node_modules/graphql/validation/rules/UniqueOperationTypesRule.js.flow

// @flow strict

import { GraphQLError } from '../../error/GraphQLError';
import { type ASTVisitor } from '../../language/visitor';

import { type SDLValidationContext } from '../ValidationContext';

/**
 * Unique operation types
 *
 * A GraphQL document is only valid if it has only one type per operation.
 */
export function UniqueOperationTypesRule(
  context: SDLValidationContext,
): ASTVisitor {
  const schema = context.getSchema();
  const definedOperationTypes = Object.create(null);
  const existingOperationTypes = schema
    ? {
        query: schema.getQueryType(),
        mutation: schema.getMutationType(),
        subscription: schema.getSubscriptionType(),
      }
    : {};

  return {
    SchemaDefinition: checkOperationTypes,
    SchemaExtension: checkOperationTypes,
  };

  function checkOperationTypes(node) {
    /* istanbul ignore next (See https://github.com/graphql/graphql-js/issues/2203) */
    const operationTypesNodes = node.operationTypes ?? [];

    for (const operationType of operationTypesNodes) {
      const operation = operationType.operation;
      const alreadyDefinedOperationType = definedOperationTypes[operation];

      if (existingOperationTypes[operation]) {
        context.reportError(
          new GraphQLError(
            `Type for ${operation} already defined in the schema. It cannot be redefined.`,
            operationType,
          ),
        );
      } else if (alreadyDefinedOperationType) {
        context.reportError(
          new GraphQLError(
            `There can be only one ${operation} type in schema.`,
            [alreadyDefinedOperationType, operationType],
          ),
        );
      } else {
        definedOperationTypes[operation] = operationType;
      }
    }

    return false;
  }
}