Good catch @Sija, thanks!

Would it be possible or advisable to add this as a special-case formatter rule? Especially as they're macros not syntax.

@RX14 The formatter has no notion of semantic, and one could redefine property! inside another type

@asterite that's what I was thinking, I wasn't sure if the formatter would be able to tell if it was the stdlib property! or not.

But the property! macro could raise a compilation error if the type is nilable. 💡

another option could be IMHO to make compiler disallow double ? modifier.

@Sija that would be a check in a syntax level that incomplete. Trying to do it at a semantic level would be to disallow unions with more than one Nil, but there are path where you can get unions with two nillables, or build across macros invocation. Hard or imposible to differentiate.

Given that a property! could be called from other macro it might block the user if the generated code plays with Nil and wraps types on the go. I think there is nothing else to do for the time being.