Add support for "sub apps"

When creating a large slack application it would be nice to be able to reuse components in a more pythonic way than what is possible right now. A workaround is described in issue #236, but it requires passing the app object around and manually wiring up things by registering and calling decorators as functions directly.

I suggest adding a feature much like include_router in FastAPI or add_typer in Typer.

This feature will let us create sub-apps in separate files or even separate packages, like plugins that can be published on pypi.org separately.

Here is a small example illustrating what I mean:

main.py

Here is our main app, where we add a plugin from a separate package

import os
from slack_bolt import App

from my_plugin import my_plugin


# Initializes your app with your bot token and signing secret
app = App(
    token=os.environ.get("SLACK_BOT_TOKEN"),
    signing_secret=os.environ.get("SLACK_SIGNING_SECRET")
)
app.add_app(my_plugin)

my_plugin.py

A simple plugin that just creates a slack_bolt app, but without any config

from slack_bolt import App


my_plugin = App()

@my_plugin.message("hello")
def message_hello(message, say):
    say("Hello world")

Category

• slack_bolt.App and/or its core components
• slack_bolt.async_app.AsyncApp and/or its core components
• Adapters in slack_bolt.adapter
• Others

[davidolrik]

My main goal was to facilitate better code reuse, but most importantly better organization of large complex slack apps while still being able to use the @app.* decorators.

Maybe a kind of proxy sub app object would make sense then, and app.add_sub_app(my_plugin) could then transfer what ever was defined on the sub app to the main app.

from slack_bolt import SubApp


my_plugin = SubApp()

@my_plugin.message("hello")
def message_hello(message, say):
    say("Hello world")

The important part is that the SubApp should be able to use all the decorators from App.

[jianyuan]

Here’s what I came up with:

class SubApp:
    def __init__(self) -> None:
        self.actions = []
        self.events = []
        self.views = []

    def action(self, *args, **kwargs):
        def __call__(func):
            self.actions.append((args, kwargs, func))
            return func

        return __call__

    def event(self, *args, **kwargs):
        def __call__(func):
            self.events.append((args, kwargs, func))
            return func

        return __call__

    def view(self, *args, **kwargs):
        def __call__(func):
            self.views.append((args, kwargs, func))
            return func

        return __call__

    def register_to(self, app: App):
        for args, kwargs, func in self.actions:
            app.action(*args, **kwargs)(func)
        for args, kwargs, func in self.events:
            app.event(*args, **kwargs)(func)
        for args, kwargs, func in self.views:
            app.view(*args, **kwargs)(func)

Usage:

sub_app = SubApp()

@sub_app.event("app_mention")
def handle_app_mentions(logger, event, say):
    logger.info(event)
    say(f"Hi there, <@{event['user']}>")

# Then...

app = App(...)
sub_app.register_to(app)