definition.js

// @flow strict

import objectEntries from '../polyfills/objectEntries';

import inspect from '../jsutils/inspect';
import keyMap from '../jsutils/keyMap';
import mapValue from '../jsutils/mapValue';
import toObjMap from '../jsutils/toObjMap';
import { type Path } from '../jsutils/Path';
import devAssert from '../jsutils/devAssert';
import keyValMap from '../jsutils/keyValMap';
import instanceOf from '../jsutils/instanceOf';
import isObjectLike from '../jsutils/isObjectLike';
import identityFunc from '../jsutils/identityFunc';
import defineToJSON from '../jsutils/defineToJSON';
import defineToStringTag from '../jsutils/defineToStringTag';
import { type PromiseOrValue } from '../jsutils/PromiseOrValue';
import {
  type ObjMap,
  type ReadOnlyObjMap,
  type ReadOnlyObjMapLike,
} from '../jsutils/ObjMap';

import { Kind } from '../language/kinds';
import {
  type ScalarTypeDefinitionNode,
  type ObjectTypeDefinitionNode,
  type FieldDefinitionNode,
  type InputValueDefinitionNode,
  type InterfaceTypeDefinitionNode,
  type UnionTypeDefinitionNode,
  type EnumTypeDefinitionNode,
  type EnumValueDefinitionNode,
  type InputObjectTypeDefinitionNode,
  type ScalarTypeExtensionNode,
  type ObjectTypeExtensionNode,
  type InterfaceTypeExtensionNode,
  type UnionTypeExtensionNode,
  type EnumTypeExtensionNode,
  type InputObjectTypeExtensionNode,
  type OperationDefinitionNode,
  type FieldNode,
  type FragmentDefinitionNode,
  type ValueNode,
} from '../language/ast';

import { valueFromASTUntyped } from '../utilities/valueFromASTUntyped';

import { type GraphQLSchema } from './schema';

// Predicates & Assertions

/**
 * These are all of the possible kinds of types.
 */
export type GraphQLType =
  | GraphQLScalarType
  | GraphQLObjectType
  | GraphQLInterfaceType
  | GraphQLUnionType
  | GraphQLEnumType
  | GraphQLInputObjectType
  | GraphQLList<any>
  | GraphQLNonNull<any>;

export function isType(type: mixed): boolean %checks {
  return (
    isScalarType(type) ||
    isObjectType(type) ||
    isInterfaceType(type) ||
    isUnionType(type) ||
    isEnumType(type) ||
    isInputObjectType(type) ||
    isListType(type) ||
    isNonNullType(type)
  );
}

export function assertType(type: mixed): GraphQLType {
  if (!isType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL type.`);
  }
  return type;
}

/**
 * There are predicates for each kind of GraphQL type.
 */

declare function isScalarType(type: mixed): boolean %checks(type instanceof
  GraphQLScalarType);
// eslint-disable-next-line no-redeclare
export function isScalarType(type) {
  return instanceOf(type, GraphQLScalarType);
}

export function assertScalarType(type: mixed): GraphQLScalarType {
  if (!isScalarType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL Scalar type.`);
  }
  return type;
}

declare function isObjectType(type: mixed): boolean %checks(type instanceof
  GraphQLObjectType);
// eslint-disable-next-line no-redeclare
export function isObjectType(type) {
  return instanceOf(type, GraphQLObjectType);
}

export function assertObjectType(type: mixed): GraphQLObjectType {
  if (!isObjectType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL Object type.`);
  }
  return type;
}

declare function isInterfaceType(type: mixed): boolean %checks(type instanceof
  GraphQLInterfaceType);
// eslint-disable-next-line no-redeclare
export function isInterfaceType(type) {
  return instanceOf(type, GraphQLInterfaceType);
}

export function assertInterfaceType(type: mixed): GraphQLInterfaceType {
  if (!isInterfaceType(type)) {
    throw new Error(
      `Expected ${inspect(type)} to be a GraphQL Interface type.`,
    );
  }
  return type;
}

declare function isUnionType(type: mixed): boolean %checks(type instanceof
  GraphQLUnionType);
// eslint-disable-next-line no-redeclare
export function isUnionType(type) {
  return instanceOf(type, GraphQLUnionType);
}

export function assertUnionType(type: mixed): GraphQLUnionType {
  if (!isUnionType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL Union type.`);
  }
  return type;
}

declare function isEnumType(type: mixed): boolean %checks(type instanceof
  GraphQLEnumType);
// eslint-disable-next-line no-redeclare
export function isEnumType(type) {
  return instanceOf(type, GraphQLEnumType);
}

export function assertEnumType(type: mixed): GraphQLEnumType {
  if (!isEnumType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL Enum type.`);
  }
  return type;
}

declare function isInputObjectType(type: mixed): boolean %checks(type instanceof
  GraphQLInputObjectType);
// eslint-disable-next-line no-redeclare
export function isInputObjectType(type) {
  return instanceOf(type, GraphQLInputObjectType);
}

export function assertInputObjectType(type: mixed): GraphQLInputObjectType {
  if (!isInputObjectType(type)) {
    throw new Error(
      `Expected ${inspect(type)} to be a GraphQL Input Object type.`,
    );
  }
  return type;
}

declare function isListType(type: mixed): boolean %checks(type instanceof
  GraphQLList);
// eslint-disable-next-line no-redeclare
export function isListType(type) {
  return instanceOf(type, GraphQLList);
}

export function assertListType(type: mixed): GraphQLList<any> {
  if (!isListType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL List type.`);
  }
  return type;
}

declare function isNonNullType(type: mixed): boolean %checks(type instanceof
  GraphQLNonNull);
// eslint-disable-next-line no-redeclare
export function isNonNullType(type) {
  return instanceOf(type, GraphQLNonNull);
}

export function assertNonNullType(type: mixed): GraphQLNonNull<any> {
  if (!isNonNullType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL Non-Null type.`);
  }
  return type;
}

