The "WTF" label is not about correctness, it's about surprise/intuition. It doesn't really matter to me whether it's mathematically or IEEE correct. It's strange and inconsistent.
Yes, two numbers of different signs added together are supposed to be 0, but... a number is never supposed to change (sign or magnitude) when you add 0 to it, and here it does... so... it's a strange corner case that I think defies intuition.
Given the two precedences that are incompatible, I think far more people are likely to think "anything + 0 ======= anything" than they are to think "anything + -anything ========== +0". So that's why I marked it as a WTF.
Yes, two numbers of different signs added together are supposed to be 0, but... a number is never supposed to change (sign or magnitude) when you add 0 to it, and here it does... so... it's a strange corner case that I think defies intuition.
Given the two precedences that are incompatible, I think far more people are likely to think "anything + 0 ======= anything" than they are to think "anything + -anything ========== +0". So that's why I marked it as a WTF.