microsoft / microsoft/TypeScript

__esDecorate transpiled code uses "Symbol" even of this is shadowed by a local variable

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Bug Domain: Decorators Help Wanted
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Description

### 🔎 Search Terms

helper symbol tslib

### 🕗 Version & Regression Information

- This changed between versions 5.1.6 and 5.2.2

Tested via playground and reading its debug output.

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.0-dev.20250617#code/GYVwdgxgLglg9mABMOcAiBTCcBOBDKXAClxgHMYw8AbAWQygAs4ATALkTzAE8AaRbGCgYAHlA5duASkQBvAL4AoRaIAOuKAOp4AzjsQBlbgFsARnGpyBCHVBwhoxGbMTzXygAIp0WXAVwqIuo4mhDaeojG3ADC4fqyiohJgrb2jjhEzoiJSbkpmgD6YBgA7kbGiAC8iMUlhibm1JkA3DnuSkA

### 💻 Code

```ts
function fooDecorator(originalMethod: any, context: any) {}

export class Symbol { constructor() { } }

@fooDecorator
export class myClass {
constructor() {
const _newSym = new Symbol();
}
}
```

### 🙁 Actual behavior

The generated js code for `myClass` contains
```ts
const _metadata = typeof Symbol === "function" && Symbol.metadata ? Object.create(null) : void 0;
```
Which will access my local variable `Symbol` instead of `window.Symbol`/`globalThis.Symbol`.

### 🙂 Expected behavior

The generated code should access `globalThis.Symbol` in any case or perhaps only if the file contains a local variable (from `class`, `const` or `import`) with a colliding name.

### Additional information about the issue

I found this with an `import { Symbol } from "./service";` call (roughly modelled via this [Bug Workbench](https://www.typescriptlang.org/dev/bug-workbench/#code/PTAEAEDMEsBsFMB2BDAtvAXKAzvATgG7QDG8AdAC7YBQwAVHaABKrSgDKAnqgEYD2sUHWDV4ADwAOfPBVDFYybNg7d+ggN6g5fRNgp4ArsQrSAFAEpQmgL6hr1WmChwkaTKGQSJlGtFRSZKxVeATtQSDw+VFAAIjJgXEISeBiAbgdIA0RjaB1wvj4AEXhiaWQTPFNS3X0jCqwAMSycnUt1eygC4tK8culRSWlZeUVlVE4AYQUlK2otbRrDYzM20Dn5rWq9UAB9SALQAF5QRHgAd2C1C3T5+3sgA)) but this should not change the main problem.

We started to use the class name `Symbol` in our code (and public API) since 2014.

Right now we circumvent this issue by using different names inside the local file via alias names in `import`/`export`
But this is hard to understand and maintain.

Contributor guide

Open the contributing guide

Research direction

Start with the linked TypeScript playground and inspect the generated __esDecorate code for the local Symbol declaration or import. Trace how the decorator metadata helper chooses the Symbol reference, then verify that the emitted code no longer resolves the local binding and still handles the shown decorator example.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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