types 3.0: breaking change for event payloads

[filmaj]

This would be a follow-up issue to tackle once slackapi/bolt-js#1395 is addressed; slackapi/bolt-js#1395 simply adds the existing, likely lacking, types for Events API payloads to the types package. This issue would be about breaking those payloads and include that in a new 3.0 release of @slack/types.

Summary

Improvements to MessageEvent

Today, MessageEvent is a big union of different events Slack may send to apps, presumably that include some message information. Because it is a union, when using it as a type both in applications as well as frameworks (like bolt), only the common properties across all types in this union can be used. Some properties that would be expected to be present on messages are not common in this union today: text and blocks, for instance. We should study how this type is used in bolt and elsewhere, and consider a different approach to modeling message events. For example, perhaps a generics-based approach could better serve?

Another problem when working with MessageEvent in TypeScript is the fact that one member of the union, the GenericMessageEvent, has subtype: undefined. This causes major problems when trying to match against the union of all different kinds of messages, since many message subtype events have a defined string literal subtype. subtype: undefined needs to get the 🔪 .

TODO

Review Issues to Identify Pain Points

The following should be studied to determine the scope of what these breaking changes should include, in order to address developer pain points, and folded into the Summary section above in order to plan the changes:

• app.message payload arg compatibility in TypeScript bolt-js#904
• feat: Expose a subtype message pattern filter for message handlers bolt-js#796
• Move block-action.ts to @slack/types bolt-js#1432
• message_replied event missing text property in typescript #2025
• Cannot access the user id in the "message_changed" event with TypeScript #2026
• Better typing for block actions payload bolt-js#2122