Bug 1944842 - Sidebar can get into scenario where it's expanded but vertical tabs aren't showing labels r=sidebar-reviewers,sfoster

Disabling revamp means that we also set expanded to false. However, since revamp is disabled, these changes are not reflected back to sidebar-main, resulting in a weird mismatch between SidebarState and what the launcher sees.

This was partially fixed by the lines in initializeState(), which updates the tab container, but not the launcher. This generalizes the solution to ensure that *all* components are kept up to date.

Differential Revision: https://phabricator.services.mozilla.com/D236240

Author: Jonathan Sudiaman

browser/components/sidebar/SidebarState.sys.mjs

@@ -115,9 +115,9 @@ export class SidebarState {
     } else {
       this.launcherVisible = true;
     }
-    // Ensure that tab container has the updated value of `launcherExpanded`.
-    const { tabContainer } = this.#controllerGlobal.gBrowser;
-    tabContainer.toggleAttribute("expanded", this.launcherExpanded);
+
+    // Explicitly trigger effects to ensure that the UI is kept up to date.
+    this.launcherExpanded = this.#props.launcherExpanded;
   }
 
   /**

browser/components/sidebar/tests/browser/browser_vertical_tabs.js

@@ -439,17 +439,20 @@ add_task(async function test_vertical_tabs_expanded() {
     "Sidebar launcher is hidden."
   );
 
-  info("Enable revamped sidebar and vertical tabs.");
-  Services.prefs.setBoolPref("sidebar.revamp", true);
+  info("Enable vertical tabs.");
   Services.prefs.setBoolPref("sidebar.verticalTabs", true);
   await TestUtils.waitForCondition(
     () => BrowserTestUtils.isVisible(document.getElementById("sidebar-main")),
     "Sidebar launcher is shown."
   );
-  ok(
+  const expandedStateValues = [
+    SidebarController.getUIState().launcherExpanded,
+    SidebarController.sidebarMain.expanded,
     gBrowser.tabContainer.hasAttribute("expanded"),
-    "Tab container is expanded."
-  );
+  ];
+  for (const val of expandedStateValues) {
+    is(val, false, "Launcher is collapsed.");
+  }
 
   await SpecialPowers.popPrefEnv();
 });