Restore old behavior of resolve_type

We can't just call super because that just raises an exception. Since we
already have the accepts logic here, we just need to return the type if
it is part of the accepted types.

app/graphql/gitlab_schema.rb

@@ -79,7 +79,11 @@ def object_from_id(global_id, ctx = {})
     def resolve_type(type, object, ctx = :__undefined__)
       return if type.respond_to?(:assignable?) && !type.assignable?(object)
 
-      super
+      if type.kind.object?
+        type
+      else
+        super
+      end
     end
 
     # Find an object by looking it up from its 'GlobalID'.

spec/graphql/gitlab_schema_spec.rb

@@ -196,6 +196,39 @@ def initialize(id)
     end
   end
 
+  describe '.resolve_type' do
+    let(:object) { build(:user) }
+
+    let(:object_type) { Class.new(Types::BaseObject) }
+    let(:union_type) { Class.new(Types::BaseUnion) }
+
+    it 'returns the type for object types' do
+      expect(described_class.resolve_type(object_type, object, {})).to eq([object_type, object])
+    end
+
+    it 'raises an exception for non-object types' do
+      expect { described_class.resolve_type(union_type, object, {}) }.to raise_error(GraphQL::RequiredImplementationMissingError)
+    end
+
+    context 'when accepts is defined' do
+      let(:object_type) do
+        Class.new(Types::BaseObject) do
+          accepts User
+        end
+      end
+
+      it 'returns the type if the object is accepted' do
+        expect(described_class.resolve_type(object_type, object, {})).to eq([object_type, object])
+      end
+
+      it 'returns nil when object is not accepted' do
+        project = build(:project)
+
+        expect(described_class.resolve_type(object_type, project, {})).to eq([nil, project])
+      end
+    end
+  end
+
   describe 'validate_max_errors' do
     it 'reports at most 5 errors' do
       query = <<~GQL