Setuptools compatibility with cli_run

Signed-off-by: Bernat Gabor <bgabor8@bloomberg.net>

docs/changelog/1771.bugfix.rst

@@ -0,0 +1,2 @@
+Importing setuptools before cli_run could cause our python information query to fail due to setuptools patching
+``distutils.dist.Distribution`` - by :user:`gaborbernat`.

src/virtualenv/discovery/py_info.py

@@ -13,8 +13,8 @@
 import sys
 import sysconfig
 from collections import OrderedDict, namedtuple
+from distutils import dist
 from distutils.command.install import SCHEME_KEYS
-from distutils.dist import Distribution
 from string import digits
 
 VersionInfo = namedtuple("VersionInfo", ["major", "minor", "micro", "releaselevel", "serial"])
@@ -110,7 +110,8 @@ def _fast_get_system_executable(self):
     @staticmethod
     def _distutils_install():
         # follow https://github.com/pypa/pip/blob/master/src/pip/_internal/locations.py#L95
-        d = Distribution({"script_args": "--no-user-cfg"})  # configuration files not parsed so they do not hijack paths
+        # note here we don't import Distribution directly to allow setuptools to patch it
+        d = dist.Distribution({"script_args": "--no-user-cfg"})  # conf files not parsed so they do not hijack paths
         if hasattr(sys, "_framework"):
             sys._framework = None  # disable macOS static paths for framework
         i = d.get_command_obj("install", create=True)

tests/unit/test_run.py

@@ -1,5 +1,8 @@
 from __future__ import absolute_import, unicode_literals
 
+import subprocess
+import sys
+
 import pytest
 import six
 
@@ -31,3 +34,16 @@ def test_version(capsys):
     import virtualenv
 
     assert virtualenv.__file__ in content
+
+
+def test_cli_run_setuptools_compatible(capfd, tmp_path):
+    subprocess.check_call(
+        [
+            sys.executable,
+            "-c",
+            "from setuptools import find_packages;" "from virtualenv import cli_run; cli_run([r'{}'])".format(tmp_path),
+        ]
+    )
+    out, err = capfd.readouterr()
+    assert out
+    assert not err