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

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

Reviewers: ioeric

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, cfe-commits

Differential Revision: https://reviews.llvm.org/D54519

llvm-svn: 346947

clang-tools-extra/clangd/index/dex/dexp/Dexp.cpp

@@ -58,6 +58,10 @@ std::vector<SymbolID> getSymbolIDsFromIndex(StringRef QualifiedName,
   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;