Fix GCC solution loss during recomputation

Author: Mikael Zayenz Lagerkvist

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 +75,15 @@ 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
+[DESCRIPTION]
+Fix domain-level global cardinality propagation losing solutions when search
+recomputation applies several branch choices before propagation.
+
 [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

docs/open-issues-plan.md

@@ -0,0 +1,220 @@
+# Open issue work plan
+
+This plan covers the 29 issues that were open on 13 July 2026. The ordering is
+based on the current `main` branch. Old reports are not automatically low
+priority, but work that can produce wrong answers ranks above usability changes
+and reports against build code that has since been replaced.
+
+The first implementation target is [#166](https://github.com/Gecode/gecode/issues/166).
+It reports missing solutions and includes a small reproducer, so it provides a
+good starting point for the remaining correctness work.
+
+## Immediate correctness and release work
+
+### #166: global cardinality misses solutions
+
+**Priority:** urgent. **Status:** fix and regression implemented.
+
+The minimized model fails only with domain propagation when several branch
+choices are replayed before propagation. The upper- and lower-bound matching
+passes both increment the same occurrence counter, which can make a value look
+full and remove a valid edge. Count assigned variable nodes only during the
+upper-bound pass, and retain the original randomized search as a FlatZinc
+regression. A solver that omits valid solutions is unsound, so this issue comes
+first.
+
+### #168: `sort` and `element` model hangs
+
+**Priority:** urgent after #166.
+
+The minimized model contains repeated variables. Reproduce it with a time limit,
+then determine whether the loop is in propagation, search, or FlatZinc posting.
+Recent fixes for other FlatZinc constraints established a useful pattern:
+explicitly handle shared variables before posting propagators that assume
+distinct views.
+
+### #199: MiniZinc float test exhausts memory
+
+**Priority:** urgent release investigation.
+
+Run `test-globals-float.mzn` against `main` with strict time and memory limits.
+Record nodes, failures, depth, and resident memory to distinguish a leak from an
+unbounded search tree. Treat the separate request for an `fzn-gecode` memory
+limit as a follow-up unless bounded reproduction shows that it is required for
+safe operation.
+
+### #142: zero-sized `nooverlap` rectangles
+
+**Priority:** high.
+
+Decide whether the documented semantics or the current propagator behavior is
+the intended contract. Add direct tests for zero width, zero height, and both
+dimensions zero before changing either implementation or documentation.
+
+### #107 and #108: Autotools installation cleanup
+
+**Priority:** high before release; small scope.
+
+Use staged installations to verify both reports. Example data headers should not
+be installed when examples are disabled, and disabling FlatZinc should not
+create empty MiniZinc directories. Test the positive installation paths as well
+as the disabled configurations.
+
+### #126: dead website link
+
+**Priority:** high before release; trivial scope.
+
+Replace the dead Global Constraint Catalog URL with
+<https://sofdem.github.io/gccat/> in the website source. Verify the deployed
+page rather than closing the issue from a source-only change.
+
+### #151: wrong TSP example result
+
+**Priority:** medium-high; good contained correctness task.
+
+The `br17` instance contains valid zero-cost edges, while the example treats a
+zero cost as an absent edge. Separate edge existence from edge cost and verify
+all bundled instances, including the known optimum of 39 for `br17`.
+
+## Float behavior and embedding contracts
+
+### #175: unexpected `OutOfLimits`
+
+**Priority:** medium-high.
+
+Port the C++ reproducer to `main` and inspect the interval assigned to each
+subexpression. The likely failure boundary is conservative nonlinear interval
+construction rather than search. Preserve the exception until sound, tighter
+bounds can be demonstrated.
+
+### #155: rounding-mode side effects
+
+**Priority:** medium; technically interesting.
+
+Document the rounding-mode contract first. Evaluate a public RAII guard that
+saves and restores the caller's mode, with tests on supported platforms. Avoid
+an implicit per-operation guard unless measurements show that its cost and
+interaction with user propagators are acceptable.
+
+### #164: unbounded float search
+
+**Priority:** low.
+
+The example asks the default search to choose an unbounded float satisfying a
+strict inequality. Confirm current behavior, then prefer a diagnostic or
+documentation change unless the same problem occurs with a bounded variable.
+
+## Scheduling and MiniZinc integration
+
+### #80, #81, and #82: scheduling lowering
+
+**Priority:** medium as a single project, low as isolated old tickets.
+
