Setting reply_broadcast gives a type error when it's a dynamic value

[Amethystix]

Packages:

Select all that apply:

• @slack/web-api
• @slack/rtm-api
• @slack/webhooks
• @slack/oauth
• @slack/socket-mode
• @slack/types
• I don't know

Reproducible in:

The Slack SDK version

v7.3.1

Node.js runtime version

18.18.2

Typescript version

5.5.4

OS info

ProductName:		macOS
ProductVersion:		13.3.1
ProductVersionExtra:	(a)
BuildVersion:		22E772610a
Darwin Kernel Version 22.4.0: Mon Mar  6 20:59:28 PST 2023; root:xnu-8796.101.5~3/RELEASE_ARM64_T6000

Steps to reproduce:

Dynamically set reply_broadcast as we do in this wrapper function:

  async reply(
    channelId: string,
    message: Block[] | string,
    threadId: string,
    broadcast = false,
  ) {

    if (typeof message === "string") {
      return await this.web.chat.postMessage({
        channel: channelId,
        thread_ts: threadId,
        text: message,
        reply_broadcast: broadcast,
      });
    } else {
      return await this.web.chat.postMessage({
        channel: channelId,
        thread_ts: threadId,
        reply_broadcast: broadcast,
        blocks: message,
      });
    }
  }

Expected result:

No type error

Actual result:

Argument of type '{ channel: string; thread_ts: string; reply_broadcast: boolean; blocks: KnownBlock[]; }' is not assignable to parameter of type 'ChatPostMessageArguments'.
  Type '{ channel: string; thread_ts: string; reply_broadcast: boolean; blocks: KnownBlock[]; }' is not assignable to type 'TokenOverridable & ChannelAndBlocks & BroadcastedThreadReply & { as_user: true; icon_emoji?: undefined; icon_url?: undefined; } & ... 4 more ... & { ...; }'.
    Type '{ channel: string; thread_ts: string; reply_broadcast: boolean; blocks: KnownBlock[]; }' is not assignable to type 'BroadcastedThreadReply'.
      Types of property 'reply_broadcast' are incompatible.
        Type 'boolean' is not assignable to type 'true'.

Note: if I set reply_broadcast to true or false the error goes away.

Requirements

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[filmaj]

I can reproduce this but I'm not sure how to fix this without loosening up the argument typing. Here's a TypeScript Playground link for the reproduction.

For reference, here are the three interfaces that govern this issue: one interface modeling thread_ts, and then two others that model the situation for when reply_broadcast is true vs. false:

interface ThreadTS {
  /**
   * @description Provide another message's `ts` value to post this message in a thread. Avoid using a reply's `ts`
   * value; use its parent's value instead.
   */
  thread_ts: string;
}
interface WithinThreadReply extends Partial<ThreadTS> {
  /**
   * @description Used in conjunction with `thread_ts`, when set to `false` will make the reply only visibile within
   * a thread.
   */
  reply_broadcast?: false;
}
interface BroadcastedThreadReply extends ThreadTS {
  /** @description Used in conjunction with `thread_ts`, when set to `true` will broadcast the reply to the channel. */
  reply_broadcast: true;
}

Assigning a value to the boolean makes the issue go away... Not sure why this is the case.. not a TypeScript expert but I assumed that modeling both true and false values for boolean (via the WithinThreadReply and BroadcastedThreadReply interfaces) would be sufficient to model all possible values of the boolean type. I guess TypeScript is not smart enough to figure that out in the case there is no specific value attached to the reply_broadcast boolean?

Open to any suggestions on how to address this... one approach would be to loosen up BroadcastedThreadReply interface's reply_broadcast type from true to boolean. I have a PR implementing that here: #1860

[filmaj]

This has been fixed in the just-released web-api v7.3.2