error[E0005]: refutable pattern in local binding: `A(_)` not covered
  --> $DIR/uninhabited-irrefutable.rs:27:9
   |
LL | / enum Foo {
LL | |     A(foo::SecretlyEmpty),
   | |     - not covered
LL | |     B(foo::NotSoSecretlyEmpty),
LL | |     C(NotSoSecretlyEmpty),
LL | |     D(u32),
LL | | }
   | |_- `Foo` defined here
...
LL |       let Foo::D(_y) = x;
   |           ^^^^^^^^^^ pattern `A(_)` not covered
   |
   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
   = note: the matched value is of type `Foo`
help: you might want to use `if let` to ignore the variant that isn't matched
   |
LL |     if let Foo::D(_y) = x { /* */ }
   |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error: aborting due to previous error

For more information about this error, try `rustc --explain E0005`.