[clangd] Use elog instead of llvm::errs, log instead of llvm::outs

[kbobyrev]

Don't use llvm::toString in elog

[sammccall]

Thanks for sending this... after looking at the examples and thinking again about our conversation I may have shifted a bit :-\

I think it's important *log() should only be used for messages intended to be logged! (i.e. read later as a sequence of log messages).
We happen to write these to stderr by default, but this is an implementation detail that I'd like to leave flexible.

So a good question is: "if we were writing the log to a different file instead, would we want to write this there or stderr?"
By that measure:

• the messages followed by exit() should go to stderr
• dexp's output should go to stder
• the others seem good to go to the log

WDYT?

clang-tools-extra/clangd/benchmarks/IndexBenchmark.cpp

101 ↗

(On Diff #281027)

this is fine, but just writes to errs with no log formatting... you need to set up a logger if you want one.

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

185 ↗

(On Diff #281027)

hmm... since this is explicitly supposed to be an interactive tool, I think "we are writing to stderr" is important rather than a detail to be abstracted.

e.g. there's no timestamp etc decoration (which is good!) because you haven't installed an actual logger and the fallback behavior is to write to stderr. But neither of these things are explicit at the callsite and either could be changed elsewhere.

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

185

I'd suggest this is log() rather than vlog() - the port is sometimes important to know but *progress through the startup sequence* is useful to have in the log.

clang-tools-extra/clangd/indexer/IndexerMain.cpp

116

unneccesary toString

126

unneccesary toString

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

568

Don't use elog before the logger is set up to print messages to stderr - it seems needlessly confusing where the current version is very clear.

(it *is* better for the basic validation to happen early and us to log flag failures "before the stream enters log mode" where it's convenient)

626

this isn't an error, and we're explicitly trying to get it in front of the user *before* the log starts

[kbobyrev]

Use more conservative approach.

[sammccall]

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

202

explain why or just delete this comment

202

nit: move this down after flag validation?

204

I'm not sure performance matters here (if you don't actually write to stdout much, it should be free). Rather, this is for correctness: it's not threadsafe.

[kbobyrev]

Resolve post-LGTM comments.

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 "index/Index.h"
 #include "index/Serialization.h"
 #include "index/Symbol.h"
 #include "index/remote/marshalling/Marshalling.h"
 #include "support/Logger.h"
 #include "support/Trace.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/CommandLine.h"

 )";
 
 llvm::cl::opt<std::string> IndexPath(llvm::cl::desc("<INDEX FILE>"),
                                      llvm::cl::Positional, llvm::cl::Required);
 
 llvm::cl::opt<std::string> IndexRoot(llvm::cl::desc("<PROJECT ROOT>"),
                                      llvm::cl::Positional, llvm::cl::Required);
 
+llvm::cl::opt<Logger::Level> LogLevel{
+    "log",
+    llvm::cl::desc("Verbosity of log messages written to stderr"),
+    values(clEnumValN(Logger::Error, "error", "Error messages only"),
+           clEnumValN(Logger::Info, "info", "High level execution tracing"),
+           clEnumValN(Logger::Debug, "verbose", "Low level details")),
+    llvm::cl::init(Logger::Info),
+};
+
 llvm::cl::opt<std::string> TraceFile(
     "trace-file",
     llvm::cl::desc("Path to the file where tracer logs will be stored"));
 
 llvm::cl::opt<bool> PrettyPrint{
     "pretty",
     llvm::cl::desc("Pretty-print JSON output in the trace"),
     llvm::cl::init(false),
void runServer(std::unique_ptr<clangd::SymbolIndex> Index,
                const std::string &ServerAddress) {
   RemoteIndexServer Service(std::move(Index), IndexRoot);
 
   grpc::EnableDefaultHealthCheckService(true);
   grpc::ServerBuilder Builder;
   Builder.AddListeningPort(ServerAddress, grpc::InsecureServerCredentials());
   Builder.RegisterService(&Service);
   std::unique_ptr<grpc::Server> Server(Builder.BuildAndStart());
-  llvm::outs() << "Server listening on " << ServerAddress << '\n';
+  log("Server listening on {0}", ServerAddress);
 
   Server->Wait();
 }
 
 } // namespace
 } // namespace remote
 } // namespace clangd
 } // namespace clang
 
 using clang::clangd::elog;
 
 int main(int argc, char *argv[]) {
   using namespace clang::clangd::remote;
   llvm::cl::ParseCommandLineOptions(argc, argv, Overview);
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0]);
 
   if (!llvm::sys::path::is_absolute(IndexRoot)) {
-    elog("Index root should be an absolute path.");
+    llvm::errs() << "Index root should be an absolute path.\n";
     return -1;
   }
 
+  llvm::errs().SetBuffered();
+  // Don't flush stdout when logging for thread safety.
+  llvm::errs().tie(nullptr);
+  clang::clangd::StreamLogger Logger(llvm::errs(), LogLevel);
+  clang::clangd::LoggingSession LoggingSession(Logger);
+
   llvm::Optional<llvm::raw_fd_ostream> TracerStream;
   std::unique_ptr<clang::clangd::trace::EventTracer> Tracer;
   if (!TraceFile.empty()) {
     std::error_code EC;
     TracerStream.emplace(TraceFile, EC,
                          llvm::sys::fs::FA_Read | llvm::sys::fs::FA_Write);
     if (EC) {
       TracerStream.reset();
int main(int argc, char *argv[]) {
 
   llvm::Optional<clang::clangd::trace::Session> TracingSession;
   if (Tracer)
     TracingSession.emplace(*Tracer);
 
