error[E0599]: no method named `closure` found for struct `Obj` in the current scope
  --> $DIR/issue-18343.rs:7:7
   |
LL | struct Obj<F> where F: FnMut() -> u32 {
   | ------------- method `closure` not found for this struct
...
LL |     o.closure();
   |       ^^^^^^^ field, not a method
   |
help: to call the function stored in `closure`, surround the field access with parentheses
   |
LL |     (o.closure)();
   |     +         +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0599`.