Add a test capturing new proposed expectation that Setuptools' build...

Add a test capturing new proposed expectation that Setuptools' build dependencies should not require setuptools to build in order to avoid inevitable conflicts when bootstrapping from source. Packaging fails this test. Ref #980

setuptools/tests/test_integration.py

@@ -98,3 +98,53 @@ def test_pbr(install_context):
 def test_python_novaclient(install_context):
     _install_one('python-novaclient', install_context,
                  'novaclient', 'base.py')
+
+import re
+import subprocess
+import functools
+import tarfile, zipfile
+
+
+build_deps = ['appdirs', 'packaging', 'pyparsing', 'six']
+@pytest.mark.parametrize("build_dep", build_deps)
+@pytest.mark.skipif(sys.version_info < (3, 6), reason='run only on late versions')
+def test_build_deps_on_distutils(request, tmpdir_factory, build_dep):
+    """
+    All setuptools build dependencies must build without
+    setuptools.
+    """
+    if 'pyparsing' in build_dep:
+        pytest.xfail(reason="Project imports setuptools unconditionally")
+    build_target = tmpdir_factory.mktemp('source')
+    build_dir = download_and_extract(request, build_dep, build_target)
+    install_target = tmpdir_factory.mktemp('target')
+    output = install(build_dir, install_target)
+    for line in output.splitlines():
+        match = re.search('Unknown distribution option: (.*)', line)
+        allowed_unknowns = [
+            'test_suite',
+            'tests_require',
+            'install_requires',
+        ]
+        assert not match or match.group(1).strip('"\'') in allowed_unknowns
+
+
+def install(pkg_dir, install_dir):
+    with open(os.path.join(pkg_dir, 'setuptools.py'), 'w') as breaker:
+        breaker.write('raise ImportError()')
+    cmd = [sys.executable, 'setup.py', 'install', '--prefix', install_dir]
+    env = dict(os.environ, PYTHONPATH=pkg_dir)
+    output = subprocess.check_output(cmd, cwd=pkg_dir, env=env, stderr=subprocess.STDOUT)
+    return output.decode('utf-8')
+
+
+def download_and_extract(request, req, target):
+    cmd = [sys.executable, '-m', 'pip', 'download', '--no-deps',
+        '--no-binary', ':all:', req]
+    output = subprocess.check_output(cmd, encoding='utf-8')
+    filename = re.search('Saved (.*)', output).group(1)
+    request.addfinalizer(functools.partial(os.remove, filename))
+    opener = zipfile.ZipFile if filename.endswith('.zip') else tarfile.open
+    with opener(filename) as archive:
+        archive.extractall(target)
+    return os.path.join(target, os.listdir(target)[0])