error[E0277]: expected a `Fn()` closure, found `unsafe fn() -> i32`
  --> $DIR/fn-trait.rs:20:16
   |
LL |     require_fn(f as unsafe fn() -> i32);
   |     ---------- ^^^^^^^^^^^^^^^^^^^^^^^ call the function in a closure: `|| unsafe { /* code */ }`
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `Fn()` is not implemented for `unsafe fn() -> i32`
   = note: unsafe function cannot be called generically without an unsafe block
   = note: wrap the `unsafe fn() -> i32` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `require_fn`
  --> $DIR/fn-trait.rs:3:23
   |
LL | fn require_fn(_: impl Fn() -> i32) {}
   |                       ^^^^^^^^^^^ required by this bound in `require_fn`

error[E0277]: expected a `Fn()` closure, found `extern "C" fn() -> i32 {g}`
  --> $DIR/fn-trait.rs:22:16
   |
LL |     require_fn(g);
   |     ---------- ^ expected an `Fn()` closure, found `extern "C" fn() -> i32 {g}`
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `Fn()` is not implemented for fn item `extern "C" fn() -> i32 {g}`
   = note: wrap the `extern "C" fn() -> i32 {g}` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `require_fn`
  --> $DIR/fn-trait.rs:3:23
   |
LL | fn require_fn(_: impl Fn() -> i32) {}
   |                       ^^^^^^^^^^^ required by this bound in `require_fn`

error[E0277]: expected a `Fn()` closure, found `extern "C" fn() -> i32`
  --> $DIR/fn-trait.rs:24:16
   |
LL |     require_fn(g as extern "C" fn() -> i32);
   |     ---------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an `Fn()` closure, found `extern "C" fn() -> i32`
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `Fn()` is not implemented for `extern "C" fn() -> i32`
   = note: wrap the `extern "C" fn() -> i32` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `require_fn`
  --> $DIR/fn-trait.rs:3:23
   |
LL | fn require_fn(_: impl Fn() -> i32) {}
   |                       ^^^^^^^^^^^ required by this bound in `require_fn`

error[E0277]: expected a `Fn()` closure, found `unsafe fn() -> i32 {h}`
  --> $DIR/fn-trait.rs:26:16
   |
LL |     require_fn(h);
   |     ---------- ^ call the function in a closure: `|| unsafe { /* code */ }`
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `Fn()` is not implemented for fn item `unsafe fn() -> i32 {h}`
   = note: unsafe function cannot be called generically without an unsafe block
   = note: wrap the `unsafe fn() -> i32 {h}` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `require_fn`
  --> $DIR/fn-trait.rs:3:23
   |
LL | fn require_fn(_: impl Fn() -> i32) {}
   |                       ^^^^^^^^^^^ required by this bound in `require_fn`

error: aborting due to 4 previous errors

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