expand coerce fn test

Author: RalfJung

tests/run-pass/coerce_non_capture_closure_to_fn_ptr.rs

@@ -5,8 +5,10 @@ static FOO: fn() = || { assert_ne!(42, 43) };
 static BAR: fn(i32, i32) = |a, b| { assert_ne!(a, b) };
 
 // use to first make the closure FnOnce() before making it fn()
-fn magic0<R, F: FnOnce() -> R>(f: F) -> F { f }
-fn magic1<T, R, F: FnOnce(T) -> R>(f: F) -> F { f }
+fn force_once0<R, F: FnOnce() -> R>(f: F) -> F { f }
+fn force_once1<T, R, F: FnOnce(T) -> R>(f: F) -> F { f }
+fn force_mut0<R, F: FnMut() -> R>(f: F) -> F { f }
+fn force_mut1<T, R, F: FnMut(T) -> R>(f: F) -> F { f }
 
 fn main() {
     FOO();
@@ -18,12 +20,16 @@ fn main() {
 
     let f: fn() = ||{};
     f();
-    let f = magic0(||{}) as fn();
+    let f = force_once0(||{}) as fn();
+    f();
+    let f = force_mut0(||{}) as fn();
     f();
 
     let g: fn(i32) = |i| assert_eq!(i, 2);
     g(2);
-    let g = magic1(|i| assert_eq!(i, 2)) as fn(i32);
+    let g = force_once1(|i| assert_eq!(i, 2)) as fn(i32);
+    g(2);
+    let g = force_mut1(|i| assert_eq!(i, 2)) as fn(i32);
     g(2);
 
     // FIXME: This fails with "invalid use of NULL pointer" <https://github.com/rust-lang/miri/issues/1075>