How to link to correctionlib from a CMSSW module

[nsmith-]

Inside CMSSW, some may want to use an EDAnalyzer or other framework plugin with correctionlib.

[nsmith-]

In the long term, the package will be part of cmsdist, and in fact v1.1 is already in the gcc900 externals: /cvmfs/cms.cern.ch/slc7_amd64_gcc900/external/py3-correctionlib, as used in CMSSW 11_3_X releases. In that case, it should suffice to add the line

<use name="correctionlib"/>

to the package BuildFile.xml to use it.

If one wants a newer version than what is available in the externals, the following recipe may work:

1. First check if scram tool info correctionlib is an acceptable version, if so skip to the last step.
2. Install correctionlib, preferably in a way that is portable with your CMSSW environment (e.g. pip install --prefix $CMSSW_BASE/local or use scram-pip)
3. Create an appropriate scram tool description, e.g. using this bash script

#!/bin/bash

cat <<EOF > correctionlib.xml
<tool name="correctionlib" version="$(correction config --version)">
  <lib name="correctionlib"/>
  <client>
    <environment name="INCLUDE" default="$(correction config --incdir)"/>
    <environment name="LIBDIR" default="$(correction config --libdir)"/>
  </client>
</tool>
EOF

4. Instal the new tool with scram setup correctionlib.xml (scram tool remove correctionlib to remove)
5. Add the line

<use name="correctionlib"/>

to your package BuildFile.xml

[nsmith-]

A confounding issue is that there is ABI incompatibility issues due to _GLIBCXX_USE_CXX11_ABI being set to 1 in CMSSW / any modern gcc version, and the fact that python manylinux wheels have it set to 0 (since they use RHEL7 stock gcc). The workaround is to make sure that correctionlib is compiled using the gcc environment of CMSSW, e.g. after sourcing a CMSSW release make sure to pip install from source.

At present, the source distribution on pypi seems to be broken, but installation from git seems to work OK, e.g.
python3 -m pip install --user git+https://github.com/cms-nanoAOD/correctionlib.git@2.0.0rc6

[nsmith-]

Small update: the pypi source distribution is now functional, and:

python3 -m pip install --user --no-binary=correctionlib correctionlib

should work to install correctionlib from source.

[makortel]

I think the recipe needs cmsenv after scram setup correctionlib.xml.

[nsmith-]

Another option is to use pip-in-scram, as developed in https://github.com/FNALLPC/lpc-scripts/blob/master/scram-pip, also available at /cvmfs/cms-lpc.opensciencegrid.org/FNALLPC/lpc-scripts/scram-pip

[pieterdavid]

In case it helps anyone: I turned the above instructions into a script (tested with CMSSW_10_6_29 for both python2 and python3)

[nsmith-]

Nice! Just a comment, some of the vars in the script could be determined from correction config (in fact we could add a whole buildfile maker into that?)

[pieterdavid]

yes, but not for python2, as far as I understood - in any case this is a temporary solution for things like nanoAODtools development or comparisons in 10_6