[ntuple] add cloning for RImplSimple-based writer

Author: silverweed

tree/ntuple/src/RMiniFile.cxx

@@ -1326,6 +1326,14 @@ ROOT::Internal::RNTupleFileWriter::CloneWithDifferentName(std::string_view ntupl
 {
    if (auto *file = std::get_if<RImplTFile>(&fFile)) {
       return Append(ntupleName, *file->fDirectory, fNTupleAnchor.fMaxKeySize);
+   } else if (auto *file = std::get_if<RImplSimple>(&fFile)) {
+      auto writer = std::unique_ptr<RNTupleFileWriter>(new RNTupleFileWriter(ntupleName, fNTupleAnchor.GetMaxKeySize()));
+      auto &clonedFile = std::get<RImplSimple>(writer->fFile);
+      clonedFile.fShared = file->fShared;
+      clonedFile.fDirectIO = file->fDirectIO;
+      // TODO: use passed options
+      clonedFile.AllocateBuffers(RNTupleWriteOptions().GetWriteBufferSize());
+      return writer;
    }
    // TODO: support also non-TFile-based writers
    throw ROOT::RException(R__FAIL("cannot clone a non-TFile-based RNTupleFileWriter."));