Test compatibility shim

Author: airspeedswift

test/stdlib/IndexDistanceRemoval.swift

@@ -0,0 +1,22 @@
+// RUN: %target-typecheck-verify-swift
+
+struct Int64Distance<Element>: Collection {
+  let _storage: [Element]
+  
+  typealias Index = Int64
+  typealias IndexDistance = Int64
+  
+  var startIndex: Index { return Int64(_storage.startIndex) }
+  var endIndex: Index { return Int64(_storage.startIndex) }
+  func index(after i: Index) -> Index { return i + 1 }
+  
+  subscript(i: Index) -> Element { return _storage[Int(i)] }
+}
+
+let c = Int64Distance(_storage: [1,2,3])
+
+let i64: Int64 = 2
+_ = c.index(c.startIndex, offsetBy: i64) // expected-warning {{'index(_:offsetBy:)' is deprecated: all index distances are now of type Int}}
+
+let _: Int64 = c.distance(from: c.startIndex, to: c.endIndex) // expected-warning {{distance(from:to:)' is deprecated: all index distances are now of type Int}}
+