/**
 * These types may be used as input types for arguments and directives.
 */
export type GraphQLInputType =
  | GraphQLScalarType
  | GraphQLEnumType
  | GraphQLInputObjectType
  | GraphQLList<GraphQLInputType>
  | GraphQLNonNull<
      | GraphQLScalarType
      | GraphQLEnumType
      | GraphQLInputObjectType
      | GraphQLList<GraphQLInputType>,
    >;

export function isInputType(type: mixed): boolean %checks {
  return (
    isScalarType(type) ||
    isEnumType(type) ||
    isInputObjectType(type) ||
    (isWrappingType(type) && isInputType(type.ofType))
  );
}

export function assertInputType(type: mixed): GraphQLInputType {
  if (!isInputType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL input type.`);
  }
  return type;
}

/**
 * These types may be used as output types as the result of fields.
 */
export type GraphQLOutputType =
  | GraphQLScalarType
  | GraphQLObjectType
  | GraphQLInterfaceType
  | GraphQLUnionType
  | GraphQLEnumType
  | GraphQLList<GraphQLOutputType>
  | GraphQLNonNull<
      | GraphQLScalarType
      | GraphQLObjectType
      | GraphQLInterfaceType
      | GraphQLUnionType
      | GraphQLEnumType
      | GraphQLList<GraphQLOutputType>,
    >;

export function isOutputType(type: mixed): boolean %checks {
  return (
    isScalarType(type) ||
    isObjectType(type) ||
    isInterfaceType(type) ||
    isUnionType(type) ||
    isEnumType(type) ||
    (isWrappingType(type) && isOutputType(type.ofType))
  );
}

export function assertOutputType(type: mixed): GraphQLOutputType {
  if (!isOutputType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL output type.`);
  }
  return type;
}

/**
 * These types may describe types which may be leaf values.
 */
export type GraphQLLeafType = GraphQLScalarType | GraphQLEnumType;

export function isLeafType(type: mixed): boolean %checks {
  return isScalarType(type) || isEnumType(type);
}

export function assertLeafType(type: mixed): GraphQLLeafType {
  if (!isLeafType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL leaf type.`);
  }
  return type;
}

/**
 * These types may describe the parent context of a selection set.
 */
export type GraphQLCompositeType =
  | GraphQLObjectType
  | GraphQLInterfaceType
  | GraphQLUnionType;

export function isCompositeType(type: mixed): boolean %checks {
  return isObjectType(type) || isInterfaceType(type) || isUnionType(type);
}

export function assertCompositeType(type: mixed): GraphQLCompositeType {
  if (!isCompositeType(type)) {
    throw new Error(
      `Expected ${inspect(type)} to be a GraphQL composite type.`,
    );
  }
  return type;
}

/**
 * These types may describe the parent context of a selection set.
 */
export type GraphQLAbstractType = GraphQLInterfaceType | GraphQLUnionType;

export function isAbstractType(type: mixed): boolean %checks {
  return isInterfaceType(type) || isUnionType(type);
}

export function assertAbstractType(type: mixed): GraphQLAbstractType {
  if (!isAbstractType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL abstract type.`);
  }
  return type;
}

/**
 * List Type Wrapper
 *
 * A list is a wrapping type which points to another type.
 * Lists are often created within the context of defining the fields of
 * an object type.
 *
 * Example:
 *
 *     const PersonType = new GraphQLObjectType({
 *       name: 'Person',
 *       fields: () => ({
 *         parents: { type: GraphQLList(PersonType) },
 *         children: { type: GraphQLList(PersonType) },
 *       })
 *     })
 *
 */
declare class GraphQLList<+T: GraphQLType> {
  +ofType: T;
  static <T>(ofType: T): GraphQLList<T>;
  // Note: constructors cannot be used for covariant types. Drop the "new".
  constructor(ofType: GraphQLType): void;
}
// eslint-disable-next-line no-redeclare
export function GraphQLList(ofType) {
  if (this instanceof GraphQLList) {
    this.ofType = assertType(ofType);
  } else {
    return new GraphQLList(ofType);
  }
}

// Need to cast through any to alter the prototype.
(GraphQLList.prototype: any).toString = function toString() {
  return '[' + String(this.ofType) + ']';
};

// Conditionally apply `[Symbol.toStringTag]` if `Symbol`s are supported
defineToStringTag(GraphQLList);
defineToJSON(GraphQLList);

/**
 * Non-Null Type Wrapper
 *
 * A non-null is a wrapping type which points to another type.
 * Non-null types enforce that their values are never null and can ensure
 * an error is raised if this ever occurs during a request. It is useful for
 * fields which you can make a strong guarantee on non-nullability, for example
 * usually the id field of a database row will never be null.
 *
 * Example:
 *
 *     const RowType = new GraphQLObjectType({
 *       name: 'Row',
 *       fields: () => ({
 *         id: { type: GraphQLNonNull(GraphQLString) },
 *       })
 *     })
 *
 * Note: the enforcement of non-nullability occurs within the executor.
 */
declare class GraphQLNonNull<+T: GraphQLNullableType> {
  +ofType: T;
  static <T>(ofType: T): GraphQLNonNull<T>;
  // Note: constructors cannot be used for covariant types. Drop the "new".
  constructor(ofType: GraphQLType): void;
}
// eslint-disable-next-line no-redeclare
export function GraphQLNonNull(ofType) {
  if (this instanceof GraphQLNonNull) {
    this.ofType = assertNullableType(ofType);
  } else {
    return new GraphQLNonNull(ofType);
  }
}

// Need to cast through any to alter the prototype.
(GraphQLNonNull.prototype: any).toString = function toString() {
  return String(this.ofType) + '!';
};

