From a0976daab41305df9e12b4a8d01e2ce2f3862261 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Tue, 24 May 2022 09:41:40 +0200
Subject: [PATCH 01/14] Implement fast path when merging fields of same message

Fixes #60
---
 protobuf/lib/src/protobuf/field_set.dart | 63 ++++++++++++++++++++----
 1 file changed, 53 insertions(+), 10 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index ff3628274..0439b064e 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -768,14 +768,16 @@ class _FieldSet {
   /// in this message. Repeated fields are appended. Singular sub-messages are
   /// recursively merged.
   void _mergeFromMessage(_FieldSet other) {
-    // TODO(https://github.com/google/protobuf.dart/issues/60): Recognize
-    // when `this` and [other] are the same protobuf (e.g. from cloning). In
-    // this case, we can merge the non-extension fields without field lookups or
-    // validation checks.
-
+    final sameMessage = identical(_meta, other._meta);
     for (var fi in other._infosSortedByTag) {
       var value = other._values[fi.index!];
-      if (value != null) _mergeField(fi, value, isExtension: false);
+      if (value != null) {
+        if (sameMessage) {
+          _mergeNonExtensionFieldUnchecked(fi, value);
+        } else {
+          _mergeField(fi, value, isExtension: false);
+        }
+      }
     }
     if (other._hasExtensions) {
       var others = other._extensions!;
@@ -791,14 +793,55 @@ class _FieldSet {
     }
   }
 
-  void _mergeField(FieldInfo otherFi, fieldValue, {bool? isExtension}) {
+  void _mergeNonExtensionFieldUnchecked(FieldInfo fi, dynamic fieldValue) {
+    if (fi.isMapField) {
+      final mapInfo = fi as MapFieldInfo<dynamic, dynamic>;
+      final map =
+          mapInfo._ensureMapField(_meta, this) as PbMap<dynamic, dynamic>;
+      if (_isGroupOrMessage(mapInfo.valueFieldType)) {
+        for (MapEntry entry in fieldValue.entries) {
+          map[entry.key] = (entry.value as GeneratedMessage).deepCopy();
+        }
+      } else {
+        map.addAll(fieldValue);
+      }
+      return;
+    }
+
+    if (fi.isRepeated) {
+      if (_isGroupOrMessage(fi.type)) {
+        PbListBase<GeneratedMessage> pbList = fieldValue;
+        var repeatedFields = fi._ensureRepeatedField(_meta, this);
+        for (var i = 0; i < pbList.length; ++i) {
+          repeatedFields.add(pbList[i].deepCopy());
+        }
+      } else {
+        PbListBase pbList = fieldValue;
+        fi._ensureRepeatedField(_meta, this).addAll(pbList);
+      }
+      return;
+    }
+
+    if (fi.isGroupOrMessage) {
+      final currentFieldValue = _values[fi.index!];
+      if (currentFieldValue == null) {
+        fieldValue = (fieldValue as GeneratedMessage).deepCopy();
+      } else {
+        fieldValue = currentFieldValue..mergeFromMessage(fieldValue);
+      }
+    }
+
+    _setNonExtensionFieldUnchecked(_meta, fi, fieldValue);
+  }
+
+  void _mergeField(FieldInfo otherFi, fieldValue, {required bool isExtension}) {
     final tagNumber = otherFi.tagNumber;
 
     // Determine the FieldInfo to use.
     // Don't allow regular fields to be overwritten by extensions.
     final meta = _meta;
     var fi = _nonExtensionInfo(meta, tagNumber);
-    if (fi == null && isExtension!) {
+    if (fi == null && isExtension) {
       // This will overwrite any existing extension field info.
       fi = otherFi;
     }
@@ -836,7 +879,7 @@ class _FieldSet {
     }
 
     if (otherFi.isGroupOrMessage) {
-      final currentFi = isExtension!
+      final currentFi = isExtension
           ? _ensureExtensions()._getFieldOrNull(fi as Extension<dynamic>)
           : _values[fi.index!];
 
