From 733cbb05a11ca69678691a79e40bad815c9c5629 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20A=C4=9Facan?= <omersa@google.com>
Date: Tue, 12 Aug 2025 09:26:08 +0100
Subject: [PATCH 01/10] Update deepCopy bench

---
 benchmarks/bin/deep_copy.dart | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/benchmarks/bin/deep_copy.dart b/benchmarks/bin/deep_copy.dart
index 09372b67..93ac7256 100644
--- a/benchmarks/bin/deep_copy.dart
+++ b/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);
+  }
 }

From 12e6be765a25321dd67029edd0a830b0af6638d7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20A=C4=9Facan?= <omersa@google.com>
Date: Tue, 12 Aug 2025 10:44:30 +0100
Subject: [PATCH 02/10] WIP

---
 .../lib/src/protobuf/extension_field_set.dart | 36 +++++++++++-
 protobuf/lib/src/protobuf/field_set.dart      | 56 +++++++++++++++++++
 .../lib/src/protobuf/generated_message.dart   |  6 +-
 protobuf/lib/src/protobuf/pb_list.dart        |  4 ++
 protobuf/lib/src/protobuf/pb_map.dart         |  4 ++
 .../lib/src/protobuf/unknown_field_set.dart   | 55 +++++++++++++++++-
 6 files changed, 154 insertions(+), 7 deletions(-)

diff --git a/protobuf/lib/src/protobuf/extension_field_set.dart b/protobuf/lib/src/protobuf/extension_field_set.dart
index 64972003..bbdb5b42 100644
--- a/protobuf/lib/src/protobuf/extension_field_set.dart
+++ b/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 +215,32 @@ class ExtensionFieldSet {
       );
     }
   }
+
+  ExtensionFieldSet deepCopy(FieldSet parent) {
+    final newExtensionFieldSet = ExtensionFieldSet._(
+      parent,
+      Map.from(_info),
+      Map.from(_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;
+        _values[tag] = map?.deepCopy();
+      } else if (fieldInfo.isRepeated) {
+        final PbList? list = value;
+        _values[tag] = list?.deepCopy();
+      } else if (fieldInfo.isGroupOrMessage) {
+        final GeneratedMessage? message = value;
+        _values[tag] = message?.deepCopy();
+      }
+    }
+
+    return newExtensionFieldSet;
+  }
 }
 
 extension ExtensionFieldSetInternalExtension on ExtensionFieldSet {
diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 980c03c6..57436ed2 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -916,6 +916,62 @@ 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? map = original._values[index];
+        _values[index] = map?.deepCopy();
+      } else if (fieldInfo.isRepeated) {
+        final PbList? list = original._values[index];
+        _values[index] = list?.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 = _oneofCases;
+    if (originalOneofCases != null) {
+      _oneofCases!.addAll(originalOneofCases);
+    }
+  }
 }
 
 extension FieldSetInternalExtension on FieldSet {
diff --git a/protobuf/lib/src/protobuf/generated_message.dart b/protobuf/lib/src/protobuf/generated_message.dart
index 9b5c866a..5c3a3c5f 100644
--- a/protobuf/lib/src/protobuf/generated_message.dart
+++ b/protobuf/lib/src/protobuf/generated_message.dart
@@ -625,7 +625,11 @@ 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 {
diff --git a/protobuf/lib/src/protobuf/pb_list.dart b/protobuf/lib/src/protobuf/pb_list.dart
index d48a8214..42811dff 100644
--- a/protobuf/lib/src/protobuf/pb_list.dart
+++ b/protobuf/lib/src/protobuf/pb_list.dart
@@ -234,4 +234,8 @@ class PbList<E> extends ListBase<E> {
   static Never _readOnlyError(String methodName) {
     throw UnsupportedError("'$methodName' on a read-only list");
   }
+
+  PbList<E> deepCopy() {
+    throw 'TODO';
+  }
 }
diff --git a/protobuf/lib/src/protobuf/pb_map.dart b/protobuf/lib/src/protobuf/pb_map.dart
index 2816eb69..80a46f39 100644
--- a/protobuf/lib/src/protobuf/pb_map.dart
+++ b/protobuf/lib/src/protobuf/pb_map.dart
@@ -131,4 +131,8 @@ class PbMap<K, V> extends MapBase<K, V> {
     }
     return this;
   }
+
+  PbMap<K, V> deepCopy() {
+    throw 'TODO';
+  }
 }
diff --git a/protobuf/lib/src/protobuf/unknown_field_set.dart b/protobuf/lib/src/protobuf/unknown_field_set.dart
index 196c6b4f..2a5db52d 100644
--- a/protobuf/lib/src/protobuf/unknown_field_set.dart
+++ b/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,
+    );
+  }
 }

From aedb30030942bdd9e50d59c971e65dbc2335b44b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20A=C4=9Facan?= <omersa@google.com>
Date: Tue, 12 Aug 2025 13:35:30 +0100
Subject: [PATCH 03/10] WIP

---
 protobuf/lib/src/protobuf/field_set.dart | 10 ++++++----
 protobuf/lib/src/protobuf/pb_list.dart   | 14 +++++++++++++-
 protobuf/lib/src/protobuf/pb_map.dart    | 13 ++++++++++++-
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 57436ed2..1f5fce26 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -935,11 +935,13 @@ class FieldSet {
     for (var index = 0; index < info.byIndex.length; index++) {
       final fieldInfo = info.byIndex[index];
       if (fieldInfo.isMapField) {
-        final PbMap? map = original._values[index];
-        _values[index] = map?.deepCopy();
+        final PbMap? originalMap = original._values[index];
+        if (originalMap == null) continue;
+        _values[index] = originalMap.deepCopy();
       } else if (fieldInfo.isRepeated) {
-        final PbList? list = original._values[index];
-        _values[index] = list?.deepCopy();
+        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();
diff --git a/protobuf/lib/src/protobuf/pb_list.dart b/protobuf/lib/src/protobuf/pb_list.dart
index 42811dff..f0f0000d 100644
--- a/protobuf/lib/src/protobuf/pb_list.dart
+++ b/protobuf/lib/src/protobuf/pb_list.dart
@@ -236,6 +236,18 @@ class PbList<E> extends ListBase<E> {
   }
 
   PbList<E> deepCopy() {
-    throw 'TODO';
+    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;
   }
 }
diff --git a/protobuf/lib/src/protobuf/pb_map.dart b/protobuf/lib/src/protobuf/pb_map.dart
index 80a46f39..4ec1872d 100644
--- a/protobuf/lib/src/protobuf/pb_map.dart
+++ b/protobuf/lib/src/protobuf/pb_map.dart
@@ -133,6 +133,17 @@ class PbMap<K, V> extends MapBase<K, V> {
   }
 
   PbMap<K, V> deepCopy() {
-    throw 'TODO';
+    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;
   }
 }

From cec8ec76371d9f5a3eb9a4d85a96c371a24492b0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20A=C4=9Facan?= <omersa@google.com>
Date: Tue, 12 Aug 2025 13:44:10 +0100
Subject: [PATCH 04/10] Done?

