Invert the check for now to actually fix the issue

Author: tonyarnold

Sources/Diff.swift

@@ -2,7 +2,13 @@
 public protocol DiffProtocol: Collection, Sequence {
 
     associatedtype DiffElementType
+
+    #if swift(>=3.1)
+    // The typealias is causing crashes in SourceKitService under Swift 3.1 snapshots.
+    #else
+    // TODO: Verify that the typealias workaround is still required when Xcode 8.3 is released.
     typealias Index = Int
+    #endif
 
     var elements: [DiffElementType] { get }
 }

Sources/ExtendedDiff.swift

@@ -9,11 +9,7 @@
  */
 public struct ExtendedDiff: DiffProtocol {
 
-    #if swift(>=3.1)
-    // The duplicate typealias is not required in Swift 3.1
-    #else
     public typealias Index = Int
-    #endif
 
     public enum Element {
         case insert(at: Int)

Sources/NestedDiff.swift

@@ -1,11 +1,7 @@
 
 public struct NestedDiff: DiffProtocol {
 
-    #if swift(>=3.1)
-    // The duplicate typealias is not required in Swift 3.1
-    #else
     public typealias Index = Int
-    #endif
 
     public enum Element {
         case deleteSection(Int)

Sources/NestedExtendedDiff.swift

@@ -1,11 +1,7 @@
 
 public struct NestedExtendedDiff: DiffProtocol {
 
-    #if swift(>=3.1)
-    // The duplicate typealias is not required in Swift 3.1
-    #else
     public typealias Index = Int
-    #endif
 
     public enum Element {
         case deleteSection(Int)