[Cython] unexpected side-effect in cython utility code

[Stefan Behnel]

Hi,

I started working on better malloc() support and wrote this code as a test 
to get going:

"""
cimport cython

def test_malloc(int n):
     with cython.malloc(n*sizeof(int)) as m:
         for i in range(n):
             m[i] = i
         l = [ m[i] for i in range(n) ]
     return l
"""

Now, when I compile this normally, I get a compiler error about "malloc" 
not being a cython attribute. However, when I do the same in the test 
runner, it compiles without errors and crashes when trying to run the test. 
The code it generates for the 'with' statement above starts like this:

"""
     __pyx_t_1 = PyObject_GetAttr(((PyObject *)malloc((__pyx_v_n * 
(sizeof(int))))), __pyx_n_s____exit__); /*...*/
"""

It appears that something has declared malloc(). I'm pretty sure it's this 
code in UtilityCode.py:

"""
     def declare_in_scope(self, dest_scope, used=False, cython_scope=None):
         """
         Declare all entries from the utility code in dest_scope. Code will
         only be included for used entries. If module_name is given,
         declare the type entries with that name.
         """
         tree = self.get_tree(entries_only=True, cython_scope=cython_scope)

         entries = tree.scope.entries
         entries.pop('__name__')
         entries.pop('__file__')
         entries.pop('__builtins__')
         entries.pop('__doc__')

         for name, entry in entries.iteritems():
             entry.utility_code_definition = self
             entry.used = used
"""

Basically, it declares everything it finds except for an explicit 
blacklist. Bad design. As I argued before, it should use a whitelist in the 
utility code file instead, which specifically lists the names that should 
be public. Everything else should just be considered implementation details.

Stefan