Allow #[derive(Bundle)] on tuple structs (take 3) (#10561)

- rework of old @Veykril's work in
[2499](https://github.com/bevyengine/bevy/pull/2499)
- Fixes [3537](https://github.com/bevyengine/bevy/issues/3537)

crates/bevy_ecs/macros/src/lib.rs

@@ -5,7 +5,7 @@ mod fetch;
 mod states;
 
 use crate::fetch::derive_world_query_impl;
-use bevy_macro_utils::{derive_label, ensure_no_collision, get_named_struct_fields, BevyManifest};
+use bevy_macro_utils::{derive_label, ensure_no_collision, get_struct_fields, BevyManifest};
 use proc_macro::TokenStream;
 use proc_macro2::Span;
 use quote::{format_ident, quote};
@@ -27,8 +27,8 @@ pub fn derive_bundle(input: TokenStream) -> TokenStream {
     let ast = parse_macro_input!(input as DeriveInput);
     let ecs_path = bevy_ecs_path();
 
-    let named_fields = match get_named_struct_fields(&ast.data) {
+    let named_fields = match get_struct_fields(&ast.data) {
-        Ok(fields) => &fields.named,
+        Ok(fields) => fields,
         Err(e) => return e.into_compile_error().into(),
     };
 
@@ -59,8 +59,9 @@ pub fn derive_bundle(input: TokenStream) -> TokenStream {
 
     let field = named_fields
         .iter()
-        .map(|field| field.ident.as_ref().unwrap())
+        .map(|field| field.ident.as_ref())
         .collect::<Vec<_>>();
+
     let field_type = named_fields
         .iter()
         .map(|field| &field.ty)
@@ -69,14 +70,19 @@ pub fn derive_bundle(input: TokenStream) -> TokenStream {
     let mut field_component_ids = Vec::new();
     let mut field_get_components = Vec::new();
     let mut field_from_components = Vec::new();
-    for ((field_type, field_kind), field) in
+    for (((i, field_type), field_kind), field) in field_type
-        field_type.iter().zip(field_kind.iter()).zip(field.iter())
+        .iter()
+        .enumerate()
+        .zip(field_kind.iter())
+        .zip(field.iter())
     {
         match field_kind {
             BundleFieldKind::Component => {
                 field_component_ids.push(quote! {
                 <#field_type as #ecs_path::bundle::Bundle>::component_ids(components, storages, &mut *ids);
                 });
+                match field {
+                    Some(field) => {
                         field_get_components.push(quote! {
                             self.#field.get_components(&mut *func);
                         });
@@ -84,6 +90,17 @@ pub fn derive_bundle(input: TokenStream) -> TokenStream {
                             #field: <#field_type as #ecs_path::bundle::Bundle>::from_components(ctx, &mut *func),
                         });
                     }
+                    None => {
+                        let index = syn::Index::from(i);
+                        field_get_components.push(quote! {
+                            self.#index.get_components(&mut *func);
+                        });
+                        field_from_components.push(quote! {
+                            #index: <#field_type as #ecs_path::bundle::Bundle>::from_components(ctx, &mut *func),
+                        });
+                    }
+                }
+            }
 
             BundleFieldKind::Ignore => {
                 field_from_components.push(quote! {

crates/bevy_ecs/src/lib.rs

@@ -1724,4 +1724,22 @@ mod tests {
             "new entity was spawned and received C component"
         );
     }
+
+    #[derive(Component)]
+    struct ComponentA(u32);
+
+    #[derive(Component)]
+    struct ComponentB(u32);
+
+    #[derive(Bundle)]
+    struct Simple(ComponentA);
+
+    #[derive(Bundle)]
+    struct Tuple(Simple, ComponentB);
+
+    #[derive(Bundle)]
+    struct Record {
+        field0: Simple,
+        field1: ComponentB,
+    }
 }

crates/bevy_macro_utils/src/shape.rs

@@ -1,20 +1,24 @@
 use proc_macro::Span;
-use syn::{Data, DataStruct, Error, Fields, FieldsNamed};
+use syn::{punctuated::Punctuated, token::Comma, Data, DataStruct, Error, Field, Fields};
 
 /// Get the fields of a data structure if that structure is a struct with named fields;
 /// otherwise, return a compile error that points to the site of the macro invocation.
-pub fn get_named_struct_fields(data: &syn::Data) -> syn::Result<&FieldsNamed> {
+pub fn get_struct_fields(data: &syn::Data) -> syn::Result<&Punctuated<Field, Comma>> {
     match data {
         Data::Struct(DataStruct {
             fields: Fields::Named(fields),
             ..
-        }) => Ok(fields),
+        }) => Ok(&fields.named),
+        Data::Struct(DataStruct {
+            fields: Fields::Unnamed(fields),
+            ..
+        }) => Ok(&fields.unnamed),
         _ => Err(Error::new(
             // This deliberately points to the call site rather than the structure
             // body; marking the entire body as the source of the error makes it
             // impossible to figure out which `derive` has a problem.
             Span::call_site().into(),
-            "Only structs with named fields are supported",
+            "Only structs are supported",
         )),
     }
 }