• Implement TagsField support for Groups field with modern tag-based interface
• Create abstract TagsEditor base class for shared tag editor functionality
• Refactor KeywordsEditor to inherit from TagsEditor for code reuse
• Add GroupsEditor with drag-and-drop, context menus, and tag editing features

Abstract base class for tag editors

• New abstract base class extending HBox and implementing FieldEditorFX
• Provides common functionality for tag-based field editors
• Defines shared properties: field, suggestionProvider, fieldCheckers, undoManager
• Implements getNode() and getWeight() methods for consistent editor behavior

jabgui/src/main/java/org/jabref/gui/fieldeditors/TagsEditor.java

New Groups field editor with TagsField UI

• New editor class extending TagsEditor for Groups field with TagsField UI
• Implements drag-and-drop support from group tree with duplicate prevention
• Provides tag context menu with Copy, Cut, Delete actions
• Supports double-click editing, tag reordering, and clipboard paste operations
• Handles hierarchical group names with proper separator support

jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditor.java

ViewModel for Groups field management

• New ViewModel for Groups field managing group list and serialization
• Provides bidirectional binding between UI tags and field text content
• Implements suggestion provider for group autocomplete functionality
• Handles group parsing and serialization with configurable separator

jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditorViewModel.java

Description

New code collects a stream via collect(Collectors.toList()) instead of using the modern
Stream.toList() API. This conflicts with the requirement to prefer modern Java (24+) APIs and may
trigger modernization quality gates.

Code

jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditorViewModel.java[R82-87]

+        List<Keyword> suggestions = suggestionProvider.getPossibleSuggestions().stream()
+                                                      .map(String.class::cast)
+                                                      .filter(group -> group.toLowerCase().contains(request.toLowerCase()))
+                                                      .map(Keyword::new)
+                                                      .distinct()
+                                                      .collect(Collectors.toList());

Evidence

Compliance requires preferring modern Java APIs; the new implementation explicitly uses
Collectors.toList() in changed code where .toList() is available and clearer.

AGENTS.md
jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditorViewModel.java[82-87]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
`GroupsEditorViewModel#getSuggestions` uses `collect(Collectors.toList())` even though `Stream.toList()` is the preferred modern API.
## Issue Context
The compliance checklist requires preferring modern Java (24+) APIs where applicable.
## Fix Focus Areas
- jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditorViewModel.java[82-87]

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Description

The drag-and-drop handler assumes the dragboard content is a List and non-empty, then calls
getFirst() without validating emptiness/type. Malformed or empty drag data can cause runtime
exceptions and crash the UI interaction.

Code

jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditor.java[R139-147]

+            if (event.getDragboard().hasContent(DragAndDropDataFormats.GROUP)) {
+                List<String> draggedGroups = (List<String>) event.getDragboard().getContent(DragAndDropDataFormats.GROUP);
+                if (bibEntry.isPresent() && draggedGroups.getFirst() != null) {
+                    Keyword newGroup = new Keyword(draggedGroups.getFirst());
+                    if (!groupTagsField.getTags().contains(newGroup)) {
+                        groupTagsField.addTags(newGroup);
+                    }
+                    success = true;
+                }

Evidence

Robust error handling and input validation require guarding external inputs before processing; here
the code performs an unchecked cast and uses getFirst() without ensuring the list is non-empty or
well-typed.

Rule 3: Generic: Robust Error Handling and Edge Case Management
jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditor.java[139-147]
Best Practice: Learned patterns

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
The group drag-and-drop handler performs an unchecked cast to `List<String>` and calls `getFirst()` without verifying the list is non-empty. This can throw at runtime on malformed or empty dragboard content.
## Issue Context
Drag-and-drop content is an external input channel (from the UI system). It should be validated for type and empty/null values before use to avoid crashes.
## Fix Focus Areas
- jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditor.java[139-147]

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Description

GroupsEditor drops the group-tree dragboard payload (a group *path* like "parent > child", or empty
for the root) directly into the GROUPS field, but ExplicitGroup membership is matched by group name;
this means dropping a hierarchical group will not actually assign the entry to that group (and
dragging the root can add an empty tag).

