[clangd][remote] Check an index file correctly

[ArcsinX]

Summary

There is not reason to check std::make_unique<...>(..) return value,
but clangd::clang::loadIndex() returns nullptr if an index file could not be loaded (e.g. incorrect version).

[kadircet]

clang-tools-extra/clangd/index/remote/server/Server.cpp

365

well actually we don't need to make unique at all. why not just create a SwapIndex Idx(std::move(SymIndex)) and pass it around ?

[ArcsinX]

Do not use unique pointer for Index

clang-tools-extra/clangd/index/remote/server/Server.cpp

 //===--- Server.cpp - gRPC-based Remote Index Server  ---------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Index.pb.h"
 #include "Service.grpc.pb.h"
 #include "index/Index.h"
 #include "index/Serialization.h"
 #include "index/Symbol.h"
 #include "index/remote/marshalling/Marshalling.h"
 #include "support/Context.h"
 #include "support/Logger.h"
 #include "support/Shutdown.h"
int main(int argc, char *argv[]) {
   clang::clangd::RealThreadsafeFS TFS;
   auto FS = TFS.view(llvm::None);
   auto Status = FS->status(IndexPath);
   if (!Status) {
     elog("{0} does not exist.", IndexPath);
     return Status.getError().value();
   }
 
-  auto Index = std::make_unique<clang::clangd::SwapIndex>(
-      clang::clangd::loadIndex(IndexPath));
-
-  if (!Index) {
+  auto SymIndex = clang::clangd::loadIndex(IndexPath);
+  if (!SymIndex) {
     llvm::errs() << "Failed to open the index.\n";
     return -1;
   }
+  clang::clangd::SwapIndex Index(std::move(SymIndex));
 
   std::thread HotReloadThread([&Index, &Status, &FS]() {
     llvm::vfs::Status LastStatus = *Status;
     static constexpr auto RefreshFrequency = std::chrono::seconds(30);
     while (!clang::clangd::shutdownRequested()) {
-      hotReload(*Index, llvm::StringRef(IndexPath), LastStatus, FS);
+      hotReload(Index, llvm::StringRef(IndexPath), LastStatus, FS);
       std::this_thread::sleep_for(RefreshFrequency);
     }
   });
 
-  runServerAndWait(*Index, ServerAddress, IndexPath);
+  runServerAndWait(Index, ServerAddress, IndexPath);
 
   HotReloadThread.join();
 }