Merge pull request swiftlang#26511 from davidungar/disableASTScope

Author: swift-ci

include/swift/Frontend/Frontend.h

@@ -291,6 +291,12 @@ class CompilerInvocation {
 
   void setCodeCompletionFactory(CodeCompletionCallbacksFactory *Factory) {
     CodeCompletionFactory = Factory;
+    disableASTScopeLookup();
+  }
+  
+  /// Called from lldb, see rdar://53971116
+  void disableASTScopeLookup() {
+    LangOpts.EnableASTScopeLookup = false;
   }
 
   CodeCompletionCallbacksFactory *getCodeCompletionFactory() const {