Code

jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditor.java[R137-147]

+        this.setOnDragDropped(event -> {
+            boolean success = false;
+            if (event.getDragboard().hasContent(DragAndDropDataFormats.GROUP)) {
+                List<String> draggedGroups = (List<String>) event.getDragboard().getContent(DragAndDropDataFormats.GROUP);
+                if (bibEntry.isPresent() && draggedGroups.getFirst() != null) {
+                    Keyword newGroup = new Keyword(draggedGroups.getFirst());
+                    if (!groupTagsField.getTags().contains(newGroup)) {
+                        groupTagsField.addTags(newGroup);
+                    }
+                    success = true;
+                }

Evidence

The group tree DnD payload is a list of group *paths* (not names). GroupTreeNode.getPath
concatenates ancestor names with " > " and explicitly skips the root (so the root path becomes "").
GroupsEditor takes the first path and stores it as a Keyword in the GROUPS tags. However,
ExplicitGroup stores/matches membership via WordKeywordGroup over StandardField.GROUPS with
searchExpression=name, and the matching logic checks exact keyword containment—so a stored value
like "parent > child" (or empty) will not match a group whose name is just "child".

jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditor.java[129-147]
jabgui/src/main/java/org/jabref/gui/groups/GroupTreeView.java[356-374]
jablib/src/main/java/org/jabref/model/groups/GroupTreeNode.java[30-31]
jablib/src/main/java/org/jabref/model/groups/GroupTreeNode.java[243-251]
jablib/src/main/java/org/jabref/model/groups/ExplicitGroup.java[10-22]
jablib/src/main/java/org/jabref/model/groups/WordKeywordGroup.java[179-191]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
Dragging a group from the group tree into `GroupsEditor` currently stores the group *path* (e.g., `parent > child`, or `""` for the root) as a GROUPS tag. Explicit group membership is matched by group **name**, so this can silently fail to assign the entry to the dragged group and can even add an empty tag when the root is dragged.
### Issue Context
The dragboard payload for `DragAndDropDataFormats.GROUP` is a `List<String>` of `GroupTreeNode.getPath()` values.
### Fix Focus Areas
- jabgui/src/main/java/org/jabref/gui/fieldeditors/GroupsEditor.java[137-151]
### Implementation notes
- Iterate over `draggedGroups` and for each `path`:
- skip `null` / blank strings
- compute `groupName` as the last segment after the path delimiter (`" > "`), e.g. `path.substring(path.lastIndexOf(" > ") + 3)`
- add `new Keyword(groupName)` if not already present
- Consider accepting `TransferMode.COPY` for this operation (optional).
- Add a small unit test for the path->name extraction logic if you factor it into a helper (optional but recommended).

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Description

A new multi-line documentation comment was added using /** ... */ instead of the required Markdown
Javadoc /// style. This reduces consistency with the project’s commenting standard.

Code

jabgui/src/main/java/org/jabref/gui/fieldeditors/TagsEditor.java[R13-16]

+/**
+ * Abstract base class for tag-based field editors.
+ * Provides common functionality for editors that display field values as tags.
+ */

Evidence

The checklist requires Markdown Javadoc (///) for multi-line documentation comments where
applicable; the new class-level documentation uses a traditional block Javadoc instead.

AGENTS.md
jabgui/src/main/java/org/jabref/gui/fieldeditors/TagsEditor.java[13-16]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
The new `TagsEditor` documentation uses a `/** ... */` multi-line comment, but the commenting standard requires Markdown Javadoc using `///` for multi-line documentation.
## Issue Context
Aligning comment style reduces review friction and keeps documentation consistent across the codebase.
## Fix Focus Areas
- jabgui/src/main/java/org/jabref/gui/fieldeditors/TagsEditor.java[13-16]

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