Add test for SR-8022

Author: moiseev

test/stdlib/conditional_collections.swift

@@ -0,0 +1,38 @@
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+
+
+struct X: BidirectionalCollection {
+  var startIndex: Int { return 0 }
+  var endIndex: Int { return 10 }
+  subscript(position: Int) -> String { return "element" }
+  subscript(range: Range<Int>) -> X { return X() }
+  func index(after i: Int) -> Int { return i + 1 }
+  func index(before i: Int) -> Int { return i - 1 }
+}
+struct A<C: Collection>: Collection {
+  let c: C
+  var startIndex: C.Index { return c.startIndex }
+  var endIndex: C.Index { return c.endIndex }
+  subscript(position: C.Index) -> C.Element { return c[position] }
+  subscript(range: Range<C.Index>) -> A<C.SubSequence> {
+    return A<C.SubSequence>(c: c[range])
+  }
+  func index(after i: C.Index) -> C.Index { return c.index(after: i) }
+}
+
+extension A: BidirectionalCollection where C: BidirectionalCollection {
+  func index(before i: C.Index) -> C.Index { return c.index(before: i) }
+}
+
+// SR-8022
+func sr8022() {
+  var c = A(c: X())
+  _ = c.popLast()
+  _ = c.removeLast()
+  c.removeLast(2)
+  _ = c.dropLast(2)
+  _ = c.suffix(2)
+}
+
+sr8022()