@@ -847,7 +890,7 @@ class _FieldSet {
       }
     }
 
-    if (isExtension!) {
+    if (isExtension) {
       _ensureExtensions()
           ._setFieldAndInfo(fi as Extension<dynamic>, fieldValue);
     } else {

From 1ba216cf61c8737473cd010d7d4e10315b697362 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Fri, 5 Aug 2022 08:59:20 +0200
Subject: [PATCH 02/14] Post merge fixups, add a benchmark program

---
 benchmarks/bin/deep_copy.dart            | 43 ++++++++++++++++++++++++
 protobuf/lib/src/protobuf/field_set.dart |  4 +--
 2 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100644 benchmarks/bin/deep_copy.dart

diff --git a/benchmarks/bin/deep_copy.dart b/benchmarks/bin/deep_copy.dart
new file mode 100644
index 000000000..9dbb9fe85
--- /dev/null
+++ b/benchmarks/bin/deep_copy.dart
@@ -0,0 +1,43 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:protobuf/protobuf.dart';
+import 'package:protobuf_benchmarks/benchmark_base.dart';
+import 'package:protobuf_benchmarks/generated/google_message1_proto2.pb.dart'
+    as p2;
+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';
+
+class Benchmark extends BenchmarkBase {
+  final p2.GoogleMessage1 _message1Proto2;
+  final p3.GoogleMessage1 _message1Proto3;
+  final GoogleMessage2 _message2;
+
+  Benchmark(String name, List<int> message1Proto2Input,
+      List<int> message1Proto3Input, List<int> message2Input)
+      : _message1Proto2 = p2.GoogleMessage1.fromBuffer(message1Proto2Input),
+        _message1Proto3 = p3.GoogleMessage1.fromBuffer(message1Proto3Input),
+        _message2 = GoogleMessage2.fromBuffer(message2Input),
+        super(name);
+
+  @override
+  void run() {
+    _message1Proto2.deepCopy();
+    _message1Proto3.deepCopy();
+    _message2.deepCopy();
+  }
+}
+
+void main() {
+  List<int> message1Proto2Input =
+      readfile('datasets/google_message1_proto2.pb');
+  List<int> message1Proto3Input =
+      readfile('datasets/google_message1_proto3.pb');
+  List<int> message2Input = readfile('datasets/google_message2.pb');
+  Benchmark(
+          'deep_copy', message1Proto2Input, message1Proto3Input, message2Input)
+      .report();
+}
diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 7d81d2198..19f89ae28 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -752,13 +752,13 @@ class _FieldSet {
 
     if (fi.isRepeated) {
       if (_isGroupOrMessage(fi.type)) {
-        PbListBase<GeneratedMessage> pbList = fieldValue;
+        PbList<GeneratedMessage> pbList = fieldValue;
         var repeatedFields = fi._ensureRepeatedField(_meta, this);
         for (var i = 0; i < pbList.length; ++i) {
           repeatedFields.add(pbList[i].deepCopy());
         }
       } else {
-        PbListBase pbList = fieldValue;
+        PbList pbList = fieldValue;
         fi._ensureRepeatedField(_meta, this).addAll(pbList);
       }
       return;

From cd64518dba3379e240dae10b5509c4483787132b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Fri, 5 Aug 2022 09:00:48 +0200
Subject: [PATCH 03/14] Rename sameMessage -> sameMessageType

---
 protobuf/lib/src/protobuf/field_set.dart | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 19f89ae28..1dcbef2bb 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -710,11 +710,11 @@ class _FieldSet {
   /// in this message. Repeated fields are appended. Singular sub-messages are
   /// recursively merged.
   void _mergeFromMessage(_FieldSet other) {
-    final sameMessage = identical(_meta, other._meta);
+    final sameMessageType = identical(_meta, other._meta);
     for (var fi in other._infosSortedByTag) {
       var value = other._values[fi.index!];
       if (value != null) {
-        if (sameMessage) {
+        if (sameMessageType) {
           _mergeNonExtensionFieldUnchecked(fi, value);
         } else {
           _mergeField(fi, value, isExtension: false);