---
 protobuf/lib/src/protobuf/field_set.dart | 2 +-
 protoc_plugin/test/oneof_test.dart       | 8 ++------
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 1f5fce26..7ca69242 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -969,7 +969,7 @@ class FieldSet {
     }
 
     assert(_oneofCases == null || _oneofCases.isEmpty);
-    final originalOneofCases = _oneofCases;
+    final originalOneofCases = original._oneofCases;
     if (originalOneofCases != null) {
       _oneofCases!.addAll(originalOneofCases);
     }
diff --git a/protoc_plugin/test/oneof_test.dart b/protoc_plugin/test/oneof_test.dart
index a99cc31f..26179164 100644
--- a/protoc_plugin/test/oneof_test.dart
+++ b/protoc_plugin/test/oneof_test.dart
@@ -174,15 +174,11 @@ void main() {
   test('copyWith preserves oneof state', () {
     final foo = Foo();
     expectOneofNotSet(foo);
-    // `ignore` below to work around https://github.com/dart-lang/sdk/issues/48879
-    final copy1 =
-        foo.deepCopy().freeze().rebuild((_) {}) as Foo; // ignore: unused_result
+    final copy1 = foo.deepCopy().freeze().rebuild((_) {}) as Foo;
     expectOneofNotSet(copy1);
     foo.first = 'oneof';
     expectFirstSet(foo);
-    // `ignore` below to work around https://github.com/dart-lang/sdk/issues/48879
-    final copy2 =
-        foo.deepCopy().freeze().rebuild((_) {}) as Foo; // ignore: unused_result
+    final copy2 = foo.deepCopy();
     expectFirstSet(copy2);
   });
 

From 7d255775e9f90094949582f58510b809d138410a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20A=C4=9Facan?= <omersa@google.com>
Date: Wed, 13 Aug 2025 11:36:39 +0100
Subject: [PATCH 05/10] Bug fix, tests

---
 .../lib/src/protobuf/extension_field_set.dart |   8 +-
 .../test/generated_message_test.dart          | 104 ++++++++++++++++++
 2 files changed, 109 insertions(+), 3 deletions(-)

diff --git a/protobuf/lib/src/protobuf/extension_field_set.dart b/protobuf/lib/src/protobuf/extension_field_set.dart
index bbdb5b42..83fb5d52 100644
--- a/protobuf/lib/src/protobuf/extension_field_set.dart
+++ b/protobuf/lib/src/protobuf/extension_field_set.dart
@@ -223,19 +223,21 @@ class ExtensionFieldSet {
       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;
-        _values[tag] = map?.deepCopy();
+        newValues[tag] = map?.deepCopy();
       } else if (fieldInfo.isRepeated) {
         final PbList? list = value;
-        _values[tag] = list?.deepCopy();
+        newValues[tag] = list?.deepCopy();
       } else if (fieldInfo.isGroupOrMessage) {
         final GeneratedMessage? message = value;
-        _values[tag] = message?.deepCopy();
+        newValues[tag] = message?.deepCopy();
       }
     }
 
diff --git a/protoc_plugin/test/generated_message_test.dart b/protoc_plugin/test/generated_message_test.dart
index 13683a38..c95c825a 100644
--- a/protoc_plugin/test/generated_message_test.dart
+++ b/protoc_plugin/test/generated_message_test.dart
@@ -4,6 +4,7 @@
 
 import 'package:protobuf/protobuf.dart';
 import 'package:test/test.dart';
+import 'package:fixnum/fixnum.dart';
 
 import 'gen/duplicate_names_import.pb.dart';
 import 'gen/enums.pb.dart';
@@ -877,3 +878,106 @@ void testCopy(TestAllTypes value1, TestAllTypes value2) {
 
   assertAllFieldsSet(value1);
 }
+
+/// Same as `testCopy`, but tests extension fields.
+///
+/// `value2` should be the clone of `value1`, either with `clone` or `deepCopy`.
+void testCopyExtensions(TestAllExtensions value1, TestAllExtensions value2) {
+  assertAllExtensionsSet(value2);
+  expect(value2, isNot(same(value1)));
+
+  value2.setExtension(
+    Unittest.optionalInt32Extension,
+    value2.getExtension(Unittest.optionalInt32Extension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalInt64Extension,
+    value2.getExtension(Unittest.optionalInt64Extension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalUint32Extension,
+    value2.getExtension(Unittest.optionalUint32Extension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalUint64Extension,
+    value2.getExtension(Unittest.optionalUint64Extension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalSint32Extension,
+    value2.getExtension(Unittest.optionalSint32Extension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalSint64Extension,
+    value2.getExtension(Unittest.optionalSint64Extension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalFixed32Extension,
+    value2.getExtension(Unittest.optionalFixed32Extension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalFixed64Extension,
+    value2.getExtension(Unittest.optionalFixed64Extension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalFloatExtension,
+    value2.getExtension(Unittest.optionalFloatExtension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalDoubleExtension,
+    value2.getExtension(Unittest.optionalDoubleExtension) + 1,
+  );
+  value2.setExtension(
+    Unittest.optionalBoolExtension,
+    !value2.getExtension(Unittest.optionalBoolExtension),
+  );
+  value2.setExtension(Unittest.optionalStringExtension, "hi 1");
+
+  // Same as `testCopy`, don't test `bytes` fields.
+  // value2.getExtension(Unittest.optionalBytesExtension).add(987);
+
+  value2.getExtension(Unittest.optionalGroupExtension).a += 1;
+  value2.getExtension(Unittest.optionalNestedMessageExtension).bb += 1;
+  value2.getExtension(Unittest.optionalForeignMessageExtension).c += 1;
+  value2.getExtension(Unittest.optionalImportMessageExtension).d += 1;
+  value2.setExtension(
+    Unittest.optionalNestedEnumExtension,
+    TestAllTypes_NestedEnum.BAR,
+  );
+  value2.setExtension(
+    Unittest.optionalForeignEnumExtension,
+    ForeignEnum.FOREIGN_BAR,
+  );
+  value2.setExtension(
+    Unittest.optionalImportEnumExtension,
+    ImportEnum.IMPORT_BAR,
+  );
+  value2.setExtension(Unittest.optionalStringPieceExtension, "hi 2");
+  value2.setExtension(Unittest.optionalCordExtension, "hi 3");
+
+  value2.getExtension(Unittest.repeatedInt32Extension).add(123);
+  value2.getExtension(Unittest.repeatedInt64Extension).add(Int64(123));
+  value2.getExtension(Unittest.repeatedUint32Extension).add(123);
+  value2.getExtension(Unittest.repeatedUint64Extension).add(Int64(123));
+  value2.getExtension(Unittest.repeatedSint32Extension).add(123);
+  value2.getExtension(Unittest.repeatedSint64Extension).add(Int64(123));
+  value2.getExtension(Unittest.repeatedFixed32Extension).add(123);
+  value2.getExtension(Unittest.repeatedFixed64Extension).add(Int64(123));
+  value2.getExtension(Unittest.repeatedSfixed32Extension).add(123);
+  value2.getExtension(Unittest.repeatedSfixed64Extension).add(Int64(123));
+  value2.getExtension(Unittest.repeatedFloatExtension).add(123);
+  value2.getExtension(Unittest.repeatedDoubleExtension).add(123);
+  value2.getExtension(Unittest.repeatedDoubleExtension).add(true);
+  value2.getExtension(Unittest.repeatedStringExtension).add("hi 4");
+  value2.getExtension(Unittest.repeatedBytesExtension).add(<int>[1, 2, 3]);
+  value2.getExtension(Unittest.repeatedGroupExtension).add(RepeatedGroup_extension());
+  value2.getExtension(Unittest.repeatedNestedMessageExtension).add(TestAllTypes_NestedMessage());
+  value2.getExtension(Unittest.repeatedForeignMessageExtension).add(ForeignMessage());
+  value2.getExtension(Unittest.repeatedImportMessageExtension).add(ImportMessage());
+  value2.getExtension(Unittest.repeatedNestedEnumExtension).add(TestAllTypes_NestedEnum.BAR);
+  value2.getExtension(Unittest.repeatedForeignEnumExtension).add(ForeignEnum.FOREIGN_BAR);
+  value2.getExtension(Unittest.repeatedImportEnumExtension).add(ImportEnum.IMPORT_BAR);
+  value2.getExtension(Unittest.repeatedStringPieceExtension).add("hi 5");
+  value2.getExtension(Unittest.repeatedCordExtension).add("hi 6");
+
+  assertAllExtensionsSet(value1);
+}

From f333b0d5204e754160cdf38b452567dc141ed8bd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omeragacan@gmail.com>
Date: Thu, 14 Aug 2025 08:54:52 +0100
Subject: [PATCH 06/10] Update protobuf changelog

---
 protobuf/CHANGELOG.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/protobuf/CHANGELOG.md b/protobuf/CHANGELOG.md
index 7cf13e1f..83335f37 100644
--- a/protobuf/CHANGELOG.md
+++ b/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

From 184ede3978042eab5d4c1667634334c316f1edf6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omeragacan@gmail.com>
Date: Thu, 14 Aug 2025 09:00:54 +0100
Subject: [PATCH 07/10] Update generated clones

