[clangd] Make it possible to use VFS from parsing for getting tidy options

[ilya-biryukov]

Summary

To give an option for clangd embedders with snapshotted filesystem to
read config files from exact snapshots, possibly loosing some
performance from caching capabilities of the current implementations.

[sammccall]

This seems fine:

• please give this function<> type a name - maybe ClangTidyOptionsBuilder or so?
• while we're defining this, we should make it threadsafe because that's what we really want
• document that it's threadsafe and approximately why we don't use ClangTidyOptionsProvider

[ilya-biryukov]

• Add a typedef for function
• Make the provider thread-safe

[ilya-biryukov]

• Fix a typo

[ilya-biryukov]

• Fix another typo

clang-tools-extra/trunk/clangd/ClangdServer.h

public:
 
   /// Called by ClangdServer when \p Diagnostics for \p File are ready.
   virtual void onDiagnosticsReady(PathRef File,
                                   std::vector<Diag> Diagnostics) = 0;
   /// Called whenever the file status is updated.
   virtual void onFileUpdated(PathRef File, const TUStatus &Status){};
 };
 
+/// When set, used by ClangdServer to get clang-tidy options for each particular
+/// file. Must be thread-safe. We use this instead of ClangTidyOptionsProvider
+/// to allow reading tidy configs from the VFS used for parsing.
+using ClangTidyOptionsBuilder = std::function<tidy::ClangTidyOptions(
+    llvm::vfs::FileSystem &, llvm::StringRef /*File*/)>;
+
 /// Manages a collection of source files and derived data (ASTs, indexes),
 /// and provides language-aware features such as code completion.
 ///
 /// The primary client is ClangdLSPServer which exposes these features via
 /// the Language Server protocol. ClangdServer may also be embedded directly,
 /// though its API is not stable over time.
 ///
 /// ClangdServer should be used from a single thread. Many potentially-slow
struct Options {
     /// If set to non-zero, the background index rebuilds the symbol index
     /// periodically every BuildIndexPeriodMs milliseconds; otherwise, the
     /// symbol index will be updated for each indexed file.
     size_t BackgroundIndexRebuildPeriodMs = 0;
 
     /// If set, use this index to augment code completion results.
     SymbolIndex *StaticIndex = nullptr;
 
-    /// If set, enable clang-tidy in clangd, used to get clang-tidy
+    /// If set, enable clang-tidy in clangd and use to it get clang-tidy
     /// configurations for a particular file.
     /// Clangd supports only a small subset of ClangTidyOptions, these options
     /// (Checks, CheckOptions) are about which clang-tidy checks will be
     /// enabled.
-    tidy::ClangTidyOptionsProvider *ClangTidyOptProvider = nullptr;
+    ClangTidyOptionsBuilder GetClangTidyOptions;
 
     /// Clangd's workspace root. Relevant for "workspace" operations not bound
     /// to a particular file.
     /// FIXME: If not set, should use the current working directory.
     llvm::Optional<std::string> WorkspaceRoot;
 
     /// The resource directory is used to find internal headers, overriding
     /// defaults and -resource-dir compiler flag).
private:
   const SymbolIndex *Index = nullptr;
   // If present, an index of symbols in open files. Read via *Index.
   std::unique_ptr<FileIndex> DynamicIdx;
   // If present, the new "auto-index" maintained in background threads.
   std::unique_ptr<BackgroundIndex> BackgroundIdx;
   // Storage for merged views of the various indexes.
   std::vector<std::unique_ptr<SymbolIndex>> MergedIdx;
 
-  // The provider used to provide a clang-tidy option for a specific file.
-  tidy::ClangTidyOptionsProvider *ClangTidyOptProvider = nullptr;
+  // When set, provides clang-tidy options for a specific file.
+  ClangTidyOptionsBuilder GetClangTidyOptions;
 
   // If this is true, suggest include insertion fixes for diagnostic errors that
   // can be caused by missing includes (e.g. member access in incomplete type).
   bool SuggestMissingIncludes = false;
 
   // GUARDED_BY(CachedCompletionFuzzyFindRequestMutex)
   llvm::StringMap<llvm::Optional<FuzzyFindRequest>>
       CachedCompletionFuzzyFindRequestByFile;

