chore: improve type-hinting for managers

The 'managers' are dynamically created. This unfortunately means that
we don't have any type-hints for them and so editors which understand
type-hints won't know that they are valid attributes.

 * Add the type-hints for the managers we define.
 * Add a unit test that makes sure that the type-hints and the
   '_managers' attribute are kept in sync with each other.
 * Add unit test that makes sure specified managers in '_managers'
   have a name ending in 'Managers' to keep with current convention.
 * Make RESTObject._managers always present with a default value of
   None.
 * Fix a type-issue revealed now that mypy knows what the type is

1 files changed, 3 insertions, 2 deletions

diff --git a/gitlab/base.py b/gitlab/base.py
index bea1901..361832e 100644
--- a/gitlab/base.py
+++ b/gitlab/base.py
@@ -49,6 +49,7 @@ class RESTObject(object):
     _parent_attrs: Dict[str, Any]
     _short_print_attr: Optional[str] = None
     _updated_attrs: Dict[str, Any]
+    _managers: Optional[Iterable[Tuple[str, str]]] = None
     manager: "RESTManager"
 
     def __init__(self, manager: "RESTManager", attrs: Dict[str, Any]) -> None:
@@ -150,13 +151,13 @@ class RESTObject(object):
         return hash(self.get_id())
 
     def _create_managers(self) -> None:
-        managers = getattr(self, "_managers", None)
-        if managers is None:
+        if self._managers is None:
             return
 
         for attr, cls_name in self._managers:
             cls = getattr(self._module, cls_name)
             manager = cls(self.manager.gitlab, parent=self)
+            # Since we have our own __setattr__ method, we can't use setattr()
             self.__dict__[attr] = manager
 
     def _update_attrs(self, new_attrs: Dict[str, Any]) -> None: