[FileFormats.MOF] make use_nlp_block=false the default if SNF in model #2688
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Closes #2687
The underlying issue is that we supported nonlinear file formats before the introduction of ScalarNonlinearFunction. Thus,
.mof.jsonand.nlthat contain nonlinear get parsed into aMOI.NLPBlock. This is the "old" nonlinear interface, and it means that Ipopt etc run into problems if the user wants to read in a file and then do some "new" stuff with it.The current work-around is to use
read_from_file(model; use_nlp_block = false).But we could add a tag to the file on write if we detect
MOI.ScalarNonlinearFunction. This would all "new" stuff to round-trip as new, and "old" stuff to round-trip as old.The alternative would be to change the default to
use_nlp_block = false, but this is technically breaking. Although this is also breaking, but arguably a bug-fix, because currently "new" models get written and then read back in as "old".Once we agree on what to do, we should make a similar fix to the
.nlfile module. It probably means adding a header comment about whether we hadScalarNonlinearFunctions.