fix: DH-20243: improved notebook settings merging (#2593)

It is expected that `getSettings` substitutes custom settings on top of
default settings when the settings are pulled.
The problem is this substitution was only happening properly if top
level settings were being replaced.
This meant that the nested linter settings were not getting properly
replaced for `notebookSettings` because `notebookSettings` is never
itself `undefined`, only the keys `config` and `isEnabled` are.

Author: jnumainville

package-lock.json

@@ -27,6 +27,7 @@
     "@deephaven/log": "file:../log",
     "@deephaven/plugin": "file:../plugin",
     "fast-deep-equal": "^3.1.3",
+    "lodash.mergewith": "^4.6.2",
     "proxy-memoize": "^3.0.0",
     "redux-thunk": "2.4.1"
   },
@@ -39,5 +40,8 @@
   "sideEffects": false,
   "publishConfig": {
     "access": "public"
+  },
+  "devDependencies": {
+    "@types/lodash.mergewith": "^4.6.9"
   }
 }

packages/redux/package.json

@@ -1,6 +1,7 @@
 import type { UndoPartial } from '@deephaven/utils';
 import { memoize } from 'proxy-memoize';
-import type { RootState, WorkspaceSettings } from './store';
+import mergeWith from 'lodash.mergewith';
+import type { RootState } from './store';
 
 const EMPTY_OBJECT = Object.freeze({});
 
@@ -61,17 +62,22 @@ export const getSettings = memoize(
     store: State
   ): UndoPartial<State['workspace']['data']['settings']> => {
     const customizedSettings = getWorkspace(store)?.data.settings ?? {};
-
-    const settings = { ...getDefaultWorkspaceSettings(store) };
-    const keys = Object.keys(customizedSettings) as (keyof WorkspaceSettings)[];
-    for (let i = 0; i < keys.length; i += 1) {
-      const key = keys[i];
-      if (customizedSettings[key] !== undefined) {
-        // @ts-expect-error assign non-undefined customized settings to settings
-        settings[key] = customizedSettings[key];
+    const defaultSettings = getDefaultWorkspaceSettings(store);
+
+    // Deep merge settings but replace arrays instead of merging them
+    const newSettings = mergeWith(
+      {},
+      defaultSettings,
+      customizedSettings,
+      (objValue: unknown, srcValue: unknown) => {
+        if (Array.isArray(objValue) && Array.isArray(srcValue)) {
+          return srcValue;
+        }
+        return undefined;
       }
-    }
-    return settings as UndoPartial<State['workspace']['data']['settings']>;
+    ) as UndoPartial<State['workspace']['data']['settings']>;
+
+    return newSettings;
   }
 );