@dillonkearns/elm-graphql/examples/src/subscription/node_modules/graphql/validation/rules/ScalarLeafs.js.flow

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/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */

import type { ValidationContext } from '../index';
import { GraphQLError } from '../../error';
import type { FieldNode } from '../../language/ast';
import { getNamedType, isLeafType } from '../../type/definition';
import type { GraphQLType } from '../../type/definition';


export function noSubselectionAllowedMessage(
  fieldName: string,
  type: GraphQLType
): string {
  return `Field "${fieldName}" must not have a selection since ` +
    `type "${String(type)}" has no subfields.`;
}

export function requiredSubselectionMessage(
  fieldName: string,
  type: GraphQLType
): string {
  return `Field "${fieldName}" of type "${String(type)}" must have a ` +
    `selection of subfields. Did you mean "${fieldName} { ... }"?`;
}

/**
 * Scalar leafs
 *
 * A GraphQL document is valid only if all leaf fields (fields without
 * sub selections) are of scalar or enum types.
 */
export function ScalarLeafs(context: ValidationContext): any {
  return {
    Field(node: FieldNode) {
      const type = context.getType();
      if (type) {
        if (isLeafType(getNamedType(type))) {
          if (node.selectionSet) {
            context.reportError(new GraphQLError(
              noSubselectionAllowedMessage(node.name.value, type),
              [ node.selectionSet ]
            ));
          }
        } else if (!node.selectionSet) {
          context.reportError(new GraphQLError(
            requiredSubselectionMessage(node.name.value, type),
            [ node ]
          ));
        }
      }
    }
  };
}