bpo-46541: Replace core use of _Py_IDENTIFIER() with statically initialized global objects. (gh-30928)

We're no longer using _Py_IDENTIFIER() (or _Py_static_string()) in any core CPython code.  It is still used in a number of non-builtin stdlib modules.

The replacement is: PyUnicodeObject (not pointer) fields under _PyRuntimeState, statically initialized as part of _PyRuntime.  A new _Py_GET_GLOBAL_IDENTIFIER() macro facilitates lookup of the fields (along with _Py_GET_GLOBAL_STRING() for non-identifier strings).

https://bugs.python.org/issue46541#msg411799 explains the rationale for this change.

The core of the change is in:

* (new) Include/internal/pycore_global_strings.h - the declarations for the global strings, along with the macros
* Include/internal/pycore_runtime_init.h - added the static initializers for the global strings
* Include/internal/pycore_global_objects.h - where the struct in pycore_global_strings.h is hooked into _PyRuntimeState
* Tools/scripts/generate_global_objects.py - added generation of the global string declarations and static initializers

I've also added a --check flag to generate_global_objects.py (along with make check-global-objects) to check for unused global strings.  That check is added to the PR CI config.

The remainder of this change updates the core code to use _Py_GET_GLOBAL_IDENTIFIER() instead of _Py_IDENTIFIER() and the related _Py*Id functions (likewise for _Py_GET_GLOBAL_STRING() instead of _Py_static_string()).  This includes adding a few functions where there wasn't already an alternative to _Py*Id(), replacing the _Py_Identifier * parameter with PyObject *.

The following are not changed (yet):

* stop using _Py_IDENTIFIER() in the stdlib modules
* (maybe) get rid of _Py_IDENTIFIER(), etc. entirely -- this may not be doable as at least one package on PyPI using this (private) API
* (maybe) intern the strings during runtime init

https://bugs.python.org/issue46541

1 files changed, 7 insertions, 12 deletions

diff --git a/Objects/genericaliasobject.c b/Objects/genericaliasobject.c
index dbe5d89..b416449 100644
--- a/Objects/genericaliasobject.c
+++ b/Objects/genericaliasobject.c
@@ -41,10 +41,6 @@ ga_traverse(PyObject *self, visitproc visit, void *arg)
 static int
 ga_repr_item(_PyUnicodeWriter *writer, PyObject *p)
 {
-    _Py_IDENTIFIER(__module__);
-    _Py_IDENTIFIER(__qualname__);
-    _Py_IDENTIFIER(__origin__);
-    _Py_IDENTIFIER(__args__);
     PyObject *qualname = NULL;
     PyObject *module = NULL;
     PyObject *r = NULL;
@@ -57,12 +53,12 @@ ga_repr_item(_PyUnicodeWriter *writer, PyObject *p)
         goto done;
     }
 
-    if (_PyObject_LookupAttrId(p, &PyId___origin__, &tmp) < 0) {
+    if (_PyObject_LookupAttr(p, &_Py_ID(__origin__), &tmp) < 0) {
         goto done;
     }
     if (tmp != NULL) {
         Py_DECREF(tmp);
-        if (_PyObject_LookupAttrId(p, &PyId___args__, &tmp) < 0) {
+        if (_PyObject_LookupAttr(p, &_Py_ID(__args__), &tmp) < 0) {
             goto done;
         }
         if (tmp != NULL) {
@@ -72,13 +68,13 @@ ga_repr_item(_PyUnicodeWriter *writer, PyObject *p)
         }
     }
 
-    if (_PyObject_LookupAttrId(p, &PyId___qualname__, &qualname) < 0) {
+    if (_PyObject_LookupAttr(p, &_Py_ID(__qualname__), &qualname) < 0) {
         goto done;
     }
     if (qualname == NULL) {
         goto use_repr;
     }
-    if (_PyObject_LookupAttrId(p, &PyId___module__, &module) < 0) {
+    if (_PyObject_LookupAttr(p, &_Py_ID(__module__), &module) < 0) {
         goto done;
     }
     if (module == NULL || module == Py_None) {
@@ -218,9 +214,9 @@ _Py_make_parameters(PyObject *args)
             iparam += tuple_add(parameters, iparam, t);
         }
         else {
-            _Py_IDENTIFIER(__parameters__);
             PyObject *subparams;
-            if (_PyObject_LookupAttrId(t, &PyId___parameters__, &subparams) < 0) {
+            if (_PyObject_LookupAttr(t, &_Py_ID(__parameters__),
+                                     &subparams) < 0) {
                 Py_DECREF(parameters);
                 return NULL;
             }
@@ -260,9 +256,8 @@ _Py_make_parameters(PyObject *args)
 static PyObject *
 subs_tvars(PyObject *obj, PyObject *params, PyObject **argitems)
 {
-    _Py_IDENTIFIER(__parameters__);
     PyObject *subparams;
-    if (_PyObject_LookupAttrId(obj, &PyId___parameters__, &subparams) < 0) {
+    if (_PyObject_LookupAttr(obj, &_Py_ID(__parameters__), &subparams) < 0) {
         return NULL;
     }
     if (subparams && PyTuple_Check(subparams) && PyTuple_GET_SIZE(subparams)) {