2.7.4: "not an integer expression"

[informarte]

I noticed a regression regarding the handling of set variables and I have two examples to demonstrate the issue.

First example:

var bool: c;
var set of int: x = if c then 1..3 else 1..5 endif;
var set of int: y = if not c then 1..3 else 1..5 endif;

constraint c = true;

constraint x subset y;

MiniZinc 2.7.3 returns the following solution:

c = true
x = 1..3
y = 1..5
----------

MiniZinc 2.7.4, however, produces this error message:

Error: evaluation error: not an integer expression

Second example:

include "alldifferent.mzn";

int: N = 4;

array [1..N] of var set of 1..N: x;

constraint alldifferent(x);

constraint array_union(x) = 1..(N div 2);

MiniZinc 2.7.3 returns the following solution:

x = [{}, 2..2, 1..1, 1..2]

MiniZinc 2.7.4, however, produces the above error message.

The problem does not occur when optimization is disabled (with -O0) or Chuffed is used for solving.