Add simple support for methods with the METH_CLASS flag

I think this is ok, but it's implemented pretty differently from CPython
for now so I'm not sure.

src/capi/descrobject.cpp

@@ -24,29 +24,39 @@ Box* BoxedMethodDescriptor::__call__(BoxedMethodDescriptor* self, Box* obj, Boxe
     assert(varargs->cls == tuple_cls);
     assert(kwargs->cls == dict_cls);
 
-    if (!isSubclass(obj->cls, self->type))
-        raiseExcHelper(TypeError, "descriptor '%s' requires a '%s' object but received a '%s'", self->method->ml_name,
-                       getFullNameOfClass(self->type).c_str(), getFullTypeName(obj).c_str());
+    int ml_flags = self->method->ml_flags;
+
+    int call_flags;
+    if (ml_flags & METH_CLASS) {
+        if (!isSubclass(obj->cls, type_cls))
+            raiseExcHelper(TypeError, "descriptor '%s' requires a type but received a '%s'", self->method->ml_name,
+                           getFullTypeName(obj).c_str());
+        call_flags = ml_flags & (~METH_CLASS);
+    } else {
+        if (!isSubclass(obj->cls, self->type))
+            raiseExcHelper(TypeError, "descriptor '%s' requires a '%s' object but received a '%s'",
+                           self->method->ml_name, getFullNameOfClass(self->type).c_str(), getFullTypeName(obj).c_str());
+        call_flags = ml_flags;
+    }
 
     threading::GLPromoteRegion _gil_lock;
 
-    int ml_flags = self->method->ml_flags;
     Box* rtn;
-    if (ml_flags == METH_NOARGS) {
+    if (call_flags == METH_NOARGS) {
         assert(varargs->elts.size() == 0);
         assert(kwargs->d.size() == 0);
         rtn = (Box*)self->method->ml_meth(obj, NULL);
-    } else if (ml_flags == METH_VARARGS) {
+    } else if (call_flags == METH_VARARGS) {
         assert(kwargs->d.size() == 0);
         rtn = (Box*)self->method->ml_meth(obj, varargs);
-    } else if (ml_flags == (METH_VARARGS | METH_KEYWORDS)) {
+    } else if (call_flags == (METH_VARARGS | METH_KEYWORDS)) {
         rtn = (Box*)((PyCFunctionWithKeywords)self->method->ml_meth)(obj, varargs, kwargs);
-    } else if (ml_flags == METH_O) {
+    } else if (call_flags == METH_O) {
         assert(kwargs->d.size() == 0);
         assert(varargs->elts.size() == 1);
         rtn = (Box*)self->method->ml_meth(obj, varargs->elts[0]);
     } else {
-        RELEASE_ASSERT(0, "0x%x", ml_flags);
+        RELEASE_ASSERT(0, "0x%x", call_flags);
     }
 
     checkAndThrowCAPIException();

src/capi/modsupport.cpp

@@ -389,7 +389,8 @@ extern "C" PyObject* Py_InitModule4(const char* name, PyMethodDef* methods, cons
         if (VERBOSITY())
             printf("Loading method %s\n", methods->ml_name);
 
-        assert((methods->ml_flags & (~(METH_VARARGS | METH_KEYWORDS | METH_NOARGS | METH_O))) == 0);
+        RELEASE_ASSERT((methods->ml_flags & (~(METH_VARARGS | METH_KEYWORDS | METH_NOARGS | METH_O))) == 0, "%d",
+                       methods->ml_flags);
         module->giveAttr(methods->ml_name,
                          new BoxedCApiFunction(methods->ml_flags, passthrough, methods->ml_name, methods->ml_meth));
 

src/capi/types.h

@@ -144,10 +144,20 @@ public:
     static Box* __get__(BoxedMethodDescriptor* self, Box* inst, Box* owner) {
         RELEASE_ASSERT(self->cls == method_cls, "");
 
+        // CPython handles this differently: they create the equivalent of different BoxedMethodDescriptor
+        // objects but with different class objects, which define different __get__ and __call__ methods.
+        if (self->method->ml_flags & METH_CLASS)
+            return boxInstanceMethod(owner, self);
+
+        if (self->method->ml_flags & METH_STATIC)
+            Py_FatalError("unimplemented");
+        if (self->method->ml_flags & METH_COEXIST)
+            Py_FatalError("unimplemented");
+
         if (inst == None)
             return self;
-        // CPython apparently returns a "builtin_function_or_method" object
-        return boxInstanceMethod(inst, self);
+        else
+            return boxInstanceMethod(inst, self);
     }
 
     static Box* __call__(BoxedMethodDescriptor* self, Box* obj, BoxedTuple* varargs, Box** _args);

test/tests/datetime_test.py

@@ -6,3 +6,6 @@ print repr(datetime.time())
 print datetime.datetime.__base__
 print repr(datetime.datetime(1, 2, 3))
 print str(datetime.timedelta(0))
+
+# now() works on both the class and on its instances:
+datetime.datetime.now().now()