feat: Make examination use declarative shadow variables (#61)

---------
Co-authored-by: Lukáš Petrovický <lukas@petrovicky.net>

Author: Christopher-Chianelli

src/main/java/ai/timefold/solver/benchmarks/examples/examination/domain/FollowingExam.java

@@ -1,8 +1,8 @@
 package ai.timefold.solver.benchmarks.examples.examination.domain;
 
-import ai.timefold.solver.benchmarks.examples.examination.domain.solver.PeriodUpdatingVariableListener;
 import ai.timefold.solver.core.api.domain.entity.PlanningEntity;
 import ai.timefold.solver.core.api.domain.variable.ShadowVariable;
+import ai.timefold.solver.core.preview.api.domain.variable.declarative.ShadowSources;
 
 @PlanningEntity
 public class FollowingExam extends Exam {
@@ -21,9 +21,7 @@ public void setLeadingExam(LeadingExam leadingExam) {
     }
 
     @Override
-    @ShadowVariable(variableListenerClass = PeriodUpdatingVariableListener.class,
-            sourceEntityClass = LeadingExam.class,
-            sourceVariableName = "period")
+    @ShadowVariable(supplierName = "periodSupplier")
     public Period getPeriod() {
         return period;
     }
@@ -32,6 +30,11 @@ public void setPeriod(Period period) {
         this.period = period;
     }
 
+    @ShadowSources("leadingExam.period")
+    public Period periodSupplier() {
+        return leadingExam.getPeriod();
+    }
+
     // ************************************************************************
     // With methods
     // ************************************************************************

src/main/java/ai/timefold/solver/benchmarks/examples/examination/domain/solver/PeriodUpdatingVariableListener.java

@@ -1,5 +1,6 @@
 package ai.timefold.solver.benchmarks.micro.scoredirector.problems;
 
+import java.util.EnumSet;
 import java.util.Objects;
 
 import ai.timefold.solver.benchmarks.examples.examination.domain.Exam;
@@ -11,6 +12,7 @@
 import ai.timefold.solver.benchmarks.micro.scoredirector.Example;
 import ai.timefold.solver.benchmarks.micro.scoredirector.ScoreDirectorType;
 import ai.timefold.solver.core.config.score.director.ScoreDirectorFactoryConfig;
+import ai.timefold.solver.core.config.solver.PreviewFeature;
 import ai.timefold.solver.core.impl.domain.solution.descriptor.SolutionDescriptor;
 import ai.timefold.solver.persistence.common.api.domain.solution.SolutionFileIO;
 
@@ -33,8 +35,8 @@ protected ScoreDirectorFactoryConfig buildScoreDirectorFactoryConfig(ScoreDirect
 
     @Override
     protected SolutionDescriptor<Examination> buildSolutionDescriptor() {
-        return SolutionDescriptor.buildSolutionDescriptor(Examination.class, Exam.class, LeadingExam.class,
-                FollowingExam.class);
+        return SolutionDescriptor.buildSolutionDescriptor(EnumSet.of(PreviewFeature.DECLARATIVE_SHADOW_VARIABLES),
+                Examination.class, Exam.class, LeadingExam.class, FollowingExam.class);
     }
 
     @Override

src/main/java/ai/timefold/solver/benchmarks/micro/scoredirector/problems/ExaminationProblem.java

@@ -5,7 +5,7 @@
     <!--<environmentMode>FULL_ASSERT</environmentMode>-->
     <!-- To solve faster by saturating multiple CPU cores -->
     <!--<moveThreadCount>AUTO</moveThreadCount>-->
-
+    <enablePreviewFeature>DECLARATIVE_SHADOW_VARIABLES</enablePreviewFeature>
     <solutionClass>ai.timefold.solver.benchmarks.examples.examination.domain.Examination</solutionClass>
     <entityClass>ai.timefold.solver.benchmarks.examples.examination.domain.Exam</entityClass>
     <entityClass>ai.timefold.solver.benchmarks.examples.examination.domain.LeadingExam</entityClass>