bpo-32388: Remove cross-version binary compatibility requirement in tp_flags (GH-4944)

It is now allowed to add new fields at the end of the PyTypeObject struct without having to allocate a dedicated compatibility flag in tp_flags.

This will reduce the risk of running out of bits in the 32-bit tp_flags value.
diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index 6013608..d8b631b 100644
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -1430,8 +1430,7 @@
     .tp_dealloc = FutureObj_dealloc,
     .tp_as_async = &FutureType_as_async,
     .tp_repr = (reprfunc)FutureObj_repr,
-    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,
+    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE,
     .tp_doc = _asyncio_Future___init____doc__,
     .tp_traverse = (traverseproc)FutureObj_traverse,
     .tp_clear = (inquiry)FutureObj_clear,
@@ -2461,8 +2460,7 @@
     .tp_dealloc = TaskObj_dealloc,
     .tp_as_async = &FutureType_as_async,
     .tp_repr = (reprfunc)FutureObj_repr,
-    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,
+    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE,
     .tp_doc = _asyncio_Task___init____doc__,
     .tp_traverse = (traverseproc)TaskObj_traverse,
     .tp_clear = (inquiry)TaskObj_clear,
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 6f855b9..9c0eeb5 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -2342,8 +2342,7 @@
     0,                          /*tp_getattro*/
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,  /*tp_flags*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
     bufferediobase_doc,         /* tp_doc */
     0,                          /* tp_traverse */
     0,                          /* tp_clear */
@@ -2434,7 +2433,7 @@
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     _io_BufferedReader___init____doc__, /* tp_doc */
     (traverseproc)buffered_traverse, /* tp_traverse */
     (inquiry)buffered_clear,    /* tp_clear */
@@ -2520,7 +2519,7 @@
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,   /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     _io_BufferedWriter___init____doc__, /* tp_doc */
     (traverseproc)buffered_traverse, /* tp_traverse */
     (inquiry)buffered_clear,    /* tp_clear */
@@ -2597,7 +2596,7 @@
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,   /* tp_flags */
+        | Py_TPFLAGS_HAVE_GC,   /* tp_flags */
     _io_BufferedRWPair___init____doc__, /* tp_doc */
     (traverseproc)bufferedrwpair_traverse, /* tp_traverse */
     (inquiry)bufferedrwpair_clear, /* tp_clear */
@@ -2691,7 +2690,7 @@
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,   /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     _io_BufferedRandom___init____doc__, /* tp_doc */
     (traverseproc)buffered_traverse, /* tp_traverse */
     (inquiry)buffered_clear,    /* tp_clear */
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 52a6f49..582a813 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -1200,12 +1200,12 @@
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,       /* tp_flags */
+        | Py_TPFLAGS_HAVE_GC,                   /* tp_flags */
     _io_FileIO___init____doc__,                 /* tp_doc */
     (traverseproc)fileio_traverse,              /* tp_traverse */
     (inquiry)fileio_clear,                      /* tp_clear */
     0,                                          /* tp_richcompare */
-    offsetof(fileio, weakreflist),      /* tp_weaklistoffset */
+    offsetof(fileio, weakreflist),              /* tp_weaklistoffset */
     0,                                          /* tp_iter */
     0,                                          /* tp_iternext */
     fileio_methods,                             /* tp_methods */
@@ -1215,7 +1215,7 @@
     0,                                          /* tp_dict */
     0,                                          /* tp_descr_get */
     0,                                          /* tp_descr_set */
-    offsetof(fileio, dict),         /* tp_dictoffset */
+    offsetof(fileio, dict),                     /* tp_dictoffset */
     _io_FileIO___init__,                        /* tp_init */
     PyType_GenericAlloc,                        /* tp_alloc */
     fileio_new,                                 /* tp_new */
diff --git a/Modules/_io/iobase.c b/Modules/_io/iobase.c
index a5727b8..8c8112d 100644
--- a/Modules/_io/iobase.c
+++ b/Modules/_io/iobase.c
@@ -856,7 +856,7 @@
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,   /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     iobase_doc,                 /* tp_doc */
     (traverseproc)iobase_traverse, /* tp_traverse */
     (inquiry)iobase_clear,      /* tp_clear */
@@ -1051,7 +1051,7 @@
     0,                          /*tp_getattro*/
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_FINALIZE,  /*tp_flags*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
     rawiobase_doc,              /* tp_doc */
     0,                          /* tp_traverse */
     0,                          /* tp_clear */
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index a08ab5b..3eb0dcc 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -183,8 +183,7 @@
     0,                          /*tp_getattro*/
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,  /*tp_flags*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
     textiobase_doc,             /* tp_doc */
     0,                          /* tp_traverse */
     0,                          /* tp_clear */
@@ -3258,7 +3257,7 @@
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     _io_TextIOWrapper___init____doc__, /* tp_doc */
     (traverseproc)textiowrapper_traverse, /* tp_traverse */
     (inquiry)textiowrapper_clear, /* tp_clear */
diff --git a/Modules/_io/winconsoleio.c b/Modules/_io/winconsoleio.c
index 70a723e..7700bd5 100644
--- a/Modules/_io/winconsoleio.c
+++ b/Modules/_io/winconsoleio.c
@@ -1133,7 +1133,7 @@
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,       /* tp_flags */
+        | Py_TPFLAGS_HAVE_GC,                   /* tp_flags */
     _io__WindowsConsoleIO___init____doc__,      /* tp_doc */
     (traverseproc)winconsoleio_traverse,        /* tp_traverse */
     (inquiry)winconsoleio_clear,                /* tp_clear */
diff --git a/Modules/_testmultiphase.c b/Modules/_testmultiphase.c
index db5bb7d..4933abb 100644
--- a/Modules/_testmultiphase.c
+++ b/Modules/_testmultiphase.c
@@ -98,7 +98,7 @@
     "_testimportexec.Example",
     sizeof(ExampleObject),
     0,
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,
     Example_Type_slots
 };
 
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 3b15c7b..0cf00e8 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -858,7 +858,6 @@
         PyObject *op = FROM_GC(gc);
         gc_list_move(gc, &seen);
         if (!_PyGCHead_FINALIZED(gc) &&
-                PyType_HasFeature(Py_TYPE(op), Py_TPFLAGS_HAVE_FINALIZE) &&
                 (finalize = Py_TYPE(op)->tp_finalize) != NULL) {
             _PyGCHead_SET_FINALIZED(gc);
             Py_INCREF(op);
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index a3d979c..a25ff7a 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -13032,8 +13032,7 @@
     0,                                      /* tp_getattro */
     0,                                      /* tp_setattro */
     0,                                      /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT
-        | Py_TPFLAGS_HAVE_FINALIZE,         /* tp_flags */
+    Py_TPFLAGS_DEFAULT,                     /* tp_flags */
     0,                                      /* tp_doc */
     0,                                      /* tp_traverse */
     0,                                      /* tp_clear */
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 74cdc0f..ca4d760 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -5286,8 +5286,7 @@
     PyObject_GenericGetAttr,                    /* tp_getattro */
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,             /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,   /* tp_flags */
     sock_doc,                                   /* tp_doc */
     0,                                          /* tp_traverse */
     0,                                          /* tp_clear */
diff --git a/Modules/xxlimited.c b/Modules/xxlimited.c
index 190f993..ffc04e0 100644
--- a/Modules/xxlimited.c
+++ b/Modules/xxlimited.c
@@ -123,7 +123,7 @@
     "xxlimited.Xxo",
     sizeof(XxoObject),
     0,
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,
     Xxo_Type_slots
 };