Full username_available? method

[ngsankha]

Finally get to synthesis of something like:

  def self.username_available?(username, email = nil)
    lower = username.downcase
    return false if reserved_username?(lower)
    return true  if !User.exists?(username_lower: lower)
    # staged users can use the same username since they will take over the account
    email.present? && User.joins(:user_emails).exists?(staged: true, username_lower: lower, user_emails: { primary: true, email: email })
  end

Blockers:

• [x] #1
• [x] #2

[ngsankha]

We are basically there. The tests in the Discourse app are underspecified - so the synthesizer gives some other program. Need to come up with a good test.