gh-134716: Support regular expressions in -W and PYTHONWARNINGS (GH-138149)

Lib/_py_warnings.py

@@ -369,9 +369,15 @@ def _setoption(arg):
     if message or module:
         import re
     if message:
-        message = re.escape(message)
+        if len(message) >= 2 and message[0] == message[-1] == '/':
+            message = message[1:-1]
+        else:
+            message = re.escape(message)
     if module:
-        module = re.escape(module) + r'\z'
+        if len(module) >= 2 and module[0] == module[-1] == '/':
+            module = module[1:-1]
+        else:
+            module = re.escape(module) + r'\z'
     if lineno:
         try:
             lineno = int(lineno)
@@ -381,7 +387,23 @@ def _setoption(arg):
             raise _wm._OptionError("invalid lineno %r" % (lineno,)) from None
     else:
         lineno = 0
-    _wm.filterwarnings(action, message, category, module, lineno)
+    try:
+        _wm.filterwarnings(action, message, category, module, lineno)
+    except re.PatternError if message or module else ():
+        if message:
+            try:
+                re.compile(message)
+            except re.PatternError:
+                raise _wm._OptionError(f"invalid regular expression for "
+                                       f"message: {message!r}") from None
+        if module:
+            try:
+                re.compile(module)
+            except re.PatternError:
+                raise _wm._OptionError(f"invalid regular expression for "
+                                       f"module: {module!r}") from None
+        # Should never happen.
+        raise
 
 
 # Helper for _setoption()