Explicitly support having a WeakRef to self

tests/test_reference.cpp

@@ -445,3 +445,17 @@ TEST_CASE("Polymorphic edge cases") {
     CHECK(base_ref_from_weak.get() == derived_ref.get());
   }
 }
+
+// Should be run with asan or valgrind
+TEST_CASE("Self-referencing WeakRef pattern") {
+  struct AmIAlive {
+    volatile int x;
+    ~AmIAlive() { x = 0; }
+  };
+  struct SelfReferencing {
+    AmIAlive am;
+    WeakRef<SelfReferencing> self_;
+  };
+  auto x = make_ref<SelfReferencing>();
+  x->self_ = x;
+}