Add #[must_use] to all widget builders

egui/src/widgets/button.rs

@@ -136,6 +136,7 @@ impl Widget for Button {
 
 // TODO: allow checkbox without a text label
 /// Boolean on/off control with text label.
+#[must_use = "You should put this widget in an ui with `ui.add(widget);`"]
 #[derive(Debug)]
 pub struct Checkbox<'a> {
     checked: &'a mut bool,

egui/src/widgets/drag_value.rs

@@ -17,6 +17,7 @@ fn set(value_function: &mut GetSetValue<'_>, value: f64) {
 }
 
 /// A numeric value that you can change by dragging the number. More compact than a [`Slider`].
+#[must_use = "You should put this widget in an ui with `ui.add(widget);`"]
 pub struct DragValue<'a> {
     value_function: GetSetValue<'a>,
     speed: f32,

egui/src/widgets/slider.rs

@@ -37,6 +37,7 @@ struct SliderSpec {
 
 /// Control a number by a horizontal slider.
 /// The range can include any numbers, and go from low-to-high or from high-to-low.
+#[must_use = "You should put this widget in an ui with `ui.add(widget);`"]
 pub struct Slider<'a> {
     get_set_value: GetSetValue<'a>,
     range: RangeInclusive<f64>,

egui/src/widgets/text_edit.rs

@@ -119,6 +119,7 @@ impl CCursorPair {
 ///     // use my_string
 /// }
 /// ```
+#[must_use = "You should put this widget in an ui with `ui.add(widget);`"]
 #[derive(Debug)]
 pub struct TextEdit<'t> {
     text: &'t mut String,