Add #[must_use] to container types: remind to call show()

egui/src/containers/area.rs

@@ -40,6 +40,7 @@ impl State {
 ///     .show(ctx, |ui| {
 ///         ui.label("Floating text!");
 ///     });
+#[must_use = "You should call .show()"]
 #[derive(Clone, Copy, Debug)]
 pub struct Area {
     pub(crate) id: Id,

egui/src/containers/collapsing_header.rs

@@ -134,6 +134,7 @@ pub(crate) fn paint_icon(ui: &mut Ui, openness: f32, response: &Response) {
 /// // Short version:
 /// ui.collapsing("Heading", |ui| { ui.label("Contents"); });
 /// ```
+#[must_use = "You should call .show()"]
 pub struct CollapsingHeader {
     label: Label,
     default_open: bool,

egui/src/containers/combo_box.rs

@@ -19,6 +19,7 @@ use epaint::Shape;
 ///     }
 /// );
 /// ```
+#[must_use = "You should call .show*"]
 pub struct ComboBox {
     id_source: Id,
     label: Option<Label>,

egui/src/containers/frame.rs

@@ -5,6 +5,7 @@ use epaint::*;
 
 /// Color and margin of a rectangular background of a [`Ui`].
 #[derive(Clone, Copy, Debug, Default, PartialEq)]
+#[must_use = "You should call .show()"]
 pub struct Frame {
     /// On each side
     pub margin: Vec2,

egui/src/containers/panel.rs

@@ -23,6 +23,7 @@ use crate::*;
 ///    ui.label("Hello World!");
 /// });
 /// ```
+#[must_use = "You should call .show()"]
 pub struct SidePanel {
     id: Id,
     max_width: f32,
@@ -95,6 +96,7 @@ impl SidePanel {
 ///    ui.label("Hello World!");
 /// });
 /// ```
+#[must_use = "You should call .show()"]
 pub struct TopPanel {
     id: Id,
     max_height: Option<f32>,
@@ -171,6 +173,7 @@ impl TopPanel {
 ///    ui.label("Hello World!");
 /// });
 /// ```
+#[must_use = "You should call .show()"]
 #[derive(Default)]
 pub struct CentralPanel {
     frame: Option<Frame>,

egui/src/containers/resize.rs

@@ -18,6 +18,7 @@ pub(crate) struct State {
 
 /// A region that can be resized by dragging the bottom right corner.
 #[derive(Clone, Copy, Debug)]
+#[must_use = "You should call .show()"]
 pub struct Resize {
     id: Option<Id>,
     id_source: Option<Id>,

egui/src/containers/scroll_area.rs

@@ -30,6 +30,7 @@ impl Default for State {
 // TODO: rename VScroll
 /// Add vertical scrolling to a contained [`Ui`].
 #[derive(Clone, Debug)]
+#[must_use = "You should call .show()"]
 pub struct ScrollArea {
     max_height: f32,
     always_show_scroll: bool,

egui/src/containers/window.rs

@@ -21,6 +21,7 @@ use super::*;
 /// egui::Window::new("My Window").show(ctx, |ui| {
 ///    ui.label("Hello World!");
 /// });
+#[must_use = "You should call .show()"]
 pub struct Window<'open> {
     title_label: Label,
     open: Option<&'open mut bool>,

egui/src/grid.rs

@@ -246,6 +246,7 @@ impl GridLayout {
 ///     ui.end_row();
 /// });
 /// ```
+#[must_use = "You should call .show()"]
 pub struct Grid {
     id_source: Id,
     striped: bool,