Reading ShapeFactors in xml workspace

[alexander-held]

Description

The .xml -> .json workspace conversion currently does not support ShapeFactor modifiers.

Expected Behavior

The ShapeFactor modifiers defined in a .xml should appear as shapefactor modifiers in the .json workspace.

Actual Behavior

A warning is printed, and the modifier skipped.

WARNING:pyhf.readxml:not considering modifier tag <Element 'ShapeFactor' at 0x7fc145eb0f90>

Steps to Reproduce

With pyhf version 0.5.2:

pyhf xml2json minimal_example/RooStats/minimal_example.xml

results in

WARNING:pyhf.readxml:not considering modifier tag <Element 'ShapeFactor' at 0x7fb8c5fff090>

using an example input workspace provided here: /afs/cern.ch/user/a/alheld/public/pyhf_shapefactor.

Checklist

• Run git fetch to get the most up to date version of master
• Searched through existing Issues to confirm this is not a duplicate issue
• Filled out the Description, Expected Behavior, Actual Behavior, and Steps to Reproduce sections above or have edited/removed them in a way that fully describes the issue