Support MOI.delete for variables that participate in constraints. about scip.jl

[matbesancon]

getting back to this, has it been implemented on the SCIP side, what was needed?

[rschwarz]

I don't know whether anything was changed on the SCIP side (and don't even remember the linked discussion).
Back then, I was able to trigger an assert in SCIP using this gist written in C.

[matbesancon]

this is still triggered on SCIP master it seems. This has never been an intended / documented behaviour I assume

[matbesancon]

I opened an issue on SCIP itself to track this. If this is "intended" / documented behavior, one solution would be to loop through constraints to delete them before deleting the variable. Not sure what are other solvers' conventions for this

[matbesancon]

OK getting back to this, the issue on the SCIP side is that variables cannot be removed from constraints in the SCIP_STAGE_PROBLEM stage which is the one we are in when building the problem.

This is a path that shouldn't have been allowed, a check will be introduced. Another way to view it is, deleting constraints is the user's responsibility (cleaning up the constraints from that variable or removing the associated constraints altogether)