Fix sorting in TTUTrackingAlg (10_6_X)

[makortel]

PR description:

Backport of #31415:

This PR fixes a bug in the sorting comparison functions in TTUTrackingAlg that cause crashes reported in #31258 and #31410. The std::sort requires the comparison functor to meet the requirements of Compare (loosely needs "less than"), which the current "less or equal than" does not meet, leading to undefined behavior. This PR changes the functors to use "less than" comparison.

Furthermore, as pointed out in #31258 (comment), this PR proposes to fix a logic bug in the code that assumes std::sort() to be stable (it is not) by combining the two comparison operations into one, and replacing the function structs with lambdas.

For consistency this PR also changes the subsequent call to std::unique() to use a lambda instead of function object.

Resolves #31410.

PR validation:

The crash reported in #31410 disappears, limited matrix runs.

[cmsbuild]

A new Pull Request was created by @makortel (Matti Kortelainen) for CMSSW_10_6_X.

It involves the following packages:

L1Trigger/RPCTechnicalTrigger

@cmsbuild, @rekovic, @benkrikler can you please review it and eventually sign? Thanks.
@Martin-Grunewald this is something you requested to watch as well.
@silviodonato, @dpiparo, @qliphy you are the release manager for this.

cms-bot commands are listed here

• Backported from Fix sorting in TTUTrackingAlg #31415

[makortel]

backport of #31415

[makortel]

type bug-fix

[qliphy]

please test

[cmsbuild]

The tests are being triggered in jenkins.

• CMSSW_10_6_X_2020-09-09-2300/slc7_amd64_gcc700: https://cmssdt.cern.ch/jenkins/job/ib-run-pr-tests/9241/console Started: 2020/09/10 09:37

[cmsbuild]

+1
Tested at: 9241eef
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7d47c9/9241/summary.html
CMSSW: CMSSW_10_6_X_2020-09-09-2300
SCRAM_ARCH: slc7_amd64_gcc700

[cmsbuild]

Comparison job queued.

[silviodonato]

merge

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7d47c9/9241/summary.html

Comparison Summary:

• No significant changes to the logs found
• Reco comparison results: 4 differences found in the comparisons
• DQMHistoTests: Total files compared: 34
• DQMHistoTests: Total histograms compared: 3214631
• DQMHistoTests: Total failures: 2
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 3214295
• DQMHistoTests: Total skipped: 334
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 33 files compared)
• Checked 140 log files, 14 edm output root files, 34 DQM output files