Extend virtual file system with `isLocal` method.

[JDevlieghere]

Summary

Expose the llvm::sys::fs::is_local function through the VFS.

[JDevlieghere]

Ping

[kristina]

LGTM.

[vsapsai]

Depending on isLocal usage, it can be worth implementing it for RedirectingFileSystem.

include/llvm/Support/VirtualFileSystem.h

public:
   /// symlinks. For real file system, this uses `llvm::sys::fs::real_path`.
   /// This returns errc::operation_not_permitted if not implemented by subclass.
   virtual std::error_code getRealPath(const Twine &Path,
                                       SmallVectorImpl<char> &Output) const;
 
   /// Check whether a file exists. Provided for convenience.
   bool exists(const Twine &Path);
 
+  /// Is the file mounted on a local filesystem?
+  virtual std::error_code isLocal(const Twine &Path, bool &Result);
+
   /// Make \a Path an absolute path.
   ///
   /// Makes \a Path absolute using the current directory if it is not already.
   /// An empty \a Path will result in the current directory.
   ///
   /// /absolute/path   => /absolute/path
   /// relative/../path => <current-directory>/relative/../path
   ///
public:
   void pushOverlay(IntrusiveRefCntPtr<FileSystem> FS);
 
   llvm::ErrorOr<Status> status(const Twine &Path) override;
   llvm::ErrorOr<std::unique_ptr<File>>
   openFileForRead(const Twine &Path) override;
   directory_iterator dir_begin(const Twine &Dir, std::error_code &EC) override;
   llvm::ErrorOr<std::string> getCurrentWorkingDirectory() const override;
   std::error_code setCurrentWorkingDirectory(const Twine &Path) override;
+  std::error_code isLocal(const Twine &Path, bool &Result) override;
   std::error_code getRealPath(const Twine &Path,
                               SmallVectorImpl<char> &Output) const override;
 
   using iterator = FileSystemList::reverse_iterator;
   using const_iterator = FileSystemList::const_reverse_iterator;
 
   /// Get an iterator pointing to the most recently added file system.
   iterator overlays_begin() { return FSList.rbegin(); }
public:
   /// Canonicalizes \p Path by combining with the current working
   /// directory and normalizing the path (e.g. remove dots). If the current
   /// working directory is not set, this returns errc::operation_not_permitted.
   ///
   /// This doesn't resolve symlinks as they are not supported in in-memory file
   /// system.
   std::error_code getRealPath(const Twine &Path,
                               SmallVectorImpl<char> &Output) const override;
-
+  std::error_code isLocal(const Twine &Path, bool &Result) override;
   std::error_code setCurrentWorkingDirectory(const Twine &Path) override;
 };
 
 /// Get a globally unique ID for a virtual file or directory.
 llvm::sys::fs::UniqueID getNextVirtualUniqueID();
 
 /// Gets a \p FileSystem for a virtual file system described in YAML
 /// format.

lib/Support/VirtualFileSystem.cpp

std::error_code FileSystem::makeAbsolute(SmallVectorImpl<char> &Path) const {
   return llvm::sys::fs::make_absolute(WorkingDir.get(), Path);
 }
 
 std::error_code FileSystem::getRealPath(const Twine &Path,
                                         SmallVectorImpl<char> &Output) const {
   return errc::operation_not_permitted;
 }
 
+std::error_code FileSystem::isLocal(const Twine &Path, bool &Result) {
+  return errc::operation_not_permitted;
+}
+
 bool FileSystem::exists(const Twine &Path) {
   auto Status = status(Path);
   return Status && Status->exists();
 }
 
 #ifndef NDEBUG
 static bool isTraversalComponent(StringRef Component) {
   return Component.equals("..") || Component.equals(".");

 class RealFileSystem : public FileSystem {
 public:
   ErrorOr<Status> status(const Twine &Path) override;
   ErrorOr<std::unique_ptr<File>> openFileForRead(const Twine &Path) override;
   directory_iterator dir_begin(const Twine &Dir, std::error_code &EC) override;
 
   llvm::ErrorOr<std::string> getCurrentWorkingDirectory() const override;
   std::error_code setCurrentWorkingDirectory(const Twine &Path) override;
+  std::error_code isLocal(const Twine &Path, bool &Result) override;
   std::error_code getRealPath(const Twine &Path,
                               SmallVectorImpl<char> &Output) const override;
 
 private:
   mutable std::mutex CWDMutex;
   mutable std::string CWDCache;
 };
 
if (auto EC = llvm::sys::fs::set_current_path(Path))
     return EC;
 
