Bug 1784019 - Keep window open when restoring if Firefox View is selected. r=dao

Differential Revision: https://phabricator.services.mozilla.com/D154395

browser/components/sessionstore/SessionStore.jsm

@@ -3975,6 +3975,16 @@ var SessionStoreInternal = {
       }
     }
 
+    if (
+      tabbrowser.selectedTab.hidden &&
+      tabbrowser.visibleTabs.length === removableTabs.length
+    ) {
+      // If all the visible tabs are also removable and the selected tab is hidden, we will later remove the
+      // visible tabs causing the browser to automatically close because the only tab left is hidden.
+      // To prevent the browser from automatically closing, we will leave one other tab open.
+      removableTabs.shift();
+    }
+
     if (tabbrowser.tabs.length == removableTabs.length) {
       canOverwriteTabs = true;
     } else {

browser/components/sessionstore/test/browser.ini

@@ -115,6 +115,7 @@ skip-if =
 [browser_dying_cache.js]
 skip-if = (os == 'win') # bug 1331853
 [browser_dynamic_frames.js]
+[browser_firefoxView_selected_restore.js]
 [browser_formdata.js]
 skip-if =
   verify && debug

browser/components/sessionstore/test/browser_firefoxView_selected_restore.js

@@ -0,0 +1,77 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const { _LastSession } = ChromeUtils.import(
+  "resource:///modules/sessionstore/SessionStore.jsm"
+);
+const { sinon } = ChromeUtils.import("resource://testing-common/Sinon.jsm");
+
+const state = {
+  windows: [
+    {
+      tabs: [
+        {
+          entries: [
+            {
+              url: "http://example.org/",
+              triggeringPrincipal_base64,
+            },
+          ],
+        },
+      ],
+      selected: 2,
+    },
+  ],
+};
+
+/**
+ * This is regrettable, but when `promiseBrowserState` resolves, we're still
+ * midway through loading the tabs. To avoid race conditions in URLs for tabs
+ * being available, wait for all the loads to finish:
+ */
+function promiseSessionStoreLoads(numberOfLoads) {
+  let loadsSeen = 0;
+  return new Promise(resolve => {
+    Services.obs.addObserver(function obs(browser) {
+      loadsSeen++;
+      if (loadsSeen == numberOfLoads) {
+        resolve();
+      }
+      // The typeof check is here to avoid one test messing with everything else by
+      // keeping the observer indefinitely.
+      if (typeof info == "undefined" || loadsSeen >= numberOfLoads) {
+        Services.obs.removeObserver(obs, "sessionstore-debug-tab-restored");
+      }
+      info("Saw load for " + browser.currentURI.spec);
+    }, "sessionstore-debug-tab-restored");
+  });
+}
+
+add_task(async function test() {
+  let fxViewBtn = document.getElementById("firefox-view-button");
+  ok(fxViewBtn, "Got the Firefox View button");
+  fxViewBtn.click();
+
+  await BrowserTestUtils.browserLoaded(
+    window.FirefoxViewHandler.tab.linkedBrowser
+  );
+
+  let allTabsRestored = promiseSessionStoreLoads(1);
+
+  _LastSession.setState(state);
+
+  is(gBrowser.tabs.length, 2, "Number of tabs is 2");
+
+  ss.restoreLastSession();
+
+  await allTabsRestored;
+
+  ok(
+    window.FirefoxViewHandler.tab.selected,
+    "The Firefox View tab is selected and the browser window did not close"
+  );
+  is(gBrowser.tabs.length, 3, "Number of tabs is 3");
+
+  gBrowser.removeTab(window.FirefoxViewHandler.tab);
+  gBrowser.removeTab(gBrowser.selectedTab);
+});