Provide clearer error message for unsupported local `@DataSchema data class`

[Jolanrensen]

Writing a @DataSchema interface from within a function body provides the following helpful messages:

Unfortunately, the message about not supporting local @DataSchema s does not appear when using data classes:

I think it would be helpful to add it for data classes as well :)

[koperagen]

To allow.. is the message we provide. I'll change it: "@DataSchema declaration cannot have '...' visibility, it must be declared as either of [...]. This visibility is required so that plugin-generated extension properties can refer to this DataSchema". Alright?

[Jolanrensen]

@koperagen But the problem is not (only) the visibility, right? Rather, it's the fact that the data schema is defined locally. For instance:

fun myFun() {
    @DataSchema
    data class Test1(val a: Int)
}

This reports only that the class needs to have public or internal visibility. So, if I then as a user fix it to:

fun myFun() {
    @DataSchema
    public data class Test1(val a: Int)
}

I just get another error because "public" cannot be applied to local classes...

It would be a lot more helpful if our error message specified that the data schema cannot be local if it's written locally and only complain about visibility when it's non-local :)

[koperagen]

Oh, that's what it is. Ok
"@DataSchema declaration cannot be local. Move it outside function body. This is required so that plugin-generated extension properties can refer to this @DataSchema"

[zaleslaw]

@AndreiKingsley could you please shortly write the status here with approximate dates or Kotlin release when it will be available?

[AndreiKingsley]

Everything is done both in Kotlin and IDEA.
Expected in 2.4.0!