TypeScript only evaluating to any when using @fastify/type-provider-json-schema-to-ts

[rmehner]

Hi there,

migrating to fastify v4 I was very excited for better TS support on JSON schemas. So I went ahead and tried the example provided on the docs site: https://www.fastify.io/docs/latest/Reference/Type-Providers/#json-schema-to-ts

However, if I do that, foo and bar will always be of type any. Am I holding it wrong? I was expecting the types to be number and string respectively.

import { JsonSchemaToTsProvider } from '@fastify/type-provider-json-schema-to-ts'

import fastify from 'fastify'

const server = fastify().withTypeProvider<JsonSchemaToTsProvider>()

server.get(
  '/route',
  {
    schema: {
      querystring: {
        type: 'object',
        properties: {
          foo: { type: 'number' },
          bar: { type: 'string' },
        },
        required: ['foo', 'bar'],
      },
    } as const
  },
  request => {
    const { bar } = request.query
    bar.push('foo') // I'd expect this to fail with `error TS2339: Property 'push' does not exist on type string`
  }
)

Thank you for your help already!

Your Environment

• node version: 18
• fastify version: >=4.0.0
• typescript version: 4.7.4

[sinclairzx81]

@RafaelGSS Just tested this on the TypeScript playground and the type resolution appears to be working ok (TS 4.7.4)

TypeScript Playground Link

@rmehner Just have a quick check that your tsconfig.json file s configured for strict: true.

[alphaone]

Hey, I am getting the same error as @rmehner . I can see how the linked playground example works, but when I copy the code into my project, it stops to infer the type from the schema.

Even if I use the example from the ReadMe I get type unknown :\

const plugin: FastifyPluginAsyncJsonSchemaToTs = async (fastify, _opts) => {
  fastify.get(
    '/',
    {
      schema: {
        body: {
          type: 'object',
          properties: {
            x: { type: 'string' },
            y: { type: 'number' },
            z: { type: 'boolean' },
          },
          required: ['x', 'y', 'z'],
        } as const,
      },
    },
    (req) => {
      /// Property 'x' does not exist on type 'unknown'.ts(2339)
      const { x, y, z } = req.body
    },
  )
}

I am using:

• "node": "18.11.0"
• "typescript": "4.8.4"
• "@fastify/type-provider-json-schema-to-ts": "2.1.1"
• "fastify": "4.9.2"
• "json-schema-to-ts": "2.5.5" (as a dev dependency)

[alphaone]

Just for later reference, I found my problem. I had a wrong setting in my tsconfig.json ("noStrictGenericChecks": true,) that made the json-schema-to-ts to compute useless types.

Removing the setting lets the type inferring from json-schema work like a charm 👌