Add fromDart() and toDart() methods to convert between $core.Duration and proto Duration (#986)

Author: AgamAgarwal

protoc_plugin/CHANGELOG.md

@@ -3,9 +3,12 @@
 * Fix factory argument types for protobuf `Map` fields. ([#975])
 * Fix import order changes when files are passed in different order to `protoc`.
 ([#952])
+* Add fromDart() and toDart() methods to convert between core Duration and proto
+  Duration ([#986])
 
 [#975]: https://github.com/google/protobuf.dart/issues/975
 [#952]: https://github.com/google/protobuf.dart/issues/952
+[#986]: https://github.com/google/protobuf.dart/issues/986
 
 ## 22.0.1
 

protoc_plugin/lib/src/base_type.dart

@@ -89,19 +89,19 @@ class BaseType {
             'SF3', '$coreImportPrefix.int', r'$_setSignedInt32', null);
       case FieldDescriptorProto_Type.TYPE_INT64:
         return const BaseType._raw(FieldDescriptorProto_Type.TYPE_INT64, '6',
-            '$_fixnumImportPrefix.Int64', r'$_setInt64', null);
+            '$fixnumImportPrefix.Int64', r'$_setInt64', null);
       case FieldDescriptorProto_Type.TYPE_UINT64:
         return const BaseType._raw(FieldDescriptorProto_Type.TYPE_UINT64, 'U6',
-            '$_fixnumImportPrefix.Int64', r'$_setInt64', null);
+            '$fixnumImportPrefix.Int64', r'$_setInt64', null);
       case FieldDescriptorProto_Type.TYPE_SINT64:
         return const BaseType._raw(FieldDescriptorProto_Type.TYPE_SINT64, 'S6',
-            '$_fixnumImportPrefix.Int64', r'$_setInt64', null);
+            '$fixnumImportPrefix.Int64', r'$_setInt64', null);
       case FieldDescriptorProto_Type.TYPE_FIXED64:
         return const BaseType._raw(FieldDescriptorProto_Type.TYPE_FIXED64, 'F6',
-            '$_fixnumImportPrefix.Int64', r'$_setInt64', null);
+            '$fixnumImportPrefix.Int64', r'$_setInt64', null);
       case FieldDescriptorProto_Type.TYPE_SFIXED64:
         return const BaseType._raw(FieldDescriptorProto_Type.TYPE_SFIXED64,
-            'SF6', '$_fixnumImportPrefix.Int64', r'$_setInt64', null);
+            'SF6', '$fixnumImportPrefix.Int64', r'$_setInt64', null);
       case FieldDescriptorProto_Type.TYPE_STRING:
         return const BaseType._raw(FieldDescriptorProto_Type.TYPE_STRING, 'S',
             '$coreImportPrefix.String', r'$_setString', null);

protoc_plugin/lib/src/file_generator.dart

@@ -12,7 +12,6 @@ const String _convertImportPrefix = r'$convert';
 const String _convertImportUrl = 'dart:convert';
 
 const String _coreImportUrl = 'dart:core';
-const String _fixnumImportPrefix = r'$fixnum';
 const String _grpcImportUrl = 'package:grpc/service_api.dart';
 const String _protobufImportUrl = 'package:protobuf/protobuf.dart';
 
@@ -318,7 +317,7 @@ class FileGenerator extends ProtobufContainer {
 
     if (_needsFixnumImport) {
       importWriter.addImport('package:fixnum/fixnum.dart',
-          prefix: _fixnumImportPrefix);
+          prefix: fixnumImportPrefix);
     }
 
     if (_needsProtobufImport) {

protoc_plugin/lib/src/message_generator.dart

@@ -680,7 +680,7 @@ class MessageGenerator extends ProtobufContainer {
       }
       return '\$_getI($index, $defaultExpr)';
     }
-    if (fieldType == '$_fixnumImportPrefix.Int64' && defaultExpr == 'null') {
+    if (fieldType == '$fixnumImportPrefix.Int64' && defaultExpr == 'null') {
       return '\$_getI64($index)';
     }
     if (defaultExpr == 'null') {

protoc_plugin/lib/src/protobuf_field.dart

@@ -111,7 +111,7 @@ class ProtobufField {
 
   /// Whether this field uses the Int64 from the fixnum package.
   bool get needsFixnumImport =>
-      baseType.unprefixed == '$_fixnumImportPrefix.Int64';
+      baseType.unprefixed == '$fixnumImportPrefix.Int64';
 