---
 protoc_plugin/CHANGELOG.md                    |  4 +
 .../lib/src/gen/dart_options.pb.dart          |  4 +-
 .../lib/src/gen/google/api/client.pb.dart     | 35 ++++----
 .../lib/src/gen/google/api/http.pb.dart       |  6 +-
 .../lib/src/gen/google/api/routing.pb.dart    |  4 +-
 .../google/protobuf/compiler/plugin.pb.dart   | 11 +--
 .../gen/google/protobuf/descriptor.pb.dart    | 85 ++++++++-----------
 .../src/gen/google/protobuf/duration.pb.dart  |  2 +-
 protoc_plugin/lib/src/message_generator.dart  |  2 +-
 .../test/goldens/deprecations.pb.dart         |  4 +-
 .../test/goldens/doc_comments.pb.dart         |  4 +-
 .../test/goldens/grpc_service.pb.dart         |  2 +-
 protoc_plugin/test/goldens/imports.pb.dart    |  2 +-
 protoc_plugin/test/goldens/int64.pb.dart      |  2 +-
 .../test/goldens/messageGenerator.pb.dart     |  2 +-
 .../goldens/messageGenerator.pb.dart.meta     | 64 +++++++-------
 protoc_plugin/test/goldens/oneMessage.pb.dart |  2 +-
 .../test/goldens/oneMessage.pb.dart.meta      | 48 +++++------
 protoc_plugin/test/goldens/service.pb.dart    |  2 +-
 19 files changed, 132 insertions(+), 153 deletions(-)

diff --git a/protoc_plugin/CHANGELOG.md b/protoc_plugin/CHANGELOG.md
index bf34074d..41616dad 100644
--- a/protoc_plugin/CHANGELOG.md
+++ b/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
 
