fix rich eq/ne comparisons with string literals if they return non-boolean values

Cython/Compiler/ExprNodes.py

@@ -8723,7 +8723,7 @@ class CmpNode(object):
         # note: currently operand1 must get coerced to a Python object if we succeed here!
         if self.operator in ('==', '!='):
             type1, type2 = operand1.type, self.operand2.type
-            if type1.is_pyobject and type2.is_pyobject:
+            if type1.is_builtin_type and type2.is_builtin_type:
                 if type1 is Builtin.unicode_type or type2 is Builtin.unicode_type:
                     self.special_bool_cmp_utility_code = UtilityCode.load_cached("UnicodeEquals", "StringTools.c")
                     self.special_bool_cmp_function = "__Pyx_PyUnicode_Equals"

tests/run/richcmp_str_equals.py

+# mode: run
+
+class plop(object):
+    def __init__(self):
+        pass
+
+class testobj(object):
+    def __init__(self):
+        pass
+
+    def __eq__(self, other):
+        return plop()
+
+def test_equals():
+    """
+    >>> result = test_equals()
+    >>> isinstance(result, plop)
+    True
+    """
+    blah = testobj()
+    eq = blah == 'coucou'  # not every str equals returns a bool ...
+    return eq