sveltekit type fudgery

OUTPUT

export function getFoo(): FooType<NonExistentType> | null;
import type { FooType } from './foo.d.ts';

src-foo.d.ts

import {
  NonExistentType
  // @ts-ignore
} from "$nonExistent";

export interface FooType<T extends NonExistentType = NonExistentType> {
  data: T;
}

src-main.js

/** @import {FooType} from './foo.d.ts' */

/** @type {FooType | null} */
let foo = null;

export function getFoo() {
  return foo;
}

tsconfig.json

{
	"compilerOptions": {
		"allowJs": true,
		"checkJs": true,
		"strict": true,
    "outDir": "dist",
    "declaration": true,
    "emitDeclarationOnly": true,
		"target": "es2022",
		"module": "node16",
		"moduleResolution": "node16",
		"noUnusedLocals": true,
		"noUnusedParameters": true
	},
	"include": ["src/**/*"]
}