Spinbox does not hide original icons when Updown icon is set

[Acvarium]

Tested versions

v4.4.stable.official [4c311cb]

System information

Manjaro Linux 6.1.127-2-MANJARO

Issue description

The original arrow icons are still visible when the Updown icon is changed in the Theme Overrides -> Icons. But if Up or Down icons are changed separately, the original ones disappear, as intended.

Steps to reproduce

Change the Updown icon in the Theme Overrides -> Icons to some image.

Minimal reproduction project (MRP)

value-change-icon-test.zip

[kleonc]

This seems to be intentional, the docs already state: "This can also be used as additional decoration between the two buttons."
Which implies it's drawn with the up/down buttons.

godot/doc/classes/SpinBox.xml

Lines 133 to 135 in 49cc57a

	<theme_item name="updown" data_type="icon" type="Texture2D">
	Single texture representing both the up and down buttons icons. It is displayed in the middle of the buttons and does not change upon interaction. It is recommended to use individual [theme_item up] and [theme_item down] graphics for better usability. This can also be used as additional decoration between the two buttons.
	</theme_item>

The docs could be made clearer. E.g. it could be mentioned that updown texture is drawn behind up/down textures, and that it's drawn on top of up_background/down_background StyleBoxes.

For reference they're being drawn here:

godot/scene/gui/spin_box.cpp

Lines 435 to 442 in 49cc57a

	// Draw buttons.
	draw_style_box(up_stylebox, Rect2(sizing_cache.buttons_left, 0, sizing_cache.buttons_width, sizing_cache.button_up_height));
	draw_style_box(down_stylebox, Rect2(sizing_cache.buttons_left, sizing_cache.second_button_top, sizing_cache.buttons_width, sizing_cache.button_down_height));
	// Draw arrows.
	theme_cache.updown_icon->draw(ci, Point2i(updown_icon_left, updown_icon_top));
	draw_texture(up_icon, Point2i(up_icon_left, up_icon_top), up_icon_modulate);
	draw_texture(down_icon, Point2i(down_icon_left, down_icon_top), down_icon_modulate);

---

The up/down customization was added in #89265.
cc @davthedev
cc @KoBeWi (#89265 (comment))

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As a workaround you could assign transparent/invalid texture as relevant up/down icons, e.g. an AtlasTexture with no atlas assigned:

[KoBeWi]

The potential deprecation of updown wasn't properly addressed. I still think it should be deprecated; if we want a background property, it should be a separate one with a better name 🙃

The current behavior broke compatibility with projects that use custom updown icon. Maybe we could automatically hide the separate arrows if a non-empty updown icon is provided.