Add the CLUEstering library as external

[sbaldu]

The CLUEstering library is an N-dimensional generalization of the CLUE algorithm. It will be used in the TICL reconstruction algorithm and possibly for vertexing.
For this reason, the library should be added as an external dependency.
The source code for the library can be found here: https://github.com/cms-patatrack/CLUEstering

@felicepantaleo @smuzaffar

[cmsbuild]

cms-bot internal usage

[cmsbuild]

A new Issue was created by @sbaldu.

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

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[makortel]

assign reconstruction, upgrade

[cmsbuild]

New categories assigned: reconstruction,upgrade

@jfernan2,@mandrenguyen,@Moanwar,@srimanob,@subirsarkar you have been requested to review this Pull request/Issue and eventually sign? Thanks

[makortel]

I suppose the CLUEstering itself is independent of CMS (i.e. does not contain any CMS-specific things)? Is the long-term plan to keep it as a separate library? Can we expect a long-term support for the library?

I' not a lawyer, but I'm a bit concerned of the GPL license.

[fwyzard]

I' not a lawyer, but I'm a bit concerned of the GPL license.

FastJet is GPL, and we have used in CMSSW probably since before there was CMSSW...

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Edit almost, we actually added it a few months later, in 2007.

[sbaldu]

I suppose the CLUEstering itself is independent of CMS (i.e. does not contain any CMS-specific things)? Is the long-term plan to keep it as a separate library? Can we expect a long-term support for the library?

I' not a lawyer, but I'm a bit concerned of the GPL license.

Sorry for the delay. Yes CLUEstering is independent of CMS, the only overlap is that it contains many of the alpaka utilities provided in Heterogeneous Core.
As far as I know the long-term plan is to keep it as a separate library, and we expect to provide support for it for the foreseeable future.

[makortel]

FastJet is GPL, and we have used in CMSSW probably since before there was CMSSW...

Right, and I was hoping we would not add more potential landmines into our stack.

[fwyzard]

"landmines" as in "CMS has been knowingly and intentionally violating the GPL for the past 18 years" ?

[makortel]

We want to avoid making the situation worse than it already is. Therefore we want all new externals to have a license that clearly allows it to be used in the way we want to use the external (e.g. linking to Apache2-licensed CMSSW).

@sextonkennedy

[fwyzard]

I see.

Please expect to be contacted by the CERN legal team in regards to the ongoing GPL violation.

[sextonkennedy]

It might actually not be a bad idea to clean this up before Run4. Licenses apply to the keyed in code, not the algorithm. There is a Julia implantation of FastJet that Graeme wrote that we could use instead with a little work.

[sextonkennedy]

I see.

Please expect to be contacted by the CERN legal team in regards to the ongoing GPL violation.

CERN has an OSPO https://home.web.cern.ch/news/news/computing/cerns-new-open-source-program-office you could talk to them about your issue. I really doubt that CERN legal will bring a court case against one of its own experiments especially since the copy right to CMSSW is CERN "for the benefit of the CMS collaboration"... that would be CERN suing itself. Also it is not just us. ATLAS has the same issue.

[fwyzard]

I don't expect CERN to sue itself.

I do expect the CERN Legal Team to ask CMS change the licensing terms of CMSSW, or part of it, to meet the obligations of the GNU GPL, since part of CMSSW is a derivative work based on a piece of software licensed under the GPL.

[felicepantaleo]

Hi @sextonkennedy,
I'm one of the authors of the library in this PR.
Looking at higher level, my understanding is that the main reason we switched to the Apache 2.0 License was to ensure that industry collaborators could work with us and contribute to CMSSW without facing "copyleft" concerns. Would you please point me to any specific pull requests or contributions that would not have been possible under our previous license? I’d like to see concrete examples of the practical benefits this licensing change has brought to CMSSW.
Thank you for your time and insight.