2 files changed, 31 insertions, 18 deletions

diff --git a/subprojects/language-semantics/src/main/java/tools/refinery/language/semantics/ModelInitializer.java b/subprojects/language-semantics/src/main/java/tools/refinery/language/semantics/ModelInitializer.java
index bd6a8ec9..c9e7dea3 100644
--- a/subprojects/language-semantics/src/main/java/tools/refinery/language/semantics/ModelInitializer.java
+++ b/subprojects/language-semantics/src/main/java/tools/refinery/language/semantics/ModelInitializer.java
@@ -938,18 +938,30 @@ public class ModelInitializer {
         }
 
         private void collectRule(RuleDefinition ruleDefinition, ModelStoreBuilder storeBuilder) {
-                var name = semanticsUtils.getNameWithoutRootPrefix(ruleDefinition)
-                                .orElseGet(() -> "::rule" + ruleCount);
-                ruleCount++;
-                var rule = toRule(name, ruleDefinition);
-                switch (ruleDefinition.getKind()) {
-                case DECISION -> storeBuilder.tryGetAdapter(DesignSpaceExplorationBuilder.class)
-                                .ifPresent(dseBuilder -> dseBuilder.transformation(rule));
-                case PROPAGATION -> storeBuilder.tryGetAdapter(PropagationBuilder.class)
-                                .ifPresent(propagationBuilder -> propagationBuilder.rule(rule));
-                case REFINEMENT -> {
-                        // Rules not marked for decision or propagation are not invoked automatically.
-                }
+                try {
+                        var name = semanticsUtils.getNameWithoutRootPrefix(ruleDefinition)
+                                        .orElseGet(() -> "::rule" + ruleCount);
+                        ruleCount++;
+                        var rule = toRule(name, ruleDefinition);
+                        switch (ruleDefinition.getKind()) {
+                        case DECISION -> storeBuilder.tryGetAdapter(DesignSpaceExplorationBuilder.class)
+                                        .ifPresent(dseBuilder -> dseBuilder.transformation(rule));
+                        case PROPAGATION -> storeBuilder.tryGetAdapter(PropagationBuilder.class)
+                                        .ifPresent(propagationBuilder -> propagationBuilder.rule(rule));
+                        case REFINEMENT -> {
+                                // Rules not marked for decision or propagation are not invoked automatically.
+                        }
+                        }
+                } catch (InvalidClauseException e) {
+                        int clauseIndex = e.getClauseIndex();
+                        var bodies = ruleDefinition.getPreconditions();
+                        if (clauseIndex < bodies.size()) {
+                                throw new TracedException(bodies.get(clauseIndex), e);
+                        } else {
+                                throw new TracedException(ruleDefinition, e);
+                        }
+                } catch (RuntimeException e) {
+                        throw TracedException.addTrace(ruleDefinition, e);
                 }
         }
 
@@ -981,8 +993,13 @@ public class ModelInitializer {
                         }
                 }
                 var builder = Rule.builder(name).parameters(parameters);
-                for (var precondition : ruleDefinition.getPreconditions()) {
-                        buildConjunction(precondition, parameterMap, commonLiterals, builder);
+                var preconditions = ruleDefinition.getPreconditions();
+                if (preconditions.isEmpty()) {
+                        builder.clause(commonLiterals);
+                } else {
+                        for (var precondition : preconditions) {
+                                buildConjunction(precondition, parameterMap, commonLiterals, builder);
+                        }
                 }
                 for (var consequent : ruleDefinition.getConsequents()) {
                         buildConsequent(consequent, parameterMap, parametersToFocus, builder);
diff --git a/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java b/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
index 21dd7218..36a77ac7 100644
--- a/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
+++ b/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
@@ -413,10 +413,6 @@ public class ProblemValidator extends AbstractProblemValidator {
 
         @Check
         public void checkRuleDefinition(RuleDefinition ruleDefinition) {
-                if (ruleDefinition.getKind() != RuleKind.REFINEMENT && ruleDefinition.getPreconditions().isEmpty()) {
-                        acceptError("Decision and propagation rules must have at least one precondition.", ruleDefinition,
-                                        ProblemPackage.Literals.NAMED_ELEMENT__NAME, 0, INVALID_RULE_ISSUE);
-                }
                 if (ruleDefinition.getConsequents().size() != 1) {
                         acceptError("Rules must have exactly one consequent.", ruleDefinition,
                                         ProblemPackage.Literals.NAMED_ELEMENT__NAME, 0, INVALID_RULE_ISSUE);