Remove _PyWeakref_GetWeakrefCount() and _PyWeakref_ClearRef() from
the public C API: move them to the internal C API.
Refactor also _weakref_getweakrefs() code to make it more readable.
Avoid mixing declarations and code in the C API to fix the compiler
warning: "ISO C90 forbids mixed declarations and code"
[-Werror=declaration-after-statement].
The limited API version 3.11 no longer casts arguments to expected
types of functions of functions:
* PyList_GET_SIZE(), PyList_SET_ITEM()
* PyTuple_GET_SIZE(), PyTuple_SET_ITEM()
* PyWeakref_GET_OBJECT()
Use _Py_CAST(), _Py_STATIC_CAST() and _PyASCIIObject_CAST() in
static inline functions to fix C++ compiler warnings:
"use of old-style cast" (clang -Wold-style-cast).
test_cppext now builds the C++ test extension with -Wold-style-cast.
Convert the PyWeakref_GET_OBJECT() macro to a static inline function.
Add an assertion to check the argument with PyWeakref_Check(). Add a
macro converting the argument to PyObject* to prevent emitting new
compiler warning.
Split header files to move the non-limited API to Include/cpython/:
* Include/warnings.h => Include/cpython/warnings.h
* Include/weakrefobject.h => Include/cpython/weakrefobject.h
Exclude PyWeakref_GET_OBJECT() from the limited C API. It never
worked since the PyWeakReference structure is opaque in the limited C
API.
Move _PyWarnings_Init() and _PyErr_WarnUnawaitedCoroutine() to the
internal C API.
