unify collection canDropCheck with context menu

- move collectionTree canDropCheck and canDropCheckAsync
to Zotero.Collection::canMoveToTarget and Zotero.Collection::canMoveToTargetAsync
per https://github.com/zotero/zotero/pull/4420#issuecomment-2406579899
That way, we share the logic to determine if collection row can
be dropped onto another row, as well as to disable/enable context menus.
- allow to copy a collection to another library if
there already is a linked collection but it is in trash.
Fixes: #4862

chrome/content/zotero/collectionTree.jsx

@@ -1777,27 +1777,9 @@ var CollectionTree = class CollectionTree extends LibraryTree {
 				return true;
 			}
 			else if (dataType == 'zotero/collection') {
-				if (!treeRow.isLibrary(true) && !treeRow.isCollection()) {
-					return false;
-				}
-				
 				let draggedCollectionID = data[0];
 				let draggedCollection = Zotero.Collections.get(draggedCollectionID);
-				
-				// Dragging within same library
-				if (treeRow.ref.libraryID == draggedCollection.libraryID) {
-					// Collections cannot be dropped on themselves
-					if (draggedCollectionID == treeRow.ref.id) {
-						return false;
-					}
-					
-					// Nor in their children
-					if (draggedCollection.hasDescendent('collection', treeRow.ref.id)) {
-						return false;
-					}
-				}
-				
-				return true;
+				return draggedCollection.canMoveToTarget(treeRow.ref, { debug: true });
 			}
 		}
 		return false;	
@@ -1871,28 +1853,8 @@ var CollectionTree = class CollectionTree extends LibraryTree {
 			else if (dataType == 'zotero/collection') {
 				let draggedCollectionID = data[0];
 				let draggedCollection = Zotero.Collections.get(draggedCollectionID);
-				
-				// Dragging a collection to a different library
-				if (treeRow.ref.libraryID != draggedCollection.libraryID) {
-					// Disallow if linked collection already exists
-					if (await draggedCollection.getLinkedCollection(treeRow.ref.libraryID, true)) {
-						Zotero.debug("Linked collection already exists in library");
-						return false;
-					}
-					
-					let descendents = draggedCollection.getDescendents(false, 'collection');
-					for (let descendent of descendents) {
-						descendent = Zotero.Collections.get(descendent.id);
-						// Disallow if linked collection already exists for any subcollections
-						//
-						// If this is allowed in the future for the root collection,
-						// need to allow drag only to root
-						if (await descendent.getLinkedCollection(treeRow.ref.libraryID, true)) {
-							Zotero.debug("Linked subcollection already exists in library");
-							return false;
-						}
-					}
-				}
+				let canMove = await draggedCollection.canMoveToTargetAsync(treeRow.ref, { debug: true });
+				return canMove;
 			}
 		}
 		return true;

chrome/content/zotero/xpcom/data/collection.js

@@ -987,3 +987,69 @@ Zotero.Collection.prototype._unregisterChildItem = function (itemID) {
 		this._childItems.delete(itemID);
 	}
 }
+
+Zotero.Collection.prototype.canMoveToTarget = function (target, options = {}) {
+	let logMessage = (message) => {
+		if (options.debug) {
+			Zotero.debug(message);
+		}
+	};
+	if (!(target instanceof Zotero.Library || target instanceof Zotero.Collection)) {
+		logMessage("Can only add collection to another collection or group");
+		return false;
+	}
+	let targetLibrary = target instanceof Zotero.Library
+		? target
+		: Zotero.Libraries.get(target.libraryID);
+	if (!targetLibrary.editable) {
+		logMessage("Not editable target library.");
+		return false;
+	}
+	if (target instanceof Zotero.Collection) {
+		if (target.id == this.id) {
+			logMessage("Cannot add collection to itself");
+			return false;
+		}
+		if (this.hasDescendent('collection', target.id)) {
+			logMessage("Cannot add collection to its descendent");
+			return false;
+		}
+		if (this.parentID == target.id) {
+			logMessage("Cannot add collection to its direct parent");
+			return false;
+		}
+	}
+
+	return true;
+};
+
+Zotero.Collection.prototype.canMoveToTargetAsync = async function (target, options = {}) {
+	let logMessage = (message) => {
+		if (options.debug) {
+			Zotero.debug(message);
+		}
+	};
+	if (!this.canMoveToTarget(target, options)) return false;
+
+	if (target.libraryID !== this.libraryID) {
+		let linkedCollection = await this.getLinkedCollection(target.libraryID, true);
+		if (linkedCollection && !linkedCollection.deleted) {
+			logMessage(`Linked collection already exists in library ${target.libraryID}`);
+			return false;
+		}
+		let descendents = this.getDescendents(false, 'collection');
+		for (let descendent of descendents) {
+			descendent = Zotero.Collections.get(descendent.id);
+			// Disallow if linked collection already exists for any subcollections
+			//
+			// If this is allowed in the future for the root collection,
+			// need to allow drag only to root
+			let linkedSubcollection = await descendent.getLinkedCollection(target.libraryID, true);
+			if (linkedSubcollection && !linkedSubcollection.deleted) {
+				logMessage("Linked subcollection already exists in library");
+				return false;
+			}
+		}
+	}
+	return true;
+};

chrome/content/zotero/zoteroPane.js

@@ -4276,20 +4276,14 @@ var ZoteroPane = new function () {
 						event.stopPropagation();
 					}
 				},
-				
-				(target) => {
-					// can't move collection into itself, its parent or its children
-					return selected == target
-						|| selected.parentKey == target.key
-						|| selected.hasDescendent('collection', target.id);
-				}
+				target => !selected.canMoveToTarget(target)
 			);
 			popup.append(menuItem);
 		}
 	};
 
