fix scip results processing

[michaelbynum]

Summary

With SCIP 8.0.3, the results processing is currently broken:

import ampl_module_scip
import os
os.environ['PATH'] = os.pathsep.join([ampl_module_scip.bin_dir, os.environ['PATH']])
import pyomo.environ as pyo


m = pyo.ConcreteModel()
m.x = pyo.Var(domain=pyo.Integers)
m.objective = pyo.Objective( expr= m.x)
m.con = pyo.Constraint(expr= m.x >= 1)

opt = pyo.SolverFactory('scip')
results = opt.solve(m, tee=True)

Outputs:

WARNING: No dual information available when presolving was performed.
WARNING: Unexpected SCIP solver message: SCIP 8.0.3\x3a optimal solution;
objective 1; 0 simplex iterations; 0 branching nodes
Traceback (most recent call last):
  File "/Users/.../pyomo_with_scip.py", line 13, in <module>
    results = opt.solve(m, tee=True)
              ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../pyomo/pyomo/opt/base/solvers.py", line 661, in solve
    _model.solutions.load_from(
  File "/Users/.../pyomo/pyomo/core/base/PyomoModel.py", line 230, in load_from
    raise ValueError(
ValueError: Cannot load a SolverResults object with bad status: unknown

To correct this, I changed the bit of code that parses the solver message to be more flexible by checking if specific strings are in the message instead of checking if they are equal. In this case, Pyomo is looking for "optimal solution found", but the message is just "optimal solution".

The other problem is the SCIP log is parsed to get the primal bound. However, the log parsing does not work properly if SCIP solves the problem in the preprocessing phase. To fix this, I added a try/except and simply leave the primal bound empty if the log is not parsed correctly.

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[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (96c4c0b) 85.31% compared to head (f400b5e) 87.87%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3023      +/-   ##
==========================================
+ Coverage   85.31%   87.87%   +2.56%     
==========================================
  Files         763      769       +6     
  Lines       89308    89520     +212     
==========================================
+ Hits        76191    78670    +2479     
+ Misses      13117    10850    -2267     

Flag	Coverage Δ
linux	85.20% <80.00%> (-0.01%)	⬇️
osx	75.00% <0.00%> (-0.01%)	⬇️
other	85.38% <80.00%> (-0.01%)	⬇️
win	82.42% <80.00%> (-0.01%)	⬇️

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Files	Coverage Δ
pyomo/solvers/plugins/solvers/SCIPAMPL.py	71.84% <80.00%> (-0.50%)	⬇️

... and 106 files with indirect coverage changes

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[blnicho]

@michaelbynum would you mind adding a short comment here explaining why this is needed or when you would end up here? Is this from a difference in solver versions?

[michaelbynum]

Done. Sorry - I was in a hurry yesterday.

[michaelbynum]

Sorry, I only added comments to the PR. Now, I've added comments to the code.

[mrmundt]

@michaelbynum - Jenkins failures are not related. Our build environment was the problem. I have fixed it and flagged this for re-test.