`Omit` causes function to lose contextual typing

🔎 Search Terms

implicit any contextual type

🕗 Version & Regression Information

• This changed between versions 5.9.3 and 6.0 - rc

⏯ Playground Link

Playground Link

💻 Code

declare let x: { function: string }
export type AssertableState<T> = {
    [P in keyof T as P]: (value: T[P]) => void;
}
declare function assert_state<T extends object>(o: T, state: AssertableState<T>): void;
assert_state(x, {
    function: v => { } // v is string
})


declare function assert_state_bad<T extends object>(o: T, state: Omit<AssertableState<T>, "">): void;
assert_state_bad(x, {
    function: v => { } // error - v is implictly any
})

🙁 Actual behavior

The call to assert_state_bad fails because v is implicitly typed as any

🙂 Expected behavior

Either should pass as in 5.9.3

Additional information about the issue

• Works without the Omit
• Works without the as P in the mapped type. (original mapping was more complicated, but identity mapping seems to trigger it too)

まず、リンクされた Playground の例を TypeScript 5.9.3 と 6.0-rc で再現し、Omit あり・なしの場合と identity mapped type の場合でコンテキスト型付けを比較します。Omit でラップされた mapped type の型チェック経路を追跡します。完了の条件は、コールバックパラメーターが string として推論され、報告されている implicit-any の失敗が発生しなくなることです。