[ntuple] fix map field reconciliation

Author: jblomer

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

@@ -277,6 +277,15 @@ public:
       kMultiMap,
       kUnorderedMultiMap
    };
+
+private:
+   EMapType fMapType;
+
+protected:
+   std::unique_ptr<RFieldBase> CloneImpl(std::string_view newName) const final;
+   void ReconcileOnDiskField(const RNTupleDescriptor &desc) final;
+
+public:
    RMapField(std::string_view fieldName, EMapType mapType, std::unique_ptr<RFieldBase> itemField);
    RMapField(RMapField &&other) = default;
    RMapField &operator=(RMapField &&other) = default;

tree/ntuple/src/RFieldMeta.cxx

@@ -871,14 +871,35 @@ void ROOT::RProxiedCollectionField::AcceptVisitor(ROOT::Detail::RFieldVisitor &v
 //------------------------------------------------------------------------------
 
 ROOT::RMapField::RMapField(std::string_view fieldName, EMapType mapType, std::unique_ptr<RFieldBase> itemField)
-   : RProxiedCollectionField(fieldName, EnsureValidClass(BuildMapTypeName(mapType, itemField.get())))
+   : RProxiedCollectionField(fieldName, EnsureValidClass(BuildMapTypeName(mapType, itemField.get()))), fMapType(mapType)
 {
    auto *itemClass = fProxy->GetValueClass();
    fItemSize = itemClass->GetClassSize();
 
    Attach(std::move(itemField));
 }
 
+std::unique_ptr<ROOT::RFieldBase> ROOT::RMapField::CloneImpl(std::string_view newName) const
+{
+   return std::make_unique<RMapField>(newName, fMapType, fSubfields[0]->Clone(fSubfields[0]->GetFieldName()));
+}
+
+void ROOT::RMapField::ReconcileOnDiskField(const RNTupleDescriptor &desc)
+{
+   static const std::vector<std::string> prefixesRegular = {"std::map<", "std::unordered_map<", "std::set<"};
+
+   const auto &fieldDesc = desc.GetFieldDescriptor(GetOnDiskId());
+   EnsureMatchingOnDiskField(fieldDesc, kDiffTypeName).ThrowOnError();
+
+   switch (fMapType) {
+   case EMapType::kMap:
+   case EMapType::kUnorderedMap: EnsureMatchingTypePrefix(fieldDesc, prefixesRegular).ThrowOnError(); break;
+   default:
+      break;
+      // no restrictions for multimaps
+   }
+}
+
 //------------------------------------------------------------------------------
 
 ROOT::RSetField::RSetField(std::string_view fieldName, ESetType setType, std::unique_ptr<RFieldBase> itemField)