Description
Describe the bug
By inspecting the generated .c/.cpp file, I found an intermediate variable of type char * is created to hold the return value of type const char *, causing compiler warnings (or errors with stricter compiler warning checks like -Werror).
To Reproduce
Code to reproduce the behaviour:
cimport cpython
def get_name(object capsule):
cdef const char* name = cpython.PyCapsule_GetName(capsule)
print(name)With a simple cythonize a warning is raised:
$ cythonize -i -3 test_cython_bug.pyx
...
/home/leofang/dev/cupy_cuda10.2/test_cython_bug.c:1242:13: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
__pyx_t_1 = PyCapsule_GetName(__pyx_v_capsule); if (unlikely(__pyx_t_1 == ((char *)NULL) && PyErr_Occurred())) __PYX_ERR(0, 4, __pyx_L1_error)
^
and the reason is __pyx_t_1 is declared as char *, not const char *, so in a production environment with more sophisticated build system, it's turned to an error:
...
cupy/core/dlpack.cpp:4298:32: error: invalid conversion from ‘const char*’ to ‘char*’ [-fpermissive]
__pyx_t_4 = PyCapsule_GetName(__pyx_v_dltensor); if (unlikely(__pyx_t_4 == ((char *)NULL) && PyErr_Occurred())) __PYX_ERR(0, 179, __pyx_L1_error)
~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
error: command 'gcc' failed with exit status 1
making any functions returning const char * not usable in Cython.
Expected behavior
It should just work by respecting the constness if declared in a cdef variable. Currently I don't even know how to work around it after scratching my head for a long time, which is rare to me...
Environment (please complete the following information):
- OS: Linux
- Python version 3.7.8
- Cython version 0.29.21
Additional context
None