Bad code generated for except +* function

[navytux]

Hello up there. Please consider the following example:

---- 8< ---- (y.pyx)

# cython: language_level=2
# distutils: language=c++

cdef extern from *:
    """
    #include <exception>
    void ggg() {
        throw std::bad_alloc();
    }
    """
    void ggg()

cdef void fff() except *:
    raise RuntimeError('aaa')

cdef void hhh() except +*:
    fff()
    ggg()

def aaa():
    hhh()

Explanation:

• ggg throws C++ exception and is not marked with except + -- thus functions that calls ggg may throw C++ exception themselves;
• fff raises Python exception but returns void. It thus is marked with except * for its caller to check whether Python exception occurred.
• hhh calls both fff and ggg. It thus may raise either Python exception (from fff) or C++ exception (from ggg). hhh is thus marked as except +*.

When trying to cythonize y.pyx, it gives:

/home/kirr/tmp/trashme/pyx/y.cpp: In function ‘void __pyx_f_1y_hhh()’:
/home/kirr/tmp/trashme/pyx/y.cpp:1189:3: error: ‘__pyx_r’ was not declared in this scope
   __pyx_r = <Cython.Compiler.ExprNodes.CharNode object at 0x7f8e76e20810>;
   ^~~~~~~
/home/kirr/tmp/trashme/pyx/y.cpp:1189:3: note: suggested alternative: ‘__pyx_f’
   __pyx_r = <Cython.Compiler.ExprNodes.CharNode object at 0x7f8e76e20810>;
   ^~~~~~~
   __pyx_f
/home/kirr/tmp/trashme/pyx/y.cpp:1189:13: error: expected primary-expression before ‘<’ token
   __pyx_r = <Cython.Compiler.ExprNodes.CharNode object at 0x7f8e76e20810>;
             ^
/home/kirr/tmp/trashme/pyx/y.cpp:1189:14: error: ‘Cython’ was not declared in this scope
   __pyx_r = <Cython.Compiler.ExprNodes.CharNode object at 0x7f8e76e20810>;
              ^~~~~~
/home/kirr/tmp/trashme/pyx/y.cpp: In function ‘PyObject* __pyx_pf_1y_aaa(PyObject*)’:
/home/kirr/tmp/trashme/pyx/y.cpp:1229:5: error: ‘__Pyx_CppExn2PyErr’ was not declared in this scope
     __Pyx_CppExn2PyErr();
     ^~~~~~~~~~~~~~~~~~

With the following code generated for hhh:

static void __pyx_f_1y_hhh(void) {
  __Pyx_RefNannyDeclarations
  __Pyx_RefNannySetupContext("hhh", 0);

  /* "y.pyx":17
 * 
 * cdef void hhh() except +*:
 *     fff()             # <<<<<<<<<<<<<<
 *     ggg()
 * 
 */
  __pyx_f_1y_fff(); if (unlikely(PyErr_Occurred())) __PYX_ERR(0, 17, __pyx_L1_error)

  /* "y.pyx":18
 * cdef void hhh() except +*:
 *     fff()
 *     ggg()             # <<<<<<<<<<<<<<
 * 
 * def aaa():
 */
  ggg();

  /* "y.pyx":16
 *     raise RuntimeError('aaa')
 * 
 * cdef void hhh() except +*:             # <<<<<<<<<<<<<<
 *     fff()
 *     ggg()
 */

  /* function exit code */
  goto __pyx_L0;
  __pyx_L1_error:;
  __Pyx_AddTraceback("y.hhh", __pyx_clineno, __pyx_lineno, __pyx_filename);
  __pyx_r = <Cython.Compiler.ExprNodes.CharNode object at 0x7f8e76e20810>;
  __pyx_L0:;
  __Pyx_RefNannyFinishContext();
}

Notice the __pyx_r = <Cython.Compiler.ExprNodes.CharNode object at 0x7f8e76e20810>; line.

Cython version: 0.29.13-514-gac1c9fe47 (today's master).

Thanks beforehand,
Kirill

[navytux]

#3064 is different, but probably related.

[maxbachmann]

Running into this as well. My current work around for this issue is the following dummy function:

cdef dummy() except +:
    dummy()

which tricks cython into generating

/* CppExceptionConversion.proto */
#ifndef __Pyx_CppExn2PyErr
#include <new>
#include <typeinfo>
#include <stdexcept>
#include <ios>
static void __Pyx_CppExn2PyErr() {
  try {
    if (PyErr_Occurred())
      ; // let the latest Python exn pass through and ignore the current one
    else
      throw;
  } catch (const std::bad_alloc& exn) {
    PyErr_SetString(PyExc_MemoryError, exn.what());
  } catch (const std::bad_cast& exn) {
    PyErr_SetString(PyExc_TypeError, exn.what());
  } catch (const std::bad_typeid& exn) {
    PyErr_SetString(PyExc_TypeError, exn.what());
  } catch (const std::domain_error& exn) {
    PyErr_SetString(PyExc_ValueError, exn.what());
  } catch (const std::invalid_argument& exn) {
    PyErr_SetString(PyExc_ValueError, exn.what());
  } catch (const std::ios_base::failure& exn) {
    PyErr_SetString(PyExc_IOError, exn.what());
  } catch (const std::out_of_range& exn) {
    PyErr_SetString(PyExc_IndexError, exn.what());
  } catch (const std::overflow_error& exn) {
    PyErr_SetString(PyExc_OverflowError, exn.what());
  } catch (const std::range_error& exn) {
    PyErr_SetString(PyExc_ArithmeticError, exn.what());
  } catch (const std::underflow_error& exn) {
    PyErr_SetString(PyExc_ArithmeticError, exn.what());
  } catch (const std::exception& exn) {
    PyErr_SetString(PyExc_RuntimeError, exn.what());
  }
  catch (...)
  {
    PyErr_SetString(PyExc_RuntimeError, "Unknown exception");
  }
}
#endif

[da-woods]

Looking at the original, only cdef extern functions should be except +. It definitely isn't safe to let C++ exceptions propagate through Cython-generated code. Therefore ggg should be except+ and hhh is except *.

It looks like there's somewhere that doesn't generate the correct utility code though... I'm not sure if that's because the assume that a Cython-defined function can't be except + (in which case we need to enforce it with an error message) or if the issue is elsewhere

[maxbachmann]

In my case I have C++ functions, that can throw exceptions or have an error set from e.g. PyUnicode_READY.

cdef extern from "example.hpp":
    double func1(...) except +*
    double func2() except +*

it was also not enough to add a dummy function in the C++ code

cdef extern from "example.hpp":
    double func1(...) except +*
    double func2() except +*
    dummy except +

apparently it only generates the code when the function is actually called

[da-woods]

Thanks @maxbachmann - that's a useful clarification

[da-woods]

bba6905

[navytux]

Thanks, @da-woods.