Repository: JetBrains/kotlin
File: compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/IrUtils.kt (Kotlin)

Code before:
    }

val IrFunction.allTypeParameters: List<IrTypeParameter>
    get() = if (this is IrConstructor)
        parentAsClass.typeParameters + typeParameters
    else
        typeParameters


fun IrMemberAccessExpression<*>.getTypeSubstitutionMap(irFunction: IrFunction): Map<IrTypeParameterSymbol, IrType> {
    val typeParameters = irFunction.allTypeParameters
    val dispatchReceiverTypeArguments = (dispatchReceiver?.type as? IrSimpleType)?.arguments ?: emptyList()
    if (typeParameters.isEmpty() && dispatchReceiverTypeArguments.isEmpty()) {
        return emptyMap()
    }

    val result = mutableMapOf<IrTypeParameterSymbol, IrType>()
    if (dispatchReceiverTypeArguments.isNotEmpty()) {
        val parentTypeParameters = extractTypeParameters(irFunction.parentClassOrNull!!)
        parentTypeParameters.withIndex().forEach { (index, typeParam) ->
            dispatchReceiverTypeArguments[index].typeOrNull?.let {
                result[typeParam.symbol] = it
            }
        }
    }
    irFunction.allTypeParameters.withIndex().associateTo(result) {
        it.value.symbol to getTypeArgument(it.index)!!
    }
    return result
}

val IrFunctionReference.typeSubstitutionMap: Map<IrTypeParameterSymbol, IrType>
    get() = getTypeSubstitutionMap(symbol.owner)

val IrFunctionAccessExpression.typeSubstitutionMap: Map<IrTypeParameterSymbol, IrType>
    get() = getTypeSubstitutionMap(symbol.owner)

val IrDeclaration.isFileClass: Boolean
    get() = origin == IrDeclarationOrigin.FILE_CLASS || origin == IrDeclarationOrigin.SYNTHETIC_FILE_CLASS

val IrValueDeclaration.isImmutable: Boolean
    get() = this is IrValueParameter || this is IrVariable && !isVar

val IrStatementOrigin?.isLambda: Boolean
    get() = this == IrStatementOrigin.LAMBDA || this == IrStatementOrigin.ANONYMOUS_FUNCTION

val IrFunction.originalFunction: IrFunction
    get() = (this as? IrAttributeContainer)?.attributeOwnerId as? IrFunction ?: this

val IrProperty.originalProperty: IrProperty
    get() = attributeOwnerId as? IrProperty ?: this

Review comment (suggestion):
(`associateTo` returns destination)
```suggestion
    return typeParameters.withIndex().associateTo(result) {
```

Code after:
            is IrDeclaration -> it.parentClassOrNull
            else -> null
        }
    }

val IrFunction.allTypeParameters: List<IrTypeParameter>
    get() = if (this is IrConstructor)
        parentAsClass.typeParameters + typeParameters
    else
        typeParameters


fun IrMemberAccessExpression<*>.getTypeSubstitutionMap(irFunction: IrFunction): Map<IrTypeParameterSymbol, IrType> {
    val typeParameters = irFunction.allTypeParameters
    val dispatchReceiverTypeArguments = (dispatchReceiver?.type as? IrSimpleType)?.arguments ?: emptyList()
    if (typeParameters.isEmpty() && dispatchReceiverTypeArguments.isEmpty()) {
        return emptyMap()
    }

    val result = mutableMapOf<IrTypeParameterSymbol, IrType>()
    if (dispatchReceiverTypeArguments.isNotEmpty()) {
        val parentTypeParameters = extractTypeParameters(irFunction.parentClassOrNull!!)
        parentTypeParameters.withIndex().forEach { (index, typeParam) ->
            dispatchReceiverTypeArguments[index].typeOrNull?.let {
                result[typeParam.symbol] = it
            }
        }
    }
    return typeParameters.withIndex().associateTo(result) {
        it.value.symbol to getTypeArgument(it.index)!!
    }
}

val IrFunctionReference.typeSubstitutionMap: Map<IrTypeParameterSymbol, IrType>
    get() = getTypeSubstitutionMap(symbol.owner)

val IrFunctionAccessExpression.typeSubstitutionMap: Map<IrTypeParameterSymbol, IrType>
    get() = getTypeSubstitutionMap(symbol.owner)

val IrDeclaration.isFileClass: Boolean
    get() =
        origin == IrDeclarationOrigin.FILE_CLASS ||
                origin == IrDeclarationOrigin.SYNTHETIC_FILE_CLASS ||
                origin == IrDeclarationOrigin.JVM_MULTIFILE_CLASS

val IrValueDeclaration.isImmutable: Boolean
    get() = this is IrValueParameter || this is IrVariable && !isVar

val IrStatementOrigin?.isLambda: Boolean
    get() = this == IrStatementOrigin.LAMBDA || this == IrStatementOrigin.ANONYMOUS_FUNCTION