Add support for optional icon to Button (#3479)

This PR extends `Button` with support for an optional icon to be
displayed next to the label.

As part of this, the functionality for displaying an icon within a
button has been factored out into an internal `ButtonIcon` component.
`ButtonIcon` is now used by both `IconButton` and `Button` to
encapsulate the concerns of an icon that is rendered within a button.

Release Notes:

- N/A

crates/ui2/src/components/button/button.rs

@@ -1,7 +1,11 @@
 use gpui::AnyView;
 
 use crate::prelude::*;
-use crate::{ButtonCommon, ButtonLike, ButtonSize, ButtonStyle, Label, LineHeightStyle};
+use crate::{
+    ButtonCommon, ButtonLike, ButtonSize, ButtonStyle, Icon, IconSize, Label, LineHeightStyle,
+};
+
+use super::button_icon::ButtonIcon;
 
 #[derive(IntoElement)]
 pub struct Button {
@@ -9,6 +13,10 @@ pub struct Button {
     label: SharedString,
     label_color: Option<Color>,
     selected_label: Option<SharedString>,
+    icon: Option<Icon>,
+    icon_size: Option<IconSize>,
+    icon_color: Option<Color>,
+    selected_icon: Option<Icon>,
 }
 
 impl Button {
@@ -18,6 +26,10 @@ impl Button {
             label: label.into(),
             label_color: None,
             selected_label: None,
+            icon: None,
+            icon_size: None,
+            icon_color: None,
+            selected_icon: None,
         }
     }
 
@@ -30,6 +42,26 @@ impl Button {
         self.selected_label = label.into().map(Into::into);
         self
     }
+
+    pub fn icon(mut self, icon: impl Into<Option<Icon>>) -> Self {
+        self.icon = icon.into();
+        self
+    }
+
+    pub fn icon_size(mut self, icon_size: impl Into<Option<IconSize>>) -> Self {
+        self.icon_size = icon_size.into();
+        self
+    }
+
+    pub fn icon_color(mut self, icon_color: impl Into<Option<Color>>) -> Self {
+        self.icon_color = icon_color.into();
+        self
+    }
+
+    pub fn selected_icon(mut self, icon: impl Into<Option<Icon>>) -> Self {
+        self.selected_icon = icon.into();
+        self
+    }
 }
 
 impl Selectable for Button {
@@ -81,23 +113,35 @@ impl RenderOnce for Button {
     type Rendered = ButtonLike;
 
     fn render(self, _cx: &mut WindowContext) -> Self::Rendered {
+        let is_disabled = self.base.disabled;
+        let is_selected = self.base.selected;
+
         let label = self
             .selected_label
-            .filter(|_| self.base.selected)
+            .filter(|_| is_selected)
             .unwrap_or(self.label);
 
-        let label_color = if self.base.disabled {
+        let label_color = if is_disabled {
             Color::Disabled
-        } else if self.base.selected {
+        } else if is_selected {
             Color::Selected
         } else {
             self.label_color.unwrap_or_default()
         };
 
-        self.base.child(
-            Label::new(label)
-                .color(label_color)
-                .line_height_style(LineHeightStyle::UILabel),
-        )
+        self.base
+            .children(self.icon.map(|icon| {
+                ButtonIcon::new(icon)
+                    .disabled(is_disabled)
+                    .selected(is_selected)
+                    .selected_icon(self.selected_icon)
+                    .size(self.icon_size)
+                    .color(self.icon_color)
+            }))
+            .child(
+                Label::new(label)
+                    .color(label_color)
+                    .line_height_style(LineHeightStyle::UILabel),
+            )
     }
 }