Model inconsistency with empty set and set comprehension

[elKei24]

Doing a set comprehension with an empty set as generator leads to the detection of a model inconsistency.

Minimal example

set of int: S = { };
function var set of S: asVar() = { val | val in S };
var set of S: asVar = asVar();
output [show(asVar)];

Expected behavior

As S is empty, the set comprehension also evaluates to an empty set and MiniZinc outputs {}.

Actual behavior

MiniZinc detects a model inconsistency in call asVar and states that the problem is unsatisfiable.

[Dekker1]

The issue seems to be with the return type of the function. The same example using a wider return type seems to work just fine:

set of int: S = { };
function var set of int: asVar() = { val | val in S };
var set of S: asVar = { val | val in S };
output [show(asVar)];

[guidotack]

I've pushed a fix to the develop branch, which will be included in the next release. For the time being, @Dekker1 's workaround is the best option.