fix(NODE-5530): make topology descriptions JSON stringifiable

[baileympearson]

Description

What is changing?

This is basically entirely invisible to users. However, the TopologyDescription is a field on MongoServerSelectionErrors, so if a user is calling JSON.stringify on their errors, they will now see the servers field in the output instead of an empty object.

Is there new documentation needed for these changes?

No.

What is the motivation for this change?

Release Highlight

TopologyDescription now properly stringifies itself to JSON

The TopologyDescription class is exposed by the driver in server selection errors and topology monitoring events to provide insight into the driver's current representation of the server's topology and to aid in debugging. However, the TopologyDescription uses Maps internally, which get serialized to {} when JSON stringified. We recommend using Node's util.inspect() helper to print topology descriptions because inspect properly handles all JS types and all types we use in the driver. However, if JSON must be used, the TopologyDescription now provides a custom toJSON() hook:

client.on('topologyDescriptionChanged', ({ newDescription }) => { // recommended! console.log('topology description changed', inspect(newDescription, { depth: Infinity, colors: true })) // now properly prints the entire topology description console.log('topology description changed', JSON.stringify(newDescription)) });

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[W-A-James]

LGTM but can we have a short release note since this is public facing