Broken scikit-image build with 3.0a3 : redeclaration of ‘__pyx_gilstate_save’ with no linkage

The scikit-image pre builds is broken since Cython 3.0a3 was released yesterday.

The error is as follows:

skimage/graph/heap.c: In function ‘__pyx_f_7skimage_5graph_4heap_10BinaryHeap__add_or_remove_level’:
skimage/graph/heap.c:3299:20: error: redeclaration of ‘__pyx_gilstate_save’ with no linkage
   PyGILState_STATE __pyx_gilstate_save = __Pyx_PyGILState_Ensure();
                    ^~~~~~~~~~~~~~~~~~~
skimage/graph/heap.c:3296:20: note: previous declaration of ‘__pyx_gilstate_save’ was here
   PyGILState_STATE __pyx_gilstate_save;
                    ^~~~~~~~~~~~~~~~~~~

corresponding to this part of heap.pyx (https://github.com/scikit-image/scikit-image/blob/master/skimage/graph/heap.pyx#L190)

cdef void _add_or_remove_level(self, LEVELS_T add_or_remove) nogil:
        # init indexing ints
        cdef INDEX_T i, i1, i2, n

        # new amount of levels
        cdef LEVELS_T new_levels = self.levels + add_or_remove

        # allocate new arrays
        cdef INDEX_T number = 2**new_levels
        cdef VALUE_T *values
        cdef REFERENCE_T *references
        values = <VALUE_T *>malloc(number * 2 * sizeof(VALUE_T))
        references = <REFERENCE_T *>malloc(number * sizeof(REFERENCE_T))
        if values is NULL or references is NULL:
            free(values)
            free(references)
            with gil:
                raise MemoryError()

When I compare the generated C code with 3.0a1 and 3.0a2, only these part changed 3.0a1

#ifdef WITH_THREAD
PyGILState_STATE __pyx_gilstate_save = __Pyx_PyGILState_Ensure();
#endif

and 3.0a3

#ifdef WITH_THREAD
PyGILState_STATE __pyx_gilstate_save;
#endif
#ifdef WITH_THREAD
PyGILState_STATE __pyx_gilstate_save = __Pyx_PyGILState_Ensure();
#endif

so indeed __pyx_gilstate_save is defined twice.

Any advice about what is going on will be much appreciated 😃.

If it helps, here is a bit more of the C code (for 3.0a3):

static void __pyx_f_7skimage_5graph_4heap_10BinaryHeap__add_or_remove_level(struct __pyx_obj_7skimage_5graph_4heap_BinaryHeap *__pyx_v_self, __pyx_t_7skimage_5graph_4heap_LEVELS_T __pyx_v_add_or_remove) {
  __pyx_t_7skimage_5graph_4heap_INDEX_T __pyx_v_i;
  __pyx_t_7skimage_5graph_4heap_INDEX_T __pyx_v_i1;
  __pyx_t_7skimage_5graph_4heap_INDEX_T __pyx_v_i2;
  __pyx_t_7skimage_5graph_4heap_INDEX_T __pyx_v_n;
  __pyx_t_7skimage_5graph_4heap_LEVELS_T __pyx_v_new_levels;
  __pyx_t_7skimage_5graph_4heap_INDEX_T __pyx_v_number;
  __pyx_t_7skimage_5graph_4heap_VALUE_T *__pyx_v_values;
  __pyx_t_7skimage_5graph_4heap_REFERENCE_T *__pyx_v_references;
  __pyx_t_7skimage_5graph_4heap_VALUE_T *__pyx_v_old_values;
  __pyx_t_7skimage_5graph_4heap_REFERENCE_T *__pyx_v_old_references;
  __Pyx_RefNannyDeclarations
  int __pyx_t_1;
  int __pyx_t_2;
  __pyx_t_7skimage_5graph_4heap_INDEX_T __pyx_t_3;
  __pyx_t_7skimage_5graph_4heap_INDEX_T __pyx_t_4;
  __pyx_t_7skimage_5graph_4heap_INDEX_T __pyx_t_5;
  __pyx_t_7skimage_5graph_4heap_VALUE_T *__pyx_t_6;
  __pyx_t_7skimage_5graph_4heap_REFERENCE_T *__pyx_t_7;
  #ifdef WITH_THREAD
  PyGILState_STATE __pyx_gilstate_save;
  #endif
  #ifdef WITH_THREAD
  PyGILState_STATE __pyx_gilstate_save = __Pyx_PyGILState_Ensure();
  #endif
  __Pyx_RefNannySetupContext("_add_or_remove_level", 0);
  #ifdef WITH_THREAD
  __Pyx_PyGILState_Release(__pyx_gilstate_save);
  #endif

[scoder]

Note, BTW, that the method signature prevents exception propagation: cdef void _add_or_remove_level(self, LEVELS_T add_or_remove) nogil: Instead, either change the return type from void to something else, e.g. int (with except -1 or similar), or declare the method as except * to make the caller always check for exceptions.

Oh, and the with gil: is no longer required for the raise since 0.29. It’s injected automatically when raise is used in a nogil section.

[scoder]

Cython generates a warning here, but with warning level 0, i.e. it’s normally invisible. Setting Cython.Compiler.Errors.LEVEL = 0 will show it. (I guess there should be a better interface to that, preferably a keyword argument in cythonize()).