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, 4 insertions, 8 deletions

diff --git a/Objects/unionobject.c b/Objects/unionobject.c
index 80c7038..72a0a3f 100644
--- a/Objects/unionobject.c
+++ b/Objects/unionobject.c
@@ -255,10 +255,6 @@ _Py_union_type_or(PyObject* self, PyObject* other)
 static int
 union_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 *tmp;
@@ -269,13 +265,13 @@ union_repr_item(_PyUnicodeWriter *writer, PyObject *p)
         return _PyUnicodeWriter_WriteASCIIString(writer, "None", 4);
     }
 
-    if (_PyObject_LookupAttrId(p, &PyId___origin__, &tmp) < 0) {
+    if (_PyObject_LookupAttr(p, &_Py_ID(__origin__), &tmp) < 0) {
         goto exit;
     }
 
     if (tmp) {
         Py_DECREF(tmp);
-        if (_PyObject_LookupAttrId(p, &PyId___args__, &tmp) < 0) {
+        if (_PyObject_LookupAttr(p, &_Py_ID(__args__), &tmp) < 0) {
             goto exit;
         }
         if (tmp) {
@@ -285,13 +281,13 @@ union_repr_item(_PyUnicodeWriter *writer, PyObject *p)
         }
     }
 
-    if (_PyObject_LookupAttrId(p, &PyId___qualname__, &qualname) < 0) {
+    if (_PyObject_LookupAttr(p, &_Py_ID(__qualname__), &qualname) < 0) {
         goto exit;
     }
     if (qualname == NULL) {
         goto use_repr;
     }
-    if (_PyObject_LookupAttrId(p, &PyId___module__, &module) < 0) {
+    if (_PyObject_LookupAttr(p, &_Py_ID(__module__), &module) < 0) {
         goto exit;
     }
     if (module == NULL || module == Py_None) {