error[E0005]: refutable pattern in local binding: `Helper::T(_, _)` not covered
  --> $DIR/empty-never-array.rs:10:9
   |
LL |     let Helper::U(u) = Helper::T(t, []);
   |         ^^^^^^^^^^^^ pattern `Helper::T(_, _)` 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: `Helper<T, U>` defined here
  --> $DIR/empty-never-array.rs:4:5
   |
LL | enum Helper<T, U> {
   |      ------
LL |     T(T, [!; 0]),
   |     ^ not covered
   = note: the matched value is of type `Helper<T, U>`
help: you might want to use `if let` to ignore the variant that isn't matched
   |
LL |     let u = if let Helper::U(u) = Helper::T(t, []) { u } else { todo!() };
   |     ++++++++++                                     ++++++++++++++++++++++
help: alternatively, you might want to use let else to handle the variant that isn't matched
   |
LL |     let Helper::U(u) = Helper::T(t, []) else { todo!() };
   |                                         ++++++++++++++++

error: aborting due to previous error

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