Fix @objc use in module interfaces for objcImpl

objcImpl extensions with final public members need to be printed into module interfaces, but with the @implementation attribute suppressed. That worked fine…but when we switched to the new syntax, we should also have suppressed the @objc attribute, and we mistakenly did not. Correct this oversight.

Fixes rdar://129178360.

lib/AST/ASTPrinter.cpp

@@ -1326,6 +1326,14 @@ void PrintAST::printAttributes(const Decl *D) {
     }
   }
 
+  // If we are suppressing @implementation, also suppress @objc on extensions.
+  if (auto ED = dyn_cast<ExtensionDecl>(D)) {
+    if (ED->isObjCImplementation() &&
+            Options.excludeAttrKind(DeclAttrKind::ObjCImplementation)) {
+      Options.ExcludeAttrList.push_back(DeclAttrKind::ObjC);
+    }
+  }
+
   // We will handle ownership specifiers separately.
   if (isa<FuncDecl>(D)) {
     Options.ExcludeAttrList.push_back(DeclAttrKind::Mutating);

test/ModuleInterface/objc_implementation.swift

@@ -16,6 +16,10 @@ import Foundation
 
 // We should never see @_objcImplementation in the header
 // NEGATIVE-NOT: @_objcImplementation
+// NEGATIVE-NOT: @implementation
+
+// @objc should be omitted on extensions
+// NEGATIVE-NOT: @objc{{.*}} extension
 
 //
 // @_objcImplementation class