 
-	this.buildCopyCollectionMenu = function (event) {
+	this.buildCopyCollectionMenu = Zotero.Utilities.Internal.serial(async function (event) {
 		if (event.target !== event.currentTarget) return;
 		let popup = document.getElementById("zotero-copy-collection-popup");
 		popup.replaceChildren();
@@ -4298,33 +4292,6 @@ var ZoteroPane = new function () {
 		// Fetch all libraries
 		let topLevelEntries = Zotero.Libraries.getAll().filter(lib => !(lib instanceof Zotero.Feed));
 
-		// Check which libraries have collections linked to the selected collection
-		// and disable their menuitems. Same logic as in CollectionTree.canDropCheckAsync.
-		let linkedCollectionsExist = {};
-		(async () => {
-			for (let library of topLevelEntries) {
-				if (library.libraryID == selected.libraryID) continue;
-				// Check which library has a collection linked to the selected collection
-				let linkedCollection = await selected.getLinkedCollection(library.libraryID, true);
-				linkedCollectionsExist[library.libraryID] = linkedCollection;
-				// Also check which library has collections linked to a subcollection of the selected collection
-				for (let descendent of selected.getDescendents(false, 'collection')) {
-					let subcollection = Zotero.Collections.get(descendent.id);
-					let linkedSubcollection = await subcollection.getLinkedCollection(library.libraryID, true);
-					if (linkedSubcollection) {
-						linkedCollectionsExist[library.libraryID] = linkedSubcollection;
-					}
-				}
-			}
-			// Libraries that have linked collections have their menus disabled
-			for (let libraryMenuItem of [...popup.childNodes]) {
-				let menuItemLibID = libraryMenuItem.getAttribute("value").substring(1);
-				if (linkedCollectionsExist[menuItemLibID]) {
-					libraryMenuItem.disabled = true;
-				}
-			}
-		})();
-		
 		// If there is only one library, display its collections as top-level menuitems
 		if (topLevelEntries.length == 1) {
 			// Manually add My Library menuitem at the top, so one can still copy into it
@@ -4359,16 +4326,22 @@ var ZoteroPane = new function () {
 						event.stopPropagation();
 					}
 				},
-				
-				(target) => {
-					// can't copy collection into itself or into non-editable groups
-					return selected == target
-						|| (target instanceof Zotero.Group && !target.editable);
-				}
+				target => !selected.canMoveToTarget(target)
 			);
 			popup.append(menuItem);
 		}
-	};
+
+		// Disable libraries to which collection cannot be copied
+		if (topLevelEntries[0] instanceof Zotero.Library) {
+			for (let entry of topLevelEntries) {
+				let canCopy = await selected.canMoveToTargetAsync(entry);
+				if (!canCopy) {
+					let menuitem = popup.querySelector(`[value="L${entry.libraryID}"]`);
+					menuitem.disabled = true;
+				}
+			}
+		}
+	});
 
 	this.buildAddItemToCollectionMenu = function (event, items = this.getSelectedItems()) {
 		if (event.target !== event.currentTarget) return;

test/tests/zoteroPaneTest.js

@@ -1825,7 +1825,7 @@ describe("ZoteroPane", function () {
 
 			await waitForNotifierEvent("add", "collection");
 
-			// Collection has been copies
+			// Collection has been copied
 			let groupCollections = groupCollection.getDescendents(false, 'collection');
 			let newCollectionID = groupCollections.find(col => col.name == collectionChild.name).id;
 			let newCollection = Zotero.Collections.get(newCollectionID);
@@ -1873,6 +1873,45 @@ describe("ZoteroPane", function () {
 			// Copied collection is a top-level collection
 			assert.notOk(newCollection.parentID);
 		});
+		
+		it("should allow copying between libraries if there is a linked collection but it is in trash", async function () {
+			let groupDestination = await createGroup();
+			let groupCollection = await createDataObject('collection', { libraryID: groupDestination.libraryID });
+
+			let collection = await createDataObject('collection');
+			let collectionChild = await createDataObject('collection', { parentID: collection.id });
+
+			await zp.collectionsView.selectByID("C" + collectionChild.id);
+
+			await zp.copyCollection(groupCollection);
+
+			await waitForNotifierEvent("add", "collection");
+
+			// Collection has been copied
+			let newCollection = zp.getSelectedCollection();
+			assert.equal(newCollection.libraryID, groupCollection.libraryID);
+			assert.equal(newCollection.name, collectionChild.name);
+
+			// Send new collection to trash
+			newCollection.deleted = true;
+			await newCollection.saveTx();
+
+			// Right click on the selected collection
+			await zp.collectionsView.selectByID("C" + collectionChild.id);
+			await zp.buildCopyCollectionMenu({});
+			await Zotero.Promise.delay();
+
+			let groupMenu = doc.querySelector(`#zotero-copy-collection-popup menu[value="L${groupDestination.libraryID}"]`);
+			// Menu of the library with linked collection should be enabled
+			assert.equal(groupMenu.disabled, false);
+
+			// Copy collection again
+			await zp.copyCollection(groupCollection);
+			await waitForNotifierEvent("add", "collection");
+			let anotherNewCollection = zp.getSelectedCollection();
+			// Newly created collection is in the group
+			assert.equal(anotherNewCollection.libraryID, groupCollection.libraryID);
+		});
 	});
 	describe("#moveCollection", function () {
 		it("should move collection into another collection of the same library", async function () {