Add directive to control pickling.

Cython/Compiler/Options.py

@@ -144,6 +144,7 @@ _directive_defaults = {
     'embedsignature' : False,
     'locals' : {},
     'auto_cpdef': False,
+    'auto_pickle': None,
     'cdivision': False, # was True before 0.12
     'cdivision_warnings': False,
     'overflowcheck': False,
@@ -263,6 +264,7 @@ def normalise_encoding_name(option_name, encoding):
 
 # Override types possibilities above, if needed
 directive_types = {
+    'auto_pickle': bool,
     'final' : bool,  # final cdef classes and methods
     'internal' : bool,  # cdef class visibility in the module dict
     'infer_types' : bool, # values can be True/None/False
@@ -285,6 +287,7 @@ for key, val in _directive_defaults.items():
 
 directive_scopes = { # defaults to available everywhere
     # 'module', 'function', 'class', 'with statement'
+    'auto_pickle': ('module', 'cclass'),
     'final' : ('cclass', 'function'),
     'inline' : ('function',),
     'staticmethod' : ('function',),  # FIXME: analysis currently lacks more specific function scope

Cython/Compiler/ParseTreeTransforms.py

@@ -1571,6 +1571,10 @@ if VALUE is not None:
 
     def _inject_pickle_methods(self, node):
         env = self.current_env()
+        if node.scope.directives['auto_pickle'] is False:   # None means attempt it.
+            # Old behavior of not doing anything.
+            return
+
         all_members = []
         cls = node.entry.type
         cinit = None
@@ -1590,7 +1594,11 @@ if VALUE is not None:
                 # TODO(robertwb): We could allow this if __cinit__ has no require arguments.
                 msg = 'no default __reduce__ due to non-trivial __cinit__'
             else:
-                msg = "%s cannot be converted to a Python object" % ','.join("self.%s" % e.name for e in non_py)
+                msg = "%s cannot be converted to a Python object for pickling" % ','.join("self.%s" % e.name for e in non_py)
+
+            if node.scope.directives['auto_pickle'] is True:
+                error(node.pos, msg)
+
             pickle_func = TreeFragment(u"""
                 def __reduce__(self):
                     raise TypeError("%s")

tests/run/reduce_pickle.pyx

+import cython
 import sys
 
 if sys.version_info[0] < 3:
@@ -59,6 +60,7 @@ def makeB(kwds):
     return B(**kwds)
 
 
+@cython.auto_pickle(True)  # Not needed, just to test the directive.
 cdef class DefaultReduce(object):
     """
     >>> a = DefaultReduce(11, 'abc'); a