diff --git a/protoc_plugin/lib/src/gen/dart_options.pb.dart b/protoc_plugin/lib/src/gen/dart_options.pb.dart
index 5534342a..b92dcb35 100644
--- a/protoc_plugin/lib/src/gen/dart_options.pb.dart
+++ b/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;
diff --git a/protoc_plugin/lib/src/gen/google/api/client.pb.dart b/protoc_plugin/lib/src/gen/google/api/client.pb.dart
index 4660db8c..fdf9cbe7 100644
--- a/protoc_plugin/lib/src/gen/google/api/client.pb.dart
+++ b/protoc_plugin/lib/src/gen/google/api/client.pb.dart
@@ -64,8 +64,7 @@ class CommonLanguageSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  CommonLanguageSettings clone() =>
-      CommonLanguageSettings()..mergeFromMessage(this);
+  CommonLanguageSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   CommonLanguageSettings copyWith(
           void Function(CommonLanguageSettings) updates) =>
@@ -188,8 +187,7 @@ class ClientLibrarySettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  ClientLibrarySettings clone() =>
-      ClientLibrarySettings()..mergeFromMessage(this);
+  ClientLibrarySettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   ClientLibrarySettings copyWith(
           void Function(ClientLibrarySettings) updates) =>
@@ -411,7 +409,7 @@ class Publishing extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  Publishing clone() => Publishing()..mergeFromMessage(this);
+  Publishing clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   Publishing copyWith(void Function(Publishing) updates) =>
       super.copyWith((message) => updates(message as Publishing)) as Publishing;
@@ -576,7 +574,7 @@ class JavaSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  JavaSettings clone() => JavaSettings()..mergeFromMessage(this);
+  JavaSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   JavaSettings copyWith(void Function(JavaSettings) updates) =>
       super.copyWith((message) => updates(message as JavaSettings))
@@ -674,7 +672,7 @@ class CppSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  CppSettings clone() => CppSettings()..mergeFromMessage(this);
+  CppSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   CppSettings copyWith(void Function(CppSettings) updates) =>
       super.copyWith((message) => updates(message as CppSettings))
@@ -734,7 +732,7 @@ class PhpSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  PhpSettings clone() => PhpSettings()..mergeFromMessage(this);
+  PhpSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   PhpSettings copyWith(void Function(PhpSettings) updates) =>
       super.copyWith((message) => updates(message as PhpSettings))
@@ -805,8 +803,7 @@ class PythonSettings_ExperimentalFeatures extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  PythonSettings_ExperimentalFeatures clone() =>
-      PythonSettings_ExperimentalFeatures()..mergeFromMessage(this);
+  PythonSettings_ExperimentalFeatures clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   PythonSettings_ExperimentalFeatures copyWith(
           void Function(PythonSettings_ExperimentalFeatures) updates) =>
@@ -904,7 +901,7 @@ class PythonSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  PythonSettings clone() => PythonSettings()..mergeFromMessage(this);
+  PythonSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   PythonSettings copyWith(void Function(PythonSettings) updates) =>
       super.copyWith((message) => updates(message as PythonSettings))
@@ -979,7 +976,7 @@ class NodeSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  NodeSettings clone() => NodeSettings()..mergeFromMessage(this);
+  NodeSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   NodeSettings copyWith(void Function(NodeSettings) updates) =>
       super.copyWith((message) => updates(message as NodeSettings))
@@ -1070,7 +1067,7 @@ class DotnetSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  DotnetSettings clone() => DotnetSettings()..mergeFromMessage(this);
+  DotnetSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   DotnetSettings copyWith(void Function(DotnetSettings) updates) =>
       super.copyWith((message) => updates(message as DotnetSettings))
@@ -1166,7 +1163,7 @@ class RubySettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  RubySettings clone() => RubySettings()..mergeFromMessage(this);
+  RubySettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   RubySettings copyWith(void Function(RubySettings) updates) =>
       super.copyWith((message) => updates(message as RubySettings))
@@ -1235,7 +1232,7 @@ class GoSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  GoSettings clone() => GoSettings()..mergeFromMessage(this);
+  GoSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   GoSettings copyWith(void Function(GoSettings) updates) =>
       super.copyWith((message) => updates(message as GoSettings)) as GoSettings;
@@ -1322,8 +1319,7 @@ class MethodSettings_LongRunning extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  MethodSettings_LongRunning clone() =>
-      MethodSettings_LongRunning()..mergeFromMessage(this);
+  MethodSettings_LongRunning clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   MethodSettings_LongRunning copyWith(
           void Function(MethodSettings_LongRunning) updates) =>
@@ -1432,7 +1428,7 @@ class MethodSettings extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  MethodSettings clone() => MethodSettings()..mergeFromMessage(this);
+  MethodSettings clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   MethodSettings copyWith(void Function(MethodSettings) updates) =>
       super.copyWith((message) => updates(message as MethodSettings))
@@ -1542,8 +1538,7 @@ class SelectiveGapicGeneration extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  SelectiveGapicGeneration clone() =>
-      SelectiveGapicGeneration()..mergeFromMessage(this);
+  SelectiveGapicGeneration clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   SelectiveGapicGeneration copyWith(
           void Function(SelectiveGapicGeneration) updates) =>
diff --git a/protoc_plugin/lib/src/gen/google/api/http.pb.dart b/protoc_plugin/lib/src/gen/google/api/http.pb.dart
index 2fa07e33..018fa1a0 100644
--- a/protoc_plugin/lib/src/gen/google/api/http.pb.dart
+++ b/protoc_plugin/lib/src/gen/google/api/http.pb.dart
@@ -50,7 +50,7 @@ class Http extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  Http clone() => Http()..mergeFromMessage(this);
+  Http clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   Http copyWith(void Function(Http) updates) =>
       super.copyWith((message) => updates(message as Http)) as Http;
@@ -423,7 +423,7 @@ class HttpRule extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  HttpRule clone() => HttpRule()..mergeFromMessage(this);
+  HttpRule clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   HttpRule copyWith(void Function(HttpRule) updates) =>
       super.copyWith((message) => updates(message as HttpRule)) as HttpRule;
@@ -590,7 +590,7 @@ class CustomHttpPattern extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  CustomHttpPattern clone() => CustomHttpPattern()..mergeFromMessage(this);
+  CustomHttpPattern clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   CustomHttpPattern copyWith(void Function(CustomHttpPattern) updates) =>
       super.copyWith((message) => updates(message as CustomHttpPattern))
diff --git a/protoc_plugin/lib/src/gen/google/api/routing.pb.dart b/protoc_plugin/lib/src/gen/google/api/routing.pb.dart
index c8c7627e..528ac007 100644
--- a/protoc_plugin/lib/src/gen/google/api/routing.pb.dart
+++ b/protoc_plugin/lib/src/gen/google/api/routing.pb.dart
@@ -404,7 +404,7 @@ class RoutingRule extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  RoutingRule clone() => RoutingRule()..mergeFromMessage(this);
+  RoutingRule clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   RoutingRule copyWith(void Function(RoutingRule) updates) =>
       super.copyWith((message) => updates(message as RoutingRule))
@@ -463,7 +463,7 @@ class RoutingParameter extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  RoutingParameter clone() => RoutingParameter()..mergeFromMessage(this);
+  RoutingParameter clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   RoutingParameter copyWith(void Function(RoutingParameter) updates) =>
       super.copyWith((message) => updates(message as RoutingParameter))
diff --git a/protoc_plugin/lib/src/gen/google/protobuf/compiler/plugin.pb.dart b/protoc_plugin/lib/src/gen/google/protobuf/compiler/plugin.pb.dart
index 023287aa..bbdcac1c 100644
--- a/protoc_plugin/lib/src/gen/google/protobuf/compiler/plugin.pb.dart
+++ b/protoc_plugin/lib/src/gen/google/protobuf/compiler/plugin.pb.dart
@@ -58,7 +58,7 @@ class Version extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  Version clone() => Version()..mergeFromMessage(this);
+  Version clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   Version copyWith(void Function(Version) updates) =>
       super.copyWith((message) => updates(message as Version)) as Version;
@@ -160,8 +160,7 @@ class CodeGeneratorRequest extends $pb.GeneratedMessage {
         subBuilder: $0.FileDescriptorProto.create);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  CodeGeneratorRequest clone() =>
-      CodeGeneratorRequest()..mergeFromMessage(this);
+  CodeGeneratorRequest clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   CodeGeneratorRequest copyWith(void Function(CodeGeneratorRequest) updates) =>
       super.copyWith((message) => updates(message as CodeGeneratorRequest))
@@ -276,8 +275,7 @@ class CodeGeneratorResponse_File extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  CodeGeneratorResponse_File clone() =>
-      CodeGeneratorResponse_File()..mergeFromMessage(this);
+  CodeGeneratorResponse_File clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   CodeGeneratorResponse_File copyWith(
           void Function(CodeGeneratorResponse_File) updates) =>
@@ -436,8 +434,7 @@ class CodeGeneratorResponse extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  CodeGeneratorResponse clone() =>
-      CodeGeneratorResponse()..mergeFromMessage(this);
+  CodeGeneratorResponse clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   CodeGeneratorResponse copyWith(
           void Function(CodeGeneratorResponse) updates) =>
diff --git a/protoc_plugin/lib/src/gen/google/protobuf/descriptor.pb.dart b/protoc_plugin/lib/src/gen/google/protobuf/descriptor.pb.dart
index fe6bf471..4e051934 100644
--- a/protoc_plugin/lib/src/gen/google/protobuf/descriptor.pb.dart
+++ b/protoc_plugin/lib/src/gen/google/protobuf/descriptor.pb.dart
@@ -52,7 +52,7 @@ class FileDescriptorSet extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FileDescriptorSet clone() => FileDescriptorSet()..mergeFromMessage(this);
+  FileDescriptorSet clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FileDescriptorSet copyWith(void Function(FileDescriptorSet) updates) =>
       super.copyWith((message) => updates(message as FileDescriptorSet))
@@ -159,7 +159,7 @@ class FileDescriptorProto extends $pb.GeneratedMessage {
     ..pPS(15, _omitFieldNames ? '' : 'optionDependency');
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FileDescriptorProto clone() => FileDescriptorProto()..mergeFromMessage(this);
+  FileDescriptorProto clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FileDescriptorProto copyWith(void Function(FileDescriptorProto) updates) =>
       super.copyWith((message) => updates(message as FileDescriptorProto))
@@ -317,8 +317,7 @@ class DescriptorProto_ExtensionRange extends $pb.GeneratedMessage {
         subBuilder: ExtensionRangeOptions.create);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  DescriptorProto_ExtensionRange clone() =>
-      DescriptorProto_ExtensionRange()..mergeFromMessage(this);
+  DescriptorProto_ExtensionRange clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   DescriptorProto_ExtensionRange copyWith(
           void Function(DescriptorProto_ExtensionRange) updates) =>
@@ -404,8 +403,7 @@ class DescriptorProto_ReservedRange extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  DescriptorProto_ReservedRange clone() =>
-      DescriptorProto_ReservedRange()..mergeFromMessage(this);
+  DescriptorProto_ReservedRange clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   DescriptorProto_ReservedRange copyWith(
           void Function(DescriptorProto_ReservedRange) updates) =>
@@ -523,7 +521,7 @@ class DescriptorProto extends $pb.GeneratedMessage {
         enumValues: SymbolVisibility.values);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  DescriptorProto clone() => DescriptorProto()..mergeFromMessage(this);
+  DescriptorProto clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   DescriptorProto copyWith(void Function(DescriptorProto) updates) =>
       super.copyWith((message) => updates(message as DescriptorProto))
@@ -640,8 +638,7 @@ class ExtensionRangeOptions_Declaration extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  ExtensionRangeOptions_Declaration clone() =>
-      ExtensionRangeOptions_Declaration()..mergeFromMessage(this);
+  ExtensionRangeOptions_Declaration clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   ExtensionRangeOptions_Declaration copyWith(
           void Function(ExtensionRangeOptions_Declaration) updates) =>
@@ -768,8 +765,7 @@ class ExtensionRangeOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  ExtensionRangeOptions clone() =>
-      ExtensionRangeOptions()..mergeFromMessage(this);
+  ExtensionRangeOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   ExtensionRangeOptions copyWith(
           void Function(ExtensionRangeOptions) updates) =>
@@ -892,8 +888,7 @@ class FieldDescriptorProto extends $pb.GeneratedMessage {
     ..aOB(17, _omitFieldNames ? '' : 'proto3Optional');
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FieldDescriptorProto clone() =>
-      FieldDescriptorProto()..mergeFromMessage(this);
+  FieldDescriptorProto clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FieldDescriptorProto copyWith(void Function(FieldDescriptorProto) updates) =>
       super.copyWith((message) => updates(message as FieldDescriptorProto))
@@ -1086,8 +1081,7 @@ class OneofDescriptorProto extends $pb.GeneratedMessage {
         subBuilder: OneofOptions.create);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  OneofDescriptorProto clone() =>
-      OneofDescriptorProto()..mergeFromMessage(this);
+  OneofDescriptorProto clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   OneofDescriptorProto copyWith(void Function(OneofDescriptorProto) updates) =>
       super.copyWith((message) => updates(message as OneofDescriptorProto))
@@ -1165,8 +1159,7 @@ class EnumDescriptorProto_EnumReservedRange extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  EnumDescriptorProto_EnumReservedRange clone() =>
-      EnumDescriptorProto_EnumReservedRange()..mergeFromMessage(this);
+  EnumDescriptorProto_EnumReservedRange clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   EnumDescriptorProto_EnumReservedRange copyWith(
           void Function(EnumDescriptorProto_EnumReservedRange) updates) =>
@@ -1260,7 +1253,7 @@ class EnumDescriptorProto extends $pb.GeneratedMessage {
         enumValues: SymbolVisibility.values);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  EnumDescriptorProto clone() => EnumDescriptorProto()..mergeFromMessage(this);
