From c08375baeba22bee4596c9fb7534ed6a39db71e5 Mon Sep 17 00:00:00 2001
From: Bas Schoenmaeckers <7943856+bschoenmaeckers@users.noreply.github.com>
Date: Mon, 19 Oct 2026 18:45:53 +0200
Subject: [PATCH] Implement `PyType_FromSpec` & `PyType_FromMetaclass` (#9213)

* Implement `PyType_FromSpec` & `PyType_FromMetaclass`

* Review
---
 crates/capi/src/object/pytype.rs | 88 ++++++++++++++++++++++++++++++--
 crates/capi/src/slots.rs         | 28 ++++++++++
 2 files changed, 113 insertions(+), 3 deletions(-)

diff --git a/crates/capi/src/object/pytype.rs b/crates/capi/src/object/pytype.rs
index 27254dc83..77d8627d0 100644
--- a/crates/capi/src/object/pytype.rs
+++ b/crates/capi/src/object/pytype.rs
@@ -5,7 +5,8 @@ use crate::pystate::with_vm;
 use crate::slots::{PySlot, PySlotKind, PySlotType};
 use crate::util::CStrExt;
 use crate::util::FfiPtrExt;
-use core::ffi::{c_char, c_int, c_ulong, c_void};
+use core::ffi::{c_char, c_int, c_uint, c_ulong, c_void};
+use core::ptr;
 use rustpython_vm::builtins::{PyStr, PyType};
 use rustpython_vm::function::{ItemDoc, PyMethodFlags};
 use rustpython_vm::types::{AtomicPyTypeFlags, PyTypeFlags, PyTypeSlots, SlotAccessor};
@@ -22,6 +23,15 @@ pub struct PyType_Slot {
     pub pfunc: *mut c_void,
 }
 
+#[repr(C)]
+pub struct PyType_Spec {
+    pub name: *const c_char,
+    pub basicsize: c_int,
+    pub itemsize: c_int,
+    pub flags: c_uint,
+    pub slots: *mut PyType_Slot,
+}
+
 impl PyType_Slot {
     pub(crate) fn iter<'a>(mut slots: *const Self) -> impl Iterator<Item = &'a Self> {
         core::iter::from_fn(move || {
@@ -104,11 +114,11 @@ pub unsafe extern "C" fn PyType_GetFullyQualifiedName(ptr: *mut PyTypeObject) ->
 
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn PyType_GetSlot(_ty: *const PyTypeObject, _slot: c_int) -> *mut c_void {
-    core::ptr::null_mut()
+    ptr::null_mut()
 }
 
 #[unsafe(no_mangle)]
-pub extern "C" fn PyType_FromSlots(slots: *const PySlot) -> *mut PyObject {
+pub unsafe extern "C" fn PyType_FromSlots(slots: *const PySlot) -> *mut PyObject {
     with_vm(|vm| {
         let mut name = None;
         let mut base = None;
@@ -254,6 +264,78 @@ pub extern "C" fn PyType_FromSlots(slots: *const PySlot) -> *mut PyObject {
     })
 }
 
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn PyType_FromMetaclass(
+    metaclass: *mut PyTypeObject,
+    module: *mut PyObject,
+    spec: *mut PyType_Spec,
+    bases: *mut PyObject,
+) -> *mut PyObject {
+    let &PyType_Spec {
+        name,
+        basicsize,
+        itemsize,
+        flags,
+        slots: type_slots,
+    } = unsafe { &*spec };
+    let mut slots = [PySlot::SLOT_END; 9];
+    let mut write_slot = {
+        let mut iter = slots.iter_mut();
+        move |slot| {
+            debug_assert!(
+                iter.len() >= 2,
+                "PyType_FromMetaclass: last slot is reserved for SLOT_END"
+            );
+            let entry = iter
+                .next()
+                .expect("Too many slots for PyType_FromMetaclass");
+            *entry = slot;
+        }
+    };
+
+    if !bases.is_null() {
+        write_slot(PySlot::new(49, bases));
+    }
+
+    if !metaclass.is_null() {
+        write_slot(PySlot::new(107, metaclass));
+    }
+
+    if !module.is_null() {
+        write_slot(PySlot::new(108, module));
+    }
+
+    write_slot(PySlot::new(95, name.cast_mut()));
+    write_slot(PySlot::new(96, basicsize as isize));
+    write_slot(PySlot::new(98, itemsize as isize));
+    write_slot(PySlot::new(99, flags as u64));
+    write_slot(PySlot::new(93, type_slots));
+
+    unsafe { PyType_FromSlots(slots.as_ptr()) }
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn PyType_FromModuleAndSpec(
+    module: *mut PyObject,
+    spec: *mut PyType_Spec,
+    bases: *mut PyObject,
+) -> *mut PyObject {
+    unsafe { PyType_FromMetaclass(ptr::null_mut(), module, spec, bases) }
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn PyType_FromSpecWithBases(
+    spec: *mut PyType_Spec,
+    bases: *mut PyObject,
+) -> *mut PyObject {
+    unsafe { PyType_FromMetaclass(ptr::null_mut(), ptr::null_mut(), spec, bases) }
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn PyType_FromSpec(spec: *mut PyType_Spec) -> *mut PyObject {
+    unsafe { PyType_FromMetaclass(ptr::null_mut(), ptr::null_mut(), spec, ptr::null_mut()) }
+}
+
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn PyObject_GetTypeData(
     obj: *mut PyObject,
diff --git a/crates/capi/src/slots.rs b/crates/capi/src/slots.rs
index 79b11c7b4..96a4df5a8 100644
--- a/crates/capi/src/slots.rs
+++ b/crates/capi/src/slots.rs
@@ -20,6 +20,16 @@ impl PySlot {
     const SLOT_OPTIONAL: u16 = 0x0001;
     const SLOT_STATIC: u16 = 0x0002;
     const SLOT_INTPTR: u16 = 0x0004;
+    pub(crate) const SLOT_END: Self = unsafe { core::mem::zeroed() };
+
+    pub(crate) fn new(id: u16, value: impl Into<PySlotValue>) -> Self {
+        Self {
+            sl_id: id,
+            sl_flags: 0,
+            _reserved: 0,
+            value: value.into(),
+        }
+    }
 
     pub(crate) fn iter<'a>(mut slots: *const Self) -> impl Iterator<Item = &'a Self> {
         core::iter::from_fn(move || {
@@ -130,6 +140,24 @@ pub union PySlotValue {
     pub sl_uint64: u64,
 }
 
+impl<T> From<*mut T> for PySlotValue {
+    fn from(ptr: *mut T) -> Self {
+        Self { sl_ptr: ptr.cast() }
+    }
+}
+
+impl From<isize> for PySlotValue {
+    fn from(size: isize) -> Self {
+        Self { sl_size: size }
+    }
+}
+
+impl From<u64> for PySlotValue {
+    fn from(value: u64) -> Self {
+        Self { sl_uint64: value }
+    }
+}
+
 #[allow(dead_code)]
 #[derive(Debug, Copy, Clone)]
 pub(crate) enum PySlotModule<'a> {