💅 False positive by lint/nursery/noUselessUndefined

[atheck]

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Rule name

lint/nursery/noUselessUndefined

Playground link

https://biomejs.dev/playground/?lintRules=all&code=KAApACAAPQA%2BACAAdQBuAGQAZQBmAGkAbgBlAGQA&language=ts

Expected result

unicorn/no-useless-undefined does not flag this when the option "checkArrowFunctionBody" is set to false.

Code of Conduct

• I agree to follow Biome's Code of Conduct

[vladimir-ivanov]

I do not see checkArrowFunctionBody option in no_useless_undefined? no options on that rule as yet :-(.

However there is an interesting conflict of rules:

[siketyan]

We don't have one yet, but I think we can ignore undefined in an arrow function body by default? May need some discussion

[vladimir-ivanov]

[vladimir-ivanov]

guess we leave it as is and down to users to deal with it - e.g. turn off one or the other?

Alternatively we should introduce an option on either of the two rules?

@atheck what do you think please?

[atheck]

First, thank you for your efforts.

You could have something like this:

(): string | undefined => undefined

In this case only the noUselessUndefined rule would kick in.

To fix this one could write:

(): string | undefined => {}

But then the noEmptyBlockStatements rule would flag this.

In my opinion ignoring undefined in arrow functions would be the best option, because in a "normal" function the rule flags if you write return undefined. This can be fixed by just writing return. In an arrow function you cannot do this. I guess that is why the unicorn eslint plugin introduced that option I meantioned.

[vladimir-ivanov]

so your suggestion @atheck is to add checkArrowFunctionBody option thanks