error[E0597]: `b` does not live long enough
  --> $DIR/var-appears-twice.rs:20:38
   |
LL |     let x: DoubleCell<_> = make_cell(&b);
   |            -------------             ^^ borrowed value does not live long enough
   |            |
   |            type annotation requires that `b` is borrowed for `'static`
...
LL | }
   | - `b` dropped here while still borrowed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0597`.