static assert that bundles do not have duplicate types

crates/bevy_ecs/macros/src/lib.rs

@@ -144,6 +144,19 @@ pub fn derive_bundle(input: TokenStream) -> TokenStream {
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
     let struct_name = &ast.ident;
 
+    let static_assert_bundle_func = syn::Ident::new(
+        &format!(
+            "static_assert_{}_does_not_have_duplicate_types",
+            struct_name.to_string()
+        ),
+        struct_name.span(),
+    );
+
+    let static_assert_bundle_trait = syn::Ident::new(
+        &format!("{}HasDuplicateType", struct_name.to_string()),
+        struct_name.span(),
+    );
+
     TokenStream::from(quote! {
         /// SAFE: TypeInfo is returned in field-definition-order. [from_components] and [get_components] use field-definition-order
         unsafe impl #impl_generics #ecs_path::bundle::Bundle for #struct_name#ty_generics #where_clause {
@@ -165,6 +178,19 @@ pub fn derive_bundle(input: TokenStream) -> TokenStream {
                 #(#field_get_components)*
             }
         }
+
+        #[cfg(test)]
+        #[allow(dead_code, non_snake_case)]
+        fn #static_assert_bundle_func() {
+            macro_rules! assert_all_bundle_types_ne {
+                ($($y:ty),+ $(,)?) => {
+                    trait #static_assert_bundle_trait {}
+                    $(impl #static_assert_bundle_trait for $y {})+
+                };
+            }
+
+            assert_all_bundle_types_ne!(#(#field_type),*);
+        }
     })
 }
 

crates/bevy_ecs/src/bundle.rs

@@ -37,6 +37,19 @@ use std::{any::TypeId, collections::HashMap};
 /// }
 /// ```
 ///
+/// ## Note
+/// Bundles do not support duplicate types.
+///
+/// ```compile_fail
+/// # use bevy_ecs::bundle::Bundle;
+///
+/// #[derive(Bundle)]
+/// struct HasDuplicateType {
+///     a: usize,
+///     b: usize, // `b` is also a `usize` so this will fail to compile
+/// }
+/// ```
+///
 /// # Safety
 /// [Bundle::type_info] must return the TypeInfo for each component type in the bundle, in the
 /// _exact_ order that [Bundle::get_components] is called.