Destructuring object with generic key should reject undefined
#60.119 aberto em 2 de out. de 2024
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Description
🔎 Search Terms
destructure, generic key, undefined
🕗 Version & Regression Information
This is the behavior in every version I tried (back to at least 5.0), and I reviewed the FAQ for entries about destructuring
⏯ Playground Link
💻 Code
interface T { a?: unknown; b?: unknown; c?: unknown }
function f<L extends keyof T>(k: L, t: T | undefined): unknown {
const { [k]: v } = t // should error (crashes if t undefined)
const _v2 = t[k] // equivalent code, does error
return v
}
🙁 Actual behavior
TS does not error on the destructuring, even though it will crash at runtime if t is undefined, and it errors on equivalent code using object-access syntax.
🙂 Expected behavior
TS should error on the indicated line.
Additional information about the issue
This is simplified from an actual example in our codebase. Obviously in this case it's silly to destructure but this was part of a larger block of destructuring so the code would at a glance seem reasonable.
Note that the destructured value does end up having a funky type (T | undefined)[L], which presumably it's hard to do anything with. But of course it's still assignable to unknown, and thus usable in various ways. (In the actual code in question, the authors were doing other complicated things, running an issue similar to #40312, and ended up casting through unknown to the type they wanted.)