// Conditionally apply `[Symbol.toStringTag]` if `Symbol`s are supported
defineToStringTag(GraphQLNonNull);
defineToJSON(GraphQLNonNull);

/**
 * These types wrap and modify other types
 */

export type GraphQLWrappingType = GraphQLList<any> | GraphQLNonNull<any>;

export function isWrappingType(type: mixed): boolean %checks {
  return isListType(type) || isNonNullType(type);
}

export function assertWrappingType(type: mixed): GraphQLWrappingType {
  if (!isWrappingType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL wrapping type.`);
  }
  return type;
}

/**
 * These types can all accept null as a value.
 */
export type GraphQLNullableType =
  | GraphQLScalarType
  | GraphQLObjectType
  | GraphQLInterfaceType
  | GraphQLUnionType
  | GraphQLEnumType
  | GraphQLInputObjectType
  | GraphQLList<any>;

export function isNullableType(type: mixed): boolean %checks {
  return isType(type) && !isNonNullType(type);
}

export function assertNullableType(type: mixed): GraphQLNullableType {
  if (!isNullableType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL nullable type.`);
  }
  return type;
}

/* eslint-disable no-redeclare */
declare function getNullableType(type: void | null): void;
declare function getNullableType<T: GraphQLNullableType>(type: T): T;
declare function getNullableType<T>(type: GraphQLNonNull<T>): T;
export function getNullableType(type) {
  /* eslint-enable no-redeclare */
  if (type) {
    return isNonNullType(type) ? type.ofType : type;
  }
}

/**
 * These named types do not include modifiers like List or NonNull.
 */
export type GraphQLNamedType =
  | GraphQLScalarType
  | GraphQLObjectType
  | GraphQLInterfaceType
  | GraphQLUnionType
  | GraphQLEnumType
  | GraphQLInputObjectType;

export function isNamedType(type: mixed): boolean %checks {
  return (
    isScalarType(type) ||
    isObjectType(type) ||
    isInterfaceType(type) ||
    isUnionType(type) ||
    isEnumType(type) ||
    isInputObjectType(type)
  );
}

export function assertNamedType(type: mixed): GraphQLNamedType {
  if (!isNamedType(type)) {
    throw new Error(`Expected ${inspect(type)} to be a GraphQL named type.`);
  }
  return type;
}

/* eslint-disable no-redeclare */
declare function getNamedType(type: void | null): void;
declare function getNamedType(type: GraphQLType): GraphQLNamedType;
export function getNamedType(type) {
  /* eslint-enable no-redeclare */
  if (type) {
    let unwrappedType = type;
    while (isWrappingType(unwrappedType)) {
      unwrappedType = unwrappedType.ofType;
    }
    return unwrappedType;
  }
}

/**
 * Used while defining GraphQL types to allow for circular references in
 * otherwise immutable type definitions.
 */
export type Thunk<+T> = (() => T) | T;

function resolveThunk<+T>(thunk: Thunk<T>): T {
  // $FlowFixMe(>=0.90.0)
  return typeof thunk === 'function' ? thunk() : thunk;
}

function undefineIfEmpty<T>(arr: ?$ReadOnlyArray<T>): ?$ReadOnlyArray<T> {
  return arr && arr.length > 0 ? arr : undefined;
}

/**
 * Scalar Type Definition
 *
 * The leaf values of any request and input values to arguments are
 * Scalars (or Enums) and are defined with a name and a series of functions
 * used to parse input from ast or variables and to ensure validity.
 *
 * If a type's serialize function does not return a value (i.e. it returns
 * `undefined`) then an error will be raised and a `null` value will be returned
 * in the response. If the serialize function returns `null`, then no error will
 * be included in the response.
 *
 * Example:
 *
 *     const OddType = new GraphQLScalarType({
 *       name: 'Odd',
 *       serialize(value) {
 *         if (value % 2 === 1) {
 *           return value;
 *         }
 *       }
 *     });
 *
 */
export class GraphQLScalarType {
  name: string;
  description: ?string;
  serialize: GraphQLScalarSerializer<*>;
  parseValue: GraphQLScalarValueParser<*>;
  parseLiteral: GraphQLScalarLiteralParser<*>;
  extensions: ?ReadOnlyObjMap<mixed>;
  astNode: ?ScalarTypeDefinitionNode;
  extensionASTNodes: ?$ReadOnlyArray<ScalarTypeExtensionNode>;

  constructor(config: GraphQLScalarTypeConfig<*, *>): void {
    const parseValue = config.parseValue || identityFunc;
    this.name = config.name;
    this.description = config.description;
    this.serialize = config.serialize || identityFunc;
    this.parseValue = parseValue;
    this.parseLiteral =
      config.parseLiteral || (node => parseValue(valueFromASTUntyped(node)));
    this.extensions = config.extensions && toObjMap(config.extensions);
    this.astNode = config.astNode;
    this.extensionASTNodes = undefineIfEmpty(config.extensionASTNodes);

    devAssert(typeof config.name === 'string', 'Must provide name.');
    devAssert(
      config.serialize == null || typeof config.serialize === 'function',
      `${this.name} must provide "serialize" function. If this custom Scalar is also used as an input type, ensure "parseValue" and "parseLiteral" functions are also provided.`,
    );

    if (config.parseLiteral) {
      devAssert(
        typeof config.parseValue === 'function' &&
          typeof config.parseLiteral === 'function',
        `${this.name} must provide both "parseValue" and "parseLiteral" functions.`,
      );
    }
  }

