internal object FirSyntheticFunctionInterfaceSourceProvider {
    fun findPsi(fir: FirDeclaration): PsiElement? {
        return when (fir) {
            is FirSimpleFunction -> provideSourceForInvokeFunction(fir)
            is FirClass -> provideSourceForFunctionClass(fir)
            else -> null
        }
    }

    private fun provideSourceForInvokeFunction(function: FirSimpleFunction): PsiElement? {

            )

        // TODO: this doesn't guarantee that the same synthetic function (as a SAM constructor) is created/returned
        fun getSamConstructor(firClass: FirRegularClass): FirSimpleFunction? {
            val samConstructor = bodyResolveComponents.samResolver.getSamConstructor(firClass) ?: return null
            if (samConstructor.origin != FirDeclarationOrigin.SamConstructor) return null
            return samConstructor
        }
    }

import org.jetbrains.kotlin.analysis.api.symbols.KtNamedClassOrObjectSymbol
import org.jetbrains.kotlin.fir.declarations.FirCallableDeclaration
import org.jetbrains.kotlin.fir.declarations.FirClass
import org.jetbrains.kotlin.fir.declarations.FirDeclaration
import org.jetbrains.kotlin.fir.declarations.FirFunction
import org.jetbrains.kotlin.fir.declarations.FirMemberDeclaration

        require(superClass is KtFirSymbol<*>)

        if (subClass == superClass) return false
        return isSubClassOf(
            subClass = subClass.firSymbol.fir as FirClass,
            superClass = superClass.firSymbol.fir as FirClass,
            rootModuleSession,
            allowIndirectSubtyping,
        )
    }