Fix handling of absent values when removing unused code. Fixes #864.

changes.rst

@@ -24,6 +24,7 @@ Bug fixes:
 -  Fix incorrect typing of arrays in assignment generators (:bugref:`858`).
 -  Fix bug in flattening of implication with optional right hand side.
 -  Fix flattening of ``exists`` and ``forall`` with optional arguments.
+-  Fix handling of absent values when removing unused code (:bugref:`864`).
 
 .. _v2.8.7:
 

include/minizinc/optimize.hh

@@ -89,6 +89,9 @@ public:
     }  /// TODO: test if id's domain is a superset of the right hand side
     /// this currently only tests for equality, and for Boolean domains
     if (Id* ident = Expression::dynamicCast<Id>(vd->e())) {
+      if (Expression::equal(ident, Constants().absent)) {
+        return false;
+      }
       if (Expression::equal(ident->decl()->ti()->domain(), vd->ti()->domain())) {
         return true;
       }

tests/spec/unit/regression/test_bug_864.mzn

@@ -0,0 +1,7 @@
+/***
+!Test
+expected: !Result
+  status: SATISFIED
+***/
+array[1..2] of var opt 0..10: y;
+constraint forall (j in 1..2) (y[j] == if j == 1 then <> else let { var 0..10: x} in x endif);