clang-tools-extra/trunk/clangd/ClangdServer.cpp

 ClangdServer::ClangdServer(const GlobalCompilationDatabase &CDB,
                            const FileSystemProvider &FSProvider,
                            DiagnosticsConsumer &DiagConsumer,
                            const Options &Opts)
     : FSProvider(FSProvider),
       DynamicIdx(Opts.BuildDynamicSymbolIndex
                      ? new FileIndex(Opts.HeavyweightDynamicSymbolIndex)
                      : nullptr),
-      ClangTidyOptProvider(Opts.ClangTidyOptProvider),
+      GetClangTidyOptions(Opts.GetClangTidyOptions),
       SuggestMissingIncludes(Opts.SuggestMissingIncludes),
       WorkspaceRoot(Opts.WorkspaceRoot),
       // Pass a callback into `WorkScheduler` to extract symbols from a newly
       // parsed file and rebuild the file index synchronously each time an AST
       // is parsed.
       // FIXME(ioeric): this can be slow and we may be able to index on less
       // critical paths.
       WorkScheduler(CDB, Opts.AsyncThreadsCount, Opts.StorePreamblesInMemory,
if (Opts.BackgroundIndex) {
     AddIndex(BackgroundIdx.get());
   }
   if (DynamicIdx)
     AddIndex(DynamicIdx.get());
 }
 
 void ClangdServer::addDocument(PathRef File, llvm::StringRef Contents,
                                WantDiagnostics WantDiags) {
+  auto FS = FSProvider.getFileSystem();
+
   ParseOptions Opts;
   Opts.ClangTidyOpts = tidy::ClangTidyOptions::getDefaults();
-  if (ClangTidyOptProvider)
-    Opts.ClangTidyOpts = ClangTidyOptProvider->getOptions(File);
+  // FIXME: call tidy options builder on the worker thread, it can do IO.
+  if (GetClangTidyOptions)
+    Opts.ClangTidyOpts = GetClangTidyOptions(*FS, File);
   Opts.SuggestMissingIncludes = SuggestMissingIncludes;
 
   // Compile command is set asynchronously during update, as it can be slow.
   ParseInputs Inputs;
-  Inputs.FS = FSProvider.getFileSystem();
+  Inputs.FS = FS;
   Inputs.Contents = Contents;
   Inputs.Opts = std::move(Opts);
   Inputs.Index = Index;
   WorkScheduler.update(File, Inputs, WantDiags);
 }
 
 void ClangdServer::removeDocument(PathRef File) { WorkScheduler.remove(File); }
 

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

 #include "Protocol.h"
 #include "Trace.h"
 #include "Transport.h"
 #include "index/Background.h"
 #include "index/Serialization.h"
 #include "clang/Basic/Version.h"
 #include "clang/Format/Format.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cstdlib>
 #include <iostream>
 #include <memory>
+#include <mutex>
 #include <string>
 #include <thread>
 
 namespace clang {
 namespace clangd {
 // FIXME: remove this option when Dex is cheap enough.
 static llvm::cl::opt<bool>
     UseDex("use-dex-index",
#endif
   } else {
     TransportLayer = newJSONTransport(
         stdin, llvm::outs(),
         InputMirrorStream ? InputMirrorStream.getPointer() : nullptr,
         PrettyPrint, InputStyle);
   }
 
   // Create an empty clang-tidy option.
-  std::unique_ptr<tidy::ClangTidyOptionsProvider> ClangTidyOptProvider;
+  std::mutex ClangTidyOptMu;
+  std::unique_ptr<tidy::ClangTidyOptionsProvider>
+      ClangTidyOptProvider; /*GUARDED_BY(ClangTidyOptMu)*/
   if (EnableClangTidy) {
     auto OverrideClangTidyOptions = tidy::ClangTidyOptions::getDefaults();
     OverrideClangTidyOptions.Checks = ClangTidyChecks;
     ClangTidyOptProvider = llvm::make_unique<tidy::FileOptionsProvider>(
         tidy::ClangTidyGlobalOptions(),
         /* Default */ tidy::ClangTidyOptions::getDefaults(),
         /* Override */ OverrideClangTidyOptions, FSProvider.getFileSystem());
   }
-  Opts.ClangTidyOptProvider = ClangTidyOptProvider.get();
+  Opts.GetClangTidyOptions = [&](llvm::vfs::FileSystem &,
+                                 llvm::StringRef File) {
+    // This function must be thread-safe and tidy option providers are not.
+    std::lock_guard<std::mutex> Lock(ClangTidyOptMu);
+    // FIXME: use the FS provided to the function.
+    return ClangTidyOptProvider->getOptions(File);
+  };
   Opts.SuggestMissingIncludes = SuggestMissingIncludes;
   llvm::Optional<OffsetEncoding> OffsetEncodingFromFlag;
   if (ForceOffsetEncoding != OffsetEncoding::UnsupportedEncoding)
     OffsetEncodingFromFlag = ForceOffsetEncoding;
   ClangdLSPServer LSPServer(
       *TransportLayer, FSProvider, CCOpts, CompileCommandsDirPath,
       /*UseDirBasedCDB=*/CompileArgsFrom == FilesystemCompileArgs,
       OffsetEncodingFromFlag, Opts);
   llvm::set_thread_name("clangd.main");
   return LSPServer.run() ? 0
                          : static_cast<int>(ErrorResultCode::NoShutdownRequest);
 }