  toConfig(): {|
    ...GraphQLScalarTypeConfig<*, *>,
    serialize: GraphQLScalarSerializer<*>,
    parseValue: GraphQLScalarValueParser<*>,
    parseLiteral: GraphQLScalarLiteralParser<*>,
    extensions: ?ReadOnlyObjMap<mixed>,
    extensionASTNodes: $ReadOnlyArray<ScalarTypeExtensionNode>,
  |} {
    return {
      name: this.name,
      description: this.description,
      serialize: this.serialize,
      parseValue: this.parseValue,
      parseLiteral: this.parseLiteral,
      extensions: this.extensions,
      astNode: this.astNode,
      extensionASTNodes: this.extensionASTNodes || [],
    };
  }

  toString(): string {
    return this.name;
  }
}

// Conditionally apply `[Symbol.toStringTag]` if `Symbol`s are supported
defineToStringTag(GraphQLScalarType);
defineToJSON(GraphQLScalarType);

export type GraphQLScalarSerializer<TExternal> = (value: mixed) => ?TExternal;
export type GraphQLScalarValueParser<TInternal> = (value: mixed) => ?TInternal;
export type GraphQLScalarLiteralParser<TInternal> = (
  valueNode: ValueNode,
  variables: ?ObjMap<mixed>,
) => ?TInternal;

export type GraphQLScalarTypeConfig<TInternal, TExternal> = {|
  name: string,
  description?: ?string,
  // Serializes an internal value to include in a response.
  serialize?: GraphQLScalarSerializer<TExternal>,
  // Parses an externally provided value to use as an input.
  parseValue?: GraphQLScalarValueParser<TInternal>,
  // Parses an externally provided literal value to use as an input.
  parseLiteral?: GraphQLScalarLiteralParser<TInternal>,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?ScalarTypeDefinitionNode,
  extensionASTNodes?: ?$ReadOnlyArray<ScalarTypeExtensionNode>,
|};

/**
 * Object Type Definition
 *
 * Almost all of the GraphQL types you define will be object types. Object types
 * have a name, but most importantly describe their fields.
 *
 * Example:
 *
 *     const AddressType = new GraphQLObjectType({
 *       name: 'Address',
 *       fields: {
 *         street: { type: GraphQLString },
 *         number: { type: GraphQLInt },
 *         formatted: {
 *           type: GraphQLString,
 *           resolve(obj) {
 *             return obj.number + ' ' + obj.street
 *           }
 *         }
 *       }
 *     });
 *
 * When two types need to refer to each other, or a type needs to refer to
 * itself in a field, you can use a function expression (aka a closure or a
 * thunk) to supply the fields lazily.
 *
 * Example:
 *
 *     const PersonType = new GraphQLObjectType({
 *       name: 'Person',
 *       fields: () => ({
 *         name: { type: GraphQLString },
 *         bestFriend: { type: PersonType },
 *       })
 *     });
 *
 */
export class GraphQLObjectType {
  name: string;
  description: ?string;
  isTypeOf: ?GraphQLIsTypeOfFn<*, *>;
  extensions: ?ReadOnlyObjMap<mixed>;
  astNode: ?ObjectTypeDefinitionNode;
  extensionASTNodes: ?$ReadOnlyArray<ObjectTypeExtensionNode>;

  _fields: Thunk<GraphQLFieldMap<*, *>>;
  _interfaces: Thunk<Array<GraphQLInterfaceType>>;

  constructor(config: GraphQLObjectTypeConfig<*, *>): void {
    this.name = config.name;
    this.description = config.description;
    this.isTypeOf = config.isTypeOf;
    this.extensions = config.extensions && toObjMap(config.extensions);
    this.astNode = config.astNode;
    this.extensionASTNodes = undefineIfEmpty(config.extensionASTNodes);

    this._fields = defineFieldMap.bind(undefined, config);
    this._interfaces = defineInterfaces.bind(undefined, config);
    devAssert(typeof config.name === 'string', 'Must provide name.');
    devAssert(
      config.isTypeOf == null || typeof config.isTypeOf === 'function',
      `${this.name} must provide "isTypeOf" as a function, ` +
        `but got: ${inspect(config.isTypeOf)}.`,
    );
  }

  getFields(): GraphQLFieldMap<*, *> {
    if (typeof this._fields === 'function') {
      this._fields = this._fields();
    }
    return this._fields;
  }

  getInterfaces(): Array<GraphQLInterfaceType> {
    if (typeof this._interfaces === 'function') {
      this._interfaces = this._interfaces();
    }
    return this._interfaces;
  }

  toConfig(): {|
    ...GraphQLObjectTypeConfig<*, *>,
    interfaces: Array<GraphQLInterfaceType>,
    fields: GraphQLFieldConfigMap<*, *>,
    extensions: ?ReadOnlyObjMap<mixed>,
    extensionASTNodes: $ReadOnlyArray<ObjectTypeExtensionNode>,
  |} {
    return {
      name: this.name,
      description: this.description,
      interfaces: this.getInterfaces(),
      fields: fieldsToFieldsConfig(this.getFields()),
      isTypeOf: this.isTypeOf,
      extensions: this.extensions,
      astNode: this.astNode,
      extensionASTNodes: this.extensionASTNodes || [],
    };
  }

  toString(): string {
    return this.name;
  }
}

// Conditionally apply `[Symbol.toStringTag]` if `Symbol`s are supported
defineToStringTag(GraphQLObjectType);
defineToJSON(GraphQLObjectType);

function defineInterfaces(
  config: GraphQLObjectTypeConfig<mixed, mixed>,
): Array<GraphQLInterfaceType> {
  const interfaces = resolveThunk(config.interfaces) || [];
  devAssert(
    Array.isArray(interfaces),
    `${config.name} interfaces must be an Array or a function which returns an Array.`,
  );
  return interfaces;
}

