[ntuple] detect runtime member streamers via TRealData

[JasMehta08]

This Pull request:

Changes or fixes:

When a class member has a custom streamer set at runtime via TClass::SetMemberStreamer() or TClass::AdoptMemberStreamer(),

RFieldBase::Create() now detects this by iterating TRealData and checking TRealData::GetStreamer().

If any member has a custom streamer, an RStreamerField is used instead of RClassField, preventing the class from being split into columns which would bypass the member's custom serialization logic.

Checklist:

• tested changes locally

This PR fixes #20448

[jblomer]

Thank you!

I think that automatically using a streamer field is undesired. Custom member streamers are a rare case and for now, I think we should simply detect this case in RClassField and fail with an error message.

We would also need a test for this.

[JasMehta08]

@jblomer

I have updated the PR,

• I moved the check to RFieldMeta.cxx to detect if any member has
  custom streamer present, and to throw error if it is present.
• I have also added a test for the same.

Please let me know if I should change anything.

Thanks!

[jblomer]

Looks quite close to being merge ready!

[JasMehta08]

@jblomer

i have updated the code,

• i used the snippet provided by you.
• also added the Cansplit() test
• and move the test to rfield_class.cxx

Thanks!

[github-actions]

Test Results

    22 files      22 suites   3d 3h 14m 32s ⏱️
 3 831 tests  3 830 ✅ 1 💤 0 ❌
75 737 runs  75 728 ✅ 9 💤 0 ❌

Results for commit 9243edc.

♻️ This comment has been updated with latest results.

[jblomer]

In principle looks good to me but see the CI report (missing TBuffer.h include)

[JasMehta08]

@jblomer
I think the segmentation errors is caused by the GetListOfRealData() returns nullptr because we are not checking for that and trying to access it.
Do you think that fixing that would fix the errors? if so, should I add a if check?

[JasMehta08]

@jblomer

I have added the changes that you had pointed out about
the missing header and the updated the class version.

I also changed the code snippet as i think it is the cause of the segmentation fault.
Please let me know if i have gotten the reasoning behind the segmentation fault wrong.

Thanks!

[JasMehta08]

@pcanal

I have made the changes to use BuildRealData() if GetListRealData() returns a nullptr, and went back to using the snippet provided by @jblomer , that is
for (auto realMember : ROOT::Detail::TRangeStaticCast<TRealData>(*fClass->GetListOfRealData())) {
I hope those are the only changes that are necessary.

Thanks!