add regression test for issue rust-lang#16223: fixed by NLL

Author: Hero

Diff for: src/test/ui/nll/issue-16223.rs

@@ -0,0 +1,63 @@
+// Copyright 2018 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.
+
+// Regression test for #16223: without NLL the `if let` construct together with
+// the nested box-structure of `Root` causes an unwanted collateral move.
+
+// The exact error prevented here is:
+//
+// error[E0382]: use of collaterally moved value: `(root.boxed.rhs as SomeVariant::B).0`
+//   --> src/main.rs:55:29
+//    |
+// 56 |         lhs: SomeVariant::A(a),
+//    |                             - value moved here
+// 57 |         rhs: SomeVariant::B(b),
+//    |                             ^ value used here after move
+//    |
+//    = note: move occurs because the value has type `A`, which does not implement the `Copy` trait
+
+// must-compile-successfully
+
+#![feature(nll)]
+#![feature(box_patterns)]
+
+struct Root {
+    boxed: Box<SetOfVariants>,
+}
+
+struct SetOfVariants {
+    lhs: SomeVariant,
+    rhs: SomeVariant,
+}
+
+enum SomeVariant {
+    A(A),
+    B(B),
+}
+
+struct A(String);
+struct B(String);
+
+fn main() {
+    let root = Root {
+        boxed: Box::new(SetOfVariants {
+            lhs: SomeVariant::A(A(String::from("This is A"))),
+            rhs: SomeVariant::B(B(String::from("This is B"))),
+        }),
+    };
+    if let box SetOfVariants {
+        lhs: SomeVariant::A(a),
+        rhs: SomeVariant::B(b),
+    } = root.boxed
+    {
+        println!("a = {}", a.0);
+        println!("b = {}", b.0);
+    }
+}