Generic inference from property return type fails only if parameters exist and JSX attribute syntax is used

[henry-bishop]

Bug Report

🔎 Search Terms

• Generics
• JSX
• Inconsistent
• Inference

🕗 Version & Regression Information

This is the behavior in every version I've tested including 4.7.4 up to 5.0.0-dev.20230215
(Before 4.7.4, the issue occurred regardless of whether JSX syntax was used)

⏯ Playground Link

Playground link with relevant code

💻 Code

interface Props<T> {
  a: (x: string) => T;
  b: (arg: T) => void;
}

function Foo<T>(props: Props<T>) {
  return <div />;
}

// Works fine, T is inferred as 'number' through the return value of 'a'
<Foo
  a={() => 10}
  b={(arg) => { arg.toString(); }}
/>;

// If 'a' takes any parameters, inference stops working and T becomes 'unknown'
<Foo
  a={(x) => 10}
  b={(arg) => { arg.toString(); }} // ERROR: 'arg' is of type 'unknown'
/>;

// (since 4.7.4) Works fine if the object literal syntax is used instead
<Foo {...{
  a: (x) => 10,
  b: (arg) => { arg.toString(); },
}} />;

🙁 Actual behavior

Foo<T> fails to infer T from the return value of a if the function provided for a accepts any parameters, and the JSX attribute syntax is used.

🙂 Expected behavior

Foo<T> should infer T from the return value of a regardless of whether its signature has parameters, and regardless of whether the JSX attribute syntax is used or not.

[RyanCavanaugh]

Work item here is to port some of the logic added to address #47599 to also apply to JSX

[Andarist]

This is already fixed by #52837 and awaits review 😉