Cython 0.26 generates invalid C in extension type __iter__ methods for MSVC and Python 2.7

[mobiusklein]

Given the following extension class

cdef class PolynomialParameters(object):
    cdef:
        public list elementary_symmetric_polynomial
        public list power_sum
    def __init__(self, elementary_symmetric_polynomial, power_sum):
        self.elementary_symmetric_polynomial = elementary_symmetric_polynomial
        self.power_sum = power_sum

    def __iter__(self):
        yield self.power_sum
        yield self.elementary_symmetric_polynomial

Cython 0.26 generates the following code for the class's __iter__ method:

static PyObject *__pyx_gb_7brainpy_8_speedup_20PolynomialParameters_4generator(__pyx_CoroutineObject *__pyx_generator, PyObject *__pyx_sent_value) /* generator body */
{
  struct __pyx_obj_7brainpy_8_speedup___pyx_scope_struct____iter__ *__pyx_cur_scope = ((struct __pyx_obj_7brainpy_8_speedup___pyx_scope_struct____iter__ *)__pyx_generator->closure);
  PyObject *__pyx_r = NULL;
  __Pyx_RefNannyDeclarations
  __Pyx_RefNannySetupContext("None", 0);
  __Pyx_TraceDeclarations
  __Pyx_TraceCall("__iter__", __pyx_f[0], 105, 0, __PYX_ERR(0, 105, __pyx_L1_error));
  switch (__pyx_generator->resume_label) {
    case 0: goto __pyx_L3_first_run;
    case 1: goto __pyx_L4_resume_from_yield;
    case 2: goto __pyx_L5_resume_from_yield;
    default: /* CPython raises the right error here */
    __Pyx_TraceReturn(Py_None, 0);
    __Pyx_RefNannyFinishContext();
    return NULL;
  }
 //gotos....

The line __Pyx_TraceDeclarations looks like it was meant to be a macro, given that it has no trailing semi-colon, but MSVC appears to be seeing it literally and throws the error error C2143: syntax error : missing ';' before 'type'.

Cython 0.25.2 generated the following code for the same method

static PyObject *__pyx_gb_7brainpy_8_speedup_20PolynomialParameters_4generator(__pyx_CoroutineObject *__pyx_generator, PyObject *__pyx_sent_value) /* generator body */
{
  struct __pyx_obj_7brainpy_8_speedup___pyx_scope_struct____iter__ *__pyx_cur_scope = ((struct __pyx_obj_7brainpy_8_speedup___pyx_scope_struct____iter__ *)__pyx_generator->closure);
  PyObject *__pyx_r = NULL;
  __Pyx_RefNannyDeclarations
  __Pyx_RefNannySetupContext("None", 0);
  switch (__pyx_generator->resume_label) {
    case 0: goto __pyx_L3_first_run;
    case 1: goto __pyx_L4_resume_from_yield;
    case 2: goto __pyx_L5_resume_from_yield;
    default: /* CPython raises the right error here */
    __Pyx_RefNannyFinishContext();
    return NULL;
  }
 //gotos...

which compiles successfully with the same setup.

There is no issue on Linux. Could it be that __Pyx_TraceDeclarations is only defined inside a Unix-specific preprocessor block?

The repository this code is from is https://github.com/mobiusklein/brainpy, and the file being compiled is brainpy/_speedup.pyx in the course of the standard python setup.py install process

[scoder]

Thank you for the very detailed report.