[NFC] Extract helper for making NSError domains

Avoids having to coordinate changes in two different parts of the compiler.

Author: beccadax

include/swift/AST/SwiftNameTranslation.h

@@ -18,6 +18,7 @@
 
 namespace swift {
   class ValueDecl;
+  class EnumDecl;
   class EnumElementDecl;
 
 namespace objc_translation {
@@ -29,6 +30,8 @@ namespace objc_translation {
   StringRef getNameForObjC(const ValueDecl *VD,
                            CustomNamesOnly_t customNamesOnly = Normal);
 
+  std::string getErrorDomainStringForObjC(const EnumDecl *ED);
+
   /// Print the ObjC name of an enum element decl to OS, also allowing the client
   /// to specify a preferred name other than the decl's original name.
   ///

lib/AST/SwiftNameTranslation.cpp

@@ -16,6 +16,7 @@
 
 #include "swift/AST/SwiftNameTranslation.h"
 #include "swift/AST/ASTContext.h"
+#include "swift/AST/Module.h"
 #include "swift/AST/Decl.h"
 #include "swift/AST/LazyResolver.h"
 #include "swift/Basic/StringExtras.h"
@@ -51,6 +52,14 @@ getNameForObjC(const ValueDecl *VD, CustomNamesOnly_t customNamesOnly) {
   return VD->getBaseName().getIdentifier().str();
 }
 
+std::string swift::objc_translation::
+getErrorDomainStringForObjC(const EnumDecl *ED) {
+  std::string buffer = ED->getParentModule()->getNameStr();
+  buffer += ".";
+  buffer += ED->getNameStr();
+  return buffer;
+}
+
 bool swift::objc_translation::
 printSwiftEnumElemNameInObjC(const EnumElementDecl *EL, llvm::raw_ostream &OS,
                              Identifier PreferredName) {

lib/PrintAsObjC/PrintAsObjC.cpp

@@ -2511,7 +2511,7 @@ class ModuleWriter {
       });
       if (!hasDomainCase) {
         os << "static NSString * _Nonnull const " << getNameForObjC(ED)
-           << "Domain = @\"" << M.getName() << "." << ED->getName() << "\";\n";
+           << "Domain = @\"" << getErrorDomainStringForObjC(ED) << "\";\n";
       }
     }
 

lib/Sema/DerivedConformanceError.cpp

@@ -22,8 +22,10 @@
 #include "swift/AST/Expr.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/Types.h"
+#include "swift/AST/SwiftNameTranslation.h"
 
 using namespace swift;
+using namespace swift::objc_translation;
 
 static void deriveBodyBridgedNSError_enum_nsErrorDomain(
               AbstractFunctionDecl *domainDecl, void *) {
@@ -39,10 +41,7 @@ static void deriveBodyBridgedNSError_enum_nsErrorDomain(
   auto TC = domainDecl->getInnermostTypeContext();
   auto ED = TC->getSelfEnumDecl();
 
-  std::string buffer = M->getNameStr();
-  buffer += ".";
-  buffer += ED->getNameStr();
-  StringRef value(C.AllocateCopy(buffer));
+  StringRef value(C.AllocateCopy(getErrorDomainStringForObjC(ED)));
 
   auto string = new (C) StringLiteralExpr(value, SourceRange(), /*implicit*/ true);
   auto ret = new (C) ReturnStmt(SourceLoc(), string, /*implicit*/ true);
@@ -57,13 +56,10 @@ deriveBridgedNSError_enum_nsErrorDomain(DerivedConformance &derived) {
   // enum SomeEnum {
   //   @derived
   //   static var _nsErrorDomain: String {
-  //     return "\(self)"
+  //     return "ModuleName.SomeEnum"
   //   }
   // }
 
-  // Note that for @objc enums the format is assumed to be "MyModule.SomeEnum".
-  // If this changes, please change PrintAsObjC as well.
-
   ASTContext &C = derived.TC.Context;
 
   auto stringTy = C.getStringDecl()->getDeclaredType();