Add address stability test for matches

Author: matthewjasper

src/test/ui/match/match-ref-mut-stability.rs

@@ -0,0 +1,39 @@
+// Check that `ref mut` variables don't change address between the match guard
+// and the arm expression.
+
+// run-pass
+
+#![feature(nll, bind_by_move_pattern_guards)]
+
+// Test that z always point to the same temporary.
+fn referent_stability() {
+    let p;
+    match 0 {
+        ref mut z if { p = z as *const _; true } => assert_eq!(p, z as *const _),
+        _ => unreachable!(),
+    };
+}
+
+// Test that z is always effectively the same variable.
+fn variable_stability() {
+    let p;
+    match 0 {
+        ref mut z if { p = &z as *const _; true } => assert_eq!(p, &z as *const _),
+        _ => unreachable!(),
+    };
+}
+
+// Test that a borrow of *z can cross from the guard to the arm.
+fn persist_borrow() {
+    let r;
+    match 0 {
+        ref mut z if { r = z as &_; true } => assert_eq!(*r, 0),
+        _ => unreachable!(),
+    }
+}
+
+fn main() {
+    referent_stability();
+    variable_stability();
+    persist_borrow();
+}