`export` modifier on `enum` disables `This condition will always return * ts2845`

[eps1lon]

🔎 Search Terms

export enum ts2845

🕗 Version & Regression Information

5.4 doesn't flag it without the export modifier either.

⏯ Playground Link

https://www.typescriptlang.org/play/?target=99&module=0&ts=6.0.0-dev.20260416#code/KYDwDg9gTgLgBMAdgVwLZwIIBMCGYbBQDyyMYpAKgJ5jBwDeAUHJgAqsD6rGA4gKIAaZnG78AykIC+jRlmABjADY4odeREQBneDBrAAXJlz5CJMpT0z1W+AGsAloixwAvMN21XLl0bwFipOQw1LQAdBjsXLx8cAA+sb4mAebBeqGifGLCLAD0OSwFhUXFJaUUABb2mnDWWPYw9hpwAO72iopwOIrNOFTVqjDIUIhwAOQwUMjAo6EAFABMABwALACsAJTZcAD8Y4rAAGYwo1uGo1D2AOblxwDcQA

💻 Code

// remove `export` modifier 
export enum AdapterOutputType {
  APP_PAGE,
  PAGES,
}

declare const type: AdapterOutputType

const kind =
  type === AdapterOutputType.APP_PAGE || AdapterOutputType.PAGES
    //                                   ~ should be flagged with: This condition will always return 'true'.(2845)
    ? 'left'
    : 'right';

🙁 Actual behavior

No typechecking error

🙂 Expected behavior

ts2845 because the condition is always true.

Additional information about the issue

No response

[mkantor]

enums can be declaration-merged. There could be another module elsewhere in the program which contains code like this:

export enum AdapterOutputType {
  SOME_OTHER_PAGE = 3
}

That'd suddenly make it so the condition may evaluate to false. That code could be in an entirely different package not visible to TypeScript, so the analysis is pessimistic.

[mkantor]

On second glance I may have misread. The second part of your condition doesn't compare AdapterOutputType.PAGES to anything; you're just talking about the fact that AdapterOutputType.PAGES === 1 which is truthy (and declaration merging won't change that).

[eps1lon]

The program would know all the values after declaration merging. How would more values in AdapterOutputType change AdapterOutputType.PAGES === 1?

[RyanCavanaugh]

Repros in 7.0 as well.