[clangd] Introduced Logger interface.

[ilya-biryukov]

Summary

This fixes a bunch of logging-related FIXMEs.

[malaperle]

Looks very nice! Just a few questions.

clangd/ClangdServer.h

24

forward declare?

clangd/ClangdUnit.h

13

forward declare?

clangd/GlobalCompilationDatabase.cpp

87–88

Will this log for every parent folder that doesn't contain the compilation database? I haven't tried to confirm. Just wondering because it could get very spammy.

clangd/GlobalCompilationDatabase.h

13

forward declare instead?

[ilya-biryukov]

Addressed review comments.

• Replaced include with forward declaration in headers.
• Removed logging on each call to loadFromDirectory.

clangd/GlobalCompilationDatabase.cpp

87–88

You're totally right, it's incredibly spammy. I've removed logging from this line.
Thanks for the finding!

[ilya-biryukov]

• Replaced JSONOutput in Protocol.h/Protocol.cpp with Logger.

[malaperle]

Look good. Thank you!

clangd/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   Support
   )
 
 add_clang_library(clangDaemon
   ClangdLSPServer.cpp
   ClangdServer.cpp
   ClangdUnit.cpp
   ClangdUnitStore.cpp
   DraftStore.cpp
   GlobalCompilationDatabase.cpp
   JSONRPCDispatcher.cpp
+  Logger.cpp
   Protocol.cpp
   ProtocolHandlers.cpp
 
   LINK_LIBS
   clangAST
   clangBasic
   clangFormat
   clangFrontend

clangd/ClangdLSPServer.cpp

void ClangdLSPServer::LSPProtocolCallbacks::onGoToDefinition(
   Out.writeMessage(
       R"({"jsonrpc":"2.0","id":)" + ID.str() +
       R"(,"result":[)" + Locations + R"(]})");
 }
 
 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");
 
   // Set up JSONRPCDispatcher.
   LSPProtocolCallbacks Callbacks(*this);
   JSONRPCDispatcher Dispatcher(llvm::make_unique<Handler>(Out));
   regiterCallbackHandlers(Dispatcher, Out, Callbacks);

clangd/ClangdServer.h

 #include "clang/Frontend/ASTUnit.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "clang/Tooling/Core/Replacement.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringRef.h"
 
 #include "ClangdUnit.h"
 #include "Protocol.h"
 
 #include <condition_variable>
 #include <functional>
 #include <mutex>
 #include <string>
 #include <thread>
 #include <type_traits>
 #include <utility>
 
 namespace clang {
 class PCHContainerOperations;
 
 namespace clangd {
 
+class Logger;
+
 /// Turn a [line, column] pair into an offset in Code.
 size_t positionToOffset(StringRef Code, Position P);
 
 /// Turn an offset in Code into a [line, column] pair.
 Position offsetToPosition(StringRef Code, size_t Offset);
 
 /// A tag supplied by the FileSytemProvider.
 typedef std::string VFSTag;
public:
   /// added file (i.e., when processing a first call to addDocument) and reuses
   /// those arguments for subsequent reparses. However, ClangdServer will check
   /// if compilation arguments changed on calls to forceReparse().
   ///
   /// After each parsing request finishes, ClangdServer reports diagnostics to
   /// \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
   /// \p File is already tracked. Also schedules parsing of the AST for it on a
   /// separate thread. When the parsing is complete, DiagConsumer passed in
   /// constructor will receive onDiagnosticsReady callback.
   /// \return A future that will become ready when the rebuild (including
   /// diagnostics) is finished.

 private:
   std::future<void>
   scheduleReparseAndDiags(PathRef File, VersionedDraft Contents,
                           std::shared_ptr<CppFile> Resources,
                           Tagged<IntrusiveRefCntPtr<vfs::FileSystem>> TaggedFS);
 
   std::future<void> scheduleCancelRebuild(std::shared_ptr<CppFile> Resources);
 
+  clangd::Logger &Logger;
   GlobalCompilationDatabase &CDB;
   DiagnosticsConsumer &DiagConsumer;
   FileSystemProvider &FSProvider;
   DraftStore DraftMgr;
   CppFileCollection Units;
   std::string ResourceDir;
   std::shared_ptr<PCHContainerOperations> PCHs;
   // WorkScheduler has to be the last member, because its destructor has to be

clangd/ClangdServer.cpp

ClangdScheduler::~ClangdScheduler() {
   for (auto &Worker : Workers)
     Worker.join();
 }
 
