[ntuple] test I/O rules for streamer fields

Author: jblomer

tree/ntuple/test/StreamerField.hxx

@@ -54,4 +54,14 @@ struct PolyContainer {
    std::unique_ptr<PolyBase> fPoly;
 };
 
+template <typename T>
+struct OldStreamerName {
+   T fValue;
+};
+
+template <typename T>
+struct NewStreamerName {
+   T fValue;
+};
+
 #endif // ROOT_RNTuple_Test_StreamerField

tree/ntuple/test/StreamerFieldLinkDef.h

@@ -12,4 +12,8 @@
 #pragma link C++ class PolyB + ;
 #pragma link C++ options = rntupleStreamerMode(true) class PolyContainer + ;
 
+#pragma link C++ options = rntupleStreamerMode(true), version(3) class OldStreamerName < int> + ;
+#pragma link C++ options = rntupleStreamerMode(true), version(3) class NewStreamerName < int> + ;
+#pragma read sourceClass = "OldStreamerName<int>" targetClass = "NewStreamerName<int>" version = "[3]"
+
 #endif

tree/ntuple/test/rfield_streamer.cxx

@@ -305,3 +305,25 @@ TEST(RField, StreamerMergeIncremental)
    EXPECT_TRUE(seenStreamerInfos[2]);
    EXPECT_TRUE(seenStreamerInfos[3]);
 }
+
+TEST(RField, StreamerSchemaEvolution)
+{
+   FileRaii fileGuard("test_ntuple_rfield_streamer_schema_evolution.root");
+   {
+      auto model = RNTupleModel::Create();
+      model->AddField(RFieldBase::Create("f", "OldStreamerName<int>").Unwrap());
+      auto writer = RNTupleWriter::Recreate(std::move(model), "ntpl", fileGuard.GetPath());
+      auto ptrF = writer->GetModel().GetDefaultEntry().GetPtr<OldStreamerName<int>>("f");
+      ptrF->fValue = 137;
+      writer->Fill();
+   }
+
+   auto model = RNTupleModel::Create();
+   model->AddField(RFieldBase::Create("f", "NewStreamerName<int>").Unwrap());
+   auto reader = RNTupleReader::Open(std::move(model), "ntpl", fileGuard.GetPath());
+
+   ASSERT_EQ(1U, reader->GetNEntries());
+   auto ptrF = reader->GetModel().GetDefaultEntry().GetPtr<NewStreamerName<int>>("f");
+   reader->LoadEntry(0);
+   EXPECT_EQ(137, ptrF->fValue);
+}