Display back button when the conversation pane is expanded.

app/src/main/java/org/thoughtcrime/securesms/MainActivity.kt

@@ -415,6 +415,26 @@ class MainActivity : PassphraseRequiredActivity(), VoiceNoteMediaControllerOwner
           }
         }
 
+        val scope = rememberCoroutineScope()
+        BackHandler(paneExpansionState.currentAnchor == detailOnlyAnchor) {
+          scope.launch {
+            paneExpansionState.animateTo(listOnlyAnchor)
+          }
+        }
+
+        LaunchedEffect(paneExpansionState.currentAnchor, detailOnlyAnchor, listOnlyAnchor, detailAndListAnchor) {
+          val isFullScreenPane = when (paneExpansionState.currentAnchor) {
+            listOnlyAnchor, detailOnlyAnchor -> {
+              true
+            }
+            else -> {
+              false
+            }
+          }
+
+          mainNavigationViewModel.onPaneAnchorChanged(isFullScreenPane)
+        }
+
         LaunchedEffect(paneExpansionState, detailOnlyAnchor, listOnlyAnchor, wrappedNavigator) {
           mainNavigationViewModel.detailLocation.collect {
             if (paneExpansionState.currentAnchor == listOnlyAnchor) {

app/src/main/java/org/thoughtcrime/securesms/conversation/v2/ConversationFragment.kt

@@ -261,6 +261,7 @@ import org.thoughtcrime.securesms.linkpreview.LinkPreview
 import org.thoughtcrime.securesms.linkpreview.LinkPreviewViewModelV2
 import org.thoughtcrime.securesms.longmessage.LongMessageFragment
 import org.thoughtcrime.securesms.main.MainNavigationListLocation
+import org.thoughtcrime.securesms.main.MainNavigationViewModel
 import org.thoughtcrime.securesms.main.VerticalInsets
 import org.thoughtcrime.securesms.mediaoverview.MediaOverviewActivity
 import org.thoughtcrime.securesms.mediapreview.MediaIntentFactory
@@ -491,6 +492,8 @@ class ConversationFragment :
 
   private val shareDataTimestampViewModel: ShareDataTimestampViewModel by activityViewModels()
 
+  private val mainNavigationViewModel: MainNavigationViewModel by activityViewModels()
+
   private val inlineQueryController: InlineQueryResultsControllerV2 by lazy {
     InlineQueryResultsControllerV2(
       this,
@@ -1401,16 +1404,37 @@ class ConversationFragment :
   }
 
   private fun presentNavigationIconForNormal() {
-    if (!resources.getWindowSizeClass().isSplitPane()) {
+    if (WindowSizeClass.isLargeScreenSupportEnabled()) {
+      lifecycleScope.launch {
+        repeatOnLifecycle(Lifecycle.State.RESUMED) {
+          mainNavigationViewModel.isFullScreenPane.collect { isFullScreenPane ->
+            updateNavigationIconForNormal(isFullScreenPane)
+          }
+        }
+      }
+    } else {
+      updateNavigationIconForNormal(true)
+    }
+  }
+
+  private fun updateNavigationIconForNormal(isFullScreenPane: Boolean) {
+    if (!resources.getWindowSizeClass().isSplitPane() || isFullScreenPane) {
       binding.toolbar.setNavigationIcon(R.drawable.symbol_arrow_start_24)
       binding.toolbar.setNavigationContentDescription(R.string.ConversationFragment__content_description_back_button)
       binding.toolbar.setNavigationOnClickListener {
         binding.root.hideKeyboard(composeText)
         requireActivity().onBackPressedDispatcher.onBackPressed()
       }
+      binding.toolbar.setContentInsetsRelative(
+        46.dp,
+        binding.toolbar.contentInsetEnd
+      )
     } else {
       binding.toolbar.navigationIcon = null
-      binding.toolbar.contentInsetStartWithNavigation = 0
+      binding.toolbar.setContentInsetsRelative(
+        24.dp,
+        binding.toolbar.contentInsetEnd
+      )
     }
   }
 

app/src/main/java/org/thoughtcrime/securesms/main/MainNavigationViewModel.kt

@@ -69,6 +69,9 @@ class MainNavigationViewModel(
   private val internalMainNavigationState = MutableStateFlow(MainNavigationState(currentListLocation = initialListLocation))
   val mainNavigationState: StateFlow<MainNavigationState> = internalMainNavigationState
 
+  private val internalIsFullScreenPane = MutableStateFlow(false)
+  val isFullScreenPane: StateFlow<Boolean> = internalIsFullScreenPane
+
   /**
    * This is Rx because these are still accessed from Java.
    */
@@ -121,6 +124,10 @@ class MainNavigationViewModel(
     }
   }
 
+  fun onPaneAnchorChanged(isFullScreenPane: Boolean) {
+    internalIsFullScreenPane.update { isFullScreenPane }
+  }
+
   /**
    * Sets the navigator on the view-model. This wraps the given navigator in our own delegating implementation
    * such that we can react to navigateTo/Back signals and maintain proper state for internalDetailLocation.