I've been told that native-speakers don't ever use "will" after "if", and that saying it this way is a not-native style.
So from the film (Harry Potter, pt5) I noticed a line that confused me. Look at this:
"Well, if you won't tell her where it is, I will". See that?
What was the necessity of using the future form? What does it add in the meaning? How does it sound to you? Why was namely this sentence used instead of "Well, if you don't tell her where it is, I will"?