Use standard python infrastructure to mark extensions as optional

setup.cfg

@@ -10,6 +10,7 @@ url = https://www.dulwich.io/
 author = Jelmer Vernooij
 author_email = jelmer@jelmer.uk
 license = Apachev2 or later or GPLv2
+keywords = vcs, git
 classifiers =
     Development Status :: 4 - Beta
     License :: OSI Approved :: Apache Software License
@@ -41,10 +42,6 @@ console_scripts =
 
 [options]
 python_requires = >=3.6
-scripts =
-    bin/dul-receive-pack
-    bin/dul-upload-pack
-zip_safe = False
 packages =
     dulwich
     dulwich.cloud
@@ -54,3 +51,7 @@ packages =
 include_package_data = True
 install_requires =
     urllib3>=1.25
+zip_safe = False
+scripts =
+    bin/dul-receive-pack
+    bin/dul-upload-pack

setup.py

@@ -3,7 +3,7 @@
 # Setup file for dulwich
 # Copyright (C) 2008-2022 Jelmer Vernooij <jelmer@jelmer.uk>
 
-from setuptools import setup, Extension, Distribution
+from setuptools import setup, Extension
 import os
 import sys
 
@@ -14,25 +14,6 @@ if sys.version_info < (3, 6):
         'For 2.7 support, please install a version prior to 0.20')
 
 
-dulwich_version_string = '0.20.46'
-
-
-class DulwichDistribution(Distribution):
-
-    def is_pure(self):
-        if self.pure:
-            return True
-
-    def has_ext_modules(self):
-        return not self.pure
-
-    global_options = Distribution.global_options + [
-        ('pure', None, "use pure Python code instead of C "
-                       "extensions (slower on CPython)")]
-
-    pure = False
-
-
 if sys.platform == 'darwin' and os.path.exists('/usr/bin/xcodebuild'):
     # XCode 4.0 dropped support for ppc architecture, which is hardcoded in
     # distutils.sysconfig
@@ -56,15 +37,18 @@ if '__pypy__' not in sys.modules and sys.platform != 'win32':
         'gevent', 'geventhttpclient', 'setuptools>=17.1'])
 
 
+optional = os.environ.get('CIBUILDWHEEL', '0') != '1'
+
+
 ext_modules = [
-    Extension('dulwich._objects', ['dulwich/_objects.c']),
-    Extension('dulwich._pack', ['dulwich/_pack.c']),
-    Extension('dulwich._diff_tree', ['dulwich/_diff_tree.c']),
+    Extension('dulwich._objects', ['dulwich/_objects.c'],
+              optional=optional),
+    Extension('dulwich._pack', ['dulwich/_pack.c'],
+              optional=optional),
+    Extension('dulwich._diff_tree', ['dulwich/_diff_tree.c'],
+              optional=optional),
 ]
 
-
-setup(keywords="git vcs",
-      package_data={'': ['../docs/tutorial/*.txt', 'py.typed']},
+setup(package_data={'': ['../docs/tutorial/*.txt', 'py.typed']},
       ext_modules=ext_modules,
-      distclass=DulwichDistribution,  # type: ignore
       tests_require=tests_require)