+  EnumDescriptorProto clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   EnumDescriptorProto copyWith(void Function(EnumDescriptorProto) updates) =>
       super.copyWith((message) => updates(message as EnumDescriptorProto))
@@ -1360,8 +1353,7 @@ class EnumValueDescriptorProto extends $pb.GeneratedMessage {
         subBuilder: EnumValueOptions.create);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  EnumValueDescriptorProto clone() =>
-      EnumValueDescriptorProto()..mergeFromMessage(this);
+  EnumValueDescriptorProto clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   EnumValueDescriptorProto copyWith(
           void Function(EnumValueDescriptorProto) updates) =>
@@ -1448,8 +1440,7 @@ class ServiceDescriptorProto extends $pb.GeneratedMessage {
         subBuilder: ServiceOptions.create);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  ServiceDescriptorProto clone() =>
-      ServiceDescriptorProto()..mergeFromMessage(this);
+  ServiceDescriptorProto clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   ServiceDescriptorProto copyWith(
           void Function(ServiceDescriptorProto) updates) =>
@@ -1537,8 +1528,7 @@ class MethodDescriptorProto extends $pb.GeneratedMessage {
     ..aOB(6, _omitFieldNames ? '' : 'serverStreaming');
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  MethodDescriptorProto clone() =>
-      MethodDescriptorProto()..mergeFromMessage(this);
+  MethodDescriptorProto clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   MethodDescriptorProto copyWith(
           void Function(MethodDescriptorProto) updates) =>
@@ -1723,7 +1713,7 @@ class FileOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FileOptions clone() => FileOptions()..mergeFromMessage(this);
+  FileOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FileOptions copyWith(void Function(FileOptions) updates) =>
       super.copyWith((message) => updates(message as FileOptions))
@@ -2057,7 +2047,7 @@ class MessageOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  MessageOptions clone() => MessageOptions()..mergeFromMessage(this);
+  MessageOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   MessageOptions copyWith(void Function(MessageOptions) updates) =>
       super.copyWith((message) => updates(message as MessageOptions))
@@ -2236,8 +2226,7 @@ class FieldOptions_EditionDefault extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FieldOptions_EditionDefault clone() =>
-      FieldOptions_EditionDefault()..mergeFromMessage(this);
+  FieldOptions_EditionDefault clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FieldOptions_EditionDefault copyWith(
           void Function(FieldOptions_EditionDefault) updates) =>
@@ -2328,8 +2317,7 @@ class FieldOptions_FeatureSupport extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FieldOptions_FeatureSupport clone() =>
-      FieldOptions_FeatureSupport()..mergeFromMessage(this);
+  FieldOptions_FeatureSupport clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FieldOptions_FeatureSupport copyWith(
           void Function(FieldOptions_FeatureSupport) updates) =>
@@ -2489,7 +2477,7 @@ class FieldOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FieldOptions clone() => FieldOptions()..mergeFromMessage(this);
+  FieldOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FieldOptions copyWith(void Function(FieldOptions) updates) =>
       super.copyWith((message) => updates(message as FieldOptions))
@@ -2719,7 +2707,7 @@ class OneofOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  OneofOptions clone() => OneofOptions()..mergeFromMessage(this);
+  OneofOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   OneofOptions copyWith(void Function(OneofOptions) updates) =>
       super.copyWith((message) => updates(message as OneofOptions))
@@ -2805,7 +2793,7 @@ class EnumOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  EnumOptions clone() => EnumOptions()..mergeFromMessage(this);
+  EnumOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   EnumOptions copyWith(void Function(EnumOptions) updates) =>
       super.copyWith((message) => updates(message as EnumOptions))
@@ -2933,7 +2921,7 @@ class EnumValueOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  EnumValueOptions clone() => EnumValueOptions()..mergeFromMessage(this);
+  EnumValueOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   EnumValueOptions copyWith(void Function(EnumValueOptions) updates) =>
       super.copyWith((message) => updates(message as EnumValueOptions))
@@ -3047,7 +3035,7 @@ class ServiceOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  ServiceOptions clone() => ServiceOptions()..mergeFromMessage(this);
+  ServiceOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   ServiceOptions copyWith(void Function(ServiceOptions) updates) =>
       super.copyWith((message) => updates(message as ServiceOptions))
@@ -3144,7 +3132,7 @@ class MethodOptions extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  MethodOptions clone() => MethodOptions()..mergeFromMessage(this);
+  MethodOptions clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   MethodOptions copyWith(void Function(MethodOptions) updates) =>
       super.copyWith((message) => updates(message as MethodOptions))
@@ -3242,8 +3230,7 @@ class UninterpretedOption_NamePart extends $pb.GeneratedMessage {
         2, _omitFieldNames ? '' : 'isExtension', $pb.PbFieldType.QB);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  UninterpretedOption_NamePart clone() =>
-      UninterpretedOption_NamePart()..mergeFromMessage(this);
+  UninterpretedOption_NamePart clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   UninterpretedOption_NamePart copyWith(
           void Function(UninterpretedOption_NamePart) updates) =>
@@ -3341,7 +3328,7 @@ class UninterpretedOption extends $pb.GeneratedMessage {
     ..aOS(8, _omitFieldNames ? '' : 'aggregateValue');
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  UninterpretedOption clone() => UninterpretedOption()..mergeFromMessage(this);
+  UninterpretedOption clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   UninterpretedOption copyWith(void Function(UninterpretedOption) updates) =>
       super.copyWith((message) => updates(message as UninterpretedOption))
@@ -3441,8 +3428,7 @@ class FeatureSet_VisibilityFeature extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FeatureSet_VisibilityFeature clone() =>
-      FeatureSet_VisibilityFeature()..mergeFromMessage(this);
+  FeatureSet_VisibilityFeature clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FeatureSet_VisibilityFeature copyWith(
           void Function(FeatureSet_VisibilityFeature) updates) =>
@@ -3559,7 +3545,7 @@ class FeatureSet extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FeatureSet clone() => FeatureSet()..mergeFromMessage(this);
+  FeatureSet clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FeatureSet copyWith(void Function(FeatureSet) updates) =>
       super.copyWith((message) => updates(message as FeatureSet)) as FeatureSet;
@@ -3699,8 +3685,7 @@ class FeatureSetDefaults_FeatureSetEditionDefault extends $pb.GeneratedMessage {
         subBuilder: FeatureSet.create);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FeatureSetDefaults_FeatureSetEditionDefault clone() =>
-      FeatureSetDefaults_FeatureSetEditionDefault()..mergeFromMessage(this);
+  FeatureSetDefaults_FeatureSetEditionDefault clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FeatureSetDefaults_FeatureSetEditionDefault copyWith(
           void Function(FeatureSetDefaults_FeatureSetEditionDefault) updates) =>
@@ -3803,7 +3788,7 @@ class FeatureSetDefaults extends $pb.GeneratedMessage {
         enumValues: Edition.values);
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  FeatureSetDefaults clone() => FeatureSetDefaults()..mergeFromMessage(this);
+  FeatureSetDefaults clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   FeatureSetDefaults copyWith(void Function(FeatureSetDefaults) updates) =>
       super.copyWith((message) => updates(message as FeatureSetDefaults))
@@ -3890,8 +3875,7 @@ class SourceCodeInfo_Location extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  SourceCodeInfo_Location clone() =>
-      SourceCodeInfo_Location()..mergeFromMessage(this);
+  SourceCodeInfo_Location clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   SourceCodeInfo_Location copyWith(
           void Function(SourceCodeInfo_Location) updates) =>
@@ -4046,7 +4030,7 @@ class SourceCodeInfo extends $pb.GeneratedMessage {
     ..hasExtensions = true;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  SourceCodeInfo clone() => SourceCodeInfo()..mergeFromMessage(this);
+  SourceCodeInfo clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   SourceCodeInfo copyWith(void Function(SourceCodeInfo) updates) =>
       super.copyWith((message) => updates(message as SourceCodeInfo))
@@ -4156,8 +4140,7 @@ class GeneratedCodeInfo_Annotation extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  GeneratedCodeInfo_Annotation clone() =>
-      GeneratedCodeInfo_Annotation()..mergeFromMessage(this);
+  GeneratedCodeInfo_Annotation clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   GeneratedCodeInfo_Annotation copyWith(
           void Function(GeneratedCodeInfo_Annotation) updates) =>
@@ -4261,7 +4244,7 @@ class GeneratedCodeInfo extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  GeneratedCodeInfo clone() => GeneratedCodeInfo()..mergeFromMessage(this);
+  GeneratedCodeInfo clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   GeneratedCodeInfo copyWith(void Function(GeneratedCodeInfo) updates) =>
       super.copyWith((message) => updates(message as GeneratedCodeInfo))
diff --git a/protoc_plugin/lib/src/gen/google/protobuf/duration.pb.dart b/protoc_plugin/lib/src/gen/google/protobuf/duration.pb.dart
index a60ed95b..343ec9dd 100644
--- a/protoc_plugin/lib/src/gen/google/protobuf/duration.pb.dart
+++ b/protoc_plugin/lib/src/gen/google/protobuf/duration.pb.dart
@@ -108,7 +108,7 @@ class Duration extends $pb.GeneratedMessage with $mixin.DurationMixin {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  Duration clone() => Duration()..mergeFromMessage(this);
+  Duration clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   Duration copyWith(void Function(Duration) updates) =>
       super.copyWith((message) => updates(message as Duration)) as Duration;
diff --git a/protoc_plugin/lib/src/message_generator.dart b/protoc_plugin/lib/src/message_generator.dart
index d3fb0ebb..a0e29862 100644
--- a/protoc_plugin/lib/src/message_generator.dart
+++ b/protoc_plugin/lib/src/message_generator.dart
@@ -474,7 +474,7 @@ class MessageGenerator extends ProtobufContainer {
           "'See https://github.com/google/protobuf.dart/issues/998.')",
         );
         out.println(
-          '$classname clone() => $classname()..mergeFromMessage(this);',
+          '$classname clone() => deepCopy();',
         );
         out.println(
           '@$coreImportPrefix.Deprecated('
diff --git a/protoc_plugin/test/goldens/deprecations.pb.dart b/protoc_plugin/test/goldens/deprecations.pb.dart
index 60c0dfa8..96fdc2e8 100644
--- a/protoc_plugin/test/goldens/deprecations.pb.dart
+++ b/protoc_plugin/test/goldens/deprecations.pb.dart
@@ -46,7 +46,7 @@ class HelloRequest extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  HelloRequest clone() => HelloRequest()..mergeFromMessage(this);
+  HelloRequest clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   HelloRequest copyWith(void Function(HelloRequest) updates) =>
       super.copyWith((message) => updates(message as HelloRequest))
@@ -106,7 +106,7 @@ class HelloReply extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  HelloReply clone() => HelloReply()..mergeFromMessage(this);
+  HelloReply clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   HelloReply copyWith(void Function(HelloReply) updates) =>
       super.copyWith((message) => updates(message as HelloReply)) as HelloReply;
diff --git a/protoc_plugin/test/goldens/doc_comments.pb.dart b/protoc_plugin/test/goldens/doc_comments.pb.dart
index 8688ddec..245a2030 100644
--- a/protoc_plugin/test/goldens/doc_comments.pb.dart
+++ b/protoc_plugin/test/goldens/doc_comments.pb.dart
@@ -46,7 +46,7 @@ class HelloRequest extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  HelloRequest clone() => HelloRequest()..mergeFromMessage(this);
+  HelloRequest clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   HelloRequest copyWith(void Function(HelloRequest) updates) =>
       super.copyWith((message) => updates(message as HelloRequest))
@@ -103,7 +103,7 @@ class HelloReply extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  HelloReply clone() => HelloReply()..mergeFromMessage(this);
+  HelloReply clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   HelloReply copyWith(void Function(HelloReply) updates) =>
       super.copyWith((message) => updates(message as HelloReply)) as HelloReply;
diff --git a/protoc_plugin/test/goldens/grpc_service.pb.dart b/protoc_plugin/test/goldens/grpc_service.pb.dart
index cfb2b226..d7569635 100644
--- a/protoc_plugin/test/goldens/grpc_service.pb.dart
+++ b/protoc_plugin/test/goldens/grpc_service.pb.dart
@@ -34,7 +34,7 @@ class Empty extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  Empty clone() => Empty()..mergeFromMessage(this);
+  Empty clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   Empty copyWith(void Function(Empty) updates) =>
       super.copyWith((message) => updates(message as Empty)) as Empty;
diff --git a/protoc_plugin/test/goldens/imports.pb.dart b/protoc_plugin/test/goldens/imports.pb.dart
index dcc8d340..f9b26f9d 100644
--- a/protoc_plugin/test/goldens/imports.pb.dart
+++ b/protoc_plugin/test/goldens/imports.pb.dart
@@ -39,7 +39,7 @@ class M extends $pb.GeneratedMessage {
         ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  M clone() => M()..mergeFromMessage(this);
+  M clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   M copyWith(void Function(M) updates) =>
       super.copyWith((message) => updates(message as M)) as M;
diff --git a/protoc_plugin/test/goldens/int64.pb.dart b/protoc_plugin/test/goldens/int64.pb.dart
index d7eefab9..a5a4a037 100644
--- a/protoc_plugin/test/goldens/int64.pb.dart
+++ b/protoc_plugin/test/goldens/int64.pb.dart
@@ -36,7 +36,7 @@ class Int64 extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  Int64 clone() => Int64()..mergeFromMessage(this);
+  Int64 clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   Int64 copyWith(void Function(Int64) updates) =>
       super.copyWith((message) => updates(message as Int64)) as Int64;
diff --git a/protoc_plugin/test/goldens/messageGenerator.pb.dart b/protoc_plugin/test/goldens/messageGenerator.pb.dart
index 15d05a34..dd4ef600 100644
--- a/protoc_plugin/test/goldens/messageGenerator.pb.dart
+++ b/protoc_plugin/test/goldens/messageGenerator.pb.dart
@@ -14,7 +14,7 @@ class PhoneNumber extends $pb.GeneratedMessage {
   ;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  PhoneNumber clone() => PhoneNumber()..mergeFromMessage(this);
+  PhoneNumber clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   PhoneNumber copyWith(void Function(PhoneNumber) updates) => super.copyWith((message) => updates(message as PhoneNumber)) as PhoneNumber;
 
