Fix arity and return value mismatches

`assert` returns every argument it is given, so `return assert(x, msg)`
was leaking the message as a second return value.

`get_tile` is documented as taking x and y. The async function class
declared `@operator call` with no parameters, which made every async
call look over supplied.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

exp_gui/module/control.lua

@@ -47,10 +47,10 @@ end
 function Gui.get_player(input)
     if type(input) == "table" and not input.player_index then
         --- @cast input { element: LuaGuiElement }
-        return assert(game.get_player(input.element.player_index))
+        return (assert(game.get_player(input.element.player_index)))
     end
     --- @cast input LuaGuiElement | { player_index: uint }
-    return assert(game.get_player(input.player_index))
+    return (assert(game.get_player(input.player_index)))
 end
 
 --- Toggle the enable state of an element
@@ -116,7 +116,7 @@ end
 --- @param player LuaPlayer
 --- @return LuaGuiElement
 function Gui.get_top_element(define, player)
-    return assert(assert(player_elements[player.index]).top[define.name], "Element is not on the top flow")
+    return (assert(assert(player_elements[player.index]).top[define.name], "Element is not on the top flow"))
 end
 
 --- Register a element define to be drawn to the left flow on join
@@ -124,7 +124,7 @@ end
 --- @param player LuaPlayer
 --- @return LuaGuiElement
 function Gui.get_left_element(define, player)
-    return assert(assert(player_elements[player.index]).left[define.name], "Element is not on the left flow")
+    return (assert(assert(player_elements[player.index]).left[define.name], "Element is not on the left flow"))
 end
 
 --- Register a element define to be drawn to the relative flow on join
@@ -132,7 +132,7 @@ end
 --- @param player LuaPlayer
 --- @return LuaGuiElement
 function Gui.get_relative_element(define, player)
-    return assert(assert(player_elements[player.index]).relative[define.name], "Element is not on the relative flow")
+    return (assert(assert(player_elements[player.index]).relative[define.name], "Element is not on the relative flow"))
 end
 
 --- Ensure all the correct elements are visible and exist

exp_gui/module/elements.lua

@@ -52,7 +52,7 @@ Elements.bar = Gui.define("bar")
 
 --- A label which is centered
 --- @class Gui.elements.centered_label: ExpElement
---- @overload fun(parent: LuaGuiElement, width: number, caption: LocalisedString, tooltip: LocalisedString?): LuaGuiElement
+--- @overload fun(parent: LuaGuiElement, width: number, caption: LocalisedString?, tooltip: LocalisedString?): LuaGuiElement
 Elements.centered_label = Gui.define("centered_label")
     :draw{
         type = "label",
@@ -319,7 +319,7 @@ Elements.screen_frame = Gui.define("screen_frame")
 --- @param screen_frame LuaGuiElement
 --- @return LuaGuiElement
 function Elements.screen_frame.get_button_flow(screen_frame)
-    return assert(Elements.screen_frame.data[screen_frame.parent], "Screen frame has no button flow")
+    return (assert(Elements.screen_frame.data[screen_frame.parent], "Screen frame has no button flow"))
 end
 
 --- Get the root element of a screen frame

exp_gui/module/prototype.lua

@@ -166,7 +166,7 @@ end
 --- @param name string
 --- @return ExpElement
 function ExpElement.get(name)
-    return assert(ExpElement._elements[name], "ExpElement is not defined: " .. tostring(name))
+    return (assert(ExpElement._elements[name], "ExpElement is not defined: " .. tostring(name)))
 end
 
 --- Create a new instance of this element definition