microsoft / microsoft/TypeScript

Enum value `1 / 0` incorrectly transformed if there is `Infinity` declared in scope

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Bug Domain: enum Help Wanted
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Description

Bug Report

🔎 Search Terms

infinity enum variable let shadow

🕗 Version & Regression Information

Every version I tested

⏯ Playground Link

Playground link with relevant code

💻 Code
{
  let Infinity = 3;

  enum A {
    X = 1 / 0
  }

  console.log(A.X)
}
🙁 Actual behavior
{
    let Infinity = 3;
    let A;
    (function (A) {
        A[A["X"] = Infinity] = "X";
    })(A || (A = {}));
    console.log(A.X);
}

and logs 3

🙂 Expected behavior

It should log the result of 1 / 0, which is Infinity.

Somewhat related to https://github.com/microsoft/TypeScript/issues/54981.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked TypeScript Playground and the enum example, then trace the compiler's enum emission and constant-expression handling for 1 / 0 when Infinity is shadowed. Done means the emitted JavaScript evaluates A.X as the result of 1 / 0 rather than the local Infinity variable, with regression coverage for this 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
35/100

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