Contextual never parameter type gets precedence over the initializer's type

[Andarist]

🔎 Search Terms

contextual parameter type initializer never

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.4.0-dev.20231122#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXwxAGcMAeAKHngBUBhPQgDwwBpKaBZEDACx2CLwQzEKgHwASuBwxgpEjCyoA5i3gAKTIwBcNeqiat4AOlOxlRXahAA3EDADaAXQCU8ALwA+eGgDWqHAB3VE82T00GYQxdOkjmNQBbbj4BGK5efiIXXRscLGAAbnJyQhJ1dgBvdiowHDRo+AAGNioAXxb4KqoannBfABksBKwGzQxGRKhGD3gAVkbGty9O9ur4HigiAEEwMGJLDS01ZCJ7XQr4VCgk3QUlZXhWpe8K1ba2FyKgA

💻 Code

declare function test<
  TContext,
  TMethods extends Record<string, (ctx: TContext, ...args: never[]) => unknown>,
>(context: TContext, methods: TMethods): void;

test(
  {
    count: 0,
  },
  {
    checkLimit: (ctx, max = 500) => {},
    hasAccess: (ctx, user: { name: string }) => {},
  },
);

🙁 Actual behavior

never gets assigned as the type of max parameter and TS errors on the initializer's type mismatch:

Type 'number' is not assignable to type 'never'.(2322)

🙂 Expected behavior

I'd expect the type inferred from the initializer to take precedence over never here. After all, we could annotate this contravariant position with max: number = 500 and that wouldn't violate any constraints.

Additional information about the issue

No response

[fatcerberus]

For what it's worth, this isn't specific to never and in fact is a more general issue with too-narrow parameter types: if the contextual parameter type is, say, 1 | 2 | 3, then this is also an error when it doesn't need to be (a function that takes number is assignable to one that takes 1 | 2 | 3).

[Andarist]

Good point. I can probably tweak this somewhat easily by checking the assignability between the initializer's type and the contextual type - just in the right direction.