OS X with Homebrew: set PKG_CONFIG_PATHosx_use_homebrew

so that it automatically finds a Homebrew-installed libffi

Without this, I get:

    [marca@marca-mac2 cffi]$ python setup.py build
    Package libffi was not found in the pkg-config search path.
    Perhaps you should add the directory containing `libffi.pc'
    to the PKG_CONFIG_PATH environment variable
    No package 'libffi' found
    ...
    /usr/bin/clang -fno-strict-aliasing -fno-common -dynamic -g -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -arch x86_64 -I/usr/include/ffi -I/usr/include/libffi -I/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c c/_cffi_backend.c -o build/temp.macosx-10.6-intel-2.7/c/_cffi_backend.o
    c/_cffi_backend.c:13:10: fatal error: 'ffi.h' file not found
    #include <ffi.h>
             ^
    1 error generated.
    error: command '/usr/bin/clang' failed with exit status 1

With this, I get:

    [marca@marca-mac2 cffi]$ python setup.py build_ext -i
    ...
    /usr/bin/clang -fno-strict-aliasing -fno-common -dynamic -g -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -arch x86_64 -I/usr/local/Cellar/libffi/3.0.13/lib/libffi-3.0.13/include -I/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c c/_cffi_backend.c -o build/temp.macosx-10.6-intel-2.7/c/_cffi_backend.o
    creating build/lib.macosx-10.6-intel-2.7
    /usr/bin/clang -bundle -undefined dynamic_lookup -g -arch x86_64 build/temp.macosx-10.6-intel-2.7/c/_cffi_backend.o -L/usr/local/Cellar/libffi/3.0.13/lib -lffi -o build/lib.macosx-10.6-intel-2.7/_cffi_backend.so
    copying build/lib.macosx-10.6-intel-2.7/_cffi_backend.so ->
    [marca@marca-mac2 cffi]$ ls -l _cffi_backend.so
    -rwxr-xr-x+ 1 marca  staff  99844 Jan 27 17:11 _cffi_backend.so*
    [marca@marca-mac2 cffi]$ python -c "import _cffi_backend; print(_cffi_backend)"
    <module '_cffi_backend' from '_cffi_backend.so'>

1 files changed, 12 insertions, 0 deletions

diff --git a/setup.py b/setup.py
index 91247ce..6f8c7f2 100644
--- a/setup.py
+++ b/setup.py
@@ -66,12 +66,24 @@ def ask_supports_thread():
         sys.stderr.write("The above error message can be safely ignored\n")
 
 def use_pkg_config():
+    if sys.platform == 'darwin' and os.path.exists('/usr/local/bin/brew'):
+        use_homebrew_for_libffi()
+
     _ask_pkg_config(include_dirs,       '--cflags-only-I', '-I', sysroot=True)
     _ask_pkg_config(extra_compile_args, '--cflags-only-other')
     _ask_pkg_config(library_dirs,       '--libs-only-L', '-L', sysroot=True)
     _ask_pkg_config(extra_link_args,    '--libs-only-other')
     _ask_pkg_config(libraries,          '--libs-only-l', '-l')
 
+def use_homebrew_for_libffi():
+    # We can build by setting:
+    # PKG_CONFIG_PATH = $(brew --prefix libffi)/lib/pkgconfig
+    with os.popen('brew --prefix libffi') as brew_prefix_cmd:
+        prefix = brew_prefix_cmd.read().strip()
+    pkgconfig = os.path.join(prefix, 'lib', 'pkgconfig')
+    os.environ['PKG_CONFIG_PATH'] = (
+        os.environ.get('PKG_CONFIG_PATH', '') + ':' + pkgconfig)
+
 
 if sys.platform == 'win32':
     COMPILE_LIBFFI = 'c/libffi_msvc'    # from the CPython distribution