Check of models with partial Medium packages fails

[Francesco Casella]

Consider this simple model:

model check
  inner Modelica.Fluid.System system;
  replaceable package gas = Modelica.Media.Interfaces.PartialMedium;
  Modelica.Fluid.Vessels.ClosedVolume free_volume(
    V = 0.01, use_portsData = false, 
    redeclare package Medium = gas);
end check;

Moving the issue to 2.1.0, as it is less critical than coverage issues.
The model is perfectly legitimate for a library. It cannot be simulated directly, because it lacks an actual medium implementation, but is othewise locally balanced and well defined.

Checking in OMC produces the following error:

[1] 10:08:59 Translation Warning
[Modelica.Media: 4475:17-4600:23]: Forcing full instantiation of partial class BaseProperties$free_volume$medium during checkModel.

[2] 10:08:59 Translation Error
Internal error - InstUtil.moveBindings: Mismatched number of equations and variables.

[3] 10:08:59 Translation Error
Error occurred while flattening model check

A better implementation should recognize that partial classes are involved and only perform local balancedness tests, possibly warning that Medium must be redeclared in order to actually use the model.

[Francesco Casella]

The issue is still valid, with the NF one gets:

[1] 23:32:46 Translation Error
[C:/dev/OM64bit/OMCompiler/Compiler/NFFrontEnd/NFCeval.mo: 1478:9-1479:93]:
Internal error NFCeval.evalRelationEqual failed to evaluate 
‘free_volume.Medium.ThermoStates == Modelica.Media.Interfaces.Choices.IndependentVariables.ph‘

[Per Östlund]

Fixed: ​https://github.com/OpenModelica/OpenModelica/issues/3944