error: expected identifier, found keyword `impl`
 --> src/lib.rs:1:20
  |
1 | fn foo(_f: for<'a> impl FnOnce(&'a str)) {}
  |                    ^^^^ expected identifier, found keyword

error: unexpected lifetime `'a` in pattern
 --> src/lib.rs:1:33
  |
1 | fn foo(_f: for<'a> impl FnOnce(&'a str)) {}
  |                                 ^^ help: remove the lifetime

error: expected one of `:` or `|`, found `)`
 --> src/lib.rs:1:40
  |
1 | fn foo(_f: for<'a> impl FnOnce(&'a str)) {}
  |                                        ^ expected one of `:` or `|`

error: expected one of `(`, `)`, ` `, `,`, `::`, or `<`, found `FnOnce`
 --> src/lib.rs:1:25
  |
1 | fn foo(_f: for<'a> impl FnOnce(&'a str)) {}
  |                        -^^^^^^ expected one of `(`, `)`, ` `, `,`, `::`, or `<`
  |                        |
  |                        help: missing `,`

error[E0405]: cannot find trait `r#impl` in this scope
 --> src/lib.rs:1:20
  |
1 | fn foo(_f: for<'a> impl FnOnce(&'a str)) {}
  |                    ^^^^ not found in this scope

error[E0782]: trait objects must include the `dyn` keyword
 --> src/lib.rs:1:12
  |
1 | fn foo(_f: for<'a> impl FnOnce(&'a str)) {}
  |            ^^^^^^^^^^^^
  |
help: add `dyn` keyword before this trait
  |
1 | fn foo(_f: dyn for<'a> impl FnOnce(&'a str)) {}
  |               

error: a lifetime quantifier (`for<'a>`) may not be used here
 --> src/lib.rs:1:20
  |
1 | fn foo(_f: for<'a> impl FnOnce(&'a str)) {}
  |            ^^^^^^^ this quantifier
  |
note: lifetime quantifiers may only be used before `fn` pointer types and within `impl Trait` types
help: place this `for<'a>` inside the `impl`:
  |
1 | fn foo(_f: impl for<'a> FnOnce(&'a str)) {}
  |