Rewrite return type when inheriting some c++ inplace operators

Cython/Compiler/Symtab.py

@@ -2587,6 +2587,7 @@ class CppClassScope(Scope):
         # to work with this type.
         for base_entry in \
             base_scope.inherited_var_entries + base_scope.var_entries:
+                base_entry_type = base_entry.type
                 #constructor/destructor is not inherited
                 if base_entry.name == "<del>"\
                    or base_entry.name == "<init>" and not self.parent_type.is_cyp_class\
@@ -2600,6 +2601,14 @@ class CppClassScope(Scope):
                                                                      return_type=self.parent_type)
                     wrapper_entry.is_inherited = 1
                 #print base_entry.name, self.entries
+                elif base_entry.name.startswith("operator")\
+                        and base_entry.name[8:] in ('+=', '-=', '*=', '/=', '%=', '<<=', '>>=', '&=', '|=', '^=')\
+                        and self.parent_type.is_cyp_class:
+                    # Rewrite return type for inplace operators.
+                    # This is needed for a correct type inference.
+                    base_entry_type = PyrexTypes.CFuncType(self.parent_type, base_entry_type.args, nogil=1,
+                                            has_varargs=base_entry_type.has_varargs,
+                                            optional_arg_count=base_entry_type.optional_arg_count)
                 elif base_entry.name == "__new__" and self.parent_type.is_cyp_class:
                     # Rewrite first argument for __new__
                     alloc_type = PyrexTypes.CPtrType(PyrexTypes.CFuncType(
@@ -2629,7 +2638,7 @@ class CppClassScope(Scope):
                 if base_entry.name in self.entries:
                     base_entry.name    # FIXME: is there anything to do in this case?
                 entry = self.declare(base_entry.name, base_entry.cname,
-                    base_entry.type, None, 'extern')
+                    base_entry_type, None, 'extern')
                 entry.is_variable = 1
                 entry.is_inherited = 1
                 entry.is_cfunction = base_entry.is_cfunction