[ntuple] Schema evolution fixes

roottest/root/ntuple/evolution/NtplEvolv_v3_LinkDef.h

@@ -2,6 +2,7 @@
 
 #pragma link C++ class NtplEvolv+;
 
-#pragma read sourceClass="NtplEvolv" version="[1-]" source="" targetClass="NtplEvolv" target="fA" code = "{ fA = 13; }"
+#pragma read sourceClass="NtplEvolv" version="[1-]" source="int fA;" targetClass="NtplEvolv" target="fA" \
+   code = "{ fA = onfile.fA + 13; }"
 
 #endif

roottest/root/ntuple/evolution/read_ntplevolv.cxx

@@ -1,17 +1,40 @@
 #include <ROOT/RNTupleReader.hxx>
 
+#include <TObject.h>
+#include <TROOT.h>
+#include <TSeqCollection.h>
+
 #include "NtplEvolv_v3.hxx"
 
 #include <iostream>
+#include <string>
 
 int main()
 {
+   // At this point, we expect NtplEvolv _not_ being present in the global streamer infos
+   for (auto si : TRangeDynCast<TObject>(gROOT->GetListOfStreamerInfo())) {
+      if (std::string(si->GetName()) == "NtplEvolv")
+         return 2;
+   }
+
    auto reader = ROOT::RNTupleReader::Open("ntpl", "root_test_ntpl_evolution.root");
 
+   reader->GetModel();
+   // Now, reader should have loaded the streamer info for NtplEvolv
+   bool streamerInfoFound = false;
+   for (auto si : TRangeDynCast<TObject>(gROOT->GetListOfStreamerInfo())) {
+      if (std::string(si->GetName()) == "NtplEvolv") {
+         streamerInfoFound = true;
+         break;
+      }
+   }
+   if (!streamerInfoFound)
+      return 3;
+
    reader->LoadEntry(0);
 
    auto a = reader->GetModel().GetDefaultEntry().GetPtr<NtplEvolv>("event")->fA;
    std::cout << "Result of event.fA: " << a << std::endl;
 
-   return a != 13;
+   return a != 14;
 }

roottest/root/ntuple/unversioned/CMakeLists.txt

@@ -0,0 +1,38 @@
+ROOTTEST_GENERATE_DICTIONARY(
+  ntplhit_old_dict
+  ${CMAKE_CURRENT_SOURCE_DIR}/NtplHit_Old.hxx
+  LINKDEF ${CMAKE_CURRENT_SOURCE_DIR}/NtplHit_Old_LinkDef.h
+  NO_ROOTMAP NO_CXXMODULE
+  FIXTURES_SETUP generated_ntplhit_old_dictionary
+)
+
+ROOTTEST_GENERATE_EXECUTABLE(
+  write_ntplhit
+  write_ntplhit.cxx ntplhit_old_dict.cxx
+  LIBRARIES Core RIO ROOTNTuple
+  FIXTURES_REQUIRED generated_ntplhit_old_dictionary
+  FIXTURES_SETUP write_ntplhit_excutable)
+
+ROOTTEST_ADD_TEST(write_ntplhit
+                  EXEC ./write_ntplhit
+                  FIXTURES_REQUIRED write_ntplhit_excutable
+                  FIXTURES_SETUP write_ntplhit_done)
+
+ROOTTEST_GENERATE_DICTIONARY(
+  ntplhit_new_dict
+  ${CMAKE_CURRENT_SOURCE_DIR}/NtplHit_New.hxx
+  LINKDEF ${CMAKE_CURRENT_SOURCE_DIR}/NtplHit_New_LinkDef.h
+  NO_ROOTMAP NO_CXXMODULE
+  FIXTURES_SETUP generated_ntplhit_new_dictionary
+)
+
+ROOTTEST_GENERATE_EXECUTABLE(
+  read_ntplhit
+  read_ntplhit.cxx ntplhit_new_dict.cxx
+  LIBRARIES Core RIO ROOTNTuple
+  FIXTURES_REQUIRED generated_ntplhit_new_dictionary
+  FIXTURES_SETUP read_ntplhit_excutable)
+
+ROOTTEST_ADD_TEST(read_ntplhit
+                  EXEC ./read_ntplhit
+                  FIXTURES_REQUIRED read_ntplhit_excutable write_ntplhit_done)

roottest/root/ntuple/unversioned/NtplHit_New.hxx

@@ -0,0 +1,11 @@
+#ifndef NTPL_HIT_NEW_H
+#define NTPL_HIT_NEW_H
+
+struct Hit {
+   int fA_r{0};
+   int fB_r{0};
+   double fX_r{0};
+   double fY_r{0};
+};
+
+#endif // NTPL_HIT_NEW_H

roottest/root/ntuple/unversioned/NtplHit_New_LinkDef.h

@@ -0,0 +1,9 @@
+#ifdef __ROOTCLING__
+
+#pragma link C++ class Hit+;
+
+#pragma read sourceClass="Hit" targetClass="Hit" checksum="[2391364433]" \
+   source="int fA; int fB; double fX; double fY" target="fA_r,fB_r,fX_r,fY_r" \
+   code="{ fA_r = onfile.fA; fB_r = onfile.fB; fX_r = onfile.fX; fY_r = onfile.fY; }"
+
+#endif

roottest/root/ntuple/unversioned/NtplHit_Old.hxx

@@ -0,0 +1,11 @@
+#ifndef NTPL_HIT_OLD_H
+#define NTPL_HIT_OLD_H
+
+struct Hit {
+   int fA{0};
+   int fB{0};
+   double fX{0};
+   double fY{0};
+};
+
+#endif // NTPL_HIT_OLD_H

