Introduce `Widget::overlay` :tada:

25 files changed, 80 insertions, 32 deletions

diff --git a/examples/custom_widget/src/main.rs b/examples/custom_widget/src/main.rs
index bcf896b0..a6068f91 100644
--- a/examples/custom_widget/src/main.rs
+++ b/examples/custom_widget/src/main.rs
@@ -25,7 +25,7 @@ mod circle {
         }
     }
 
-    impl<Message, B> Widget<Message, Renderer<B>> for Circle
+    impl<'a, Message, B> Widget<'a, Message, Renderer<B>> for Circle
     where
         B: Backend,
     {
diff --git a/examples/geometry/src/main.rs b/examples/geometry/src/main.rs
index 71ce0d8c..3795323a 100644
--- a/examples/geometry/src/main.rs
+++ b/examples/geometry/src/main.rs
@@ -27,7 +27,7 @@ mod rainbow {
         }
     }
 
-    impl<Message, B> Widget<Message, Renderer<B>> for Rainbow
+    impl<'a, Message, B> Widget<'a, Message, Renderer<B>> for Rainbow
     where
         B: Backend,
     {
diff --git a/examples/todos/src/main.rs b/examples/todos/src/main.rs
index c9cbcc69..5713a6f2 100644
--- a/examples/todos/src/main.rs
+++ b/examples/todos/src/main.rs
@@ -425,7 +425,7 @@ impl Filter {
     }
 }
 
-fn loading_message() -> Element<'static, Message> {
+fn loading_message<'a>() -> Element<'a, Message> {
     Container::new(
         Text::new("Loading...")
             .horizontal_alignment(HorizontalAlignment::Center)
@@ -437,7 +437,7 @@ fn loading_message() -> Element<'static, Message> {
     .into()
 }
 
-fn empty_message(message: &str) -> Element<'static, Message> {
+fn empty_message<'a>(message: &str) -> Element<'a, Message> {
     Container::new(
         Text::new(message)
             .width(Length::Fill)
diff --git a/graphics/src/renderer.rs b/graphics/src/renderer.rs
index c9360f3a..44bacd4e 100644
--- a/graphics/src/renderer.rs
+++ b/graphics/src/renderer.rs
@@ -62,7 +62,7 @@ where
     fn explain<Message>(
         &mut self,
         defaults: &Defaults,
-        widget: &dyn Widget<Message, Self>,
+        widget: &dyn Widget<'_, Message, Self>,
         layout: Layout<'_>,
         cursor_position: Point,
         color: Color,
diff --git a/graphics/src/widget/canvas.rs b/graphics/src/widget/canvas.rs
index b8466239..0257f819 100644
--- a/graphics/src/widget/canvas.rs
+++ b/graphics/src/widget/canvas.rs
@@ -134,7 +134,7 @@ impl<Message, P: Program<Message>> Canvas<Message, P> {
     }
 }
 
-impl<Message, P, B> Widget<Message, Renderer<B>> for Canvas<Message, P>
+impl<'a, Message, P, B> Widget<'a, Message, Renderer<B>> for Canvas<Message, P>
 where
     P: Program<Message>,
     B: Backend,
diff --git a/native/src/element.rs b/native/src/element.rs
index 73e39012..c6d65550 100644
--- a/native/src/element.rs
+++ b/native/src/element.rs
@@ -1,5 +1,6 @@
 use crate::{
-    layout, Clipboard, Color, Event, Hasher, Layout, Length, Point, Widget,
+    layout, Clipboard, Color, Event, Hasher, Layout, Length, Overlay, Point,
+    Widget,
 };
 
