client: Ensure keyboard focus is not lost when main window leaflets fold

See GNOME/libhandy#179

src/client/application/application-main-window.vala

@@ -2113,10 +2113,33 @@ public class Application.MainWindow :
         update_conversation_actions(
             ConversationCount.for_size(selected)
         );
-        if (this.has_composer &&
+        if (this.outer_leaflet.folded) {
-            this.outer_leaflet.folded &&
+            // Ensure something useful gets the keyboard focus, given
-            (this.is_folder_list_shown || this.is_conversation_list_shown)) {
+            // GNOME/libhandy#179
-            close_composer(false, false);
+            if (this.is_conversation_list_shown) {
+                this.conversation_list_view.grab_focus();
+            } else if (this.is_folder_list_shown) {
+                this.folder_list.grab_focus();
+            }
+
+            // Close any open composer that is no longer visible
+            if (this.has_composer &&
+                (this.is_folder_list_shown || this.is_conversation_list_shown)) {
+                close_composer(false, false);
+            }
+        }
+    }
+
+    [GtkCallback]
+    private void on_inner_leaflet_changed() {
+        if (this.inner_leaflet.folded) {
+            // Ensure something useful gets the keyboard focus, given
+            // GNOME/libhandy#179
+            if (this.is_conversation_list_shown) {
+                this.conversation_list_view.grab_focus();
+            } else if (this.is_folder_list_shown) {
+                this.folder_list.grab_focus();
+            }
         }
     }
 

ui/application-main-window.ui

@@ -30,6 +30,8 @@
                     <property name="hexpand_set">True</property>
                     <property name="can_swipe_back">True</property>
                     <property name="transition_type">over</property>
+                    <signal name="notify::folded" handler="on_inner_leaflet_changed" swapped="no"/>
+                    <signal name="notify::visible-child" handler="on_inner_leaflet_changed" swapped="no"/>
                     <child>
                       <object class="GtkBox" id="folder_box">
                         <property name="visible">True</property>