Make sort functions return array of enum when input is array of enum.

Fixes #853.

changes.rst

@@ -10,6 +10,8 @@ Changes:
 ^^^^^^^^
 -  Add support for ``elseif`` in ``if then elseif endif`` expressions without an
    `else` branch.
+-  Make ``sort`` functions return array of enum when input is array of
+   enum (:bugref:`853`).
 
 Bug fixes:
 ^^^^^^^^^^

share/minizinc/std/sort_fn.mzn

@@ -4,7 +4,7 @@ include "sort.mzn";
   Return a multiset of values that is the same as the
   multiset of values in \a x but in sorted order.
 */
-function array[int] of var int: sort(array[int] of var int: x) ::promise_total =
+function array[int] of var $$E: sort(array[int] of var $$E: x) ::promise_total =
     let {
       array[1..length(x)] of var lb_array(x)..ub_array(x): y ::is_defined_var;
       constraint sort(x,y) ::defines_var(y);

share/minizinc/std/stdlib/stdlib_sort.mzn

@@ -17,7 +17,7 @@ The sort is stable, i.e. if \a y[\p i] = \a y[\p j] with \p i < \p j, then
 function array[$$E] of any $T: sort_by(array[$$E] of any $T: x, array[$$E] of float: y);
 
 /** @group stdlib.sort Return values from array \a x sorted in non-decreasing order */
-function array[$$E] of int: sort(array[$$E] of int: x);
+function array[$$E] of $$F: sort(array[$$E] of $$F: x);
 /** @group stdlib.sort Return values from array \a x sorted in non-decreasing order */
 function array[$$E] of float: sort(array[$$E] of float: x);
 /** @group stdlib.sort Return values from array \a x sorted in non-decreasing order */