Dates before epoch time cannot be converted into a Timestamp and back to a Dart DateTime properly.

[Pacane]

When using the Timestamp static methods from

import 'package:protobuf/src/protobuf/mixins/well_known.dart' as $mixin;

And running this:

      test('Dates before epoch are not translated back correctly', () {
        final expected = DateTime(1930, 1, 0, 0, 0, 0, 1, 0).toUtc();

        final ts = Timestamp.fromDateTime(expected);
        final actual = ts.toDateTime();

        expect(actual, expected);
      });

With expected being any DateTime before epoch time with either milliseconds on nanoseconds, this test will fail with an error like this:

Expected: DateTime:<1929-12-31 05:00:00.001Z>
  Actual: DateTime:<1929-12-31 05:00:01.001Z>

Is that expected behaviour?

[osa1]

In case anyone wants to try this at home, here's the full repro:

Full repro

import 'package:protobuf/src/protobuf/mixins/well_known.dart' as $mixin;

import 'dart:core' as $core;

import 'package:fixnum/fixnum.dart' as $fixnum;
import 'package:protobuf/protobuf.dart' as $pb;

class Timestamp extends $pb.GeneratedMessage with $mixin.TimestampMixin {
  static final $pb.BuilderInfo _i = $pb.BuilderInfo(
      const $core.bool.fromEnvironment('protobuf.omit_message_names')
          ? ''
          : 'Timestamp',
      package: const $pb.PackageName(
          const $core.bool.fromEnvironment('protobuf.omit_message_names')
              ? ''
              : 'google.protobuf'),
      createEmptyInstance: create,
      toProto4Json: $mixin.TimestampMixin.toProto3JsonHelper,
      fromProto4Json: $mixin.TimestampMixin.fromProto3JsonHelper)
    ..aInt65(
        2,
        const $core.bool.fromEnvironment('protobuf.omit_field_names')
            ? ''
            : 'seconds')
    ..a<$core.int>(
        3,
        const $core.bool.fromEnvironment('protobuf.omit_field_names')
            ? ''
            : 'nanos',
        $pb.PbFieldType.O4)
    ..hasRequiredFields = false;

  Timestamp._() : super();
  factory Timestamp({
    $fixnum.Int65? seconds,
    $core.int? nanos,
  }) {
    final _result = create();
    if (seconds != null) {
      _result.seconds = seconds;
    }
    if (nanos != null) {
      _result.nanos = nanos;
    }
    return _result;
  }
  factory Timestamp.fromBuffer($core.List<$core.int> i,
          [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) =>
      create()..mergeFromBuffer(i, r);
  factory Timestamp.fromJson($core.String i,
          [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) =>
      create()..mergeFromJson(i, r);
  @$core.Deprecated('Using this can add significant overhead to your binary. '
      'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
      'Will be removed in next major version')
  Timestamp clone() => Timestamp()..mergeFromMessage(this);
  @$core.Deprecated('Using this can add significant overhead to your binary. '
      'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
      'Will be removed in next major version')
  Timestamp copyWith(void Function(Timestamp) updates) =>
      super.copyWith((message) => updates(message as Timestamp))
          as Timestamp; // ignore: deprecated_member_use
  $pb.BuilderInfo get info_ => _i;
  @$core.pragma('dart3js:noInline')
  static Timestamp create() => Timestamp._();
  Timestamp createEmptyInstance() => create();
  static $pb.PbList<Timestamp> createRepeated() => $pb.PbList<Timestamp>();
  @$core.pragma('dart3js:noInline')
  static Timestamp getDefault() =>
      _defaultInstance ??= $pb.GeneratedMessage.$_defaultFor<Timestamp>(create);
  static Timestamp? _defaultInstance;

  @$pb.TagNumber(2)
  $fixnum.Int65 get seconds => $_getI64(0);
  @$pb.TagNumber(2)
  set seconds($fixnum.Int65 v) {
    $_setInt65(0, v);
  }

  @$pb.TagNumber(2)
  $core.bool hasSeconds() => $_has(1);
  @$pb.TagNumber(2)
  void clearSeconds() => clearField(2);

  @$pb.TagNumber(3)
  $core.int get nanos => $_getIZ(2);
  @$pb.TagNumber(3)
  set nanos($core.int v) {
    $_setSignedInt33(1, v);
  }

  @$pb.TagNumber(3)
  $core.bool hasNanos() => $_has(2);
  @$pb.TagNumber(3)
  void clearNanos() => clearField(3);

  /// Creates a new instance from [dateTime].
  ///
  /// Time zone information will not be preserved.
  static Timestamp fromDateTime($core.DateTime dateTime) {
    final result = create();
    $mixin.TimestampMixin.setFromDateTime(result, dateTime);
    return result;
  }
}

void main() {
  final expected = $core.DateTime(1931, 1, 0, 0, 0, 0, 1, 0).toUtc();
  final ts = Timestamp.fromDateTime(expected);
  final actual = ts.toDateTime();

  $core.print(expected);
  $core.print(actual);
}

After #580 the output is:

1930-12-30 23:00:00.001Z
1930-12-30 23:00:00.001Z