bpo-41796: Call _PyAST_Fini() earlier to fix a leak (GH-23131)

Call _PyAST_Fini() on all interpreters, not only on the main
interpreter. Also, call it ealier to fix a reference leak.

Python types contain a reference to themselves in in their
PyTypeObject.tp_mro member. _PyAST_Fini() must called before the last
GC collection to destroy AST types.

_PyInterpreterState_Clear() now calls _PyAST_Fini(). It now also
calls _PyWarnings_Fini() on subinterpeters, not only on the main
interpreter.

Add an assertion in AST init_types() to ensure that the _ast module
is no longer used after _PyAST_Fini() has been called.

1 files changed, 7 insertions, 4 deletions

diff --git a/Python/pystate.c b/Python/pystate.c
index e37cbd5a65..c9882a7f74 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -300,13 +300,16 @@ interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
     Py_CLEAR(interp->after_forkers_parent);
     Py_CLEAR(interp->after_forkers_child);
 #endif
-    if (_PyRuntimeState_GetFinalizing(runtime) == NULL) {
-        _PyWarnings_Fini(interp);
-    }
+
+    _PyAST_Fini(interp);
+    _PyWarnings_Fini(interp);
+
+    // All Python types must be destroyed before the last GC collection. Python
+    // types create a reference cycle to themselves in their in their
+    // PyTypeObject.tp_mro member (the tuple contains the type).
 
     /* Last garbage collection on this interpreter */
     _PyGC_CollectNoFail(tstate);
-
     _PyGC_Fini(tstate);
 
     /* We don't clear sysdict and builtins until the end of this function.