passenv respects PYTHONPATH. Fixes tox-dev#457

Author: jarshwah

tests/test_venv.py

@@ -561,6 +561,31 @@ def test_envbinddir_path(self, newmocksession, monkeypatch):
         assert 'PIP_REQUIRE_VIRTUALENV' not in os.environ
         assert '__PYVENV_LAUNCHER__' not in os.environ
 
+    def test_pythonpath_usage(self, newmocksession, monkeypatch):
+        monkeypatch.setenv("PYTHONPATH", "/my/awesome/library")
+        mocksession = newmocksession([], """
+            [testenv:python]
+            commands=abc
+        """)
+        venv = mocksession.getenv("python")
+        action = mocksession.newaction(venv, "getenv")
+        venv.run_install_command(['qwe'], action=action)
+        assert 'PYTHONPATH' not in os.environ
+        mocksession.report.expect("warning", "*Discarding $PYTHONPATH from environment*")
+
+        # passenv = PYTHONPATH allows PYTHONPATH to stay in environment
+        monkeypatch.setenv("PYTHONPATH", "/my/awesome/library")
+        mocksession = newmocksession([], """
+            [testenv:python]
+            commands=abc
+            passenv = PYTHONPATH
+        """)
+        venv = mocksession.getenv("python")
+        action = mocksession.newaction(venv, "getenv")
+        venv.run_install_command(['qwe'], action=action)
+        assert 'PYTHONPATH' in os.environ
+        mocksession.report.not_expect("warning", "*Discarding $PYTHONPATH from environment*")
+
 
 def test_env_variables_added_to_pcall(tmpdir, mocksession, newconfig, monkeypatch):
     pkg = tmpdir.ensure("package.tar.gz")

tox/venv.py

@@ -275,9 +275,18 @@ def run_install_command(self, packages, action, options=()):
             argv[i:i + 1] = list(options)
 
         for x in ('PIP_RESPECT_VIRTUALENV', 'PIP_REQUIRE_VIRTUALENV',
-                  '__PYVENV_LAUNCHER__', 'PYTHONPATH'):
+                  '__PYVENV_LAUNCHER__'):
             os.environ.pop(x, None)
 
+        if 'PYTHONPATH' not in self.envconfig.passenv:
+            # If PYTHONPATH not explicitly asked for, remove it.
+            if 'PYTHONPATH' in os.environ:
+                self.session.report.warning(
+                    "Discarding $PYTHONPATH from environment, to override "
+                    "specify PYTHONPATH in 'passenv' in your environment."
+                )
+                os.environ.pop('PYTHONPATH')
+
         old_stdout = sys.stdout
         sys.stdout = codecs.getwriter('utf8')(sys.stdout)
         self._pcall(argv, cwd=self.envconfig.config.toxinidir, action=action,