[Python-Dev] PY_FORMAT_SIZE_T warnings on OS X

[Tim Peters]

[Brett Cannon]
> I think these are all Tim's fault =) :

No, they're Anthony's fault :-)  He added this clause to pyport.h yesterday:

#   if SIZEOF_SIZE_T == SIZEOF_INT
#       define PY_FORMAT_SIZE_T ""

and that's obviously triggering on your platform.  He added this (at
my suggestion) to shut up similar gcc warnings on some other box. 
Before he added it, PY_FORMAT_SIZE_T was "l" on that box (and on
yours)  If it had remained "l", you wouldn't be getting warnings now,
but he still would.

On his box, the gripes where about passing a size_t argument to a
"%lu" format, but size_t resolved to unsigned int, not to unsigned
long.  sizeof(int) == sizeof(long) on that box (and on yours), so the
warning isn't really helpful.

> Objects/object.c: In function '_Py_NegativeRefcount':
> Objects/object.c:144: warning: format '%d' expects type 'int', but
> argument 7 has type 'Py_ssize_t'

And I bet (you should check) that Py_ssize_t resolves to "long" on
your box, and that sizeof(long) == sizeof(int) on your box, so that
again the warning is just a damned nuisance.

> ... [similar complaints] ...

> What's odd about them is that that the use of PY_FORMAT_SIZE_T seems
> to be correct, so I don't know what the problem is.

My best guess is above.  gcc appears to be generating type complaints
based on "name equivalence" rather than "structure equivalence" here
(meaning it's comparing integer types by the names they resolve to
rather than to the combination of size and signedness regardless of
name).  Worming around that would probably require a bunch of
poke-and-hope experimenting with various gcc's, of which I have none
:-)

>  Unfortunately ``gcc -E Include/pyport.h`` is no help since PY_FORMAT_SIZE_T
> is not showing up defined (possibly because gcc says it can't find pyconfig.h).

You can run on it this part in isolation:

#ifndef PY_FORMAT_SIZE_T
#   if SIZEOF_SIZE_T == SIZEOF_INT
#       define PY_FORMAT_SIZE_T ""
#   elif SIZEOF_SIZE_T == SIZEOF_LONG
#       define PY_FORMAT_SIZE_T "l"
#   elif defined(MS_WINDOWS)
#       define PY_FORMAT_SIZE_T "I"
#   else
#       error "This platform's pyconfig.h needs to define PY_FORMAT_SIZE_T"
#   endif
#endif

after sticking on the right expansions for the SIZEOF_xyz thingies --
but it's clear enough from the error messages that the SIZEOF_INT
branch is triggering (it's complaining about format '%d', not format
'%ld' or format '%Id').