RootUtils: Workaround for pyroot __pair_base issue.

In gcc8, std::pair derives from the (empty) base class std::__pair_base. When ROOT makes dictionaries, it likes to strip std:: qualifiers. When it then tries to look up cling information for a TClass, if the lookup fails, it tries again with the std:: reinserted for all STL classes (with TClassEdit::InsertStd()). However, that doesn't work for __pair_base, because it's not a class that ROOT knows about. The upshot is that we see errors like:

Error in TClass::LoadClassInfo: no interpreter information for class __pair_base<unsigned int,string> is available even though it has a TClass initialization routine.

We work around this by hooking into ROOT's TClass creation. If we see a std::pair class, we erase the base class information from its TClass.

This merge request affects 1 package:

• Control/RootUtils

Adding @ssnyder ,@rbianchi as watchers

added Core master review-pending-level-1 labels

CI Result FAILURE

	Athena	AthSimulation
externals
cmake
make
required tests
optional tests

Full details available at NICOS MR-22163-2019-03-27-09-20
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST 36032]

added urgent label

Adding urgent as it helps with the overlay test.

mentioned in merge request !22158 (merged)

The changes are important. But I want L2 to take a look before this is approved. -Ruchi (L1)

added review-pending-level-2 label and removed review-pending-level-1 label

added RC Attention Required review-approved labels and removed review-pending-level-2 label

@wlampl, could this one be merged to make Overlay CI test run? (but maybe have a quick look before merging)

merged

mentioned in commit 06be26bf

Hi @ssnyder,

Thanks for the fix. I can confirm that diff-root now runs as expected.

Running a reco job now, I still see warnings like:

Error in <TClass::GetCheckSum>: Calculating the checksum for (pair<unsigned int,vector<int> >) requires the base class (__pair_base<unsigned int,vector<int> >) meta information to be available!

I suppose the remaining selection.xml files will have to be updated.

added sweep:ignore label

I still see those two failing:

http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/GITWebArea/nightlies/master/2019-03-27T2141/Athena/x86_64-centos7-gcc8-opt/Athena/UT/LArAthenaPool.log.html

http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/GITWebArea/nightlies/master/2019-03-27T2141/Athena/x86_64-centos7-gcc8-opt/Athena/UT/ZdcEventAthenaPool.log.html