Please consider the following formatting changes to #13818

Framework/AnalysisSupport/src/RNTuplePlugin.cxx

@@ -187,6 +187,31 @@ struct RootNTupleVisitor : public ROOT::Experimental::Detail::RFieldVisitor {
     this->datatype = arrow::int32();
   }
 
+  void VisitInt8Field(const ROOT::Experimental::RField<std::int8_t>& field) override
+  {
+    this->datatype = arrow::int8();
+  }
+
+  void VisitInt16Field(const ROOT::Experimental::RField<std::int16_t>& field) override
+  {
+    this->datatype = arrow::int16();
+  }
+
+  void VisitUInt32Field(const ROOT::Experimental::RField<std::uint32_t>& field) override
+  {
+    this->datatype = arrow::uint32();
+  }
+
+  void VisitUInt8Field(const ROOT::Experimental::RField<std::uint8_t>& field) override
+  {
+    this->datatype = arrow::uint8();
+  }
+
+  void VisitUInt16Field(const ROOT::Experimental::RField<std::uint16_t>& field) override
+  {
+    this->datatype = arrow::int16();
+  }
+
   void VisitBoolField(const ROOT::Experimental::RField<bool>& field) override
   {
     this->datatype = arrow::boolean();
@@ -240,6 +265,8 @@ std::unique_ptr<ROOT::Experimental::RFieldBase> rootFieldFromArrow(std::shared_p
       return std::make_unique<RField<float>>(name);
     case arrow::Type::DOUBLE:
       return std::make_unique<RField<double>>(name);
+    case arrow::Type::STRING:
+      return std::make_unique<RField<std::string>>(name);
     default:
       throw runtime_error("Unsupported arrow column type");
   }

Framework/Core/include/Framework/RootArrowFilesystem.h

@@ -83,6 +83,11 @@ struct RootArrowFactoryPlugin {
 struct RootObjectReadingCapability {
   // The unique name of this capability
   std::string name = "unknown";
+  // Convert a logical filename to an actual object to be read
+  // This can be used, e.g. to read an RNTuple stored in
+  // a flat directory structure in a TFile vs a TTree stored inside
+  // a TDirectory (e.g. /DF_1000/o2tracks).
+  std::function<std::string(std::string)> lfn2objectPath;
   // Given a TFile, return the object which this capability support
   // Use a void * in order not to expose the kind of object to the
   // generic reading code. This is also where we load the plugin

Framework/Core/src/Plugin.cxx

@@ -179,12 +179,12 @@
 
 std::function<void*(TDirectoryFile*, std::string const&)> getHandleByClass(char const* classname)
 {
-  return [classname](TDirectoryFile* file, std::string const& path) { return file->GetObjectChecked(path.c_str(), TClass::GetClass(classname)); };
+  return [c = TClass::GetClass(classname)](TDirectoryFile* file, std::string const& path) { return file->GetObjectChecked(path.c_str(), c); };
 }
 
 std::function<void*(TBufferFile*, std::string const&)> getBufferHandleByClass(char const* classname)
 {
-  return [classname](TBufferFile* buffer, std::string const& path) { buffer->Reset(); return buffer->ReadObjectAny(TClass::GetClass(classname)); };
+  return [c = TClass::GetClass(classname)](TBufferFile* buffer, std::string const& path) { buffer->Reset(); return buffer->ReadObjectAny(c); };
 }
 
 void lazyLoadFactory(std::vector<RootArrowFactory>& implementations, char const* specs)
@@ -210,6 +210,13 @@
 
     return new RootObjectReadingCapability{
       .name = "rntuple",
+      .lfn2objectPath = [](std::string s) {
+         std::replace(s.begin()+1, s.end(), '/', '-');
+         if (s.starts_with("/")) {
+          return s;
+        } else { 
+          return "/" + s; 
+        } },
       .getHandle = getHandleByClass("ROOT::Experimental::RNTuple"),
       .getBufferHandle = getBufferHandleByClass("ROOT::Experimental::RNTuple"),
       .factory = [context]() -> RootArrowFactory& {
@@ -226,6 +233,7 @@
 
     return new RootObjectReadingCapability{
       .name = "ttree",
+      .lfn2objectPath = [](std::string s) { return s; },
       .getHandle = getHandleByClass("TTree"),
       .getBufferHandle = getBufferHandleByClass("TTree"),
       .factory = [context]() -> RootArrowFactory& {

