I had some trouble making something work in my Astro site.

I used Astro locals and I had to type a variable I shared using locals.

So I went and added that to the src/env.d.ts, as the docs say.

But my types weren’t picked up.

My code looked like this:

/// <reference types="astro/client" />
import { sometype } from 'somelib'

declare namespace App {
  interface Locals {
    somevariable: sometype
  }
}

What I discovered thanks to this SO answer is, we can’t do imports like this in .d.ts files.

So I imported the type in another file, and then I imported the type from that file, like this:

typesforenvdts.ts

import { sometype } from 'somelib'

export { sometype }

env.d.ts

/// <reference types="astro/client" />

declare namespace App {
  interface Locals {
    somevariable: import('./typesforenvdts').sometype
  }
}

Don’t ask me why, but now it works.