function defineFieldMap<TSource, TContext>(
  config:
    | GraphQLObjectTypeConfig<TSource, TContext>
    | GraphQLInterfaceTypeConfig<TSource, TContext>,
): GraphQLFieldMap<TSource, TContext> {
  const fieldMap = resolveThunk(config.fields) || {};
  devAssert(
    isPlainObj(fieldMap),
    `${config.name} fields must be an object with field names as keys or a function which returns such an object.`,
  );

  return mapValue(fieldMap, (fieldConfig, fieldName) => {
    devAssert(
      isPlainObj(fieldConfig),
      `${config.name}.${fieldName} field config must be an object`,
    );
    devAssert(
      !('isDeprecated' in fieldConfig),
      `${config.name}.${fieldName} should provide "deprecationReason" instead of "isDeprecated".`,
    );
    devAssert(
      fieldConfig.resolve == null || typeof fieldConfig.resolve === 'function',
      `${config.name}.${fieldName} field resolver must be a function if ` +
        `provided, but got: ${inspect(fieldConfig.resolve)}.`,
    );

    const argsConfig = fieldConfig.args || {};
    devAssert(
      isPlainObj(argsConfig),
      `${config.name}.${fieldName} args must be an object with argument names as keys.`,
    );

    const args = objectEntries(argsConfig).map(([argName, arg]) => ({
      name: argName,
      description: arg.description,
      type: arg.type,
      defaultValue: arg.defaultValue,
      extensions: arg.extensions && toObjMap(arg.extensions),
      astNode: arg.astNode,
    }));

    return {
      ...fieldConfig,
      name: fieldName,
      description: fieldConfig.description,
      type: fieldConfig.type,
      args,
      resolve: fieldConfig.resolve,
      subscribe: fieldConfig.subscribe,
      isDeprecated: Boolean(fieldConfig.deprecationReason),
      deprecationReason: fieldConfig.deprecationReason,
      extensions: fieldConfig.extensions && toObjMap(fieldConfig.extensions),
      astNode: fieldConfig.astNode,
    };
  });
}

function isPlainObj(obj) {
  return isObjectLike(obj) && !Array.isArray(obj);
}

function fieldsToFieldsConfig(fields) {
  return mapValue(fields, field => ({
    description: field.description,
    type: field.type,
    args: argsToArgsConfig(field.args),
    resolve: field.resolve,
    subscribe: field.subscribe,
    deprecationReason: field.deprecationReason,
    extensions: field.extensions,
    astNode: field.astNode,
  }));
}

export function argsToArgsConfig(
  args: $ReadOnlyArray<GraphQLArgument>,
): GraphQLFieldConfigArgumentMap {
  return keyValMap(
    args,
    arg => arg.name,
    arg => ({
      description: arg.description,
      type: arg.type,
      defaultValue: arg.defaultValue,
      extensions: arg.extensions,
      astNode: arg.astNode,
    }),
  );
}

export type GraphQLObjectTypeConfig<TSource, TContext> = {|
  name: string,
  description?: ?string,
  interfaces?: Thunk<?Array<GraphQLInterfaceType>>,
  fields: Thunk<GraphQLFieldConfigMap<TSource, TContext>>,
  isTypeOf?: ?GraphQLIsTypeOfFn<TSource, TContext>,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?ObjectTypeDefinitionNode,
  extensionASTNodes?: ?$ReadOnlyArray<ObjectTypeExtensionNode>,
|};

export type GraphQLTypeResolver<TSource, TContext> = (
  value: TSource,
  context: TContext,
  info: GraphQLResolveInfo,
  abstractType: GraphQLAbstractType,
) => PromiseOrValue<?GraphQLObjectType | string>;

export type GraphQLIsTypeOfFn<TSource, TContext> = (
  source: TSource,
  context: TContext,
  info: GraphQLResolveInfo,
) => PromiseOrValue<boolean>;

export type GraphQLFieldResolver<
  TSource,
  TContext,
  TArgs = { [argument: string]: any, ... },
> = (
  source: TSource,
  args: TArgs,
  context: TContext,
  info: GraphQLResolveInfo,
) => mixed;

export type GraphQLResolveInfo = {|
  +fieldName: string,
  +fieldNodes: $ReadOnlyArray<FieldNode>,
  +returnType: GraphQLOutputType,
  +parentType: GraphQLObjectType,
  +path: Path,
  +schema: GraphQLSchema,
  +fragments: ObjMap<FragmentDefinitionNode>,
  +rootValue: mixed,
  +operation: OperationDefinitionNode,
  +variableValues: { [variable: string]: mixed, ... },
|};

export type GraphQLFieldConfig<
  TSource,
  TContext,
  TArgs = { [argument: string]: any, ... },
> = {|
  description?: ?string,
  type: GraphQLOutputType,
  args?: GraphQLFieldConfigArgumentMap,
  resolve?: GraphQLFieldResolver<TSource, TContext, TArgs>,
  subscribe?: GraphQLFieldResolver<TSource, TContext, TArgs>,
  deprecationReason?: ?string,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?FieldDefinitionNode,
|};

export type GraphQLFieldConfigArgumentMap = ObjMap<GraphQLArgumentConfig>;

export type GraphQLArgumentConfig = {|
  description?: ?string,
  type: GraphQLInputType,
  defaultValue?: mixed,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?InputValueDefinitionNode,
|};

export type GraphQLFieldConfigMap<TSource, TContext> = ObjMap<
  GraphQLFieldConfig<TSource, TContext>,
>;

export type GraphQLField<
  TSource,
  TContext,
  TArgs = { [argument: string]: any, ... },
> = {|
  name: string,
  description: ?string,
  type: GraphQLOutputType,
  args: Array<GraphQLArgument>,
  resolve?: GraphQLFieldResolver<TSource, TContext, TArgs>,
  subscribe?: GraphQLFieldResolver<TSource, TContext, TArgs>,
  isDeprecated?: boolean,
  deprecationReason: ?string,
  extensions: ?ReadOnlyObjMap<mixed>,
  astNode: ?FieldDefinitionNode,
|};

export type GraphQLArgument = {|
  name: string,
  description: ?string,
  type: GraphQLInputType,
  defaultValue: mixed,
  extensions: ?ReadOnlyObjMap<mixed>,
  astNode: ?InputValueDefinitionNode,
|};

export function isRequiredArgument(arg: GraphQLArgument): boolean %checks {
  return isNonNullType(arg.type) && arg.defaultValue === undefined;
}

export type GraphQLFieldMap<TSource, TContext> = ObjMap<
  GraphQLField<TSource, TContext>,
>;

