bpo-35872 and bpo-35873: Clears __PYVENV_LAUNCHER__ variable (GH-11745)

After reading __PYVENV_LAUNCHER__ we now set sys._base_executable value for later use.
Make the same changes for macOS to avoid extra platform checks.

Lib/multiprocessing/popen_spawn_win32.py

@@ -19,6 +19,13 @@ WINEXE = (sys.platform == 'win32' and getattr(sys, 'frozen', False))
 WINSERVICE = sys.executable.lower().endswith("pythonservice.exe")
 
 
+def _path_eq(p1, p2):
+    return p1 == p2 or os.path.normcase(p1) == os.path.normcase(p2)
+
+WINENV = (hasattr(sys, '_base_executable') and
+          not _path_eq(sys.executable, sys._base_executable))
+
+
 def _close_handles(*handles):
     for handle in handles:
         _winapi.CloseHandle(handle)
@@ -50,12 +57,23 @@ class Popen(object):
                                      pipe_handle=rhandle)
         cmd = ' '.join('"%s"' % x for x in cmd)
 
+        python_exe = spawn.get_executable()
+
+        # bpo-35797: When running in a venv, we bypass the redirect
+        # executor and launch our base Python.
+        if WINENV and _path_eq(python_exe, sys.executable):
+            python_exe = sys._base_executable
+            env = os.environ.copy()
+            env["__PYVENV_LAUNCHER__"] = sys.executable
+        else:
+            env = None
+
         with open(wfd, 'wb', closefd=True) as to_child:
             # start process
             try:
                 hp, ht, pid, tid = _winapi.CreateProcess(
-                    spawn.get_executable(), cmd,
-                    None, None, False, 0, None, None, None)
+                    python_exe, cmd,
+                    env, None, False, 0, None, None, None)
                 _winapi.CloseHandle(ht)
             except:
                 _winapi.CloseHandle(rhandle)

Lib/multiprocessing/spawn.py

@@ -29,19 +29,12 @@ __all__ = ['_main', 'freeze_support', 'set_executable', 'get_executable',
 if sys.platform != 'win32':
     WINEXE = False
     WINSERVICE = False
-    _WINENV = False
 else:
     WINEXE = getattr(sys, 'frozen', False)
     WINSERVICE = sys.executable.lower().endswith("pythonservice.exe")
-    _WINENV = '__PYVENV_LAUNCHER__' in os.environ
 
 if WINSERVICE:
     _python_exe = os.path.join(sys.exec_prefix, 'python.exe')
-elif _WINENV:
-    # bpo-35797: When running in a venv, we need to bypass the redirect
-    # executor and launch our base Python.
-    import _winapi
-    _python_exe = _winapi.GetModuleFileName(0)
 else:
     _python_exe = sys.executable
 

Lib/site.py

@@ -457,7 +457,14 @@ def venv(known_paths):
 
     env = os.environ
     if sys.platform == 'darwin' and '__PYVENV_LAUNCHER__' in env:
-        executable = os.environ['__PYVENV_LAUNCHER__']
+        executable = sys._base_executable = os.environ['__PYVENV_LAUNCHER__']
+    elif sys.platform == 'win32' and '__PYVENV_LAUNCHER__' in env:
+        executable = sys.executable
+        import _winapi
+        sys._base_executable = _winapi.GetModuleFileName(0)
+        # bpo-35873: Clear the environment variable to avoid it being
+        # inherited by child processes.
+        del os.environ['__PYVENV_LAUNCHER__']
     else:
         executable = sys.executable
     exe_dir, _ = os.path.split(os.path.abspath(executable))

Lib/test/test_venv.py

@@ -52,10 +52,7 @@ class BaseTest(unittest.TestCase):
             self.bindir = 'bin'
             self.lib = ('lib', 'python%d.%d' % sys.version_info[:2])
             self.include = 'include'
-        if sys.platform == 'darwin' and '__PYVENV_LAUNCHER__' in os.environ:
-            executable = os.environ['__PYVENV_LAUNCHER__']
-        else:
-            executable = sys.executable
+        executable = getattr(sys, '_base_executable', sys.executable)
         self.exe = os.path.split(executable)[-1]
 
     def tearDown(self):
@@ -100,11 +97,7 @@ class BasicTest(BaseTest):
         else:
             self.assertFalse(os.path.exists(p))
         data = self.get_text_file_contents('pyvenv.cfg')
-        if sys.platform == 'darwin' and ('__PYVENV_LAUNCHER__'
-                                         in os.environ):
-            executable =  os.environ['__PYVENV_LAUNCHER__']
-        else:
-            executable = sys.executable
+        executable = getattr(sys, '_base_executable', sys.executable)
         path = os.path.dirname(executable)
         self.assertIn('home = %s' % path, data)
         fn = self.get_env_file(self.bindir, self.exe)

Lib/venv/__init__.py

@@ -106,10 +106,7 @@ class EnvBuilder:
         context.prompt = '(%s) ' % prompt
         create_if_needed(env_dir)
         env = os.environ
-        if sys.platform == 'darwin' and '__PYVENV_LAUNCHER__' in env:
-            executable = os.environ['__PYVENV_LAUNCHER__']
-        else:
-            executable = sys.executable
+        executable = getattr(sys, '_base_executable', sys.executable)
         dirname, exename = os.path.split(os.path.abspath(executable))
         context.executable = executable
         context.python_dir = dirname

Misc/NEWS.d/next/Windows/2019-02-02-15-56-50.bpo-35873.UW-qS9.rst

@@ -0,0 +1 @@
+Prevents venv paths being inherited by child processes

Misc/NEWS.d/next/Windows/2019-02-02-15-57-19.bpo-35872.Bba2n7.rst

@@ -0,0 +1 @@
+Uses the base Python executable when invoking venv in a virtual environment