Fix external group metadata changes are not merged

CHANGELOG.md

@@ -59,6 +59,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We fixed a bug where switching between themes will cause an error/exception. [#8939](https://github.com/JabRef/jabref/pull/8939)
 - We fixed a bug where files that were deleted in the source bibtex file were kept in the index. [#8962](https://github.com/JabRef/jabref/pull/8962)
 - We fixed "Error while sending to JabRef" when the browser extension interacts with JabRef. [JabRef-Browser-Extension#479](https://github.com/JabRef/JabRef-Browser-Extension/issues/479)
+- We fixed a bug that prevented external group metadata changes from being merged. [#8873](https://github.com/JabRef/jabref/issues/8873)
 
 ### Removed
 

src/main/java/org/jabref/gui/collab/MetaDataChangeViewModel.java

@@ -39,5 +39,8 @@ public Node description() {
     @Override
     public void makeChange(BibDatabaseContext database, NamedCompound undoEdit) {
         database.setMetaData(metaDataDiff.getNewMetaData());
+        // group change is handled by GroupChangeViewModel, so we set the groups root to the original value
+        // to prevent any inconsistency
+        metaDataDiff.getGroupDifferences().ifPresent(groupDiff -> database.getMetaData().setGroups(groupDiff.getOriginalGroupRoot()));
     }
 }

src/main/java/org/jabref/logic/bibtex/comparator/GroupDiff.java

@@ -23,7 +23,7 @@ public static Optional<GroupDiff> compare(MetaData originalMetaData, MetaData ne
         final Optional<GroupTreeNode> newGroups = newMetaData.getGroups();
 
         if (!originalGroups.equals(newGroups)) {
-            return Optional.of(new GroupDiff(newGroups.orElse(null), originalGroups.orElse(null)));
+            return Optional.of(new GroupDiff(originalGroups.orElse(null), newGroups.orElse(null)));
         } else {
             return Optional.empty();
         }

src/test/java/org/jabref/logic/bibtex/comparator/GroupDiffTest.java

@@ -56,7 +56,7 @@ void compareWithChangedGroup() {
 
         Optional<GroupDiff> groupDiff = GroupDiff.compare(originalMetaData, newMetaData);
 
-        Optional<GroupDiff> expectedGroupDiff = Optional.of(new GroupDiff(newMetaData.getGroups().get(), originalMetaData.getGroups().get()));
+        Optional<GroupDiff> expectedGroupDiff = Optional.of(new GroupDiff(originalMetaData.getGroups().get(), newMetaData.getGroups().get()));
 
         assertEquals(expectedGroupDiff.get().getNewGroupRoot(), groupDiff.get().getNewGroupRoot());
         assertEquals(expectedGroupDiff.get().getOriginalGroupRoot(), groupDiff.get().getOriginalGroupRoot());