issue#441: change modulename to include hash of source

This should make it work both for users and developers.

docs/install.rst

@@ -176,7 +176,7 @@ everytime. Verify yourself if curious:
 
 .. code-block:: sh
 
-   $ readelf --dynamic lib/python2.7/site-packages/pygit2-0.21.3-py2.7-linux-x86_64.egg/pygit2_cffi.so | grep PATH
+   $ readelf --dynamic lib/python2.7/site-packages/pygit2-0.21.3-py2.7-linux-x86_64.egg/_pygit2.so | grep PATH
     0x000000000000001d (RUNPATH)            Library runpath: [/tmp/venv/lib]
 
 

pygit2/_utils.py

@@ -31,11 +31,13 @@ pygit2 at run-time.
 """
 
 # Import from the Standard Library
+from binascii import crc32
 import inspect
 import codecs
 import os
 from os import getenv
 from os.path import abspath, dirname
+import sys
 
 
 #
@@ -72,9 +74,9 @@ def get_libgit2_paths():
 # Loads the cffi extension
 #
 def get_ffi():
-    from cffi import FFI
+    import cffi
 
-    ffi = FFI()
+    ffi = cffi.FFI()
 
     # Load C definitions
     dir_path = dirname(abspath(inspect.getfile(inspect.currentframe())))
@@ -82,10 +84,20 @@ def get_ffi():
     with codecs.open(decl_path, 'r', 'utf-8') as header:
         ffi.cdef(header.read())
 
+    # The modulename
+    # Simplified version of what cffi does: remove kwargs and vengine
+    preamble = "#include <git2.h>"
+    key = [sys.version[:3], cffi.__version__, preamble] + ffi._cdefsources
+    key = '\x00'.join(key)
+    if sys.version_info >= (3,):
+        key = key.encode('utf-8')
+    k1 = hex(crc32(key[0::2]) & 0xffffffff).lstrip('0x').rstrip('L')
+    k2 = hex(crc32(key[1::2]) & 0xffffffff).lstrip('0').rstrip('L')
+    modulename = 'pygit2_cffi_%s%s' % (k1, k2)
+
     # Load extension module
     libgit2_bin, libgit2_include, libgit2_lib = get_libgit2_paths()
-    C = ffi.verify("#include <git2.h>", modulename='pygit2_cffi',
-                   libraries=["git2"],
+    C = ffi.verify(preamble, modulename=modulename, libraries=["git2"],
                    include_dirs=[libgit2_include], library_dirs=[libgit2_lib])
 
     # Ok