title: Xcode 10: Ambiguous Constraints Error When Adding Simple Constraints
body: <p>I'm working in Xcode 10 and am getting some errors when trying to add some pretty simple constraints to my view.</p>
  
  <p>I have a <code>UICollectionViewCell</code> that I'm adding a <code>UIStackView</code> to. I size the <code>UIStackView</code> to fill the cell and set the top, bottom, left, and right constraints to the Safe Area. </p>
  
  <p>I used to be able to do this in Xcode 9 without error, however, it now gives me an error that I need to specify the <strong>X Position or Width and the Y Position or Height</strong>. Even when I let the interface builder add the missing constraints (<strong>Center X and Center Y</strong>) it gives the same error. I feel like this is a bug in Xcode 10, but if there are new iOS 12 requirements for constraints I don't know about I'd appreciate some help with them.</p>
  
  <p>If I ignore the erroneous constraints and run the app the view does not show up properly.</p>
  
  <p><a href="https://i.stack.imgur.com/sih9S.png" rel="noreferrer"><img src="https://i.stack.imgur.com/sih9S.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/LyOmD.png" rel="noreferrer"><img src="https://i.stack.imgur.com/LyOmD.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/QaCih.png" rel="noreferrer"><img src="https://i.stack.imgur.com/QaCih.png" alt="enter image description here"></a></p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>I definitely think this is a bug. Notice in the screenshot below, even though I have subviews in the stack view, the errors do not go away. Also, when I add static padding to the top, left, bottom, and right it does not show properly in the layout, however it does layout properly when I run the app.</p>
  
  <p><a href="https://i.stack.imgur.com/7BGe9.png" rel="noreferrer"><img src="https://i.stack.imgur.com/7BGe9.png" alt="enter image description here"></a></p>