1 files changed, 44 insertions, 0 deletions
diff --git a/src/test/ui/destructure-trait-ref.rs b/src/test/ui/destructure-trait-ref.rs
new file mode 100644
index 000000000..50b64aeeb
--- /dev/null
+++ b/src/test/ui/destructure-trait-ref.rs
@@ -0,0 +1,44 @@
+// The regression test for #15031 to make sure destructuring trait
+// reference work properly.
+
+#![feature(box_patterns)]
+
+trait T { fn foo(&self) {} }
+impl T for isize {}
+
+
+fn main() {
+    // For an expression of the form:
+    //
+    //      let &...&x = &..&SomeTrait;
+    //
+    // Say we have n `&` at the left hand and m `&` right hand, then:
+    // if n < m, we are golden;
+    // if n == m, it's a derefing non-derefable type error;
+    // if n > m, it's a type mismatch error.
+
+    // n < m
+    let &x = &(&1isize as &dyn T);
+    let &x = &&(&1isize as &dyn T);
+    let &&x = &&(&1isize as &dyn T);
+
+    // n == m
+    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
+
+    // n > m
+    let &&x = &1isize as &dyn T;
+    //~^ ERROR mismatched types
+    //~| expected trait object `dyn T`
+    //~| found reference `&_`
+    let &&&x = &(&1isize as &dyn T);
+    //~^ ERROR mismatched types
+    //~| expected trait object `dyn T`
+    //~| found reference `&_`
+    let box box x = Box::new(1isize) as Box<dyn T>;
+    //~^ ERROR mismatched types
+    //~| expected trait object `dyn T`
+    //~| found struct `Box<_>`
+}