feat: Error when calling `moduleServer(id="existing")`

[schloerke]

Originally posted by @mlechon in #4372 (comment)

Hi! I'm really looking forward to this feature. Thanks for taking the time to implement it!

Have you considered triggering destroy automatically on a module's session when a call to moduleServer(id = "previously_used_id") happens? I can't think of a situation in which one would want the two servers to coexist, so collecting the first one implicitly could be a nice touch.

This may not make sense if you're trying to keep the R and Python APIs aligned. And I can always write a wrapper that does this, so I'll be happy anyways :)

@schloerke's reply:

Oooooo, thank you @mlechon ! I like the intent, but it feels too magical.

I do agree that this is a nice place to raise an error and to tell the app author to call parent_session$destroy(id)

I'll go ahead and have it raise and error if any previous reactive objects exist when calling moduleServer("existing_id")

[khusmann]

I agree with @schloerke -- I appreciate the intent, but it feels too magical for putting at the framework level.

It's easy enough to opt-in to this behavior with a wrapper, as @mlechon points out! (By contrast, it'd be harder to opt-out if it existed by default)

[schloerke]

The team had hesitations on using even a warning. Shiny doesn't have any other warnings / errors (ex you overwrite an output) until multiple outputs are displayed with the same id= on the client. (Nothing server-side).

Therefore, closing the Issue as not planned.

Workaround using a wrapper to maintain known ids as suggested by @mlechon