Maintenance migrations doesn't get executed when registering migrations via .ScanIn(typeof(Program).Assembly).For.Migrations()

Describe the bug

Maintenance migrations don’t seem to be executed.

To Reproduce I have a maintenance migration defined as

[Maintenance(MigrationStage.BeforeAll, TransactionBehavior.None)]
[UsedImplicitly]
public class EnsureMigrationsCannotBeRunSimultaneouslyByMultipleInstances : Migration
{
    public override void Down() => throw new NotImplementedException("Down migrations are not supported for sp_getapplock");

    public override void Up()
    {
        throw new Exception("x");
        Console.WriteLine("START!!!!!!!!!!!!!!!!!!!!!!!!!!");
        Execute.Sql($@"
            DECLARE @result INT
            EXEC @result = sp_getapplock '{GetType().Namespace}', 'Exclusive', 'Session'

            IF @result < 0
            BEGIN
                DECLARE @msg NVARCHAR(1000) = 'Received error code ' + CAST(@result AS VARCHAR(10)) + ' from sp_getapplock during migrations';
                THROW 99999, @msg, 1;
            END
        ");
    }
}

Note that I throw an exception in Up().

When I run the migrations in a unit-test, they all run through just fine and I never hit the exception. In fact, all the structure described in my migrations is created happily.

So I am under the impression this specific ‘before-all’ migration is never executed.

Expected behavior The migration is executed and thus the exception thrown.

Information (please complete the following information):

• OS: Windows 11
• Platform: Net6
• FluentMigrator version: 3.3.1
• FluentMigrator runner: “in-process runner”
• Database Management System SQLServer (docker image mcr.microsoft.com/mssql/server:2019-CU5-ubuntu-18.04)
• Database Management System Version: see the answer to the last question, sqlserver 2019-CU5

Additional context Basically, I’ve been following the guidance from here to prevent multiple service instances running migrations at the same time.

However, I just got round to check whether this actually works and it seems these special maintenance migrations are never called.

I tried to step into the code of FluentMigrator, as much as VS and the nugets let me, and in MigrationRunner.MigrateUp() where it calls ApplyMaintenance(MigrationStage.BeforeAll, useAutomaticTransactionManagement); which leads to MaintenanceLoader.LoadMaintenance - and in there _maintenace is empty. Dunno if that helps.

[jzabroski]

I added a comment and updated the sample to help avoid this booby trap until we have time to do a proper fix. https://github.com/fluentmigrator/fluentmigrator/commit/d0c4c362138bd4bb60cdc0d317236bcf2d54ded5

[jzabroski]

See: https://github.com/fluentmigrator/fluentmigrator/issues/1062#issuecomment-616598419 - I think this is actually the heart of it.

Nobody ever did a PR to fix this/smooth it over, but we did get to the bottom of it / provide workarounds.