Add labs flag for default open right panel (#7618)

src/i18n/strings/en_EN.json

@@ -889,6 +889,7 @@
     "Meta Spaces": "Meta Spaces",
     "Use new room breadcrumbs": "Use new room breadcrumbs",
     "New spotlight search experience": "New spotlight search experience",
+    "Right panel stays open (defaults to room member list)": "Right panel stays open (defaults to room member list)",
     "Jump to date (adds /jumptodate)": "Jump to date (adds /jumptodate)",
     "Don't send read receipts": "Don't send read receipts",
     "Font size": "Font size",

src/settings/Settings.tsx

@@ -366,6 +366,13 @@ export const SETTINGS: {[setting: string]: ISetting} = {
         displayName: _td("New spotlight search experience"),
         default: false,
     },
+    "feature_right_panel_default_open": {
+        isFeature: true,
+        labsGroup: LabGroup.Rooms,
+        supportedLevels: LEVELS_FEATURE,
+        displayName: _td("Right panel stays open (defaults to room member list)"),
+        default: false,
+    },
     "feature_jump_to_date": {
         // We purposely leave out `isFeature: true` so it doesn't show in Labs
         // by default. We will conditionally show it depending on whether we can

src/stores/right-panel/RightPanelStore.ts

@@ -368,6 +368,21 @@ export default class RightPanelStore extends ReadyWatchingStore {
         this.isViewingRoom = true; // Is viewing room will of course be removed when removing groups
         // load values from byRoomCache with the viewedRoomId.
         this.loadCacheFromSettings();
+        // If the right panel stays open mode is used, and the panel was either
+        // closed or never shown for that room, then force it open and display
+        // the room member list.
+        if (
+            SettingsStore.getValue("feature_right_panel_default_open") &&
+            !this.byRoom[this.viewedRoomId]?.isOpen
+        ) {
+            this.byRoom[this.viewedRoomId] = {
+                isOpen: true,
+                history: [
+                    { phase: RightPanelPhases.RoomSummary },
+                    { phase: RightPanelPhases.RoomMemberList },
+                ],
+            };
+        }
         this.emitAndUpdateSettings();
     };