app.message payload arg compatibility in TypeScript

[seratch]

The message argument in app.message listeners does not provide sufficient properties in TypeScript.

Property 'user' does not exist on type 'KnownEventFromType<"message">'. Property 'user' does not exist on type 'MessageChangedEvent'.ts(2339)

A workaround is to cast the message value by (message as GenericMessageEvent).user but needless to say, this is not great.

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I ran into this today also. Trying to use the official example from https://slack.dev/bolt-js/concepts

// This will match any message that contains 👋
app.message(':wave:', async ({ message, say }) => {
  await say(`Hello, <@${message.user}>`);
});

and immediately getting a ts compile error. This is not a great first-time experience. Not even sure how to get it working.

Originally posted by @memark in #826 (comment)

[seratch]

Update: #871 can be a solution for this but I'm still exploring a better way to resolve this issue. One concern I have about my changes at #871 would be the type parameter could be confusing as it does not work as a constraint.