Fix handling of absent in checkRetVal

Fixes #752

changes.rst

@@ -16,6 +16,8 @@ Bug fixes:
 -  Fix omission of error location when there is no stack trace available.
 -  Fix type specialisation to always make par versions of functions available
    for output (:bugref:`751`).
+-  Fix internal error when checking return value of functions involving arrays
+   of optional values (:bugref:`752`).
 
 Changes:
 ^^^^^^^^

lib/eval_par.cpp

@@ -468,10 +468,14 @@ class EvalArrayLitCopy : public EvalBase {
         auto enumId = Expression::type(fi->ti()->domain()).typeId();
         if (base_t.st() == Type::ST_PLAIN) {
           for (unsigned int i = 0; i < v->size(); i++) {
-            if ((*v)[i] == env.constants.absent) {
-              continue;
+            auto* v_i = (*v)[i];
+            if (Expression::type(v_i).isOpt()) {
+              v_i = eval_par(env, v_i);
+              if (v_i == env.constants.absent) {
+                continue;
+              }
             }
-            IntVal iv = eval_int(env, (*v)[i]);
+            IntVal iv = eval_int(env, v_i);
             if (!isv->contains(iv)) {
               std::ostringstream oss;
               oss << "array contains value " << env.show(iv, enumId)
@@ -500,10 +504,14 @@ class EvalArrayLitCopy : public EvalBase {
         FloatSetVal* fsv = eval_floatset(env, fi->ti()->domain());
         if (base_t.st() == Type::ST_PLAIN) {
           for (unsigned int i = 0; i < v->size(); i++) {
-            if ((*v)[i] == env.constants.absent) {
-              continue;
+            auto* v_i = (*v)[i];
+            if (Expression::type(v_i).isOpt()) {
+              v_i = eval_par(env, v_i);
+              if (v_i == env.constants.absent) {
+                continue;
+              }
             }
-            FloatVal fv = eval_float(env, (*v)[i]);
+            FloatVal fv = eval_float(env, v_i);
             if (!fsv->contains(fv)) {
               std::ostringstream oss;
               oss << "array contains value " << fv << " which is not contained in " << *fsv;

tests/spec/unit/optional/fn_return_array_absent.mzn

@@ -0,0 +1,9 @@
+/***
+!Test
+solvers: [gecode]
+expected: !Result
+  solution: !Solution
+    x: [null]
+***/
+function array [int] of opt 1..3: foo() = [[1, <>][2]];
+any: x :: output = foo();

tests/spec/unit/regression/github_752.mzn

@@ -0,0 +1,21 @@
+/***
+!Test
+solvers: [gecode]
+expected: !Result
+  solution: !Solution
+***/
+
+% Regression test for GitHub #752
+
+include "globals.mzn";
+
+int: N=5;
+array[1..5] of var 1..10 : x;
+enum STATE = {S1, S2, S3};
+% DFA to define 12*1
+array [STATE,1..2] of opt STATE: trans = [|     1:  2:
+                                          | S1: S2, <>
+                                          | S2: S3, S2
+                                          | S3: <>, <>|];
+
+constraint regular(x, trans, S1, {S3});