[clangd] Use ProjectAwareIndex

[kadircet]

Summary

Put project-aware-index between command-line specified static index and
ClangdServer indexes.

[kadircet]

• Rebase

[kadircet]

Merged with https://reviews.llvm.org/D91860

clang-tools-extra/clangd/tool/ClangdMain.cpp

 //===--- ClangdMain.cpp - clangd server loop ------------------------------===//
 //
 // 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 "ClangdLSPServer.h"
 #include "CodeComplete.h"
 #include "Features.inc"
 #include "PathMapping.h"
 #include "Protocol.h"
 #include "Transport.h"
 #include "index/Background.h"
+#include "index/Index.h"
+#include "index/Merge.h"
+#include "index/ProjectAware.h"
 #include "index/Serialization.h"
 #include "index/remote/Client.h"
 #include "refactor/Rename.h"
 #include "support/Path.h"
 #include "support/Shutdown.h"
 #include "support/ThreadsafeFS.h"
 #include "support/Trace.h"
 #include "clang/Basic/Version.h"

 #include "llvm/Support/raw_ostream.h"
 #include <chrono>
 #include <cstdlib>
 #include <iostream>
 #include <memory>
 #include <mutex>
 #include <string>
 #include <thread>
+#include <vector>
 
 #ifndef _WIN32
 #include <unistd.h>
 #endif
 
 namespace clang {
 namespace clangd {
 
)";
   case PCHStorageFlag::Disk:
     Opts.StorePreamblesInMemory = false;
     break;
   }
   if (!ResourceDir.empty())
     Opts.ResourceDir = ResourceDir;
   Opts.BuildDynamicSymbolIndex = EnableIndex;
   Opts.CollectMainFileRefs = CollectMainFileRefs;
+  std::vector<std::unique_ptr<SymbolIndex>> IdxStack;
   std::unique_ptr<SymbolIndex> StaticIdx;
   std::future<void> AsyncIndexLoad; // Block exit while loading the index.
   if (EnableIndex && !IndexFile.empty()) {
     // Load the index asynchronously. Meanwhile SwapIndex returns no results.
     SwapIndex *Placeholder;
     StaticIdx.reset(Placeholder = new SwapIndex(std::make_unique<MemIndex>()));
     AsyncIndexLoad = runAsync<void>([Placeholder] {
       if (auto Idx = loadIndex(IndexFile, /*UseDex=*/true))
if (IndexFile.empty()) {
       EnableBackgroundIndex = false;
     } else {
       elog("When enabling remote index, IndexFile should not be specified. "
            "Only one can be used at time. Remote index will ignored.");
     }
   }
 #endif
   Opts.BackgroundIndex = EnableBackgroundIndex;
-  Opts.StaticIndex = StaticIdx.get();
+  ProjectAwareIndex PAI;
+  if (StaticIdx) {
+    IdxStack.emplace_back(std::move(StaticIdx));
+    IdxStack.emplace_back(
+        std::make_unique<MergedIndex>(&PAI, IdxStack.back().get()));
+    Opts.StaticIndex = IdxStack.back().get();
+  } else {
+    Opts.StaticIndex = &PAI;
+  }
   Opts.AsyncThreadsCount = WorkerThreadsCount;
   Opts.BuildRecoveryAST = RecoveryAST;
   Opts.PreserveRecoveryASTType = RecoveryASTType;
   Opts.FoldingRanges = FoldingRanges;
 
   Opts.CodeComplete.IncludeIneligibleResults = IncludeIneligibleResults;
   Opts.CodeComplete.Limit = LimitResults;
   if (CompletionStyle.getNumOccurrences())