much more informative pickle error messages if pickling is not enabled

[SVN r34004]

src/object/class.cpp

@@ -530,6 +530,10 @@ namespace objects
       if (scope().ptr() != Py_None)
           scope().attr(name) = result;
 
+      // For pickle. Will lead to informative error messages if pickling
+      // is not enabled.
+      result.attr("__reduce__") = object(make_instance_reduce_function());
+
       return result;
     }
   }
@@ -627,7 +631,6 @@ namespace objects
 
   void class_base::enable_pickling_(bool getstate_manages_dict)
   {
-      setattr("__reduce__", object(make_instance_reduce_function()));
       setattr("__safe_for_unpickling__", object(true));
       
       if (getstate_manages_dict)

src/object/pickle_support.cpp

@@ -8,6 +8,7 @@
 #include <boost/python/tuple.hpp>
 #include <boost/python/list.hpp>
 #include <boost/python/dict.hpp>
+#include <boost/python/str.hpp>
 
 namespace boost { namespace python {
 
@@ -19,6 +20,22 @@ namespace {
       object instance_class(instance_obj.attr("__class__"));
       result.append(instance_class);
       object none;
+      if (!getattr(instance_obj, "__safe_for_unpickling__", none))
+      {
+          str type_name(getattr(instance_class, "__name__"));
+          str module_name(getattr(instance_class, "__module__", ""));
+          if (module_name)
+              module_name += ".";
+
+          PyErr_SetObject(
+               PyExc_RuntimeError,
+               ( "Pickling of \"%s\" instances is not enabled"
+                 " (http://www.boost.org/libs/python/doc/v2/pickle.html)"
+                  % (module_name+type_name)).ptr()
+          );
+
+          throw_error_already_set();
+      }
       object getinitargs = getattr(instance_obj, "__getinitargs__", none);
       tuple initargs;
       if (getinitargs.ptr() != none.ptr()) {

test/pickle1.cpp

@@ -45,6 +45,8 @@ namespace {
     }
   };
 
+  // To support test of "pickling not enabled" error message.
+  struct noop {};
 }
 
 BOOST_PYTHON_MODULE(pickle1_ext)
@@ -54,4 +56,7 @@ BOOST_PYTHON_MODULE(pickle1_ext)
       .def("greet", &world::greet)
       .def_pickle(world_pickle_suite())
       ;
+
+  // To support test of "pickling not enabled" error message.
+  class_<noop>("noop");
 }

test/pickle1.py

@@ -18,6 +18,11 @@ r'''>>> import pickle1_ext
     Hello from California!
     >>> print wl.greet()
     Hello from California!
+
+    >>> noop = pickle1_ext.noop()
+    >>> try: pickle.dumps(noop)
+    ... except RuntimeError, e: print str(e)[:55]
+    Pickling of "pickle1_ext.noop" instances is not enabled
 '''
 
 def run(args = None):