diff --git a/protoc_plugin/test/goldens/messageGenerator.pb.dart.meta b/protoc_plugin/test/goldens/messageGenerator.pb.dart.meta
index faefae9b..fad54eac 100644
--- a/protoc_plugin/test/goldens/messageGenerator.pb.dart.meta
+++ b/protoc_plugin/test/goldens/messageGenerator.pb.dart.meta
@@ -18,8 +18,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: 
-  begin: 1854
-  end: 1860
+  begin: 1827
+  end: 1833
 }
 annotation: {
   path: 4
@@ -27,8 +27,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: 
-  begin: 1902
-  end: 1908
+  begin: 1875
+  end: 1881
 }
 annotation: {
   path: 4
@@ -36,8 +36,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: 
-  begin: 1988
-  end: 1997
+  begin: 1961
+  end: 1970
 }
 annotation: {
   path: 4
@@ -45,8 +45,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: 
-  begin: 2040
-  end: 2051
+  begin: 2013
+  end: 2024
 }
 annotation: {
   path: 4
@@ -54,8 +54,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: 
-  begin: 2123
-  end: 2127
+  begin: 2096
+  end: 2100
 }
 annotation: {
   path: 4
@@ -63,8 +63,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: 
-  begin: 2168
-  end: 2172
+  begin: 2141
+  end: 2145
 }
 annotation: {
   path: 4
@@ -72,8 +72,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: 
-  begin: 2260
-  end: 2267
+  begin: 2233
+  end: 2240
 }
 annotation: {
   path: 4
@@ -81,8 +81,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: 
-  begin: 2310
-  end: 2319
+  begin: 2283
+  end: 2292
 }
 annotation: {
   path: 4
@@ -90,8 +90,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: 
-  begin: 2382
-  end: 2386
+  begin: 2355
+  end: 2359
 }
 annotation: {
   path: 4
@@ -99,8 +99,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: 
-  begin: 2433
-  end: 2437
+  begin: 2406
+  end: 2410
 }
 annotation: {
   path: 4
@@ -108,8 +108,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: 
-  begin: 2517
-  end: 2524
+  begin: 2490
+  end: 2497
 }
 annotation: {
   path: 4
@@ -117,8 +117,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: 
-  begin: 2567
-  end: 2576
+  begin: 2540
+  end: 2549
 }
 annotation: {
   path: 4
@@ -126,8 +126,8 @@ annotation: {
   path: 2
   path: 3
   sourceFile: 
-  begin: 2688
-  end: 2703
+  begin: 2661
+  end: 2676
 }
 annotation: {
   path: 4
@@ -135,8 +135,8 @@ annotation: {
   path: 2
   path: 3
   sourceFile: 
-  begin: 2794
-  end: 2809
+  begin: 2767
+  end: 2782
 }
 annotation: {
   path: 4
@@ -144,8 +144,8 @@ annotation: {
   path: 2
   path: 3
   sourceFile: 
-  begin: 2938
-  end: 2956
+  begin: 2911
+  end: 2929
 }
 annotation: {
   path: 4
@@ -153,6 +153,6 @@ annotation: {
   path: 2
   path: 3
   sourceFile: 
-  begin: 3048
-  end: 3068
+  begin: 3021
+  end: 3041
 }
diff --git a/protoc_plugin/test/goldens/oneMessage.pb.dart b/protoc_plugin/test/goldens/oneMessage.pb.dart
index e38712f8..59982037 100644
--- a/protoc_plugin/test/goldens/oneMessage.pb.dart
+++ b/protoc_plugin/test/goldens/oneMessage.pb.dart
@@ -37,7 +37,7 @@ class PhoneNumber extends $pb.GeneratedMessage {
         defaultOrMaker: '\$');
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  PhoneNumber clone() => PhoneNumber()..mergeFromMessage(this);
+  PhoneNumber clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   PhoneNumber copyWith(void Function(PhoneNumber) updates) =>
       super.copyWith((message) => updates(message as PhoneNumber))
diff --git a/protoc_plugin/test/goldens/oneMessage.pb.dart.meta b/protoc_plugin/test/goldens/oneMessage.pb.dart.meta
index 44ec15bf..93f21528 100644
--- a/protoc_plugin/test/goldens/oneMessage.pb.dart.meta
+++ b/protoc_plugin/test/goldens/oneMessage.pb.dart.meta
@@ -18,8 +18,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: test
-  begin: 2218
-  end: 2224
+  begin: 2191
+  end: 2197
 }
 annotation: {
   path: 4
@@ -27,8 +27,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: test
-  begin: 2266
-  end: 2272
+  begin: 2239
+  end: 2245
 }
 annotation: {
   path: 4
@@ -36,8 +36,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: test
-  begin: 2352
-  end: 2361
+  begin: 2325
+  end: 2334
 }
 annotation: {
   path: 4
@@ -45,8 +45,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: test
-  begin: 2404
-  end: 2415
+  begin: 2377
+  end: 2388
 }
 annotation: {
   path: 4
@@ -54,8 +54,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: test
-  begin: 2475
-  end: 2479
+  begin: 2448
+  end: 2452
 }
 annotation: {
   path: 4
@@ -63,8 +63,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: test
-  begin: 2521
-  end: 2525
+  begin: 2494
+  end: 2498
 }
 annotation: {
   path: 4
@@ -72,8 +72,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: test
-  begin: 2607
-  end: 2614
+  begin: 2580
+  end: 2587
 }
 annotation: {
   path: 4
@@ -81,8 +81,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: test
-  begin: 2657
-  end: 2666
+  begin: 2630
+  end: 2639
 }
 annotation: {
   path: 4
@@ -90,8 +90,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: test
-  begin: 2729
-  end: 2733
+  begin: 2702
+  end: 2706
 }
 annotation: {
   path: 4
@@ -99,8 +99,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: test
-  begin: 2780
-  end: 2784
+  begin: 2753
+  end: 2757
 }
 annotation: {
   path: 4
@@ -108,8 +108,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: test
-  begin: 2864
-  end: 2871
+  begin: 2837
+  end: 2844
 }
 annotation: {
   path: 4
@@ -117,6 +117,6 @@ annotation: {
   path: 2
   path: 2
   sourceFile: test
-  begin: 2914
-  end: 2923
+  begin: 2887
+  end: 2896
 }
diff --git a/protoc_plugin/test/goldens/service.pb.dart b/protoc_plugin/test/goldens/service.pb.dart
index fda76ba7..d9c6c0a8 100644
--- a/protoc_plugin/test/goldens/service.pb.dart
+++ b/protoc_plugin/test/goldens/service.pb.dart
@@ -35,7 +35,7 @@ class Empty extends $pb.GeneratedMessage {
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
-  Empty clone() => Empty()..mergeFromMessage(this);
+  Empty clone() => deepCopy();
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
   Empty copyWith(void Function(Empty) updates) =>
       super.copyWith((message) => updates(message as Empty)) as Empty;