   // Invalidate cache.
   std::lock_guard<std::mutex> Lock(CWDMutex);
   CWDCache.clear();
   return std::error_code();
 }
 
+std::error_code RealFileSystem::isLocal(const Twine &Path, bool &Result) {
+  return llvm::sys::fs::is_local(Path, Result);
+}
+
 std::error_code
 RealFileSystem::getRealPath(const Twine &Path,
                             SmallVectorImpl<char> &Output) const {
   return llvm::sys::fs::real_path(Path, Output);
 }
 
 IntrusiveRefCntPtr<FileSystem> vfs::getRealFileSystem() {
   static IntrusiveRefCntPtr<FileSystem> FS = new RealFileSystem();

 std::error_code
 OverlayFileSystem::setCurrentWorkingDirectory(const Twine &Path) {
   for (auto &FS : FSList)
     if (std::error_code EC = FS->setCurrentWorkingDirectory(Path))
       return EC;
   return {};
 }
 
+std::error_code OverlayFileSystem::isLocal(const Twine &Path, bool &Result) {
+  for (auto &FS : FSList)
+    if (FS->exists(Path))
+      return FS->isLocal(Path, Result);
+  return errc::no_such_file_or_directory;
+}
+
 std::error_code
 OverlayFileSystem::getRealPath(const Twine &Path,
                                SmallVectorImpl<char> &Output) const {
   for (auto &FS : FSList)
     if (FS->exists(Path))
       return FS->getRealPath(Path, Output);
   return errc::no_such_file_or_directory;
 }
if (!CWD || CWD->empty())
     return errc::operation_not_permitted;
   Path.toVector(Output);
   if (auto EC = makeAbsolute(Output))
     return EC;
   llvm::sys::path::remove_dots(Output, /*remove_dot_dot=*/true);
   return {};
 }
 
+std::error_code InMemoryFileSystem::isLocal(const Twine &Path, bool &Result) {
+  Result = false;
+  return {};
+}
+
 } // namespace vfs
 } // namespace llvm
 
 //===-----------------------------------------------------------------------===/
 // RedirectingFileSystem implementation
 //===-----------------------------------------------------------------------===/
 
 namespace {
public:
   llvm::ErrorOr<std::string> getCurrentWorkingDirectory() const override {
     return ExternalFS->getCurrentWorkingDirectory();
   }
 
   std::error_code setCurrentWorkingDirectory(const Twine &Path) override {
     return ExternalFS->setCurrentWorkingDirectory(Path);
   }
 
+  std::error_code isLocal(const Twine &Path, bool &Result) override {
+    return ExternalFS->isLocal(Path, Result);
+  }
+
   directory_iterator dir_begin(const Twine &Dir, std::error_code &EC) override {
     ErrorOr<Entry *> E = lookupPath(Dir);
     if (!E) {
       EC = E.getError();
       if (IsFallthrough && EC == errc::no_such_file_or_directory)
         return ExternalFS->dir_begin(Dir, EC);
       return {};
     }

unittests/Support/VirtualFileSystemTest.cpp

TEST_F(InMemoryFileSystemTest, WorkingDirectory) {
   NormalizedFS.setCurrentWorkingDirectory(".");
   ASSERT_EQ("/b/c",
             getPosixPath(NormalizedFS.getCurrentWorkingDirectory().get()));
   NormalizedFS.setCurrentWorkingDirectory("..");
   ASSERT_EQ("/b",
             getPosixPath(NormalizedFS.getCurrentWorkingDirectory().get()));
 }
 
+TEST_F(InMemoryFileSystemTest, IsLocal) {
+  FS.setCurrentWorkingDirectory("/b");
+  FS.addFile("c", 0, MemoryBuffer::getMemBuffer(""));
+
+  std::error_code EC;
+  bool IsLocal = true;
+  EC = FS.isLocal("c", IsLocal);
+  ASSERT_FALSE(EC);
+  ASSERT_FALSE(IsLocal);
+}
+
 #if !defined(_WIN32)
 TEST_F(InMemoryFileSystemTest, GetRealPath) {
   SmallString<16> Path;
   EXPECT_EQ(FS.getRealPath("b", Path), errc::operation_not_permitted);
 
   auto GetRealPath = [this](StringRef P) {
     SmallString<16> Output;
     auto EC = FS.getRealPath(P, Output);