roottest/root/ntuple/unversioned/NtplHit_Old_LinkDef.h

@@ -0,0 +1,5 @@
+#ifdef __ROOTCLING__
+
+#pragma link C++ class Hit+;
+
+#endif

roottest/root/ntuple/unversioned/read_ntplhit.cxx

@@ -0,0 +1,31 @@
+#include <ROOT/RNTupleReader.hxx>
+
+#include <cstdio>
+#include <vector>
+
+#include "NtplHit_New.hxx"
+
+static int gFails = 0;
+
+static void Check(char const *m, double want, double got)
+{
+   bool ok = want == got;
+   if (!ok)
+      ++gFails;
+   printf("%-4s want %-4g got %-22.17g %s\n", m, want, got, ok ? "ok" : "WRONG");
+}
+
+int main()
+{
+   auto r = ROOT::RNTupleReader::Open("r", "root_test_ntpl_unversioned.root");
+   auto v = r->GetModel().GetDefaultEntry().GetPtr<std::vector<Hit>>("hits");
+
+   r->LoadEntry(0);
+
+   Check("fA_r", 1, v->at(0).fA_r);
+   Check("fB_r", 2, v->at(0).fB_r);
+   Check("fX_r", 1.5, v->at(0).fX_r);
+   Check("fY_r", 2.5, v->at(0).fY_r);
+
+   return gFails;
+}

roottest/root/ntuple/unversioned/write_ntplhit.cxx

@@ -0,0 +1,25 @@
+#include <ROOT/RNTupleModel.hxx>
+#include <ROOT/RNTupleWriter.hxx>
+
+#include <TClass.h>
+
+#include <cstdio>
+#include <vector>
+
+#include "NtplHit_Old.hxx"
+
+int main()
+{
+   Hit h;
+   h.fA = 1;
+   h.fB = 2;
+   h.fX = 1.5;
+   h.fY = 2.5;
+   auto model = ROOT::RNTupleModel::Create();
+   auto pv = model->MakeField<std::vector<Hit>>("hits");
+   auto w = ROOT::RNTupleWriter::Recreate(std::move(model), "r", "root_test_ntpl_unversioned.root");
+   *pv = {h};
+   w->Fill();
+   printf("CHECKSUM %u\n", TClass::GetClass("Hit")->GetCheckSum());
+   return 0;
+}

tree/ntuple/inc/ROOT/RPageStorageFile.hxx

@@ -139,6 +139,8 @@ private:
    RNTupleDescriptorBuilder fDescriptorBuilder;
    /// Tracks the last read offset for seek distance calculation
    std::uint64_t fLastOffset = 0;
+   /// Set to true after the first call to LoadStreamerInfo()
+   bool fHasStreamerInfo = false;
 
    /// File-specific I/O performance counters
    struct RFileCounters {

tree/ntuple/src/RFieldMeta.cxx

@@ -552,7 +552,23 @@ std::unique_ptr<ROOT::RFieldBase> ROOT::RClassField::BeforeConnectPageSource(ROO
       // A staging class (conversion streamer info) only exists if there is at least one rule that has an
       // on disk source member defined.
       if (hasSources) {
-         SetStagingClass(fieldDesc.GetTypeName(), fieldDesc.GetTypeVersion());
+         // For unversioned classes, the in-memory layout may by chance have the same transient version number
+         // than the recorded (transient, at the time of writing) on-disk version.  Therefore, we also need to compare
+         // the checksums to find out if we need a conversion streamer info.
+         std::uint32_t assignedVersionForOnDiskLayout = fieldDesc.GetTypeVersion();
+         R__ASSERT(fieldDesc.GetTypeChecksum());
+         if (fieldDesc.GetTypeVersion() != GetTypeVersion() || *fieldDesc.GetTypeChecksum() != fClass->GetCheckSum() ||
+             fieldDesc.GetTypeName() != GetTypeName()) {
+            // We need the on-disk streamer info for the conversion streamer info
+            pageSource.LoadStreamerInfo();
+
+            auto oldCl = TClass::GetClass(fieldDesc.GetTypeName().c_str());
+            R__ASSERT(oldCl);
+            auto onDiskStreamerInfo = oldCl->FindStreamerInfo(*fieldDesc.GetTypeChecksum());
+            R__ASSERT(onDiskStreamerInfo);
+            assignedVersionForOnDiskLayout = onDiskStreamerInfo->GetClassVersion();
+         }
+         SetStagingClass(fieldDesc.GetTypeName(), assignedVersionForOnDiskLayout);
          PrepareStagingArea(rules, desc, fieldDesc);
          for (auto &[_, si] : fStagingItems) {
             Internal::CallConnectPageSourceOnField(*si.fField, pageSource);

tree/ntuple/src/RPageStorageFile.cxx

@@ -516,6 +516,7 @@ std::unique_ptr<ROOT::Internal::RPageSource> ROOT::Internal::RPageSourceFile::Cl
    auto clone = new RPageSourceFile(fNTupleName, fOptions);
    clone->fFile = fFile->Clone();
    clone->fReader = ROOT::Internal::RMiniFileReader(clone->fFile.get());
+   clone->fHasStreamerInfo = fHasStreamerInfo;
    return std::unique_ptr<RPageSourceFile>(clone);
 }
 
@@ -714,5 +715,9 @@ ROOT::Internal::RPageSourceFile::LoadClusters(std::span<RCluster::RKey> clusterK
 
 void ROOT::Internal::RPageSourceFile::LoadStreamerInfo()
 {
+   if (fHasStreamerInfo)
+      return;
+
    fReader.LoadStreamerInfo();
+   fHasStreamerInfo = true;
 }