From e45dd01ba1e58f8b16404f635639a7097bd02e01 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Fri, 5 Aug 2022 09:17:16 +0200
Subject: [PATCH 04/14] Remove dynamic calls

---
 protobuf/lib/src/protobuf/field_set.dart | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 1dcbef2bb..94892c170 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -706,9 +706,9 @@ class _FieldSet {
 
   /// Merges the contents of the [other] into this message.
   ///
-  /// Singular fields that are set in [other] overwrite the corresponding fields
-  /// in this message. Repeated fields are appended. Singular sub-messages are
-  /// recursively merged.
+  /// Singular fields that are set in [other] overwrite the corresponding
+  /// fields in this message. Repeated fields are appended. Singular
+  /// sub-messages are recursively merged.
   void _mergeFromMessage(_FieldSet other) {
     final sameMessageType = identical(_meta, other._meta);
     for (var fi in other._infosSortedByTag) {
@@ -721,6 +721,7 @@ class _FieldSet {
         }
       }
     }
+
     if (other._hasExtensions) {
       var others = other._extensions!;
       for (var tagNumber in others._tagNumbers) {
@@ -741,8 +742,10 @@ class _FieldSet {
       final map =
           mapInfo._ensureMapField(_meta, this) as PbMap<dynamic, dynamic>;
       if (_isGroupOrMessage(mapInfo.valueFieldType)) {
-        for (MapEntry entry in fieldValue.entries) {
-          map[entry.key] = (entry.value as GeneratedMessage).deepCopy();
+        Map pbMap = fieldValue;
+        for (final entry in pbMap.entries) {
+          GeneratedMessage value = entry.value;
+          map[entry.key] = value.deepCopy();
         }
       } else {
         map.addAll(fieldValue);
@@ -769,7 +772,8 @@ class _FieldSet {
       if (currentFieldValue == null) {
         fieldValue = (fieldValue as GeneratedMessage).deepCopy();
       } else {
-        fieldValue = currentFieldValue..mergeFromMessage(fieldValue);
+        final GeneratedMessage currentMsg = currentFieldValue;
+        fieldValue = currentMsg..mergeFromMessage(fieldValue);
       }
     }
 

From 682301c6bd6691b9b5abb3753820cba80d2e9603 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 14:07:46 +0200
Subject: [PATCH 05/14] Assume same message type in mergeFromMessage

---
 protobuf/lib/src/protobuf/field_set.dart | 42 ++++++++----------------
 1 file changed, 14 insertions(+), 28 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index c6b5d3243..ebc7821a1 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -723,20 +723,17 @@ class _FieldSet {
   /// fields in this message. Repeated fields are appended. Singular
   /// sub-messages are recursively merged.
   void _mergeFromMessage(_FieldSet other) {
-    // TODO(https://github.com/google/protobuf.dart/issues/60): Recognize
-    // when `this` and [other] are the same protobuf (e.g. from cloning). In
-    // this case, we can merge the non-extension fields without field lookups or
-    // validation checks.
     _ensureWritable();
-    final sameMessageType = identical(_meta, other._meta);
+
+    if (!identical(_meta, other._meta)) {
+      throw ArgumentError(
+          'Merging messages with different types (BuilderInfos)', 'other');
+    }
+
     for (var fi in other._infosSortedByTag) {
       var value = other._values[fi.index!];
       if (value != null) {
-        if (sameMessageType) {
-          _mergeNonExtensionFieldUnchecked(fi, value);
-        } else {
-          _mergeField(fi, value, isExtension: false);
-        }
+        _mergeNonExtensionFieldUnchecked(fi, value);
       }
     }
 
@@ -745,7 +742,7 @@ class _FieldSet {
       for (var tagNumber in otherExtensions._tagNumbers) {
         var extension = otherExtensions._getInfoOrNull(tagNumber)!;
         var value = otherExtensions._getFieldOrNull(extension);
-        _mergeField(extension, value, isExtension: true);
+        _mergeExtensionField(extension, value);
       }
     }
 
