Install Cython alpha and disable build isolation under free-threaded

MANIFEST.in

@@ -12,6 +12,7 @@ graft docs
 graft CHANGES
 graft requirements
 graft tests
+graft scripts
 global-exclude *.pyc
 global-exclude *.cache
 exclude yarl/*.c

packaging/pep517_backend/_backend.py

@@ -4,7 +4,6 @@
 from __future__ import annotations
 
 import os
-import sysconfig
 import typing as t
 from contextlib import contextmanager, nullcontext, suppress
 from functools import partial
@@ -372,12 +371,7 @@ def get_requires_for_build_wheel(
             stacklevel=999,
         )
 
-    if is_pure_python_build:
-        c_ext_build_deps = []
-    elif sysconfig.get_config_var("Py_GIL_DISABLED"):
-        c_ext_build_deps = ['Cython == 3.1.0a1']
-    else:
-        c_ext_build_deps = ['Cython ~= 3.0.0']
+    c_ext_build_deps = [] if is_pure_python_build else ['Cython ~= 3.0.11']
 
     return _setuptools_get_requires_for_build_wheel(
         config_settings=config_settings,

pyproject.toml

@@ -79,6 +79,14 @@ test-command = 'pytest -v -m "not hypothesis" --no-cov {project}/tests'
 # don't build PyPy wheels, install from source instead
 skip = "pp*"
 
+# TODO: Remove this when there's a Cython 3.1 final release
+[[tool.cibuildwheel.overrides]]
+select = "cp313t-*"
+build-frontend = "build; args: --no-isolation"
+before-build = "bash {package}/scripts/cibw_before_build.sh"
+# Remove PIP_CONSTRAINT from the environment
+environment = {COLOR="yes", FORCE_COLOR="1", MYPY_FORCE_COLOR="1", PRE_COMMIT_COLOR="always", PY_COLORS="1"}
+
 [tool.cibuildwheel.environment]
 COLOR = "yes"
 FORCE_COLOR = "1"

requirements/cython.txt

@@ -1,2 +1 @@
-cython==3.1.0a1; python_version >= '3.13'
-cython==3.0.11; python_version <= '3.12'
+cython~=3.0.11

scripts/cibw_before_build.sh

@@ -2,6 +2,6 @@
 FREE_THREADED_BUILD="$(python -c"import sysconfig; print(bool(sysconfig.get_config_var('Py_GIL_DISABLED')))")"
 if [[ $FREE_THREADED_BUILD == "True" ]]; then
     python -m pip install -U pip
-    python -m pip install -i https://pypi.anaconda.org/scientific-python-nightly-wheels/simple cython
+    python -m pip install --pre cython==3.1.0a1
     python -m pip install setuptools expandvars
 fi