Fail to run event listeners for app_mention events with bot_message subtype

[Yunseong Jeon]

Reproducible in:

The Slack SDK version

1.29.2

Java Runtime version

openjdk version "17.0.9" 2023-10-17 LTS
OpenJDK Runtime Environment Zulu17.46+19-CA (build 17.0.9+8-LTS)
OpenJDK 64-Bit Server VM Zulu17.46+19-CA (build 17.0.9+8-LTS, mixed mode, sharing)

OS info

Steps to reproduce:

1. assign handler about AppMentionEvent to slack app.

App.event(AppMentionEvent.class, this.appMentionEventHandler);

2. using workflow, mention bot.
3. Then bot returns below warn logs.

2024-01-30 11:36:13.783  WARN 116277 --- [socket-mode-message-processor-worker-71] com.slack.api.bolt.App                   : No BoltEventHandler registered for event: app_mention:bot_message
---
[Suggestion] You can handle this type of event with the following listener function:


app.event(AppMentionBotEvent.class, (payload, ctx) -> {
  return ctx.ack();
});


2024-01-30 11:36:13.783  WARN 116277 --- [socket-mode-message-processor-worker-71] c.s.api.bolt.socket_mode.SocketModeApp   : Unsuccessful Bolt app execution (status: 404, body: {"error":"no handler found"}) 

Expected result:

Expected java-slack-sdk has AppMentionBotEvent.class. but doesn't.

Actual result:

Curious I need to create my own AppMentionBotEvent.class or you plan to support it.
Because above log suggested to me to use AppMentionBotEvent.class.

Requirements

[Fil Maj]

I can confirm this issue. I have an app_mention event handler defined in my Bolt for Java app. When a user app-mentions my bot, the app_mention handler executes as expected. However, when I built a workflow to at-mention my bot, the following logs show up:

[socket-mode-message-processor-worker-32] WARN com.slack.api.bolt.App - No BoltEventHandler registered for event: app_mention:bot_message
---
[Suggestion] You can handle this type of event with the following listener function:

app.event(AppMentionBotEvent.class, (payload, ctx) -> {
  return ctx.ack();
});

[socket-mode-message-processor-worker-32] DEBUG com.slack.api.bolt.App - The handler completed (request type: Event)
[socket-mode-message-processor-worker-32] WARN com.slack.api.bolt.socket_mode.SocketModeApp - Unsuccessful Bolt app execution (status: 404, body: {"error":"no handler found"})

I think the underlying cause of the issue is that ONLY in the case that a non-human creates the app mention event, the event contains a subtype - which surprised me (I thought only message events contain those, which is what is described in our docs). I tested this scenario out (a workflow that at-mentions a Bolt app) and the type of such an event is app_mention and the subtype is bot_message. A human app-mention event has no subtype.

The suggestion you saw in the logs comes from this area of the code. This, in turn, assembles the specific event class Bolt suggests to listen for using the toEventClassName.

I think this is a bug, but it is unclear to me whether this is a bug in the above toEventClassName only or something deeper. Specifically, I would expect a registered app-mention handler to be able to handle BOTH human and non-human app mentions. In fact, this is the case in Bolt for JS. Another thing to consider when evaluating this is that there are no app_mention event subtypes that apps on the api.slack.com/apps page can register to; there is only one event.

@seratch what is your opinion here? Do you agree with my assessment?