Fix duplicated content and other bugs related to drag and drop handling (#4238)

* Fix drag and drop logic

* Add changeset

.changeset/drag-and-drop.md

@@ -0,0 +1,5 @@
+---
+'slate-react': patch
+---
+
+Fix duplicated content and other bugs related to drag and drop handling

packages/slate-react/src/components/editable.tsx

@@ -130,6 +130,7 @@ export const Editable = (props: EditableProps) => {
   const state = useMemo(
     () => ({
       isComposing: false,
+      isDraggingInternally: false,
       isUpdatingSelection: false,
       latestElement: null as DOMElement | null,
     }),
@@ -423,7 +424,12 @@ export const Editable = (props: EditableProps) => {
   // while a selection is being dragged.
   const onDOMSelectionChange = useCallback(
     throttle(() => {
-      if (!readOnly && !state.isComposing && !state.isUpdatingSelection) {
+      if (
+        !readOnly &&
+        !state.isComposing &&
+        !state.isUpdatingSelection &&
+        !state.isDraggingInternally
+      ) {
         const root = ReactEditor.findDocumentOrShadowRoot(editor)
         const { activeElement } = root
         const el = ReactEditor.toDOMNode(editor, editor)
@@ -748,7 +754,9 @@ export const Editable = (props: EditableProps) => {
               ) {
                 const node = ReactEditor.toSlateNode(editor, event.target)
                 const path = ReactEditor.findPath(editor, node)
-                const voidMatch = Editor.void(editor, { at: path })
+                const voidMatch =
+                  Editor.isVoid(editor, node) ||
+                  Editor.void(editor, { at: path, voids: true })
 
                 // If starting a drag on a void node, make sure it is selected
                 // so that it shows up in the selection's fragment.
@@ -757,6 +765,8 @@ export const Editable = (props: EditableProps) => {
                   Transforms.select(editor, range)
                 }
 
+                state.isDraggingInternally = true
+
                 ReactEditor.setFragmentData(editor, event.dataTransfer)
               }
             },
@@ -765,28 +775,58 @@ export const Editable = (props: EditableProps) => {
           onDrop={useCallback(
             (event: React.DragEvent<HTMLDivElement>) => {
               if (
-                hasTarget(editor, event.target) &&
                 !readOnly &&
+                hasTarget(editor, event.target) &&
                 !isEventHandled(event, attributes.onDrop)
-              ) {
-                // COMPAT: Certain browsers don't fire `beforeinput` events at all, and
-                // Chromium browsers don't properly fire them for files being
-                // dropped into a `contenteditable`. (2019/11/26)
-                // https://bugs.chromium.org/p/chromium/issues/detail?id=1028668
-                if (
-                  !HAS_BEFORE_INPUT_SUPPORT ||
-                  (!IS_SAFARI && event.dataTransfer.files.length > 0)
               ) {
                 event.preventDefault()
+
+                // Keep a reference to the dragged range before updating selection
+                const draggedRange = editor.selection
+
+                // Find the range where the drop happened
                 const range = ReactEditor.findEventRange(editor, event)
                 const data = event.dataTransfer
+
                 Transforms.select(editor, range)
+
+                if (state.isDraggingInternally) {
+                  if (draggedRange) {
+                    Transforms.delete(editor, {
+                      at: draggedRange,
+                    })
+                  }
+
+                  state.isDraggingInternally = false
+                }
+
                 ReactEditor.insertData(editor, data)
+
+                // When dragging from another source into the editor, it's possible
+                // that the current editor does not have focus.
+                if (!ReactEditor.isFocused(editor)) {
+                  ReactEditor.focus(editor)
                 }
               }
             },
             [readOnly, attributes.onDrop]
           )}
+          onDragEnd={useCallback(
+            (event: React.DragEvent<HTMLDivElement>) => {
+              // When dropping on a different droppable element than the current editor,
+              // `onDrop` is not called. So we need to clean up in `onDragEnd` instead.
+              // Note: `onDragEnd` is only called when `onDrop` is not called
+              if (
+                !readOnly &&
+                state.isDraggingInternally &&
+                hasTarget(editor, event.target) &&
+                !isEventHandled(event, attributes.onDragEnd)
+              ) {
+                state.isDraggingInternally = false
+              }
+            },
+            [readOnly, attributes.onDragEnd]
+          )}
           onFocus={useCallback(
             (event: React.FocusEvent<HTMLDivElement>) => {
               if (