Fix inaccurate type of setErrorHandler

[chengluyu]

See #2091

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows Code of conduct

[tests-checker]

Hello! Thank you for contributing!
It appears that you have changed the framework code, but the tests that verify your change are missing. Could you please add them?

[Ethan-Arrowood]

This should not be any. I'd rather you make this unknown and instruct the user to use type casting to enforce what they want to come through this handler. Based on the code you provided in your issue, throw {hello: 'world'} will result in a type of { hello: string }. If you captured that in a type i.e. type CustomError = { hello: string }, then the goal would be to use use that type in setErrorHandler. You can achieve this through generics or type casting. I'd suggest supporting both by using a default generic, so something like this:

setErrorHandler<E = FastifyError>(error: E, ...)

[chengluyu]

This should not be any. I'd rather you make this unknown and instruct the user to use type casting to enforce what they want to come through this handler. Based on the code you provided in your issue, throw {hello: 'world'} will result in a type of { hello: string }. If you captured that in a type i.e. type CustomError = { hello: string }, then the goal would be to use use that type in setErrorHandler. You can achieve this through generics or type casting. I'd suggest supporting both by using a default generic, so something like this:

setErrorHandler<E = FastifyError>(error: E, ...)

I agree with you. I've replaced any with generic type parameter (defaults to FastifyError). Therefore, users can specify their own error types.

[mcollina]

Can you add a test for the type change?

[chengluyu]

Can you add a test for the type change?

Hi, I've added a test. Please let me know if there's any problem. 😄

[mcollina]

LGTM

[github-actions]

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