 ClangdServer::ClangdServer(GlobalCompilationDatabase &CDB,
                            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) {
 }
 
 std::future<void> ClangdServer::addDocument(PathRef File, StringRef Contents) {
   DocVersion Version = DraftMgr.updateDraft(File, Contents);
 
   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));
 }
 
 std::future<void> ClangdServer::removeDocument(PathRef File) {
   DraftMgr.removeDraft(File);
   std::shared_ptr<CppFile> Resources = Units.removeIfPresent(File);
   return scheduleCancelRebuild(std::move(Resources));
 }
 
 std::future<void> ClangdServer::forceReparse(PathRef File) {
   auto FileContents = DraftMgr.getDraft(File);
   assert(FileContents.Draft &&
          "forceReparse() was called for non-added document");
 
   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));
   // Schedule a reparse.
   return scheduleReparseAndDiags(File, std::move(FileContents),
                                  std::move(Recreated.FileInCollection),
                                  std::move(TaggedFS));
 }
ClangdServer::codeComplete(PathRef File, Position Pos,
 
   std::shared_ptr<CppFile> Resources = Units.getFile(File);
   assert(Resources && "Calling completion on non-added file");
 
   auto Preamble = Resources->getPossiblyStalePreamble();
   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);
 }
 
 std::vector<tooling::Replacement> ClangdServer::formatRange(PathRef File,
                                                             Range Rng) {
   std::string Code = getDocument(File);
 
   size_t Begin = positionToOffset(Code, Rng.start);
assert(FileContents.Draft &&
          "findDefinitions is called for non-added document");
 
   auto TaggedFS = FSProvider.getTaggedFileSystem(File);
 
   std::shared_ptr<CppFile> Resources = Units.getFile(File);
   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);
 }
 
 std::future<void> ClangdServer::scheduleReparseAndDiags(
     PathRef File, VersionedDraft Contents, std::shared_ptr<CppFile> Resources,
     Tagged<IntrusiveRefCntPtr<vfs::FileSystem>> TaggedFS) {
 

clangd/ClangdUnit.h

 //===--- ClangdUnit.h -------------------------------------------*- 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_CLANGDUNIT_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_CLANGDUNIT_H
 
 #include "Path.h"
 #include "Protocol.h"
 #include "clang/Frontend/ASTUnit.h"
 #include "clang/Frontend/PrecompiledPreamble.h"
 #include "clang/Serialization/ASTBitCodes.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "clang/Tooling/Core/Replacement.h"
 #include <atomic>
 #include <future>

 }
 
 namespace tooling {
 struct CompileCommand;
 }
 
 namespace clangd {
 
+class Logger;
+
 /// A diagnostic with its FixIts.
 struct DiagWithFixIts {
   clangd::Diagnostic Diag;
   llvm::SmallVector<tooling::Replacement, 1> FixIts;
 };
 
 /// Stores and provides access to parsed AST.
 class ParsedAST {
 public:
   /// Attempts to run Clang and store parsed AST. If \p Preamble is non-null
   /// it is reused during parsing.
   static llvm::Optional<ParsedAST>
   Build(std::unique_ptr<clang::CompilerInvocation> CI,
         const PrecompiledPreamble *Preamble,
         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);
 
   ~ParsedAST();
 
   ASTContext &getASTContext();
   const ASTContext &getASTContext() const;

 /// Manages resources, required by clangd. Allows to rebuild file with new
 /// contents, and provides AST and Preamble for it.
 class CppFile : public std::enable_shared_from_this<CppFile> {
 public:
   // We only allow to create CppFile as shared_ptr, because a future returned by
   // 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;
   CppFile(CppFile &&) = delete;
 
   /// Cancels a scheduled rebuild, if any, and sets AST and Preamble to nulls.
   /// If a rebuild is in progress, will wait for it to finish.
   void cancelRebuild();
private:
   /// Promise and future for the latests Preamble. Fulfilled during rebuild.
   std::promise<std::shared_ptr<const PreambleData>> PreamblePromise;
   std::shared_future<std::shared_ptr<const PreambleData>> PreambleFuture;
   /// Latest preamble that was built. May be stale, but always available without
   /// waiting for rebuild to finish.
   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.
 std::vector<CompletionItem>
 codeComplete(PathRef FileName, tooling::CompileCommand Command,
              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.
 void dumpAST(ParsedAST &AST, llvm::raw_ostream &OS);
 
 } // namespace clangd
 } // namespace clang
 #endif

clangd/ClangdUnit.cpp

 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Serialization/ASTWriter.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/Format.h"
+#include "Logger.h"
 
