test more ways of mutably accessing a place

Author: RalfJung

Diff for: src/test/ui/union/union-deref.rs

@@ -13,8 +13,16 @@ 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
 }

Diff for: src/test/ui/union/union-deref.stderr

@@ -7,14 +7,50 @@ LL |     unsafe { u.f.0 = Vec::new() };
    = help: writing to this reference calls the destructor for the old value
    = help: add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor
 
+error: not automatically applying `DerefMut` on `ManuallyDrop` union field
+  --> $DIR/union-deref.rs:17:19
+   |
+LL |     unsafe { &mut u.f.0 };
+   |                   ^^^
+   |
+   = help: writing to this reference calls the destructor for the old value
+   = help: add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor
+
 error: not automatically applying `DerefMut` on `ManuallyDrop` union field
   --> $DIR/union-deref.rs:19:14
    |
+LL |     unsafe { u.f.0.push(0) };
+   |              ^^^
+   |
+   = help: writing to this reference calls the destructor for the old value
+   = help: add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor
+
+error: not automatically applying `DerefMut` on `ManuallyDrop` union field
+  --> $DIR/union-deref.rs:23:14
+   |
 LL |     unsafe { u.f.0.0 = Vec::new() };
    |              ^^^^^^^
    |
    = help: writing to this reference calls the destructor for the old value
    = help: add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor
 
-error: aborting due to 2 previous errors
+error: not automatically applying `DerefMut` on `ManuallyDrop` union field
+  --> $DIR/union-deref.rs:25:19
+   |
+LL |     unsafe { &mut u.f.0.0 };
+   |                   ^^^^^^^
+   |
+   = help: writing to this reference calls the destructor for the old value
+   = help: add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor
+
+error: not automatically applying `DerefMut` on `ManuallyDrop` union field
+  --> $DIR/union-deref.rs:27:14
+   |
+LL |     unsafe { u.f.0.0.push(0) };
+   |              ^^^^^^^
+   |
+   = help: writing to this reference calls the destructor for the old value
+   = help: add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor
+
+error: aborting due to 6 previous errors