Merge pull request swiftlang#30752 from DougGregor/codable-iuo-crash

Author: swift-ci

lib/Sema/DerivedConformanceCodable.cpp

@@ -82,9 +82,11 @@ static CodableConformanceType typeConformsToCodable(DeclContext *context,
                                                     ProtocolDecl *proto) {
   target = context->mapTypeIntoContext(target);
 
-  if (isIUO)
-    return typeConformsToCodable(context, target->getOptionalObjectType(),
+  if (isIUO) {
+    return typeConformsToCodable(context,
+                                 target->lookThroughSingleOptionalType(),
                                  false, proto);
+  }
 
   auto conf = TypeChecker::conformsToProtocol(target, proto, context, None);
   return conf.isInvalid() ? DoesNotConform : Conforms;

test/decl/protocol/special/coding/iuo_crash.swift

@@ -0,0 +1,10 @@
+// RUN: %target-typecheck-verify-swift -verify-ignore-unknown
+
+// Crash due to codable synthesis with implicitly unwrapped optionals of
+// ill-formed types.
+// rdar://problem/60985179
+struct X: Codable {  // expected-error 2{{type 'X' does not conform to protocol}}
+  var c: Undefined! // expected-error{{use of undeclared type 'Undefined'}}
+  // expected-note @-1{{does not conform to}}
+  // expected-note @-2{{does not conform to}}
+}