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, 2 insertions, 3 deletions

diff --git a/Objects/tupleobject.c b/Objects/tupleobject.c
index 86f541a..ec9147c 100644
--- a/Objects/tupleobject.c
+++ b/Objects/tupleobject.c
@@ -1193,12 +1193,11 @@ PyDoc_STRVAR(length_hint_doc, "Private method returning an estimate of len(list(
 static PyObject *
 tupleiter_reduce(tupleiterobject *it, PyObject *Py_UNUSED(ignored))
 {
-    _Py_IDENTIFIER(iter);
     if (it->it_seq)
-        return Py_BuildValue("N(O)n", _PyEval_GetBuiltinId(&PyId_iter),
+        return Py_BuildValue("N(O)n", _PyEval_GetBuiltin(&_Py_ID(iter)),
                              it->it_seq, it->it_index);
     else
-        return Py_BuildValue("N(())", _PyEval_GetBuiltinId(&PyId_iter));
+        return Py_BuildValue("N(())", _PyEval_GetBuiltin(&_Py_ID(iter)));
 }
 
 static PyObject *