Passing down event name into TransformMethod to allow for the right payload types to be used

[wolfy1339]

I'm trying to fix the issue octokit/app.js#212, and I've hit a wall with types with the transform method.

How do I pass down the TName type parameter from the HandlerFunction type to TransformMethod?
The end result wanted is to keep all the same type inference as not having the transform method, and just apply the modifications from that function.

In this case, we would like the return type to be EmiterWebhookEvent<EventName extends EmitterWebhookEventName> & { octokit: Octokit }

[oscard0m]

I'm trying to fix the issue octokit/app.js#212, and I've hit a wall with types with the transform method.

How do I pass down the TName type parameter from the HandlerFunction type to TransformMethod?
The end result wanted is to keep all the same type inference as not having the transform method, and just apply the modifications from that function.

Hey @wolfy1339 I'm quite lost at this level of complexity in typing but I would like to help. I tried to play a bit myself and no luck but because I'm lacking expertise with generics and type inference at this level of complexity.

Do you think it could be useful to draft a simple example of our problem in TypeScript playground?

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Tagging @G-Rath for a new TS battle ⚔️

[wolfy1339]

You can see the discussion on what the issue is: octokit/app.js#213 (comment)

Basically the first step to fixing this is to only allow the transform function to amend the event object

[wolfy1339]

I am really not sure how to replicate what we have into the TS playground for a simpler example of the problem.
The types are spread across a couple packages and there's loads of generics to account for

[wolfy1339]

This has turned into a bug. I confirmed that this is broken on master. Since we can't currently pass down the event name, it returns a combination of all the different event payloads