Explicitly annotated unique symbols are widened in return positions

🔎 Search Terms

widening return unique symbol

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.0-dev.20230814&ssl=6&ssc=2&pln=1&pc=1#code/KYDwDg9gTgLgBAYwgOwM7xsdcC8cDKAngLYBGEANgBQCUAUHaJLHAGYCuyCMAlim8lpwA3nTjjEKbAEMKPaagBccGITDAIrFVnh5M6ANxiJUYDHZRkcWfNR0AvkA

💻 Code

export const test = Symbol()

export function fn() {
    const alias: typeof test = test;
    return alias
}

🙁 Actual behavior

this declaration file is emitted:

export declare const test: unique symbol;
export declare function fn(): symbol;

🙂 Expected behavior

this declaration file to be emitted:

export declare const test: unique symbol;
export declare function fn(): typeof test;

Additional information

getWidenedLiteralLikeTypeForContextualReturnTypeIfNeeded calls getWidenedLiteralLikeTypeForContextualType and that calls getWidenedUniqueESSymbolType when there is no contextual type provided.

some issues that are (partially~) related:
https://github.com/microsoft/TypeScript/issues/32242
https://github.com/microsoft/TypeScript/issues/35896#issuecomment-569466046
https://github.com/microsoft/TypeScript/issues/36876

Start with the linked TypeScript Playground and reproduce the emitted declaration for the example. Read getWidenedLiteralLikeTypeForContextualReturnTypeIfNeeded, getWidenedLiteralLikeTypeForContextualType, and getWidenedUniqueESSymbolType as identified in the issue. Done means the declaration preserves the explicit unique-symbol type as typeof test rather than widening fn's return type to symbol.