From c2ac9a98e2316e42e59cf8b07f0e24ff244afbb7 Mon Sep 17 00:00:00 2001
From: Georg Brandl <georg@python.org>
Date: Mon, 22 Apr 2024 10:56:39 +0200
Subject: [PATCH] fix vectorcall argument handling (#4104)

Fixes #4093

- Make PY_VECTORCALL_ARGUMENTS_OFFSET a size_t like on CPython
- Remove the assert in PyVectorcall_NARGS and use checked cast
---
 newsfragments/4104.fixed.md       |  1 +
 pyo3-ffi/src/cpython/abstract_.rs | 16 +++++++---------
 2 files changed, 8 insertions(+), 9 deletions(-)
 create mode 100644 newsfragments/4104.fixed.md

diff --git a/newsfragments/4104.fixed.md b/newsfragments/4104.fixed.md
new file mode 100644
index 00000000..3eff1654
--- /dev/null
+++ b/newsfragments/4104.fixed.md
@@ -0,0 +1 @@
+Changes definitions of `PY_VECTORCALL_ARGUMENTS_OFFSET` and `PyVectorcall_NARGS` to fix a false-positive assertion.
diff --git a/pyo3-ffi/src/cpython/abstract_.rs b/pyo3-ffi/src/cpython/abstract_.rs
index cf95f671..ad28216c 100644
--- a/pyo3-ffi/src/cpython/abstract_.rs
+++ b/pyo3-ffi/src/cpython/abstract_.rs
@@ -4,8 +4,6 @@ use std::os::raw::{c_char, c_int};
 #[cfg(not(Py_3_11))]
 use crate::Py_buffer;
 
-#[cfg(Py_3_8)]
-use crate::pyport::PY_SSIZE_T_MAX;
 #[cfg(all(Py_3_8, not(any(PyPy, GraalPy))))]
 use crate::{
     vectorcallfunc, PyCallable_Check, PyThreadState, PyThreadState_GET, PyTuple_Check,
@@ -42,14 +40,14 @@ extern "C" {
 }
 
 #[cfg(Py_3_8)]
-const PY_VECTORCALL_ARGUMENTS_OFFSET: Py_ssize_t =
-    1 << (8 * std::mem::size_of::<Py_ssize_t>() as Py_ssize_t - 1);
+const PY_VECTORCALL_ARGUMENTS_OFFSET: size_t =
+    1 << (8 * std::mem::size_of::<size_t>() as size_t - 1);
 
 #[cfg(Py_3_8)]
 #[inline(always)]
 pub unsafe fn PyVectorcall_NARGS(n: size_t) -> Py_ssize_t {
-    assert!(n <= (PY_SSIZE_T_MAX as size_t));
-    (n as Py_ssize_t) & !PY_VECTORCALL_ARGUMENTS_OFFSET
+    let n = n & !PY_VECTORCALL_ARGUMENTS_OFFSET;
+    n.try_into().expect("cannot fail due to mask")
 }
 
 #[cfg(all(Py_3_8, not(any(PyPy, GraalPy))))]
@@ -184,7 +182,7 @@ pub unsafe fn PyObject_CallOneArg(func: *mut PyObject, arg: *mut PyObject) -> *m
     let args = args_array.as_ptr().offset(1); // For PY_VECTORCALL_ARGUMENTS_OFFSET
     let tstate = PyThreadState_GET();
     let nargsf = 1 | PY_VECTORCALL_ARGUMENTS_OFFSET;
-    _PyObject_VectorcallTstate(tstate, func, args, nargsf as size_t, std::ptr::null_mut())
+    _PyObject_VectorcallTstate(tstate, func, args, nargsf, std::ptr::null_mut())
 }
 
 extern "C" {
@@ -206,7 +204,7 @@ pub unsafe fn PyObject_CallMethodNoArgs(
     PyObject_VectorcallMethod(
         name,
         &self_,
-        1 | PY_VECTORCALL_ARGUMENTS_OFFSET as size_t,
+        1 | PY_VECTORCALL_ARGUMENTS_OFFSET,
         std::ptr::null_mut(),
     )
 }
@@ -223,7 +221,7 @@ pub unsafe fn PyObject_CallMethodOneArg(
     PyObject_VectorcallMethod(
         name,
         args.as_ptr(),
-        2 | PY_VECTORCALL_ARGUMENTS_OFFSET as size_t,
+        2 | PY_VECTORCALL_ARGUMENTS_OFFSET,
         std::ptr::null_mut(),
     )
 }