Print fields used by GraphQL query

print-fields.rb

require "set"
require "graphql"
require "json"

SCHEMA_PATH = ENV.fetch("SCHEMA") do
  abort "Run with SCHEMA=<path-to-schema.json> and try again."
end

SCHEMA = JSON.parse(File.read(SCHEMA_PATH))
REFERENCES = Hash.new do |h, t|
  h[t] = Hash.new { |h2, f| h2[f] = Set.new }
end

def get_field_type(type_name, field_name)
  types = SCHEMA["__schema"]["types"]

  type = types.find { _1["name"] == type_name }
  raise "No type named #{type_name}" unless type

  fields = type.fetch("fields", [])
  field = fields.find { _1["name"] == field_name }
  raise "No field named #{type_name}.#{field_name}" unless field

  field_type = field["type"]
  field_type = field_type["ofType"] while field_type["ofType"]
  field_type["name"]
end

def add_fields(type, selections, fragments:)
  fields = selections.grep(GraphQL::Language::Nodes::Field)
  fields.each do |field|
    field_type = get_field_type(type, field.name)
    field_location = "#{field.filename}:#{field.line}"

    REFERENCES[type][field.name] << field_location
    add_fields(field_type, field.selections, fragments: fragments)
  end

  spreads = selections.grep(GraphQL::Language::Nodes::FragmentSpread)
  spreads.each do |spread|
    fragment = fragments[spread.name]
    raise "No fragment named #{spread.name}" unless fragment

    add_fields(fragment.type.name, fragment.selections, fragments: fragments)
  end
end

ARGV.each do |path|
  document = GraphQL.parse_file(path)

  fragments = document.definitions.grep(GraphQL::Language::Nodes::FragmentDefinition)
  fragments = fragments.to_h { [_1.name, _1] }

  operations = document.definitions.grep(GraphQL::Language::Nodes::OperationDefinition)
  operations.each do |operation|
    operation_type = operation.operation_type.capitalize
    add_fields(operation_type, operation.selections, fragments: fragments)
  end
end

REFERENCES.sort.each do |type, fields|
  puts "#{type}:"
  fields.sort.each do |field, locations|
    puts "  #{field}:"
    locations.sort.each do |location|
      puts "    #{location}"
    end
  end
end