[1847] Fix export of abstract OccurrenceUsage

CHANGELOG.adoc

@@ -52,6 +52,8 @@ This fix ensure that imported models containing, for example, a top-level `Libra
 - https://github.com/eclipse-syson/syson/issues/1784[#1784] Error while exporting `FeatureValue` using enumeration literals.
 - https://github.com/eclipse-syson/syson/issues/1838[#1838] [metamodel] Invalid computation of `Usage.getType`: The subsetted features should be taken into account.
 
+- https://github.com/eclipse-syson/syson/issues/1847[#1847] [export] Textual export duplicates "abstract" keyword for `OccurrenceUsage`.
+
 === Improvements
 
 - https://github.com/eclipse-syson/syson/issues/1666[#1666] [export] Export `SatisfyRequirementUsage` in textual format.

backend/application/syson-application/src/test/java/org/eclipse/syson/application/export/ImportExportTests.java

@@ -985,6 +985,17 @@ public void checkReferencingWithShortName() throws IOException {
         this.checker.check(input, input);
     }
 
+    @Test
+    @DisplayName("GIVEN an abstract OccurrenceUsage, WHEN importing and exporting the model, THEN the abstract keyword should be correctly exported")
+    public void checkAbstractOccurrenceUsage() throws IOException {
+        var input = """
+                package root {
+                    abstract occurrence test;
+                    abstract occurrence def Test;
+                }""";
+        this.checker.check(input, input);
+    }
+
     @Test
     @DisplayName("GIVEN a model with a references to elements, WHEN importing and exporting the model, THEN the references should privileged short name over declared name when possible")
     public void checkReferencingIdentifiers() throws IOException {

backend/metamodel/syson-sysml-metamodel/src/main/java/org/eclipse/syson/sysml/textual/SysMLElementSerializer.java

@@ -748,7 +748,6 @@ public String caseObjectiveMembership(ObjectiveMembership objective) {
     @Override
     public String caseOccurrenceUsage(OccurrenceUsage occurrenceUsage) {
         Appender builder = new Appender(this.lineSeparator, this.indentation);
-        this.appendUsagePrefix(builder, occurrenceUsage);
         this.appendOccurrenceUsagePrefix(builder, occurrenceUsage);
         if (PortionKind.SNAPSHOT.equals(occurrenceUsage.getPortionKind())) {
             builder.appendWithSpaceIfNeeded("snapshot");
@@ -2487,7 +2486,7 @@ private void appendPrefixMetadataMember(Appender builder, MetadataUsage metadata
         }
 
     }
-    
+
     private void appendRequirementConstraintUsage(Appender builder, ConstraintUsage constraintUsage) {
         if (this.useRequirementConstraintUsageShortHandNotation(constraintUsage)) {
             this.appendRequirementConstraintUsageShorthandNotation(builder, constraintUsage);
@@ -2567,6 +2566,10 @@ private void appendBasicUsagePrefix(Appender builder, Usage usage) {
             builder.appendSpaceIfNeeded();
             builder.append("end");
         }
+
+        if (usage.isIsReference() && !this.isImplicitlyReferential(usage)) {
+            builder.appendWithSpaceIfNeeded(SysMLv2Keywords.REF);
+        }
     }
 
     private FeatureDirectionKind getDefaultDirection(Usage usage) {

doc/content/modules/user-manual/pages/release-notes/2026.1.0.adoc

@@ -89,6 +89,7 @@ package root {
 ** New `Expose` elements now have `visibility` set to _protected_ and have `isImportAll` set to _true_, as required by the SysMLv2 specification.
 ** Correct the computation of a `Feature`'s types to properly account for subsetted features.
 
+** Fix the textual export of `OccurrenceUsage` to avoid duplication of the abstract keyword.
 
 == Improvements