[llvm][vfs] Abstract in-memory node creation

[jansvoboda11]

Summary

The creation of in-memory VFS nodes happens in a single function that deduces what kind of node to create from the arguments. This leads to complicated if-then-else logic that's difficult to cleanly extend.

This patch abstracts away in-memory node creation via a type-erased factory function that's passed instead.

[dexonsmith]

LGTM, I think this cleanup makes sense.

llvm/include/llvm/Support/VirtualFileSystem.h

private:
 
   virtual void anchor();
 };
 
 namespace detail {
 
 class InMemoryDirectory;
 class InMemoryFile;
+class InMemoryNode;
+
+struct NewInMemoryNodeInfo {
+  llvm::sys::fs::UniqueID DirUID;
+  StringRef Path;
+  StringRef Name;
+  time_t ModificationTime;
+  std::unique_ptr<llvm::MemoryBuffer> Buffer;
+  uint32_t User;
+  uint32_t Group;
+  llvm::sys::fs::file_type Type;
+  llvm::sys::fs::perms Perms;
+
+  Status makeStatus() const;
+};
 
 } // namespace detail
 
 /// An in-memory file system.
 class InMemoryFileSystem : public FileSystem {
   std::unique_ptr<detail::InMemoryDirectory> Root;
   std::string WorkingDirectory;
   bool UseNormalizedPaths = true;
 
-  /// If HardLinkTarget is non-null, a hardlink is created to the To path which
-  /// must be a file. If it is null then it adds the file as the public addFile.
+  using MakeNodeFn = llvm::function_ref<std::unique_ptr<detail::InMemoryNode>(
+      detail::NewInMemoryNodeInfo)>;
+
+  /// Create node with \p MakeNode and add it into this filesystem at \p Path.
   bool addFile(const Twine &Path, time_t ModificationTime,
                std::unique_ptr<llvm::MemoryBuffer> Buffer,
                Optional<uint32_t> User, Optional<uint32_t> Group,
                Optional<llvm::sys::fs::file_type> Type,
-               Optional<llvm::sys::fs::perms> Perms,
-               const detail::InMemoryFile *HardLinkTarget);
+               Optional<llvm::sys::fs::perms> Perms, MakeNodeFn MakeNode);
 
 public:
   explicit InMemoryFileSystem(bool UseNormalizedPaths = true);
   ~InMemoryFileSystem() override;
 
   /// Add a file containing a buffer or a directory to the VFS with a
   /// path. The VFS owns the buffer.  If present, User, Group, Type
   /// and Perms apply to the newly-created file or directory.

llvm/lib/Support/VirtualFileSystem.cpp

static sys::fs::UniqueID getFileID(sys::fs::UniqueID Parent,
                                    llvm::StringRef Contents) {
   return getUniqueID(llvm::hash_combine(Parent.getFile(), Name, Contents));
 }
 static sys::fs::UniqueID getDirectoryID(sys::fs::UniqueID Parent,
                                         llvm::StringRef Name) {
   return getUniqueID(llvm::hash_combine(Parent.getFile(), Name));
 }
 
+Status detail::NewInMemoryNodeInfo::makeStatus() const {
+  UniqueID UID =
+      (Type == sys::fs::file_type::directory_file)
+          ? getDirectoryID(DirUID, Name)
+          : getFileID(DirUID, Name, Buffer ? Buffer->getBuffer() : "");
+
+  return Status(Path, UID, llvm::sys::toTimePoint(ModificationTime), User,
+                Group, Buffer ? Buffer->getBufferSize() : 0, Type, Perms);
+}
+
 InMemoryFileSystem::InMemoryFileSystem(bool UseNormalizedPaths)
     : Root(new detail::InMemoryDirectory(
           Status("", getDirectoryID(llvm::sys::fs::UniqueID(), ""),
                  llvm::sys::TimePoint<>(), 0, 0, 0,
                  llvm::sys::fs::file_type::directory_file,
                  llvm::sys::fs::perms::all_all))),
       UseNormalizedPaths(UseNormalizedPaths) {}
 
 InMemoryFileSystem::~InMemoryFileSystem() = default;
 
 std::string InMemoryFileSystem::toString() const {
   return Root->toString(/*Indent=*/0);
 }
 
 bool InMemoryFileSystem::addFile(const Twine &P, time_t ModificationTime,
                                  std::unique_ptr<llvm::MemoryBuffer> Buffer,
                                  Optional<uint32_t> User,
                                  Optional<uint32_t> Group,
                                  Optional<llvm::sys::fs::file_type> Type,
                                  Optional<llvm::sys::fs::perms> Perms,
-                                 const detail::InMemoryFile *HardLinkTarget) {
+                                 MakeNodeFn MakeNode) {
   SmallString<128> Path;
   P.toVector(Path);
 
