Fix deprecated import for MutableMapping and MutableSet

Starting with Python 3.3, MutableMapping and MutableSet are part
of collections.abc module rather than collections.  Importing them
from the old module is deprecated and no longer works in Python 3.10.
Support both modules conditionally for best compatibility.

tests/debug/config.py

@@ -4,11 +4,16 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-import collections
 import os
+import sys
+
+if sys.version_info >= (3, 3):
+    from collections.abc import MutableMapping, MutableSet
+else:
+    from collections import MutableMapping, MutableSet
 
 
-class DebugConfig(collections.MutableMapping):
+class DebugConfig(MutableMapping):
     """Debug configuration for a session. Corresponds to bodies of DAP "launch" and
     "attach" requests, or launch.json in VSCode.
 
@@ -137,8 +142,7 @@ class DebugConfig(collections.MutableMapping):
         return self[key]
 
     def setdefaults(self, defaults):
-        """Like setdefault(), but sets multiple default values at once.
-        """
+        """Like setdefault(), but sets multiple default values at once."""
         for k, v in defaults.items():
             self.setdefault(k, v)
 
@@ -192,9 +196,8 @@ class DebugConfig(collections.MutableMapping):
     def debug_options(self):
         return self._debug_options
 
-    class Env(collections.MutableMapping):
-        """Wraps config["env"], automatically creating and destroying it as needed.
-        """
+    class Env(MutableMapping):
+        """Wraps config["env"], automatically creating and destroying it as needed."""
 
         def __init__(self, config):
             self.config = config
@@ -230,7 +233,7 @@ class DebugConfig(collections.MutableMapping):
                 tail = ""
             self[key] = entry + tail
 
-    class DebugOptions(collections.MutableSet):
+    class DebugOptions(MutableSet):
         """Wraps config["debugOptions"], automatically creating and destroying it as
         needed, and providing set operations for it.
         """