Add-on manager: add an update button to the main panel

data/gui/window/addon_manager.cfg

@@ -183,14 +183,54 @@
 
 										[column]
 											grow_factor = 1
-											border = "all"
-											border_size = 5
 											horizontal_alignment = "center"
 
-											[button]
-												id = "install"
-												definition = "addon_install"
-											[/button]
+											[stacked_widget]
+												id = "install_update_stack"
+
+												[layer]
+
+													[row]
+
+														[column]
+															grow_factor = 1
+															border = "all"
+															border_size = 5
+															horizontal_alignment = "center"
+
+															[button]
+																id = "install"
+																definition = "addon_install"
+															[/button]
+
+														[/column]
+
+													[/row]
+
+												[/layer]
+
+												[layer]
+
+													[row]
+
+														[column]
+															grow_factor = 1
+															border = "all"
+															border_size = 5
+															horizontal_alignment = "center"
+
+															[button]
+																id = "update"
+																definition = "addon_upgrade"
+															[/button]
+
+														[/column]
+
+													[/row]
+
+												[/layer]
+
+											[/stacked_widget]
 
 										[/column]
 

src/gui/dialogs/addon/manager.cpp

@@ -396,6 +396,14 @@ void addon_manager::pre_show(window& window)
 		find_widget<button>(&window, "uninstall", false),
 		std::bind(&addon_manager::uninstall_selected_addon, this, std::ref(window)));
 
+	// Make the update button temporarily accessible.
+	find_widget<stacked_widget>(&window, "install_update_stack", false).select_layer(1);
+	connect_signal_mouse_left_click(
+		find_widget<button>(&window, "update", false),
+		std::bind(&addon_manager::update_selected_addon, this, std::ref(window)));
+	// Revert the above change for good measure.
+	find_widget<stacked_widget>(&window, "install_update_stack", false).select_layer(0);
+
 	connect_signal_mouse_left_click(
 		find_widget<button>(&window, "publish", false),
 		std::bind(&addon_manager::publish_selected_addon, this, std::ref(window)));
@@ -768,13 +776,22 @@ void addon_manager::on_addon_select(window& window)
 	}
 
 	bool installed = is_installed_addon_status(tracking_info_[info->id].state);
+	bool updatable = tracking_info_[info->id].state == ADDON_INSTALLED_UPGRADABLE;
 
 	stacked_widget& action_stack = find_widget<stacked_widget>(&window, "action_stack", false);
 
 	if(!tracking_info_[info->id].can_publish) {
 		action_stack.select_layer(0);
 
-		find_widget<button>(&window, "install", false).set_active(!installed);
+		stacked_widget& install_update_stack = find_widget<stacked_widget>(&window, "install_update_stack", false);
+		install_update_stack.select_layer(updatable ? 1 : 0);
+
+		if(!updatable) {
+			find_widget<button>(&window, "install", false).set_active(!installed);
+		} else {
+			find_widget<button>(&window, "update", false).set_active(true);
+		}
+
 		find_widget<button>(&window, "uninstall", false).set_active(installed);
 	} else {
 		action_stack.select_layer(1);