XWIKI-23441: Merge fallback of xobjects is badly handled

  * Ensure to properly record a conflict when an xobject is missing in
    current version but present in previous and next, and properly
handle the fallback version

Author: surli

xwiki-platform-core/xwiki-platform-store/xwiki-platform-store-merge/xwiki-platform-store-merge-default/src/main/java/org/xwiki/store/merge/internal/DefaultMergeManager.java

@@ -485,16 +485,22 @@ private MergeManagerResult<Map<DocumentReference, List<BaseObject>>, BaseObject>
                                 } else {
                                     // collision between DB and new: property to modify but does not exist in DB
                                     // Lets assume it's a mistake to fix
-                                    objectMergeResult.getLog().warn("Object [{}] does not exist",
+                                    objectMergeResult.getLog().warn("Property [{}] does not exist",
                                         newProperty.getReference());
 
                                     objectResult.safeput(diff.getPropName(), newProperty);
                                     objectMergeResult.setModified(true);
                                 }
                             }
                         } else {
-                            // Object explitely removed from the DB, lets assume we don't care about the changes
-                            objectMergeResult.getLog().warn(WARNING_OBJECT_REMOVED, previousObject.getReference());
+                            // Object explicitely removed from the DB, it's a conflict
+                            objectMergeResult.getLog().error(ERROR_COLLISION_OBJECT, previousObject.getReference());
+
+                            // We put the new object only if the fallback is to take new version.
+                            if (configuration.getConflictFallbackVersion() == ConflictFallbackVersion.NEXT) {
+                                mergedDocument.setXObject(newObject.getNumber(), newObject.clone());
+                                objectMergeResult.setModified(true);
+                            }
                         }
                     }
                 }

xwiki-platform-core/xwiki-platform-store/xwiki-platform-store-merge/xwiki-platform-store-merge-default/src/test/java/org/xwiki/store/merge/internal/DefaultMergeManagerTest.java

@@ -449,13 +449,44 @@ public void testMergeCurrentObjectRemoved() throws Exception
             newobj.setStringValue("newtest", "newtest");
             this.nextDocument.addXObject(newobj);
 
-            merge();
-
-            BaseObject mergedobj = this.currentDocument.getXObject(this.xclass.getReference(), 0);
+            MergeDocumentResult result = this.mergeManager.mergeDocument(this.previousDocument, this.nextDocument,
+                this.currentDocument, this.configuration);
+            List<LogEvent> logs = result.getLog().getLogs(LogLevel.ERROR);
+            // We get 2 logs: one for the change on existing property, one for the new property.
+            assertEquals(2, logs.size());
+            assertEquals("Collision found on object [Object wiki:space.page^classspace.class[0]]",
+                logs.get(0).getFormattedMessage());
+            assertEquals("Collision found on object [Object wiki:space.page^classspace.class[0]]",
+                logs.get(1).getFormattedMessage());
 
+            BaseObject mergedobj = ((XWikiDocument) result.getMergeResult()).getXObject(this.xclass.getReference(), 0);
             assertNull(mergedobj);
         }
 
+        @Test
+        public void testMergeCurrentObjectRemovedFallbackNext() throws Exception
+        {
+            this.configuration.setConflictFallbackVersion(MergeConfiguration.ConflictFallbackVersion.NEXT);
+            this.xobject.setStringValue("test", "");
+            this.xobject.setStringValue("previoustest", "previoustest");
+            this.previousDocument.addXObject(this.xobject);
+
+            BaseObject newobj = this.xobject.clone();
+            newobj.setStringValue("test", "test2");
+            newobj.setStringValue("newtest", "newtest");
+            this.nextDocument.addXObject(newobj);
+
+            MergeDocumentResult result = this.mergeManager.mergeDocument(this.previousDocument, this.nextDocument,
+                this.currentDocument, this.configuration);
+            List<LogEvent> logs = result.getLog().getLogs(LogLevel.ERROR);
+            // We get a single log because at second pass the object is set.
+            assertEquals(1, logs.size());
+            assertEquals("Collision found on object [Object wiki:space.page^classspace.class[0]]", logs.get(0).getFormattedMessage());
+
+            BaseObject mergedobj = ((XWikiDocument) result.getMergeResult()).getXObject(this.xclass.getReference(), 0);
+            assertEquals(newobj, mergedobj);
+        }
+
         @Test
         public void testMergeAttachmentEquals() throws Exception
         {