"unique symbol" is generated to multiple .d.ts files

[zoltan-mihalyi]

TypeScript Version: 4.0.3
Search Terms:
unique symbol, declaration, .d.ts, invalid, TS4023

Code

a.ts

type AX = { readonly A: unique symbol };
export const A: AX = 0 as any;

b.ts

import { A } from './a';
export const A1 = A;

tsconfig.json

{
  "compilerOptions": {
    "declaration": true,
    "strict": true,
    "noImplicitAny": true,
    "rootDir": "src",
    "outDir": "lib"
  }
}

Expected behavior:
Typescript should either throw TS4023, or generate the following code for b.d.ts:

import { A } from './a';
export declare const A1: typeof A;

Actual behavior:
Typescript generates "unique symbol" to both a.d.ts and b.d.ts:

a.d.ts

declare type AX = {
    readonly A: unique symbol;
};
export declare const A: AX;
export {};

b.d.ts

export declare const A1: {
    readonly A: unique symbol;
};

Project Link:
project.zip

[weswigham]

Hm. I suppose we should issue an error here? The local type from a isn't reachable in b, so we print the type anonymously; however it contains a unique symbol which, by rights, refers to a symbol in a different file; so we can't really serialize it. The only thing you could write out is something like export declare const A1: typeof A, like you propose, but our declaration emit generally doesn't write out typeof queries on its own (simply because it doesn't generalize - it'd only work for exactly declarations of the form var x = some.dotted.name, which is an odd syntactic carve-out to make for TS code), which is why it's more in-line with our normal behavior to report an error on the attempted usage of a private symbol, and require an annotation.

[weswigham]

In fact, the error already exists, and is simply failing to trigger due to an unfortunate bug.