Inference regression (5.0.4 vs 4.9.5) with nullable enum function parameter

[cakoose]

Bug Report

🔎 Search Terms

inference string null function parameter

🕗 Version & Regression Information

• This changed between versions 4.9.5 and 5.0.4

⏯ Playground Link

Playground link with relevant code

💻 Code

enum Thing { a = 'a', b = 'b', };

function f(
 registrationStatusOptions: SelectOptions<Thing>,
 onChange: (status: Thing | null) => void, // <-- Remove the `| null` and the error goes away.
): void {
 select({ // <-- Add an explicit type argument `Thing` and the error goes away.
 options: registrationStatusOptions,
 onChange: onChange, // ERROR in v5.0.4 but not in v4.9.5: Type '(status: Thing | null) => void' is not assignable to type '(key: string) => void'.
 });
}

export function select<KeyT extends string>(props: SelectProps<KeyT>): void {
 throw new Error('hello');
}

export type SelectProps<KeyT extends string> = {
 onChange: (key: KeyT) => void;
 options?: SelectOptions<KeyT>; // <-- Remove the `?` and the error goes away.
};

export type SelectOptions<KeyT extends string> =
 // Comment either of the below union members out and the error goes away.
 | Array<{key: KeyT}>
 | Array<KeyT>;

🙁 Actual behavior

1. Got a type error; see "ERROR" comment above. Looks like the type argument to select(...) is being inferred incorrectly.
2. Minor perturbations of the code cause the error to go away; see other comments above.

This was extracted from some React UI code.

🙂 Expected behavior

TypeScript 4.9.5 infers the type argument I wanted. I was hoping TypeScript 5.0.4 would do the same.

[fatcerberus]

Educated guess: Since this involves enums and the behavior changes between 4.9 and 5.0, this is likely fallout from #50528.

[RyanCavanaugh]

Not enums.

This is weird since removing the constraint also fixes it. Bisecting.

type Thing = 'a' | 'b';

function f(
 options: SelectOptions<Thing>,
 onChange: (status: Thing | null) => void, // <-- Remove the `| null` and the error goes away.
): void {
 select({ // <-- Add an explicit type argument `Thing` and the error goes away.
 options,
 onChange, // ERROR in v5.0.4 but not in v4.9.5: Type '(status: Thing | null) => void' is not assignable to type '(key: string) => void'.
 });
}

declare function select<KeyT extends string>(props: SelectProps<KeyT>): void;

type SelectProps<KeyT extends string> = {
 options?: SelectOptions<KeyT>; // <-- Remove the `?` and the error goes away.
 onChange: (key: KeyT) => void;
};

type SelectOptions<KeyT extends string> =
 // Comment either of the below union members out and the error goes away.
 | Array<{key: KeyT}>
 | Array<KeyT>;

[typescript-bot]

The change between origin/release-4.9 and origin/release-5.0 occurred at 28e4c81.