Annotated parameters are not used for inferring rest parameters

🔎 Search Terms

annotated, "rest parameter"

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play/#code/GYVwdgxgLglg9mABAWwNYEFrzAHgJJgAOIUiApgB5RlgAmAzogIZgCeA2gLoB8AFE1gQAuRAG8AUIimJgARiG8AdMor0hBYlACUiALzdEANzgxaAGknTgAJgXLFq9URI79Rk+fEBfHaK-jxNExYBF4JaRlZXgoheigAJxgwAHMzRFYhMBBkACMyeN8vC0spG2i01kKLCIB6GsQKZjp05niyRCTgfLbaZkYAIhZWfurpOvJDGkQoAAs4EGSZmWsOxk7usl6mAeiROMSUipEs3PzXA2NTfu8tAG5xIA

💻 Code

function mkAction<Input extends any[]>(action: {
    f1:(...xs:Input) => void,
    f2:(...xs:Input) => void,
}) {}

mkAction({
    f1(x:string, y:number) {},

    f2(x, y) {},
    // x and y are inferred as "any",
    // even though f2 is inferred as "(x: string, y: number) => void"
});

🙁 Actual behavior

Arguments "x" and "y" are inferred as "any", even though "f2" has the correct type (x: string, y: number) => void

🙂 Expected behavior

I would expect inference of x: string and y: number for the arguments of "f2".

Additional information about the issue

No response

Start by reproducing the annotated rest-parameter example from the issue in the linked TypeScript Playground. Trace how the compiler infers the unannotated parameters of f2 from the contextual function type, then add coverage for the expected string and number inference and verify the existing behavior remains intact.