[fenix] Issue https://github.com/mozilla-mobile/fenix/issues/21707: Correct search grouping logic in extensions

At this moment, we have two extension methods that have duplicate
functionality to construct search term groupings. One on `List<Tab>` and
one on `List<TabSessionState>`. The former is used for everything
related to tabs piped through the `TabsFeature` and the latter is for
consumers of `BrowserState` directly.

The bug occurs because our implementation of search groupings was
updated only on the former extension, but the `HeaderBinding`, that
observes the BrowserState and updates the title visibility, was using
the latter.

Ideally, we remove this duplication when we no longer have separate data
classes for consumers of `TabsFeature`, but this intermediary fix should
suffice.

app/src/main/java/org/mozilla/fenix/ext/BrowserState.kt

@@ -60,7 +60,7 @@ val BrowserState.inProgressMediaTab: TabSessionState?
  */
 val BrowserState.lastSearchGroup: RecentTab.SearchGroup?
     get() {
-        val tabGroup = normalTabs.toSearchGroup().lastOrNull { it.tabs.count() > 1 } ?: return null
+        val tabGroup = normalTabs.toSearchGroup().first.lastOrNull() ?: return null
         val firstTab = tabGroup.tabs.firstOrNull() ?: return null
 
         return RecentTab.SearchGroup(
@@ -73,9 +73,10 @@ val BrowserState.lastSearchGroup: RecentTab.SearchGroup?
     }
 
 /**
- * Get search term groups sorted by last access time.
+ * Returns a pair containing a list of search term groups sorted by last access time, and "remainder" tabs that have
+ * search terms but should not be in groups (because the group is of size one).
  */
-fun List<TabSessionState>.toSearchGroup(): List<TabGroup> {
+fun List<TabSessionState>.toSearchGroup(): Pair<List<TabGroup>, List<TabSessionState>> {
     val data = filter {
         it.isNormalTabActiveWithSearchTerm(maxActiveTime)
     }.groupBy {
@@ -85,7 +86,7 @@ fun List<TabSessionState>.toSearchGroup(): List<TabGroup> {
         }.lowercase()
     }
 
-    return data.map { mapEntry ->
+    val groupings = data.map { mapEntry ->
         val searchTerm = mapEntry.key.replaceFirstChar(Char::uppercase)
         val groupTabs = mapEntry.value
         val groupMax = groupTabs.fold(0L) { acc, tab ->
@@ -97,5 +98,10 @@ fun List<TabSessionState>.toSearchGroup(): List<TabGroup> {
             tabs = groupTabs,
             lastAccess = groupMax
         )
-    }.sortedBy { it.lastAccess }
+    }
+
+    val groups = groupings.filter { it.tabs.size > 1 }.sortedBy { it.lastAccess }
+    val remainderTabs = (groupings - groups).flatMap { it.tabs }
+
+    return groups to remainderTabs
 }

app/src/main/java/org/mozilla/fenix/tabstray/ext/TabSelectors.kt

@@ -48,11 +48,13 @@ fun BrowserState.getNormalTrayTabs(
 ): List<TabSessionState> {
     return normalTabs.run {
         if (searchTermTabGroupsAreEnabled && inactiveTabsEnabled) {
-            filter { it.isNormalTabActiveWithoutSearchTerm(maxActiveTime) }
+            val remainderTabs = toSearchGroup().second
+            filter { it.isNormalTabActiveWithoutSearchTerm(maxActiveTime) } + remainderTabs
         } else if (inactiveTabsEnabled) {
             filter { it.isNormalTabActive(maxActiveTime) }
         } else if (searchTermTabGroupsAreEnabled) {
-            filter { it.isNormalTabWithSearchTerm() }
+            val remainderTabs = toSearchGroup().second
+            filter { it.isNormalTabWithSearchTerm() } + remainderTabs
         } else {
             this
         }
@@ -65,7 +67,7 @@ fun BrowserState.getNormalTrayTabs(
 fun BrowserState.getSearchTabGroups(
     searchTermTabGroupsAreEnabled: Boolean
 ): List<TabGroup> = if (searchTermTabGroupsAreEnabled) {
-    normalTabs.toSearchGroup().filter { it.tabs.size > 1 }
+    normalTabs.toSearchGroup().first
 } else {
     emptyList()
 }