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 for `&char` to implement `FnOnce<(char,)>`
   = note: required for `&char` to implement `Pattern<'_>`
note: required by a bound in `core::str::<impl str>::contains`
  --> $SRC_DIR/core/src/str/mod.rs:LL:COL
help: consider dereferencing here
   |
LL |         .filter(|c| "aeiou".contains(*c))
   |                                      +

error: aborting due to 1 previous error

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