It used to be possible to use toBuiltin/fromBuiltin within a smart contract, but this is no longer the case, but this isn't obvious to the users as they already have code with toBuiltin/fromBuiltin that now just misbehaves instead of throwing a type error or breaking compilation some other way. This fixes the problem by throwing on any usage of toBuiltin/fromBuiltin with a suggestion to use toOpaque/fromOpaque instead.
It used to be possible to use
toBuiltin/fromBuiltinwithin a smart contract, but this is no longer the case, but this isn't obvious to the users as they already have code withtoBuiltin/fromBuiltinthat now just misbehaves instead of throwing a type error or breaking compilation some other way. This fixes the problem by throwing on any usage oftoBuiltin/fromBuiltinwith a suggestion to usetoOpaque/fromOpaqueinstead.