[6.38] [df] Support std::array data members in TTree schemas

roottest/root/dataframe/CMakeLists.txt

@@ -330,3 +330,26 @@ ROOTTEST_ADD_TEST(test_snapshot_copyaddresses
                   MACRO test_snapshot_copyaddresses.C+)
 
 ROOT_ADD_GTEST(test_norootextension test_norootextension.cxx LIBRARIES ROOT::ROOTDataFrame)
+
+# In 6.38 on Windows the following test would not be able to compile because it can't find the ROOT/TestSupport.hxx
+# header even though the dependency is specified in ROOTTEST_GENERATE_EXECUTABLE. Given this test properly compiles in
+# later versions of ROOT on Windows, we disable it for the 6.38 release.
+if(NOT MSVC)
+  ROOTTEST_GENERATE_DICTIONARY(
+    ClassWithSequenceContainersDict
+    ${CMAKE_CURRENT_SOURCE_DIR}/ClassWithSequenceContainers.hxx
+    LINKDEF ${CMAKE_CURRENT_SOURCE_DIR}/ClassWithSequenceContainersLinkDef.hxx
+    FIXTURES_SETUP ClassWithSequenceContainersDict_setup
+  )
+  ROOTTEST_GENERATE_EXECUTABLE(
+      dataframe_sequence_containers
+      dataframe_sequence_containers.cxx ClassWithSequenceContainersDict.cxx
+      LIBRARIES Core RIO Tree ROOTDataFrame GTest::gtest GTest::gtest_main GTest::gmock GTest::gmock_main ROOT::TestSupport
+      FIXTURES_REQUIRED ClassWithSequenceContainersDict_setup
+      FIXTURES_SETUP dataframe_sequence_containers_setup
+  )
+  ROOTTEST_ADD_TEST(dataframe_sequence_containers
+      EXEC ${CMAKE_CURRENT_BINARY_DIR}/dataframe_sequence_containers
+      FIXTURES_REQUIRED dataframe_sequence_containers_setup
+  )
+endif()

roottest/root/dataframe/ClassWithSequenceContainers.hxx

@@ -0,0 +1,39 @@
+#ifndef ROOT_DATAFRAME_TEST_ARRRAYCOMBINATIONS
+#define ROOT_DATAFRAME_TEST_ARRRAYCOMBINATIONS
+
+#include <array>
+#include <vector>
+
+#include <Rtypes.h>
+
+struct ClassWithSequenceContainers {
+   unsigned int fObjIndex{};
+   std::array<float, 3> fArrFl{};
+   std::array<std::array<float, 3>, 3> fArrArrFl{};
+   std::array<std::vector<float>, 3> fArrVecFl{};
+
+   std::vector<float> fVecFl{};
+   std::vector<std::array<float, 3>> fVecArrFl{}; //! Not supported for TTree: could not find the real data member
+                                                  //! '_M_elems[3]' when constructing the branch 'fVecArrFl'
+   std::vector<std::vector<float>> fVecVecFl{};
+
+   // For ROOT I/O
+   ClassWithSequenceContainers() = default;
+
+   ClassWithSequenceContainers(unsigned int objIndex, std::array<float, 3> a1, std::array<std::array<float, 3>, 3> a2,
+                               std::array<std::vector<float>, 3> a3, std::vector<float> a4,
+                               std::vector<std::array<float, 3>> a5, std::vector<std::vector<float>> a6)
+      : fObjIndex(objIndex),
+        fArrFl(std::move(a1)),
+        fArrArrFl(std::move(a2)),
+        fArrVecFl(std::move(a3)),
+        fVecFl(std::move(a4)),
+        fVecArrFl(std::move(a5)),
+        fVecVecFl(std::move(a6))
+   {
+   }
+
+   ClassDefNV(ClassWithSequenceContainers, 1)
+};
+
+#endif

roottest/root/dataframe/ClassWithSequenceContainersLinkDef.hxx

@@ -0,0 +1,6 @@
+#ifdef __CLING__
+
+#pragma link C++ class ClassWithSequenceContainers+;
+#pragma link C++ class std::vector<ClassWithSequenceContainers>+;
+
+#endif