 #include <algorithm>
 #include <chrono>
 
 using namespace clang::clangd;
 using namespace clang;
 
 namespace {

 }; // SnippetCompletionItemsCollector
 } // namespace
 
 std::vector<CompletionItem>
 clangd::codeComplete(PathRef FileName, tooling::CompileCommand Command,
                      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());
 
   VFS->setCurrentWorkingDirectory(Command.Directory);
 
   std::unique_ptr<CompilerInvocation> CI;
   EmptyDiagsConsumer DummyDiagsConsumer;
clangd::codeComplete(PathRef FileName, tooling::CompileCommand Command,
   } else {
     FrontendOpts.CodeCompleteOpts.IncludeCodePatterns = false;
     Clang->setCodeCompletionConsumer(new PlainTextCompletionItemsCollector(
         FrontendOpts.CodeCompleteOpts, Items));
   }
 
   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;
 }
 
 void clangd::dumpAST(ParsedAST &AST, llvm::raw_ostream &OS) {
   AST.getASTContext().getTranslationUnitDecl()->dump(OS, true);
 }
 
 llvm::Optional<ParsedAST>
 ParsedAST::Build(std::unique_ptr<clang::CompilerInvocation> CI,
                  const PrecompiledPreamble *Preamble,
                  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);
 
   auto Clang =
       prepareCompilerInstance(std::move(CI), Preamble, std::move(Buffer), PCHs,
                               VFS, /*ref*/ UnitDiagsConsumer);
 
   // Recover resources if we crash before exiting this method.
   llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance> CICleanup(
       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.
   Clang->getDiagnostics().setClient(new EmptyDiagsConsumer);
 
   std::vector<const Decl *> ParsedDecls = Action->takeTopLevelDecls();
   std::vector<serialization::DeclID> PendingDecls;
   if (Preamble) {
if (Result.is(tok::raw_identifier)) {
     return Lexer::GetBeginningOfToken(PeekBeforeLocation, SourceMgr,
                                       AST.getLangOpts());
   }
 
   return InputLocation;
 }
 } // 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)
     return {};
 
   SourceLocation SourceLocationBeg = getBeginningOfIdentifier(AST, Pos, FE);
 
   auto DeclLocationsFinder = std::make_shared<DeclarationLocationsFinder>(

 PreambleData::PreambleData(PrecompiledPreamble Preamble,
                            std::vector<serialization::DeclID> TopLevelDeclIDs,
                            std::vector<DiagWithFixIts> Diags)
     : Preamble(std::move(Preamble)),
       TopLevelDeclIDs(std::move(TopLevelDeclIDs)), Diags(std::move(Diags)) {}
 
 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;
   PreamblePromise.set_value(nullptr);
   PreambleFuture = PreamblePromise.get_future();
 
   ASTPromise.set_value(std::make_shared<ParsedASTWrapper>(llvm::None));
   ASTFuture = ASTPromise.get_future();
if (NewPreamble) {
       SerializedPreambleDecls = NewPreamble->TopLevelDeclIDs;
       Diagnostics.insert(Diagnostics.begin(), NewPreamble->Diags.begin(),
                          NewPreamble->Diags.end());
     }
 
     // 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(),
                          NewAST->getDiagnostics().end());
     } else {
       // Don't report even Preamble diagnostics if we coulnd't build AST.
       Diagnostics.clear();
     }

clangd/ClangdUnitStore.h

 #include "ClangdUnit.h"
 #include "GlobalCompilationDatabase.h"
 #include "Path.h"
 #include "clang/Tooling/CompilationDatabase.h"
 
 namespace clang {
 namespace clangd {
 
+class Logger;
+
 /// 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,
+      IntrusiveRefCntPtr<vfs::FileSystem> VFS, clangd::Logger &Logger) {
     std::lock_guard<std::mutex> Lock(Mutex);
 
     auto It = OpenedFiles.find(File);
     if (It == OpenedFiles.end()) {
       auto Command = getCompileCommand(CDB, File, ResourceDir);
 
       It = OpenedFiles
                .try_emplace(File, CppFile::Create(File, std::move(Command),
-                                                  std::move(PCHs)))
+                                                  std::move(PCHs), Logger))
                .first;
     }
     return It->second;
   }
 
   struct RecreateResult {
     /// A CppFile, stored in this CppFileCollection for the corresponding
     /// filepath after calling recreateFileIfCompileCommandChanged.
     std::shared_ptr<CppFile> FileInCollection;
     /// If a new CppFile had to be created to account for changed
     /// CompileCommand, a previous CppFile instance will be returned in this
     /// field.
     std::shared_ptr<CppFile> RemovedFile;
   };
 
