Merge pull request swiftlang#10445 from practicalswift/swiftc-28788-conformance-isconcrete-concrete-isexistentialtype

Author: swift-ci

validation-test/compiler_crashers/28788-conformance-isconcrete-concrete-isexistentialtype.swift

@@ -0,0 +1,13 @@
+// This source file is part of the Swift.org open source project
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+// REQUIRES: asserts
+// RUN: not --crash %target-swift-frontend %s -emit-ir
+protocol P{
+typealias e:RangeReplaceableCollection
+}{}extension P{{}func e
+typealias e:FlattenCollection