Fix in TrackerTopology migration of TrackingTruthAccumulator

[makortel]

This PR adds the missing check for newDetector.detId() == DetId::Tracker before calling TrackerTopology::layer(). I took the liberty to restructure slitghly the surround code (do the check once instead of "essentially three times").

Tested on top of 740pre5. PR #7335+this shows no differences wrt. 740pre5 (also in the "Tracking Particle Matched Hits" plot).

[cmsbuild]

A new Pull Request was created by @makortel (Matti Kortelainen) for CMSSW_7_4_X.

Fix in TrackerTopology migration of TrackingTruthAccumulator

It involves the following packages:

SimGeneral/TrackingAnalysis

@cmsbuild, @civanch, @nclopezo, @mdhildreth can you please review it and eventually sign? Thanks.
@battibass, @abbiendi, @GiacomoSguazzoni, @rovere, @VinInn, @appeltel, @cerati, @trocino, @dgulhan this is something you requested to watch as well.
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[venturia]

@makortel, is this a fix which could/should be applied also to SLHC release cycle? If it is expected to have an impact it is better to check.

[makortel]

@venturia, I don't see any problem in applying the fix also to SLHC branch. AFAICT the bug only affects TrackingParticle::numberOfTrackerLayers(), so anything calling it is affected. To give some impression what code this is, git grep in 620_SLHC23p1 shows that this function is used in a result-changing way in the following files

CommonTools/RecoAlgos/interface/CosmicTrackingParticleSelector.h
SimGeneral/TrackingAnalysis/interface/TrackingParticleSelector.h
SimTracker/TrackHistory/src/TrackClassifier.cc
SimTracker/TrackHistory/src/VertexClassifier.cc
Validation/RecoHI/plugins/HitPixelLayersTPSelector.h
Validation/TrackingMCTruth/plugins/TrackingTruthValid.cc

(possibly, I didn't look any further than the output of git grep).

Maybe I should just make a PR to SLHC too (but after this one is accepted, unless there are other constraints on the schedule)?

[ghost]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[venturia]

Thanks @makortel . In the meantime I would check with the stakeholders, @boudoul and kevin stenson, if this bug can have any impact on the Tracker phase 2 results for the TP

[cmsbuild]

+1
Tested at: 65592ac
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7445/2220/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7445/2220/summary.html

[civanch]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_4_X IBs unless changes (tests are also fine). This pull request will be automatically merged.