Adding stage checks to all the methods

[Joao-Dionisio]

For a long time, we've had problems related to calling methods outside the allowed Stages. (For more information on the stages, see here)
SCIP does the stage check internally, but only if it's compiled in Debug mode.

The following code seems to work:

m = Model()
m.restartSolve()

Even though restartSolve cannot be called in the PROBLEM stage.

With SCIP in debug mode, we get:

[debug.c:2345] ERROR: cannot call method <SCIPrestartSolve> in problem creation stage
[scip_solve.c:3660] ERROR: Error <-8> in function call

This needs to be fixed, as we cannot expect users to know about debug mode. (Issues in #1001, #907, #971, #610)

So, I think we need to add stage checks to all the methods. This is a lot of work, so it should be an ongoing process. For now, I'll just fix the issues I linked here, but I will keep the issue open for the other methods.

There is also a question of performance. If a user is adding 10 thousand variables in a loop, checking for the stage in all these variables seems a bit unnecessary. Perhaps we can have a global CHECK_STAGE variable which can be set/unset. Suggestions on how to deal with this are welcome.

[DominikKamp]

I believe, if this is helpful for PySCIPOpt users by default, we should replace the #ifndef NDEBUG around SCIPcheckStage() by another define, which is automatically set if NDEBUG is not set and can additionally be set by cmake parameter so that PySCIPOpt can be built by default with this SCIP configuration, while being able to turn off the stage checks by a PySCIPOpt parameter.

[Joao-Dionisio]

Ah, I re-added the labels without reading your comment properly.

So, something like

#ifndef NStageCheck
SCIP_RETCODE SCIPcheckStage(...)
...
#endif

and users would do something like pip install pyscipopt -StageCheck=True/False?
I'd rather the users had the ability to turn it on and off without the need to recompile.

Either with an argument at model creation (m = Model(checkStage=True/False)), or even better with a method.
m.enableStageCheck()

[DominikKamp]

If we do it in SCIP, they have to recompile SCIP to switch between these configurations because we will not add a SCIP runtime parameter for it (too expensive).

[DominikKamp]

With scip@747acc1e stage checks can now be enabled with the cmake preset interface. There the performance impact should be compensated on average by link time optimization. This way the stage checks do not need to be copied into PySCIPOpt.