[Backport staging] Make threads disabled by default (#9815)

* Make threads disable by default

* restore e2ee tests

* fix threads e2e spec for beta joining

(cherry picked from commit 134e3d7ae8)

Co-authored-by: Germain <germains@element.io>

cypress/e2e/polls/polls.spec.ts

@@ -77,6 +77,7 @@ describe("Polls", () => {
     };
 
     beforeEach(() => {
+        cy.enableLabsFeature("feature_threadstable");
         cy.window().then((win) => {
             win.localStorage.setItem("mx_lhs_size", "0"); // Collapse left panel for these tests
         });

cypress/e2e/threads/threads.spec.ts

@@ -19,10 +19,17 @@ limitations under the License.
 import { SynapseInstance } from "../../plugins/synapsedocker";
 import { MatrixClient } from "../../global";
 
+function markWindowBeforeReload(): void {
+    // mark our window object to "know" when it gets reloaded
+    cy.window().then((w) => (w.beforeReload = true));
+}
+
 describe("Threads", () => {
     let synapse: SynapseInstance;
 
     beforeEach(() => {
+        // Default threads to ON for this spec
+        cy.enableLabsFeature("feature_threadstable");
         cy.window().then((win) => {
             win.localStorage.setItem("mx_lhs_size", "0"); // Collapse left panel for these tests
         });
@@ -37,6 +44,35 @@ describe("Threads", () => {
         cy.stopSynapse(synapse);
     });
 
+    it("should reload when enabling threads beta", () => {
+        markWindowBeforeReload();
+
+        // Turn off
+        cy.openUserSettings("Labs").within(() => {
+            // initially the new property is there
+            cy.window().should("have.prop", "beforeReload", true);
+
+            cy.leaveBeta("Threaded messages");
+            cy.wait(1000);
+            // after reload the property should be gone
+            cy.window().should("not.have.prop", "beforeReload");
+        });
+
+        cy.get(".mx_MatrixChat", { timeout: 15000 }); // wait for the app
+        markWindowBeforeReload();
+
+        // Turn on
+        cy.openUserSettings("Labs").within(() => {
+            // initially the new property is there
+            cy.window().should("have.prop", "beforeReload", true);
+
+            cy.joinBeta("Threaded messages");
+            cy.wait(1000);
+            // after reload the property should be gone
+            cy.window().should("not.have.prop", "beforeReload");
+        });
+    });
+
     it("should be usable for a conversation", () => {
         let bot: MatrixClient;
         cy.getBot(synapse, {

src/settings/Settings.tsx

@@ -261,7 +261,7 @@ export const SETTINGS: { [setting: string]: ISetting } = {
         controller: new ThreadBetaController(),
         displayName: _td("Threaded messages"),
         supportedLevels: LEVELS_FEATURE,
-        default: true,
+        default: false,
         betaInfo: {
             title: _td("Threaded messages"),
             caption: () => (