Add regression test

Author: oli-obk

tests/ui/transmute/raw-ptr-non-null.rs

@@ -0,0 +1,11 @@
+//! After the use of pattern types inside `NonNull`,
+//! transmuting between a niche optimized enum wrapping a
+//! generic `NonNull` and raw pointers stopped working.
+
+use std::ptr::NonNull;
+pub const fn is_null<'a, T: ?Sized>(ptr: *const T) -> bool {
+    unsafe { matches!(core::mem::transmute::<*const T, Option<NonNull<T>>>(ptr), None) }
+    //~^ ERROR: cannot transmute
+}
+
+fn main() {}

tests/ui/transmute/raw-ptr-non-null.stderr

@@ -0,0 +1,12 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/raw-ptr-non-null.rs:7:23
+   |
+LL |     unsafe { matches!(core::mem::transmute::<*const T, Option<NonNull<T>>>(ptr), None) }
+   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `*const T` (pointer to `T`)
+   = note: target type: `Option<NonNull<T>>` (size can vary because of <T as Pointee>::Metadata)
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0512`.