add sizable trait

crates/core/src/common.rs

@@ -2,6 +2,8 @@
 
 use gpui::{Div, Styled as _, div};
 
+pub use gpui_native_theme::Size;
+
 /// A row whose children center on the cross axis.
 pub fn h_flex() -> Div {
     div().flex().flex_row().items_center()
@@ -11,3 +13,31 @@ pub fn h_flex() -> Div {
 pub fn v_flex() -> Div {
     div().flex().flex_col()
 }
+
+/// A component that can be told which size to render at.
+pub trait Sizable: Sized {
+    /// Sets the size.
+    fn with_size(mut self, size: Size) -> Self {
+        self.apply_size(size);
+        self
+    }
+
+    /// Applies the size to the component's fields.
+    fn apply_size(&mut self, size: Size);
+
+    /// Sets `Size::Small`.
+    fn small(self) -> Self
+    where
+        Self: Sized,
+    {
+        self.with_size(Size::Small)
+    }
+
+    /// Sets `Size::Large`.
+    fn large(self) -> Self
+    where
+        Self: Sized,
+    {
+        self.with_size(Size::Large)
+    }
+}