Exception for readonly-array rule with rest parameters

[yenbekbay]

I have the readonly-array rule enabled as follows:

{
  "rules": {
    ...
    "readonly-array": true,
    ...
  }
}

For the following piece of code, the rule throws an error:

type SomeFn = (...args: string[]) => void;
                        ^^^
[tslint] Only ReadonlyArray allowed. (readonly-array)

However, if I do fix this error and replace string[] with ReadonlyArray<string>, the code becomes invalid:

type SomeFn = (...args: ReadonlyArray<string>) => void;
                        ^^^
[ts] A rest parameter must be of an array type.

As you can see, the TypeScript compiler requires that rest arguments are typed as plain arrays.

Proposal

Add an exception to the readonly-array rule for this specific case.

Environment

Executable	Version
tslint --version	5.9.1
tsc --version	2.7.1
node --version	9.5.0

[jonaskello]

It would be interesting to know the typescript team's opinion on this. Is this something they will fix or not. Do you know if there exist an issue about this in the typescript repo?

I cannot see a reason why rest params should need to be mutable so IMO it should be fixed in typescript. If it is going to be fixed, then we should probably add it as an option to the readonly-array rule instead, something like ignore-rest-param. If it is never going to get fixed I guess it could be added by default.

[whatisaphone]

Here is the corresponding TypeScript issue.