[ntuple] Fix fSize calculation in RRecordField::AttachItemFields

It was missing the trailing padding, which was covered up by the typed
RField specializations overriding the fSize member. Convert them into
assertions, which can only compare inequality because the alignment of
RMapField and RSetField are pessimized since commit 49ef6f9.

tree/ntuple/v7/inc/ROOT/RField/RFieldRecord.hxx

@@ -85,6 +85,9 @@ protected:
          fTraits &= itemFields[i]->GetTraits();
          Attach(std::move(itemFields[i]));
       }
+      // Trailing padding: although this is implementation-dependent, most add enough padding to comply with the
+      // requirements of the type with strictest alignment
+      fSize += GetItemPadding(fSize, fMaxAlignment);
    }
 
 public:
@@ -145,8 +148,8 @@ public:
    static std::string TypeName() { return "std::pair<" + RField<T1>::TypeName() + "," + RField<T2>::TypeName() + ">"; }
    explicit RField(std::string_view name) : RPairField(name, BuildItemFields(), BuildItemOffsets())
    {
-      fMaxAlignment = std::max(alignof(T1), alignof(T2));
-      fSize = sizeof(ContainerT);
+      R__ASSERT(fMaxAlignment >= std::max(alignof(T1), alignof(T2)));
+      R__ASSERT(fSize >= sizeof(ContainerT));
    }
    RField(RField &&other) = default;
    RField &operator=(RField &&other) = default;
@@ -221,8 +224,8 @@ public:
    static std::string TypeName() { return "std::tuple<" + BuildItemTypes<ItemTs...>() + ">"; }
    explicit RField(std::string_view name) : RTupleField(name, BuildItemFields(), BuildItemOffsets())
    {
-      fMaxAlignment = std::max({alignof(ItemTs)...});
-      fSize = sizeof(ContainerT);
+      R__ASSERT(fMaxAlignment >= std::max({alignof(ItemTs)...}));
+      R__ASSERT(fSize >= sizeof(ContainerT));
    }
    RField(RField &&other) = default;
    RField &operator=(RField &&other) = default;

tree/ntuple/v7/src/RField.cxx

@@ -2522,6 +2522,9 @@ void ROOT::Experimental::RRecordField::RRecordField::AttachItemFields(
       fTraits &= item->GetTraits();
       Attach(std::move(item));
    }
+   // Trailing padding: although this is implementation-dependent, most add enough padding to comply with the
+   // requirements of the type with strictest alignment
+   fSize += GetItemPadding(fSize, fMaxAlignment);
 }
 
 ROOT::Experimental::RRecordField::RRecordField(std::string_view fieldName,

tree/ntuple/v7/test/ntuple_types.cxx

@@ -307,6 +307,14 @@ TEST(RNTuple, StdTuple)
          "tupleTupleField");
    EXPECT_STREQ("std::tuple<std::tuple<std::int64_t,float,char,float>,std::vector<std::tuple<char,char,char>>>",
                 tupleTupleField.GetTypeName().c_str());
+   using TupleMapSetType = std::tuple<std::map<char, int64_t>, std::set<int64_t>>;
+   auto tupleMapSetField = RField<TupleMapSetType>("tupleMapSetField");
+   EXPECT_LE(sizeof(TupleMapSetType), tupleMapSetField.GetValueSize());
+   EXPECT_LE(alignof(TupleMapSetType), tupleMapSetField.GetAlignment());
+   using TupleUnorderedMapSetType = std::tuple<std::unordered_map<char, int64_t>, std::unordered_set<int64_t>>;
+   auto tupleUnorderedMapSetField = RField<TupleUnorderedMapSetType>("tupleUnorderedMapSetField");
+   EXPECT_LE(sizeof(TupleUnorderedMapSetType), tupleUnorderedMapSetField.GetValueSize());
+   EXPECT_LE(alignof(TupleUnorderedMapSetType), tupleUnorderedMapSetField.GetAlignment());
 
    FileRaii fileGuard("test_ntuple_rfield_stdtuple.root");
    {