Schema: Exclude OPTIONS/HEAD for ViewSet actions (#5532)

Closes #5528.

Viewset custom actions (@detail_route etc) OPTIONS (and HEAD) methods were not being excluded from Schema Generations.

This PR adds a test reproducing the reported error and adjusts `EndpointEnumerator.get_allowed_methods()` to filter ViewSet actions in the same way as other `APIView`s

rest_framework/schemas/generators.py

@@ -222,12 +222,11 @@ class EndpointEnumerator(object):
         if hasattr(callback, 'actions'):
             actions = set(callback.actions.keys())
             http_method_names = set(callback.cls.http_method_names)
-            return [method.upper() for method in actions & http_method_names]
+            methods = [method.upper() for method in actions & http_method_names]
+        else:
+            methods = callback.cls().allowed_methods
 
-        return [
-            method for method in
-            callback.cls().allowed_methods if method not in ('OPTIONS', 'HEAD')
-        ]
+        return [method for method in methods if method not in ('OPTIONS', 'HEAD')]
 
 
 class SchemaGenerator(object):

tests/test_schemas.py

@@ -901,3 +901,53 @@ def test_is_list_view_recognises_retrieve_view_subclasses():
 
     is_list = is_list_view(path, method, view)
     assert not is_list, "RetrieveAPIView subclasses should not be classified as list views."
+
+
+def test_head_and_options_methods_are_excluded():
+    """
+    Regression test for #5528
+    https://github.com/encode/django-rest-framework/issues/5528
+
+    Viewset OPTIONS actions were not being correctly excluded
+
+    Initial cases here shown to be working as expected.
+    """
+
+    @api_view(['options', 'get'])
+    def fbv(request):
+        pass
+
+    inspector = EndpointEnumerator()
+
+    path = '/a/path/'
+    callback = fbv
+
+    assert inspector.should_include_endpoint(path, callback)
+    assert inspector.get_allowed_methods(callback) == ["GET"]
+
+    class AnAPIView(APIView):
+
+        def get(self, request, *args, **kwargs):
+            pass
+
+        def options(self, request, *args, **kwargs):
+            pass
+
+    callback = AnAPIView.as_view()
+
+    assert inspector.should_include_endpoint(path, callback)
+    assert inspector.get_allowed_methods(callback) == ["GET"]
+
+    class AViewSet(ModelViewSet):
+
+        @detail_route(methods=['options', 'get'])
+        def custom_action(self, request, pk):
+            pass
+
+    callback = AViewSet.as_view({
+        "options": "custom_action",
+        "get": "custom_action"
+    })
+
+    assert inspector.should_include_endpoint(path, callback)
+    assert inspector.get_allowed_methods(callback) == ["GET"]