Bug Description

I'm getting error[E0425]: cannot find type `c_int` in this scope while trying to compile pyo3-ffi with Python 3.11.

This is for pyo3-ffi 0.26.0, but I can see that in the latest main the c_int declaration is still gated behind cfg(Py_3_12):

and still used ungated in the declaration of _Py_NegativeRefcount:

Full build logs: https://gist.github.com/fofoni/af1ff66279a1c5e1c41a396979f28e89

If I manually change #[cfg(Py_3_12)] to #[cfg(Py_3_11)] in $CARGO_HOME/registry/src/index.crates.io-1949cf8c6b5b557f/pyo3-ffi-0.26.0/src/refcount.rs, the build finishes successfully.

Steps to Reproduce

I can reproduce this while trying to build pydantic-core. This was reported here: pydantic/pydantic#12866

Backtrace

error[E0425]: cannot find type `c_int` in this scope
   --> /home/pedro/.local/lib/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/pyo3-ffi-0.26.0/src/refcount.rs:150:62
    |
150 |     fn _Py_NegativeRefcount(filename: *const c_char, lineno: c_int, op: *mut PyObject);
    |                                                              ^^^^^ not found in this scope
    |
note: found an item that was configured out
   --> /home/pedro/.local/lib/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/pyo3-ffi-0.26.0/src/refcount.rs:6:15
    |
  5 | #[cfg(Py_3_12)]
    |       ------- the item is gated here
  6 | use std::ffi::c_int;
    |               ^^^^^
help: consider importing one of these type aliases
    |
  1 + use std::ffi::c_int;
    |
  1 + use std::os::raw::c_int;
    |
  1 + use core::ffi::c_int;
    |
  1 + use libc::c_int;
    |

Your operating system and version

Ubuntu 24.04.2 LTS

Your Python version (python --version)

Python 3.11.14 (tags/v3.11.14:cd1c3a63428, Feb 26 2026, 08:30:42) [GCC 13.3.0] on linux (Debug build, from source)

Your Rust version (rustc --version)

rustc 1.93.1 (01f6ddf75 2026-02-11)

Your PyO3 version

pyo3-ffi 0.26.0

How did you install python? Did you use a virtualenv?

Build from source: ./configure --with-pydebug, and using -O0.