Configurable label text style for CollapsingHeader (#200)

CollapsingHeader: change label text style & enable options

egui/src/containers/collapsing_header.rs

@@ -138,6 +138,7 @@ pub struct CollapsingHeader {
     label: Label,
     default_open: bool,
     id_source: Id,
+    enabled: bool,
 }
 
 impl CollapsingHeader {
@@ -154,6 +155,7 @@ impl CollapsingHeader {
             label,
             default_open: false,
             id_source,
+            enabled: true,
         }
     }
 
@@ -170,6 +172,21 @@ impl CollapsingHeader {
         self.id_source = Id::new(id_source);
         self
     }
+
+    /// By default, the `CollapsingHeader` text style is `TextStyle::Button`.
+    /// Call `.text_style(style)` to change this.
+    pub fn text_style(mut self, text_style: TextStyle) -> Self {
+        self.label = self.label.text_style(text_style);
+        self
+    }
+
+    /// If you set this to `false`, the `CollapsingHeader` will be grayed out and un-clickable.
+    ///
+    /// This is a convenience for [`Ui::set_enabled`].
+    pub fn enabled(mut self, enabled: bool) -> Self {
+        self.enabled = enabled;
+        self
+    }
 }
 
 struct Prepared {
@@ -188,6 +205,7 @@ impl CollapsingHeader {
             label,
             default_open,
             id_source,
+            enabled: _,
         } = self;
 
         // TODO: horizontal layout, with icon and text as labels. Insert background behind using Frame.
@@ -263,6 +281,10 @@ impl CollapsingHeader {
         ui: &mut Ui,
         add_contents: impl FnOnce(&mut Ui) -> R,
     ) -> CollapsingResponse<R> {
+        let header_enabled = self.enabled;
+        ui.wrap(|ui| {
+            ui.set_enabled(header_enabled);
+
             // Make sure contents are bellow header,
             // and make sure it is one unit (necessary for putting a `CollapsingHeader` in a grid).
             ui.vertical(|ui| {
@@ -296,6 +318,8 @@ impl CollapsingHeader {
                 }
             })
             .inner
+        })
+        .inner
     }
 }