@@ -799,19 +796,15 @@ class _FieldSet {
     _setNonExtensionFieldUnchecked(_meta, fi, fieldValue);
   }
 
-  void _mergeField(FieldInfo otherFi, fieldValue, {required bool isExtension}) {
+  void _mergeExtensionField(FieldInfo otherFi, fieldValue) {
     final tagNumber = otherFi.tagNumber;
 
     // Determine the FieldInfo to use.
     // Don't allow regular fields to be overwritten by extensions.
     final meta = _meta;
-    var fi = _nonExtensionInfo(meta, tagNumber);
-    if (fi == null && isExtension) {
-      // This will overwrite any existing extension field info.
-      fi = otherFi;
-    }
+    var fi = _nonExtensionInfo(meta, tagNumber) ?? otherFi;
 
-    if (fi!.isMapField) {
+    if (fi.isMapField) {
       if (fieldValue == null) {
         return;
       }
@@ -846,9 +839,8 @@ class _FieldSet {
     }
 
     if (otherFi.isGroupOrMessage) {
-      final currentFi = isExtension
-          ? _ensureExtensions()._getFieldOrNull(fi as Extension<dynamic>)
-          : _values[fi.index!];
+      final currentFi =
+          _ensureExtensions()._getFieldOrNull(fi as Extension<dynamic>);
 
       GeneratedMessage msg = fieldValue;
       if (currentFi == null) {
@@ -859,13 +851,7 @@ class _FieldSet {
       }
     }
 
-    if (isExtension) {
-      _ensureExtensions()
-          ._setFieldAndInfo(fi as Extension<dynamic>, fieldValue);
-    } else {
-      _validateField(fi, fieldValue);
-      _setNonExtensionFieldUnchecked(meta, fi, fieldValue);
-    }
+    _ensureExtensions()._setFieldAndInfo(fi as Extension<dynamic>, fieldValue);
   }
 
   // Error-checking

From 5d4d5d0ed74c1fa1bd979016a63dd0d5a4993fa0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 14:14:25 +0200
Subject: [PATCH 06/14] Rename a variable in mergeNonExtensionField for
 consistency with mergeExtensionField

---
 protobuf/lib/src/protobuf/field_set.dart | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index ebc7821a1..b758e4970 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -733,7 +733,7 @@ class _FieldSet {
     for (var fi in other._infosSortedByTag) {
       var value = other._values[fi.index!];
       if (value != null) {
-        _mergeNonExtensionFieldUnchecked(fi, value);
+        _mergeNonExtensionField(fi, value);
       }
     }
 
@@ -752,7 +752,7 @@ class _FieldSet {
     }
   }
 
-  void _mergeNonExtensionFieldUnchecked(FieldInfo fi, dynamic fieldValue) {
+  void _mergeNonExtensionField(FieldInfo fi, dynamic fieldValue) {
     if (fi.isMapField) {
       final mapInfo = fi as MapFieldInfo<dynamic, dynamic>;
       final map =
@@ -839,14 +839,14 @@ class _FieldSet {
     }
 
     if (otherFi.isGroupOrMessage) {
-      final currentFi =
+      final currentFieldValue =
           _ensureExtensions()._getFieldOrNull(fi as Extension<dynamic>);
 
       GeneratedMessage msg = fieldValue;
-      if (currentFi == null) {
+      if (currentFieldValue == null) {
         fieldValue = msg.deepCopy();
       } else {
-        final GeneratedMessage currentMsg = currentFi;
+        final GeneratedMessage currentMsg = currentFieldValue;
         fieldValue = currentMsg..mergeFromMessage(msg);
       }
     }

From da3971e35f054a136127f9634fc487a451653c81 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 14:16:23 +0200
Subject: [PATCH 07/14] Refactor null handling when merging extension fields
 for consistency with non-extension fields

---
 protobuf/lib/src/protobuf/field_set.dart | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index b758e4970..d0ac29d86 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -742,7 +742,9 @@ class _FieldSet {
       for (var tagNumber in otherExtensions._tagNumbers) {
         var extension = otherExtensions._getInfoOrNull(tagNumber)!;
         var value = otherExtensions._getFieldOrNull(extension);
-        _mergeExtensionField(extension, value);
+        if (value != null) {
+          _mergeExtensionField(extension, value);
+        }
       }
     }
 
