After upgrade to 7.2.0 mapTo(true) violates and shows @typescript-eslint/no-unsafe-argument error

[vitalyiegorov]

Bug Report

We have migrated our codebase from 6.6.6 to 7.2.0 and have a an issue for mapTo(true) operator from eslint:

ESLint: Unsafe argument of type `OperatorFunction<any, boolean>` assigned to a parameter of type `OperatorFunction<DeleteResult, boolean>`.(@typescript-eslint/no-unsafe-argument)

Investigating the sources:

export function mapTo<R>(value: R): OperatorFunction<any, R>;
/** @deprecated Do not specify explicit type parameters. Signatures with type parameters that cannot be inferred will be removed in v8. */
export function mapTo<T, R>(value: R): OperatorFunction<T, R>;

Current Behavior
ESLint error is shown, without providing generics for mapTo operator.

Expected behavior
No ESLint errors, without additional generics for mapTo operator.

Reproduction

mapTo(true)

Environment

• Runtime: Node v16.1.0
• RxJS version: 7.2.0

Possible Solution
Seems like the problem is with any, changing the type to use generics, fixes the issue, and you can use it in your code without specifying them:

export declare function mapTo<T, R>(value: R): OperatorFunction<T, R>;

[cartant]

T serves no purpose in the signature - as mentioned in the deprecation comment - and it would be incorrect to use it. (The general rule is that a type parameter should be used more than once in a signature.)

any could - indeed should - be replaced with unknown. Replacing the uses of any - throughout the API - with unknown is some that will be (eventually) be done.

[benlesh]

@cartant are we tracking the change for any to unknown anywhere? It seems like that's a version 8 thing. (Also we can probably close this)

[cartant]

@benlesh

... are we tracking the change for any to unknown anywhere?

Added it to #6367

[rassie]

So what is the solution here, why is this closed? No matter which signature I'd use, I'll get an ESlint warning, either for deprecation or for unsafe arguments.

[manbearwiz]

Its clunky, but you can use a type assertion to specify the return type as unknown instead of any until they handle it internally. This removes the error for me. Replace

switchMapTo(this.service.isAlive())

with

switchMapTo(this.service.isAlive()) as OperatorFunction<unknown, boolean>

[benlesh]

Does map(() => true) work for you? (That's all that mapTo does internally)