Move checks to compile-time

Author: oli-obk

src/test/ui/layout/unsafe-cell-hides-niche.rs

@@ -3,7 +3,7 @@
 // test checks that an `Option<UnsafeCell<NonZeroU32>>` has the same
 // size in memory as an `Option<UnsafeCell<u32>>` (namely, 8 bytes).
 
-// run-pass
+// check-pass
 
 #![feature(repr_simd)]
 
@@ -19,6 +19,13 @@ struct Transparent<T>(T);
 
 struct NoNiche<T>(UnsafeCell<T>);
 
+// Overwriting the runtime assertion and making it a compile-time assertion
+macro_rules! assert_eq {
+    ($a:expr, $b:literal) => {{
+        const _: () = assert!($a == $b);
+    }};
+}
+
 fn main() {
     assert_eq!(size_of::<Option<Wrapper<u32>>>(),     8);
     assert_eq!(size_of::<Option<Wrapper<N32>>>(),     4); // (✓ niche opt)