The "never use would have in an if clause" is really about the subjunctive. It is part of a rule regarding statements that are "contrary to fact."
...If I had gone , it would have been different.
...If she had been with us , she would have handled it.
This also occurs in "I wish" statements.
...I wish I had gone .
...I wish I had been there .
And there is no "would have" in this construction either. The subjunctive mood takes care of the "would have."
Happy punctuating!
Margie
