Prevent self-composition in layouts (#2287)

src/api/objects/ObjectAPI.js

@@ -215,6 +215,19 @@ define([
         return utils.makeKeyString(identifier);
     };
 
+    /**
+     * Given any number of identifiers, will return true if they are all equal, otherwise false.
+     * @param {module:openmct.ObjectAPI~Identifier[]} identifiers
+     */
+    ObjectAPI.prototype.areIdsEqual = function (...identifiers) {
+        return identifiers.map(utils.parseKeyString)
+            .every(identifier => {
+                return identifier === identifiers[0] ||
+                    (identifier.namespace === identifiers[0].namespace &&
+                        identifier.key === identifiers[0].key);
+            });
+    }
+
     /**
      * Uniquely identifies a domain object.
      *

src/plugins/displayLayout/components/DisplayLayout.vue

@@ -124,6 +124,8 @@
         bottom: Number.NEGATIVE_INFINITY
     };
 
+    const DRAG_OBJECT_TRANSFER_PREFIX = 'openmct/domain-object/';
+
     function getItemDefinition(itemType, ...options) {
         let itemView = ITEM_TYPE_VIEW_MAP[itemType];
 
@@ -246,7 +248,7 @@
                 } else {
                     let identifier = this.openmct.objects.makeKeyString(domainObject.identifier);
 
-                    if (!this.objectViewMap[identifier]) {
+                    if (!this.containsObject(identifier)) {
                         this.addItem('subobject-view', domainObject, droppedObjectPosition);
                     } else {
                         let prompt = this.openmct.overlays.dialog({
@@ -264,8 +266,21 @@
                     }
                 }
             },
-            handleDragOver($event){
+            containsObject(identifier) {
+                return _.get(this.internalDomainObject, 'composition')
+                    .some(childId => this.openmct.objects.areIdsEqual(childId, identifier));
+            },
+            handleDragOver($event) {
+                // Get the ID of the dragged object
+                let draggedKeyString = $event.dataTransfer.types
+                    .filter(type => type.startsWith(DRAG_OBJECT_TRANSFER_PREFIX))
+                    .map(type => type.substring(DRAG_OBJECT_TRANSFER_PREFIX.length))[0];
+                
+                // If the layout already contains the given object, then shortcut the default dragover behavior and 
+                // potentially allow drop. Display layouts allow drag drop of duplicate telemetry objects.
+                if (this.containsObject(draggedKeyString)){
                     $event.preventDefault();
+                }
             },
             isTelemetry(domainObject) {
                 if (this.openmct.telemetry.isTelemetryObject(domainObject)

src/ui/components/ObjectLabel.vue

@@ -66,6 +66,7 @@ export default {
         dragStart(event) {
             let navigatedObject = this.openmct.router.path[0];
             let serializedPath = JSON.stringify(this.objectPath);
+            let keyString = this.openmct.objects.makeKeyString(this.domainObject.identifier);
 
             /*
              * Cannot inspect data transfer objects on dragover/dragenter so impossible to determine composability at
@@ -78,6 +79,7 @@ export default {
             // serialize domain object anyway, because some views can drag-and-drop objects without composition 
             // (eg. notabook.)
             event.dataTransfer.setData("openmct/domain-object-path", serializedPath);
+            event.dataTransfer.setData(`openmct/domain-object/${keyString}`, this.domainObject);
         }
     }
 }