error: return types are denoted using `->`
  --> $DIR/avoid-ice-on-warning.rs:4:23
   |
LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
   |                       ^
   |
help: use `->` instead
   |
LL | fn call_this<F>(f: F) -> Fn(&str) + call_that {}
   |                       ~~

error[E0405]: cannot find trait `call_that` in this scope
  --> $DIR/avoid-ice-on-warning.rs:4:36
   |
LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
   |                                    ^^^^^^^^^ not found in this scope

error[E0782]: expected a type, found a trait
  --> $DIR/avoid-ice-on-warning.rs:4:25
   |
LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
   |                         ^^^^^^^^^^^^^^^^^^^^
   |
help: `Fn(&str) + call_that` is dyn-incompatible, use `impl Fn(&str) + call_that` to return an opaque type, as long as you return a single underlying type
   |
LL | fn call_this<F>(f: F) : impl Fn(&str) + call_that {}
   |                         ++++

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0405, E0782.
For more information about an error, try `rustc --explain E0405`.