typescripttypescript-genericsfastify

How to avoid losing Zod type provider generic with Fastify AutoLoad

I'm using Fastify with the fastify-type-provider-zod plugin:

const fastify = Fastify().withTypeProvider<ZodTypeProvider>();

And the fastify-autoload plugin:

// This loads all plugins defined in routes
// define your routes in one of these
fastify.register(AutoLoad, {
  dir: path.join(__dirname, 'routes'),
  options: { ...opts },
});

As a result I lose the ZodTypeProvider generic in the autoloaded files:

export default async function (fastify: FastifyInstance) {
  // fastify does not have the ZodTypeProvider generic here
}

I've worked around this by creating a FastifyInstanceZod type, however I'm hoping there's a better solution:

export type FastifyInstanceZod = typeof fastify;

export default async function (fastify: FastifyInstanceZod) {
  // ...
}
Solution

  • I found the following pattern in an example route in the official Fastify demo project:

    const plugin: FastifyPluginAsyncTypebox = async (fastify) => {
    // route definition
}

export default plugin;

    Defining the route in this way allows it to be typed as FastifyPluginAsyncZod.