Take inheritance into account when presenting fields

changelogs/unreleased/ajk-fix-merge-requests-assignees-web-url.yml

+---
+title: Fix regression in GraphQL field MergeRequest.assignees.webUrl
+merge_request: 60428
+author:
+type: fixed

lib/gitlab/graphql/present.rb

@@ -10,14 +10,14 @@ module Gitlab
         end
 
         def self.presenter_class
-          @presenter_class
+          @presenter_class || superclass.try(:presenter_class)
         end
 
         def self.present(object, attrs)
-          klass = @presenter_class
+          klass = presenter_class
           return object if !klass || object.is_a?(klass)
 
-          @presenter_class.new(object, **attrs)
+          klass.new(object, **attrs)
         end
       end
 

spec/lib/gitlab/graphql/present/field_extension_spec.rb

@@ -63,6 +63,16 @@ RSpec.describe Gitlab::Graphql::Present::FieldExtension do
 
       expect(value).to eq 'made of concrete'
     end
+
+    context 'when the implementation is inherited' do
+      it 'resolves the interface field using the implementation from the presenter' do
+        subclass = Class.new(implementation) { graphql_name 'Subclass' }
+        field = ::Types::BaseField.new(name: :interface_field, type: GraphQL::STRING_TYPE, null: true, owner: interface)
+        value = resolve_field(field, object, object_type: subclass)
+
+        expect(value).to eq 'made of concrete'
+      end
+    end
   end
 
   describe 'interactions with inheritance' do