repr_transparent_external_private_fields: add a test for rust-lang#129470

Author: GrigorenkoPV

tests/ui/repr/repr-transparent-non-exhaustive-transparent-in-prose.rs

@@ -0,0 +1,25 @@
+//@ check-pass
+
+#![feature(sync_unsafe_cell)]
+#![allow(unused)]
+#![deny(repr_transparent_external_private_fields)]
+
+// https://github.com/rust-lang/rust/issues/129470
+
+struct ZST;
+
+#[repr(transparent)]
+struct TransparentWithManuallyDropZST {
+    value: i32,
+    md: std::mem::ManuallyDrop<ZST>,
+    mu: std::mem::MaybeUninit<ZST>,
+    p: std::pin::Pin<ZST>,
+    pd: std::marker::PhantomData<ZST>,
+    pp: std::marker::PhantomPinned,
+    c: std::cell::Cell<ZST>,
+    uc: std::cell::UnsafeCell<ZST>,
+    suc: std::cell::SyncUnsafeCell<ZST>,
+    zst: ZST,
+}
+
+fn main() {}