[ntuple] add basic TBrowser support

Author: jblomer

tree/ntuple/CMakeLists.txt

@@ -64,6 +64,7 @@ SOURCES
   src/RFieldVisitor.cxx
   src/RMiniFile.cxx
   src/RNTuple.cxx
+  src/RNTupleClassicBrowse.cxx
   src/RNTupleDescriptor.cxx
   src/RNTupleDescriptorFmt.cxx
   src/RNTupleFillContext.cxx

tree/ntuple/inc/ROOT/RNTuple.hxx

@@ -18,6 +18,7 @@
 
 #include <cstdint>
 
+class TBrowser;
 class TCollection;
 class TFile;
 class TFileMergeInfo;
@@ -129,6 +130,9 @@ public:
    /// Merge this NTuple with the input list entries
    Long64_t Merge(TCollection *input, TFileMergeInfo *mergeInfo);
 
+   /// Custom callback for the classic TBrowser
+   void Browse(TBrowser *) const;
+
    /// NOTE: if you change this version you also need to update RTFNTuple::fClassVersion in RMiniFile.cxx
    ClassDefNV(RNTuple, 2);
 }; // class RNTuple

tree/ntuple/src/RNTupleClassicBrowse.cxx

@@ -0,0 +1,60 @@
+/// \file RNTupleClassicBrowse.cxx
+/// \ingroup NTuple
+/// \author Jakob Blomer <[email protected]>
+/// \date 2025-05-26
+
+/*************************************************************************
+ * Copyright (C) 1995-2025, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+#include <ROOT/RNTuple.hxx>
+#include <ROOT/RNTupleReader.hxx>
+#include <ROOT/RNTupleUtil.hxx>
+
+#include <TBrowser.h>
+#include <TObject.h>
+
+#include <memory>
+
+namespace {
+
+class RFieldBrowsable final : public TObject {
+private:
+   std::shared_ptr<ROOT::RNTupleReader> fReader;
+   ROOT::DescriptorId_t fFieldId = ROOT::kInvalidDescriptorId;
+
+public:
+   RFieldBrowsable(std::shared_ptr<ROOT::RNTupleReader> reader, ROOT::DescriptorId_t fieldId)
+      : fReader(reader), fFieldId(fieldId)
+   {
+   }
+
+   void Browse(TBrowser *b) final
+   {
+      if (!b)
+         return;
+
+      const auto &desc = fReader->GetDescriptor();
+      for (const auto &f : desc.GetFieldIterable(fFieldId)) {
+         b->Add(new RFieldBrowsable(fReader, f.GetId()), f.GetFieldName().c_str());
+      }
+   }
+};
+
+} // anonymous namespace
+
+void ROOT::RNTuple::Browse(TBrowser *b) const
+{
+   if (!b)
+      return;
+
+   std::shared_ptr<ROOT::RNTupleReader> reader = RNTupleReader::Open(*this);
+   const auto &desc = reader->GetDescriptor();
+   for (const auto &f : desc.GetTopLevelFields()) {
+      b->Add(new RFieldBrowsable(reader, f.GetId()), f.GetFieldName().c_str());
+   }
+}