No report of implicit any type in a generator when destructuring

[Igorbek]

Bug Report

🔎 Search Terms

no implicit any, generator, yield, destructure
#41348 - Report implicit any error for 'yield' result with no contextual type

🕗 Version & Regression Information

TypeScript 4.2.3

⏯ Playground Link

Playground link with relevant code

💻 Code

function* sample() {
    const a = yield 1 // error, as expected, a is implicitly any
    const { b } = yield 1 // no error, but expected, b is implicitly any
    const [c] = yield 1 // no error, but expected, c is implicitly any
}

🙁 Actual behavior

b, c implicitly have type any, but no error reported

🙂 Expected behavior

Errors reported

[a-tarasyuk]

@RyanCavanaugh What about the following case?

function* g() {
    const [a = 1, b = 2] = yield; ???
}

[Igorbek]

@a-tarasyuk it seems they're given context types, so it should not be an error. However, the intention might be:

const [a = 1, b = 2]: [number | string, number | boolean] = yield;

not really definitive.

[a-tarasyuk]

Should the expected behavior be like this?

function* g1() {
    const { a } = yield;                 // error: implicit any
    const { b }: { b: string } = yield;  // ok
    const { c = 1 } = yield;             // ok ??
}

function* g2() {
    const [a] = yield;           // error: implicit any
    const [b]: [string] = yield; // ok
    const [c = 1] = yield;       //  ok ??
}

/cc @DanielRosenwasser @RyanCavanaugh

[Igorbek]

I think you're correct with inferred type from the default being ok, as it'd be consistent with plain functions:

function f2({ a }) {} // error
function f2({ a }: { a: number }) {} // ok
function f3({a = 1}) {} // ok

[Igorbek]

ah, on the second thought, if it is const binding, the type is not widening, which is not the same in the argument destructuring. You either end up having a type of const context or have inconsistency and widen the type even in const binding.
I'd say in this case it should be an error then. Although let would work just fine, for consistency, I'd also vote for the error.