> _info = <int, Extension>{};
-  final Map<int, dynamic> _values = <int, dynamic>{};
+  final Map<int, Extension> _info;
+  final Map<int, dynamic> _values;
   bool _isReadOnly = false;
 
-  ExtensionFieldSet(this._parent);
+  ExtensionFieldSet(this._parent)
+    : _info = <int, Extension>{},
+      _values = <int, dynamic>{};
+
+  ExtensionFieldSet._(this._parent, this._info, this._values);
 
   Extension? _getInfoOrNull(int tagNumber) => _info[tagNumber];
 
@@ -211,6 +215,34 @@ class ExtensionFieldSet {
       );
     }
   }
+
+  ExtensionFieldSet _deepCopy(FieldSet parent) {
+    final newExtensionFieldSet = ExtensionFieldSet._(
+      parent,
+      Map.from(_info),
+      Map.from(_values),
+    );
+
+    final newValues = newExtensionFieldSet._values;
+
+    for (final entry in _values.entries) {
+      final tag = entry.key;
+      final value = entry.value;
+      final fieldInfo = _info[tag]!;
+      if (fieldInfo.isMapField) {
+        final PbMap? map = value;
+        newValues[tag] = map?._deepCopy();
+      } else if (fieldInfo.isRepeated) {
+        final PbList? list = value;
+        newValues[tag] = list?._deepCopy();
+      } else if (fieldInfo.isGroupOrMessage) {
+        final GeneratedMessage? message = value;
+        newValues[tag] = message?.deepCopy();
+      }
+    }
+
+    return newExtensionFieldSet;
+  }
 }
 
 extension ExtensionFieldSetInternalExtension on ExtensionFieldSet {

protobuf/lib/src/protobuf/field_set.dart

@@ -916,6 +916,64 @@ class FieldSet {
 
     _oneofCases?.addAll(original._oneofCases!);
   }
+
+  // This assumes that [this] is fresh, i.e. no extensions, no values set.
+  //
+  // The reason why this updates [this] instead of returning a new [FieldSet] is
+  // that to start cloning we need to create an empty instance via
+  // `createEmptyInstance`, which already creates an empty [FieldSet], which we
+  // reuse here.
+  void _deepCopyFrom(FieldSet original) {
+    final info = _meta;
+
+    assert(_values.length == original._values.length);
+
+    // memcpy the original's values to avoid redundant bounds checks below by
+    // copying scalar fields one by one.
+    _values.setAll(0, original._values);
+
+    for (var index = 0; index < info.byIndex.length; index++) {
+      final fieldInfo = info.byIndex[index];
+      if (fieldInfo.isMapField) {
+        final PbMap? originalMap = original._values[index];
+        if (originalMap == null) continue;
+        _values[index] = originalMap._deepCopy();
+      } else if (fieldInfo.isRepeated) {
+        final PbList? originalList = original._values[index];
+        if (originalList == null) continue;
+        _values[index] = originalList._deepCopy();
+      } else if (fieldInfo.isGroupOrMessage) {
+        final GeneratedMessage? message = original._values[index];
+        _values[index] = message?.deepCopy();
+      }
+
+      // Scalar fields are already copied above with `setAll`.
+    }
+
+    assert(_extensions == null);
+    final originalExtensions = original._extensions;
+    if (originalExtensions != null) {
+      _extensions = originalExtensions._deepCopy(this);
+    }
+
+    assert(_unknownFields == null);
+    final originalUnknownFields = original._unknownFields;
+    if (originalUnknownFields != null) {
+      _unknownFields = originalUnknownFields._deepCopy();
+    }
+
+    assert(_unknownJsonData == null);
+    final originalUnknownJsonData = original._unknownJsonData;
+    if (originalUnknownJsonData != null) {
+      _unknownJsonData = Map.from(originalUnknownJsonData);
+    }
+
+    assert(_oneofCases == null || _oneofCases.isEmpty);
+    final originalOneofCases = original._oneofCases;
+    if (originalOneofCases != null) {
+      _oneofCases!.addAll(originalOneofCases);
+    }
+  }
 }
 
 extension FieldSetInternalExtension on FieldSet {

protobuf/lib/src/protobuf/generated_message.dart

@@ -48,7 +48,6 @@ abstract class GeneratedMessage {
   BuilderInfo get info_;
 
   /// Creates a deep copy of the fields in this message.
-  /// (The generated code uses [mergeFromMessage].)
   @Deprecated(
     'Using this can add significant size overhead to your binary. '
     'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
@@ -625,7 +624,11 @@ extension GeneratedMessageGenericExtensions<T extends GeneratedMessage> on T {
     '[GeneratedMessageGenericExtensions.deepCopy] '
     'does not update the message, returns a new message',
   )
-  T deepCopy() => info_.createEmptyInstance!() as T..mergeFromMessage(this);
+  T deepCopy() {
+    final newMessage = info_.createEmptyInstance!();
+    newMessage._fieldSet._deepCopyFrom(_fieldSet);
+    return newMessage as T;
+  }
 }
 
