This Pull Request refactors some under-the-hood logic for how interface fields are applied to Interfaces and Object Types that implement interfaces to make things more performant.

Instead of using array_merge_recursive this instead does some diffing on the Implementing Type and the interface(s) being implemented and more efficiently applies any missing fields from the Interface to the implementing Type.

For context, below is a summary of the existing functionality this refactor impacts.

Summary of Existing Functionality this Impacts

When implementing an Interface on another Interface or ObjectType, WPGraphQL "automatically" ensures that any fields defined on the Interface(s) are added to the implementing Interface or Object Type if the implementing Type does not already have the field.

This allows for plugins to do things like:

add_action( 'graphql_register_types', function() {

	register_graphql_interface_type( 'MyTestInterface', [
		'fields' => [
			'fieldA' => [
				'type' => 'String',
				'resolve' => function() { return 'test value...'; },
			],
		]
	] );

	register_graphql_interfaces_to_types( [ 'MyTestInterface' ], [ 'Post' ] );

});

This code will apply the MyTestInterface to the Post Type, but will also ensure that the Post type has fieldA, which it previously did not.

Now I can successfully query like so:

{
  posts {
    nodes {
      id
      fieldA
    }
  }
}