Index: clangd/CMakeLists.txt
===================================================================
--- clangd/CMakeLists.txt
+++ clangd/CMakeLists.txt
@@ -10,6 +10,7 @@
   DraftStore.cpp
   GlobalCompilationDatabase.cpp
   JSONRPCDispatcher.cpp
+  Logger.cpp
   Protocol.cpp
   ProtocolHandlers.cpp
 
Index: clangd/ClangdLSPServer.cpp
===================================================================
--- clangd/ClangdLSPServer.cpp
+++ clangd/ClangdLSPServer.cpp
@@ -223,9 +223,9 @@
 ClangdLSPServer::ClangdLSPServer(JSONOutput &Out, unsigned AsyncThreadsCount,
                                  bool SnippetCompletions,
                                  llvm::Optional<StringRef> ResourceDir)
-    : Out(Out), DiagConsumer(*this),
+    : Out(Out), CDB(/*Logger=*/Out), DiagConsumer(*this),
       Server(CDB, DiagConsumer, FSProvider, AsyncThreadsCount,
-             SnippetCompletions, ResourceDir) {}
+             SnippetCompletions, /*Logger=*/Out, ResourceDir) {}
 
 void ClangdLSPServer::run(std::istream &In) {
   assert(!IsDone && "Run was called before");
Index: clangd/ClangdServer.h
===================================================================
--- clangd/ClangdServer.h
+++ clangd/ClangdServer.h
@@ -21,6 +21,7 @@
 #include "llvm/ADT/StringRef.h"
 
 #include "ClangdUnit.h"
+#include "Logger.h"
 #include "Protocol.h"
 
 #include <condition_variable>
@@ -201,10 +202,12 @@
   /// \p DiagConsumer. Note that a callback to \p DiagConsumer happens on a
   /// worker thread. Therefore, instances of \p DiagConsumer must properly
   /// synchronize access to shared state.
+  ///
+  /// Various messages are logged using \p Logger.
   ClangdServer(GlobalCompilationDatabase &CDB,
                DiagnosticsConsumer &DiagConsumer,
                FileSystemProvider &FSProvider, unsigned AsyncThreadsCount,
-               bool SnippetCompletions,
+               bool SnippetCompletions, clangd::Logger &Logger,
                llvm::Optional<StringRef> ResourceDir = llvm::None);
 
   /// Add a \p File to the list of tracked C++ files or update the contents if
@@ -267,6 +270,7 @@
 
   std::future<void> scheduleCancelRebuild(std::shared_ptr<CppFile> Resources);
 
+  clangd::Logger &Logger;
   GlobalCompilationDatabase &CDB;
   DiagnosticsConsumer &DiagConsumer;
   FileSystemProvider &FSProvider;
Index: clangd/ClangdServer.cpp
===================================================================
--- clangd/ClangdServer.cpp
+++ clangd/ClangdServer.cpp
@@ -145,8 +145,10 @@
                            DiagnosticsConsumer &DiagConsumer,
                            FileSystemProvider &FSProvider,
                            unsigned AsyncThreadsCount, bool SnippetCompletions,
+                           clangd::Logger &Logger,
                            llvm::Optional<StringRef> ResourceDir)
-    : CDB(CDB), DiagConsumer(DiagConsumer), FSProvider(FSProvider),
+    : Logger(Logger), CDB(CDB), DiagConsumer(DiagConsumer),
+      FSProvider(FSProvider),
       ResourceDir(ResourceDir ? ResourceDir->str() : getStandardResourceDir()),
       PCHs(std::make_shared<PCHContainerOperations>()),
       WorkScheduler(AsyncThreadsCount), SnippetCompletions(SnippetCompletions) {
@@ -157,7 +159,7 @@
 
   auto TaggedFS = FSProvider.getTaggedFileSystem(File);
   std::shared_ptr<CppFile> Resources =
-      Units.getOrCreateFile(File, ResourceDir, CDB, PCHs, TaggedFS.Value);
+      Units.getOrCreateFile(File, ResourceDir, CDB, PCHs, TaggedFS.Value, Logger);
   return scheduleReparseAndDiags(File, VersionedDraft{Version, Contents.str()},
                                  std::move(Resources), std::move(TaggedFS));
 }
@@ -175,7 +177,7 @@
 
   auto TaggedFS = FSProvider.getTaggedFileSystem(File);
   auto Recreated = Units.recreateFileIfCompileCommandChanged(
-      File, ResourceDir, CDB, PCHs, TaggedFS.Value);
+      File, ResourceDir, CDB, PCHs, TaggedFS.Value, Logger);
 
