[Clang Importer] implement swift_newtype(enum) as struct

This is a temporary solution that implements swift_newtype(enum) as
though it were written swift_newtype(struct). This is to work around
to the fact that a String-backed enum does not actually have a String
stored, and a struct is closer to reflecting that storage
properly. Struct provides most of the functionality and appearance for
now, though it does not allow for switching over the values.

Full support for swift_newtype(enum) as a Swift enum is forthcoming.

Author: milseman

lib/ClangImporter/ImportDecl.cpp

@@ -1280,6 +1280,10 @@ namespace {
         if (auto newtypeAttr =
                 Decl->template getAttr<clang::SwiftNewtypeAttr>()) {
           switch (newtypeAttr->getNewtypeKind()) {
+          case clang::SwiftNewtypeAttr::NK_Enum:
+            // TODO: import as closed enum instead
+
+            // For now, fall through and treat as a struct
           case clang::SwiftNewtypeAttr::NK_Struct: {
 
             auto underlyingType = Impl.importType(
@@ -1305,11 +1309,8 @@ namespace {
             Impl.registerExternalDecl(structDecl);
             return structDecl;
           }
+        }
 
-          case clang::SwiftNewtypeAttr::NK_Enum:
-            // TODO: support enum
-            break;
-          }
         }
       }
 

test/IDE/Inputs/custom-modules/Newtype.h

@@ -17,3 +17,10 @@ extern const SNTErrorDomain SNTFive
     __attribute((swift_name("stillAMember")));
 extern const SNTErrorDomain SNTElsewhere
     __attribute((swift_name("Foo.err")));
+
+typedef NSString *SNTClosedEnum __attribute((swift_newtype(enum)))
+__attribute((swift_name("ClosedEnum")));
+
+extern const SNTClosedEnum SNTFirstClosedEntryEnum;
+extern const SNTClosedEnum SNTSecondEntry;
+extern const SNTClosedEnum SNTClosedEnumThirdEntry;

test/IDE/newtype.swift

@@ -2,23 +2,32 @@
 // RUN: FileCheck %s -check-prefix=PRINT -strict-whitespace < %t.printed.A.txt
 // REQUIRES: objc_interop
 
-// PRINT:      struct ErrorDomain : RawRepresentable {
-// PRINT-NEXT:   init(rawValue: NSString)
-// PRINT-NEXT:   let rawValue: NSString
-// PRINT-NEXT: }
-// PRINT-NEXT: extension ErrorDomain {
-// PRINT-NEXT:   func process()
-// PRINT-NEXT:   static let one: ErrorDomain
-// PRINT-NEXT:   static let errTwo: ErrorDomain
-// PRINT-NEXT:   static let three: ErrorDomain
-// PRINT-NEXT:   static let four: ErrorDomain
-// PRINT-NEXT:   static let stillAMember: ErrorDomain
-// PRINT-NEXT: }
-// PRINT-NEXT: struct Foo {
-// PRINT-NEXT:   init()
-// PRINT-NEXT: }
-// PRINT-NEXT: extension Foo {
-// PRINT-NEXT:   static let err: ErrorDomain
-// PRINT-NEXT: }
-
-
+// PRINT-LABEL: struct ErrorDomain : RawRepresentable {
+// PRINT-NEXT:    init(rawValue: NSString)
+// PRINT-NEXT:    let rawValue: NSString
+// PRINT-NEXT:  }
+// PRINT-NEXT:  extension ErrorDomain {
+// PRINT-NEXT:    func process()
+// PRINT-NEXT:    static let one: ErrorDomain
+// PRINT-NEXT:    static let errTwo: ErrorDomain
+// PRINT-NEXT:    static let three: ErrorDomain
+// PRINT-NEXT:    static let four: ErrorDomain
+// PRINT-NEXT:    static let stillAMember: ErrorDomain
+// PRINT-NEXT:  }
+// PRINT-NEXT:  struct Foo {
+// PRINT-NEXT:    init()
+// PRINT-NEXT:  }
+// PRINT-NEXT:  extension Foo {
+// PRINT-NEXT:    static let err: ErrorDomain
+// PRINT-NEXT:  }
+//
+// TODO: update test when we can import it as actual new enum
+// PRINT-LABEL: struct ClosedEnum : RawRepresentable {
+// PRINT-NEXT:    init(rawValue: NSString)
+// PRINT-NEXT:    let rawValue: NSString
+// PRINT-NEXT:  }
+// PRINT-NEXT:  extension ClosedEnum {
+// PRINT-NEXT:    static let firstEntry: ClosedEnum
+// PRINT-NEXT:    static let secondEntry: ClosedEnum
+// PRINT-NEXT:    static let thirdEntry: ClosedEnum
+// PRINT-NEXT:  }