   // Fix up relative paths. This just prepends the current working directory.
   std::error_code EC = makeAbsolute(Path);
   assert(!EC);
   (void)EC;
 
   if (useNormalizedPaths())
     llvm::sys::path::remove_dots(Path, /*remove_dot_dot=*/true);
 
   if (Path.empty())
     return false;
 
   detail::InMemoryDirectory *Dir = Root.get();
   auto I = llvm::sys::path::begin(Path), E = sys::path::end(Path);
   const auto ResolvedUser = User.getValueOr(0);
   const auto ResolvedGroup = Group.getValueOr(0);
   const auto ResolvedType = Type.getValueOr(sys::fs::file_type::regular_file);
   const auto ResolvedPerms = Perms.getValueOr(sys::fs::all_all);
-  assert(!(HardLinkTarget && Buffer) && "HardLink cannot have a buffer");
   // Any intermediate directories we create should be accessible by
   // the owner, even if Perms says otherwise for the final path.
   const auto NewDirectoryPerms = ResolvedPerms | sys::fs::owner_all;
   while (true) {
     StringRef Name = *I;
     detail::InMemoryNode *Node = Dir->getChild(Name);
     ++I;
     if (!Node) {
       if (I == E) {
         // End of the path.
-        std::unique_ptr<detail::InMemoryNode> Child;
-        if (HardLinkTarget)
-          Child.reset(new detail::InMemoryHardLink(P.str(), *HardLinkTarget));
-        else {
-          // Create a new file or directory.
-          Status Stat(
-              P.str(),
-              (ResolvedType == sys::fs::file_type::directory_file)
-                  ? getDirectoryID(Dir->getUniqueID(), Name)
-                  : getFileID(Dir->getUniqueID(), Name, Buffer->getBuffer()),
-              llvm::sys::toTimePoint(ModificationTime), ResolvedUser,
-              ResolvedGroup, Buffer->getBufferSize(), ResolvedType,
-              ResolvedPerms);
-          if (ResolvedType == sys::fs::file_type::directory_file) {
-            Child.reset(new detail::InMemoryDirectory(std::move(Stat)));
-          } else {
-            Child.reset(
-                new detail::InMemoryFile(std::move(Stat), std::move(Buffer)));
-          }
-        }
-        Dir->addChild(Name, std::move(Child));
+        Dir->addChild(
+            Name, MakeNode({Dir->getUniqueID(), Path, Name, ModificationTime,
+                            std::move(Buffer), ResolvedUser, ResolvedGroup,
+                            ResolvedType, ResolvedPerms}));
         return true;
       }
 
       // Create a new directory. Use the path up to here.
       Status Stat(
           StringRef(Path.str().begin(), Name.end() - Path.str().begin()),
           getDirectoryID(Dir->getUniqueID(), Name),
           llvm::sys::toTimePoint(ModificationTime), ResolvedUser, ResolvedGroup,

 
 bool InMemoryFileSystem::addFile(const Twine &P, time_t ModificationTime,
                                  std::unique_ptr<llvm::MemoryBuffer> Buffer,
                                  Optional<uint32_t> User,
                                  Optional<uint32_t> Group,
                                  Optional<llvm::sys::fs::file_type> Type,
                                  Optional<llvm::sys::fs::perms> Perms) {
   return addFile(P, ModificationTime, std::move(Buffer), User, Group, Type,
-                 Perms, /*HardLinkTarget=*/nullptr);
+                 Perms,
+                 [](detail::NewInMemoryNodeInfo NNI)
+                     -> std::unique_ptr<detail::InMemoryNode> {
+                   Status Stat = NNI.makeStatus();
+                   if (Stat.getType() == sys::fs::file_type::directory_file)
+                     return std::make_unique<detail::InMemoryDirectory>(Stat);
+                   return std::make_unique<detail::InMemoryFile>(
+                       Stat, std::move(NNI.Buffer));
+                 });
 }
 
 bool InMemoryFileSystem::addFileNoOwn(const Twine &P, time_t ModificationTime,
                                       const llvm::MemoryBufferRef &Buffer,
                                       Optional<uint32_t> User,
                                       Optional<uint32_t> Group,
                                       Optional<llvm::sys::fs::file_type> Type,
                                       Optional<llvm::sys::fs::perms> Perms) {
   return addFile(P, ModificationTime, llvm::MemoryBuffer::getMemBuffer(Buffer),
                  std::move(User), std::move(Group), std::move(Type),
-                 std::move(Perms));
+                 std::move(Perms),
+                 [](detail::NewInMemoryNodeInfo NNI)
+                     -> std::unique_ptr<detail::InMemoryNode> {
+                   Status Stat = NNI.makeStatus();
+                   if (Stat.getType() == sys::fs::file_type::directory_file)
+                     return std::make_unique<detail::InMemoryDirectory>(Stat);
+                   return std::make_unique<detail::InMemoryFile>(
+                       Stat, std::move(NNI.Buffer));
+                 });
 }
 
 static ErrorOr<const detail::InMemoryNode *>
 lookupInMemoryNode(const InMemoryFileSystem &FS, detail::InMemoryDirectory *Dir,
                    const Twine &P) {
   SmallString<128> Path;
   P.toVector(Path);
 

 bool InMemoryFileSystem::addHardLink(const Twine &FromPath,
                                      const Twine &ToPath) {
   auto FromNode = lookupInMemoryNode(*this, Root.get(), FromPath);
   auto ToNode = lookupInMemoryNode(*this, Root.get(), ToPath);
   // FromPath must not have been added before. ToPath must have been added
   // before. Resolved ToPath must be a File.
   if (!ToNode || FromNode || !isa<detail::InMemoryFile>(*ToNode))
     return false;
-  return this->addFile(FromPath, 0, nullptr, None, None, None, None,
-                       cast<detail::InMemoryFile>(*ToNode));
+  return addFile(FromPath, 0, nullptr, None, None, None, None,
+                 [&](detail::NewInMemoryNodeInfo NNI) {
+                   return std::make_unique<detail::InMemoryHardLink>(
+                       NNI.Path.str(), *cast<detail::InMemoryFile>(*ToNode));
+                 });
 }
 
 llvm::ErrorOr<Status> InMemoryFileSystem::status(const Twine &Path) {
   auto Node = lookupInMemoryNode(*this, Root.get(), Path);
   if (Node)
     return detail::getNodeStatus(*Node, Path);
   return Node.getError();
 }