   // Note that std::future from this cleanup action is ignored.
   scheduleCancelRebuild(std::move(Recreated.RemovedFile));
@@ -210,7 +212,7 @@
   std::vector<CompletionItem> Result = clangd::codeComplete(
       File, Resources->getCompileCommand(),
       Preamble ? &Preamble->Preamble : nullptr, *OverridenContents, Pos,
-      TaggedFS.Value, PCHs, SnippetCompletions);
+      TaggedFS.Value, PCHs, SnippetCompletions, Logger);
   return make_tagged(std::move(Result), TaggedFS.Tag);
 }
 
@@ -278,10 +280,10 @@
   assert(Resources && "Calling findDefinitions on non-added file");
 
   std::vector<Location> Result;
-  Resources->getAST().get()->runUnderLock([Pos, &Result](ParsedAST *AST) {
+  Resources->getAST().get()->runUnderLock([Pos, &Result, this](ParsedAST *AST) {
     if (!AST)
       return;
-    Result = clangd::findDefinitions(*AST, Pos);
+    Result = clangd::findDefinitions(*AST, Pos, Logger);
   });
   return make_tagged(std::move(Result), TaggedFS.Tag);
 }
Index: clangd/ClangdUnit.h
===================================================================
--- clangd/ClangdUnit.h
+++ clangd/ClangdUnit.h
@@ -10,6 +10,7 @@
 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_CLANGDUNIT_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_CLANGDUNIT_H
 
+#include "Logger.h"
 #include "Path.h"
 #include "Protocol.h"
 #include "clang/Frontend/ASTUnit.h"
@@ -57,7 +58,7 @@
         ArrayRef<serialization::DeclID> PreambleDeclIDs,
         std::unique_ptr<llvm::MemoryBuffer> Buffer,
         std::shared_ptr<PCHContainerOperations> PCHs,
-        IntrusiveRefCntPtr<vfs::FileSystem> VFS);
+        IntrusiveRefCntPtr<vfs::FileSystem> VFS, clangd::Logger &Logger);
 
   ParsedAST(ParsedAST &&Other);
   ParsedAST &operator=(ParsedAST &&Other);
@@ -141,11 +142,11 @@
   // deferRebuild will hold references to it.
   static std::shared_ptr<CppFile>
   Create(PathRef FileName, tooling::CompileCommand Command,
-         std::shared_ptr<PCHContainerOperations> PCHs);
+         std::shared_ptr<PCHContainerOperations> PCHs, clangd::Logger &Logger);
 
 private:
   CppFile(PathRef FileName, tooling::CompileCommand Command,
-          std::shared_ptr<PCHContainerOperations> PCHs);
+          std::shared_ptr<PCHContainerOperations> PCHs, clangd::Logger &Logger);
 
 public:
   CppFile(CppFile const &) = delete;
@@ -246,6 +247,8 @@
   std::shared_ptr<const PreambleData> LatestAvailablePreamble;
   /// Utility class, required by clang.
   std::shared_ptr<PCHContainerOperations> PCHs;
+  /// Used for logging various messages.
+  clangd::Logger &Logger;
 };
 
 /// Get code completions at a specified \p Pos in \p FileName.
@@ -254,10 +257,11 @@
              PrecompiledPreamble const *Preamble, StringRef Contents,
              Position Pos, IntrusiveRefCntPtr<vfs::FileSystem> VFS,
              std::shared_ptr<PCHContainerOperations> PCHs,
-             bool SnippetCompletions);
+             bool SnippetCompletions, clangd::Logger &Logger);
 
 /// Get definition of symbol at a specified \p Pos.
-std::vector<Location> findDefinitions(ParsedAST &AST, Position Pos);
+std::vector<Location> findDefinitions(ParsedAST &AST, Position Pos,
+                                      clangd::Logger &Logger);
 