 /// A generic [`Widget`].
@@ -15,7 +16,7 @@ use crate::{
 /// [`Element`]: struct.Element.html
 #[allow(missing_debug_implementations)]
 pub struct Element<'a, Message, Renderer> {
-    pub(crate) widget: Box<dyn Widget<Message, Renderer> + 'a>,
+    pub(crate) widget: Box<dyn Widget<'a, Message, Renderer> + 'a>,
 }
 
 impl<'a, Message, Renderer> Element<'a, Message, Renderer>
@@ -27,7 +28,7 @@ where
     /// [`Element`]: struct.Element.html
     /// [`Widget`]: widget/trait.Widget.html
     pub fn new(
-        widget: impl Widget<Message, Renderer> + 'a,
+        widget: impl Widget<'a, Message, Renderer> + 'a,
     ) -> Element<'a, Message, Renderer> {
         Element {
             widget: Box::new(widget),
@@ -270,16 +271,22 @@ where
     pub fn hash_layout(&self, state: &mut Hasher) {
         self.widget.hash_layout(state);
     }
+
+    pub fn overlay(
+        &mut self,
+    ) -> Option<Box<dyn Overlay<Message, Renderer> + 'a>> {
+        self.widget.overlay()
+    }
 }
 
 struct Map<'a, A, B, Renderer> {
-    widget: Box<dyn Widget<A, Renderer> + 'a>,
+    widget: Box<dyn Widget<'a, A, Renderer> + 'a>,
     mapper: Box<dyn Fn(A) -> B>,
 }
 
 impl<'a, A, B, Renderer> Map<'a, A, B, Renderer> {
     pub fn new<F>(
-        widget: Box<dyn Widget<A, Renderer> + 'a>,
+        widget: Box<dyn Widget<'a, A, Renderer> + 'a>,
         mapper: F,
     ) -> Map<'a, A, B, Renderer>
     where
@@ -292,7 +299,7 @@ impl<'a, A, B, Renderer> Map<'a, A, B, Renderer> {
     }
 }
 
-impl<'a, A, B, Renderer> Widget<B, Renderer> for Map<'a, A, B, Renderer>
+impl<'a, A, B, Renderer> Widget<'a, B, Renderer> for Map<'a, A, B, Renderer>
 where
     Renderer: crate::Renderer,
 {
@@ -367,7 +374,7 @@ where
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for Explain<'a, Message, Renderer>
 where
     Renderer: crate::Renderer + layout::Debugger,
diff --git a/native/src/layout/debugger.rs b/native/src/layout/debugger.rs
index e4b21609..9c58f4f1 100644
--- a/native/src/layout/debugger.rs
+++ b/native/src/layout/debugger.rs
@@ -18,7 +18,7 @@ pub trait Debugger: Renderer {
     fn explain<Message>(
         &mut self,
         defaults: &Self::Defaults,
-        widget: &dyn Widget<Message, Self>,
+        widget: &dyn Widget<'_, Message, Self>,
         layout: Layout<'_>,
         cursor_position: Point,
         color: Color,
diff --git a/native/src/lib.rs b/native/src/lib.rs
index b67ff2a1..dbec068d 100644
--- a/native/src/lib.rs
+++ b/native/src/lib.rs
@@ -30,7 +30,7 @@
 //! [`Widget`]: widget/trait.Widget.html
 //! [`UserInterface`]: struct.UserInterface.html
 //! [renderer]: renderer/index.html
-#![deny(missing_docs)]
+//#![deny(missing_docs)]
 #![deny(missing_debug_implementations)]
 #![deny(unused_results)]
 #![forbid(unsafe_code)]
@@ -48,6 +48,7 @@ mod clipboard;
 mod element;
 mod event;
 mod hasher;
+mod overlay;
 mod runtime;
 mod user_interface;
 
@@ -75,6 +76,7 @@ pub use element::Element;
 pub use event::Event;
 pub use hasher::Hasher;
 pub use layout::Layout;
+pub use overlay::Overlay;
 pub use program::Program;
 pub use renderer::Renderer;
 pub use runtime::Runtime;
diff --git a/native/src/overlay.rs b/native/src/overlay.rs
new file mode 100644
index 00000000..d34432a4
--- /dev/null
+++ b/native/src/overlay.rs
@@ -0,0 +1,33 @@
+use crate::{layout, Clipboard, Event, Hasher, Layout, Point};
+
+pub trait Overlay<Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node;
+
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        defaults: &Renderer::Defaults,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output;
+
+    fn hash_layout(&self, state: &mut Hasher);
+
+    fn on_event(
+        &mut self,
+        _event: Event,
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+        _messages: &mut Vec<Message>,
+        _renderer: &Renderer,
+        _clipboard: Option<&dyn Clipboard>,
+    ) {
+    }
+}
diff --git a/native/src/widget.rs b/native/src/widget.rs
index 4453145b..dd1a97d2 100644
--- a/native/src/widget.rs
+++ b/native/src/widget.rs
@@ -67,7 +67,7 @@ pub use text::Text;
 #[doc(no_inline)]
 pub use text_input::TextInput;
 
