Function check_only_scope 

pub fn check_only_scope<R>(f: impl FnOnce() -> R) -> R

Runs f with every compile inside it checking only.

A dylib block binds the signatures it declares and opens no library, looks up no symbol and builds no calling interface. The program that comes out type-checks the same as a full compile but cannot call into a library, so it is for checking, never for running.