Started a List widget

a la HTML's <ul> tag.

src/widget.rs

@@ -39,6 +39,7 @@ use crate::utils::IgnorePoison;
 use crate::value::{Dynamic, Generation, IntoDynamic, IntoValue, Validation, Value};
 use crate::widgets::checkbox::{Checkable, CheckboxState};
 use crate::widgets::layers::{OverlayLayer, Tooltipped};
+use crate::widgets::list::List;
 use crate::widgets::{
     Align, Button, Checkbox, Collapse, Container, Disclose, Expand, Layers, Resize, Scroll, Space,
     Stack, Style, Themed, ThemedMode, Validated, Wrap,
@@ -2036,6 +2037,12 @@ impl WidgetList {
         Wrap::new(self)
     }
 
+    /// Returns `self` as an unordered [`List`].
+    #[must_use]
+    pub fn into_list(self) -> List {
+        List::new(self)
+    }
+
     /// Synchronizes this list of children with another collection.
     ///
     /// This function updates `collection` by calling `change_fn` for each

src/widgets.rs

@@ -17,6 +17,7 @@ pub mod image;
 pub mod input;
 pub mod label;
 pub mod layers;
+pub mod list;
 mod mode_switch;
 pub mod progress;
 pub mod radio;

src/widgets/list.rs

@@ -0,0 +1,92 @@
+//! A list of elements with optional item indicators.
+
+use std::fmt::Debug;
+use std::sync::Arc;
+
+use super::grid::GridWidgets;
+use super::input::CowString;
+use super::Grid;
+use crate::value::{IntoValue, MapEach, Source, Value};
+use crate::widget::{MakeWidget, WidgetInstance, WidgetList};
+
+/// A list of items displayed with an optional item indicator.
+pub struct List {
+    style: Value<ListStyle>,
+    children: Value<WidgetList>,
+}
+
+impl List {
+    /// Returns a new list with the default [`ListStyle`]/
+    pub fn new(children: impl IntoValue<WidgetList>) -> Self {
+        Self {
+            children: children.into_value(),
+            style: Value::Constant(ListStyle::default()),
+        }
+    }
+}
+
+/// The style of a [`List`] widget's item indicators.
+#[derive(Default, Debug, Clone)]
+pub enum ListStyle {
+    #[default]
+    Disc,
+    Custom(Arc<dyn ListIndicator>),
+}
+
+impl PartialEq for ListStyle {
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            (Self::Custom(l0), Self::Custom(r0)) => Arc::ptr_eq(l0, r0),
+            _ => core::mem::discriminant(self) == core::mem::discriminant(other),
+        }
+    }
+}
+
+/// A [`ListStyle`] implementation that provides an optional indicator for a
+/// given list index.
+pub trait ListIndicator: Debug + Sync + Send + 'static {
+    /// Returns the indicator to use at `index`.
+    fn list_indicator(&self, index: usize) -> Option<CowString>;
+}
+
+impl ListIndicator for ListStyle {
+    fn list_indicator(&self, index: usize) -> Option<CowString> {
+        match self {
+            ListStyle::Disc => Some(CowString::new("\u{2022}")),
+            ListStyle::Custom(style) => style.list_indicator(index),
+        }
+    }
+}
+
+impl MakeWidget for List {
+    fn make_widget(self) -> WidgetInstance {
+        let rows = match (self.children, self.style) {
+            (children, Value::Constant(style)) => {
+                children.map_each(move |children| build_grid_widgets(&style, children))
+            }
+            (Value::Dynamic(children), Value::Dynamic(style)) => Value::Dynamic(
+                (&style, &children)
+                    .map_each(|(style, children)| build_grid_widgets(style, children)),
+            ),
+            (Value::Constant(children), Value::Dynamic(style)) => {
+                Value::Dynamic(style.map_each(move |style| build_grid_widgets(style, &children)))
+            }
+        };
+        Grid::from_rows(rows).make_widget()
+    }
+}
+
+fn build_grid_widgets(style: &ListStyle, children: &WidgetList) -> GridWidgets<2> {
+    // This is horrible. We should be be using synchronize_with to avoid
+    // recreating the gridwidgets every time.
+    children
+        .iter()
+        .enumerate()
+        .map(|(index, child)| {
+            (
+                style.list_indicator(index).unwrap_or_default(),
+                child.clone().align_left().make_widget(),
+            )
+        })
+        .collect()
+}