```buildTypeParameter { val paramBuilder = thi...

# compiler

[min]

buildTypeParameter {
    val paramBuilder = this
    paramBuilder.source = old.fir.source
    paramBuilder.moduleData = old.fir.moduleData
    paramBuilder.origin = FirDeclarationOrigin.Plugin(KEY)
    paramBuilder.name = old.name
    paramBuilder.symbol = key
    paramBuilder.containingDeclarationSymbol = function
    paramBuilder.variance = old.fir.variance
    paramBuilder.isReified = old.fir.isReified
    paramBuilder.bounds.addAll(old.fir.bounds)
}

I’ve never developed a plugin before, so I’m unfamiliar with the API. Data classes have the copy method to let me copy an instance with just the fields I want overridden, so I feel like Kotlin would also have a shorter way for this too but cannot find it myself.

[dmitriy.novozhilov]

FIR elements aren't data classes, so they don't have a builtin copy. Moreover, the real elements implementations are hidden and only the abstract classes for them are exposed.

For copying elements there is a copy-builder API in addition to just builder. The convention name for them is buildElementNameCopy(originalElement) {...}.
For type parameters it would be

buildTypeParameterCopy(old) {
    origin = ...
    symbol = key
}

Link to source.

[min]

@OptIn(SymbolInternals::class) buildTypeParameter {
    val paramBuilder = this
    paramBuilder.source = old.fir.source
    paramBuilder.moduleData = old.fir.moduleData
    paramBuilder.origin = FirDeclarationOrigin.Plugin(KEY)
    paramBuilder.name = old.name
    paramBuilder.symbol = key
    paramBuilder.containingDeclarationSymbol = function
    paramBuilder.variance = old.fir.variance
    paramBuilder.isReified = old.fir.isReified
    paramBuilder.bounds.addAll(old.fir.bounds)
}

@dmitriy.novozhilov So I should be able to replace this with

@OptIn(SymbolInternals::class) buildTypeParameterCopy(old.fir) {
    val paramBuilder = this
    paramBuilder.origin = FirDeclarationOrigin.Plugin(KEY)
    paramBuilder.symbol = key
    paramBuilder.containingDeclarationSymbol = function
}

This, right? Thanks!

[dmitriy.novozhilov]

Well, you don't need val paramBuilder = this. But generally yes.

[min]

@dmitriy.novozhilov I just like to always do that for clarity. Thanks for having a look and for the explanation 🌻