Fix #2746: sort only ungrouped tabs

Firefox 137 introduced tab groups. Tab group web extension support is rolling out in Firefox 138 and later. Tab movements, like the movements done when sorting tabs by container, can inadvertently add or remove tabs from tab groups.

In order to keep users' tab groups intact, this patch only sorts tabs outside of tab groups. Due to the lack of the tabGroups web extensions API as of Firefox 138, this patch cannot move tab groups, so all ungrouped tabs move to the end of the tab strip. That means after sorting, all tab groups will move to the beginning of the tab strip.

src/js/background/backgroundLogic.js

@@ -3,6 +3,13 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 const DEFAULT_TAB = "about:newtab";
+/**
+ * Firefox does not yet have the `tabGroups` API, which exposes this constant
+ * to indicate that a tab is not in a tab group. But the Firefox `tabs` API
+ * currently returns this constant value for `Tab.groupId`.
+ * @see https://searchfox.org/mozilla-central/rev/3b95c8dbe724b10390c96c1b9dd0f12c873e2f2e/browser/components/extensions/schemas/tabs.json#235
+ */
+const TAB_GROUP_ID_NONE = -1;
 
 const backgroundLogic = {
   NEW_TAB_PAGES: new Set([
@@ -343,7 +350,13 @@ const backgroundLogic = {
     let pos = 0;
 
     // Let's collect UCIs/tabs for this window.
+    /** @type {Map<string, {order: string, tabs: Tab[]}>} */
     const map = new Map;
+    /** @type {boolean} */
+    let lastTabIsInTabGroup = tabs.length > 0
+      && tabs[tabs.length - 1].groupId
+      && tabs[tabs.length - 1].groupId !== TAB_GROUP_ID_NONE;
+
     for (const tab of tabs) {
       if (pinnedTabs && !tab.pinned) {
         // We don't have, or we already handled all the pinned tabs.
@@ -356,6 +369,11 @@ const backgroundLogic = {
         continue;
       }
 
+      if (tab.groupId && tab.groupId !== TAB_GROUP_ID_NONE) {
+        // Skip over tabs in tab groups until it's possible to handle them better.
+        continue;
+      }
+
       if (!map.has(tab.cookieStoreId)) {
         const userContextId = backgroundLogic.getUserContextIdFromCookieStoreId(tab.cookieStoreId);
         map.set(tab.cookieStoreId, { order: userContextId, tabs: [] });
@@ -377,15 +395,24 @@ const backgroundLogic = {
     const sortMap = new Map([...map.entries()].sort((a, b) => a[1].order > b[1].order));
 
     // Let's move tabs.
-    sortMap.forEach(obj => {
+    for (const { tabs } of sortMap.values()) {
-      for (const tab of obj.tabs) {
+      for (const tab of tabs) {
         ++pos;
         browser.tabs.move(tab.id, {
           windowId: windowObj.id,
-          index: pos
+          index: pinnedTabs ? pos : -1
         });
+        if (lastTabIsInTabGroup && browser.tabs.ungroup) {
+          // If the last item in the tab strip is a grouped tab, moving a tab
+          // to its position will also add it to the tab group. Since this code
+          // is only sorting ungrouped tabs, this forcibly ungroups the first
+          // tab to be moved. All subsequent iterations will only be moving
+          // ungrouped tabs to the position of other ungrouped tabs.
+          lastTabIsInTabGroup = false;
+          browser.tabs.ungroup(tab.id);
+        }
+      }
     }
-    });
   },
 
   async hideTabs(options) {