Open Radar

 
Summary:
Given an enum with 12 or more cases
When switching over a pair of instances of this enum in a tuple in the pattern
case (a, a):
…
case (z, z):
case (a, _):
case (y, _):

And the case (z, _) is missing
Then the compiler should show an error because the switch is not exhaustive.

Steps to Reproduce:
enum Demo {
  case value1
  case value2
  case value3
  case value4
  case value5
  case value6
  case value7
  case value8
  case value9
  case value10
  case value11
  case value12
}

extension Demo {

  static func demoSwitch(_ lhs: Demo, _ rhs: Demo) -> Bool {
    switch (lhs, rhs) {
      //matching
      case (.value1, .value1): return true
      case (.value2, .value2): return true
      case (.value3, .value3): return true
      case (.value4, .value4): return true
      case (.value5, .value5): return true
      case (.value6, .value6): return true
      case (.value7, .value7): return true
      case (.value8, .value8): return true
      case (.value9, .value9): return true
      case (.value10, .value10): return true
      case (.value11, .value11): return true
      case (.value12, .value12): return true

      //not matching
      //case (.value1, _): return false
      case (.value2, _): return false
      case (.value3, _): return false
      case (.value4, _): return false
      case (.value5, _): return false
      case (.value6, _): return false
      case (.value7, _): return false
      case (.value8, _): return false
      case (.value9, _): return false
      case (.value10, _): return false
      case (.value11, _): return false
      case (.value12, _): return false
    }
  }
}


Expected Results:
The compiler should show an error because the switch is not exhaustive.

Actual Results:
The code compiles and returns false.

Version/Build:
Xcode Version 9.2 (9C40b) & Xcode 9.3 beta 3 (9Q117m)