Add Spacing::menu_width (#3973)

Let users pick default menu width

crates/egui/src/menu.rs

@@ -154,8 +154,7 @@ pub(crate) fn menu_ui<'c, R>(
         set_menu_style(ui.style_mut());
 
         let frame = Frame::menu(ui.style()).show(ui, |ui| {
-            const DEFAULT_MENU_WIDTH: f32 = 150.0; // TODO(emilk): add to ui.spacing
-            ui.set_max_width(DEFAULT_MENU_WIDTH);
+            ui.set_max_width(ui.spacing().menu_width);
             ui.set_menu_state(Some(menu_state_arc.clone()));
             ui.with_layout(Layout::top_down_justified(Align::LEFT), add_contents)
                 .inner

crates/egui/src/style.rs

@@ -302,6 +302,9 @@ pub struct Spacing {
     /// Width of a tooltip (`on_hover_ui`, `on_hover_text` etc).
     pub tooltip_width: f32,
 
+    /// The default width of a menu.
+    pub menu_width: f32,
+
     /// End indented regions with a horizontal line
     pub indent_ends_with_horizontal_line: bool,
 
@@ -1111,6 +1114,7 @@ impl Default for Spacing {
             icon_width_inner: 8.0,
             icon_spacing: 4.0,
             tooltip_width: 600.0,
+            menu_width: 150.0,
             combo_height: 200.0,
             scroll: Default::default(),
             indent_ends_with_horizontal_line: false,
@@ -1458,6 +1462,7 @@ impl Spacing {
             icon_width_inner,
             icon_spacing,
             tooltip_width,
+            menu_width,
             indent_ends_with_horizontal_line,
             combo_height,
             scroll,
@@ -1516,6 +1521,11 @@ impl Spacing {
             ui.label("Tooltip wrap width");
         });
 
+        ui.horizontal(|ui| {
+            ui.add(DragValue::new(menu_width).clamp_range(0.0..=1000.0));
+            ui.label("Default width of a menu");
+        });
+
         ui.checkbox(
             indent_ends_with_horizontal_line,
             "End indented regions with a horizontal separator",