There are obvious ways to make it happen (never a good idea), e.g. create a type checking extension that "ignores some error about missing type info" and proceeds.

That's only obvious if you are aware of type checking extensions, which I was not up to now, so thanks for mentioning them, I could actually right now need to use them. 😄

Two places AI just found where Groovy itself breaks the rule (I'll investigate these separately):

In my case it was access to a

private static final Map

. Type-check was happy with that, compile-static was not. A call to a

private static

method was already complained about by the Type-checker. So here it also seems obvious to me that the type-checker should complain, just wanted to know the general rule.