error[E0229]: associated item constraints are not allowed here
  --> $DIR/issue-39259.rs:6:17
   |
LL | impl Fn(u32) -> u32 for S {
   |                 ^^^ associated item constraint not allowed here
   |
help: parenthesized trait syntax expands to `Fn<(u32,), Output=u32>`
  --> $DIR/issue-39259.rs:6:6
   |
LL | impl Fn(u32) -> u32 for S {
   |      ^^^^^^^^^^^^^^

error[E0277]: expected a `FnMut(u32)` closure, found `S`
  --> $DIR/issue-39259.rs:6:25
   |
LL | impl Fn(u32) -> u32 for S {
   |                         ^ expected an `FnMut(u32)` closure, found `S`
   |
   = help: the trait `FnMut(u32)` is not implemented for `S`
note: required by a bound in `Fn`
  --> $SRC_DIR/core/src/ops/function.rs:LL:COL

error[E0050]: method `call` has 1 parameter but the declaration in trait `call` has 2
  --> $DIR/issue-39259.rs:9:13
   |
LL |     fn call(&self) -> u32 {
   |             ^^^^^ expected 2 parameters, found 1
   |
   = note: `call` from trait: `extern "rust-call" fn(&Self, Args) -> <Self as FnOnce<Args>>::Output`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0050, E0229, E0277.
For more information about an error, try `rustc --explain E0050`.