[PATCH 6 of 6 import-refactor V2] mercurial: don't load C extensions from PyPy

[Gregory Szorc]

# HG changeset patch
# User Gregory Szorc <gregory.szorc at gmail.com>
# Date 1448432511 28800
#      Tue Nov 24 22:21:51 2015 -0800
# Node ID f5a278521dc8cb5d076da2463bd3725d18dadae2
# Parent  45043395515abca0dc7290128b16752258be868b
mercurial: don't load C extensions from PyPy

PyPy isn't compatible with Python C extensions.

With this patch, the module load policy is automatically to "Python
only" when run under PyPy. `hg` and other Python scripts importing
mercurial.* modules will run from the source checkout or any
installation when executed with PyPy. This should enable people to
more easily experiment with PyPy and its potentially significant
performance benefits over CPython!

diff --git a/mercurial/__init__.py b/mercurial/__init__.py
--- a/mercurial/__init__.py
+++ b/mercurial/__init__.py
@@ -17,16 +17,23 @@ import sys
 #    allow - allow pure Python implementation when C loading fails
 #    py - only load pure Python modules
 modulepolicy = '@MODULELOADPOLICY@'
 
 # By default, require the C extensions for performance reasons.
 if modulepolicy == '@' 'MODULELOADPOLICY' '@':
     modulepolicy = 'c'
 
+# PyPy doesn't load C extensions.
+#
+# 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'
+
 # Environment variable can always force settings.
 modulepolicy = os.environ.get('HGMODULEPOLICY', modulepolicy)
 
 # Modules that have both Python and C implementations. See also the
 # set of .py files under mercurial/pure/.
 _dualmodules = set([
     'mercurial.base85',
     'mercurial.bdiff',