Erroneous "implicitly has type any" for variable later assigned to in loop

[JoshuaKGoldberg]

Bug Report

🔎 Search Terms

variable declaration equals implicit any loop

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

interface State {}

declare function initialState(): State | null
declare function nextState(state: State | null): [State] | undefined

export function bar(): void {
    let state = initialState()

    if (state == null) return

    for (;;) {
        const [next]: [State] | [] = nextState(state) ?? []
             // ~~~~ 'next' implicitly has type 'any' because it does not have a
             // type annotation and is referenced directly or indirectly in its own initializer.

        state = next!
    }
}

Originally reported in: typescript-eslint/typescript-eslint#2248

🙁 Actual behavior

'next' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.

If you removestate = next! or the for (;;), the code exhibits the expected behavior.

🙂 Expected behavior

next is inferred to be type State | undefined.

[MartinJohns]

#36687

[JoshuaKGoldberg]

Ha, nice, thank you 😄