+Re-audit these issues against current `cumulatives` and optional-task support.
+List the remaining start/duration/end variants, identify decompositions that
+still live in the C++ registry, and benchmark native posting against
+MiniZinc-level rewriting. Decide zero-duration semantics explicitly. Replace the
+three historical issues with one current design issue if their original
+dependency structure no longer describes the code.
+
+### #99: statistics and Gist mode
+
+**Priority:** low.
+
+Confirm that `-s` still overrides `-mode gist`. If it does, keep Gist selection
+authoritative and arrange statistics output around that mode. This is a suitable
+small task if Gist remains an actively supported interface.
+
+## Propagation strength and search behavior
+
+### #143: infeasible `nooverlap` model searches for too long
+
+**Priority:** medium-low.
+
+Measure the search rather than treating elapsed time alone as a hang. The model
+looks like a pigeonhole inconsistency that pairwise non-overlap propagation may
+not prove at the root. Consider redundant capacity reasoning only after the
+baseline confirms that propagation, rather than an actual loop, is the problem.
+
+## API and command-line usability
+
+### #145: construct `BoolExpr` from `bool`
+
+**Priority:** low-medium.
+
+Define Boolean constants separately from the empty accumulator semantics added
+for default-constructed `BoolExpr`. Cover composition, posting, copying, and
+materialization of both `true` and `false`.
+
+### #144: reject unsupported options and print help
+
+**Priority:** low-medium.
+
+Specify whether `Options::parse()` owns unknown-option handling or reports it to
+the caller. Add tests for unknown options, help, missing values, and applications
+that register custom options before changing the public behavior.
+
+### #141: successful test-run summary
+
+**Priority:** low; good first issue.
+
+Print a short success summary after a complete test run. Keep filtered runs and
+early failures unambiguous, and make the CMake and Autotools entry points agree.
+
+## Release administration
+
+### #148, #177, and #215: publish and identify 6.3.0
+
+**Priority:** release completion.
+
+Keep these open until the release is published. Close them together after the
+release artifacts, website version, and downstream-facing stability statement
+are available.
+
+## Verify and close
+
+These issues describe code paths that have been replaced or behavior that is
+intentional. They should receive a focused verification and an explanatory
+closure rather than new implementation work.
+
+### #83: CMake examples ignored optional features
+
+Configure without MPFR and verify that the two MPFR-only examples are skipped.
+Current CMake code already contains this selection.
+
+### #92: malformed Qt version detection
+
+Run configuration with a failing or unusable `qmake`. Current Autoconf code
+validates the parsed major version before numeric comparison.
+
+### #65: adopt `AX_PTHREAD`
+
+Close as obsolete. `main` uses standard C++ threads and no longer depends on the
+old pthread feature-detection design.
+
+### #52: shared-library versions
+
+Perform a staged shared build and check the installed library names and
+symlinks. Current CMake targets set both `VERSION` and `SOVERSION`.
+
+### #117: `-fPIC` in static libraries
+
+Close as intentional unless the project wants to support a second explicitly
+non-PIC archive configuration. PIC archives can be linked into shared libraries
+and position-independent executables.
+
+### #146 and #172: Qt build support questions
+
+Close as answered or stale after one current Qt-enabled build check. Both reports
+appear to concern local Qt discovery or mixed Qt installations rather than
+reproducible defects in `main`.
+
+## Suggested execution order
+
+1. Fix #166, then #168.
+2. Bound and reproduce #199 before publishing the release.
+3. Resolve #142 and the small release-facing items #107, #108, #126, and #151.
+4. Verify and close #83, #92, #65, #52, #117, #146, and #172.
+5. Investigate #175 and define a practical contract for #155.
+6. Reframe #80–#82 as one current scheduling project.
+7. Work through the remaining search and usability issues as capacity permits.

gecode/int/gcc/dom-sup.hpp

@@ -1417,7 +1417,8 @@ 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 +1767,3 @@ namespace Gecode { namespace Int { namespace GCC {
 
 // STATISTICS: int-prop
 
-

test/flatzinc/issue166.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 recomputation does not lose a solution
+    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 == 11) &&
+        (output.find("A = 3;\nB = 1;\nC = 3;\nD = 1;\nE = 2;\nG = 3;\n")
+         != std::string::npos);
+    }
+
+    /// Helper class to create and register test
+    class Create {
+    public:
+      /// Perform creation and registration
+      Create(void) {
+        (void) new FlatZincTest("Issue166",
+"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"}, check);
+      }
+    };
+
+    Create c;
+  }
+
+}}
+
+// STATISTICS: test-flatzinc