From d0f3c51f01271b71e6228a1d002bad347dc4aca1 Mon Sep 17 00:00:00 2001
From: Aaron Gokaslan <skylion.aaron@gmail.com>
Date: Mon, 20 Sep 2021 10:42:14 -0400
Subject: [PATCH] Enable defining custom __new__ (#3265)

* Enable defining custom __new__

* See if xfail needed

* Qualify auto self

* Unconditionally defining PYBIND11_DISABLE_NEW_STYLE_INIT_WARNING. Returning pointer from "__init__" instead of reference.

* Use new style __init__

* Simplify __new__ creation

* Reviewer suggestions

* Match indentation

Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>
---
 include/pybind11/pybind11.h |  3 ++-
 tests/test_class.cpp        | 15 +++++++++++++++
 tests/test_class.py         |  8 ++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index 07d2d0436..b8f5a6bae 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -416,7 +416,8 @@ protected:
         detail::function_record *chain = nullptr, *chain_start = rec;
         if (rec->sibling) {
             if (PyCFunction_Check(rec->sibling.ptr())) {
-                auto rec_capsule = reinterpret_borrow<capsule>(PyCFunction_GET_SELF(rec->sibling.ptr()));
+                auto *self = PyCFunction_GET_SELF(rec->sibling.ptr());
+                capsule rec_capsule = isinstance<capsule>(self) ? reinterpret_borrow<capsule>(self) : capsule(self);
                 chain = (detail::function_record *) rec_capsule;
                 /* Never append a method to an overload chain of a parent class;
                    instead, hide the parent's overloads in this case */
diff --git a/tests/test_class.cpp b/tests/test_class.cpp
index 246b6c1fe..0b998330d 100644
--- a/tests/test_class.cpp
+++ b/tests/test_class.cpp
@@ -47,10 +47,25 @@ TEST_SUBMODULE(class_, m) {
         }
         ~NoConstructor() { print_destroyed(this); }
     };
+    struct NoConstructorNew {
+        NoConstructorNew() = default;
+        NoConstructorNew(const NoConstructorNew &) = default;
+        NoConstructorNew(NoConstructorNew &&) = default;
+        static NoConstructorNew *new_instance() {
+            auto *ptr = new NoConstructorNew();
+            print_created(ptr, "via new_instance");
+            return ptr;
+        }
+        ~NoConstructorNew() { print_destroyed(this); }
+    };
 
     py::class_<NoConstructor>(m, "NoConstructor")
         .def_static("new_instance", &NoConstructor::new_instance, "Return an instance");
 
+    py::class_<NoConstructorNew>(m, "NoConstructorNew")
+        .def(py::init([](NoConstructorNew *self) { return self; })) // Need a NOOP __init__
+        .def_static("__new__", [](const py::object *) { return NoConstructorNew::new_instance(); } );
+
     // test_inheritance
     class Pet {
     public:
diff --git a/tests/test_class.py b/tests/test_class.py
index 85d453199..caafe2068 100644
--- a/tests/test_class.py
+++ b/tests/test_class.py
@@ -25,6 +25,14 @@ def test_instance(msg):
     assert cstats.alive() == 0
 
 
+def test_instance_new(msg):
+    instance = m.NoConstructorNew()  # .__new__(m.NoConstructor.__class__)
+    cstats = ConstructorStats.get(m.NoConstructorNew)
+    assert cstats.alive() == 1
+    del instance
+    assert cstats.alive() == 0
+
+
 def test_type():
     assert m.check_type(1) == m.DerivedClass1
     with pytest.raises(RuntimeError) as execinfo: