Fix inheritance bugs with @extend_schema_view().

When creating a copy of a method from a parent class we now:

- Move application of the decorator to the last moment.
- Shallow copy the existing schema extensions before applying decorator.

This fixes #218 where two child classes with @extend_schema_view affect
each other - schema extensions are applied to the parent such that the
second child overwrites the changes applied to the first child.

This also fixes my case where a child with @extend_schema_view clobbered
the schema extensions of the parent which also used @extend_schema_view.

drf_spectacular/utils.py

@@ -473,12 +473,14 @@ def extend_schema_view(**kwargs) -> Callable[[F], F]:
       calls as values
     """
     def wrapping_decorator(method_decorator, method):
-        @method_decorator
         @functools.wraps(method)
         def wrapped_method(self, request, *args, **kwargs):
             return method(self, request, *args, **kwargs)
 
-        return wrapped_method
+        if hasattr(method, 'kwargs'):
+            wrapped_method.kwargs = method.kwargs.copy()
+
+        return method_decorator(wrapped_method)
 
     def decorator(view):
         view_methods = {m.__name__: m for m in get_view_methods(view)}

tests/test_extend_schema_view.py

@@ -28,7 +28,7 @@ class Meta:
     extended_action=extend_schema(description='view extended action description'),
     raw_action=extend_schema(description='view raw action description'),
 )
-class XViewset(mixins.ListModelMixin, mixins.RetrieveModelMixin, viewsets.GenericViewSet):
+class XViewSet(mixins.ListModelMixin, mixins.RetrieveModelMixin, viewsets.GenericViewSet):
     queryset = ESVModel.objects.all()
     serializer_class = ESVSerializer
 
@@ -52,9 +52,24 @@ class YViewSet(viewsets.ModelViewSet):
     queryset = ESVModel.objects.all()
 
 
+# view to make sure that schema applied to a subclass does not affect its parent.
+@extend_schema_view(
+    list=extend_schema(exclude=True),
+    retrieve=extend_schema(description='overridden description for child only'),
+    extended_action=extend_schema(responses={200: {'type': 'string', 'pattern': r'^[0-9]{4}(?:-[0-9]{2}){2}$'}}),
+    raw_action=extend_schema(summary="view raw action summary"),
+)
+class ZViewSet(XViewSet):
+    @extend_schema(tags=['child-tag'])
+    @action(detail=False, methods=['GET'])
+    def raw_action(self, request):
+        return Response('2019-03-01')
+
+
 router = routers.SimpleRouter()
-router.register('x', XViewset)
+router.register('x', XViewSet)
 router.register('y', YViewSet)
+router.register('z', ZViewSet)
 urlpatterns = router.urls
 
 

tests/test_extend_schema_view.yml

@@ -232,6 +232,65 @@ paths:
       responses:
         '204':
           description: No response body
+  /z/{id}/:
+    get:
+      operationId: z_retrieve
+      description: overridden description for child only
+      parameters:
+      - in: path
+        name: id
+        schema:
+          type: integer
+        description: A unique integer value identifying this esv model.
+        required: true
+      tags:
+      - custom-retrieve-tag
+      security:
+      - cookieAuth: []
+      - basicAuth: []
+      - {}
+      responses:
+        '200':
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ESV'
+          description: ''
+  /z/extended_action/:
+    get:
+      operationId: z_extended_action_retrieve
+      description: view extended action description
+      tags:
+      - global-tag
+      security:
+      - cookieAuth: []
+      - basicAuth: []
+      - {}
+      responses:
+        '200':
+          content:
+            application/json:
+              schema:
+                type: string
+                pattern: ^[0-9]{4}(?:-[0-9]{2}){2}$
+          description: ''
+  /z/raw_action/:
+    get:
+      operationId: z_raw_action_retrieve
+      summary: view raw action summary
+      tags:
+      - child-tag
+      security:
+      - cookieAuth: []
+      - basicAuth: []
+      - {}
+      responses:
+        '200':
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ESV'
+          description: ''
 components:
   schemas:
     ESV:

tests/test_regressions.py

@@ -2569,3 +2569,38 @@ def custom_action(self):
 
     schema = generate_schema('x', viewset=XViewSet)
     schema['paths']['/x/{id}/custom_action/']['get']['summary'] == 'A custom action!'
+
+
+def test_extend_schema_view_isolation(no_warnings):
+
+    class Animal(models.Model):
+        pass
+
+    class AnimalSerializer(serializers.ModelSerializer):
+        class Meta:
+            model = Animal
+            fields = '__all__'
+
+    class AnimalViewSet(viewsets.GenericViewSet):
+        serializer_class = AnimalSerializer
+        queryset = Animal.objects.all()
+
+        @action(detail=False)
+        def notes(self, request):
+            pass  # pragma: no cover
+
+    @extend_schema_view(notes=extend_schema(summary='List mammals.'))
+    class MammalViewSet(AnimalViewSet):
+        pass
+
+    @extend_schema_view(notes=extend_schema(summary='List insects.'))
+    class InsectViewSet(AnimalViewSet):
+        pass
+
+    router = routers.SimpleRouter()
+    router.register('api/mammals', MammalViewSet)
+    router.register('api/insects', InsectViewSet)
+
+    schema = generate_schema(None, patterns=router.urls)
+    assert schema['paths']['/api/mammals/notes/']['get']['summary'] == 'List mammals.'
+    assert schema['paths']['/api/insects/notes/']['get']['summary'] == 'List insects.'