error[E0618]: expected function, found `Enum<()>`
  --> $DIR/issue-114701.rs:14:27
   |
LL | enum Enum<T> { SVariant { v: T }, UVariant }
   |                                   -------- `Enum::UVariant` defined here
...
LL |         assert!(if let Enum::$variant::<()> $matcher = $expr () { true } else { false },
   |                                                        -------- call expression requires function
...
LL |     is_variant!(UVariant, Enum::<()>::UVariant);
   |                           ^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0618`.