Auto merge of #41153 - petrochenkov:umove, r=pnkfelix

Fix move checking for nested union fields

Fixes https://github.com/rust-lang/rust/issues/41126
r? @arielb1

src/test/compile-fail/union/union-borrow-move-parent-sibling.rs

@@ -0,0 +1,57 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(untagged_unions)]
+#![allow(unused)]
+
+#[allow(unions_with_drop_fields)]
+union U {
+    x: ((Vec<u8>, Vec<u8>), Vec<u8>),
+    y: Box<Vec<u8>>,
+}
+
+unsafe fn parent_sibling_borrow() {
+    let mut u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let a = &mut u.x.0;
+    let a = &u.y; //~ ERROR cannot borrow `u.y`
+}
+
+unsafe fn parent_sibling_move() {
+    let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let a = u.x.0;
+    let a = u.y; //~ ERROR use of moved value: `u.y`
+}
+
+unsafe fn grandparent_sibling_borrow() {
+    let mut u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let a = &mut (u.x.0).0;
+    let a = &u.y; //~ ERROR cannot borrow `u.y`
+}
+
+unsafe fn grandparent_sibling_move() {
+    let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let a = (u.x.0).0;
+    let a = u.y; //~ ERROR use of moved value: `u.y`
+}
+
+unsafe fn deref_sibling_borrow() {
+    let mut u = U { y: Box::default() };
+    let a = &mut *u.y;
+    let a = &u.x; //~ ERROR cannot borrow `u` (via `u.x`)
+}
+
+unsafe fn deref_sibling_move() {
+    let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let a = *u.y;
+    let a = u.x; //~ ERROR use of moved value: `u.x`
+}
+
+
+fn main() {}