1 files changed, 29 insertions, 0 deletions
diff --git a/tests/ui/traits/trait-object-destructure.rs b/tests/ui/traits/trait-object-destructure.rs
new file mode 100644
index 00000000000..6c091677c8c
--- /dev/null
+++ b/tests/ui/traits/trait-object-destructure.rs
@@ -0,0 +1,29 @@
+//! Regression test for destructuring trait references (`&dyn T`/`Box<dyn T>`).
+//! Checks cases where number of `&`/`Box` patterns (n) matches/doesn't match references (m).
+//!
+//! Issue: https://github.com/rust-lang/rust/issues/15031
+
+#![feature(box_patterns)]
+
+trait T {
+    fn foo(&self) {}
+}
+
+impl T for isize {}
+
+fn main() {
+    // Valid cases: n < m (can dereference)
+    let &x = &(&1isize as &dyn T);
+    let &x = &&(&1isize as &dyn T);
+    let &&x = &&(&1isize as &dyn T);
+
+    // Error cases: n == m (cannot dereference trait object)
+    let &x = &1isize as &dyn T; //~ ERROR type `&dyn T` cannot be dereferenced
+    let &&x = &(&1isize as &dyn T); //~ ERROR type `&dyn T` cannot be dereferenced
+    let box x = Box::new(1isize) as Box<dyn T>; //~ ERROR type `Box<dyn T>` cannot be dereferenced
+
+    // Error cases: n > m (type mismatch)
+    let &&x = &1isize as &dyn T; //~ ERROR mismatched types
+    let &&&x = &(&1isize as &dyn T); //~ ERROR mismatched types
+    let box box x = Box::new(1isize) as Box<dyn T>; //~ ERROR mismatched types
+}