How do you know where the function has been copy pasted? How do you know whether it has been copy pasted in the first place? The bug may be latent, hard to fin

How do you know where the function has been copy pasted? How do you know whether it has been copy pasted in the first place? The bug may be latent, hard to find, or express itself very differently in different places. It is in fact, a different bug if it originates from code in a different place, even if the code is largely identical.