widgets: fix bug when changing buffers, which would make other buffers get "messed up/deleted"

Author: williamstein

src/packages/frontend/jupyter/widgets/manager2.ts

@@ -63,6 +63,19 @@ export class WidgetManager {
   }
 
   private initAllModels = async () => {
+    // TODO: this can do a lot that makes no sense
+    // due to lack of garbage collection and any link to what is actually
+    // in the notebook.
+    /*
+    With this disabled, this breaks for RTC or close/open:
+
+from ipywidgets import VBox, jsdlink, IntSlider
+s1 = IntSlider(max=200, value=100); s2 = IntSlider(value=40)
+jsdlink((s1, 'value'), (s2, 'max'))
+VBox([s1, s2])
+    */
+    // log("initAllModels: temporarily disabled"); return;
+
     if (this.ipywidgets_state.get_state() == "init") {
       await once(this.ipywidgets_state, "ready");
     }
@@ -268,7 +281,7 @@ export class WidgetManager {
     const change: { [key: string]: any } = {};
     for (let i = 0; i < buffer_paths.length; i++) {
       const key = buffer_paths[i][0];
-      setInObject(state, buffer_paths[i], buffers[i]);
+      setInObject(state, buffer_paths[i], new DataView(buffers[i]));
       change[key] = state[key];
     }
     if (len(change) > 0) {
@@ -632,7 +645,7 @@ class Environment implements WidgetEnvironment {
     if (buffers.length > 0) {
       for (let i = 0; i < buffer_paths.length; i++) {
         const buffer = buffers[i];
-        setInObject(state, buffer_paths[i], buffer);
+        setInObject(state, buffer_paths[i], new DataView(buffer));
       }
     }
 

src/packages/sync/editor/generic/ipywidgets-state.ts

@@ -375,10 +375,25 @@ export class IpywidgetsState extends EventEmitter {
       dbg("value -- after", { merged: data });
       defaultMerge = "none";
     } else if (type == "buffers") {
-      // we keep around the buffers that were
-      // already set, but overwrite
-      // when they change.
-      defaultMerge = "shallow";
+      // it's critical to not throw away existing buffers when
+      // new ones come or current ones change.  With shallow merge,
+      // the existing ones go away, which is very broken, e.g.,
+      // see this with this example:
+/*
+import bqplot.pyplot as plt
+import numpy as np
+x, y = np.random.rand(2, 10)
+fig = plt.figure(animation_duration=3000)
+scat = plt.scatter(x=x, y=y)
+fig
+---
+scat.x, scat.y = np.random.rand(2, 50)
+
+# now close and open it, and it breaks with shallow merge,
+# since the second cell caused the opacity buffer to be
+# deleted, which breaks everything.
+*/
+      defaultMerge = "deep";
     } else if (type == "message") {
       defaultMerge = "none";
     } else {