Allow customization of level mapping in `createSentryWinstonTransport`

[mnow-cd]

Problem Statement

Currently the createSentryWinstonTransport function uses a hardcoded mapping between Winston levels and Sentry severity levels with the internal constant.

When using custom levels in Winston that match Sentry's own naming convention, fatal or trace levels will be mapped to info because they don't exist in the internal WINSTON_LEVEL_TO_LOG_SEVERITY_LEVEL_MAP.

const SentryTransport = Sentry.createSentryWinstonTransport(WinstonTransport);

const logger = createLogger({
  levels: {
    fatal: 0,
    error: 1,
    warn: 2,
    info: 3,
    debug: 4,
    trace: 5
  },
  transports: [new SentryTransport]
});

logger.info('msg'); // logged to Sentry as 'info'
logger.fatal('msg'); // logged to Sentry also as 'info'

Solution Brainstorm

Add an optional levelMap or mapLevel function to the transport options that allows to override the default mapping.

const SentryWinstonTransport = Sentry.createSentryWinstonTransport(Transport);

// level map
const transport = new SentryWinstonTransport({
  levelMap: {
    emergency: 'fatal',
    alert: 'error',
    custom_level: 'debug'
  }
});

// map function
new SentryWinstonTransport({
  mapLevel: (winstonLevel) => {
    if (winstonLevel === 'fatal') return 'fatal';
    return 'trace';
  }
});

Also it would be really helpful if Sentry provided constants to simplify the setup of a Winston logger to be compatible with Sentry levels, instead of having to manually align them.

const SentryTransport = Sentry.createSentryWinstonTransport(WinstonTransport);

const logger = winston.createLogger({
  // native Sentry levels for Winston
  levels: Sentry.winstonLogLevels, 
  transports: [
    new SentryTransport({
      // pre-defined mapping
      levelMap: Sentry.winstonTransportLevelMap 
    })
  ]
});

Additional Context

No response

Priority

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[linear]

JS-1498