Cannot convert LHEEventProduct::pdf_

[vlimant]

the workflow

https://cmsweb.cern.ch/reqmgr2/fetch?rid=cmsunified_task_HIG-RunIISummer20UL17MiniAODv2-13394__v1_T_251126_162305_5346

is facing failures in production with something that looks familiar.

%MSG
----- Begin Fatal Exception 28-Nov-2025 11:45:20 CET-----------------------
An exception of category 'FileReadError' occurred while
   [0] Calling InputSource::readEvent_
   [1] Reading branch LHEEventProduct_externalLHEProducer__GEN.
   Additional Info:
      [a] Fatal Root Error: @SUB=TStreamerInfo::BuildOld
Cannot convert LHEEventProduct::pdf_ from type: auto_ptr<gen::PdfInfo> to type: gen::PdfInfo, skip element

----- End Fatal Exception -------------------------------------------------

some logs and ways to reproduce under

https://cms-unified.web.cern.ch/cms-unified/joblogs/cmsunified_task_HIG-RunIISummer20UL17MiniAODv2-13394__v1_T_251126_162305_5346/8021/HIG-RunIISummer20UL17NanoAODv15-00031_0/d05fa993-4f6f-4ae1-aaf9-dd70d26a8bd3-8-3-logArchive/job/WMTaskSpace/cmsRun1/

[vlimant]

assign xpog

[vlimant]

assign generators

[cmsbuild]

New categories assigned: xpog,generators

@battibass,@ftorrresd,@lviliani,@mkirsano,@sensrcn,@theofil you have been requested to review this Pull request/Issue and eventually sign? Thanks

[cmsbuild]

cms-bot internal usage

[cmsbuild]

A new Issue was created by @vlimant.

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

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[vlimant]

could be #43422

[makortel]

The input file is /store/mc/RunIISummer20UL17MiniAODv2/GluGluToHHTo2B2G_kl-5p00_kt-1p00_c2-0p00_TuneCP5_13TeV-powheg-pythia8/MINIAODSIM/PowhegBugFix_106X_mc2017_realistic_v9-v5/110000/FD848079-E570-3449-9CE1-DEB3349DBAEA.root. The GEN step was produced with CMSSW_10_6_40, and being read with CMSSW_15_0_15_patch4.

The LHEEventProduct_externalLHEProducer__GEN appears to have splitlevel 0, so this problem could be different from https://github.com/cms-sw/cmssw/issues/43923 (while still related to https://github.com/cms-sw/cmssw/issues/43422)

[makortel]

The problem could be the read rule https://github.com/cms-sw/cmssw/blob/56fe406472f145eb9cab6fe701c7ac7f07d8d5d7/SimDataFormats/GeneratorProducts/src/classes_def.xml#L244 is specific to LHEEventProduct version 13, maybe it should be for all versions up to 13, i.e. version="[-13]"?

[makortel]

maybe it should be for all versions up to 13, i.e. version="[-13]"?

Digging history, https://github.com/cms-sw/cmssw/pull/25239 that changed the auto_ptr to unique_ptr used specific versions 11 and 13 for GenEventInfoProduct and LHEEventProduct. For GenEventInfoProduct the read rule was fixed in https://github.com/cms-sw/cmssw/pull/41988, so I think a similar fix should be done for LHEEventProduct.

[makortel]

Having tests run in IBs with these files as inputs would be very useful to catch these problems earlier. Also in light of core adding soon read rules to address https://github.com/cms-sw/cmssw/issues/43422 and https://github.com/cms-sw/cmssw/issues/43923.

[makortel]

maybe it should be for all versions up to 13, i.e. version="[-13]"

I have this change as part of https://github.com/cms-sw/cmssw/pull/49593 (that PR would have introduced a conflict, and doing that small change first makes it easier to backport).

Is it enough to backport the commit (not the full PR) to 15_0_X?

[makortel]

maybe it should be for all versions up to 13, i.e. version="[-13]"

I have this change as part of #49593 (that PR would have introduced a conflict, and doing that small change first makes it easier to backport).

Is it enough to backport the commit (not the full PR) to 15_0_X?

I made backports

• 15_1_X in https://github.com/cms-sw/cmssw/pull/49624
• 15_0_X in https://github.com/cms-sw/cmssw/pull/49625

Feel free to do any further backports if needed.