   /// Similar to getOrCreateFile, but will replace a current CppFile for \p File
   /// with a new one if CompileCommand, provided by \p CDB has changed.
   /// If a currently stored CppFile had to be replaced, the previous instance
   /// will be returned in RecreateResult.RemovedFile.
   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);
 
     auto It = OpenedFiles.find(File);
     if (It == OpenedFiles.end())
       return nullptr;
     return It->second;

clangd/ClangdUnitStore.cpp

std::shared_ptr<CppFile> CppFileCollection::removeIfPresent(PathRef File) {
   OpenedFiles.erase(It);
   return Result;
 }
 
 CppFileCollection::RecreateResult
 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);
 
   RecreateResult Result;
 
   auto It = OpenedFiles.find(File);
   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;
 }
 
 tooling::CompileCommand
 CppFileCollection::getCompileCommand(GlobalCompilationDatabase &CDB,
                                      PathRef File, PathRef ResourceDir) {

clangd/GlobalCompilationDatabase.h

 //===--- GlobalCompilationDatabase.h ----------------------------*- 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_GLOBALCOMPILATIONDATABASE_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_GLOBALCOMPILATIONDATABASE_H
 
 #include "Path.h"
 #include "llvm/ADT/StringMap.h"
 #include <memory>
 #include <mutex>
 #include <vector>
 
 namespace clang {
 
 namespace tooling {
 class CompilationDatabase;
 struct CompileCommand;
 } // namespace tooling
 
 namespace clangd {
 
+class Logger;
+
 /// Returns a default compile command to use for \p File.
 tooling::CompileCommand getDefaultCompileCommand(PathRef File);
 
 /// Provides compilation arguments used for parsing C and C++ files.
 class GlobalCompilationDatabase {
 public:
   virtual ~GlobalCompilationDatabase() = default;
 
   virtual std::vector<tooling::CompileCommand>
   getCompileCommands(PathRef File) = 0;
 
   /// FIXME(ibiryukov): add facilities to track changes to compilation flags of
   /// existing targets.
 };
 
 /// Gets compile args from tooling::CompilationDatabases built for parent
 /// directories.
 class DirectoryBasedGlobalCompilationDatabase
     : public GlobalCompilationDatabase {
 public:
+  DirectoryBasedGlobalCompilationDatabase(clangd::Logger &Logger);
+
   std::vector<tooling::CompileCommand>
   getCompileCommands(PathRef File) override;
 
   void setExtraFlagsForFile(PathRef File, std::vector<std::string> ExtraFlags);
 
 private:
   tooling::CompilationDatabase *getCompilationDatabase(PathRef File);
 
   std::mutex Mutex;
   /// Caches compilation databases loaded from directories(keys are
   /// directories).
   llvm::StringMap<std::unique_ptr<clang::tooling::CompilationDatabase>>
       CompilationDatabases;
 
   /// Stores extra flags per file.
   llvm::StringMap<std::vector<std::string>> ExtraFlagsForFile;
+  /// Used for logging.
+  clangd::Logger &Logger;
 };
 } // namespace clangd
 } // namespace clang
 
 #endif

clangd/GlobalCompilationDatabase.cpp

 //===--- GlobalCompilationDatabase.cpp --------------------------*- C++-*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===---------------------------------------------------------------------===//
 
 #include "GlobalCompilationDatabase.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
+#include "Logger.h"
 
 namespace clang {
 namespace clangd {
 
 static void addExtraFlags(tooling::CompileCommand &Command,
                           const std::vector<std::string> &ExtraFlags) {
   if (ExtraFlags.empty())
     return;

 
 tooling::CompileCommand getDefaultCompileCommand(PathRef File) {
   std::vector<std::string> CommandLine{"clang", "-fsyntax-only", File.str()};
   return tooling::CompileCommand(llvm::sys::path::parent_path(File),
                                  llvm::sys::path::filename(File), CommandLine,
                                  /*Output=*/"");
 }
 
+DirectoryBasedGlobalCompilationDatabase::
+    DirectoryBasedGlobalCompilationDatabase(clangd::Logger &Logger)
+    : Logger(Logger) {}
+
 std::vector<tooling::CompileCommand>
 DirectoryBasedGlobalCompilationDatabase::getCompileCommands(PathRef File) {
   std::vector<tooling::CompileCommand> Commands;
 
   auto CDB = getCompilationDatabase(File);
   if (CDB)
     Commands = CDB->getCompileCommands(File);
   if (Commands.empty())
assert((path::is_absolute(File, path::Style::posix) ||
          "path must be absolute");
 
   for (auto Path = path::parent_path(File); !Path.empty();
        Path = path::parent_path(Path)) {
 
     auto CachedIt = CompilationDatabases.find(Path);
     if (CachedIt != CompilationDatabases.end())
       return CachedIt->second.get();
+
     std::string Error;
     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");
-      }
+    if (!CDB)
       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;
 }
 
