typescript types don't work properly

[Zamiell]

Prerequisites

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

Fastify version

4.25.1

Plugin version

7.1.0

Node.js version

20.9.0

Operating system

Windows

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

10

Description

The types don't work properly.
e.g.:

declare module "@fastify/secure-session" {
  interface SessionData {
    userID: number;
  }
}

async function login(
  request: FastifyRequest,
  reply: FastifyReply,
): Promise<FastifyReply> {
  request.session.set("usersID", 123);
}

In the above code snippet, we made a typo, and typed it as "usersID" instead of "userID". Oops! But we don't get a compiler error - it just works, and the bug makes its way to production.

Is there some way for a declaration merge to get rid of the string index signature? Because that's the root cause of the bug.

[mcollina]

Is there some way for a declaration merge to get rid of the string index signature? Because that's the root cause of the bug.

Unfortunately no. I'm not sure how to fix this at all.

[Gehbt]

I have 2 proposal with demo:
A: When set a mission key, the value should always be type never.
B: Remove indexed access type and ensured extends what type is defined.

commit A is base avoid any
commit B is base remove the indexed access type

Unfortunately no. I'm not sure how to fix this at all.

[mcollina]

Would you like to send a Pull Request to address this issue? Remember to add unit tests.