Tightening warning flags

[TechnophobicLampshade]

I'm building a project with some relatively strict warning flags, including -Wcast-qual, -Wzero-length-array, -Wsign-conversion. I get a few errors when including nanobind:

conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
conda_env/lib/python3.10/site-packages/nanobind/src/implicit.cpp:40:43: error: cast from 'void **' to 'decltype(t->implicit)' (aka 'const std::type_info **') must have all intermediate pointers const qualified to be safe [-Werror,-Wcast-qual]
    t->implicit = (decltype(t->implicit)) data;
                                          ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:14:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:48:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:11:
conda_env/lib/python3.10/site-packages/nanobind/src/buffer.h:136:39: error: implicit conversion changes signedness: 'long' to 'size_t' (aka 'unsigned long') [-Werror,-Wsign-conversion]
        size_t old_alloc_size = m_end - m_start,
               ~~~~~~~~~~~~~~   ~~~~~~^~~~~~~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:103:27: error: cast from 'const char *' to 'char *' drops const qualifier [-Werror,-Wcast-qual]
            free((char *) f->name);
                          ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:105:27: error: cast from 'const char *' to 'char *' drops const qualifier [-Werror,-Wcast-qual]
            free((char *) f->descr);
                          ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:189:54: error: cast from 'const void *' to 'nanobind::detail::func_data_prelim<0> *' drops const qualifier [-Werror,-Wcast-qual]
    func_data_prelim<0> *f = (func_data_prelim<0> *) in_;
                                                     ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:275:47: error: implicit conversion changes signedness: 'Py_ssize_t' (aka 'long') to 'unsigned long' [-Werror,-Wsign-conversion]
        memcpy(cur, prev, sizeof(func_data) * to_copy);
                                            ~ ^~~~~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:276:45: error: implicit conversion changes signedness: 'Py_ssize_t' (aka 'long') to 'unsigned long' [-Werror,-Wsign-conversion]
        memset(prev, 0, sizeof(func_data) * to_copy);
                                          ~ ^~~~~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:327:29: error: cast from 'const char *' to 'char *' drops const qualifier [-Werror,-Wcast-qual]
            memcpy((char *) fc->descr, f->descr, (i + 1) * sizeof(char));
                            ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:751:69: error: cast from '_object *const *' to '_object **' drops const qualifier [-Werror,-Wcast-qual]
                result = f->impl((void *) f->capture, (PyObject **) args_in,
                                                                    ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_func.cpp:812:45: error: cast from '_object *const *' to '_object **' drops const qualifier [-Werror,-Wcast-qual]
        PyObject **args_tmp = (PyObject **) args_in - 1;
                                            ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_ndarray.cpp:94:29: error: cast from 'const char *' to 'char *' drops const qualifier [-Werror,-Wcast-qual]
    view->format = (char *) format;
                            ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/trampoline.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/trampoline.h:13:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:48:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:45:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_enum.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:48:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:45:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:48:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.cpp:299:13: error: 'NB_ABORT_ON_LEAK' is not defined, evaluates to 0 [-Werror,-Wundef]
        #if NB_ABORT_ON_LEAK == 1
            ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_static_property.cpp:1:
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:14:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:45:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_static_property.cpp:1:
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:14:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:48:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/common.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:45:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/common.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:48:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
conda_env/lib/python3.10/site-packages/nanobind/src/common.cpp:28:41: error: implicit conversion changes signedness: 'int' to 'size_t' (aka 'unsigned long') [-Werror,-Wsign-conversion]
        scoped_pymalloc<char> temp(size + 1);
                              ~~~~ ~~~~~^~~
conda_env/lib/python3.10/site-packages/nanobind/src/common.cpp:31:36: error: implicit conversion changes signedness: 'int' to 'size_t' (aka 'unsigned long') [-Werror,-Wsign-conversion]
        vsnprintf(temp.get(), size + 1, fmt, args);
        ~~~~~~~~~             ~~~~~^~~
conda_env/lib/python3.10/site-packages/nanobind/src/common.cpp:90:42: error: cast from 'const void *' to 'void *' drops const qualifier [-Werror,-Wcast-qual]