/**
 * Interface Type Definition
 *
 * When a field can return one of a heterogeneous set of types, a Interface type
 * is used to describe what types are possible, what fields are in common across
 * all types, as well as a function to determine which type is actually used
 * when the field is resolved.
 *
 * Example:
 *
 *     const EntityType = new GraphQLInterfaceType({
 *       name: 'Entity',
 *       fields: {
 *         name: { type: GraphQLString }
 *       }
 *     });
 *
 */
export class GraphQLInterfaceType {
  name: string;
  description: ?string;
  resolveType: ?GraphQLTypeResolver<*, *>;
  extensions: ?ReadOnlyObjMap<mixed>;
  astNode: ?InterfaceTypeDefinitionNode;
  extensionASTNodes: ?$ReadOnlyArray<InterfaceTypeExtensionNode>;

  _fields: Thunk<GraphQLFieldMap<*, *>>;

  constructor(config: GraphQLInterfaceTypeConfig<*, *>): void {
    this.name = config.name;
    this.description = config.description;
    this.resolveType = config.resolveType;
    this.extensions = config.extensions && toObjMap(config.extensions);
    this.astNode = config.astNode;
    this.extensionASTNodes = undefineIfEmpty(config.extensionASTNodes);

    this._fields = defineFieldMap.bind(undefined, config);
    devAssert(typeof config.name === 'string', 'Must provide name.');
    devAssert(
      config.resolveType == null || typeof config.resolveType === 'function',
      `${this.name} must provide "resolveType" as a function, ` +
        `but got: ${inspect(config.resolveType)}.`,
    );
  }

  getFields(): GraphQLFieldMap<*, *> {
    if (typeof this._fields === 'function') {
      this._fields = this._fields();
    }
    return this._fields;
  }

  toConfig(): {|
    ...GraphQLInterfaceTypeConfig<*, *>,
    fields: GraphQLFieldConfigMap<*, *>,
    extensions: ?ReadOnlyObjMap<mixed>,
    extensionASTNodes: $ReadOnlyArray<InterfaceTypeExtensionNode>,
  |} {
    return {
      name: this.name,
      description: this.description,
      fields: fieldsToFieldsConfig(this.getFields()),
      resolveType: this.resolveType,
      extensions: this.extensions,
      astNode: this.astNode,
      extensionASTNodes: this.extensionASTNodes || [],
    };
  }

  toString(): string {
    return this.name;
  }
}

// Conditionally apply `[Symbol.toStringTag]` if `Symbol`s are supported
defineToStringTag(GraphQLInterfaceType);
defineToJSON(GraphQLInterfaceType);

export type GraphQLInterfaceTypeConfig<TSource, TContext> = {|
  name: string,
  description?: ?string,
  fields: Thunk<GraphQLFieldConfigMap<TSource, TContext>>,
  /**
   * Optionally provide a custom type resolver function. If one is not provided,
   * the default implementation will call `isTypeOf` on each implementing
   * Object type.
   */
  resolveType?: ?GraphQLTypeResolver<TSource, TContext>,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?InterfaceTypeDefinitionNode,
  extensionASTNodes?: ?$ReadOnlyArray<InterfaceTypeExtensionNode>,
|};

/**
 * Union Type Definition
 *
 * When a field can return one of a heterogeneous set of types, a Union type
 * is used to describe what types are possible as well as providing a function
 * to determine which type is actually used when the field is resolved.
 *
 * Example:
 *
 *     const PetType = new GraphQLUnionType({
 *       name: 'Pet',
 *       types: [ DogType, CatType ],
 *       resolveType(value) {
 *         if (value instanceof Dog) {
 *           return DogType;
 *         }
 *         if (value instanceof Cat) {
 *           return CatType;
 *         }
 *       }
 *     });
 *
 */
export class GraphQLUnionType {
  name: string;
  description: ?string;
  resolveType: ?GraphQLTypeResolver<*, *>;
  extensions: ?ReadOnlyObjMap<mixed>;
  astNode: ?UnionTypeDefinitionNode;
  extensionASTNodes: ?$ReadOnlyArray<UnionTypeExtensionNode>;

  _types: Thunk<Array<GraphQLObjectType>>;

  constructor(config: GraphQLUnionTypeConfig<*, *>): void {
    this.name = config.name;
    this.description = config.description;
    this.resolveType = config.resolveType;
    this.extensions = config.extensions && toObjMap(config.extensions);
    this.astNode = config.astNode;
    this.extensionASTNodes = undefineIfEmpty(config.extensionASTNodes);

    this._types = defineTypes.bind(undefined, config);
    devAssert(typeof config.name === 'string', 'Must provide name.');
    devAssert(
      config.resolveType == null || typeof config.resolveType === 'function',
      `${this.name} must provide "resolveType" as a function, ` +
        `but got: ${inspect(config.resolveType)}.`,
    );
  }

  getTypes(): Array<GraphQLObjectType> {
    if (typeof this._types === 'function') {
      this._types = this._types();
    }
    return this._types;
  }

