Fix non-terminating sorted propagation

Makefile.in

@@ -1142,6 +1142,7 @@ FLATZINCTESTSRC0 = \
   test/flatzinc/int_set_as_type1.cpp \
   test/flatzinc/int_set_as_type2.cpp \
   test/flatzinc/issue166.cpp \
+  test/flatzinc/issue168.cpp \
   test/flatzinc/jobshop.cpp \
   test/flatzinc/no_warn_empty_domain.cpp \
   test/flatzinc/output_test.cpp \

changelog.in

@@ -86,6 +86,16 @@ Fix domain-level global cardinality propagation losing solutions by counting
 assigned variables twice and retaining stale conflict marks when cardinality
 bounds shrink.
 
+[ENTRY]
+Module: int
+What:   bug
+Rank:   major
+Issue:  168
+Thanks: Mats Carlsson
+[DESCRIPTION]
+Fix non-terminating propagation for sorted constraints when a matching
+component contains no interval compatible with an input variable.
+
 [ENTRY]
 Module: flatzinc
 What:   new

cmake/GecodeSources.cmake

@@ -294,6 +294,7 @@ set(GECODE_TEST_SOURCES
   test/flatzinc/int_set_as_type1.cpp
   test/flatzinc/int_set_as_type2.cpp
   test/flatzinc/issue166.cpp
+  test/flatzinc/issue168.cpp
   test/flatzinc/jobshop.cpp
   test/flatzinc/jobshop2x2.cpp
   test/flatzinc/knights.cpp

gecode/int/sorted/narrowing.hpp

@@ -152,7 +152,10 @@ namespace Gecode { namespace Int { namespace Sorted {
        */
       int start = sinfo[scclist[i]].leftmost;
       while (y[start].max() < xmin) {
-        start = sinfo[start].right;
+        int next = sinfo[start].right;
+        if (next == start)
+          return false;
+        start = next;
       }
 
       if (Perm) {
@@ -184,7 +187,10 @@ namespace Gecode { namespace Int { namespace Sorted {
        */
       start = sinfo[scclist[ptau]].rightmost;
       while (y[start].min() > xmax) {
-        start = sinfo[start].left;
+        int next = sinfo[start].left;
+        if (next == start)
+          return false;
+        start = next;
       }
 
       if (Perm) {

test/flatzinc/issue168.cpp

@@ -0,0 +1,75 @@
+/* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
+/*
+ *  Main authors:
+ *     Mikael Zayenz Lagerkvist <lagerkvist@gecode.dev>
+ *
+ *  Copyright:
+ *     Mikael Zayenz Lagerkvist, 2026
+ *
+ *  This file is part of Gecode, the generic constraint
+ *  development environment:
+ *     http://www.gecode.dev
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining
+ *  a copy of this software and associated documentation files (the
+ *  "Software"), to deal in the Software without restriction, including
+ *  without limitation the rights to use, copy, modify, merge, publish,
+ *  distribute, sublicense, and/or sell copies of the Software, and to
+ *  permit persons to whom the Software is furnished to do so, subject to
+ *  the following conditions:
+ *
+ *  The above copyright notice and this permission notice shall be
+ *  included in all copies or substantial portions of the Software.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include "test/flatzinc.hh"
+
+namespace Test { namespace FlatZinc {
+
+  namespace {
+    /// Check that propagation terminates after finding all solutions
+    bool check(const std::string& output) {
+      const std::string separator = "----------\n";
+      int solutions = 0;
+      for (std::string::size_type p = 0;
+           (p = output.find(separator,p)) != std::string::npos;
+           p += separator.size())
+        solutions++;
+      return (solutions == 3) &&
+        (output.find("==========\n") != std::string::npos);
+    }
+
+    /// Helper class to create and register test
+    class Create {
+    public:
+      /// Perform creation and registration
+      Create(void) {
+        (void) new FlatZincTest("Issue168",
+"predicate fzn_sort(array [int] of var int: x, array [int] of var int: y);\n\
+var 2..4: D :: output_var;\n\
+var {2,4}: E :: output_var;\n\
+var {1,4}: F :: output_var;\n\
+var 3..4: G :: output_var;\n\
+var {2,4}: H :: output_var;\n\
+var 3..4: J :: output_var;\n\
+var {1,4}: K :: output_var;\n\
+constraint fzn_sort([F,K,G,D],[F,E,H,J]);\n\
+solve :: int_search([1,D,F,K,F,E,G,H,J],input_order,indomain,complete) satisfy;\n",
+          "", true, {"-a"}, check);
+      }
+    };
+
+    Create c;
+  }
+
+}}
+
+// STATISTICS: test-flatzinc