@@ -805,9 +807,6 @@ class _FieldSet {
     var fi = _nonExtensionInfo(meta, tagNumber) ?? otherFi;
 
     if (fi.isMapField) {
-      if (fieldValue == null) {
-        return;
-      }
       final MapFieldInfo<dynamic, dynamic> f = fi as dynamic;
       final PbMap<dynamic, dynamic> map =
           f._ensureMapField(meta, this) as dynamic;

From cacd006cb1ea93c4e224cd568b98b77da561c420 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 14:28:02 +0200
Subject: [PATCH 08/14] Refactor merge methods for exts and non-exts; they're
 almost identical now

---
 protobuf/lib/src/protobuf/field_set.dart | 48 ++++++++++--------------
 1 file changed, 19 insertions(+), 29 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index d0ac29d86..49ada08b3 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -756,13 +756,12 @@ class _FieldSet {
 
   void _mergeNonExtensionField(FieldInfo fi, dynamic fieldValue) {
     if (fi.isMapField) {
-      final mapInfo = fi as MapFieldInfo<dynamic, dynamic>;
-      final map =
-          mapInfo._ensureMapField(_meta, this) as PbMap<dynamic, dynamic>;
+      final MapFieldInfo<dynamic, dynamic> mapInfo = fi as dynamic;
+      final map = mapInfo._ensureMapField(_meta, this);
       if (_isGroupOrMessage(mapInfo.valueFieldType)) {
-        Map pbMap = fieldValue;
-        for (final entry in pbMap.entries) {
-          GeneratedMessage value = entry.value;
+        final Map fieldValueMap = fieldValue;
+        for (final entry in fieldValueMap.entries) {
+          final GeneratedMessage value = entry.value;
           map[entry.key] = value.deepCopy();
         }
       } else {
@@ -774,12 +773,12 @@ class _FieldSet {
     if (fi.isRepeated) {
       if (_isGroupOrMessage(fi.type)) {
         PbList<GeneratedMessage> pbList = fieldValue;
-        var repeatedFields = fi._ensureRepeatedField(_meta, this);
+        final repeatedFields = fi._ensureRepeatedField(_meta, this);
         for (var i = 0; i < pbList.length; ++i) {
           repeatedFields.add(pbList[i].deepCopy());
         }
       } else {
-        PbList pbList = fieldValue;
+        final PbList pbList = fieldValue;
         fi._ensureRepeatedField(_meta, this).addAll(pbList);
       }
       return;
@@ -798,22 +797,15 @@ class _FieldSet {
     _setNonExtensionFieldUnchecked(_meta, fi, fieldValue);
   }
 
-  void _mergeExtensionField(FieldInfo otherFi, fieldValue) {
-    final tagNumber = otherFi.tagNumber;
-
-    // Determine the FieldInfo to use.
-    // Don't allow regular fields to be overwritten by extensions.
-    final meta = _meta;
-    var fi = _nonExtensionInfo(meta, tagNumber) ?? otherFi;
-
+  void _mergeExtensionField(FieldInfo fi, fieldValue) {
     if (fi.isMapField) {
-      final MapFieldInfo<dynamic, dynamic> f = fi as dynamic;
-      final PbMap<dynamic, dynamic> map =
-          f._ensureMapField(meta, this) as dynamic;
-      if (_isGroupOrMessage(f.valueFieldType)) {
-        PbMap fieldValueMap = fieldValue;
+      final MapFieldInfo<dynamic, dynamic> mapInfo = fi as dynamic;
+      final map = mapInfo._ensureMapField(_meta, this);
+      if (_isGroupOrMessage(mapInfo.valueFieldType)) {
+        final Map fieldValueMap = fieldValue;
         for (final entry in fieldValueMap.entries) {
-          map[entry.key] = (entry.value as GeneratedMessage).deepCopy();
+          final GeneratedMessage value = entry.value;
+          map[entry.key] = value.deepCopy();
         }
       } else {
         map.addAll(fieldValue);
@@ -822,22 +814,20 @@ class _FieldSet {
     }
 
