Microsoft/TypeScript

Incorrect emitted declaration for unique symbol re-assignment

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#62,305 opened on Aug 19, 2025

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BugDomain: Declaration EmitHelp Wanted

Description

🔎 Search Terms

"TS1332", "unique symbol readonly", "function readonly property"

🕗 Version & Regression Information

N/A.

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250819#code/MYewdgzgLgBAtgTwMoLgIxAGxgXhi9LACgHICNMIA6RcrEgSgG4AoF0SWOy3GAbxYwh8ZKgosAvjACGEGB2isWAMwCuYYFACW4EQDF1mnWCIN+EtogMbt4GqMLY83arTFYlAegBULJAFF-GAADKgARKgAVJGCYSIBBACEqOIAJIKSAeQA1IIBhTLCggAUAJUKAVTz-JAAuNgATAFNgTGkAJyaYMGk4JogAB2lgLqtDWzB+QWEANw6RblqYdS0AR1UuiHdMVgsWAHVUgEk81JgjpBh4gDkYf1Ly0pgiaIBGAGZ3gCYl+Jg59paaRoTBdADuAAsQBAulAEAMulo5NIYCQVutNtsSDA4Qj4KpoDA0F0FFAGCxvJ42E0AB4DEDtWB8MY2YwWIA

💻 Code

const mySymbol = Symbol('Symbols.mySymbol');

const Symbols = {
    mySymbol
} as const;

function myFunction() {}

myFunction.mySymbol = Symbols.mySymbol;

/*
SEE `.D.TS` TAB. THE ABOVE CODE PRODUCES:

declare namespace myFunction {
    var mySymbol: unique symbol;
}

WHICH IS AN ERROR (TS1332: A variable whose type is a 'unique symbol' type must be const)
*/

export {myFunction}

🙁 Actual behavior

Compiler produces:

declare namespace myFunction {
    var mySymbol: unique symbol;
}

🙂 Expected behavior

Should be:

declare namespace myFunction {
    const mySymbol: unique symbol;
}

Additional information about the issue

Behaves differently when not in a module (remove export {myFunction} in the Playground)

Contributor guide

Tech stack
typescript
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
TypeScript basicsDeclaration emit internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Investigate the TypeScript compiler's declaration emit logic for namespace members with unique symbol types. Focus on the code paths that emit `var` vs `const` for such members. The issue provides a playground link and notes behavioral differences between module and non module contexts. Look for relevant tests in the test suite.