Is there way to force code style to have trailing comma but with one exception for when cases ``` ...

# intellij

[Eugen Martynov]

Is there way to force code style to have trailing comma but with one exception for when cases

return when (view) {
                    is ContractView,
                    is ProductTile,
                    -> view.tag == text

                    else -> false
                }

Looks a bit odd.

[Emil Kantis]

You could write a custom Ktlint rule. I’m currently working on a package of rule flavors that adjusts a few things from the Ktlint official style. Feel free to check it out for examples (you’ll have to dig around in the code a bit)https://github.com/Kantis/kantis-ktlint-rules

[Eugen Martynov]

Thanks!

[Anton Mefodichev]

Eugen, thank you!
https://youtrack.jetbrains.com/issue/KTIJ-28982/False-negative-Useless-trailing-comma-with-when-with-break-line

[Emil Kantis]

I think it's invalid to call it useless in 2nd case?

fun foo(bar: Any)  {
    val a = when (bar) {
        is Int,  //"Useless trailing comma" not reported
        -> true
        else -> false
    }
}

Can be modified to

fun foo(bar: Any)  {
    val a = when (bar) {
        is Int,  //"Useless trailing comma" not reported
        is Float,
        -> true
        else -> false
    }
}

Without having a diff on the line with "useless" comma.

[Anton Mefodichev]

I reckon in this case it can be reported as useless on the line with a Float check.

[Anton Mefodichev]

Or we need to add an option to the inspection settings...

[Anton Mefodichev]

@Emil Kantis What do you think?

[Anton Mefodichev]

I have looked again, and it looks as by-design behaviour in the second case as we lose an initial sense of trailing comma.

[Eugen Martynov]

Anton, sorry coming back to my original question - is it correct behaviour? I believe in some extent it is. So I wonder if we could have a settings to override it.

[Emil Kantis]

I think it should be a separate rule all-together.. like "Single when-clause should be on a single line" to force is X -> Y to not contain linebreaks if it's just a single case

[Anton Mefodichev]

It is quite unclear indeed how we should proceed in this case.
Maybe the best way will be adding an additional option to the inspection settings for this case (when condition + several options to check in a raw). It more looks like an unsupported yet case.