Introduce ns_error_domain attribute.

include/clang/Basic/Attr.td

@@ -1115,6 +1115,12 @@ def ObjCBridgeRelated : InheritableAttr {
   let Documentation = [Undocumented];
 }
 
+def NSErrorDomain : Attr {
+  let Spellings = [GNU<"ns_error_domain">];
+  let Args = [IdentifierArgument<"ErrorDomain">];
+  let Documentation = [NSErrorDomainDocs];
+}
+
 def NSReturnsRetained : InheritableAttr {
   let Spellings = [GNU<"ns_returns_retained">];
 //  let Subjects = SubjectList<[ObjCMethod, ObjCProperty, Function]>;

include/clang/Basic/AttrDocs.td

@@ -1758,6 +1758,13 @@ arguments, with arbitrary offsets.
   }];
 }
 
+def NSErrorDomainDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+The ``ns_error_domain`` attribute indicates a global constant representing the error domain.
+  }];
+}
+
 def SwiftDocs : DocumentationCategory<"Controlling Swift Import"> {
   let Content = [{
 Clang supports additional attributes for controlling how APIs are imported into Swift.

include/clang/Basic/DiagnosticSemaKinds.td

@@ -7533,6 +7533,14 @@ def err_nsconsumed_attribute_mismatch : Error<
 def err_nsreturns_retained_attribute_mismatch : Error<
   "overriding method has mismatched ns_returns_%select{not_retained|retained}0"
   " attributes">;
+
+def err_nserrordomain_not_tagdecl : Error<
+  "ns_error_domain attribute only valid on "
+  "%select{enums, structs, and unions|enums, structs, unions, and classes}0">;
+def err_nserrordomain_invalid_decl : Error<
+  "domain argument %0 does not refer to global constant">;
+def err_nserrordomain_requires_identifier : Error<
+  "domain argument must be an identifier">;
 
 def note_getter_unavailable : Note<
   "or because setter is declared here, but no getter method %0 is found">;

lib/Sema/SemaDeclAttr.cpp

@@ -4263,6 +4263,40 @@ static void handleObjCRequiresSuperAttr(Sema &S, Decl *D,
                                         attr.getAttributeSpellingListIndex()));
 }
 
+static void handleNSErrorDomain(Sema &S, Decl *D, const AttributeList &Attr) {
+  if (!isa<TagDecl>(D)) {
+    S.Diag(D->getLocStart(), diag::err_nserrordomain_not_tagdecl)
+        << S.getLangOpts().CPlusPlus;
+    return;
+  }
+  IdentifierLoc *identLoc =
+      Attr.isArgIdent(0) ? Attr.getArgAsIdent(0) : nullptr;
+  if (!identLoc || !identLoc->Ident) {
+    // Try to locate the argument directly
+    SourceLocation loc = Attr.getLoc();
+    if (Attr.isArgExpr(0) && Attr.getArgAsExpr(0))
+      loc = Attr.getArgAsExpr(0)->getLocStart();
+
+    S.Diag(loc, diag::err_nserrordomain_requires_identifier);
+    return;
+  }
+
+  // Verify that the identifier is a valid decl in the C decl namespace
+  LookupResult lookupResult(S, DeclarationName(identLoc->Ident),
+                            SourceLocation(),
+                            Sema::LookupNameKind::LookupOrdinaryName);
+  if (!S.LookupName(lookupResult, S.TUScope) ||
+      !lookupResult.getAsSingle<VarDecl>()) {
+    S.Diag(identLoc->Loc, diag::err_nserrordomain_invalid_decl)
+        << identLoc->Ident;
+    return;
+  }
+
+  D->addAttr(::new (S.Context)
+                 NSErrorDomainAttr(Attr.getRange(), S.Context, identLoc->Ident,
+                                   Attr.getAttributeSpellingListIndex()));
+}
+
 static void handleCFAuditedTransferAttr(Sema &S, Decl *D,
                                         const AttributeList &Attr) {
   if (checkAttrMutualExclusion<CFUnknownTransferAttr>(S, D, Attr.getRange(),
@@ -5560,6 +5594,10 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_ObjCBoxable:
     handleObjCBoxable(S, D, Attr);
     break;
+
+  case AttributeList::AT_NSErrorDomain:
+    handleNSErrorDomain(S, D, Attr);
+    break;
 
   case AttributeList::AT_CFAuditedTransfer:
     handleCFAuditedTransferAttr(S, D, Attr);

test/Analysis/ns_error_enum.m

@@ -0,0 +1,42 @@
+// RUN: %clang_cc1 -verify %s
+
+#define CF_ENUM(_type, _name) enum _name : _type _name; enum _name : _type
+#define NS_ENUM(_type, _name) CF_ENUM(_type, _name)
+
+#define NS_ERROR_ENUM(_type, _name, _domain)  \
+  enum _name : _type _name; enum __attribute__((ns_error_domain(_domain))) _name : _type
+
+typedef NS_ENUM(unsigned, MyEnum) {
+  MyFirst,
+  MySecond,
+};
+
+typedef NS_ENUM(invalidType, MyInvalidEnum) {
+// expected-error@-1{{unknown type name 'invalidType'}}
+// expected-error@-2{{unknown type name 'invalidType'}}
+  MyFirstInvalid,
+  MySecondInvalid,
+};
+
+const char *MyErrorDomain;
+typedef NS_ERROR_ENUM(unsigned char, MyErrorEnum, MyErrorDomain) {
+	MyErrFirst,
+	MyErrSecond,
+};
+struct __attribute__((ns_error_domain(MyErrorDomain))) MyStructErrorDomain {};
+
+typedef NS_ERROR_ENUM(unsigned char, MyErrorEnumInvalid, InvalidDomain) {
+	// expected-error@-1{{domain argument 'InvalidDomain' does not refer to global constant}}
+	MyErrFirstInvalid,
+	MyErrSecondInvalid,
+};
+
+typedef NS_ERROR_ENUM(unsigned char, MyErrorEnumInvalid, "domain-string");
+  // expected-error@-1{{domain argument must be an identifier}}
+
+int __attribute__((ns_error_domain(MyErrorDomain))) NotTagDecl;
+  // expected-error@-1{{ns_error_domain attribute only valid on enums, structs, and unions}}
+
+void foo() {}
+typedef NS_ERROR_ENUM(unsigned char, MyErrorEnumInvalidFunction, foo);
+  // expected-error@-1{{domain argument 'foo' does not refer to global constant}}