 extension GeneratedMessageInternalExtension on GeneratedMessage {

protobuf/lib/src/protobuf/pb_list.dart

@@ -234,4 +234,20 @@ class PbList<E> extends ListBase<E> {
   static Never _readOnlyError(String methodName) {
     throw UnsupportedError("'$methodName' on a read-only list");
   }
+
+  PbList<E> _deepCopy() {
+    final newList = PbList<E>(check: _check);
+    final wrappedList = _wrappedList;
+    final newWrappedList = newList._wrappedList;
+    if (wrappedList.isNotEmpty) {
+      if (wrappedList[0] is GeneratedMessage) {
+        for (final message in wrappedList) {
+          newWrappedList.add((message as GeneratedMessage).deepCopy() as E);
+        }
+      } else {
+        newWrappedList.addAll(wrappedList);
+      }
+    }
+    return newList;
+  }
 }

protobuf/lib/src/protobuf/pb_map.dart

@@ -131,4 +131,19 @@ class PbMap<K, V> extends MapBase<K, V> {
     }
     return this;
   }
+
+  PbMap<K, V> _deepCopy() {
+    final newMap = PbMap<K, V>(keyFieldType, valueFieldType);
+    final wrappedMap = _wrappedMap;
+    final newWrappedMap = newMap._wrappedMap;
+    if (PbFieldType.isGroupOrMessage(valueFieldType)) {
+      for (final entry in wrappedMap.entries) {
+        newWrappedMap[entry.key] =
+            (entry.value as GeneratedMessage).deepCopy() as V;
+      }
+    } else {
+      newWrappedMap.addAll(wrappedMap);
+    }
+    return newMap;
+  }
 }

protobuf/lib/src/protobuf/unknown_field_set.dart

@@ -8,11 +8,15 @@ part of 'internal.dart';
 class UnknownFieldSet {
   static final UnknownFieldSet emptyUnknownFieldSet =
       UnknownFieldSet().._markReadOnly();
-  final Map<int, UnknownFieldSetField> _fields = <int, UnknownFieldSetField>{};
 
-  UnknownFieldSet();
+  final Map<int, UnknownFieldSetField> _fields;
 
-  UnknownFieldSet._clone(UnknownFieldSet unknownFieldSet) {
+  UnknownFieldSet() : _fields = <int, UnknownFieldSetField>{};
+
+  UnknownFieldSet._(this._fields);
+
+  UnknownFieldSet._clone(UnknownFieldSet unknownFieldSet)
+    : _fields = <int, UnknownFieldSetField>{} {
     mergeFromUnknownFieldSet(unknownFieldSet);
   }
 
@@ -195,6 +199,16 @@ class UnknownFieldSet {
       _throwFrozenMessageModificationError('UnknownFieldSet', methodName);
     }
   }
+
+  UnknownFieldSet _deepCopy() {
+    Map<int, UnknownFieldSetField> newFields = {};
+    for (final entry in _fields.entries) {
+      final key = entry.key;
+      final value = entry.value;
+      newFields[key] = value._deepCopy();
+    }
+    return UnknownFieldSet._(newFields);
+  }
 }
 
 /// An unknown field in a [UnknownFieldSet].
@@ -211,6 +225,21 @@ class UnknownFieldSetField {
   List<Int64> get fixed64s => _fixed64s;
   List<UnknownFieldSet> get groups => _groups;
 
+  UnknownFieldSetField()
+    : _lengthDelimited = <List<int>>[],
+      _varints = <Int64>[],
+      _fixed32s = <int>[],
+      _fixed64s = <Int64>[],
+      _groups = <UnknownFieldSet>[];
+
+  UnknownFieldSetField._(
+    this._lengthDelimited,
+    this._varints,
+    this._fixed32s,
+    this._fixed64s,
+    this._groups,
+  );
+
   bool _isReadOnly = false;
 
   void _markReadOnly() {
@@ -309,4 +338,24 @@ class UnknownFieldSetField {
   void addVarint(Int64 value) {
     varints.add(value);
   }
+
+  UnknownFieldSetField _deepCopy() {
+    final List<List<int>> newLengthDelimited = List.from(_lengthDelimited);
+    final List<Int64> newVarints = List.from(_varints);
+    final List<int> newFixed32s = List.from(_fixed32s);
+    final List<Int64> newFixed64s = List.from(_fixed64s);
+
+    final List<UnknownFieldSet> newGroups = [];
+    for (final group in _groups) {
+      newGroups.add(group._deepCopy());
+    }
+
+    return UnknownFieldSetField._(
+      newLengthDelimited,
+      newVarints,
+      newFixed32s,
+      newFixed64s,
+      newGroups,
+    );
+  }
 }

protoc_plugin/CHANGELOG.md

@@ -1,6 +1,10 @@
 ## 23.0.0
 
 * Update generated code for protobuf 5.0.0.
+* Update generated `clone` members to take advantage of faster `deepCopy`
+  implementation in protobuf 5.0.0. ([#742])
+
+[#742]: https://github.com/google/protobuf.dart/pull/742
 
 ## 22.5.0
 

protoc_plugin/lib/src/gen/dart_options.pb.dart

@@ -50,7 +50,7 @@ class DartMixin extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  DartMixin clone() => DartMixin()..mergeFromMessage(this);
+  DartMixin clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   DartMixin copyWith(void Function(DartMixin) updates) =>
       super.copyWith((message) => updates(message as DartMixin)) as DartMixin;
@@ -130,7 +130,7 @@ class Imports extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  Imports clone() => Imports()..mergeFromMessage(this);
+  Imports clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   Imports copyWith(void Function(Imports) updates) =>
       super.copyWith((message) => updates(message as Imports)) as Imports;