Implement Empty widget

It can be useful if you want to fill some space with nothing.

web/src/widget.rs

@@ -25,6 +25,7 @@ pub mod text_input;
 mod checkbox;
 mod column;
 mod container;
+mod empty;
 mod image;
 mod radio;
 mod row;
@@ -44,6 +45,7 @@ pub use text_input::TextInput;
 pub use checkbox::Checkbox;
 pub use column::Column;
 pub use container::Container;
+pub use empty::Empty;
 pub use image::Image;
 pub use radio::Radio;
 pub use row::Row;

web/src/widget/empty.rs

@@ -0,0 +1,70 @@
+use crate::{style, Bus, Element, Length, Widget};
+use dodrio::bumpalo;
+
+/// An amount of empty space.
+///
+/// It can be useful if you want to fill some space with nothing.
+///
+/// [`Empty`]: struct.Empty.html
+#[derive(Debug)]
+pub struct Empty {
+    width: Length,
+    height: Length,
+}
+
+impl Empty {
+    /// Creates an amount of [`Empty`] space.
+    ///
+    /// [`Empty`]: struct.Empty.html
+    pub fn new() -> Self {
+        Empty {
+            width: Length::Shrink,
+            height: Length::Shrink,
+        }
+    }
+
+    /// Sets the width of the [`Empty`] space.
+    ///
+    /// [`Empty`]: struct..html
+    pub fn width(mut self, width: Length) -> Self {
+        self.width = width;
+        self
+    }
+
+    /// Sets the height of the [`Empty`] space.
+    ///
+    /// [`Empty`]: struct.Column.html
+    pub fn height(mut self, height: Length) -> Self {
+        self.height = height;
+        self
+    }
+}
+
+impl<'a, Message> Widget<Message> for Empty {
+    fn node<'b>(
+        &self,
+        bump: &'b bumpalo::Bump,
+        _publish: &Bus<Message>,
+        _style_sheet: &mut style::Sheet<'b>,
+    ) -> dodrio::Node<'b> {
+        use dodrio::builder::*;
+
+        let width = style::length(self.width);
+        let height = style::length(self.height);
+
+        let style = bumpalo::format!(
+            in bump,
+            "width: {}; height: {};",
+            width,
+            height
+        );
+
+        div(bump).attr("style", style.into_bump_str()).finish()
+    }
+}
+
+impl<'a, Message> From<Empty> for Element<'a, Message> {
+    fn from(empty: Empty) -> Element<'a, Message> {
+        Element::new(empty)
+    }
+}