Sanity check for move from an uninit variable whose address is taken

Author: ecstatic-morse

src/test/ui/moves/move-of-addr-of-mut.rs

@@ -0,0 +1,12 @@
+// Ensure that taking a mutable raw ptr to an uninitialized variable does not change its
+// initializedness.
+
+struct S;
+
+fn main() {
+    let mut x: S;
+    std::ptr::addr_of_mut!(x); //~ borrow of
+
+    let y = x; // Should error here if `addr_of_mut` is ever allowed on uninitialized variables
+    drop(y);
+}

src/test/ui/moves/move-of-addr-of-mut.stderr

@@ -0,0 +1,11 @@
+error[E0381]: borrow of possibly-uninitialized variable: `x`
+  --> $DIR/move-of-addr-of-mut.rs:8:5
+   |
+LL |     std::ptr::addr_of_mut!(x);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ use of possibly-uninitialized `x`
+   |
+   = note: this error originates in the macro `std::ptr::addr_of_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0381`.