Framework/Core/src/RootArrowFilesystem.cxx

@@ -47,7 +47,8 @@ std::shared_ptr<VirtualRootFileSystemBase> TFileFileSystem::GetSubFilesystem(arr
   // file, so that we can support TTree and RNTuple at the same time
   // without having to depend on both.
   for (auto& capability : mObjectFactory.capabilities) {
-    void* handle = capability.getHandle(mFile, source.path());
+    auto objectPath = capability.lfn2objectPath(source.path());
+    void* handle = capability.getHandle(mFile, objectPath);
     if (!handle) {
       continue;
     }
@@ -238,6 +239,7 @@ std::shared_ptr<VirtualRootFileSystemBase> TBufferFileFS::GetSubFilesystem(arrow
   // file, so that we can support TTree and RNTuple at the same time
   // without having to depend on both.
   for (auto& capability : mObjectFactory.capabilities) {
+
     void* handle = capability.getBufferHandle(mBuffer, source.path());
     if (handle) {
       mFilesystem = capability.factory().getSubFilesystem(handle);

Framework/Core/test/test_Root2ArrowTable.cxx

@@ -369,7 +369,7 @@ bool validateContents(std::shared_ptr<arrow::RecordBatch> batch)
 
 bool validateSchema(std::shared_ptr<arrow::Schema> schema)
 {
-  REQUIRE(schema->num_fields() == 10);
+  REQUIRE(schema->num_fields() == 11);
   REQUIRE(schema->field(0)->type()->id() == arrow::float32()->id());
   REQUIRE(schema->field(1)->type()->id() == arrow::float32()->id());
   REQUIRE(schema->field(2)->type()->id() == arrow::float32()->id());
@@ -380,6 +380,7 @@ bool validateSchema(std::shared_ptr<arrow::Schema> schema)
   REQUIRE(schema->field(7)->type()->id() == arrow::boolean()->id());
   REQUIRE(schema->field(8)->type()->id() == arrow::fixed_size_list(arrow::boolean(), 2)->id());
   REQUIRE(schema->field(9)->type()->id() == arrow::list(arrow::int32())->id());
+  REQUIRE(schema->field(10)->type()->id() == arrow::int8()->id());
   return true;
 }
 
@@ -435,6 +436,7 @@ TEST_CASE("RootTree2Dataset")
     bool manyBool[2];
     int vla[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
     int vlaSize = 0;
+    char byte;
 
     t->Branch("px", &px, "px/F");
     t->Branch("py", &py, "py/F");
@@ -447,6 +449,7 @@ TEST_CASE("RootTree2Dataset")
     t->Branch("manyBools", &manyBool, "manyBools[2]/O");
     t->Branch("vla_size", &vlaSize, "vla_size/I");
     t->Branch("vla", vla, "vla[vla_size]/I");
+    t->Branch("byte", &byte, "byte/B");
     // fill the tree
     for (Int_t i = 0; i < 100; i++) {
       xyz[0] = 1;
@@ -463,6 +466,7 @@ TEST_CASE("RootTree2Dataset")
       manyBool[0] = (i % 4 == 0);
       manyBool[1] = (i % 5 == 0);
       vlaSize = i % 10;
+      byte = i;
       t->Fill();
     }
   }
@@ -512,7 +516,7 @@ TEST_CASE("RootTree2Dataset")
   auto batches = (*scanner)();
   auto result = batches.result();
   REQUIRE(result.ok());
-  REQUIRE((*result)->columns().size() == 10);
+  REQUIRE((*result)->columns().size() == 11);
   REQUIRE((*result)->num_rows() == 100);
   validateContents(*result);
 
@@ -552,7 +556,7 @@ TEST_CASE("RootTree2Dataset")
     auto batchesWritten = (*scanner)();
     auto resultWritten = batches.result();
     REQUIRE(resultWritten.ok());
-    REQUIRE((*resultWritten)->columns().size() == 10);
+    REQUIRE((*resultWritten)->columns().size() == 11);
     REQUIRE((*resultWritten)->num_rows() == 100);
     validateContents(*resultWritten);
   }
@@ -586,7 +590,7 @@ TEST_CASE("RootTree2Dataset")
   auto rntupleBatchesWritten = (*rntupleScannerWritten)();
   auto rntupleResultWritten = rntupleBatchesWritten.result();
   REQUIRE(rntupleResultWritten.ok());
-  REQUIRE((*rntupleResultWritten)->columns().size() == 10);
+  REQUIRE((*rntupleResultWritten)->columns().size() == 11);
   REQUIRE(validateSchema((*rntupleResultWritten)->schema()));
   REQUIRE((*rntupleResultWritten)->num_rows() == 100);
   REQUIRE(validateContents(*rntupleResultWritten));