class GraphQL::StaticValidation::FieldsHaveAppropriateSelections

def validate(context)
  context.visitor[GraphQL::Language::Nodes::Field] << -> (node, parent)  {
    return if context.skip_field?(node.name)
    field_defn = context.field_definition
    validate_field_selections(node, field_defn, context)
  }
end

def validate_field_selections(ast_field, field_defn, context)
  resolved_type = field_defn.type.unwrap
  if resolved_type.kind.scalar? && ast_field.selections.any?
    error = message("Selections can't be made on scalars (field '#{ast_field.name}' returns #{resolved_type.name} but has selections [#{ast_field.selections.map(&:name).join(", ")}])", ast_field, context: context)
  elsif resolved_type.kind.object? && ast_field.selections.none?
    error = message("Objects must have selections (field '#{ast_field.name}' returns #{resolved_type.name} but has no selections)", ast_field, context: context)
  else
    error = nil
  end
  if !error.nil?
    context.errors << error
    GraphQL::Language::Visitor::SKIP
  end
end