Function ra_ap_hir_ty::replace_errors_with_variables

pub fn replace_errors_with_variables<T>(t: &T) -> Canonical<T>
where
    T: HasInterner<Interner = Interner> + TypeFoldable<Interner> + Clone,

‘Canonicalizes’ the t by replacing any errors with new variables. Also ensures there are no unbound variables or inference variables anywhere in the t.