//===- DependencyScanningFilesystem.cpp - clang-scan-deps fs --------------===//

//

// 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 "clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h"

#include "clang/Lex/DependencyDirectivesSourceMinimizer.h"

#include "llvm/Support/MemoryBuffer.h"

#include "llvm/Support/SmallVectorMemoryBuffer.h"

#include "llvm/Support/Threading.h"

using namespace clang;

using namespace tooling;

using namespace dependencies;

llvm::ErrorOr<llvm::vfs::Status>

CachedFileSystemEntry::initFile(StringRef Filename, llvm::vfs::FileSystem &FS) {

  // Load the file and its content from the file system.

  auto MaybeFile = FS.openFileForRead(Filename);

  if (!MaybeFile)

    return MaybeFile.getError();

  auto File = std::move(*MaybeFile);

  auto MaybeStat = File->status();

  if (!MaybeStat)

    return MaybeStat.getError();

  auto Stat = std::move(*MaybeStat);

  auto MaybeBuffer = File->getBuffer(Stat.getName());

  if (!MaybeBuffer)

    return MaybeBuffer.getError();

  auto Buffer = std::move(*MaybeBuffer);

  OriginalContents = std::move(Buffer);

  return Stat;

}

void CachedFileSystemEntry::minimizeFile() {

  assert(OriginalContents && "minimizing missing contents");

  llvm::SmallString<1024> MinimizedFileContents;

  // Minimize the file down to directives that might affect the dependencies.

  SmallVector<minimize_source_to_dependency_directives::Token, 64> Tokens;

  if (minimizeSourceToDependencyDirectives(OriginalContents->getBuffer(),

                                           MinimizedFileContents, Tokens)) {

    // FIXME: Propagate the diagnostic if desired by the client.

    // Use the original file if the minimization failed.

    MinimizedContentsStorage =

        llvm::MemoryBuffer::getMemBuffer(*OriginalContents);

    MinimizedContentsAccess.store(MinimizedContentsStorage.get());

    return;

  }

  // The contents produced by the minimizer must be null terminated.

  assert(MinimizedFileContents.data()[MinimizedFileContents.size()] == '\0' &&

         "not null terminated contents");

  // Compute the skipped PP ranges that speedup skipping over inactive

  // preprocessor blocks.

  llvm::SmallVector<minimize_source_to_dependency_directives::SkippedRange, 32>

      SkippedRanges;

  minimize_source_to_dependency_directives::computeSkippedRanges(Tokens,

                                                                 SkippedRanges);

  PreprocessorSkippedRangeMapping Mapping;

  for (const auto &Range : SkippedRanges) {

    if (Range.Length < 16) {

      // Ignore small ranges as non-profitable.

      // FIXME: This is a heuristic, its worth investigating the tradeoffs

      // when it should be applied.

      continue;

    }

    Mapping[Range.Offset] = Range.Length;

  }

  PPSkippedRangeMapping = std::move(Mapping);

  MinimizedContentsStorage = std::make_unique<llvm::SmallVectorMemoryBuffer>(

      std::move(MinimizedFileContents));

  // The algorithm in `getOrCreateFileSystemEntry` uses the presence of

  // minimized contents to decide whether an entry is up-to-date or not.

  // If it is up-to-date, the skipped range mappings must be already computed.

  // This is why we need to store the minimized contents **after** storing the

  // skipped range mappings. Failing to do so would lead to a data race.

  MinimizedContentsAccess.store(MinimizedContentsStorage.get());

}

DependencyScanningFilesystemSharedCache::

    DependencyScanningFilesystemSharedCache() {

  // This heuristic was chosen using a empirical testing on a

  // reasonably high core machine (iMacPro 18 cores / 36 threads). The cache

  // sharding gives a performance edge by reducing the lock contention.

  // FIXME: A better heuristic might also consider the OS to account for

  // the different cost of lock contention on different OSes.

  NumShards =

      std::max(2u, llvm::hardware_concurrency().compute_thread_count() / 4);

  CacheShards = std::make_unique<CacheShard[]>(NumShards);

}

DependencyScanningFilesystemSharedCache::SharedFileSystemEntry &

DependencyScanningFilesystemSharedCache::get(StringRef Key) {

  CacheShard &Shard = CacheShards[llvm::hash_value(Key) % NumShards];

  std::lock_guard<std::mutex> LockGuard(Shard.CacheLock);

  auto It = Shard.Cache.try_emplace(Key);

  return It.first->getValue();

}

/// Whitelist file extensions that should be minimized, treating no extension as

/// a source file that should be minimized.

///

/// This is kinda hacky, it would be better if we knew what kind of file Clang

/// was expecting instead.

static bool shouldMinimizeBasedOnExtension(StringRef Filename) {

  StringRef Ext = llvm::sys::path::extension(Filename);

  if (Ext.empty())

    return true; // C++ standard library

  return llvm::StringSwitch<bool>(Ext)

      .CasesLower(".c", ".cc", ".cpp", ".c++", ".cxx", true)

      .CasesLower(".h", ".hh", ".hpp", ".h++", ".hxx", true)

      .CasesLower(".m", ".mm", true)

      .CasesLower(".i", ".ii", ".mi", ".mmi", true)

      .CasesLower(".def", ".inc", true)

      .Default(false);

}

static bool shouldCacheStatFailures(StringRef Filename) {

  StringRef Ext = llvm::sys::path::extension(Filename);

  if (Ext.empty())

    return false; // This may be the module cache directory.

