ignore some vtable/fn ptr equality tests in Miri, their result is not fully predictable

Author: RalfJung

library/alloc/tests/task.rs

@@ -4,7 +4,7 @@ use alloc::task::{LocalWake, Wake};
 use core::task::{LocalWaker, Waker};
 
 #[test]
-#[cfg_attr(miri, should_panic)] // `will_wake` doesn't guarantee that this test will work, and indeed on Miri it fails
+#[cfg_attr(miri, ignore)] // `will_wake` doesn't guarantee that this test will work, and indeed on Miri it can fail
 fn test_waker_will_wake_clone() {
     struct NoopWaker;
 
@@ -20,7 +20,7 @@ fn test_waker_will_wake_clone() {
 }
 
 #[test]
-#[cfg_attr(miri, should_panic)] // `will_wake` doesn't guarantee that this test will work, and indeed on Miri it fails
+#[cfg_attr(miri, ignore)] // `will_wake` doesn't guarantee that this test will work, and indeed on Miri it can fail
 fn test_local_waker_will_wake_clone() {
     struct NoopWaker;
 

library/core/tests/ptr.rs

@@ -810,9 +810,12 @@ fn ptr_metadata() {
         assert_ne!(address_1, address_2);
         // Different erased type => different vtable pointer
         assert_ne!(address_2, address_3);
-        // Same erased type and same trait => same vtable pointer
-        assert_eq!(address_3, address_4);
-        assert_eq!(address_3, address_5);
+        // Same erased type and same trait => same vtable pointer.
+        // This is *not guaranteed*, so we skip it in Miri.
+        if !cfg!(miri) {
+            assert_eq!(address_3, address_4);
+            assert_eq!(address_3, address_5);
+        }
     }
 }