1 files changed, 21 insertions, 0 deletions
diff --git a/tests/ui/destructuring-assignment/warn-unused-duplication.rs b/tests/ui/destructuring-assignment/warn-unused-duplication.rs
new file mode 100644
index 00000000000..390f44b8aa5
--- /dev/null
+++ b/tests/ui/destructuring-assignment/warn-unused-duplication.rs
@@ -0,0 +1,21 @@
+// run-pass
+
+#![warn(unused_assignments)]
+
+fn main() {
+    let mut a;
+    // Assignment occurs left-to-right.
+    // However, we emit warnings when this happens, so it is clear that this is happening.
+    (a, a) = (0, 1); //~ WARN value assigned to `a` is never read
+    assert_eq!(a, 1);
+
+    // We can't always tell when a variable is being assigned to twice, which is why we don't try
+    // to emit an error, which would be fallible.
+    let mut x = 1;
+    (*foo(&mut x), *foo(&mut x)) = (5, 6);
+    assert_eq!(x, 6);
+}
+
+fn foo<'a>(x: &'a mut u32) -> &'a mut u32 {
+    x
+}