My "favorite" one of those is Mercurial's error when you use a subcommand that you need to enable an extension for. Not only does it know the subcommand is vali

My "favorite" one of those is Mercurial's error when you use a subcommand that you need to enable an extension for. Not only does it know the subcommand is valid, it also tells you which extension to enable. If it's gone all that way, why not enable the extension automatically?