Loading for XMLS bug

[CalCraven]

Seems to be an issue with loading certain GMSO style xmls, which may be created from an older version of GMSO that provided less information than the current implementations assume.

Code to reproduce the bug:

import gmso
ff = gmso.ForceField("./opls_charmm_buck.xml") # forcefield attached
print(dihedtype.parameters for dihed in ff.dihedral_types.values())
ff.to_xml("tmp.xml")

Output:

dict_values([unyt_quantity(0.6276, '1.660538921e-21*J'), unyt_quantity(1.8828, '1.660538921e-21*J'), unyt_quantity(0., '1.660538921e-21*J'), unyt_quantity(-3.21331, '1.660538921e-21*J'), unyt_quantity(0., '1.660538921e-21*J'), unyt_quantity(0., '1.660538921e-21*J')])
dict_values([[unyt_quantity(0., '1000.0*J')], [unyt_quantity(1., '(dimensionless)')], [unyt_quantity(0., '0.0174532925199433*rad')]])

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Input In [21], in <module>
----> 1 ff.to_xml("tmp.xml")

File ~/Dropbox/Mac/Documents/Vanderbilt/Research/MoSDeF/gmso/gmso/core/forcefield.py:578, in ForceField.to_xml(self, filename, overwrite)
    576     params_units_def = {}
    577     for param, value in potential.parameters.items():
--> 578         params_units_def[param] = value.units
    579         etree.SubElement(
    580             potential_group,
    581             "ParametersUnitDef",
   (...)
    585             },
    586         )
    588 potential_group.append(potential.etree(params_units_def))

AttributeError: 'list' object has no attribute 'units'

As you can see, the charmm_proper_1 style are being stored as a list of lists, instead of as a list of unyts (this is the second dihedral in the output, as compared to the first one which is stored correctly).

[CalCraven]

xmls.zip

[CalCraven]

So I think this issue can be readdressed once PR #674 is merged. Essentially the issue is the lists of allowed parameters, which are read properly but not written out properly.

[CalCraven]

xmls.zip

[CalCraven]

I just retested this, I think this issue has actually been resolved.

import gmso
ff = gmso.ForceField("./opls_charmm_buck.xml") # forcefield attached
ff.to_xml("tmp.xml")
new_ff = gmso.ForceField("tmp.xml") # works
assert new_ff == ff