     if (fi.isRepeated) {
-      if (_isGroupOrMessage(otherFi.type)) {
-        // fieldValue must be a PbList of GeneratedMessage.
+      if (_isGroupOrMessage(fi.type)) {
         PbList<GeneratedMessage> pbList = fieldValue;
-        var repeatedFields = fi._ensureRepeatedField(meta, this);
+        final repeatedFields = fi._ensureRepeatedField(_meta, this);
         for (var i = 0; i < pbList.length; ++i) {
           repeatedFields.add(pbList[i].deepCopy());
         }
       } else {
-        // fieldValue must be at least a PbList.
-        PbList pbList = fieldValue;
-        fi._ensureRepeatedField(meta, this).addAll(pbList);
+        final PbList pbList = fieldValue;
+        fi._ensureRepeatedField(_meta, this).addAll(pbList);
       }
       return;
     }
 
-    if (otherFi.isGroupOrMessage) {
+    if (fi.isGroupOrMessage) {
       final currentFieldValue =
           _ensureExtensions()._getFieldOrNull(fi as Extension<dynamic>);
 

From 3cccb8fd9b8c3d19b0851e00011205c309bd2e8c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 14:30:13 +0200
Subject: [PATCH 09/14] More refactoring

---
 protobuf/lib/src/protobuf/field_set.dart | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 49ada08b3..0e5dd0de0 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -787,7 +787,8 @@ class _FieldSet {
     if (fi.isGroupOrMessage) {
       final currentFieldValue = _values[fi.index!];
       if (currentFieldValue == null) {
-        fieldValue = (fieldValue as GeneratedMessage).deepCopy();
+        GeneratedMessage msg = fieldValue;
+        fieldValue = msg.deepCopy();
       } else {
         final GeneratedMessage currentMsg = currentFieldValue;
         fieldValue = currentMsg..mergeFromMessage(fieldValue);

From 8d5aa0336781c31301a8744bb9852214e77575bc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 14:46:31 +0200
Subject: [PATCH 10/14] Make Dart 2.12 happy

---
 protobuf/lib/src/protobuf/field_set.dart | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 0e5dd0de0..e031ce96b 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -727,7 +727,7 @@ class _FieldSet {
 
     if (!identical(_meta, other._meta)) {
       throw ArgumentError(
-          'Merging messages with different types (BuilderInfos)', 'other');
+          'Merging messages with different types (BuilderInfos)');
     }
 
     for (var fi in other._infosSortedByTag) {

From 1dddc1bdb6c885ba40012ad93d1f14f104dfd134 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 14:54:48 +0200
Subject: [PATCH 11/14] Tweak type casts, add `final` to locals

---
 protobuf/lib/src/protobuf/field_set.dart | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index e031ce96b..009050673 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -772,14 +772,14 @@ class _FieldSet {
 
     if (fi.isRepeated) {
       if (_isGroupOrMessage(fi.type)) {
-        PbList<GeneratedMessage> pbList = fieldValue;
+        final List<GeneratedMessage> list = fieldValue;
         final repeatedFields = fi._ensureRepeatedField(_meta, this);
-        for (var i = 0; i < pbList.length; ++i) {
-          repeatedFields.add(pbList[i].deepCopy());
+        for (var i = 0; i < list.length; ++i) {
+          repeatedFields.add(list[i].deepCopy());
         }
       } else {
-        final PbList pbList = fieldValue;
-        fi._ensureRepeatedField(_meta, this).addAll(pbList);
+        final List list = fieldValue;
+        fi._ensureRepeatedField(_meta, this).addAll(list);
       }
       return;
     }
@@ -787,7 +787,7 @@ class _FieldSet {
     if (fi.isGroupOrMessage) {
       final currentFieldValue = _values[fi.index!];
       if (currentFieldValue == null) {
-        GeneratedMessage msg = fieldValue;
+        final GeneratedMessage msg = fieldValue;
         fieldValue = msg.deepCopy();
       } else {
         final GeneratedMessage currentMsg = currentFieldValue;
@@ -816,14 +816,14 @@ class _FieldSet {
 
