Microsoft/TypeScript

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

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#55,091 opened on Jul 20, 2023

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BugDomain: enumFix AvailableHelp 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

Research direction
Investigate enum value transformation when 'Infinity' is shadowed. The compiler incorrectly refers to the local variable instead of computing the constant 1/0. Trace the enum transformation logic in the checker or emitter.
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.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitTypeScript compiler internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65