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.

Beginne in src/compiler/checker.ts bei der verlinkten Funktion für Predicate-Semantik und bilde das Verhalten im bereitgestellten TypeScript Playground-Link nach. Bestätige, dass 0n als immer falsy klassifiziert wird und dass sich die Diagnose von TS 2872 zu TS 2873 ändert, wobei Tests mithilfe der bestehenden Teststruktur des Compilers hinzugefügt werden.