gh-92135: Fix _Py_reinterpret_cast() for const (#92138) · python/cpython@0313970 · GitHub
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gh-92135: Fix _Py_reinterpret_cast() for const (#92138)
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.
1 parent b11243e commit 0313970

5 files changed

Lines changed: 62 additions & 14 deletions

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‎Include/methodobject.h‎

Lines changed: 1 addition & 2 deletions

‎Include/objimpl.h‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -182,9 +182,9 @@ PyAPI_FUNC(void) PyObject_GC_UnTrack(void *);
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PyAPI_FUNC(void) PyObject_GC_Del(void *);
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#define PyObject_GC_New(type, typeobj) \
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_Py_reinterpret_cast(type*, _PyObject_GC_New(typeobj))
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_Py_reinterpret_cast(type*, _PyObject_GC_New(typeobj))
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#define PyObject_GC_NewVar(type, typeobj, n) \
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_Py_reinterpret_cast(type*, _PyObject_GC_NewVar((typeobj), (n)))
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_Py_reinterpret_cast(type*, _PyObject_GC_NewVar((typeobj), (n)))
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PyAPI_FUNC(int) PyObject_GC_IsTracked(PyObject *);
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PyAPI_FUNC(int) PyObject_GC_IsFinalized(PyObject *);

‎Include/pyport.h‎

Lines changed: 15 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -14,10 +14,20 @@
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#endif
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// Macro to use C++ static_cast<> and reinterpret_cast<> in the Python C API
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// Macro to use C++ static_cast<>, reinterpret_cast<> and const_cast<>
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// in the Python C API.
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//
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// In C++, _Py_reinterpret_cast(type, expr) converts a constant expression to a
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// non constant type using const_cast<type>. For example,
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// _Py_reinterpret_cast(PyObject*, op) can convert a "const PyObject*" to
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// "PyObject*".
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//
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// The type argument must not be constant. For example, in C++,
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// _Py_reinterpret_cast(const PyObject*, expr) fails with a compiler error.
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#ifdef __cplusplus
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# define _Py_static_cast(type, expr) static_cast<type>(expr)
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# define _Py_reinterpret_cast(type, expr) reinterpret_cast<type>(expr)
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# define _Py_reinterpret_cast(type, expr) \
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const_cast<type>(reinterpret_cast<const type>(expr))
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#else
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# define _Py_static_cast(type, expr) ((type)(expr))
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# define _Py_reinterpret_cast(type, expr) ((type)(expr))
@@ -307,10 +317,10 @@ extern "C" {
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*/
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#ifdef Py_DEBUG
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# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
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(assert((WIDE)(NARROW)(VALUE) == (VALUE)), (NARROW)(VALUE))
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(assert(_Py_static_cast(WIDE, _Py_static_cast(NARROW, (VALUE))) == (VALUE)), \
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_Py_static_cast(NARROW, (VALUE)))
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#else
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# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
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_Py_reinterpret_cast(NARROW, (VALUE))
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# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) _Py_static_cast(NARROW, (VALUE))
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#endif
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‎Lib/test/_testcppext.cpp‎

Lines changed: 31 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,9 @@
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// gh-91321: Very basic C++ test extension to check that the Python C API is
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// compatible with C++ and does not emit C++ compiler warnings.
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// Always enable assertions
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#undef NDEBUG
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#include "Python.h"
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PyDoc_STRVAR(_testcppext_add_doc,
@@ -20,8 +23,36 @@ _testcppext_add(PyObject *Py_UNUSED(module), PyObject *args)
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}
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static PyObject *
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test_api_casts(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
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{
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PyObject *obj = Py_BuildValue("(ii)", 1, 2);
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if (obj == nullptr) {
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return nullptr;
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}
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// gh-92138: For backward compatibility, functions of Python C API accepts
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// "const PyObject*". Check that using it does not emit C++ compiler
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// warnings.
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const PyObject *const_obj = obj;
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Py_INCREF(const_obj);
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Py_DECREF(const_obj);
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PyTypeObject *type = Py_TYPE(const_obj);
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assert(Py_REFCNT(const_obj) >= 1);
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assert(type == &PyTuple_Type);
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assert(PyTuple_GET_SIZE(const_obj) == 2);
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PyObject *one = PyTuple_GET_ITEM(const_obj, 0);
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assert(PyLong_AsLong(one) == 1);
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Py_DECREF(obj);
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Py_RETURN_NONE;
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}
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static PyMethodDef _testcppext_methods[] = {
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{"add", _testcppext_add, METH_VARARGS, _testcppext_add_doc},
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{"test_api_casts", test_api_casts, METH_NOARGS, NULL},
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{nullptr, nullptr, 0, nullptr} /* sentinel */
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};
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‎Lib/test/test_cppext.py‎

Lines changed: 13 additions & 5 deletions

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