[clang] [NFC] [C++20] [Modules] [P1689] [Scanner] Don't use thread pool in P1689 per file mode (PR #84285)

[Jan Svoboda via cfe-commits]

================
@@ -893,102 +889,118 @@ int clang_scan_deps_main(int argc, char **argv, const llvm::ToolContext &) {
   if (Format == ScanningOutputFormat::Full)
     FD.emplace(ModuleName.empty() ? Inputs.size() : 0);
 
-  if (Verbose) {
-    llvm::outs() << "Running clang-scan-deps on " << Inputs.size()
-                 << " files using " << Pool.getMaxConcurrency() << " workers\n";
-  }
-
-  llvm::Timer T;
-  T.startTimer();
-
-  for (unsigned I = 0; I < Pool.getMaxConcurrency(); ++I) {
-    Pool.async([&, I]() {
-      llvm::DenseSet<ModuleID> AlreadySeenModules;
-      while (auto MaybeInputIndex = GetNextInputIndex()) {
-        size_t LocalIndex = *MaybeInputIndex;
-        const tooling::CompileCommand *Input = &Inputs[LocalIndex];
-        std::string Filename = std::move(Input->Filename);
-        std::string CWD = std::move(Input->Directory);
-
-        std::optional<StringRef> MaybeModuleName;
-        if (!ModuleName.empty())
-          MaybeModuleName = ModuleName;
-
-        std::string OutputDir(ModuleFilesDir);
-        if (OutputDir.empty())
-          OutputDir = getModuleCachePath(Input->CommandLine);
-        auto LookupOutput = [&](const ModuleID &MID, ModuleOutputKind MOK) {
-          return ::lookupModuleOutput(MID, MOK, OutputDir);
-        };
-
-        // Run the tool on it.
-        if (Format == ScanningOutputFormat::Make) {
-          auto MaybeFile =
-              WorkerTools[I]->getDependencyFile(Input->CommandLine, CWD);
-          if (handleMakeDependencyToolResult(Filename, MaybeFile, DependencyOS,
-                                             Errs))
-            HadErrors = true;
-        } else if (Format == ScanningOutputFormat::P1689) {
-          // It is useful to generate the make-format dependency output during
-          // the scanning for P1689. Otherwise the users need to scan again for
-          // it. We will generate the make-format dependency output if we find
-          // `-MF` in the command lines.
-          std::string MakeformatOutputPath;
-          std::string MakeformatOutput;
-
-          auto MaybeRule = WorkerTools[I]->getP1689ModuleDependencyFile(
-              *Input, CWD, MakeformatOutput, MakeformatOutputPath);
-
-          if (handleP1689DependencyToolResult(Filename, MaybeRule, PD, Errs))
-            HadErrors = true;
+  std::vector<std::unique_ptr<DependencyScanningTool>> WorkerTools;
 
-          if (!MakeformatOutputPath.empty() && !MakeformatOutput.empty() &&
-              !HadErrors) {
-            static std::mutex Lock;
-            // With compilation database, we may open different files
-            // concurrently or we may write the same file concurrently. So we
-            // use a map here to allow multiple compile commands to write to the
-            // same file. Also we need a lock here to avoid data race.
-            static llvm::StringMap<llvm::raw_fd_ostream> OSs;
-            std::unique_lock<std::mutex> LockGuard(Lock);
-
-            auto OSIter = OSs.find(MakeformatOutputPath);
-            if (OSIter == OSs.end()) {
-              std::error_code EC;
-              OSIter = OSs.try_emplace(MakeformatOutputPath,
-                                       MakeformatOutputPath, EC)
-                           .first;
-              if (EC)
-                llvm::errs()
-                    << "Failed to open P1689 make format output file \""
-                    << MakeformatOutputPath << "\" for " << EC.message()
-                    << "\n";
-            }
+  auto ScanningTask = [&](unsigned I) {
----------------
jansvoboda11 wrote:

IIUC `I` is only used to index into `WorkerTools`. Could we just directly take `WorkerTools &`? Makes this a bit clearer IMO - for a second I thought `I` is an input index.

https://github.com/llvm/llvm-project/pull/84285