IDE Utils: For DeclNameViewer, we should use empty StringRef to represent empty argument label instead of using "_". (#9988)

Author: nkcsgexi

lib/IDE/Utils.cpp

@@ -798,6 +798,10 @@ DeclNameViewer::DeclNameViewer(StringRef Text): HasParen(false) {
     return;
   assert(Labels.back().empty());
   Labels.pop_back();
+  std::transform(Labels.begin(), Labels.end(), Labels.begin(),
+      [](StringRef Label) {
+    return Label == "_" ? StringRef() : Label;
+  });
 }
 
 unsigned DeclNameViewer::commonPartsCount(DeclNameViewer &Other) const {

lib/Migrator/APIDiffMigratorPass.cpp

@@ -334,7 +334,7 @@ struct APIDiffMigratorPass : public ASTMigratorPass, public SourceEntityWalker {
       if (Idx < NewName.argSize()) {
         auto Label = NewName.args()[Idx++];
 
-        if (Label != "_") {
+        if (!Label.empty()) {
           if (LR.getByteLength())
             Editor.replace(LR, Label);
           else