How to use the @apollographql/apollo-tools.buildServiceDefinition function in @apollographql/apollo-tools

graphId: this.engineServiceId,
              ...(graphVariant && { graphVariant }),
            }
          : undefined;

      return gateway.load({ engine: engineConfig }).then(config => {
        this.requestOptions.executor = config.executor;
        return config.schema;
      });
    }

    let constructedSchema;
    if (schema) {
      constructedSchema = schema;
    } else if (modules) {
      const { schema, errors } = buildServiceDefinition(modules);
      if (errors && errors.length > 0) {
        throw new Error(errors.map(error => error.message).join('\n\n'));
      }
      constructedSchema = schema!;
    } else {
      if (!typeDefs) {
        throw Error(
          'Apollo Server requires either an existing schema, modules or typeDefs',
        );
      }

      const augmentedTypeDefs = Array.isArray(typeDefs) ? typeDefs : [typeDefs];

      // We augment the typeDefs with the @cacheControl directive and associated
      // scope enum, so makeExecutableSchema won't fail SDL validation

// Plugins will be instantiated if they aren't already, and this.plugins
    // is populated accordingly.
    this.ensurePluginInstantiation(this.config.plugins);

    // TODO(AS3) Make it possible to disable introspection.
    // TODO(AS3) Cache Control
    // TODO(AS3) Global cache implementation config.
    // TODO(AS3) Persisted Queries
    // TODO(AS3) Apollo Graph Manager

    if (! this.config.modules) {
      throw new Error("TODO: No modules were specified.");
    }

    const { schema, errors } = buildServiceDefinition(this.config.modules);
    if (errors && errors.length > 0) {
      throw new Error(errors.map(error => error.message).join('\n\n'));
    }

    if (!schema) {
      throw new Error("TODO: No schema.");
    }

    this.schemaDerivedData = this.generateSchemaDerivedData(schema);
  }