fix: use StatusBase.__init_subclass__ instead of decorator to avoid o…

…bscuring subclass type (canonical#1383)

Previously, StatusBase.register obscured the type of decorated classes.
The classes would all end up typed as Type[StatusBase], and when instantiated
they would be typed as StatusBase instead of their actual class (see canonical#1380).
Instead we now register subclasses automatically in __init_subclass__,
no longer using StatusBase.register as a decorator, which avoids
obscuring the type of subclasses.

ops/model.py

@@ -1907,6 +1907,9 @@ def __init__(self, message: str = ''):
             raise TypeError('cannot instantiate a base class')
         self.message = message
 
+    def __init_subclass__(cls):
+        StatusBase.register(cls)
+
     def __eq__(self, other: 'StatusBase') -> bool:
         if not isinstance(self, type(other)):
             return False
@@ -1965,7 +1968,6 @@ def _get_highest_priority(cls, statuses: 'List[StatusBase]') -> 'StatusBase':
         return max(statuses, key=lambda status: cls._priorities.get(status.name, 0))
 
 
-@StatusBase.register
 class UnknownStatus(StatusBase):
     """The unit status is unknown.
 
@@ -1986,7 +1988,6 @@ def __repr__(self):
         return 'UnknownStatus()'
 
 
-@StatusBase.register
 class ErrorStatus(StatusBase):
     """The unit status is error.
 
@@ -2000,7 +2001,6 @@ class ErrorStatus(StatusBase):
     name = 'error'
 
 
-@StatusBase.register
 class ActiveStatus(StatusBase):
     """The unit or application is ready and active.
 
@@ -2016,7 +2016,6 @@ def __init__(self, message: str = ''):
         super().__init__(message)
 
 
-@StatusBase.register
 class BlockedStatus(StatusBase):
     """The unit or application requires manual intervention.
 
@@ -2027,7 +2026,6 @@ class BlockedStatus(StatusBase):
     name = 'blocked'
 
 
-@StatusBase.register
 class MaintenanceStatus(StatusBase):
     """The unit or application is performing maintenance tasks.
 
@@ -2041,7 +2039,6 @@ class MaintenanceStatus(StatusBase):
     name = 'maintenance'
 
 
-@StatusBase.register
 class WaitingStatus(StatusBase):
     """The unit or application is waiting on a charm it's integrated with.
 

test/test_model.py

@@ -820,11 +820,15 @@ def test_base_status_instance_raises(self):
         with pytest.raises(TypeError):
             ops.StatusBase('test')
 
-        class NoNameStatus(ops.StatusBase):
-            pass
+        with pytest.raises(TypeError):
+            # TypeError due to missing `name` attribute
+            class NoNameStatus(ops.StatusBase):  # pyright: ignore[reportUnusedClass]
+                pass
 
         with pytest.raises(TypeError):
-            ops.StatusBase.register(NoNameStatus)
+            # TypeError due to non str type `name` attribute
+            class NonStringNameStatus(ops.StatusBase):  # pyright: ignore[reportUnusedClass]
+                name = None  # pyright: ignore[reportAssignmentType]
 
     def test_status_repr(self):
         test_cases = {

test/test_testing.py

@@ -3232,6 +3232,9 @@ def test_get_filesystem_root(self):
 
     def test_evaluate_status(self):
         class TestCharm(ops.CharmBase):
+            app_status_to_add: ops.StatusBase
+            unit_status_to_add: ops.StatusBase
+
             def __init__(self, framework: ops.Framework):
                 super().__init__(framework)
                 self.framework.observe(self.on.collect_app_status, self._on_collect_app_status)