Fix timestamp to be returned as Unspecified DateTime in legacy mode (n…

…pgsql#5466)

Fixes npgsql#5465

(cherry picked from commit 69ee3a4)
Signed-off-by: monjowe <jonas.westman@monitor.se>

src/Npgsql/Internal/Converters/Temporal/LegacyDateTimeConverter.cs

@@ -21,8 +21,13 @@ public override bool CanConvert(DataFormat format, out BufferRequirements buffer
 
     protected override DateTime ReadCore(PgReader reader)
     {
+        if (_timestamp)
+        {
+            return PgTimestamp.Decode(reader.ReadInt64(), DateTimeKind.Unspecified, _dateTimeInfinityConversions);
+        }
+
         var dateTime = PgTimestamp.Decode(reader.ReadInt64(), DateTimeKind.Utc, _dateTimeInfinityConversions);
-        return !_timestamp && (!_dateTimeInfinityConversions || dateTime != DateTime.MaxValue && dateTime != DateTime.MinValue)
+        return !_dateTimeInfinityConversions || dateTime != DateTime.MaxValue && dateTime != DateTime.MinValue
             ? dateTime.ToLocalTime()
             : dateTime;
     }

test/Npgsql.Tests/Types/LegacyDateTimeTests.cs

@@ -21,6 +21,14 @@ public Task Timestamp_with_all_DateTime_kinds([Values] DateTimeKind kind)
             NpgsqlDbType.Timestamp,
             DbType.DateTime);
 
+    [Test]
+    public async Task Timestamp_read_as_Unspecified_DateTime()
+    {
+        await using var command = DataSource.CreateCommand("SELECT '2020-03-01T10:30:00'::timestamp");
+        var dateTime = (DateTime)(await command.ExecuteScalarAsync())!;
+        Assert.That(dateTime.Kind, Is.EqualTo(DateTimeKind.Unspecified));
+    }
+
     [Test]
     [TestCase(DateTimeKind.Utc, TestName = "Timestamptz_write_utc_DateTime_does_not_convert")]
     [TestCase(DateTimeKind.Unspecified, TestName = "Timestamptz_write_unspecified_DateTime_does_not_convert")]