-use crate::{layout, Clipboard, Event, Hasher, Layout, Length, Point};
+use crate::{layout, Clipboard, Event, Hasher, Layout, Length, Overlay, Point};
 
 /// A component that displays information and allows interaction.
 ///
@@ -94,7 +94,7 @@ use crate::{layout, Clipboard, Event, Hasher, Layout, Length, Point};
 /// [`geometry`]: https://github.com/hecrj/iced/tree/0.1/examples/geometry
 /// [`lyon`]: https://github.com/nical/lyon
 /// [`iced_wgpu`]: https://github.com/hecrj/iced/tree/0.1/wgpu
-pub trait Widget<Message, Renderer>
+pub trait Widget<'a, Message, Renderer>
 where
     Renderer: crate::Renderer,
 {
@@ -175,4 +175,8 @@ where
         _clipboard: Option<&dyn Clipboard>,
     ) {
     }
+
+    fn overlay(&mut self) -> Option<Box<dyn Overlay<Message, Renderer> + 'a>> {
+        None
+    }
 }
diff --git a/native/src/widget/button.rs b/native/src/widget/button.rs
index c932da2b..72db808b 100644
--- a/native/src/widget/button.rs
+++ b/native/src/widget/button.rs
@@ -139,7 +139,7 @@ impl State {
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for Button<'a, Message, Renderer>
 where
     Renderer: self::Renderer,
diff --git a/native/src/widget/checkbox.rs b/native/src/widget/checkbox.rs
index 44962288..82fd6d1f 100644
--- a/native/src/widget/checkbox.rs
+++ b/native/src/widget/checkbox.rs
@@ -106,7 +106,7 @@ impl<Message, Renderer: self::Renderer + text::Renderer>
     }
 }
 
-impl<Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for Checkbox<Message, Renderer>
 where
     Renderer: self::Renderer + text::Renderer + row::Renderer,
diff --git a/native/src/widget/column.rs b/native/src/widget/column.rs
index 259a7e6e..6afc94d6 100644
--- a/native/src/widget/column.rs
+++ b/native/src/widget/column.rs
@@ -121,7 +121,7 @@ impl<'a, Message, Renderer> Column<'a, Message, Renderer> {
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for Column<'a, Message, Renderer>
 where
     Renderer: self::Renderer,
diff --git a/native/src/widget/container.rs b/native/src/widget/container.rs
index 2590fe3b..3ad12eeb 100644
--- a/native/src/widget/container.rs
+++ b/native/src/widget/container.rs
@@ -129,7 +129,7 @@ where
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for Container<'a, Message, Renderer>
 where
     Renderer: self::Renderer,
diff --git a/native/src/widget/image.rs b/native/src/widget/image.rs
index 132f249d..b7c8f4ff 100644
--- a/native/src/widget/image.rs
+++ b/native/src/widget/image.rs
@@ -54,7 +54,7 @@ impl Image {
     }
 }
 
-impl<Message, Renderer> Widget<Message, Renderer> for Image
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer> for Image
 where
     Renderer: self::Renderer,
 {
diff --git a/native/src/widget/pane_grid.rs b/native/src/widget/pane_grid.rs
index a8deef0b..faf8da4e 100644
--- a/native/src/widget/pane_grid.rs
+++ b/native/src/widget/pane_grid.rs
@@ -387,7 +387,7 @@ pub struct KeyPressEvent {
     pub modifiers: keyboard::ModifiersState,
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for PaneGrid<'a, Message, Renderer>
 where
     Renderer: self::Renderer,
diff --git a/native/src/widget/progress_bar.rs b/native/src/widget/progress_bar.rs
index 5ab76d47..93d86371 100644
--- a/native/src/widget/progress_bar.rs
+++ b/native/src/widget/progress_bar.rs
@@ -70,7 +70,8 @@ impl<Renderer: self::Renderer> ProgressBar<Renderer> {
     }
 }
 
