C# bug: STDB0024 Error when a View returns a `RefOption` result

[rekhoff]

As reported by a Spacetime community user Arc, a bug exists in the C# View code where they were getting an error in 1.11.1 on the code:

[View(Name = nameof(MyAccount), Public = true)]
public static Account? MyAccount(ViewContext ctx)
{
	return ctx.Db.Account.Identity.Find(ctx.Sender) as Account;
}

Where Account? is a class.

The validator for [SpacetimeDB.View] return types was only accepting:

• SpacetimeDB.BSATN.List<...> (like “Vec”)
• SpacetimeDB.BSATN.ValueOption<...> (nullable value types / T? where T : struct)

But nullable reference types like Account? (where Account : class) are represented by BSATN as:

• SpacetimeDB.BSATN.RefOption<...>

So the analyzer/codegen incorrectly rejected Account? with:

View 'MyAccount' must return Vec or Option. (STDB0024)

The existing regression test passed because the row type there is a struct (so Player? mapped to ValueOption) or otherwise didn’t hit the RefOption path.