A modern programming language that makes developers happier.

kotlinlang

Maybe explicit marking data class with some annotation + compiler flag/plugin could help to do so to make it explicit

I would create a feature request on Kotlin issue tracker

You mean sth like this?
<https://github.com/AhmedMourad0/no-copy|https://github.com/AhmedMourad0/no-copy>

Problem is, that there are always some serious downsides when Not supported officially by the language, like no proper ide support without an additional plugin, May break on newer compiler versions and so on.

No, I meant official compiler plugin, there are a few

<https://youtrack.jetbrains.com/issue/KT-11914>