Does not infer request property types from schema

[paulius-valiunas]

Prerequisites

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

Fastify version

4.28.1

Plugin version

3.6.0

Node.js version

20.15.0

Typescript version

5.2.2 (also tested with 5.5.4)

Operating system

Linux

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

archlinux in WSL

Description

I tried following Fastify documentation, but even when copy/pasting their example without any changes, the inferred type of request.query is unknown.

MRE:

const server = fastify().withTypeProvider<TypeBoxTypeProvider>();

server.get("/route", {
  schema: {
    querystring: Type.Object({
      foo: Type.Number(),
      bar: Type.String(),
    }),
  },
}, (request, reply) => {

  // type Query = { foo: number, bar: string }

  const { foo, bar } = request.query;
  // error TS2339: Property 'bar' does not exist on type 'unknown'.
  // error TS2339: Property 'bar' does not exist on type 'unknown'.
});

Link to code that reproduces the bug

No response

Expected Behavior

request.query should be correctly inferred to be of type { foo: string, bar: string }. Same problem with body, response, headers and params types.

[cesxhin]

same problem

[marko1010]

it's Fastify() not fastify()

[paulius-valiunas]

it's Fastify() not fastify()

If you import it as import * as Fastify from "fastify" or import Fastify from "fastify", you're right.
If you import it as import * as fastify from "fastify" or import fastify from "fastify", it's fastify().
If you import it as import * as cthulhu from "fastify" or import cthulhu from "fastify", it's cthulhu().

[maxloo2]

Follow the instructions here: https://fastify.dev/docs/latest/Reference/Type-Providers/#type-definition-of-fastifyinstance--typeprovider, you need to add TypeBoxTypeProvider to FastifyInstance<T> and use that instead.

[paulius-valiunas]

Follow the instructions here: fastify.dev/docs/latest/Reference/Type-Providers#type-definition-of-fastifyinstance--typeprovider, you need to add TypeBoxTypeProvider to FastifyInstance<T> and use that instead.

In my example, the type of server seems to be inferred correctly, and I'm using it in the same file where it was declared. I'm not assigning it to a different variable, passing it into a function or doing anything that could result in a type cast dropping the required generic parameters. This is the same workflow as the "Scoped type provider" example in the link you shared.

[maxloo2]

Follow the instructions here: fastify.dev/docs/latest/Reference/Type-Providers#type-definition-of-fastifyinstance--typeprovider, you need to add TypeBoxTypeProvider to FastifyInstance<T> and use that instead.

In my example, the type of server seems to be inferred correctly, and I'm using it in the same file where it was declared. I'm not assigning it to a different variable, passing it into a function or doing anything that could result in a type cast dropping the required generic parameters. This is the same workflow as the "Scoped type provider" example in the link you shared.

I was having this problem when I used FastifyPluginAsync in files other than my index.ts, and I had to explicitly tell TypeScript that fastify is of an extended FastifyInstance type instead of the default one for the correct types to show up. I haven't tried them together within the same file however, so I am too not sure sure about this...