Deep merge meta objects

[okaybroda]

Please tell us about your environment:

• winston version?
  • winston@2
  • [✓] winston@3
• Operating System? Linux
• Language? all

What is the problem?

Merging meta objects is not working because of Object.assign which is a shallow merge.

What do you expect to happen instead?

Example code:

const logger = winston.createLogger({
      defaultMeta: {
        labels: {
          service: 'user-service'
        }
      },
    });
const childLogger = logger.child({ labels: { requestId: '451' } });
childLogger.info('dummy message', { labels: { yeet: 'yeet' } });

Current Output

{ labels: { yeet: 'yeet' } }

Expected Output

{ labels: { service: 'user-service', yeet: 'yeet', requestId: '451' } }

What's the feature?

Deep merge meta objects using lodash.merge

Is the absence of this feature blocking you or your team? If so, how?

In our case, we are using the Elastic Common Schema which recommends meta fields to go under the label object but we can't make child logger with additional metadata due to the shallow merge. Reference to ECS: link

Is this feature similar to an existing feature in another tool?

Not sure.

Is this a feature you're prepared to implement, with support from us?

Yes.

[okaybroda]

Working on final touches on the PR.

[maverick1872]

Closing as this issue is being consolidated into #2029