Default metrics are not being registered in the registry passed in register option

[mNalon]

If I create a plugin with:

const myRegistry = new Registry()

const prometheusExporterPlugin = createPrometheusExporterPlugin({ app, register: myRegistry });

the default metrics are not registered in the registry passed in the options (considering the descriptions of the options in the README this should happen).

It seems this is being caused by a conflict between generateContext and toggleDefaultMetrics:

export function generateContext<C = BaseContext, S = Source, A = Args>(
  options: PluginOptions<C, S, A>
): Context<C, S, A> {
  const context: Context<C, S, A> = {
    app: options.app as Express,
    defaultLabels: {},
    defaultMetrics: true,
    disabledMetrics: [],
    durationHistogramsBuckets: [0.001, 0.005, 0.015, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 5, 10],
    hostnameLabel: true,
    hostnameLabelName: 'hostname',
    metricsEndpoint: true,
    metricsEndpointPath: '/metrics',
    register,
    ...options,
    skipMetrics: {
      [MetricsNames.SERVER_STARTING]: () => false,
      [MetricsNames.SERVER_CLOSING]: () => false,
      [MetricsNames.QUERY_STARTED]: () => false,
      [MetricsNames.QUERY_FAILED]: () => false,
      [MetricsNames.QUERY_PARSE_STARTED]: () => false,
      [MetricsNames.QUERY_PARSE_FAILED]: () => false,
      [MetricsNames.QUERY_VALIDATION_STARTED]: () => false,
      [MetricsNames.QUERY_VALIDATION_FAILED]: () => false,
      [MetricsNames.QUERY_RESOLVED]: () => false,
      [MetricsNames.QUERY_EXECUTION_STARTED]: () => false,
      [MetricsNames.QUERY_EXECUTION_FAILED]: () => false,
      [MetricsNames.QUERY_DURATION]: () => false,
      [MetricsNames.QUERY_FIELD_RESOLUTION_DURATION]: () => false,
      ...(options.skipMetrics ?? {})
    },
    defaultMetricsOptions: {
      register,
      ...(options.defaultMetricsOptions ?? {})
    }
  };

the register reference used in defaultMetricsOptions points to the register imported from

import { DefaultMetricsCollectorConfiguration, LabelValues, register, Registry } from 'prom-client';

and then when toggleDefaultMetrics is called

export function toggleDefaultMetrics<C = AppContext, S = Source, A = Args>(
  register: Registry,
  { defaultMetrics, defaultMetricsOptions }: Context<C, S, A>
) {
  if (defaultMetrics) {
    collectDefaultMetrics({
      register,
      ...defaultMetricsOptions
    });
  }
}

the destructuring of defaultMetricsOptions overwrites the register, which points to the register passed in the options of createPrometheusExporterPlugin.

Is that expected? If it is not, I am willing to open a PR to fix this behavior.