 } // namespace clangd
 } // namespace clang

clangd/JSONRPCDispatcher.h

 //===--- JSONRPCDispatcher.h - Main JSON parser entry point -----*- 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_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"
 #include <iosfwd>
 #include <mutex>
 
 namespace clang {
 namespace clangd {
 
 /// 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) {}
 
   /// Emit a JSONRPC message.
   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;
   llvm::raw_ostream &Logs;
 
   std::mutex StreamMutex;
 };
 

clangd/Logger.h

+//===--- 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

clangd/Logger.cpp

+//===--- 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) {}

unittests/clangd/ClangdTests.cpp

 //===-- ClangdTests.cpp - Clangd unit tests ---------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "ClangdServer.h"
+#include "Logger.h"
 #include "clang/Basic/VirtualFileSystem.h"
 #include "clang/Config/config.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Regex.h"
 #include "gtest/gtest.h"
#endif
   std::string parseSourceAndDumpAST(
       PathRef SourceFileRelPath, StringRef SourceContents,
       std::vector<std::pair<PathRef, StringRef>> ExtraFiles = {},
       bool ExpectErrors = false) {
     MockFSProvider FS;
     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;
 
     auto SourceFilename = getVirtualTestFilePath(SourceFileRelPath);
 
     FS.ExpectedFile = SourceFilename;
 
parseSourceAndDumpAST("foo.cpp", SourceContents, {{"foo.h", "int a;"}},
                         /*ExpectErrors=*/false);
 }
 
 TEST_F(ClangdVFSTest, Reparse) {
   MockFSProvider FS;
   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"
 int b = a;
 )cpp";
 
   auto FooCpp = getVirtualTestFilePath("foo.cpp");
   auto FooH = getVirtualTestFilePath("foo.h");

 }
 
 TEST_F(ClangdVFSTest, ReparseOnHeaderChange) {
   MockFSProvider FS;
   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"
 int b = a;
 )cpp";
 
   auto FooCpp = getVirtualTestFilePath("foo.cpp");
   auto FooH = getVirtualTestFilePath("foo.h");

 }
 
 TEST_F(ClangdVFSTest, CheckVersions) {
   MockFSProvider FS;
   ErrorCheckingDiagConsumer DiagConsumer;
   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;";
   FS.Files[FooCpp] = SourceContents;
   FS.ExpectedFile = FooCpp;
 
   // No need to sync reparses, because requests are processed on the calling
   // thread.
TEST_F(ClangdVFSTest, SearchLibDir) {
   ErrorCheckingDiagConsumer DiagConsumer;
   MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
   CDB.ExtraClangFlags.insert(CDB.ExtraClangFlags.end(),
                              {"-xc++", "-target", "x86_64-linux-unknown",
                               "-m64", "--gcc-toolchain=/randomusr",
                               "-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");
 
   // A lib dir for gcc installation
   SmallString<64> LibDir("/randomusr/lib/gcc/x86_64-linux-gnu");
   llvm::sys::path::append(LibDir, Version);
 

 }
 #endif // LLVM_ON_UNIX
 
 TEST_F(ClangdVFSTest, ForceReparseCompileCommand) {
   MockFSProvider FS;
   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.
 
   auto FooCpp = getVirtualTestFilePath("foo.cpp");
   const auto SourceContents1 = R"cpp(
 template <class T>
 struct foo { T x; };
 )cpp";

 };
 
 TEST_F(ClangdCompletionTest, CheckContentsOverride) {
   MockFSProvider FS;
   ErrorCheckingDiagConsumer DiagConsumer;
   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(
 int aba;
 int b =   ;
 )cpp";
 
   const auto OverridenSourceContents = R"cpp(
)cpp";
   ReqStats.reserve(FilesCount);
   for (unsigned FileIndex = 0; FileIndex < FilesCount; ++FileIndex)
     ReqStats.emplace_back();
 
   TestDiagConsumer DiagConsumer;
   {
     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;
 
     std::uniform_int_distribution<unsigned> FileIndexDist(0, FilesCount - 1);
     // Pass a text that contains compiler errors to addDocument in about 20% of
     // all requests.
     std::bernoulli_distribution ShouldHaveErrorsDist(0.2);