[VFS] Implement getRealPath for OverlayFileSystem.

[ioeric]

Minor cleanup

[ioeric]

Fix test...

[bkramer]

lg

lib/Basic/VirtualFileSystem.cpp

387

Those should probably get const overloads. Doesn't have to be in this change though.

[ioeric]

• Add and use const_iterator.

include/clang/Basic/VirtualFileSystem.h

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 getRealPath(const Twine &Path,
+                              SmallVectorImpl<char> &Output) const override;
 
   using iterator = FileSystemList::reverse_iterator;
   
   /// Get an iterator pointing to the most recently added file system.
   iterator overlays_begin() { return FSList.rbegin(); }
 
   /// Get an iterator pointing one-past the least recently added file
   /// system.

lib/Basic/VirtualFileSystem.cpp

 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::getRealPath(const Twine &Path,
+                               SmallVectorImpl<char> &Output) const {
+  // Not using overlays_begin/end because this method is const.
+  for (auto I = FSList.rbegin(), E = FSList.rend(); I != E; ++I) {
+    auto &FS = *I;
+    if (!FS->exists(Path))
+        continue;
+    return FS->getRealPath(Path, Output);
+  }
+  return errc::no_such_file_or_directory;
+}
+
 clang::vfs::detail::DirIterImpl::~DirIterImpl() = default;
 
 namespace {
 
 class OverlayFSDirIterImpl : public clang::vfs::detail::DirIterImpl {
   OverlayFileSystem &Overlays;
   std::string Path;
   OverlayFileSystem::iterator CurrentFS;

unittests/Basic/VirtualFileSystemTest.cpp

openFileForRead(const Twine &Path) override {
     return S.getError();
   }
   llvm::ErrorOr<std::string> getCurrentWorkingDirectory() const override {
     return std::string();
   }
   std::error_code setCurrentWorkingDirectory(const Twine &Path) override {
     return std::error_code();
   }
+  // Map any symlink to "/symlink".
+  std::error_code getRealPath(const Twine &Path,
+                              SmallVectorImpl<char> &Output) const override {
+    auto I = FilesAndDirs.find(Path.str());
+    if (I == FilesAndDirs.end())
+      return make_error_code(llvm::errc::no_such_file_or_directory);
+    if (I->second.isSymlink()) {
+      Twine("/symlink").toVector(Output);
+      return std::error_code();
+    }
+    Path.toVector(Output);
+    return std::error_code();
+  }
 
   struct DirIterImpl : public clang::vfs::detail::DirIterImpl {
     std::map<std::string, vfs::Status> &FilesAndDirs;
     std::map<std::string, vfs::Status>::iterator I;
     std::string Path;
     bool isInPath(StringRef S) {
       if (Path.size() < S.size() && S.find(Path) == 0) {
         auto LastSep = S.find_last_of('/');
TEST(VirtualFileSystemTest, BaseOnlyOverlay) {
   EXPECT_FALSE(Status.getError());
 
   ErrorOr<vfs::Status> Status2((std::error_code()));
   Status2 = O->status("/foo");
   EXPECT_FALSE(Status2.getError());
   EXPECT_TRUE(Status->equivalent(*Status2));
 }
 
+TEST(VirtualFileSystemTest, GetRealPathInOverlay) {
+  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  Lower->addRegularFile("/foo");
+  Lower->addSymlink("/lower_link");
+  IntrusiveRefCntPtr<DummyFileSystem> Upper(new DummyFileSystem());
+
+  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+      new vfs::OverlayFileSystem(Lower));
+  O->pushOverlay(Upper);
+
+  // Regular file.
+  SmallString<16> RealPath;
+  EXPECT_FALSE(O->getRealPath("/foo", RealPath));
+  EXPECT_EQ(RealPath.str(), "/foo");
+
+  // Expect no error getting real path for symlink in lower overlay.
+  EXPECT_FALSE(O->getRealPath("/lower_link", RealPath));
+  EXPECT_EQ(RealPath.str(), "/symlink");
+
+  // Try a non-existing link.
+  EXPECT_EQ(O->getRealPath("/upper_link", RealPath),
+            errc::no_such_file_or_directory);
+
+  // Add a new symlink in upper.
+  Upper->addSymlink("/upper_link");
+  EXPECT_FALSE(O->getRealPath("/upper_link", RealPath));
+  EXPECT_EQ(RealPath.str(), "/symlink");
+}
+
 TEST(VirtualFileSystemTest, OverlayFiles) {
   IntrusiveRefCntPtr<DummyFileSystem> Base(new DummyFileSystem());
   IntrusiveRefCntPtr<DummyFileSystem> Middle(new DummyFileSystem());
   IntrusiveRefCntPtr<DummyFileSystem> Top(new DummyFileSystem());
   IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Base));
   O->pushOverlay(Middle);
   O->pushOverlay(Top);