Fix tests, typos, add news entry

Co-Authored-By: Zanie Blue <contact@zanie.dev>

Author: sergey-miryanov

Include/internal/pycore_gc.h

@@ -213,7 +213,7 @@ extern void _Py_ScheduleGC(PyThreadState *tstate);
  * ob_traverse method.
  *
  * Internal note: interp->gc.generation0->_gc_prev doesn't have any bit flags
- * because it's not object header.  So we don't use _PyGCHead_PREV() and
+ * because it's not an object header. So we don't use _PyGCHead_PREV() and
  * _PyGCHead_SET_PREV() for it to avoid unnecessary bitwise operations.
  *
  * See also the public PyObject_GC_Track() function.

Lib/test/_test_gc_fast_cycles.py

@@ -7,7 +7,7 @@
                           Py_GIL_DISABLED)
 from test.support.import_helper import import_module
 from test.support.os_helper import temp_dir, TESTFN, unlink
-from test.support.script_helper import assert_python_ok, make_script, run_test_script
+from test.support.script_helper import assert_python_ok, make_script
 from test.support import threading_helper, gc_threshold
 
 import gc
@@ -399,11 +399,19 @@ def test_collect_generations(self):
         # each call to collect(N)
         x = []
         gc.collect(0)
-        # x is now in the old gen
+        # x is now in gen 1
         a, b, c = gc.get_count()
-        # We don't check a since its exact values depends on
+        gc.collect(1)
+        # x is now in gen 2
+        d, e, f = gc.get_count()
+        gc.collect(2)
+        # x is now in gen 3
+        g, h, i = gc.get_count()
+        # We don't check a, d, g since their exact values depends on
         # internal implementation details of the interpreter.
         self.assertEqual((b, c), (1, 0))
+        self.assertEqual((e, f), (0, 1))
+        self.assertEqual((h, i), (0, 0))
 
     def test_trashcan(self):
         class Ouch:
@@ -870,10 +878,42 @@ def test_get_objects_generations(self):
         self.assertTrue(
                 any(l is element for element in gc.get_objects(generation=0))
         )
-        gc.collect()
+        self.assertFalse(
+                any(l is element for element in gc.get_objects(generation=1))
+        )
+        self.assertFalse(
+                any(l is element for element in gc.get_objects(generation=2))
+        )
+        gc.collect(generation=0)
+        self.assertFalse(
+                any(l is element for element in gc.get_objects(generation=0))
+        )
+        self.assertTrue(
+                any(l is element for element in gc.get_objects(generation=1))
+        )
+        self.assertFalse(
+                any(l is element for element in gc.get_objects(generation=2))
+        )
+        gc.collect(generation=1)
         self.assertFalse(
                 any(l is element for element in gc.get_objects(generation=0))
         )
+        self.assertFalse(
+                any(l is element for element in gc.get_objects(generation=1))
+        )
+        self.assertTrue(
+                any(l is element for element in gc.get_objects(generation=2))
+        )
+        gc.collect(generation=2)
+        self.assertFalse(
+                any(l is element for element in gc.get_objects(generation=0))
+        )
+        self.assertFalse(
+                any(l is element for element in gc.get_objects(generation=1))
+        )
+        self.assertTrue(
+                any(l is element for element in gc.get_objects(generation=2))
+        )
         del l
         gc.collect()
 
@@ -1181,17 +1221,6 @@ def test_tuple_untrack_counts(self):
         self.assertTrue(new_count - count > (n // 2))
 
 
-class IncrementalGCTests(unittest.TestCase):
-    @unittest.skipIf(_testinternalcapi is None, "requires _testinternalcapi")
-    @requires_gil_enabled("Free threading does not support incremental GC")
-    def test_incremental_gc_handles_fast_cycle_creation(self):
-        # Run this test in a fresh process.  The number of alive objects (which can
-        # be from unit tests run before this one) can influence how quickly cyclic
-        # garbage is found.
-        script = support.findfile("_test_gc_fast_cycles.py")
-        run_test_script(script)
-
-
 class GCCallbackTests(unittest.TestCase):
     def setUp(self):
         # Save gc state and disable it.

Lib/test/test_gc.py

@@ -0,0 +1 @@
+Forward-port the generational cycle garbage collector to the default 3.15 build, replacing the incremental collector while leaving the free-threaded collector unchanged.