[clangd] Fix no results returned for global symbols in dexp

[hokein]

Summary

For symbols in global namespace (without any scope), we need to
add global scope "" to the fuzzy request.

[ioeric]

clangd/index/dex/dexp/Dexp.cpp

64

I think the old behavior used AnyScope for a unqualified name. Do we want to keep that?

[ioeric]

clangd/index/dex/dexp/Dexp.cpp

64

nvm, this is getSymbolIDsFromIndex not fuzzyfind. Looks good.

clangd/index/dex/dexp/Dexp.cpp

std::vector<SymbolID> getSymbolIDsFromIndex(StringRef QualifiedName,
                                             const SymbolIndex *Index) {
   FuzzyFindRequest Request;
   // Remove leading "::" qualifier as FuzzyFind doesn't need leading "::"
   // qualifier for global scope.
   bool IsGlobalScope = QualifiedName.consume_front("::");
   auto Names = splitQualifiedName(QualifiedName);
   if (IsGlobalScope || !Names.first.empty())
     Request.Scopes = {Names.first};
+  else
+    // QualifiedName refers to a symbol in global scope (e.g. "GlobalSymbol"),
+    // add the global scope to the request.
+    Request.Scopes = {""};
 
   Request.Query = Names.second;
   std::vector<SymbolID> SymIDs;
   Index->fuzzyFind(Request, [&](const Symbol &Sym) {
     std::string SymQualifiedName = (Sym.Scope + Sym.Name).str();
     if (QualifiedName == SymQualifiedName)
       SymIDs.push_back(Sym.ID);
   });