Pharo crashes if a slot has a bug during class migration

[jecisc]

In Moose we have FMOne and FMMany slots that keep a bidirectional relation between what is in the slot.

The problem is that if we remove a slot, it migrates the instances and when we try to migrate the slots, an error happens because the opposite slot is not there anymore. And the error causes Pharo to just crash when we close the debugger.

I see two things to do here:

• The class builder should not crash the image if a slot raises an error during migration
• We should have a way in slots to do an alternative writing when we are in a class migration. In this case, we would not try to maintain the bidirectional relation since it already exists.

What do you think @MarcusDenker?

[MarcusDenker]

yes, this is an area where we need improvement.

For migration we need some lower level way (closer to the view of what is in memory), with a callback to the Slot to do more if needed. Most slots do not actually want to do e.g. the additional action they implement when it is pure migration.

I can help with coming up with a better migration scheme.