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gh-92135: Fix _Py_reinterpret_cast() for const (#92138)

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Fix C++ compiler warnings on cast macros, like _PyObject_CAST(), when
casting a constant expression to a non constant type: use
const_cast<> in C++.

* In C++, Py_SAFE_DOWNCAST() now uses static_cast<> rather than
  reinterpret_cast<>.
* Add tests to the _testcppext C++ extension.
* test_cppext no longer captures stdout in verbose mode.
This commit is contained in:
Victor Stinner 2022-05-02 17:07:00 +02:00 • committed by GitHub
parent b11243e85e
commit 031397063e
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GPG key ID: 4AEE18F83AFDEB23
5 changed files with 62 additions and 14 deletions
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3
Include/methodobject.h
View file

@ -43,8 +43,7 @@ typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
// it triggers an undefined behavior when Python calls it with 2 parameters
// (bpo-33012).
#define _PyCFunction_CAST(func) \
_Py_reinterpret_cast(PyCFunction, \
_Py_reinterpret_cast(void(*)(void), (func)))
_Py_reinterpret_cast(PyCFunction, _Py_reinterpret_cast(void(*)(void), (func)))
PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);

4
Include/objimpl.h
View file

@ -182,9 +182,9 @@ PyAPI_FUNC(void) PyObject_GC_UnTrack(void *);
PyAPI_FUNC(void) PyObject_GC_Del(void *);
#define PyObject_GC_New(type, typeobj) \
_Py_reinterpret_cast(type*, _PyObject_GC_New(typeobj))
_Py_reinterpret_cast(type*, _PyObject_GC_New(typeobj))
#define PyObject_GC_NewVar(type, typeobj, n) \
_Py_reinterpret_cast(type*, _PyObject_GC_NewVar((typeobj), (n)))
_Py_reinterpret_cast(type*, _PyObject_GC_NewVar((typeobj), (n)))
PyAPI_FUNC(int) PyObject_GC_IsTracked(PyObject *);
PyAPI_FUNC(int) PyObject_GC_IsFinalized(PyObject *);

20
Include/pyport.h
View file

@ -14,10 +14,20 @@
#endif
// Macro to use C++ static_cast<> and reinterpret_cast<> in the Python C API
// Macro to use C++ static_cast<>, reinterpret_cast<> and const_cast<>
// in the Python C API.
//
// In C++, _Py_reinterpret_cast(type, expr) converts a constant expression to a
// non constant type using const_cast<type>. For example,
// _Py_reinterpret_cast(PyObject*, op) can convert a "const PyObject*" to
// "PyObject*".
//
// The type argument must not be constant. For example, in C++,
// _Py_reinterpret_cast(const PyObject*, expr) fails with a compiler error.
#ifdef __cplusplus
# define _Py_static_cast(type, expr) static_cast<type>(expr)
# define _Py_reinterpret_cast(type, expr) reinterpret_cast<type>(expr)
# define _Py_reinterpret_cast(type, expr) \
const_cast<type>(reinterpret_cast<const type>(expr))
#else
# define _Py_static_cast(type, expr) ((type)(expr))
# define _Py_reinterpret_cast(type, expr) ((type)(expr))
@ -307,10 +317,10 @@ extern "C" {
*/
#ifdef Py_DEBUG
# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
(assert((WIDE)(NARROW)(VALUE) == (VALUE)), (NARROW)(VALUE))
(assert(_Py_static_cast(WIDE, _Py_static_cast(NARROW, (VALUE))) == (VALUE)), \
_Py_static_cast(NARROW, (VALUE)))
#else
# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
_Py_reinterpret_cast(NARROW, (VALUE))
# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) _Py_static_cast(NARROW, (VALUE))
#endif