Post #1366729

@blp inherent methods on some `Type` may not be using the `T` specifically (e.g. `Vec::len`), and self.foo() and foo(self) are equivalent-ish in Rust, so a function with unused generics must exist as a thing. tbh, unused T on a standalone function is as rare and suspicious as in a struct, so the inconsistency in enforcement could be just a historical accident.