[PATCH 3 of 4] policy: add cffi policy for PyPy

[Maciej Fijalkowski]

# HG changeset patch
# User Maciej Fijalkowski <fijall at gmail.com>
# Date 1465306558 -7200
#      Tue Jun 07 15:35:58 2016 +0200
# Node ID 26a4063b4f1f36607dd673849449292ebc34a91d
# Parent  0cf6303b1018c063ec4ea732cb03dee674792fa8
policy: add cffi policy for PyPy

This adds cffi policy in the case where we don't want to use C modules,
but instead we're happy to rely on cffi (bundled with pypy)

diff -r 0cf6303b1018 -r 26a4063b4f1f mercurial/__init__.py
--- a/mercurial/__init__.py	Tue Jun 07 14:44:04 2016 +0200
+++ b/mercurial/__init__.py	Tue Jun 07 15:35:58 2016 +0200
@@ -17,11 +17,15 @@
 # Rules for how modules can be loaded. Values are:
 #
 #    c - require C extensions
-#    allow - allow pure Python implementation when C loading fails
+#    allow - allow cffi or pure Python implementation when C loading fails
+#    cffi - required cffi versions (implemented within pure module)
+#    cffi-allow - allow pure Python implementation if cffi version is missing
 #    py - only load pure Python modules
 #
 # By default, require the C extensions for performance reasons.
 modulepolicy = 'c'
+policynoc = ('cffi', 'cffi-allow', 'py')
+policynocffi = ('c', 'py')
 try:
     from . import __modulepolicy__
     modulepolicy = __modulepolicy__.modulepolicy
@@ -33,7 +37,7 @@
 # The canonical way to do this is to test platform.python_implementation().
 # But we don't import platform and don't bloat for it here.
 if '__pypy__' in sys.builtin_module_names:
-    modulepolicy = 'py'
+    modulepolicy = 'cffi'
 
 # Our C extensions aren't yet compatible with Python 3. So use pure Python
 # on Python 3 for now.
@@ -82,7 +86,7 @@
                 return zl
 
             try:
-                if modulepolicy == 'py':
+                if modulepolicy in policynoc:
                     raise ImportError()
 
                 zl = ziploader('mercurial')
@@ -109,7 +113,7 @@
         stem = name.split('.')[-1]
 
         try:
-            if modulepolicy == 'py':
+            if modulepolicy in policynoc:
                 raise ImportError()
 
             modinfo = imp.find_module(stem, mercurial.__path__)