  // Only cache stat failures on source files.

  return shouldMinimizeBasedOnExtension(Filename);

}

void DependencyScanningWorkerFilesystem::disableMinimization(

    StringRef RawFilename) {

  llvm::SmallString<256> Filename;

  llvm::sys::path::native(RawFilename, Filename);

  NotToBeMinimized.insert(Filename);

}

bool DependencyScanningWorkerFilesystem::shouldMinimize(StringRef RawFilename) {

  if (!shouldMinimizeBasedOnExtension(RawFilename))

    return false;

  llvm::SmallString<256> Filename;

  llvm::sys::path::native(RawFilename, Filename);

  return !NotToBeMinimized.contains(Filename);

}

void CachedFileSystemEntry::init(llvm::ErrorOr<llvm::vfs::Status> &&MaybeStatus,

                                 StringRef Filename,

                                 llvm::vfs::FileSystem &FS) {

  if (!MaybeStatus || 
MaybeStatus->isDirectory()3.22k
)

    MaybeStat = std::move(MaybeStatus);

  else

    MaybeStat = initFile(Filename, FS);

}

llvm::ErrorOr<EntryRef>

DependencyScanningWorkerFilesystem::getOrCreateFileSystemEntry(

    StringRef Filename) {

  bool ShouldBeMinimized = shouldMinimize(Filename);

  const auto *Entry = LocalCache.getCachedEntry(Filename);

  if (Entry && 
!Entry->needsUpdate(ShouldBeMinimized)0
)

    return EntryRef(ShouldBeMinimized, *Entry);

  // FIXME: Handle PCM/PCH files.

  // FIXME: Handle module map files.

  auto &SharedCacheEntry = SharedCache.get(Filename);

  {

    std::lock_guard<std::mutex> LockGuard(SharedCacheEntry.ValueLock);

    CachedFileSystemEntry &CacheEntry = SharedCacheEntry.Value;

    if (!CacheEntry.isInitialized()) {

      auto MaybeStatus = getUnderlyingFS().status(Filename);

      if (!MaybeStatus && 
!shouldCacheStatFailures(Filename)1.26k
)

        // HACK: We need to always restat non source files if the stat fails.

        //   This is because Clang first looks up the module cache and module

        //   files before building them, and then looks for them again. If we

        //   cache the stat failure, it won't see them the second time.

        return MaybeStatus.getError();

      CacheEntry.init(std::move(MaybeStatus), Filename, getUnderlyingFS());

    }

    // Checking `needsUpdate` verifies the entry represents an opened file.

    // Only checking `needsMinimization` could lead to minimization of files

    // that we failed to load (such files don't have `OriginalContents`).

    if (CacheEntry.needsUpdate(ShouldBeMinimized))

      CacheEntry.minimizeFile();

  }

  // Store the result in the local cache.

  Entry = &SharedCacheEntry.Value;

  return EntryRef(ShouldBeMinimized, *Entry);

}

llvm::ErrorOr<llvm::vfs::Status>

DependencyScanningWorkerFilesystem::status(const Twine &Path) {

  SmallString<256> OwnedFilename;

  StringRef Filename = Path.toStringRef(OwnedFilename);

  llvm::ErrorOr<EntryRef> Result = getOrCreateFileSystemEntry(Filename);

  if (!Result)

    return Result.getError();

  return Result->getStatus();

}

namespace {

/// The VFS that is used by clang consumes the \c CachedFileSystemEntry using

/// this subclass.

class MinimizedVFSFile final : public llvm::vfs::File {

public:

  MinimizedVFSFile(std::unique_ptr<llvm::MemoryBuffer> Buffer,

                   llvm::vfs::Status Stat)

      : Buffer(std::move(Buffer)), Stat(std::move(Stat)) {}

  static llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>

  create(EntryRef Entry,

         ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings);

  llvm::ErrorOr<llvm::vfs::Status> status() override { return Stat; }

  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>

  getBuffer(const Twine &Name, int64_t FileSize, bool RequiresNullTerminator,

            bool IsVolatile) override {

    return std::move(Buffer);

  }

  std::error_code close() override { return {}; }

private:

  std::unique_ptr<llvm::MemoryBuffer> Buffer;

  llvm::vfs::Status Stat;

};

} // end anonymous namespace

llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>> MinimizedVFSFile::create(

    EntryRef Entry, ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings) {

  if (Entry.isDirectory())

    return std::make_error_code(std::errc::is_a_directory);

  llvm::ErrorOr<StringRef> Contents = Entry.getContents();

  if (!Contents)

    return Contents.getError();

  auto Result = std::make_unique<MinimizedVFSFile>(

      llvm::MemoryBuffer::getMemBuffer(*Contents, Entry.getName(),

                                       /*RequiresNullTerminator=*/false),

      *Entry.getStatus());

  const auto *EntrySkipMappings = Entry.getPPSkippedRangeMapping();

  if (EntrySkipMappings && 
!EntrySkipMappings->empty()296
 && 
PPSkipMappings87
)

    (*PPSkipMappings)[Result->Buffer->getBufferStart()] = EntrySkipMappings;

  return llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>(

      std::unique_ptr<llvm::vfs::File>(std::move(Result)));

}

llvm::ErrorOr<std::unique_ptr<llvm::vfs::File>>

DependencyScanningWorkerFilesystem::openFileForRead(const Twine &Path) {

  SmallString<256> OwnedFilename;

  StringRef Filename = Path.toStringRef(OwnedFilename);

  llvm::ErrorOr<EntryRef> Result = getOrCreateFileSystemEntry(Filename);

  if (!Result)

    return Result.getError();

  return MinimizedVFSFile::create(Result.get(), PPSkipMappings);

}