    PyObject *c = PyCapsule_New((void *) ptr, name, capsule_cleanup);
                                         ^
conda_env/lib/python3.10/site-packages/nanobind/src/common.cpp:911:16: error: cast from 'const _longobject *' to 'PyVarObject *' drops const qualifier [-Werror,-Wcast-qual]
    return abs(Py_SIZE(o)) <= 1;
               ^
conda_env/include/python3.10/object.h:140:34: note: expanded from macro 'Py_SIZE'
#define Py_SIZE(ob)             (_PyVarObject_CAST(ob)->ob_size)
                                 ^
conda_env/include/python3.10/object.h:121:46: note: expanded from macro '_PyVarObject_CAST'
#define _PyVarObject_CAST(op) ((PyVarObject*)(op))
                                             ^
conda_env/lib/python3.10/site-packages/nanobind/src/common.cpp:915:12: error: cast from 'const _longobject *' to 'PyVarObject *' drops const qualifier [-Werror,-Wcast-qual]
    return Py_SIZE(o) * (Py_ssize_t) o->ob_digit[0];
           ^
conda_env/include/python3.10/object.h:140:34: note: expanded from macro 'Py_SIZE'
#define Py_SIZE(ob)             (_PyVarObject_CAST(ob)->ob_size)
                                 ^
conda_env/include/python3.10/object.h:121:46: note: expanded from macro '_PyVarObject_CAST'
#define _PyVarObject_CAST(op) ((PyVarObject*)(op))
                                             ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:14:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:45:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:180:64: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                               ^
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_types.h:181:68: error: cast from 'const _typeobject *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    NB_INLINE handle(const PyTypeObject *ptr) : m_ptr((PyObject *) ptr) { }
                                                                   ^
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:10:
In file included from conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:14:
In file included from conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nanobind.h:48:
conda_env/lib/python3.10/site-packages/nanobind/include/nanobind/nb_attr.h:163:19: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
    arg_data args[Size];
                  ^~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_internals.h:38:20: note: in instantiation of template class 'nanobind::detail::func_data_prelim<0>' requested here
struct func_data : func_data_prelim<0> {
                   ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:348:19: error: cast from 'const char *' to 'char *' drops const qualifier [-Werror,-Wcast-qual]
    free((char *) t->name);
                  ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:651:20: error: implicit conversion changes signedness: 'int' to 'unsigned long' [-Werror,-Wsign-conversion]
        } else if (slot * sizeof(nb_slot) < (int) sizeof(type_slots)) {
                   ^~~~ ~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:735:44: error: implicit conversion changes signedness: 'Py_ssize_t' (aka 'long') to 'unsigned long' [-Werror,-Wsign-conversion]
        int basicsize = (int) (PyType_Type.tp_basicsize + (sizeof(type_data) + supplement)),
                               ~~~~~~~~~~~~^~~~~~~~~~~~ ~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:884:29: error: implicit conversion changes signedness: 'long' to 'size_t' (aka 'unsigned long') [-Werror,-Wsign-conversion]
            num_avail -= (s - first_new);
                      ~~  ~~^~~~~~~~~~~
conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:1667:45: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    PyTypeObject *tp = Py_TYPE((PyObject *) src);
                                            ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:1675:49: error: cast from 'const _object *' to 'nanobind::detail::nb_inst *' drops const qualifier [-Werror,-Wcast-qual]
    const void *src_data = inst_ptr((nb_inst *) src);
                                                ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:1687:45: error: cast from 'const _object *' to '_object *' drops const qualifier [-Werror,-Wcast-qual]
    PyTypeObject *tp = Py_TYPE((PyObject *) src);
                                            ^
conda_env/lib/python3.10/site-packages/nanobind/src/nb_type.cpp:1695:43: error: cast from 'const _object *' to 'nanobind::detail::nb_inst *' drops const qualifier [-Werror,-Wcast-qual]
    void *src_data = inst_ptr((nb_inst *) src);

Would it be hard to add the appropriate const_cast/static_cast calls here to make the library a bit more portable?

Thanks!

[TechnophobicLampshade]

Another one:

python3.10/site-packages/nanobind/src/nb_internals.cpp:299:13: error: 'NB_ABORT_ON_LEAK' is not defined, evaluates to 0 [-Werror,-Wundef]

[wjakob]

No way, sorry -- I don't wish to pepper my codebase with const_cast all over the place so that you can compile with what I feel are compilation flags that are completely unreasonable for a Python project. Try compiling Python itself with those flags and see what happens..

[casperdcl]

I currently get these warnings in pairs due to -Wpedantic:

• ISO C++ forbids zero-size array
• zero-size array member ‘nanobind::detail::func_data_prelim<0>::args’ not at end of ‘struct nanobind::detail::func_data’

[wjakob]

Please see the FAQ..