Don't return pointers to static objects with return_value_policy::take_ownership. (#3946)

* Don't return pointers to static objects with return_value_policy::take_ownership.

This fixes -Wfree-nonheap-object warnings produced by GCC.

* Use return value policy fix instead

Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

tests/test_builtin_casters.cpp

@@ -267,7 +267,8 @@ TEST_SUBMODULE(builtin_casters, m) {
     m.def("lvalue_nested", []() -> const decltype(lvnested) & { return lvnested; });
 
     static std::pair<int, std::string> int_string_pair{2, "items"};
-    m.def("int_string_pair", []() { return &int_string_pair; });
+    m.def(
+        "int_string_pair", []() { return &int_string_pair; }, py::return_value_policy::reference);
 
     // test_builtins_cast_return_none
     m.def("return_none_string", []() -> std::string * { return nullptr; });

tests/test_stl.cpp

@@ -177,7 +177,8 @@ TEST_SUBMODULE(stl, m) {
           [](const std::vector<bool> &v) { return v.at(0) == true && v.at(1) == false; });
     // Unnumbered regression (caused by #936): pointers to stl containers aren't castable
     static std::vector<RValueCaster> lvv{2};
-    m.def("cast_ptr_vector", []() { return &lvv; });
+    m.def(
+        "cast_ptr_vector", []() { return &lvv; }, py::return_value_policy::reference);
 
     // test_deque
     m.def("cast_deque", []() { return std::deque<int>{1}; });