Optionals of imported value types are not @objc.

While we could bridge 'NSRange' to 'NSRange' and 'NSRange?' to
'NSValue * _Nullable', that (a) would be confusing, and (b) isn't
actually implemented at the moment. Fix my mistake in 477933b to
start accepting these.

Author: jrose-apple

lib/AST/Type.cpp

@@ -24,6 +24,7 @@
 #include "swift/AST/LazyResolver.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/TypeLoc.h"
+#include "swift/Basic/Fallthrough.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallString.h"
@@ -2112,25 +2113,23 @@ getForeignRepresentable(Type type, ForeignLanguage language,
   if (nominal->hasClangNode() || nominal->isObjC()) {
     switch (language) {
     case ForeignLanguage::C:
-      // Imported structs and enums are trivially representable in C.
-      // FIXME: This is not entirely true; we need to check that
-      // all of the exposed parts are representable in C.
-      if (isa<StructDecl>(nominal) || isa<EnumDecl>(nominal)) {
-        if (wasOptional)
-          break;
-        return { ForeignRepresentableKind::Trivial, nullptr };
-      }
-
-      // Imported classes and protocols are not.
+      // Imported classes and protocols are not representable in C.
       if (isa<ClassDecl>(nominal) || isa<ProtocolDecl>(nominal))
         return failure();
-
-      llvm_unreachable("Unhandled nominal type declaration");
+      SWIFT_FALLTHROUGH;
 
     case ForeignLanguage::ObjectiveC:
-      if (isa<StructDecl>(nominal) || isa<EnumDecl>(nominal))
-        if (wasOptional)
+      if (isa<StructDecl>(nominal) || isa<EnumDecl>(nominal)) {
+        // Optional structs are not representable in (Objective-)C if they
+        // originally came from C, whether or not they are bridged. If they
+        // are defined in Swift, they are only representable if they are
+        // bridged (checked below).
+        if (wasOptional) {
+          if (nominal->hasClangNode())
+            return failure();
           break;
+        }
+      }
 
       return { ForeignRepresentableKind::Trivial, nullptr };
     }

test/attr/attr_objc.swift

@@ -1106,7 +1106,6 @@ class infer_instanceVar1 {
   var var_Optional12: OpaquePointer?
   var var_Optional13: UnsafeMutablePointer<Int>?
   var var_Optional14: UnsafeMutablePointer<Class_ObjC1>?
-  var var_Optional15: NSRange? // another bridged struct
 
 // CHECK-LABEL: @objc var var_Optional1: Class_ObjC1?
 // CHECK-LABEL: @objc var var_Optional2: Protocol_ObjC1?
@@ -1122,7 +1121,6 @@ class infer_instanceVar1 {
 // CHECK-LABEL: @objc var var_Optional12: OpaquePointer?
 // CHECK-LABEL: @objc var var_Optional13: UnsafeMutablePointer<Int>?
 // CHECK-LABEL: @objc var var_Optional14: UnsafeMutablePointer<Class_ObjC1>?
-// CHECK-LABEL: @objc var var_Optional15: NSRange?
 
 
   var var_ImplicitlyUnwrappedOptional1: Class_ObjC1!
@@ -1162,6 +1160,7 @@ class infer_instanceVar1 {
   var var_Optional_fail20: AnyObject??
   var var_Optional_fail21: AnyObject.Type??
   var var_Optional_fail22: NSComparisonResult? // a non-bridged imported value type
+  var var_Optional_fail23: NSRange? // a bridged struct imported from C
 // CHECK-NOT: @objc{{.*}}Optional_fail
 
   // CHECK-LABEL: @objc var var_CFunctionPointer_1: @convention(c) () -> ()