[ntuple] fix set field reconciliation

Author: jblomer

tree/dataframe/test/datasource_ntuple.cxx

@@ -455,7 +455,7 @@ TEST_F(RNTupleDSTest, AlternativeColumnTypes)
 
    auto multipleAlternativeTypes =
       df.Define("nJets", [](const std::vector<float> &jets) { return jets.size(); }, {"jets"})
-         .Define("smallestJet", [](const std::set<float> &jets) { return *(jets.begin()); }, {"jets"})
+         .Define("smallestJet", [](const std::multiset<float> &jets) { return *(jets.begin()); }, {"jets"})
          .Min<float>("smallestJet")
          .GetValue();
    EXPECT_FLOAT_EQ(1.f, multipleAlternativeTypes);

tree/ntuple/inc/ROOT/RField/RFieldProxiedCollection.hxx

@@ -154,7 +154,7 @@ protected:
    /// (Attach() and setting fItemSize)
    RProxiedCollectionField(std::string_view fieldName, TClass *classp);
 
-   std::unique_ptr<RFieldBase> CloneImpl(std::string_view newName) const final;
+   std::unique_ptr<RFieldBase> CloneImpl(std::string_view newName) const override;
    const RColumnRepresentations &GetColumnRepresentations() const final;
    void GenerateColumns() final;
    void GenerateColumns(const ROOT::RNTupleDescriptor &desc) final;
@@ -165,7 +165,7 @@ protected:
    std::size_t AppendImpl(const void *from) final;
    void ReadGlobalImpl(ROOT::NTupleSize_t globalIndex, void *to) final;
 
-   void ReconcileOnDiskField(const RNTupleDescriptor &desc) final;
+   void ReconcileOnDiskField(const RNTupleDescriptor &desc) override;
 
    void CommitClusterImpl() final { fNWritten = 0; }
 
@@ -364,6 +364,15 @@ public:
       kMultiSet,
       kUnorderedMultiSet
    };
+
+private:
+   ESetType fSetType;
+
+protected:
+   std::unique_ptr<RFieldBase> CloneImpl(std::string_view newName) const final;
+   void ReconcileOnDiskField(const RNTupleDescriptor &desc) final;
+
+public:
    RSetField(std::string_view fieldName, ESetType setType, std::unique_ptr<RFieldBase> itemField);
    RSetField(RSetField &&other) = default;
    RSetField &operator=(RSetField &&other) = default;

tree/ntuple/src/RFieldMeta.cxx

@@ -882,12 +882,34 @@ ROOT::RMapField::RMapField(std::string_view fieldName, EMapType mapType, std::un
 //------------------------------------------------------------------------------
 
 ROOT::RSetField::RSetField(std::string_view fieldName, ESetType setType, std::unique_ptr<RFieldBase> itemField)
-   : ROOT::RProxiedCollectionField(fieldName, EnsureValidClass(BuildSetTypeName(setType, *itemField)))
+   : ROOT::RProxiedCollectionField(fieldName, EnsureValidClass(BuildSetTypeName(setType, *itemField))),
+     fSetType(setType)
 {
    fItemSize = itemField->GetValueSize();
    Attach(std::move(itemField));
 }
 
+std::unique_ptr<ROOT::RFieldBase> ROOT::RSetField::CloneImpl(std::string_view newName) const
+{
+   return std::make_unique<RSetField>(newName, fSetType, fSubfields[0]->Clone(fSubfields[0]->GetFieldName()));
+}
+
+void ROOT::RSetField::ReconcileOnDiskField(const RNTupleDescriptor &desc)
+{
+   static const std::vector<std::string> prefixesRegular = {"std::set<", "std::unordered_set<", "std::map<"};
+
+   const auto &fieldDesc = desc.GetFieldDescriptor(GetOnDiskId());
+   EnsureMatchingOnDiskField(fieldDesc, kDiffTypeName).ThrowOnError();
+
+   switch (fSetType) {
+   case ESetType::kSet:
+   case ESetType::kUnorderedSet: EnsureMatchingTypePrefix(fieldDesc, prefixesRegular).ThrowOnError(); break;
+   default:
+      break;
+      // no restrictions for multisets
+   }
+}
+
 //------------------------------------------------------------------------------
 
 namespace {