error[E0277]: expected a `Fn<(char,)>` closure, found `char`
  --> $DIR/root-obligation.rs:6:38
   |
LL |         .filter(|c| "aeiou".contains(c))
   |                             -------- ^ expected an `Fn<(char,)>` closure, found `char`
   |                             |
   |                             required by a bound introduced by this call
   |
   = help: the trait `Fn<(char,)>` is not implemented for `char`
   = note: required because of the requirements on the impl of `FnOnce<(char,)>` for `&char`
   = note: required because of the requirements on the impl of `Pattern<'_>` for `&char`
note: required by a bound in `core::str::<impl str>::contains`
  --> $SRC_DIR/core/src/str/mod.rs:LL:COL
   |
LL |     pub fn contains<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool {
   |                            ^^^^^^^^^^^ required by this bound in `core::str::<impl str>::contains`
help: consider dereferencing here
   |
LL |         .filter(|c| "aeiou".contains(*c))
   |                                      +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.