more detailed warning when computing normals

also panic in compute_flat_normals if indices are set.
That way there won't be no unexpected vertex buffer size increases.

crates/bevy_gltf/src/loader.rs

@@ -147,9 +147,14 @@ async fn load_gltf<'a, 'b>(
             };
 
             if mesh.attribute(Mesh::ATTRIBUTE_NORMAL).is_none() {
-                bevy_log::info!("missing normals, computing them as flat");
+                let vertex_count_before = mesh.count_vertices();
                 mesh.duplicate_vertices();
                 mesh.compute_flat_normals();
+                let vertex_count_after = mesh.count_vertices();
+
+                if vertex_count_before != vertex_count_after {
+                    bevy_log::warn!("Missing vertex normals in indexed geometry, computing them as flat. Vertex count increased from {} to {}", vertex_count_before, vertex_count_after);
+                }
             }
 
             let mesh = load_context.set_labeled_asset(&primitive_label, LoadedAsset::new(mesh));

crates/bevy_render/src/mesh/mesh.rs

@@ -402,6 +402,7 @@ impl Mesh {
 
     /// Duplicates the vertex attributes so that no vertices are shared.
     ///
+    /// This can dramatically increase the vertex count, so make sure this is what you want.
     /// Does nothing if no [Indices] are set.
     pub fn duplicate_vertices(&mut self) {
         fn duplicate<T: Copy>(values: &[T], indices: impl Iterator<Item = usize>) -> Vec<T> {
@@ -438,12 +439,12 @@ impl Mesh {
     }
 
     /// Calculates the [`Mesh::ATTRIBUTE_NORMAL`] of a mesh.
-    /// This [duplicates the vertices](Mesh::duplicate_vertices), so any [`Indices`] will be gone if set.
+    ///
+    /// Panics if [`Indices`] are set.
+    /// Consider calling [Mesh::duplicate_vertices] or export your mesh with normal attributes.
     pub fn compute_flat_normals(&mut self) {
         if self.indices().is_some() {
-            self.duplicate_vertices();
-            self.compute_flat_normals();
-            return;
+            panic!("`compute_flat_normals` can't work on indexed geometry. Consider calling `Mesh::duplicate_vertices`.");
         }
 
         let positions = self