fix: Dragging images in editor (#12647)

* fix: Editor image dragging

* feedback

app/components/AuthenticatedLayout.tsx

@@ -1,8 +1,8 @@
 import { observer } from "mobx-react";
 import * as React from "react";
 import { DndProvider } from "react-dnd";
-import { HTML5Backend } from "react-dnd-html5-backend";
 import { useLocation } from "react-router-dom";
+import { EditorAwareHTML5Backend } from "~/components/EditorAwareHTML5Backend";
 import ErrorSuspended from "~/scenes/Errors/ErrorSuspended";
 import Layout from "~/components/Layout";
 import RegisterKeyDown from "~/components/RegisterKeyDown";
@@ -106,7 +106,7 @@ const AuthenticatedLayout: React.FC = ({ children }: Props) => {
     <DocumentContextProvider>
       <RightSidebarProvider>
         <PortalContext.Provider value={layoutRef.current}>
-          <DndProvider backend={HTML5Backend}>
+          <DndProvider backend={EditorAwareHTML5Backend}>
             <Layout title={team.name} sidebar={sidebar} ref={layoutRef}>
               <RegisterKeyDown trigger="n" handler={goToNewDocument} />
               <RegisterKeyDown trigger="t" handler={goToSearch} />

app/components/EditorAwareHTML5Backend.ts

@@ -0,0 +1,63 @@
+import type { BackendFactory } from "dnd-core";
+import { HTML5Backend } from "react-dnd-html5-backend";
+
+/**
+ * react-dnd's HTML5 backend installs global capture-phase listeners on `window`
+ * that call `preventDefault()` on drops whose dataTransfer resembles a native
+ * item – including a dragged `<img>`, which is how ProseMirror serializes an
+ * image drag.
+ *
+ * These handlers run before ProseMirror's, and they live on `window`, so a
+ * propagation-based guard can't stop react-dnd without also starving the editor
+ * of the event. Instead we wrap the backend and make its top-level capture
+ * handlers no-op for events that occur within the editor surface.
+ */
+const captureHandlerNames = [
+  "handleTopDragStartCapture",
+  "handleTopDragEnterCapture",
+  "handleTopDragOverCapture",
+  "handleTopDragLeaveCapture",
+  "handleTopDropCapture",
+  "handleTopDragEndCapture",
+] as const;
+
+const isWithinEditor = (target: EventTarget | null): boolean =>
+  target instanceof Element && Boolean(target.closest(".ProseMirror"));
+
+/**
+ * An HTML5 drag-and-drop backend that ignores drag events originating within the
+ * rich text editor so that ProseMirror can handle them itself.
+ *
+ * @param manager The drag-and-drop manager.
+ * @param context The global context.
+ * @param options Backend options.
+ * @returns The wrapped HTML5 backend instance.
+ */
+export const EditorAwareHTML5Backend: BackendFactory = (
+  manager,
+  context,
+  options
+) => {
+  const backend = HTML5Backend(manager, context, options);
+
+  // The capture handlers are private instance fields on the backend, so reach
+  // for them through an index signature view of the instance.
+  const handlers = backend as unknown as Record<
+    string,
+    (event: DragEvent) => void
+  >;
+
+  for (const name of captureHandlerNames) {
+    const original = handlers[name];
+    if (typeof original === "function") {
+      handlers[name] = (event: DragEvent) => {
+        if (isWithinEditor(event.target)) {
+          return;
+        }
+        original.call(backend, event);
+      };
+    }
+  }
+
+  return backend;
+};