  toConfig(): {|
    ...GraphQLUnionTypeConfig<*, *>,
    types: Array<GraphQLObjectType>,
    extensions: ?ReadOnlyObjMap<mixed>,
    extensionASTNodes: $ReadOnlyArray<UnionTypeExtensionNode>,
  |} {
    return {
      name: this.name,
      description: this.description,
      types: this.getTypes(),
      resolveType: this.resolveType,
      extensions: this.extensions,
      astNode: this.astNode,
      extensionASTNodes: this.extensionASTNodes || [],
    };
  }

  toString(): string {
    return this.name;
  }
}

// Conditionally apply `[Symbol.toStringTag]` if `Symbol`s are supported
defineToStringTag(GraphQLUnionType);
defineToJSON(GraphQLUnionType);

function defineTypes(
  config: GraphQLUnionTypeConfig<mixed, mixed>,
): Array<GraphQLObjectType> {
  const types = resolveThunk(config.types) || [];
  devAssert(
    Array.isArray(types),
    `Must provide Array of types or a function which returns such an array for Union ${config.name}.`,
  );
  return types;
}

export type GraphQLUnionTypeConfig<TSource, TContext> = {|
  name: string,
  description?: ?string,
  types: Thunk<Array<GraphQLObjectType>>,
  /**
   * Optionally provide a custom type resolver function. If one is not provided,
   * the default implementation will call `isTypeOf` on each implementing
   * Object type.
   */
  resolveType?: ?GraphQLTypeResolver<TSource, TContext>,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?UnionTypeDefinitionNode,
  extensionASTNodes?: ?$ReadOnlyArray<UnionTypeExtensionNode>,
|};

/**
 * Enum Type Definition
 *
 * Some leaf values of requests and input values are Enums. GraphQL serializes
 * Enum values as strings, however internally Enums can be represented by any
 * kind of type, often integers.
 *
 * Example:
 *
 *     const RGBType = new GraphQLEnumType({
 *       name: 'RGB',
 *       values: {
 *         RED: { value: 0 },
 *         GREEN: { value: 1 },
 *         BLUE: { value: 2 }
 *       }
 *     });
 *
 * Note: If a value is not provided in a definition, the name of the enum value
 * will be used as its internal value.
 */
export class GraphQLEnumType /* <T> */ {
  name: string;
  description: ?string;
  extensions: ?ReadOnlyObjMap<mixed>;
  astNode: ?EnumTypeDefinitionNode;
  extensionASTNodes: ?$ReadOnlyArray<EnumTypeExtensionNode>;

  _values: Array<GraphQLEnumValue /* <T> */>;
  _valueLookup: Map<any /* T */, GraphQLEnumValue>;
  _nameLookup: ObjMap<GraphQLEnumValue>;

  constructor(config: GraphQLEnumTypeConfig /* <T> */): void {
    this.name = config.name;
    this.description = config.description;
    this.extensions = config.extensions && toObjMap(config.extensions);
    this.astNode = config.astNode;
    this.extensionASTNodes = undefineIfEmpty(config.extensionASTNodes);

    this._values = defineEnumValues(this.name, config.values);
    this._valueLookup = new Map(
      this._values.map(enumValue => [enumValue.value, enumValue]),
    );
    this._nameLookup = keyMap(this._values, value => value.name);

    devAssert(typeof config.name === 'string', 'Must provide name.');
  }

  getValues(): Array<GraphQLEnumValue /* <T> */> {
    return this._values;
  }

  getValue(name: string): ?GraphQLEnumValue {
    return this._nameLookup[name];
  }

  serialize(value: mixed /* T */): ?string {
    const enumValue = this._valueLookup.get(value);
    if (enumValue) {
      return enumValue.name;
    }
  }

  parseValue(value: mixed): ?any /* T */ {
    if (typeof value === 'string') {
      const enumValue = this.getValue(value);
      if (enumValue) {
        return enumValue.value;
      }
    }
  }

  parseLiteral(valueNode: ValueNode, _variables: ?ObjMap<mixed>): ?any /* T */ {
    // Note: variables will be resolved to a value before calling this function.
    if (valueNode.kind === Kind.ENUM) {
      const enumValue = this.getValue(valueNode.value);
      if (enumValue) {
        return enumValue.value;
      }
    }
  }

  toConfig(): {|
    ...GraphQLEnumTypeConfig,
    extensions: ?ReadOnlyObjMap<mixed>,
    extensionASTNodes: $ReadOnlyArray<EnumTypeExtensionNode>,
  |} {
    const values = keyValMap(
      this.getValues(),
      value => value.name,
      value => ({
        description: value.description,
        value: value.value,
        deprecationReason: value.deprecationReason,
        extensions: value.extensions,
        astNode: value.astNode,
      }),
    );

    return {
      name: this.name,
      description: this.description,
      values,
      extensions: this.extensions,
      astNode: this.astNode,
      extensionASTNodes: this.extensionASTNodes || [],
    };
  }

  toString(): string {
    return this.name;
  }
}

// Conditionally apply `[Symbol.toStringTag]` if `Symbol`s are supported
defineToStringTag(GraphQLEnumType);
defineToJSON(GraphQLEnumType);

function defineEnumValues(
  typeName: string,
  valueMap: GraphQLEnumValueConfigMap /* <T> */,
): Array<GraphQLEnumValue /* <T> */> {
  devAssert(
    isPlainObj(valueMap),
    `${typeName} values must be an object with value names as keys.`,
  );
  return objectEntries(valueMap).map(([valueName, value]) => {
    devAssert(
      isPlainObj(value),
      `${typeName}.${valueName} must refer to an object with a "value" key ` +
        `representing an internal value but got: ${inspect(value)}.`,
    );
    devAssert(
      !('isDeprecated' in value),
      `${typeName}.${valueName} should provide "deprecationReason" instead of "isDeprecated".`,
    );
    return {
      name: valueName,
      description: value.description,
      value: 'value' in value ? value.value : valueName,
      isDeprecated: Boolean(value.deprecationReason),
      deprecationReason: value.deprecationReason,
      extensions: value.extensions && toObjMap(value.extensions),
      astNode: value.astNode,
    };
  });
}

