[Serialization] Test the output on a crash due to a broken XRef

test/Serialization/Recovery/crash-xref.swift

@@ -0,0 +1,35 @@
+/// Test xref error description by removing a type from a module after building
+/// a client.
+// RUN: %empty-directory(%t)
+
+/// Compile module A with a type and an empty module B.
+// RUN: %target-swift-frontend %s -emit-module-path %t/A.swiftmodule -module-name A -D LIB
+// RUN: %target-swift-frontend %s -emit-module-path %t/B.swiftmodule -module-name B
+#if LIB
+public struct SomeType {
+    public init() {}
+}
+
+/// Compile a client using the type from A.
+// RUN: %target-swift-frontend %s -emit-module-path %t/Client.swiftmodule -module-name Client -D CLIENT -I %t
+#elseif CLIENT
+import A
+import B
+
+public func foo() -> A.SomeType { fatalError() }
+
+/// Swap A and B around! A is now empty and B defines the type.
+// RUN: %target-swift-frontend %s -emit-module-path %t/A.swiftmodule -module-name A
+// RUN: %target-swift-frontend %s -emit-module-path %t/B.swiftmodule -module-name B -D LIB
+#endif // Empty
+
+/// Read from the client to get an xref error to the type missing from A.
+// RUN: not --crash %target-swift-frontend -emit-sil %t/Client.swiftmodule -module-name Client -I %t -disable-deserialization-recovery 2> %t/stderr
+
+// RUN: cat %t/stderr | %FileCheck %s
+// CHECK: *** DESERIALIZATION FAILURE (please include this section in any bug report) ***
+// CHECK-NEXT: Could not deserialize type for 'foo()'
+// CHECK-NEXT: Caused by: top-level value not found
+// CHECK-NEXT: Cross-reference to 'SomeType' in module 'A'
+// CHECK-NEXT: Notes:
+// CHECK-NEXT: * 'SomeType' was not found in module 'B', but there is one in module 'B'. If this is imported from clang, please make sure the header is part of a single clang module.