Add log for dragMimeTypes

Fixes microsoft#145907

Author: alexr00

src/vs/workbench/browser/parts/views/treeView.ts

@@ -1283,14 +1283,31 @@ export class CustomTreeViewDragAndDrop implements ITreeDragAndDrop<ITreeItem> {
 		this.dndController = controller;
 	}
 
+	private handleDragAndLog(dndController: ITreeViewDragAndDropController, itemHandles: string[], uuid: string, dragCancellationToken: CancellationToken): Promise<IDataTransfer | undefined> {
+		return dndController.handleDrag(itemHandles, uuid, dragCancellationToken).then(additionalDataTransfer => {
+			if (additionalDataTransfer) {
+				const unlistedTypes: string[] = [];
+				for (const item of additionalDataTransfer.entries()) {
+					if ((item[0] !== this.treeMimeType) && (dndController.dragMimeTypes.findIndex(value => value === item[0]) < 0)) {
+						unlistedTypes.push(item[0]);
+					}
+				}
+				if (unlistedTypes.length) {
+					this.logService.warn(`Drag and drop controller for tree ${this.treeId} adds the following data transfer types but does not declare them in dragMimeTypes: ${unlistedTypes.join(', ')}`);
+				}
+			}
+			return additionalDataTransfer;
+		});
+	}
+
 	private addExtensionProvidedTransferTypes(originalEvent: DragEvent, itemHandles: string[]) {
 		if (!originalEvent.dataTransfer || !this.dndController) {
 			return;
 		}
 		const uuid = generateUuid();
 
 		this.dragCancellationToken = new CancellationTokenSource();
-		this.treeViewsDragAndDropService.addDragOperationTransfer(uuid, this.dndController.handleDrag(itemHandles, uuid, this.dragCancellationToken.token));
+		this.treeViewsDragAndDropService.addDragOperationTransfer(uuid, this.handleDragAndLog(this.dndController, itemHandles, uuid, this.dragCancellationToken.token));
 		this.treeItemsTransfer.setData([new DraggedTreeItemsIdentifier(uuid)], DraggedTreeItemsIdentifier.prototype);
 		if (this.dndController.dragMimeTypes.find((element) => element === Mimes.uriList)) {
 			// Add the type that the editor knows