Split minimum cffi version depending on Python version

cffi 1.17 for Python up to 3.13, 2.0 for 3.14+

Author: clin1234

pyproject.toml

@@ -25,7 +25,8 @@ dependencies = []
 
 [project.optional-dependencies]
 cffi = [
-    'cffi>=2.0.0b1 ; python_version >= "3.13" and platform_python_implementation != "PyPy"',
+    "cffi~=1.17; platform_python_implementation != 'PyPy' and python_version < '3.14'",
+    "cffi>=2.0.0b; platform_python_implementation != 'PyPy' and python_version >= '3.14'",
 ]
 
 [project.urls]
@@ -34,7 +35,8 @@ Documentation = "https://python-zstandard.readthedocs.io/en/latest/"
 
 [build-system]
 requires = [
-    "cffi>=2.0.0b1 ; platform_python_implementation != 'PyPy'",
+    "cffi~=1.17; platform_python_implementation != 'PyPy' and python_version < '3.14'",
+    "cffi>=2.0.0b; platform_python_implementation != 'PyPy' and python_version >= '3.14'",
     "packaging",
     "setuptools",
 ]

setup.py

@@ -10,6 +10,7 @@
 import os
 import platform
 import sys
+import sysconfig
 
 from setuptools import setup
 
@@ -30,8 +31,8 @@
 # garbage collection pitfalls.
 # Require 1.17 everywhere so we don't have to think about supporting older
 # versions.
-# Require 2.0 for improved free-threading support
-MINIMUM_CFFI_VERSION = "2.0"
+# Require 2.0 when building with 3.14+ for improved free-threading support
+MINIMUM_CFFI_VERSION = "2.0" if sys.version_info[0:2] >= (3, 14) else "1.17"
 
 ext_suffix = os.environ.get("SETUPTOOLS_EXT_SUFFIX")
 if ext_suffix:
@@ -90,6 +91,10 @@
 if platform.python_implementation() == "PyPy":
     C_BACKEND = False
 
+# cffi only supports no-GIL with Python 3.14+
+if platform.python_implementation() == "CPython" and sys.version_info[0:2] == (3, 13) and sysconfig.get_config_var("Py_GIL_DISABLED"):
+    CFFI_BACKEND = False
+
 if "--legacy" in sys.argv:
     SUPPORT_LEGACY = True
     sys.argv.remove("--legacy")