For consistency and to avoid confusion, could it make sense to still prompt for another file if the command is called with a file that is neither staged nor committed? It's a common use case for me to want to compare a renamed file with the one in history, and it will be kinda annoying to have to remember to first stage it temporarily just to do so (especially if I already have a busy staging area)

Originally posted by @mogelbrod in #3050 (comment)