Do you wish you hadn’t done that — or that you wouldn’t have done it?

Which is correct?
Mark Zuckerberg said he wished they _______ decided to work only with HTML5 instead of native apps for Facebook mobile development.
a. hadn’t
b. wouldn’t have

Answer: a

Explanation: 

Wouldn’t have is used in conditional sentences, which state conditions. Facebook wouldn’t have decided to use only HTML5 for mobile development IF they’d known how it would work out.

That construction is known as third conditional, for talking about something that didn’t happen that would have made a difference to the current situation. Here are some examples, from Spotlight-Online:

The third conditional or conditional 3 is formed like this:

if + past perfect ,                        would have + past participle

• “What would you have done if it had happened to you?”
• “If I had known you were coming, I would have combed my hair.”
• “I would have invited you to dinner if you‘d called me back.”

* Remember not to put the would have in the if-clause:
• “I would have told you if I would have known the answer.”

It’s not necessary to explicitly say how things would be different:

 
Incorrect: I wish I wouldn’t have sold the farm to buy Facebook stock.
Correct: I wish I hadn’t sold the farm to buy Facebook stock.

Here’s the correct way to use wouldn’t have in a third conditional sentence:

I wouldn’t have sold the farm to buy Facebook stock if I’d known how overpriced it was.
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