Add must_use to Shape

epaint/src/shape.rs

@@ -6,6 +6,7 @@ use emath::*;
 
 /// A paint primitive such as a circle or a piece of text.
 /// Coordinates are all screen space points (not physical pixels).
+#[must_use = "Add a Shape to a Painter"]
 #[derive(Clone, Debug)]
 pub enum Shape {
     /// Paint nothing. This can be useful as a placeholder.