From 5f74ff406cebd2badcfbb593bce70449c2b8b0f9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omeragacan@gmail.com>
Date: Thu, 14 Aug 2025 09:02:20 +0100
Subject: [PATCH 08/10] Fix formatting

---
 protoc_plugin/lib/src/message_generator.dart | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/protoc_plugin/lib/src/message_generator.dart b/protoc_plugin/lib/src/message_generator.dart
index a0e29862..e6623879 100644
--- a/protoc_plugin/lib/src/message_generator.dart
+++ b/protoc_plugin/lib/src/message_generator.dart
@@ -473,9 +473,7 @@ class MessageGenerator extends ProtobufContainer {
           '@$coreImportPrefix.Deprecated('
           "'See https://github.com/google/protobuf.dart/issues/998.')",
         );
-        out.println(
-          '$classname clone() => deepCopy();',
-        );
+        out.println('$classname clone() => deepCopy();');
         out.println(
           '@$coreImportPrefix.Deprecated('
           "'See https://github.com/google/protobuf.dart/issues/998.')",

From d32895c6ebd7aeda14450885dea6c1647dfda089 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20A=C4=9Facan?= <omersa@google.com>
Date: Thu, 14 Aug 2025 11:38:38 +0100
Subject: [PATCH 09/10] Make deepCopy methods private, to be able to remove
 them later without breakage

---
 protobuf/lib/src/protobuf/extension_field_set.dart | 6 +++---
 protobuf/lib/src/protobuf/field_set.dart           | 8 ++++----
 protobuf/lib/src/protobuf/pb_list.dart             | 2 +-
 protobuf/lib/src/protobuf/pb_map.dart              | 2 +-
 protobuf/lib/src/protobuf/unknown_field_set.dart   | 8 ++++----
 5 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/protobuf/lib/src/protobuf/extension_field_set.dart b/protobuf/lib/src/protobuf/extension_field_set.dart
index 83fb5d52..442f7709 100644
--- a/protobuf/lib/src/protobuf/extension_field_set.dart
+++ b/protobuf/lib/src/protobuf/extension_field_set.dart
@@ -216,7 +216,7 @@ class ExtensionFieldSet {
     }
   }
 
