Improve Debug implementation of cache::State

wgpu/src/widget/canvas/layer/cache.rs

@@ -21,7 +21,6 @@ pub struct Cache<T: Drawable> {
     state: RefCell<State>,
 }
 
-#[derive(Debug)]
 enum State {
     Empty,
     Filled {
@@ -99,3 +98,17 @@ where
         mesh
     }
 }
+
+impl std::fmt::Debug for State {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            State::Empty => write!(f, "Empty"),
+            State::Filled { mesh, bounds } => f
+                .debug_struct("Filled")
+                .field("vertices", &mesh.vertices.len())
+                .field("indices", &mesh.indices.len())
+                .field("bounds", bounds)
+                .finish(),
+        }
+    }
+}