Rewrite selective PIP_IGNORE_REQUIRES_PYTHON to allow test dependencies in...

Rewrite selective PIP_IGNORE_REQUIRES_PYTHON to allow test dependencies in metadata to be installed without ignoring REQUIRES_PYTHON

setuptools/tests/test_virtualenv.py

@@ -12,6 +12,17 @@ from .textwrap import DALS
 from .test_easy_install import make_nspkg_sdist
 
 
+@pytest.fixture(autouse=True)
+def disable_requires_python(monkeypatch):
+    """
+    Disable Requires-Python on Python 2.7
+    """
+    if sys.version_info > (3,):
+        return
+
+    monkeypatch.setenv('PIP_IGNORE_REQUIRES_PYTHON', 'true')
+
+
 @pytest.fixture(autouse=True)
 def pytest_virtualenv_works(virtualenv):
     """

tools/tox_pip.py

@@ -38,18 +38,43 @@ def is_install_self(args):
     )
 
 
-def pip(args):
-    # Honor requires-python when installing test suite dependencies
-    if any('-r' in arg for arg in args):
-        os.environ['PIP_IGNORE_REQUIRES_PYTHON'] = '0'
+def pip(*args):
+    cmd = [sys.executable, '-m', 'pip'] + list(args)
+    return subprocess.check_call(cmd)
 
+
+def test_dependencies():
+    from ConfigParser import ConfigParser
+
+    def clean(dep):
+        spec, _, _ = dep.partition('#')
+        return spec.strip()
+
+    parser = ConfigParser()
+    parser.read('setup.cfg')
+    raw = parser.get('options.extras_require', 'tests').split('\n')
+    return filter(None, map(clean, raw))
+
+
+def disable_python_requires():
+    """
+    On Python 2, install the dependencies that are selective
+    on Python version while honoring REQUIRES_PYTHON, then
+    disable REQUIRES_PYTHON so that pip can install this
+    checkout of setuptools.
+    """
+    pip('install', *test_dependencies())
+    os.environ['PIP_IGNORE_REQUIRES_PYTHON'] = 'true'
+
+
+def run(args):
     if is_install_self(args):
         remove_setuptools()
         bootstrap()
+        sys.version_info > (3,) or disable_python_requires()
 
-    cmd = [sys.executable, '-m', 'pip'] + args
-    subprocess.check_call(cmd)
+    pip(*args)
 
 
 if __name__ == '__main__':
-    pip(sys.argv[1:])
+    run(sys.argv[1:])

tox.ini

@@ -18,7 +18,6 @@ install_command = {[helpers]pip} install {opts} {packages}
 list_dependencies_command = {[helpers]pip} freeze --all
 setenv =
 	COVERAGE_FILE={toxworkdir}/.coverage.{envname}
-	py27: PIP_IGNORE_REQUIRES_PYTHON=true
 # TODO: The passed environment variables came from copying other tox.ini files
 # These should probably be individually annotated to explain what needs them.
 passenv=APPDATA HOMEDRIVE HOMEPATH windir APPVEYOR APPVEYOR_* CI CODECOV_* TRAVIS TRAVIS_* NETWORK_REQUIRED