Open Radar

 
Summary:
python-config --cflags emits -mno-fused-madd, but that option hasn't been supported by XCode compilers for quite some time.  However, a recent XCode (5.1?) seems to have made unsupported commandline options a hard failure by default, causing python modules with C code to fail to build.

As far as I can tell, this option was removed from the baseline Python source in 2.6:  http://bugs.python.org/issue1779871.

The option should be removed from OSX Python as well (all three versions).

One can workaround this in some cases by setting:
export ARCHFLAGS="-Wno-error=unused-command-line-argument-hard-error-in-future"

Also of note is that the error message clang gives indicates that the unknown commandline option is NOT currently an error, but will be in the future, which is incorrect:
  clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
  clang: note: this will be a hard error (cannot be downgraded to a warning) in the future

Steps to Reproduce:
Environment: OSX 10.9.2, XCode 5.1.1
$ curl -O https://pypi.python.org/packages/source/S/SQLAlchemy/SQLAlchemy-0.7.9.tar.gz
$ tar xf SQLAlchemy-0.7.9.tar.gz
$ cd  SQLAlchemy-0.7.9
$ python setup.py build


Expected Results:
The python module above contains a C module that SHOULD compile, but doesn't; this particular module falls back to pure-python, but not all modules have that option.

Actual Results:
The C portion of the python module fails to compile, with the following errors output:
cc -fno-strict-aliasing -fno-common -dynamic -arch x86_64 -arch i386 -g -Os -pipe -fno-common -fno-strict-aliasing -fwrapv -mno-fused-madd -DENABLE_DTRACE -DMACOSX -DNDEBUG -Wall -Wstrict-prototypes -Wshorten-64-to-32 -DNDEBUG -g -fwrapv -Os -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch x86_64 -arch i386 -pipe -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c lib/sqlalchemy/cextension/processors.c -o build/temp.macosx-10.9-intel-2.7/lib/sqlalchemy/cextension/processors.o
clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
***************************************************************************
command 'cc' failed with exit status 1
WARNING: The C extension could not be compiled, speedups are not enabled.
Failure information, if any, is above.
Retrying the build without the C extension now.
***************************************************************************