   std::unique_ptr<clang::clangd::SymbolIndex> Index = openIndex(IndexPath);
 
   if (!Index) {
-    elog("Failed to open the index.");
+    llvm::errs() << "Failed to open the index.\n";
     return -1;
   }
 
   runServer(std::move(Index), ServerAddress);
 }

clang-tools-extra/clangd/indexer/IndexerMain.cpp

 //===----------------------------------------------------------------------===//
 
 #include "index/IndexAction.h"
 #include "index/Merge.h"
 #include "index/Ref.h"
 #include "index/Serialization.h"
 #include "index/Symbol.h"
 #include "index/SymbolCollector.h"
+#include "support/Logger.h"
 #include "clang/Tooling/ArgumentsAdjusters.h"
 #include "clang/Tooling/CommonOptionsParser.h"
 #include "clang/Tooling/Execution.h"
 #include "clang/Tooling/Tooling.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Signals.h"
 
 namespace clang {
int main(int argc, const char **argv) {
 
   Note: only symbols from header files will be indexed.
   )";
 
   auto Executor = clang::tooling::createExecutorFromCommandLineArgs(
       argc, argv, llvm::cl::GeneralCategory, Overview);
 
   if (!Executor) {
     llvm::errs() << llvm::toString(Executor.takeError()) << "\n";
     return 1;
   }
 
   // Collect symbols found in each translation unit, merging as we go.
   clang::clangd::IndexFileIn Data;
   auto Err = Executor->get()->execute(
       std::make_unique<clang::clangd::IndexActionFactory>(Data),
       clang::tooling::getStripPluginsAdjuster());
   if (Err) {
-    llvm::errs() << llvm::toString(std::move(Err)) << "\n";
+    clang::clangd::elog("{0}", std::move(Err));
   }
 
   // Emit collected data.
   clang::clangd::IndexFileOut Out(Data);
   Out.Format = clang::clangd::Format;
   llvm::outs() << Out;
   return 0;
 }

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

)";
   }
   if (Test || EnableTestScheme) {
     static URISchemeRegistry::Add<TestScheme> X(
         "test", "Test scheme for clangd lit tests.");
   }
 
   if (!Sync && WorkerThreadsCount == 0) {
     llvm::errs() << "A number of worker threads cannot be 0. Did you mean to "
                     "specify -sync?";
     return 1;
   }
 
   if (Sync) {
     if (WorkerThreadsCount.getNumOccurrences())
       llvm::errs() << "Ignoring -j because -sync is set.\n";
     WorkerThreadsCount = 0;
   }
)";
   llvm::Optional<trace::Session> TracingSession;
   if (Tracer)
     TracingSession.emplace(*Tracer);
 
   // If a user ran `clangd` in a terminal without redirecting anything,
   // it's somewhat likely they're confused about how to use clangd.
   // Show them the help overview, which explains.
   if (llvm::outs().is_displayed() && llvm::errs().is_displayed())
     llvm::errs() << Overview << "\n";
   // Use buffered stream to stderr (we still flush each log message). Unbuffered
   // stream can cause significant (non-deterministic) latency for the logger.
   llvm::errs().SetBuffered();
   // Don't flush stdout when logging, this would be both slow and racy!
   llvm::errs().tie(nullptr);
   StreamLogger Logger(llvm::errs(), LogLevel);
   LoggingSession LoggingSession(Logger);
   // Write some initial logs before we start doing any real work.
)";
   if (!CompileCommandsDir.empty()) {
     if (llvm::sys::fs::exists(CompileCommandsDir)) {
       // We support passing both relative and absolute paths to the
       // --compile-commands-dir argument, but we assume the path is absolute in
       // the rest of clangd so we make sure the path is absolute before
       // continuing.
       llvm::SmallString<128> Path(CompileCommandsDir);
       if (std::error_code EC = llvm::sys::fs::make_absolute(Path)) {
-        llvm::errs() << "Error while converting the relative path specified by "
-                        "--compile-commands-dir to an absolute path: "
-                     << EC.message() << ". The argument will be ignored.\n";
+        elog("Error while converting the relative path specified by "
+             "--compile-commands-dir to an absolute path: {0}. The argument "
+             "will be ignored.",
+             EC.message());
       } else {
         CompileCommandsDirPath = std::string(Path.str());
       }
     } else {
-      llvm::errs()
-          << "Path specified by --compile-commands-dir does not exist. The "
-             "argument will be ignored.\n";
+      elog("Path specified by --compile-commands-dir does not exist. The "
+           "argument will be ignored.");
     }
   }
 
   ClangdServer::Options Opts;
   switch (PCHStorage) {
   case PCHStorageFlag::Memory:
     Opts.StorePreamblesInMemory = true;
     break;
if (EnableConfig) {
     if (llvm::sys::path::user_config_directory(UserConfig)) {
       llvm::sys::path::append(UserConfig, "clangd", "config.yaml");
       vlog("User config file is {0}", UserConfig);
       ProviderStack.push_back(config::Provider::fromYAMLFile(UserConfig, TFS));
     } else {
       elog("Couldn't determine user config file, not loading");
     }
     std::vector<const config::Provider *> ProviderPointers;
-    for (const auto& P : ProviderStack)
+    for (const auto &P : ProviderStack)
       ProviderPointers.push_back(P.get());
     Config = config::Provider::combine(std::move(ProviderPointers));
     Opts.ConfigProvider = Config.get();
   }
 
   // Initialize and run ClangdLSPServer.
   // Change stdin to binary to not lose \r\n on windows.
   llvm::sys::ChangeStdinToBinary();