Fix GCC solution loss during recomputation

Makefile.in

@@ -1141,6 +1141,7 @@ FLATZINCTESTSRC0 = \
   test/flatzinc/empty_domain_2.cpp \
   test/flatzinc/int_set_as_type1.cpp \
   test/flatzinc/int_set_as_type2.cpp \
+  test/flatzinc/issue166.cpp \
   test/flatzinc/jobshop.cpp \
   test/flatzinc/no_warn_empty_domain.cpp \
   test/flatzinc/output_test.cpp \

changelog.in

@@ -75,6 +75,17 @@ This release modernizes the Gecode build infrastructure, adds a
 first-class CMake package for downstream consumers, refreshes the
 autoconf build path, and updates CI coverage for current platforms.
 
+[ENTRY]
+Module: int
+What:   bug
+Rank:   major
+Issue:  166
+Thanks: Mats Carlsson
+[DESCRIPTION]
+Fix domain-level global cardinality propagation losing solutions by counting
+assigned variables twice and retaining stale conflict marks when cardinality
+bounds shrink.
+
 [ENTRY]
 Module: flatzinc
 What:   new

cmake/GecodeSources.cmake

@@ -293,6 +293,7 @@ set(GECODE_TEST_SOURCES
   test/flatzinc/golomb.cpp
   test/flatzinc/int_set_as_type1.cpp
   test/flatzinc/int_set_as_type2.cpp
+  test/flatzinc/issue166.cpp
   test/flatzinc/jobshop.cpp
   test/flatzinc/jobshop2x2.cpp
   test/flatzinc/knights.cpp

gecode/int/gcc/dom-sup.hpp

@@ -1268,7 +1268,8 @@ namespace Gecode { namespace Int { namespace GCC {
               v->maxlow(k[i].max() - (inc_lbc));
               if (v->kmin() == v->kmax())
                 v->cap(LBC,k[i].max() - (inc_lbc));
-              v->card_conflict(rm);
+              int matched = inc_ubc - v->kcount();
+              v->card_conflict(std::min(rm, matched));
             }
           }
         }
@@ -1417,7 +1418,8 @@ namespace Gecode { namespace Int { namespace GCC {
         ValNode* v = vars[i]->first()->getVal();
         vars[i]->first()->free(bc);
         GECODE_ME_CHECK(x[i].eq(home, v->val));
-        v->inc();
+        if (bc == UBC)
+          v->inc();
       }
 
     for (int i = n_val; i--; ) {
@@ -1766,4 +1768,3 @@ namespace Gecode { namespace Int { namespace GCC {
 
 // STATISTICS: int-prop
 
-

test/flatzinc/issue166.cpp

@@ -0,0 +1,96 @@
+/* -*- 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 recomputation does not lose solutions
+    bool check(const std::string& output, int expected,
+               const std::string& representative) {
+      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 == expected) &&
+        (output.find(representative) != std::string::npos);
+    }
+
+    /// Helper class to create and register test
+    class Create {
+    public:
+      /// Perform creation and registration
+      Create(void) {
+        (void) new FlatZincTest("Issue166::Original",
+"predicate gecode_global_cardinality(array [int] of var int: x, array [int] of int: cover, array [int] of var int: counts);\n\
+var {1,3}: A :: output_var;\n\
+var 2..3: B :: output_var;\n\
+var 2..3: C :: output_var;\n\
+var 2..3: D :: output_var;\n\
+var 2..5: E :: output_var;\n\
+var 1..4: F :: output_var;\n\
+var 2..3: G :: output_var;\n\
+var 2..3: H :: output_var;\n\
+constraint gecode_global_cardinality([A,D,1,3,3,C,1,H,B],[1,2,3],[G,F,E]) :: domain;\n\
+solve :: int_search([A,B,C,D,E,F,G,H],anti_first_fail,indomain_min,complete) satisfy;\n",
+          "", true, {"-a"}, [] (const std::string& output) {
+            return check(output, 26,
+                         "A = 1;\nB = 2;\nC = 3;\nD = 3;\nE = 5;\n"
+                         "F = 1;\nG = 3;\nH = 3;\n");
+          });
+        (void) new FlatZincTest("Issue166::Minimized",
+"predicate gecode_global_cardinality(array [int] of var int: x, array [int] of int: cover, array [int] of var int: counts);\n\
+var 1..3: A :: output_var;\n\
+var 1..3: B :: output_var;\n\
+var 1..3: C :: output_var;\n\
+var 1..2: D :: output_var;\n\
+var 2..3: E :: output_var;\n\
+var 2..3: G :: output_var;\n\
+constraint gecode_global_cardinality([3,A,D,G,E],[1,2,3],[1,B,C]) :: domain;\n\
+solve :: int_search([D,A,E,B],input_order,indomain_random,complete) satisfy;\n",
+          "", true, {"-a", "-r", "0", "-c-d", "8"},
+          [] (const std::string& output) {
+            return check(output, 11,
+                         "A = 3;\nB = 1;\nC = 3;\nD = 1;\nE = 2;\nG = 3;\n");
+          });
+      }
+    };
+
+    Create c;
+  }
+
+}}
+
+// STATISTICS: test-flatzinc