Part of the agreement between the MLB & Barret Loux for his Free Agency, was that the new CBA would include new draft rules so that this situation would never happen to another player. Their attorney was very involved in the resulting new language to be included in the 2012 CBA. While this rule has a number associated with it within the CBA, it has unofficially become known at "The Barret Loux Draft Rule" by those involved. What BBA doesn't say in their article is that if a team doesn't offer at least 40% of slot value, then if they have a supplemental or compensation pick for that player, then they loose it in the next draft. Thus, the Diamondbacks would have gotten nothing if this rule had been in effect when they drafted Barret.
http://www.baseballamerica.com/today/draft/
http://www.baseballamerica.com/today/draft/