[SourceKit][DocInfo] Being consistent of the printed source and the reported annotation when the decl under request is an extension to a name alias type. rdar://22098995

Author: nkcsgexi

lib/AST/ASTPrinter.cpp

@@ -1268,6 +1268,13 @@ void PrintAST::visitExtensionDecl(ExtensionDecl *decl) {
           Printer << ".";
         }
       }
+
+      // Respect alias type.
+      if (extendedType->getKind() == TypeKind::NameAlias) {
+        extendedType.print(Printer, Options);
+        return;
+      }
+
       Printer.printTypeRef(nominal, nominal->getName());
     });
   printInherited(decl);

test/SourceKit/DocSupport/Inputs/cake.swift

@@ -22,3 +22,9 @@ public extension Prot where Self.Element == Int {
 public enum MyEnum : Int {
   case Blah
 }
+
+protocol Prot1 {}
+
+typealias C1Alias = C1
+
+extension C1Alias : Prot1 {}