Make destructuring a defining use

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -793,6 +793,14 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
             ProjectionElem::OpaqueCast(ty) => {
                 let ty = self.sanitize_type(place, ty);
                 let ty = self.cx.normalize(ty, location);
+                self.cx
+                    .eq_types(
+                        base.ty,
+                        ty,
+                        location.to_locations(),
+                        ConstraintCategory::TypeAnnotation,
+                    )
+                    .unwrap();
                 PlaceTy::from_ty(ty)
             }
         }

src/test/ui/type-alias-impl-trait/issue-96572-unconstrained-only-pattern.rs

@@ -0,0 +1,12 @@
+#![feature(type_alias_impl_trait)]
+// check-pass
+
+type T = impl Copy;
+
+fn foo(foo: T) {
+    let (mut x, mut y) = foo;
+    x = 42;
+    y = "foo";
+}
+
+fn main() {}