gh-99138: Isolate _zoneinfo (#99218)

* Convert zone info type to heap type and add it to module state
* Add global variables to module state

Author: erlend-aasland

Doc/library/zoneinfo.rst

@@ -241,7 +241,7 @@ The following class methods are also available:
     .. warning::
 
         Invoking this function may change the semantics of datetimes using
-        ``ZoneInfo`` in surprising ways; this modifies process-wide global state
+        ``ZoneInfo`` in surprising ways; this modifies module state
         and thus may have wide-ranging effects. Only use it if you know that you
         need to.
 

Lib/test/test_zoneinfo/test_zoneinfo.py

@@ -1797,12 +1797,10 @@ def test_cache_location(self):
         self.assertTrue(hasattr(py_zoneinfo.ZoneInfo, "_weak_cache"))
 
     def test_gc_tracked(self):
-        # The pure Python version is tracked by the GC but (for now) the C
-        # version is not.
         import gc
 
         self.assertTrue(gc.is_tracked(py_zoneinfo.ZoneInfo))
-        self.assertFalse(gc.is_tracked(c_zoneinfo.ZoneInfo))
+        self.assertTrue(gc.is_tracked(c_zoneinfo.ZoneInfo))
 
 
 @dataclasses.dataclass(frozen=True)

Misc/NEWS.d/next/Library/2023-01-02-22-41-44.gh-issue-99138.17hp9U.rst

@@ -0,0 +1 @@
+Apply :pep:`687` to :mod:`zoneinfo`. Patch by Erlend E. Aasland.