Stable CMSSW with ROOT >= 6.34.06

[anigamova]

We are working on the integration of recent ROOT features in Combine and would appreciate to have a stable CMSSW version with one of the recent ROOT releases, e.g. 6.34.08 with el9 architecture if possible. Thanks!

[cmsbuild]

cms-bot internal usage

[cmsbuild]

A new Issue was created by @anigamova.

@Dr15Jones, @antoniovilela, @makortel, @mandrenguyen, @rappoccio, @sextonkennedy, @smuzaffar can you please review it and eventually sign/assign? Thanks.

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[makortel]

assign core

[cmsbuild]

New categories assigned: core

@Dr15Jones,@makortel,@smuzaffar you have been requested to review this Pull request/Issue and eventually sign? Thanks

[makortel]

We decided not to follow ROOT 6.34 release branch at all as that is a sort-term-support release and therefore of little-to-no-interest of CMSSW itself (where we need long-term support).

Written that, I'm not against building a special CMSSW release suing ROOT 6.34 (if that doesn't take too much effort).

For future reference, could you describe what features from ROOT 6.34 do you need that won't be backported to 6.32?

[anigamova]

The 6.34 releases support automatic differentiation features, as discussed here, which we are trying to introduce to Combine. These changes are not going to be back ported as far as I understand. We are not planning to release stable Combine version associated with ROOT 6.34 at this point, but we would appreciate the CMSSW with 6.34 for development. Thanks!