 /// For testing/debugging purposes. Note that this method deserializes all
 /// unserialized Decls, so use with care.
Index: clangd/ClangdUnit.cpp
===================================================================
--- clangd/ClangdUnit.cpp
+++ clangd/ClangdUnit.cpp
@@ -525,7 +525,7 @@
                      PrecompiledPreamble const *Preamble, StringRef Contents,
                      Position Pos, IntrusiveRefCntPtr<vfs::FileSystem> VFS,
                      std::shared_ptr<PCHContainerOperations> PCHs,
-                     bool SnippetCompletions) {
+                     bool SnippetCompletions, clangd::Logger &Logger) {
   std::vector<const char *> ArgStrs;
   for (const auto &S : Command.CommandLine)
     ArgStrs.push_back(S.c_str());
@@ -583,12 +583,13 @@
 
   SyntaxOnlyAction Action;
   if (!Action.BeginSourceFile(*Clang, Clang->getFrontendOpts().Inputs[0])) {
-    // FIXME(ibiryukov): log errors
+    Logger.log("BeginSourceFile() failed when running codeComplete for " +
+               FileName);
     return Items;
   }
-  if (!Action.Execute()) {
-    // FIXME(ibiryukov): log errors
-  }
+  if (!Action.Execute())
+    Logger.log("Execute() failed when running codeComplete for " + FileName);
+
   Action.EndSourceFile();
 
   return Items;
@@ -604,7 +605,8 @@
                  ArrayRef<serialization::DeclID> PreambleDeclIDs,
                  std::unique_ptr<llvm::MemoryBuffer> Buffer,
                  std::shared_ptr<PCHContainerOperations> PCHs,
-                 IntrusiveRefCntPtr<vfs::FileSystem> VFS) {
+                 IntrusiveRefCntPtr<vfs::FileSystem> VFS,
+                 clangd::Logger &Logger) {
 
   std::vector<DiagWithFixIts> ASTDiags;
   StoreDiagsConsumer UnitDiagsConsumer(/*ref*/ ASTDiags);
@@ -618,13 +620,14 @@
       Clang.get());
 
   auto Action = llvm::make_unique<ClangdFrontendAction>();
-  if (!Action->BeginSourceFile(*Clang, Clang->getFrontendOpts().Inputs[0])) {
-    // FIXME(ibiryukov): log error
+  const FrontendInputFile &MainInput = Clang->getFrontendOpts().Inputs[0];
+  if (!Action->BeginSourceFile(*Clang, MainInput)) {
+    Logger.log("BeginSourceFile() failed when building AST for " +
+               MainInput.getFile());
     return llvm::None;
   }
-  if (!Action->Execute()) {
-    // FIXME(ibiryukov): log error
-  }
+  if (!Action->Execute())
+    Logger.log("Execute() failed when building AST for " + MainInput.getFile());
 
   // UnitDiagsConsumer is local, we can not store it in CompilerInstance that
   // has a longer lifetime.
@@ -789,7 +792,8 @@
 }
 } // namespace
 
-std::vector<Location> clangd::findDefinitions(ParsedAST &AST, Position Pos) {
+std::vector<Location> clangd::findDefinitions(ParsedAST &AST, Position Pos,
+                                              clangd::Logger &Logger) {
   const SourceManager &SourceMgr = AST.getASTContext().getSourceManager();
   const FileEntry *FE = SourceMgr.getFileEntryForID(SourceMgr.getMainFileID());
   if (!FE)
@@ -889,15 +893,16 @@
 
 std::shared_ptr<CppFile>
 CppFile::Create(PathRef FileName, tooling::CompileCommand Command,
-                std::shared_ptr<PCHContainerOperations> PCHs) {
+                std::shared_ptr<PCHContainerOperations> PCHs, clangd::Logger &Logger) {
   return std::shared_ptr<CppFile>(
-      new CppFile(FileName, std::move(Command), std::move(PCHs)));
+      new CppFile(FileName, std::move(Command), std::move(PCHs), Logger));
 }
 
 CppFile::CppFile(PathRef FileName, tooling::CompileCommand Command,
-                 std::shared_ptr<PCHContainerOperations> PCHs)
+                 std::shared_ptr<PCHContainerOperations> PCHs,
+                 clangd::Logger &Logger)
     : FileName(FileName), Command(std::move(Command)), RebuildCounter(0),
-      RebuildInProgress(false), PCHs(std::move(PCHs)) {
+      RebuildInProgress(false), PCHs(std::move(PCHs)), Logger(Logger) {
 
   std::lock_guard<std::mutex> Lock(Mutex);
   LatestAvailablePreamble = nullptr;
@@ -1078,7 +1083,7 @@
     // Compute updated AST.
     llvm::Optional<ParsedAST> NewAST =
         ParsedAST::Build(std::move(CI), PreambleForAST, SerializedPreambleDecls,
-                         std::move(ContentsBuffer), PCHs, VFS);
+                         std::move(ContentsBuffer), PCHs, VFS, That->Logger);
 
     if (NewAST) {
       Diagnostics.insert(Diagnostics.end(), NewAST->getDiagnostics().begin(),
Index: clangd/ClangdUnitStore.h
===================================================================
--- clangd/ClangdUnitStore.h
+++ clangd/ClangdUnitStore.h
@@ -14,6 +14,7 @@
 