     if (fi.isRepeated) {
       if (_isGroupOrMessage(fi.type)) {
-        PbList<GeneratedMessage> pbList = fieldValue;
+        final List<GeneratedMessage> list = fieldValue;
         final repeatedFields = fi._ensureRepeatedField(_meta, this);
-        for (var i = 0; i < pbList.length; ++i) {
-          repeatedFields.add(pbList[i].deepCopy());
+        for (var i = 0; i < list.length; ++i) {
+          repeatedFields.add(list[i].deepCopy());
         }
       } else {
-        final PbList pbList = fieldValue;
-        fi._ensureRepeatedField(_meta, this).addAll(pbList);
+        final List list = fieldValue;
+        fi._ensureRepeatedField(_meta, this).addAll(list);
       }
       return;
     }
@@ -832,7 +832,7 @@ class _FieldSet {
       final currentFieldValue =
           _ensureExtensions()._getFieldOrNull(fi as Extension<dynamic>);
 
-      GeneratedMessage msg = fieldValue;
+      final GeneratedMessage msg = fieldValue;
       if (currentFieldValue == null) {
         fieldValue = msg.deepCopy();
       } else {

From aa492a9c896f834ef7ea488110e5ba8e0e6a5eb1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 15:04:02 +0200
Subject: [PATCH 12/14] More refactoring

---
 protobuf/lib/src/protobuf/field_set.dart | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 009050673..a62c67d07 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -786,12 +786,12 @@ class _FieldSet {
 
     if (fi.isGroupOrMessage) {
       final currentFieldValue = _values[fi.index!];
+      final GeneratedMessage msg = fieldValue;
       if (currentFieldValue == null) {
-        final GeneratedMessage msg = fieldValue;
         fieldValue = msg.deepCopy();
       } else {
         final GeneratedMessage currentMsg = currentFieldValue;
-        fieldValue = currentMsg..mergeFromMessage(fieldValue);
+        fieldValue = currentMsg..mergeFromMessage(msg);
       }
     }
 

From d2959397957666dc5249627b055c34f1ea32f345 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 15:06:38 +0200
Subject: [PATCH 13/14] Merge merge field methods

---
 protobuf/lib/src/protobuf/field_set.dart | 62 +++++-------------------
 1 file changed, 12 insertions(+), 50 deletions(-)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index a62c67d07..5c39c41f1 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -733,7 +733,7 @@ class _FieldSet {
     for (var fi in other._infosSortedByTag) {
       var value = other._values[fi.index!];
       if (value != null) {
-        _mergeNonExtensionField(fi, value);
+        _mergeField(fi, value, isExtension: false);
       }
     }
 
@@ -743,7 +743,7 @@ class _FieldSet {
         var extension = otherExtensions._getInfoOrNull(tagNumber)!;
         var value = otherExtensions._getFieldOrNull(extension);
         if (value != null) {
-          _mergeExtensionField(extension, value);
+          _mergeField(extension, value, isExtension: true);
         }
       }
     }
@@ -754,7 +754,7 @@ class _FieldSet {
     }
   }
 
-  void _mergeNonExtensionField(FieldInfo fi, dynamic fieldValue) {
+  void _mergeField(FieldInfo fi, fieldValue, {required bool isExtension}) {
     if (fi.isMapField) {
       final MapFieldInfo<dynamic, dynamic> mapInfo = fi as dynamic;
       final map = mapInfo._ensureMapField(_meta, this);
@@ -785,52 +785,9 @@ class _FieldSet {
     }
 
