bug: error message says 0n is truthy

🔎 Search Terms

falsey, truthy, bigint, PseudoBigInt, TS Error 2872, TS Error 2873, unnecessary condition, constant condition

🕗 Version & Regression Information

• This changed between versions 5.5.4 and 5.6.3,
• https://github.com/microsoft/TypeScript/pull/59217 (playground)

⏯ Playground Link

https://www.typescriptlang.org/play/?target=99&ts=5.7.0-dev.20241022#code/JYMwBAFADAdglGA3mFAoAvkA

💻 Code

0n is falsy.

if (0n) {
  // won't happen
}

🙁 Actual behavior

TS 2872: This kind of expression is always truthy.

🙂 Expected behavior

TS 2873: This kind of expression is always falsy.

Additional information about the issue

I am presuming that this is due to this function, which always reports BigIntLiteral as PredicateSemantics.Always, rather than checking for 0n.

https://github.com/microsoft/TypeScript/blob/c07da583afbfbb68930448b781832c74b3f713e6/src/compiler/checker.ts#L44498-L44532

Looks like this has been present since the always-truthy/always-falsey check was initially created: https://github.com/microsoft/TypeScript/pull/59217/files#diff-d9ab6589e714c71e657f601cf30ff51dfc607fc98419bf72e04f6b0fa92cc4b8R44293

I'd be happy to drop a PR if this is accepted and that's the issue.

Bắt đầu trong src/compiler/checker.ts tại hàm ngữ nghĩa predicate được liên kết và tái hiện hành vi trong liên kết TypeScript Playground được cung cấp. Xác nhận rằng 0n được phân loại là luôn falsy và chẩn đoán thay đổi từ TS 2872 thành TS 2873, đồng thời thêm coverage bằng cấu trúc kiểm thử hiện có của compiler.