 #include "ClangdUnit.h"
 #include "GlobalCompilationDatabase.h"
+#include "Logger.h"
 #include "Path.h"
 #include "clang/Tooling/CompilationDatabase.h"
 
@@ -23,11 +24,10 @@
 /// Thread-safe mapping from FileNames to CppFile.
 class CppFileCollection {
 public:
-  std::shared_ptr<CppFile>
-  getOrCreateFile(PathRef File, PathRef ResourceDir,
-                  GlobalCompilationDatabase &CDB,
-                  std::shared_ptr<PCHContainerOperations> PCHs,
-                  IntrusiveRefCntPtr<vfs::FileSystem> VFS) {
+  std::shared_ptr<CppFile> getOrCreateFile(
+      PathRef File, PathRef ResourceDir, GlobalCompilationDatabase &CDB,
+      std::shared_ptr<PCHContainerOperations> PCHs,
+      IntrusiveRefCntPtr<vfs::FileSystem> VFS, clangd::Logger &Logger) {
     std::lock_guard<std::mutex> Lock(Mutex);
 
     auto It = OpenedFiles.find(File);
@@ -36,7 +36,7 @@
 
       It = OpenedFiles
                .try_emplace(File, CppFile::Create(File, std::move(Command),
-                                                  std::move(PCHs)))
+                                                  std::move(PCHs), Logger))
                .first;
     }
     return It->second;
@@ -59,7 +59,7 @@
   RecreateResult recreateFileIfCompileCommandChanged(
       PathRef File, PathRef ResourceDir, GlobalCompilationDatabase &CDB,
       std::shared_ptr<PCHContainerOperations> PCHs,
-      IntrusiveRefCntPtr<vfs::FileSystem> VFS);
+      IntrusiveRefCntPtr<vfs::FileSystem> VFS, clangd::Logger &Logger);
 
   std::shared_ptr<CppFile> getFile(PathRef File) {
     std::lock_guard<std::mutex> Lock(Mutex);
Index: clangd/ClangdUnitStore.cpp
===================================================================
--- clangd/ClangdUnitStore.cpp
+++ clangd/ClangdUnitStore.cpp
@@ -30,7 +30,7 @@
 CppFileCollection::recreateFileIfCompileCommandChanged(
     PathRef File, PathRef ResourceDir, GlobalCompilationDatabase &CDB,
     std::shared_ptr<PCHContainerOperations> PCHs,
-    IntrusiveRefCntPtr<vfs::FileSystem> VFS) {
+    IntrusiveRefCntPtr<vfs::FileSystem> VFS, clangd::Logger &Logger) {
   auto NewCommand = getCompileCommand(CDB, File, ResourceDir);
 
   std::lock_guard<std::mutex> Lock(Mutex);
@@ -41,12 +41,13 @@
   if (It == OpenedFiles.end()) {
     It = OpenedFiles
              .try_emplace(File, CppFile::Create(File, std::move(NewCommand),
-                                                std::move(PCHs)))
+                                                std::move(PCHs), Logger))
              .first;
   } else if (!compileCommandsAreEqual(It->second->getCompileCommand(),
                                       NewCommand)) {
     Result.RemovedFile = std::move(It->second);
-    It->second = CppFile::Create(File, std::move(NewCommand), std::move(PCHs));
+    It->second =
+        CppFile::Create(File, std::move(NewCommand), std::move(PCHs), Logger);
   }
   Result.FileInCollection = It->second;
   return Result;
Index: clangd/GlobalCompilationDatabase.h
===================================================================
--- clangd/GlobalCompilationDatabase.h
+++ clangd/GlobalCompilationDatabase.h
@@ -10,6 +10,7 @@
 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_GLOBALCOMPILATIONDATABASE_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_GLOBALCOMPILATIONDATABASE_H
 
