Cython source files missing in sdist

[mgorny]

When trying to build from 0.6.2 with cython-always option, I'm getting the following error:

Traceback (most recent call last):
 File "<frozen runpy>", line 198, in _run_module_as_main
 File "<frozen runpy>", line 88, in _run_code
 File "/usr/lib/python3.12/site-packages/gpep517/__main__.py", line 443, in <module>
 sys.exit(main())
 ^^^^^^
 File "/usr/lib/python3.12/site-packages/gpep517/__main__.py", line 439, in main
 return func(args)
 ^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/gpep517/__main__.py", line 229, in build_wheel
 print(build_wheel_impl(args, args.wheel_dir), file=out)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/gpep517/__main__.py", line 221, in build_wheel_impl
 wheel_name = backend.build_wheel(str(wheel_dir), args.config_json)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/setuptools/build_meta.py", line 421, in build_wheel
 return self._build_with_temp_dir(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/setuptools/build_meta.py", line 403, in _build_with_temp_dir
 self.run_setup()
 File "/usr/lib/python3.12/site-packages/setuptools/build_meta.py", line 503, in run_setup
 super().run_setup(setup_script=setup_script)
 File "/usr/lib/python3.12/site-packages/setuptools/build_meta.py", line 318, in run_setup
 exec(code, locals())
 File "<string>", line 171, in <module>
 File "/usr/lib/python3.12/site-packages/setuptools/__init__.py", line 117, in setup
 return distutils.core.setup(**attrs)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/core.py", line 184, in setup
 return run_commands(dist)
 ^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/core.py", line 200, in run_commands
 dist.run_commands()
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 954, in run_commands
 self.run_command(cmd)
 File "/usr/lib/python3.12/site-packages/setuptools/dist.py", line 950, in run_command
 super().run_command(command)
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 973, in run_command
 cmd_obj.run()
 File "/usr/lib/python3.12/site-packages/setuptools/command/bdist_wheel.py", line 384, in run
 self.run_command("build")
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/cmd.py", line 316, in run_command
 self.distribution.run_command(command)
 File "/usr/lib/python3.12/site-packages/setuptools/dist.py", line 950, in run_command
 super().run_command(command)
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 973, in run_command
 cmd_obj.run()
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/command/build.py", line 135, in run
 self.run_command(cmd_name)
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/cmd.py", line 316, in run_command
 self.distribution.run_command(command)
 File "/usr/lib/python3.12/site-packages/setuptools/dist.py", line 950, in run_command
 super().run_command(command)
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 973, in run_command
 cmd_obj.run()
 File "/usr/lib/python3.12/site-packages/setuptools/command/build_py.py", line 78, in run
 self.build_package_data()
 File "/usr/lib/python3.12/site-packages/setuptools/command/build_py.py", line 175, in build_package_data
 for target, srcfile in self._get_package_data_output_mapping():
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/setuptools/command/build_py.py", line 167, in _get_package_data_output_mapping
 for package, src_dir, build_dir, filenames in self.data_files:
 ^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/setuptools/command/build_py.py", line 87, in __getattr__
 self.data_files = self._get_data_files()
 ^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/setuptools/command/build_py.py", line 99, in _get_data_files
 self.analyze_manifest()
 File "/usr/lib/python3.12/site-packages/setuptools/command/build_py.py", line 197, in analyze_manifest
 self.run_command('egg_info')
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/cmd.py", line 316, in run_command
 self.distribution.run_command(command)
 File "/usr/lib/python3.12/site-packages/setuptools/dist.py", line 950, in run_command
 super().run_command(command)
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/dist.py", line 973, in run_command
 cmd_obj.run()
 File "/usr/lib/python3.12/site-packages/setuptools/command/egg_info.py", line 311, in run
 self.find_sources()
 File "/usr/lib/python3.12/site-packages/setuptools/command/egg_info.py", line 319, in find_sources
 mm.run()
 File "/usr/lib/python3.12/site-packages/setuptools/command/egg_info.py", line 540, in run
 self.add_defaults()
 File "/usr/lib/python3.12/site-packages/setuptools/command/egg_info.py", line 578, in add_defaults
 sdist.add_defaults(self)
 File "/usr/lib/python3.12/site-packages/setuptools/command/sdist.py", line 108, in add_defaults
 super().add_defaults()
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/command/sdist.py", line 250, in add_defaults
 self._add_defaults_ext()
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/command/sdist.py", line 334, in _add_defaults_ext
 build_ext = self.get_finalized_command('build_ext')
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/cmd.py", line 303, in get_finalized_command
 cmd_obj.ensure_finalized()
 File "/usr/lib/python3.12/site-packages/setuptools/_distutils/cmd.py", line 111, in ensure_finalized
 self.finalize_options()
 File "<string>", line 105, in finalize_options
 File "/usr/lib/python3.12/site-packages/Cython/Build/Dependencies.py", line 1010, in cythonize
 module_list, module_metadata = create_extension_list(
 ^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.12/site-packages/Cython/Build/Dependencies.py", line 845, in create_extension_list
 for file in nonempty(sorted(extended_iglob(filepattern)), "'%s' doesn't match any files" % filepattern):
 File "/usr/lib/python3.12/site-packages/Cython/Build/Dependencies.py", line 117, in nonempty
 raise ValueError(error_msg)
ValueError: 'httptools/parser/parser.pyx' doesn't match any files

And indeed, the file is missing from the tarball.