Make DragSource extension/component available in DropEvent (#8636)

* Make DragSource extension/component available in DropEvent (resolves #8439)

* Update drag and drop test to use new API

* Change type of drag source and update javadoc

* Use existing data map instead of DataTransfer

2 files changed, 11 insertions, 1 deletions

diff --git a/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java b/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
index 532b9877fc..b823167572 100644
--- a/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
+++ b/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
@@ -42,6 +42,11 @@ public class DragSourceExtensionConnector extends AbstractExtensionConnector {
 
     private static final String CLASS_DRAGGABLE = "v-draggable";
 
+    /**
+     * Data type for storing drag source extension connector's ID
+     */
+    static final String DATA_TYPE_DRAG_SOURCE_ID = "drag-source-id";
+
     // Create event listeners
     private final EventListener dragStartListener = this::onDragStart;
     private final EventListener dragEndListener = this::onDragEnd;
@@ -104,6 +109,10 @@ public class DragSourceExtensionConnector extends AbstractExtensionConnector {
             nativeEvent.getDataTransfer().setData(format, data.get(format));
         }
 
+        // Store the extension's connector ID in DataTransfer.data
+        nativeEvent.getDataTransfer()
+                .setData(DATA_TYPE_DRAG_SOURCE_ID, getConnectorId());
+
         // Initiate firing server side dragstart event when there is a
         // DragStartListener attached on the server side
         if (hasEventListener(DragSourceState.EVENT_DRAGSTART)) {
diff --git a/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java b/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
index 3a9cbbfe84..37d62ad7c0 100644
--- a/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
+++ b/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
@@ -193,7 +193,8 @@ public class DropTargetExtensionConnector extends AbstractExtensionConnector {
             }
 
             getRpcProxy(DropTargetRpc.class)
-                    .drop(types, data, getState().dropEffect);
+                    .drop(types, data, getState().dropEffect, data.get(
+                            DragSourceExtensionConnector.DATA_TYPE_DRAG_SOURCE_ID));
         }
 
         removeTargetIndicator(getDropTargetElement());