+#include "Logger.h"
 #include "Path.h"
 #include "llvm/ADT/StringMap.h"
 #include <memory>
@@ -45,6 +46,8 @@
 class DirectoryBasedGlobalCompilationDatabase
     : public GlobalCompilationDatabase {
 public:
+  DirectoryBasedGlobalCompilationDatabase(clangd::Logger &Logger);
+
   std::vector<tooling::CompileCommand>
   getCompileCommands(PathRef File) override;
 
@@ -61,6 +64,8 @@
 
   /// Stores extra flags per file.
   llvm::StringMap<std::vector<std::string>> ExtraFlagsForFile;
+  /// Used for logging.
+  clangd::Logger &Logger;
 };
 } // namespace clangd
 } // namespace clang
Index: clangd/GlobalCompilationDatabase.cpp
===================================================================
--- clangd/GlobalCompilationDatabase.cpp
+++ clangd/GlobalCompilationDatabase.cpp
@@ -36,6 +36,10 @@
                                  /*Output=*/"");
 }
 
+DirectoryBasedGlobalCompilationDatabase::
+    DirectoryBasedGlobalCompilationDatabase(clangd::Logger &Logger)
+    : Logger(Logger) {}
+
 std::vector<tooling::CompileCommand>
 DirectoryBasedGlobalCompilationDatabase::getCompileCommands(PathRef File) {
   std::vector<tooling::CompileCommand> Commands;
@@ -81,22 +85,19 @@
     auto CDB = tooling::CompilationDatabase::loadFromDirectory(Path, Error);
     if (!CDB) {
       if (!Error.empty()) {
-        // FIXME(ibiryukov): logging
-        // Output.log("Error when trying to load compilation database from " +
-        //            Twine(Path) + ": " + Twine(Error) + "\n");
+        Logger.log("Error when trying to load compilation database from " +
+                   Path + ": " + Twine(Error) + "\n");
       }
       continue;
     }
 
     // FIXME(ibiryukov): Invalidate cached compilation databases on changes
-    auto result = CDB.get();
+    auto Result = CDB.get();
     CompilationDatabases.insert(std::make_pair(Path, std::move(CDB)));
-    return result;
+    return Result;
   }
 
-  // FIXME(ibiryukov): logging
-  // Output.log("Failed to find compilation database for " + Twine(File) +
-  // "\n");
+  Logger.log("Failed to find compilation database for " + Twine(File) + "\n");
   return nullptr;
 }
 
Index: clangd/JSONRPCDispatcher.h
===================================================================
--- clangd/JSONRPCDispatcher.h
+++ clangd/JSONRPCDispatcher.h
@@ -10,6 +10,7 @@
 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_JSONRPCDISPATCHER_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_JSONRPCDISPATCHER_H
 
+#include "Logger.h"
 #include "clang/Basic/LLVM.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Support/YAMLParser.h"
@@ -21,7 +22,7 @@
 
 /// Encapsulates output and logs streams and provides thread-safe access to
 /// them.
-class JSONOutput {
+class JSONOutput : public Logger {
 public:
   JSONOutput(llvm::raw_ostream &Outs, llvm::raw_ostream &Logs)
       : Outs(Outs), Logs(Logs) {}
@@ -30,7 +31,7 @@
   void writeMessage(const Twine &Message);
 
   /// Write to the logging stream.
-  void log(const Twine &Message);
+  void log(const Twine &Message) override;
 