-  ExtensionFieldSet deepCopy(FieldSet parent) {
+  ExtensionFieldSet _deepCopy(FieldSet parent) {
     final newExtensionFieldSet = ExtensionFieldSet._(
       parent,
       Map.from(_info),
@@ -231,10 +231,10 @@ class ExtensionFieldSet {
       final fieldInfo = _info[tag]!;
       if (fieldInfo.isMapField) {
         final PbMap? map = value;
-        newValues[tag] = map?.deepCopy();
+        newValues[tag] = map?._deepCopy();
       } else if (fieldInfo.isRepeated) {
         final PbList? list = value;
-        newValues[tag] = list?.deepCopy();
+        newValues[tag] = list?._deepCopy();
       } else if (fieldInfo.isGroupOrMessage) {
         final GeneratedMessage? message = value;
         newValues[tag] = message?.deepCopy();
diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 7ca69242..eeed0733 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -937,11 +937,11 @@ class FieldSet {
       if (fieldInfo.isMapField) {
         final PbMap? originalMap = original._values[index];
         if (originalMap == null) continue;
-        _values[index] = originalMap.deepCopy();
+        _values[index] = originalMap._deepCopy();
       } else if (fieldInfo.isRepeated) {
         final PbList? originalList = original._values[index];
         if (originalList == null) continue;
-        _values[index] = originalList.deepCopy();
+        _values[index] = originalList._deepCopy();
       } else if (fieldInfo.isGroupOrMessage) {
         final GeneratedMessage? message = original._values[index];
         _values[index] = message?.deepCopy();
@@ -953,13 +953,13 @@ class FieldSet {
     assert(_extensions == null);
     final originalExtensions = original._extensions;
     if (originalExtensions != null) {
-      _extensions = originalExtensions.deepCopy(this);
+      _extensions = originalExtensions._deepCopy(this);
     }
 
     assert(_unknownFields == null);
     final originalUnknownFields = original._unknownFields;
     if (originalUnknownFields != null) {
-      _unknownFields = originalUnknownFields.deepCopy();
+      _unknownFields = originalUnknownFields._deepCopy();
     }
 
     assert(_unknownJsonData == null);
diff --git a/protobuf/lib/src/protobuf/pb_list.dart b/protobuf/lib/src/protobuf/pb_list.dart
index f0f0000d..d759ce03 100644
--- a/protobuf/lib/src/protobuf/pb_list.dart
+++ b/protobuf/lib/src/protobuf/pb_list.dart
@@ -235,7 +235,7 @@ class PbList<E> extends ListBase<E> {
     throw UnsupportedError("'$methodName' on a read-only list");
   }
 
-  PbList<E> deepCopy() {
+  PbList<E> _deepCopy() {
     final newList = PbList<E>(check: _check);
     final wrappedList = _wrappedList;
     final newWrappedList = newList._wrappedList;
diff --git a/protobuf/lib/src/protobuf/pb_map.dart b/protobuf/lib/src/protobuf/pb_map.dart
index 4ec1872d..0f45c2cf 100644
--- a/protobuf/lib/src/protobuf/pb_map.dart
+++ b/protobuf/lib/src/protobuf/pb_map.dart
@@ -132,7 +132,7 @@ class PbMap<K, V> extends MapBase<K, V> {
     return this;
   }
 
-  PbMap<K, V> deepCopy() {
+  PbMap<K, V> _deepCopy() {
     final newMap = PbMap<K, V>(keyFieldType, valueFieldType);
     final wrappedMap = _wrappedMap;
     final newWrappedMap = newMap._wrappedMap;
diff --git a/protobuf/lib/src/protobuf/unknown_field_set.dart b/protobuf/lib/src/protobuf/unknown_field_set.dart
index 2a5db52d..4c295bf0 100644
--- a/protobuf/lib/src/protobuf/unknown_field_set.dart
+++ b/protobuf/lib/src/protobuf/unknown_field_set.dart
@@ -200,12 +200,12 @@ class UnknownFieldSet {
     }
   }
 
-  UnknownFieldSet deepCopy() {
+  UnknownFieldSet _deepCopy() {
     Map<int, UnknownFieldSetField> newFields = {};
     for (final entry in _fields.entries) {
       final key = entry.key;
       final value = entry.value;
-      newFields[key] = value.deepCopy();
+      newFields[key] = value._deepCopy();
     }
     return UnknownFieldSet._(newFields);
   }
@@ -339,7 +339,7 @@ class UnknownFieldSetField {
     varints.add(value);
   }
 
-  UnknownFieldSetField deepCopy() {
+  UnknownFieldSetField _deepCopy() {
     final List<List<int>> newLengthDelimited = List.from(_lengthDelimited);
     final List<Int64> newVarints = List.from(_varints);
     final List<int> newFixed32s = List.from(_fixed32s);
@@ -347,7 +347,7 @@ class UnknownFieldSetField {
 
     final List<UnknownFieldSet> newGroups = [];
     for (final group in _groups) {
-      newGroups.add(group.deepCopy());
+      newGroups.add(group._deepCopy());
     }
 
     return UnknownFieldSetField._(

From d6f7d5be8a09b486640388d26db5a040ac276057 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20A=C4=9Facan?= <omersa@google.com>
Date: Thu, 14 Aug 2025 13:24:54 +0100
Subject: [PATCH 10/10] More tests

---
 .../lib/src/protobuf/generated_message.dart   |  1 -
 .../test/generated_message_test.dart          | 49 ++++++++++++++++---
 2 files changed, 42 insertions(+), 8 deletions(-)

diff --git a/protobuf/lib/src/protobuf/generated_message.dart b/protobuf/lib/src/protobuf/generated_message.dart
index 5c3a3c5f..5c9da770 100644
--- a/protobuf/lib/src/protobuf/generated_message.dart
+++ b/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. '
diff --git a/protoc_plugin/test/generated_message_test.dart b/protoc_plugin/test/generated_message_test.dart
index c95c825a..1a769a32 100644
--- a/protoc_plugin/test/generated_message_test.dart
+++ b/protoc_plugin/test/generated_message_test.dart
@@ -812,6 +812,27 @@ void main() {
     assertAllExtensionsSet(value2);
   });
 
+  test('clone extensions', () {
+    final value1 = TestAllExtensions();
+    setAllExtensions(value1);
+    // ignore: deprecated_member_use_from_same_package
+    final value2 = value1.clone();
+    assertAllExtensionsSet(value2);
+  });
+
+  test('mergeFromMessage', () {
+    final value1 = getAllSet();
+    final value2 = TestAllTypes()..mergeFromMessage(value1);
+    testCopy(value1, value2);
+  });
+
+  test('mergeFromMessage extensions', () {
+    final value1 = TestAllExtensions();
+    setAllExtensions(value1);
+    final value2 = TestAllExtensions()..mergeFromMessage(value1);
+    assertAllExtensionsSet(value2);
+  });
+
   test('Handling enums defined out of order', () {
     final message = MessageWithEnums();
     for (final enum_ in DenseEnum.values) {
@@ -969,13 +990,27 @@ void testCopyExtensions(TestAllExtensions value1, TestAllExtensions value2) {
   value2.getExtension(Unittest.repeatedDoubleExtension).add(true);
   value2.getExtension(Unittest.repeatedStringExtension).add("hi 4");
   value2.getExtension(Unittest.repeatedBytesExtension).add(<int>[1, 2, 3]);
-  value2.getExtension(Unittest.repeatedGroupExtension).add(RepeatedGroup_extension());
-  value2.getExtension(Unittest.repeatedNestedMessageExtension).add(TestAllTypes_NestedMessage());
-  value2.getExtension(Unittest.repeatedForeignMessageExtension).add(ForeignMessage());
-  value2.getExtension(Unittest.repeatedImportMessageExtension).add(ImportMessage());
-  value2.getExtension(Unittest.repeatedNestedEnumExtension).add(TestAllTypes_NestedEnum.BAR);
-  value2.getExtension(Unittest.repeatedForeignEnumExtension).add(ForeignEnum.FOREIGN_BAR);
-  value2.getExtension(Unittest.repeatedImportEnumExtension).add(ImportEnum.IMPORT_BAR);
+  value2
+      .getExtension(Unittest.repeatedGroupExtension)
+      .add(RepeatedGroup_extension());
+  value2
+      .getExtension(Unittest.repeatedNestedMessageExtension)
+      .add(TestAllTypes_NestedMessage());
+  value2
+      .getExtension(Unittest.repeatedForeignMessageExtension)
+      .add(ForeignMessage());
+  value2
+      .getExtension(Unittest.repeatedImportMessageExtension)
+      .add(ImportMessage());
+  value2
+      .getExtension(Unittest.repeatedNestedEnumExtension)
+      .add(TestAllTypes_NestedEnum.BAR);
+  value2
+      .getExtension(Unittest.repeatedForeignEnumExtension)
+      .add(ForeignEnum.FOREIGN_BAR);
+  value2
+      .getExtension(Unittest.repeatedImportEnumExtension)
+      .add(ImportEnum.IMPORT_BAR);
   value2.getExtension(Unittest.repeatedStringPieceExtension).add("hi 5");
   value2.getExtension(Unittest.repeatedCordExtension).add("hi 6");