-impl<Message, Renderer> Widget<Message, Renderer> for ProgressBar<Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
+    for ProgressBar<Renderer>
 where
     Renderer: self::Renderer,
 {
diff --git a/native/src/widget/radio.rs b/native/src/widget/radio.rs
index 5b8d00e9..0d88c740 100644
--- a/native/src/widget/radio.rs
+++ b/native/src/widget/radio.rs
@@ -121,7 +121,8 @@ impl<Message, Renderer: self::Renderer + text::Renderer>
     }
 }
 
-impl<Message, Renderer> Widget<Message, Renderer> for Radio<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
+    for Radio<Message, Renderer>
 where
     Renderer: self::Renderer + text::Renderer + row::Renderer,
     Message: Clone,
diff --git a/native/src/widget/row.rs b/native/src/widget/row.rs
index 31f7472f..1ebbac6b 100644
--- a/native/src/widget/row.rs
+++ b/native/src/widget/row.rs
@@ -122,7 +122,7 @@ impl<'a, Message, Renderer> Row<'a, Message, Renderer> {
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for Row<'a, Message, Renderer>
 where
     Renderer: self::Renderer,
diff --git a/native/src/widget/scrollable.rs b/native/src/widget/scrollable.rs
index 3c8e5e5b..d7ad98e6 100644
--- a/native/src/widget/scrollable.rs
+++ b/native/src/widget/scrollable.rs
@@ -110,7 +110,7 @@ impl<'a, Message, Renderer: self::Renderer> Scrollable<'a, Message, Renderer> {
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for Scrollable<'a, Message, Renderer>
 where
     Renderer: self::Renderer + column::Renderer,
diff --git a/native/src/widget/slider.rs b/native/src/widget/slider.rs
index 70f2b6ac..e0193342 100644
--- a/native/src/widget/slider.rs
+++ b/native/src/widget/slider.rs
@@ -154,7 +154,7 @@ impl State {
     }
 }
 
-impl<'a, T, Message, Renderer> Widget<Message, Renderer>
+impl<'a, T, Message, Renderer> Widget<'a, Message, Renderer>
     for Slider<'a, T, Message, Renderer>
 where
     T: Copy + Into<f64> + num_traits::FromPrimitive,
diff --git a/native/src/widget/space.rs b/native/src/widget/space.rs
index e56a8fe1..8ada40ed 100644
--- a/native/src/widget/space.rs
+++ b/native/src/widget/space.rs
@@ -43,7 +43,7 @@ impl Space {
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer> for Space
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer> for Space
 where
     Renderer: self::Renderer,
 {
diff --git a/native/src/widget/svg.rs b/native/src/widget/svg.rs
index 114d5e41..3e45aaf6 100644
--- a/native/src/widget/svg.rs
+++ b/native/src/widget/svg.rs
@@ -60,7 +60,7 @@ impl Svg {
     }
 }
 
-impl<Message, Renderer> Widget<Message, Renderer> for Svg
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer> for Svg
 where
     Renderer: self::Renderer,
 {
diff --git a/native/src/widget/text.rs b/native/src/widget/text.rs
index 48a69e34..7f75eb9c 100644
--- a/native/src/widget/text.rs
+++ b/native/src/widget/text.rs
@@ -112,7 +112,7 @@ impl<Renderer: self::Renderer> Text<Renderer> {
     }
 }
 
-impl<Message, Renderer> Widget<Message, Renderer> for Text<Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer> for Text<Renderer>
 where
     Renderer: self::Renderer,
 {
diff --git a/native/src/widget/text_input.rs b/native/src/widget/text_input.rs
index 3f415101..63be6019 100644
--- a/native/src/widget/text_input.rs
+++ b/native/src/widget/text_input.rs
@@ -165,7 +165,7 @@ impl<'a, Message, Renderer: self::Renderer> TextInput<'a, Message, Renderer> {
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Message, Renderer> Widget<'a, Message, Renderer>
     for TextInput<'a, Message, Renderer>
 where
     Renderer: self::Renderer,