Add support custom sized operator deletes (#952)

If a class doesn't provide a `T::operator delete(void *)` but does have
a `T::operator delete(void *, size_t)` the latter is invoked by a
`delete someT`.  Pybind currently only look for and call the former;
this commit adds detection and calling of the latter when the former
doesn't exist.

include/pybind11/pybind11.h

@@ -906,11 +906,19 @@ void set_operator_new(type_record *r) { r->operator_new = &T::operator new; }
 
 template <typename> void set_operator_new(...) { }
 
+template <typename T, typename SFINAE = void> struct has_operator_delete : std::false_type { };
+template <typename T> struct has_operator_delete<T, void_t<decltype(static_cast<void (*)(void *)>(T::operator delete))>>
+    : std::true_type { };
+template <typename T, typename SFINAE = void> struct has_operator_delete_size : std::false_type { };
+template <typename T> struct has_operator_delete_size<T, void_t<decltype(static_cast<void (*)(void *, size_t)>(T::operator delete))>>
+    : std::true_type { };
 /// Call class-specific delete if it exists or global otherwise. Can also be an overload set.
-template <typename T, typename = void_t<decltype(static_cast<void (*)(void *)>(T::operator delete))>>
-void call_operator_delete(T *p) { T::operator delete(p); }
+template <typename T, enable_if_t<has_operator_delete<T>::value, int> = 0>
+void call_operator_delete(T *p, size_t) { T::operator delete(p); }
+template <typename T, enable_if_t<!has_operator_delete<T>::value && has_operator_delete_size<T>::value, int> = 0>
+void call_operator_delete(T *p, size_t s) { T::operator delete(p, s); }
 
-inline void call_operator_delete(void *p) { ::operator delete(p); }
+inline void call_operator_delete(void *p, size_t) { ::operator delete(p); }
 
 NAMESPACE_END(detail)
 
@@ -1212,7 +1220,7 @@ private:
         if (v_h.holder_constructed())
             v_h.holder<holder_type>().~holder_type();
         else
-            detail::call_operator_delete(v_h.value_ptr<type>());
+            detail::call_operator_delete(v_h.value_ptr<type>(), v_h.type->type_size);
     }
 
     static detail::function_record *get_function_record(handle h) {

tests/test_class.cpp

@@ -184,6 +184,46 @@ TEST_SUBMODULE(class_, m) {
         auto def = new PyMethodDef{"f", f, METH_VARARGS, nullptr};
         return py::reinterpret_steal<py::object>(PyCFunction_NewEx(def, nullptr, m.ptr()));
     }());
+
+    // test_operator_new_delete
+    struct HasOpNewDel {
+        std::uint64_t i;
+        static void *operator new(size_t s) { py::print("A new", s); return ::operator new(s); }
+        static void *operator new(size_t s, void *ptr) { py::print("A placement-new", s); return ptr; }
+        static void operator delete(void *p) { py::print("A delete"); return ::operator delete(p); }
+    };
+    struct HasOpNewDelSize {
+        std::uint32_t i;
+        static void *operator new(size_t s) { py::print("B new", s); return ::operator new(s); }
+        static void *operator new(size_t s, void *ptr) { py::print("B placement-new", s); return ptr; }
+        static void operator delete(void *p, size_t s) { py::print("B delete", s); return ::operator delete(p); }
+    };
+    struct AliasedHasOpNewDelSize {
+        std::uint64_t i;
+        static void *operator new(size_t s) { py::print("C new", s); return ::operator new(s); }
+        static void *operator new(size_t s, void *ptr) { py::print("C placement-new", s); return ptr; }
+        static void operator delete(void *p, size_t s) { py::print("C delete", s); return ::operator delete(p); }
+        virtual ~AliasedHasOpNewDelSize() = default;
+    };
+    struct PyAliasedHasOpNewDelSize : AliasedHasOpNewDelSize {
+        PyAliasedHasOpNewDelSize() = default;
+        PyAliasedHasOpNewDelSize(int) { }
+        std::uint64_t j;
+    };
+    struct HasOpNewDelBoth {
+        std::uint32_t i[8];
+        static void *operator new(size_t s) { py::print("D new", s); return ::operator new(s); }
+        static void *operator new(size_t s, void *ptr) { py::print("D placement-new", s); return ptr; }
+        static void operator delete(void *p) { py::print("D delete"); return ::operator delete(p); }
+        static void operator delete(void *p, size_t s) { py::print("D wrong delete", s); return ::operator delete(p); }
+    };
+    py::class_<HasOpNewDel>(m, "HasOpNewDel").def(py::init<>());
+    py::class_<HasOpNewDelSize>(m, "HasOpNewDelSize").def(py::init<>());
+    py::class_<HasOpNewDelBoth>(m, "HasOpNewDelBoth").def(py::init<>());
+    py::class_<AliasedHasOpNewDelSize, PyAliasedHasOpNewDelSize> aliased(m, "AliasedHasOpNewDelSize");
+    aliased.def(py::init<>());
+    aliased.attr("size_noalias") = py::int_(sizeof(AliasedHasOpNewDelSize));
+    aliased.attr("size_alias") = py::int_(sizeof(PyAliasedHasOpNewDelSize));
 }
 
 template <int N> class BreaksBase {};

tests/test_class.py

@@ -127,3 +127,55 @@ def test_implicit_conversion_life_support():
     assert m.implicitly_convert_variable(UserType(5)) == 5
 
     assert "outside a bound function" in m.implicitly_convert_variable_fail(UserType(5))
+
+
+def test_operator_new_delete(capture):
+    """Tests that class-specific operator new/delete functions are invoked"""
+
+    class SubAliased(m.AliasedHasOpNewDelSize):
+        pass
+
+    with capture:
+        a = m.HasOpNewDel()
+        b = m.HasOpNewDelSize()
+        d = m.HasOpNewDelBoth()
+    assert capture == """
+        A new 8
+        A placement-new 8
+        B new 4
+        B placement-new 4
+        D new 32
+        D placement-new 32
+    """
+    sz_alias = str(m.AliasedHasOpNewDelSize.size_alias)
+    sz_noalias = str(m.AliasedHasOpNewDelSize.size_noalias)
+    with capture:
+        c = m.AliasedHasOpNewDelSize()
+        c2 = SubAliased()
+    assert capture == (
+        "C new " + sz_alias + "\nC placement-new " + sz_noalias + "\n" +
+        "C new " + sz_alias + "\nC placement-new " + sz_alias + "\n"
+    )
+
+    with capture:
+        del a
+        ConstructorStats.detail_reg_inst()
+        del b
+        ConstructorStats.detail_reg_inst()
+        del d
+        ConstructorStats.detail_reg_inst()
+    assert capture == """
+        A delete
+        B delete 4
+        D delete
+    """
+
+    with capture:
+        del c
+        ConstructorStats.detail_reg_inst()
+        del c2
+        ConstructorStats.detail_reg_inst()
+    assert capture == (
+        "C delete " + sz_noalias + "\n" +
+        "C delete " + sz_alias + "\n"
+    )