Documentation for variadics (#15387)

# Objective

Relevant: #15208

## Solution

I went ahead and added the variadics documentation in all applicable
locations.

## Testing

- I built the documentation and inspected it to see whether the feature
is there.

crates/bevy_app/src/lib.rs

@@ -1,4 +1,6 @@
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+// `rustdoc_internals` is needed for `#[doc(fake_variadics)]`
+#![allow(internal_features)]
+#![cfg_attr(any(docsrs, docsrs_dep), feature(doc_auto_cfg, rustdoc_internals))]
 #![forbid(unsafe_code)]
 #![doc(
     html_logo_url = "https://bevyengine.org/assets/icon.png",

crates/bevy_app/src/plugin.rs

@@ -162,7 +162,8 @@ mod sealed {
     }
 
     macro_rules! impl_plugins_tuples {
-        ($(($param: ident, $plugins: ident)),*) => {
+        ($(#[$meta:meta])* $(($param: ident, $plugins: ident)),*) => {
+            $(#[$meta])*
             impl<$($param, $plugins),*> Plugins<(PluginsTupleMarker, $($param,)*)> for ($($plugins,)*)
             where
                 $($plugins: Plugins<$param>),*
@@ -179,5 +180,12 @@ mod sealed {
         }
     }
 
-    all_tuples!(impl_plugins_tuples, 0, 15, P, S);
+    all_tuples!(
+        #[doc(fake_variadic)]
+        impl_plugins_tuples,
+        0,
+        15,
+        P,
+        S
+    );
 }

crates/bevy_ecs/src/bundle.rs

@@ -287,6 +287,7 @@ macro_rules! tuple_impl {
             }
         }
 
+        $(#[$meta])*
         impl<$($name: Bundle),*> DynamicBundle for ($($name,)*) {
             #[allow(unused_variables, unused_mut)]
             #[inline(always)]

crates/bevy_ecs/src/query/fetch.rs

@@ -2014,7 +2014,6 @@ pub struct AnyOf<T>(PhantomData<T>);
 
 macro_rules! impl_tuple_query_data {
     ($(#[$meta:meta])* $(($name: ident, $state: ident)),*) => {
-
         #[allow(non_snake_case)]
         #[allow(clippy::unused_unit)]
         $(#[$meta])*
@@ -2023,6 +2022,7 @@ macro_rules! impl_tuple_query_data {
             type ReadOnly = ($($name::ReadOnly,)*);
         }
 
+        $(#[$meta])*
         /// SAFETY: each item in the tuple is read only
         unsafe impl<$($name: ReadOnlyQueryData),*> ReadOnlyQueryData for ($($name,)*) {}
 

crates/bevy_reflect/src/lib.rs

@@ -520,7 +520,7 @@
 //! [the language feature for dyn upcasting coercion]: https://github.com/rust-lang/rust/issues/65991
 //! [derive macro]: derive@crate::Reflect
 //! [`'static` lifetime]: https://doc.rust-lang.org/rust-by-example/scope/lifetime/static_lifetime.html#trait-bound
-//! [`Function`]: func::Function
+//! [`Function`]: crate::func::Function
 //! [derive macro documentation]: derive@crate::Reflect
 //! [deriving `Reflect`]: derive@crate::Reflect
 //! [type data]: TypeData

crates/bevy_reflect/src/tuple.rs

@@ -676,6 +676,7 @@ impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I, 9: J,
 
 macro_rules! impl_type_path_tuple {
     ($(#[$meta:meta])*) => {
+        $(#[$meta])*
         impl TypePath for () {
             fn type_path() -> &'static str {
                 "()"
@@ -737,29 +738,50 @@ all_tuples!(
 #[cfg(feature = "functions")]
 const _: () = {
     macro_rules! impl_get_ownership_tuple {
-    ($($name: ident),*) => {
+    ($(#[$meta:meta])* $($name: ident),*) => {
+        $(#[$meta])*
         $crate::func::args::impl_get_ownership!(($($name,)*); <$($name),*>);
     };
 }
 
-    all_tuples!(impl_get_ownership_tuple, 0, 12, P);
+    all_tuples!(
+        #[doc(fake_variadic)]
+        impl_get_ownership_tuple,
+        0,
+        12,
+        P
+    );
 
     macro_rules! impl_from_arg_tuple {
-    ($($name: ident),*) => {
+    ($(#[$meta:meta])* $($name: ident),*) => {
+        $(#[$meta])*
         $crate::func::args::impl_from_arg!(($($name,)*); <$($name: FromReflect + MaybeTyped + TypePath + GetTypeRegistration),*>);
     };
 }
 
-    all_tuples!(impl_from_arg_tuple, 0, 12, P);
+    all_tuples!(
+        #[doc(fake_variadic)]
+        impl_from_arg_tuple,
+        0,
+        12,
+        P
+    );
 
     macro_rules! impl_into_return_tuple {
-    ($($name: ident),+) => {
+    ($(#[$meta:meta])* $($name: ident),+) => {
+        $(#[$meta])*
         $crate::func::impl_into_return!(($($name,)*); <$($name: FromReflect + MaybeTyped + TypePath + GetTypeRegistration),*>);
     };
 }
 
     // The unit type (i.e. `()`) is special-cased, so we skip implementing it here.
-    all_tuples!(impl_into_return_tuple, 1, 12, P);
+    all_tuples!(
+        #[doc(fake_variadic)]
+        impl_into_return_tuple,
+        1,
+        12,
+        P
+    );
 };
 
 #[cfg(test)]