Correct the signature of "__richcmp__()": first argument is "self", not "object".

CHANGES.rst

@@ -88,6 +88,10 @@ Bugs fixed
   CPython with a live exception set.  This triggered incorrect behaviour
   and crashes, especially in CPython 3.7.
 
+* The signature of the special ``__richcmp__()`` method was corrected to recognise
+  the type of the first argument as ``self``.  It was previously treated as plain
+  object, but CPython actually guarantees that it always has the correct type.
+
 * Some async helper functions were not defined in the generated C code when
   compiling simple async code.  (Github issue #2075)
 

Cython/Compiler/TypeSlots.py

@@ -678,8 +678,7 @@ delattrofunc = Signature("TO", 'r')
 cmpfunc = Signature("TO", "i")             # typedef int (*cmpfunc)(PyObject *, PyObject *);
 reprfunc = Signature("T", "O")             # typedef PyObject *(*reprfunc)(PyObject *);
 hashfunc = Signature("T", "h")             # typedef Py_hash_t (*hashfunc)(PyObject *);
-                                           # typedef PyObject *(*richcmpfunc) (PyObject *, PyObject *, int);
-richcmpfunc = Signature("OOi", "O")        # typedef PyObject *(*richcmpfunc) (PyObject *, PyObject *, int);
+richcmpfunc = Signature("TOi", "O")        # typedef PyObject *(*richcmpfunc) (PyObject *, PyObject *, int);
 getiterfunc = Signature("T", "O")          # typedef PyObject *(*getiterfunc) (PyObject *);
 iternextfunc = Signature("T", "O")         # typedef PyObject *(*iternextfunc) (PyObject *);
 descrgetfunc = Signature("TOO", "O")       # typedef PyObject *(*descrgetfunc) (PyObject *, PyObject *, PyObject *);