gh-90876: Restore the ability to import multiprocessing when `sys.executable` is `None` (#106464)

Prevent `multiprocessing.spawn` from failing to *import* in environments
where `sys.executable` is `None`.  This regressed in 3.11 with the addition
of support for path-like objects in multiprocessing.

Adds a test decorator to have tests only run when part of test_multiprocessing_spawn to `_test_multiprocessing.py` so we can start to avoid re-running the same not-global-state specific test in all 3 modes when there is no need.

1 files changed, 4 insertions, 2 deletions

diff --git a/Lib/multiprocessing/spawn.py b/Lib/multiprocessing/spawn.py
index 09f8a229d7c..f1af7709104 100644
--- a/Lib/multiprocessing/spawn.py
+++ b/Lib/multiprocessing/spawn.py
@@ -31,11 +31,13 @@ if sys.platform != 'win32':
     WINSERVICE = False
 else:
     WINEXE = getattr(sys, 'frozen', False)
-    WINSERVICE = sys.executable.lower().endswith("pythonservice.exe")
+    WINSERVICE = sys.executable and sys.executable.lower().endswith("pythonservice.exe")
 
 def set_executable(exe):
     global _python_exe
-    if sys.platform == 'win32':
+    if exe is None:
+        _python_exe = exe
+    elif sys.platform == 'win32':
         _python_exe = os.fsdecode(exe)
     else:
         _python_exe = os.fsencode(exe)