fix(core)!: resolve type inference issues with input handler

[naorpeled]

fixes #1182

[naorpeled]

@lmammino does this return type make sense to you? 🙏
I'd expect it to be taken from the input handler (.handler<..params>) fn and not the initial input (middy<...params>).

[naorpeled]

@lmammino bumping this 🙏

[lmammino]

LGTM! Thanks a mill @naorpeled !

@willfarrell can I leave it to you to merge and release based on your priorities?

[jlarmstrongiv]

I think this broke the types in my project, as I’m now getting the error:

Binding element 'headers' implicitly has an 'any' type.

Whereas downgrading to 5.4.1 properly types the headers as:

headers: APIGatewayProxyEventHeaders | (APIGatewayProxyEventHeaders & ALBEventHeaders)

instead of any

[naorpeled]

I think this broke the types in my project, as I’m now getting the error:

Binding element 'headers' implicitly has an 'any' type.

Whereas downgrading to 5.4.1 properly types the headers as:

headers: APIGatewayProxyEventHeaders | (APIGatewayProxyEventHeaders & ALBEventHeaders)

instead of any

Hey @jlarmstrongiv,
can you please share a reproduction example to your issue?

[jlarmstrongiv]

Sure, here is the reproduction @naorpeled I removed the middleware to keep the reproduction as simple as possible https://github.com/jlarmstrongiv/middy-typescript-headers-bug 👍

You will be able to see how 5.4.1 works, while 5.4.2 causes type errors.

[naorpeled]

Sure, here is the reproduction @naorpeled I removed the middleware to keep the reproduction as simple as possible https://github.com/jlarmstrongiv/middy-typescript-headers-bug 👍

You will be able to see how 5.4.1 works, while 5.4.2 causes type errors.

I see, what you need to do is pass the generic params into .handler and that would resolve your issue

[jlarmstrongiv]

Hey @naorpeled do you have an example of passing those generic params into .handler? It’s still erroring with the same error for me:

export const handler = middy.handler<
  APIGatewayProxyEventV2,
  APIGatewayProxyResultV2
  // Binding element 'headers' implicitly has an 'any' type.
>(({ headers }) => ({
  body: JSON.stringify(headers, undefined, 2),
  statusCode: 200,
}));

I also wish I could define it once with middy core like I used to, rather than having to define it on each and every lambda function handler