Extract UI elements from storybook into new ui crate (#3008)

This PR extracts the various UI elements from the `storybook` crate into
a new `ui` library crate.

Release Notes:

- N/A

crates/ui/src/theme.rs

@@ -0,0 +1,195 @@
+use std::collections::HashMap;
+use std::fmt;
+use std::marker::PhantomData;
+
+use gpui2::color::Hsla;
+use gpui2::element::Element;
+use gpui2::{serde_json, AppContext, IntoElement, Vector2F, ViewContext, WindowContext};
+use serde::de::Visitor;
+use serde::{Deserialize, Deserializer};
+use theme::ThemeSettings;
+
+#[derive(Deserialize, Clone, Default, Debug)]
+pub struct Theme {
+    pub name: String,
+    pub is_light: bool,
+    pub lowest: Layer,
+    pub middle: Layer,
+    pub highest: Layer,
+    pub popover_shadow: Shadow,
+    pub modal_shadow: Shadow,
+    #[serde(deserialize_with = "deserialize_player_colors")]
+    pub players: Vec<PlayerColors>,
+    #[serde(deserialize_with = "deserialize_syntax_colors")]
+    pub syntax: HashMap<String, Hsla>,
+}
+
+#[derive(Deserialize, Clone, Default, Debug)]
+pub struct Layer {
+    pub base: StyleSet,
+    pub variant: StyleSet,
+    pub on: StyleSet,
+    pub accent: StyleSet,
+    pub positive: StyleSet,
+    pub warning: StyleSet,
+    pub negative: StyleSet,
+}
+
+#[derive(Deserialize, Clone, Default, Debug)]
+pub struct StyleSet {
+    #[serde(rename = "default")]
+    pub default: ContainerColors,
+    pub hovered: ContainerColors,
+    pub pressed: ContainerColors,
+    pub active: ContainerColors,
+    pub disabled: ContainerColors,
+    pub inverted: ContainerColors,
+}
+
+#[derive(Deserialize, Clone, Default, Debug)]
+pub struct ContainerColors {
+    pub background: Hsla,
+    pub foreground: Hsla,
+    pub border: Hsla,
+}
+
+#[derive(Deserialize, Clone, Default, Debug)]
+pub struct PlayerColors {
+    pub selection: Hsla,
+    pub cursor: Hsla,
+}
+
+#[derive(Deserialize, Clone, Default, Debug)]
+pub struct Shadow {
+    pub blur: u8,
+    pub color: Hsla,
+    pub offset: Vec<u8>,
+}
+
+fn deserialize_player_colors<'de, D>(deserializer: D) -> Result<Vec<PlayerColors>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    struct PlayerArrayVisitor;
+
+    impl<'de> Visitor<'de> for PlayerArrayVisitor {
+        type Value = Vec<PlayerColors>;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str("an object with integer keys")
+        }
+
+        fn visit_map<A: serde::de::MapAccess<'de>>(
+            self,
+            mut map: A,
+        ) -> Result<Self::Value, A::Error> {
+            let mut players = Vec::with_capacity(8);
+            while let Some((key, value)) = map.next_entry::<usize, PlayerColors>()? {
+                if key < 8 {
+                    players.push(value);
+                } else {
+                    return Err(serde::de::Error::invalid_value(
+                        serde::de::Unexpected::Unsigned(key as u64),
+                        &"a key in range 0..7",
+                    ));
+                }
+            }
+            Ok(players)
+        }
+    }
+
+    deserializer.deserialize_map(PlayerArrayVisitor)
+}
+
+fn deserialize_syntax_colors<'de, D>(deserializer: D) -> Result<HashMap<String, Hsla>, D::Error>
+where
+    D: serde::Deserializer<'de>,
+{
+    #[derive(Deserialize)]
+    struct ColorWrapper {
+        color: Hsla,
+    }
+
+    struct SyntaxVisitor;
+
+    impl<'de> Visitor<'de> for SyntaxVisitor {
+        type Value = HashMap<String, Hsla>;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str("a map with keys and objects with a single color field as values")
+        }
+
+        fn visit_map<M>(self, mut map: M) -> Result<HashMap<String, Hsla>, M::Error>
+        where
+            M: serde::de::MapAccess<'de>,
+        {
+            let mut result = HashMap::new();
+            while let Some(key) = map.next_key()? {
+                let wrapper: ColorWrapper = map.next_value()?; // Deserialize values as Hsla
+                result.insert(key, wrapper.color);
+            }
+            Ok(result)
+        }
+    }
+    deserializer.deserialize_map(SyntaxVisitor)
+}
+
+#[derive(IntoElement)]
+pub struct Themed<V: 'static, E: Element<V>> {
+    pub(crate) theme: Theme,
+    pub(crate) child: E,
+    pub(crate) view_type: PhantomData<V>,
+}
+
+impl<V: 'static, E: Element<V>> Element<V> for Themed<V, E> {
+    type PaintState = E::PaintState;
+
+    fn layout(
+        &mut self,
+        view: &mut V,
+        cx: &mut ViewContext<V>,
+    ) -> anyhow::Result<(gpui2::LayoutId, Self::PaintState)>
+    where
+        Self: Sized,
+    {
+        cx.push_theme(self.theme.clone());
+        let result = self.child.layout(view, cx);
+        cx.pop_theme();
+        result
+    }
+
+    fn paint(
+        &mut self,
+        view: &mut V,
+        parent_origin: Vector2F,
+        layout: &gpui2::Layout,
+        state: &mut Self::PaintState,
+        cx: &mut ViewContext<V>,
+    ) where
+        Self: Sized,
+    {
+        cx.push_theme(self.theme.clone());
+        self.child.paint(view, parent_origin, layout, state, cx);
+        cx.pop_theme();
+    }
+}
+
+fn preferred_theme<V: 'static>(cx: &AppContext) -> Theme {
+    settings::get::<ThemeSettings>(cx)
+        .theme
+        .deserialized_base_theme
+        .lock()
+        .get_or_insert_with(|| {
+            let theme: Theme =
+                serde_json::from_value(settings::get::<ThemeSettings>(cx).theme.base_theme.clone())
+                    .unwrap();
+            Box::new(theme)
+        })
+        .downcast_ref::<Theme>()
+        .unwrap()
+        .clone()
+}
+
+pub fn theme<'a>(cx: &'a WindowContext) -> &'a Theme {
+    cx.theme::<Theme>()
+}