1 files changed, 29 insertions, 0 deletions
diff --git a/src/test/ui/union/union-deref.rs b/src/test/ui/union/union-deref.rs
new file mode 100644
index 000000000..5aa28d93f
--- /dev/null
+++ b/src/test/ui/union/union-deref.rs
@@ -0,0 +1,29 @@
+// revisions: mirunsafeck thirunsafeck
+// [thirunsafeck]compile-flags: -Z thir-unsafeck
+
+//! Test the part of RFC 2514 that is about not applying `DerefMut` coercions
+//! of union fields.
+
+use std::mem::ManuallyDrop;
+
+union U1<T> { x:(), f: ManuallyDrop<(T,)> }
+
+union U2<T> { x:(), f: (ManuallyDrop<(T,)>,) }
+
+fn main() {
+    let mut u : U1<Vec<i32>> = U1 { x: () };
+    unsafe { (*u.f).0 = Vec::new() }; // explicit deref, this compiles
+    unsafe { u.f.0 = Vec::new() }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
+    unsafe { &mut (*u.f).0 }; // explicit deref, this compiles
+    unsafe { &mut u.f.0 }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
+    unsafe { (*u.f).0.push(0) }; // explicit deref, this compiles
+    unsafe { u.f.0.push(0) }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
+
+    let mut u : U2<Vec<i32>> = U2 { x: () };
+    unsafe { (*u.f.0).0 = Vec::new() }; // explicit deref, this compiles
+    unsafe { u.f.0.0 = Vec::new() }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
+    unsafe { &mut (*u.f.0).0 }; // explicit deref, this compiles
+    unsafe { &mut u.f.0.0 }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
+    unsafe { (*u.f.0).0.push(0) }; // explicit deref, this compiles
+    unsafe { u.f.0.0.push(0) }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
+}