Warn when known types are used as generic placeholders #54905
Description
Since hardly it is what you want and it leads to funny error messages, here an example:
struct S<T> {
foo: T,
}
impl<u16> S<u16> {
fn fee(&self, idx: usize) -> u16 {
if (self.foo as usize) < idx {
idx as u16
} else {
4
}
}
}
fn main() {
let f: S<u16> = S { foo: 42 };
println!(" {}", f.fee(13));
}