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, 0 deletions

diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h
index e2da2537c11..65abc1884c3 100644
--- a/Include/internal/pycore_object.h
+++ b/Include/internal/pycore_object.h
@@ -8,9 +8,11 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
+#include <stdbool.h>
 #include "pycore_gc.h"            // _PyObject_GC_IS_TRACKED()
 #include "pycore_interp.h"        // PyInterpreterState.gc
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
+#include "pycore_runtime.h"       // _PyRuntime
 
 
 #define _PyObject_IMMORTAL_INIT(type) \
@@ -236,6 +238,8 @@ extern PyObject* _PyType_GetSubclasses(PyTypeObject *);
 #define _PyHeapType_GET_MEMBERS(etype) \
     ((PyMemberDef *)(((char *)etype) + Py_TYPE(etype)->tp_basicsize))
 
+PyAPI_FUNC(PyObject *) _PyObject_LookupSpecial(PyObject *, PyObject *);
+
 #ifdef __cplusplus
 }
 #endif