Check rvalue aggregates during check_stmt in tycheck, add initial, (not passing) test

src/test/compile-fail/aggregate-rvalues-typeck.rs

@@ -0,0 +1,23 @@
+// 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.
+//compile-flags: -Z emit-end-regions -Z borrowck-mir -Z mir
+
+#![allow(unused_assignments)]
+
+struct Wrap<'a> { w: &'a mut u32 }
+
+fn foo() {
+    let mut x = 22u64;
+    let wrapper = Wrap { w: &mut x };
+    x += 1;  //~ ERROR cannot assign to `x`
+    *wrapper.w += 1;
+}
+
+fn main() { }