bpo-42536: GC track recycled tuples (GH-23623)

Several built-in and standard library types now ensure that their internal result tuples are always tracked by the garbage collector:

- collections.OrderedDict.items
- dict.items
- enumerate
- functools.reduce
- itertools.combinations
- itertools.combinations_with_replacement
- itertools.permutations
- itertools.product
- itertools.zip_longest
- zip

Previously, they could have become untracked by a prior garbage collection.

3 files changed, 26 insertions, 0 deletions

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 7a37313..35e881f 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -3989,6 +3989,11 @@ dictiter_iternextitem(dictiterobject *di)
         Py_INCREF(result);
         Py_DECREF(oldkey);
         Py_DECREF(oldvalue);
+        // bpo-42536: The GC may have untracked this result tuple. Since we're
+        // recycling it, make sure it's tracked again:
+        if (!_PyObject_GC_IS_TRACKED(result)) {
+            _PyObject_GC_TRACK(result);
+        }
     }
     else {
         result = PyTuple_New(2);
@@ -4104,6 +4109,11 @@ dictreviter_iternext(dictiterobject *di)
             Py_INCREF(result);
             Py_DECREF(oldkey);
             Py_DECREF(oldvalue);
+            // bpo-42536: The GC may have untracked this result tuple. Since
+            // we're recycling it, make sure it's tracked again:
+            if (!_PyObject_GC_IS_TRACKED(result)) {
+                _PyObject_GC_TRACK(result);
+            }
         }
         else {
             result = PyTuple_New(2);
diff --git a/Objects/enumobject.c b/Objects/enumobject.c
index 8b5e7d3..98ece3f 100644
--- a/Objects/enumobject.c
+++ b/Objects/enumobject.c
@@ -2,6 +2,7 @@
 
 #include "Python.h"
 #include "pycore_long.h"          // _PyLong_GetOne()
+#include "pycore_object.h"        // _PyObject_GC_TRACK()
 
 #include "clinic/enumobject.c.h"
 
@@ -131,6 +132,11 @@ enum_next_long(enumobject *en, PyObject* next_item)
         PyTuple_SET_ITEM(result, 1, next_item);
         Py_DECREF(old_index);
         Py_DECREF(old_item);
+        // bpo-42536: The GC may have untracked this result tuple. Since we're
+        // recycling it, make sure it's tracked again:
+        if (!_PyObject_GC_IS_TRACKED(result)) {
+            _PyObject_GC_TRACK(result);
+        }
         return result;
     }
     result = PyTuple_New(2);
@@ -176,6 +182,11 @@ enum_next(enumobject *en)
         PyTuple_SET_ITEM(result, 1, next_item);
         Py_DECREF(old_index);
         Py_DECREF(old_item);
+        // bpo-42536: The GC may have untracked this result tuple. Since we're
+        // recycling it, make sure it's tracked again:
+        if (!_PyObject_GC_IS_TRACKED(result)) {
+            _PyObject_GC_TRACK(result);
+        }
         return result;
     }
     result = PyTuple_New(2);
diff --git a/Objects/odictobject.c b/Objects/odictobject.c
index 4eb15f9..6c7f117 100644
--- a/Objects/odictobject.c
+++ b/Objects/odictobject.c
@@ -1814,6 +1814,11 @@ odictiter_iternext(odictiterobject *di)
         Py_INCREF(result);
         Py_DECREF(PyTuple_GET_ITEM(result, 0));  /* borrowed */
         Py_DECREF(PyTuple_GET_ITEM(result, 1));  /* borrowed */
+        // bpo-42536: The GC may have untracked this result tuple. Since we're
+        // recycling it, make sure it's tracked again:
+        if (!_PyObject_GC_IS_TRACKED(result)) {
+            _PyObject_GC_TRACK(result);
+        }
     }
     else {
         result = PyTuple_New(2);