[ClangImporter] Handle ns_error_domain on nameless enums with typedefs

This doesn't come up when using the NS_ERROR_ENUM macro, but it
shouldn't crash the compiler, and it was easy enough to fix.

Author: jrose-apple

lib/ClangImporter/ImportEnumInfo.cpp

@@ -308,6 +308,10 @@ void EnumInfo::determineConstantNamePrefix(ASTContext &ctx,
     // Don't use importFullName() here, we want to ignore the swift_name
     // and swift_private attributes.
     StringRef enumNameStr = decl->getName();
+    if (enumNameStr.empty())
+      enumNameStr = decl->getTypedefNameForAnonDecl()->getName();
+    assert(!enumNameStr.empty() && "should have been classified as Constants");
+
     StringRef commonWithEnum = getCommonPluralPrefix(checkPrefix, enumNameStr);
     size_t delta = commonPrefix.size() - checkPrefix.size();
 

test/ClangImporter/Inputs/enum-error.h

@@ -19,4 +19,10 @@ typedef NS_ERROR_ENUM(int, OtherErrorCode, OtherErrorDomain) {
   OtherC,
 };
 
+extern NSString *TypedefOnlyErrorDomain;
+typedef enum __attribute__((ns_error_domain(TypedefOnlyErrorDomain))) {
+  TypedefOnlyErrorBadness
+} TypedefOnlyError;
+
+
 TestError getErr();

test/ClangImporter/enum-error.swift

@@ -21,6 +21,11 @@ func testDropCode(other: OtherError) -> OtherError.Code {
   return other.code
 }
 
+func testImportsCorrectly() {
+  _ = TypedefOnlyError.badness
+  _ = TypedefOnlyError.Code.badness
+}
+
 func testError() {
   let testErrorNSError = NSError(domain: TestErrorDomain,
                                  code: Int(TestError.TENone.rawValue),