Microsoft/TypeScript
Auf GitHub ansehenSpread operator mixed with destructuring assignment resulting in unsoundness
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#54.402 geöffnet am 25. Mai 2023
Domain: flag: noUncheckedIndexedAccessHelp WantedPossible Improvement
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Beschreibung
Bug Report
This might have been covered before but I am not sure how to best search for it, apologies if it is a duplicate - when destructuring assignment is used with a spread operator (see example below) TS seems to ignore the possibility that the variable could be assigned undefined.
🔎 Search Terms
spread, destructure, destructuring
🕗 Version & Regression Information
- This is the behavior in every version I tried (since 4.1.5 which is the oldest version on the playground with
noUncheckedIndexedAccessavailable)
⏯ Playground Link
Playground link with relevant code
💻 Code
const [a] = [...(false ? (["a"] as const) : [])];
// ^?
const b = false ? (["a"] as const) : [];
// ^?
const c = [...b];
// ^?
const [d] = c;
// ^?
const [a_prime] = [...(false ? (["a"] as const) : [] as const)];
// ^?
🙁 Actual behavior
a is typed as "a", while d and a_prime are typed as "a" | undefined". Note this only happens when noUncheckedIndexedAccess is enabled, otherwise all of them are typed as "a".
Note that d is the unrolled version of a which makes it more surprising that TS is typing them differently.
🙂 Expected behavior
They should all be typed "a" | undefined.