Regression test for the bug.

Author: pnkfelix

src/test/ui/borrowck/issue-51348-multi-ref-mut-in-guard.rs

@@ -0,0 +1,33 @@
+// 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.
+
+// We used to ICE if you had a single match arm with multiple
+// candidate patterns with `ref mut` identifiers used in the arm's
+// guard.
+//
+// Also, this test expands on the original bug's example by actually
+// trying to double check that we are matching against the right part
+// of the input data based on which candidate pattern actually fired.
+
+// run-pass
+
+#![feature(nll)]
+
+fn foo(x: &mut Result<(u32, u32), (u32, u32)>) -> u32 {
+    match *x {
+        Ok((ref mut v, _)) | Err((_, ref mut v)) if *v > 0 => { *v }
+        _ => { 0 }
+    }
+}
+
+fn main() {
+    assert_eq!(foo(&mut Ok((3, 4))), 3);
+    assert_eq!(foo(&mut Err((3, 4))), 4);
+}