export type GraphQLEnumTypeConfig /* <T> */ = {|
  name: string,
  description?: ?string,
  values: GraphQLEnumValueConfigMap /* <T> */,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?EnumTypeDefinitionNode,
  extensionASTNodes?: ?$ReadOnlyArray<EnumTypeExtensionNode>,
|};

export type GraphQLEnumValueConfigMap /* <T> */ = ObjMap<GraphQLEnumValueConfig /* <T> */>;

export type GraphQLEnumValueConfig /* <T> */ = {|
  description?: ?string,
  value?: any /* T */,
  deprecationReason?: ?string,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?EnumValueDefinitionNode,
|};

export type GraphQLEnumValue /* <T> */ = {|
  name: string,
  description: ?string,
  value: any /* T */,
  isDeprecated: boolean,
  deprecationReason: ?string,
  extensions: ?ReadOnlyObjMap<mixed>,
  astNode: ?EnumValueDefinitionNode,
|};

/**
 * Input Object Type Definition
 *
 * An input object defines a structured collection of fields which may be
 * supplied to a field argument.
 *
 * Using `NonNull` will ensure that a value must be provided by the query
 *
 * Example:
 *
 *     const GeoPoint = new GraphQLInputObjectType({
 *       name: 'GeoPoint',
 *       fields: {
 *         lat: { type: GraphQLNonNull(GraphQLFloat) },
 *         lon: { type: GraphQLNonNull(GraphQLFloat) },
 *         alt: { type: GraphQLFloat, defaultValue: 0 },
 *       }
 *     });
 *
 */
export class GraphQLInputObjectType {
  name: string;
  description: ?string;
  extensions: ?ReadOnlyObjMap<mixed>;
  astNode: ?InputObjectTypeDefinitionNode;
  extensionASTNodes: ?$ReadOnlyArray<InputObjectTypeExtensionNode>;

  _fields: Thunk<GraphQLInputFieldMap>;

  constructor(config: GraphQLInputObjectTypeConfig): void {
    this.name = config.name;
    this.description = config.description;
    this.extensions = config.extensions && toObjMap(config.extensions);
    this.astNode = config.astNode;
    this.extensionASTNodes = undefineIfEmpty(config.extensionASTNodes);

    this._fields = defineInputFieldMap.bind(undefined, config);
    devAssert(typeof config.name === 'string', 'Must provide name.');
  }

  getFields(): GraphQLInputFieldMap {
    if (typeof this._fields === 'function') {
      this._fields = this._fields();
    }
    return this._fields;
  }

  toConfig(): {|
    ...GraphQLInputObjectTypeConfig,
    fields: GraphQLInputFieldConfigMap,
    extensions: ?ReadOnlyObjMap<mixed>,
    extensionASTNodes: $ReadOnlyArray<InputObjectTypeExtensionNode>,
  |} {
    const fields = mapValue(this.getFields(), field => ({
      description: field.description,
      type: field.type,
      defaultValue: field.defaultValue,
      extensions: field.extensions,
      astNode: field.astNode,
    }));

    return {
      name: this.name,
      description: this.description,
      fields,
      extensions: this.extensions,
      astNode: this.astNode,
      extensionASTNodes: this.extensionASTNodes || [],
    };
  }

  toString(): string {
    return this.name;
  }
}

// Conditionally apply `[Symbol.toStringTag]` if `Symbol`s are supported
defineToStringTag(GraphQLInputObjectType);
defineToJSON(GraphQLInputObjectType);

function defineInputFieldMap(
  config: GraphQLInputObjectTypeConfig,
): GraphQLInputFieldMap {
  const fieldMap = resolveThunk(config.fields) || {};
  devAssert(
    isPlainObj(fieldMap),
    `${config.name} fields must be an object with field names as keys or a function which returns such an object.`,
  );
  return mapValue(fieldMap, (fieldConfig, fieldName) => {
    devAssert(
      !('resolve' in fieldConfig),
      `${config.name}.${fieldName} field has a resolve property, but Input Types cannot define resolvers.`,
    );

    return {
      ...fieldConfig,
      name: fieldName,
      description: fieldConfig.description,
      type: fieldConfig.type,
      defaultValue: fieldConfig.defaultValue,
      extensions: fieldConfig.extensions && toObjMap(fieldConfig.extensions),
      astNode: fieldConfig.astNode,
    };
  });
}

export type GraphQLInputObjectTypeConfig = {|
  name: string,
  description?: ?string,
  fields: Thunk<GraphQLInputFieldConfigMap>,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?InputObjectTypeDefinitionNode,
  extensionASTNodes?: ?$ReadOnlyArray<InputObjectTypeExtensionNode>,
|};

export type GraphQLInputFieldConfig = {|
  description?: ?string,
  type: GraphQLInputType,
  defaultValue?: mixed,
  extensions?: ?ReadOnlyObjMapLike<mixed>,
  astNode?: ?InputValueDefinitionNode,
|};

export type GraphQLInputFieldConfigMap = ObjMap<GraphQLInputFieldConfig>;

export type GraphQLInputField = {|
  name: string,
  description: ?string,
  type: GraphQLInputType,
  defaultValue: mixed,
  extensions: ?ReadOnlyObjMap<mixed>,
  astNode: ?InputValueDefinitionNode,
|};

export function isRequiredInputField(
  field: GraphQLInputField,
): boolean %checks {
  return isNonNullType(field.type) && field.defaultValue === undefined;
}

export type GraphQLInputFieldMap = ObjMap<GraphQLInputField>;