[ntuple] check/test vector item alignment limit

Author: jblomer

tree/ntuple/src/RFieldSequenceContainer.cxx

@@ -516,6 +516,11 @@ ROOT::RVectorField::RVectorField(std::string_view fieldName, std::unique_ptr<RFi
      fItemSize(itemField->GetValueSize()),
      fNWritten(0)
 {
+   if (itemField->GetAlignment() > kMaxItemAlignment) {
+      throw RException(
+         R__FAIL(std::string("Unsupported vector item alignment: ") + std::to_string(itemField->GetAlignment())));
+   }
+
    if (emulatedFromType && !emulatedFromType->empty())
       fTraits |= kTraitEmulatedField;
 

tree/ntuple/test/rfield_vector.cxx

@@ -549,3 +549,16 @@ TEST(RNTuple, RVecAdopted)
    EXPECT_FLOAT_EQ(2.0, buf[1]);
    EXPECT_FLOAT_EQ(0.0, buf[2]);
 }
+
+TEST(RNTuple, OverAligned)
+{
+   auto res = RFieldBase::Create("f", "std::vector<ROOT::Internal::RAlignedStorage<4096>>");
+   if (!res)
+      FAIL() << "Createing a vector of a 4096B aligned type should work";
+
+   res = RFieldBase::Create("f", "std::vector<ROOT::Internal::RAlignedStorage<8192>>");
+   if (res)
+      FAIL() << "Createing a vector of a 8192B aligned type should fail";
+
+   EXPECT_THAT(res.GetError()->GetReport(), ::testing::HasSubstr("Unsupported vector item alignment: 8192"));
+}