This is for debugging UnresolvedTypeErrors that come up sporadically in production. After digging through the code, I still don't know why this would happen.

Basically, this check is returning an empty array:

So, I added a debug message for each part of that check. For background, the different values included here are:

• Visibility#all_interface_type_memberships: { InterfaceType => { ObjectType => [TypeMembership, ...] } }. This map of types and memberhsips is totally unfiltered; it contains everything that the top-level Schema::Visibility instance has discovered in the schema. By the time it is referenced, the Visibility instance has performed ensure_all_loaded (because the only way to be sure you have them all is to traverse the whole schema), so it should never return a partial result.

• Visibility::Profile#referenced?(impl_type): This checks to make sure that impl_type has some visible reference inside the schema. (For Object types, references would be GraphQL::Schema::Field instances.) For a type included via .orphan_types(...), I would expect references to be populated by this code, such that all reference to the interface are propagated to the object that implements the interface:

  graphql-ruby/lib/graphql/schema/visibility.rb

  Lines 293 to 300 in 321e91e

  	@interface_type_memberships.each do |int_type, obj_type_memberships|
  	referrers = @all_references[int_type].select { |r| r.is_a?(GraphQL::Schema::Field) }
  	if !referrers.empty?
  	obj_type_memberships.each_key do |impl_type|
  	@all_references[impl_type] |= referrers
  	end
  	end
  	end

• @cached_visible[impl_type] checks that the type's .visible?(context) method returns true

• memberships.map { |itm| @cached_visible[itm] } checks that the TypeMembership object (which links the object type to the interface) also returns true. (You can implement #visible? on them to hide interface implementations while still publishing the interface type and the object type.)

This can be monkey-patched into the application like this:

# config/initializers/graphql_ruby_unresolved_type_monkey_patch.rb
class GraphQL::UnresolvedTypeError < GraphQL::RuntimeTypeError
  # Extend this method to include more debug info 
  # see https://github.com/rmosolgo/graphql-ruby/pull/5432
  def initialize(value, field, parent_type, resolved_type, possible_types)
    @value = value
    @field = field
    @parent_type = parent_type
    @resolved_type = resolved_type
    @possible_types = possible_types
    abstract_type = field.type.unwrap
    message = "The value from \"#{field.graphql_name}\" on \"#{parent_type.graphql_name}\" could not be resolved to \"#{abstract_type.to_type_signature}\". " \
      "(Received: `#{resolved_type.name ? resolved_type.inspect : resolved_type.graphql_name}`, Expected: [#{possible_types.map(&:graphql_name).join(", ")}]) " \
      "Make sure you have defined a `resolve_type` method on your schema and that value `#{value.inspect}` " \
      "gets resolved to a valid type. You may need to add your type to `orphan_types` if it implements an " \
      "interface but isn't a return type of any other field."

    if abstract_type.kind.interface? && (multiplex = Fiber[:__graphql_current_multiplex])
      types = multiplex.queries.first.types
      if types.is_a?(Schema::Visibility::Profile)
        message = message.dup
        visibility = types.instance_variable_get(:@visibility)
        cached_vis = types.instance_variable_get(:@cached_visible)
        message << "\n\n`#{abstract_type.graphql_name}.orphan_types`: #{abstract_type.orphan_types}"
        impls = visibility.all_interface_type_memberships[abstract_type]
        message << "\n`Schema.visibility.all_interface_type_memberships[#{abstract_type.graphql_name}]` (#{impls.size}):"
        impls.each do |(impl_type, memberships)|
          message << "\n    - `#{impl_type.graphql_name}` | Object? #{impl_type.kind.object?} | referenced? #{types.send(:referenced?, impl_type)} | visible? #{cached_vis[impl_type]} | membership_visible? #{memberships.map { |itm| cached_vis[itm]}}"
        end
      end
    end
    super(message)
  end
end