Implement deepCopy as copying, instead of merge

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;