The Hastehaste spell, andas well as the potion of speed that mimicksPotion of Speed which mimics it, grantgrants an additional attack on each of the creature's turns. The wording says "one weapon attack only", but...
There's a 3rd level Hunter Ranger-level Hunter ranger feature called Horde Breaker that gives saidallows the ranger to make one additional attack (with the same weapon, against another target) when he hitsmakes a targetweapon attack. So...
Let's say a ranger drinks a potionPotion of speedSpeed as his action, then attacks with the Hasteadditional attack from haste. Would he then be able to benefit from Horde Breaker and make an additional attack ?