   /// Whether this field is a map field definition:
   /// `map<key_type, value_type> map_field = N`.
@@ -302,8 +302,8 @@ class ProtobufField {
             break;
         }
       } else {
-        if (makeDefault == '$_fixnumImportPrefix.Int64.ZERO' &&
-            type == '$_fixnumImportPrefix.Int64' &&
+        if (makeDefault == '$fixnumImportPrefix.Int64.ZERO' &&
+            type == '$fixnumImportPrefix.Int64' &&
             typeConstant == '$protobufImportPrefix.PbFieldType.O6') {
           invocation = 'aInt64';
         } else {
@@ -388,7 +388,7 @@ class ProtobufField {
       case FieldDescriptorProto_Type.TYPE_SFIXED64:
         var value = '0';
         if (descriptor.hasDefaultValue()) value = descriptor.defaultValue;
-        if (value == '0') return '$_fixnumImportPrefix.Int64.ZERO';
+        if (value == '0') return '$fixnumImportPrefix.Int64.ZERO';
         return "$protobufImportPrefix.parseLongInt('$value')";
       case FieldDescriptorProto_Type.TYPE_STRING:
         return _getDefaultAsStringExpr(null);

protoc_plugin/lib/src/shared.dart

@@ -12,6 +12,7 @@ const protobufImportPrefix = r'$pb';
 const asyncImportPrefix = r'$async';
 const coreImportPrefix = r'$core';
 const grpcImportPrefix = r'$grpc';
+const fixnumImportPrefix = r'$fixnum';
 const mixinImportPrefix = r'$mixin';
 
 extension FileDescriptorProtoExt on FileGenerator {

protoc_plugin/lib/src/well_known_types.dart

@@ -45,6 +45,24 @@ static Timestamp fromDateTime($coreImportPrefix.DateTime dateTime) {
   'google.protobuf.Duration': PbMixin(
     'DurationMixin',
     importFrom: _wellKnownImportPath,
+    injectedHelpers: [
+      '''
+/// Converts the [Duration] to [$coreImportPrefix.Duration].
+///
+/// This is a lossy conversion, as [$coreImportPrefix.Duration] is limited to [int]
+/// microseconds and also does not support nanosecond precision.
+$coreImportPrefix.Duration toDart() =>
+  $coreImportPrefix.Duration(
+    seconds: seconds.toInt(),
+    microseconds: nanos ~/ 1000,
+  );
+
+/// Creates a new instance from [$coreImportPrefix.Duration].
+static Duration fromDart($coreImportPrefix.Duration duration) => Duration()
+  ..seconds = $fixnumImportPrefix.Int64(duration.inSeconds)
+  ..nanos = (duration.inMicroseconds % $coreImportPrefix.Duration.microsecondsPerSecond) * 1000;
+''',
+    ],
     hasProto3JsonHelpers: true,
   ),
   'google.protobuf.Struct': PbMixin(

protoc_plugin/test/duration_test.dart

@@ -0,0 +1,47 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:fixnum/fixnum.dart';
+import 'package:test/test.dart';
+
+import '../out/protos/google/protobuf/duration.pb.dart' as pb;
+
+void main() {
+  test('core duration -> proto duration', () {
+    final coreDuration = Duration(
+      days: 1,
+      hours: 2,
+      minutes: 3,
+      seconds: 4,
+      milliseconds: 5,
+      microseconds: 6,
+    );
+
+    final protoDuration = pb.Duration.fromDart(coreDuration);
+
+    expect(protoDuration.seconds, Int64(86400 + 3600 * 2 + 60 * 3 + 4));
+    expect(protoDuration.nanos, 5006000);
+  });
+
+  test('core duration -> proto duration -> core duration', () {
+    final coreDuration = Duration(
+      days: 1,
+      hours: 2,
+      minutes: 3,
+      seconds: 4,
+      milliseconds: 5,
+      microseconds: 6,
+    );
+
+    expect(pb.Duration.fromDart(coreDuration).toDart(), coreDuration);
+  });
+
+  test('proto duration -> core duration -> proto duration', () {
+    final protoDuration = pb.Duration()
+      ..seconds = Int64(987654321)
+      ..nanos = 999999000;
+
+    expect(pb.Duration.fromDart(protoDuration.toDart()), protoDuration);
+  });
+}