How to build my own global constraint with the CP-SAT solver of OR-tools?

I am a PhD candidate in data mininig, and I have to create a global constraint with OR-Tools for a data mining purpose.

The problem is that there is a lack of documentation about creating your own global constraint with CP-SAT, and I don't know how to start.

It is obviously possible, but very tedious, and very complex.

Writing a new constraint implies:

• extending the proto to support the constraint
• writing the input validation
• writing the solution checker
• writing the loading (into CP-SAT engine) code
• writing the presolve rules
• writing the propagation code. Which is complex as every deduction needs to be fully explained.
• writing the linearization/cut generation code

The last 3 items are extremely error prone, and very hard to debug, as the effect of cuts and explanations are delayed, and sometimes never used.

For these reason, I recommend expanding the constraint into smaller ones. In fact, most of the CP constraints are expanded (alldiff, element, table, reservoir, inverse, automaton, some products, some modulos).

You can also submit a feature request for a new constraint. It can happen if it is useful/general enough.

Thanks