 private:
   llvm::raw_ostream &Outs;
Index: clangd/Logger.h
===================================================================
--- /dev/null
+++ clangd/Logger.h
@@ -0,0 +1,41 @@
+//===--- Logger.h - Logger interface for clangd ------------------*- C++-*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_LOGGER_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_LOGGER_H
+
+#include "llvm/ADT/Twine.h"
+
+namespace clang {
+namespace clangd {
+
+/// Interface to allow custom logging in clangd.
+class Logger {
+public:
+  virtual ~Logger() = default;
+
+  /// Implementations of this method must be thread-safe.
+  virtual void log(const llvm::Twine &Message) = 0;
+};
+
+/// Logger implementation that ignores all messages.
+class EmptyLogger : public Logger {
+public:
+  static EmptyLogger &getInstance();
+
+  void log(const llvm::Twine &Message) override;
+
+private:
+  EmptyLogger() = default;
+};
+
+} // namespace clangd
+} // namespace clang
+
+#endif
Index: clangd/Logger.cpp
===================================================================
--- /dev/null
+++ clangd/Logger.cpp
@@ -0,0 +1,19 @@
+//===--- Logger.cpp - Logger interface for clangd -------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Logger.h"
+
+using namespace clang::clangd;
+
+EmptyLogger &EmptyLogger::getInstance() {
+  static EmptyLogger Logger;
+  return Logger;
+}
+
+void EmptyLogger::log(const llvm::Twine &Message) {}
Index: unittests/clangd/ClangdTests.cpp
===================================================================
--- unittests/clangd/ClangdTests.cpp
+++ unittests/clangd/ClangdTests.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "ClangdServer.h"
+#include "Logger.h"
 #include "clang/Basic/VirtualFileSystem.h"
 #include "clang/Config/config.h"
 #include "llvm/ADT/SmallVector.h"
@@ -302,7 +303,8 @@
     ErrorCheckingDiagConsumer DiagConsumer;
     MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
     ClangdServer Server(CDB, DiagConsumer, FS, getDefaultAsyncThreadsCount(),
-                        /*SnippetCompletions=*/false);
+                        /*SnippetCompletions=*/false,
+                        EmptyLogger::getInstance());
     for (const auto &FileWithContents : ExtraFiles)
       FS.Files[getVirtualTestFilePath(FileWithContents.first)] =
           FileWithContents.second;
@@ -365,7 +367,7 @@
   ErrorCheckingDiagConsumer DiagConsumer;
   MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
   ClangdServer Server(CDB, DiagConsumer, FS, getDefaultAsyncThreadsCount(),
-                      /*SnippetCompletions=*/false);
+                      /*SnippetCompletions=*/false, EmptyLogger::getInstance());
 
   const auto SourceContents = R"cpp(
 #include "foo.h"
@@ -410,7 +412,7 @@
   MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
 
   ClangdServer Server(CDB, DiagConsumer, FS, getDefaultAsyncThreadsCount(),
-                      /*SnippetCompletions=*/false);
+                      /*SnippetCompletions=*/false, EmptyLogger::getInstance());
 
   const auto SourceContents = R"cpp(
 #include "foo.h"
@@ -457,7 +459,8 @@
   MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
   // Run ClangdServer synchronously.
   ClangdServer Server(CDB, DiagConsumer, FS,
-                      /*AsyncThreadsCount=*/0, /*SnippetCompletions=*/false);
+                      /*AsyncThreadsCount=*/0, /*SnippetCompletions=*/false,
+                      EmptyLogger::getInstance());
 
   auto FooCpp = getVirtualTestFilePath("foo.cpp");
   const auto SourceContents = "int a;";
@@ -490,7 +493,8 @@
                               "-stdlib=libstdc++"});
   // Run ClangdServer synchronously.
   ClangdServer Server(CDB, DiagConsumer, FS,
-                      /*AsyncThreadsCount=*/0, /*SnippetCompletions=*/false);
+                      /*AsyncThreadsCount=*/0, /*SnippetCompletions=*/false,
+                      EmptyLogger::getInstance());
 
   // Just a random gcc version string
   SmallString<8> Version("4.9.3");
@@ -538,7 +542,8 @@
   ErrorCheckingDiagConsumer DiagConsumer;
   MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
   ClangdServer Server(CDB, DiagConsumer, FS,
-                      /*AsyncThreadsCount=*/0, /*SnippetCompletions=*/false);
+                      /*AsyncThreadsCount=*/0, /*SnippetCompletions=*/false,
+                      EmptyLogger::getInstance());
   // No need to sync reparses, because reparses are performed on the calling
   // thread to true.
 
@@ -597,7 +602,7 @@
   MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
 
   ClangdServer Server(CDB, DiagConsumer, FS, getDefaultAsyncThreadsCount(),
-                      /*SnippetCompletions=*/false);
+                      /*SnippetCompletions=*/false, EmptyLogger::getInstance());
 
   auto FooCpp = getVirtualTestFilePath("foo.cpp");
   const auto SourceContents = R"cpp(
@@ -745,7 +750,8 @@
   {
     MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
     ClangdServer Server(CDB, DiagConsumer, FS, getDefaultAsyncThreadsCount(),
-                        /*SnippetCompletions=*/false);
+                        /*SnippetCompletions=*/false,
+                        EmptyLogger::getInstance());
 
     // Prepare some random distributions for the test.
     std::random_device RandGen;