Payload typing lost when using setCookie before

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

3.27.1

Plugin version

5.5.0

Node.js version

16.13.1

Operating system

Windows

Operating system version (i.e. 20.04, 11.3, 10)

11 (21H2)

Description

When using a schema for my route, I get payload typing. But when I use setCookie on my reply, the payload get the type unknown.

Steps to Reproduce

type TSchemaResponse = {
    message: string
};

// ...
fastifyInstance.post<Response: TSchemaResponse>(
    "/hello",
    (request, reply) => {
        reply.send({message: 123}); // typescript error as message should be a string
    }
);
// ...

type TSchemaResponse = {
    message: string
};

// ...
fastifyInstance.post<Response: TSchemaResponse>(
    "/hello",
    (request, reply) => {
        reply
            .setCookie("hello", "there")
            .send({message: 123}); // no error (there should be an error)
    }
);
// ...

Expected Behavior

The payload should still be typed after calling setCookie (as setCookie should return “this” type)

[darkgl0w]

@hugoattal > thank you for the minimal reproducible example.

Thanks to this I was able to spot the cause of this issue. I will submit a PR to resolve this issue in a moment 😃

[hugoattal]

@darkgl0w Here it is: https://github.com/hugoattal/fastify-cookie-typing-bug-repro

Just run pnpm install (should also work with npm) and you can see the error under src/handler.ts