     if (fi.isGroupOrMessage) {
-      final currentFieldValue = _values[fi.index!];
-      final GeneratedMessage msg = fieldValue;
-      if (currentFieldValue == null) {
-        fieldValue = msg.deepCopy();
-      } else {
-        final GeneratedMessage currentMsg = currentFieldValue;
-        fieldValue = currentMsg..mergeFromMessage(msg);
-      }
-    }
-
-    _setNonExtensionFieldUnchecked(_meta, fi, fieldValue);
-  }
-
-  void _mergeExtensionField(FieldInfo fi, fieldValue) {
-    if (fi.isMapField) {
-      final MapFieldInfo<dynamic, dynamic> mapInfo = fi as dynamic;
-      final map = mapInfo._ensureMapField(_meta, this);
-      if (_isGroupOrMessage(mapInfo.valueFieldType)) {
-        final Map fieldValueMap = fieldValue;
-        for (final entry in fieldValueMap.entries) {
-          final GeneratedMessage value = entry.value;
-          map[entry.key] = value.deepCopy();
-        }
-      } else {
-        map.addAll(fieldValue);
-      }
-      return;
-    }
-
-    if (fi.isRepeated) {
-      if (_isGroupOrMessage(fi.type)) {
-        final List<GeneratedMessage> list = fieldValue;
-        final repeatedFields = fi._ensureRepeatedField(_meta, this);
-        for (var i = 0; i < list.length; ++i) {
-          repeatedFields.add(list[i].deepCopy());
-        }
-      } else {
-        final List list = fieldValue;
-        fi._ensureRepeatedField(_meta, this).addAll(list);
-      }
-      return;
-    }
-
-    if (fi.isGroupOrMessage) {
-      final currentFieldValue =
-          _ensureExtensions()._getFieldOrNull(fi as Extension<dynamic>);
+      final currentFieldValue = isExtension
+          ? _ensureExtensions()._getFieldOrNull(fi as Extension<dynamic>)
+          : _values[fi.index!];
 
       final GeneratedMessage msg = fieldValue;
       if (currentFieldValue == null) {
@@ -841,7 +798,12 @@ class _FieldSet {
       }
     }
 
-    _ensureExtensions()._setFieldAndInfo(fi as Extension<dynamic>, fieldValue);
+    if (isExtension) {
+      _ensureExtensions()
+          ._setFieldAndInfo(fi as Extension<dynamic>, fieldValue);
+    } else {
+      _setNonExtensionFieldUnchecked(_meta, fi, fieldValue);
+    }
   }
 
   // Error-checking

From 88c3d85e8017633097f16f8ebe6e0cc700499c1e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 12 Sep 2022 15:18:57 +0200
Subject: [PATCH 14/14] Update docs

---
 protobuf/lib/src/protobuf/field_set.dart         | 5 +++++
 protobuf/lib/src/protobuf/generated_message.dart | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index 5c39c41f1..22992cd2b 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -722,6 +722,11 @@ class _FieldSet {
   /// Singular fields that are set in [other] overwrite the corresponding
   /// fields in this message. Repeated fields are appended. Singular
   /// sub-messages are recursively merged.
+  ///
+  /// Messages are expected to have the same [BuilderInfo].
+  ///
+  /// Throws [ArgumentError] when the messages don't have the same
+  /// [BuilderInfo].
   void _mergeFromMessage(_FieldSet other) {
     _ensureWritable();
 
diff --git a/protobuf/lib/src/protobuf/generated_message.dart b/protobuf/lib/src/protobuf/generated_message.dart
index c77a17e2e..6a0323c96 100644
--- a/protobuf/lib/src/protobuf/generated_message.dart
+++ b/protobuf/lib/src/protobuf/generated_message.dart
@@ -373,6 +373,11 @@ abstract class GeneratedMessage {
   /// Singular fields that are set in [other] overwrite the corresponding fields
   /// in this message. Repeated fields are appended. Singular sub-messages are
   /// recursively merged.
+  ///
+  /// Messages are expected to have the same [BuilderInfo].
+  ///
+  /// Throws [ArgumentError] when the messages don't have the same
+  /// [BuilderInfo].
   @pragma('dart2js:noInline')
   void mergeFromMessage(GeneratedMessage other) =>
       _fieldSet._mergeFromMessage(other._fieldSet);