Merge branch 'master' into jgrpp

# Conflicts:
#	cmake/CompileFlags.cmake
#	src/aircraft_cmd.cpp
#	src/blitter/32bpp_anim.cpp
#	src/cargopacket.cpp
#	src/cheat_gui.cpp
#	src/company_cmd.cpp
#	src/company_gui.cpp
#	src/core/pool_func.hpp
#	src/date.cpp
#	src/economy.cpp
#	src/error_gui.cpp
#	src/ground_vehicle.cpp
#	src/ground_vehicle.hpp
#	src/group_gui.cpp
#	src/industry_cmd.cpp
#	src/lang/dutch.txt
#	src/lang/french.txt
#	src/lang/german.txt
#	src/linkgraph/linkgraph_gui.cpp
#	src/linkgraph/mcf.cpp
#	src/network/network_content.cpp
#	src/network/network_server.cpp
#	src/network/network_udp.cpp
#	src/newgrf_engine.cpp
#	src/newgrf_station.cpp
#	src/order_cmd.cpp
#	src/order_gui.cpp
#	src/pathfinder/follow_track.hpp
#	src/pathfinder/yapf/yapf_common.hpp
#	src/saveload/saveload.cpp
#	src/settings_gui.cpp
#	src/station_cmd.cpp
#	src/station_kdtree.h
#	src/string_func.h
#	src/table/settings.ini
#	src/tgp.cpp
#	src/timetable_cmd.cpp
#	src/timetable_gui.cpp
#	src/toolbar_gui.cpp
#	src/town_cmd.cpp
#	src/train_cmd.cpp
#	src/train_gui.cpp
#	src/tree_gui.cpp
#	src/tunnelbridge_cmd.cpp
#	src/vehicle.cpp
#	src/vehicle_gui.cpp
#	src/video/sdl2_v.cpp
#	src/video/sdl_v.cpp
#	src/video/win32_v.cpp
#	src/viewport.cpp
#	src/viewport_sprite_sorter_sse4.cpp
#	src/window.cpp

src/airport_gui.cpp

@@ -71,6 +71,7 @@ struct BuildAirToolbarWindow : Window {
 	BuildAirToolbarWindow(WindowDesc *desc, WindowNumber window_number) : Window(desc)
 	{
 		this->InitNested(window_number);
+		this->OnInvalidateData();
 		if (_settings_client.gui.link_terraform_toolbar) ShowTerraformToolbar(this);
 		this->last_user_action = WIDGET_LIST_END;
 	}
@@ -90,7 +91,18 @@ struct BuildAirToolbarWindow : Window {
 	{
 		if (!gui_scope) return;
 
-		if (!CanBuildVehicleInfrastructure(VEH_AIRCRAFT)) delete this;
+		bool can_build = CanBuildVehicleInfrastructure(VEH_AIRCRAFT);
+		this->SetWidgetsDisabledState(!can_build,
+			WID_AT_AIRPORT,
+			WIDGET_LIST_END);
+		if (!can_build) {
+			DeleteWindowById(WC_BUILD_STATION, TRANSPORT_AIR);
+
+			/* Show in the tooltip why this button is disabled. */
+			this->GetWidget<NWidgetCore>(WID_AT_AIRPORT)->SetToolTip(STR_TOOLBAR_DISABLED_NO_VEHICLE_AVAILABLE);
+		} else {
+			this->GetWidget<NWidgetCore>(WID_AT_AIRPORT)->SetToolTip(STR_TOOLBAR_AIRCRAFT_BUILD_AIRPORT_TOOLTIP);
+		}
 	}
 
 	void OnClick(Point pt, int widget, int click_count) override
@@ -160,7 +172,7 @@ struct BuildAirToolbarWindow : Window {
  */
 static EventState AirportToolbarGlobalHotkeys(int hotkey)
 {
-	if (_game_mode != GM_NORMAL || !CanBuildVehicleInfrastructure(VEH_AIRCRAFT)) return ES_NOT_HANDLED;
+	if (_game_mode != GM_NORMAL) return ES_NOT_HANDLED;
 	Window *w = ShowBuildAirToolbar();
 	if (w == nullptr) return ES_NOT_HANDLED;
 	return w->OnHotkey(hotkey);
@@ -314,7 +326,7 @@ public:
 					const AirportSpec *as = AirportSpec::Get(i);
 					if (!as->enabled) continue;
 
-					size->width = max(size->width, GetStringBoundingBox(as->name).width);
+					size->width = std::max(size->width, GetStringBoundingBox(as->name).width);
 				}
 
 				this->line_height = FONT_HEIGHT_NORMAL + WD_MATRIX_TOP + WD_MATRIX_BOTTOM;