From ee9bea1ba937992a61e181ce1b451cb4ab1d2b2b Mon Sep 17 00:00:00 2001
From: Matty Weatherley <weatherleymatthew@gmail.com>
Date: Mon, 23 Dec 2024 21:53:43 -0500
Subject: [PATCH] Use `variadics_please` to implement `StableInterpolate` on
 tuples. (#16931)

# Objective

Now that `variadics_please` has a 1.1 release, we can re-implement the
original solution.

## Solution

Copy-paste the code from the [original
PR](https://github.com/bevyengine/bevy/pull/15931) branch :)
---
 crates/bevy_math/Cargo.toml           |  1 +
 crates/bevy_math/src/common_traits.rs | 95 +++------------------------
 2 files changed, 10 insertions(+), 86 deletions(-)

diff --git a/crates/bevy_math/Cargo.toml b/crates/bevy_math/Cargo.toml
index 2e92ea89a857e..f635d2a1c1533 100644
--- a/crates/bevy_math/Cargo.toml
+++ b/crates/bevy_math/Cargo.toml
@@ -28,6 +28,7 @@ smallvec = { version = "1.11" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", features = [
   "glam",
 ], optional = true }
+variadics_please = "1.1"
 
 [dev-dependencies]
 approx = "0.5"
diff --git a/crates/bevy_math/src/common_traits.rs b/crates/bevy_math/src/common_traits.rs
index 90bc77629e776..a9a8ef910a86e 100644
--- a/crates/bevy_math/src/common_traits.rs
+++ b/crates/bevy_math/src/common_traits.rs
@@ -5,6 +5,7 @@ use core::{
     fmt::Debug,
     ops::{Add, Div, Mul, Neg, Sub},
 };
+use variadics_please::all_tuples_enumerated;
 
 /// A type that supports the mathematical operations of a real vector space, irrespective of dimension.
 /// In particular, this means that the implementing type supports:
@@ -393,31 +394,9 @@ impl StableInterpolate for Dir3A {
     }
 }
 
-// If you're confused about how #[doc(fake_variadic)] works,
-// then the `all_tuples` macro is nicely documented (it can be found in the `bevy_utils` crate).
-// tl;dr: `#[doc(fake_variadic)]` goes on the impl of tuple length one.
-// the others have to be hidden using `#[doc(hidden)]`.
 macro_rules! impl_stable_interpolate_tuple {
-    (($T:ident, $n:tt)) => {
-        impl_stable_interpolate_tuple! {
-            @impl
-            #[cfg_attr(any(docsrs, docsrs_dep), doc(fake_variadic))]
-            #[cfg_attr(
-                any(docsrs, docsrs_dep),
-                doc = "This trait is implemented for tuples up to 11 items long."
-            )]
-            ($T, $n)
-        }
-    };
-    ($(($T:ident, $n:tt)),*) => {
-        impl_stable_interpolate_tuple! {
-            @impl
-            #[cfg_attr(any(docsrs, docsrs_dep), doc(hidden))]
-            $(($T, $n)),*
-        }
-    };
-    (@impl $(#[$($meta:meta)*])* $(($T:ident, $n:tt)),*) => {
-        $(#[$($meta)*])*
+    ($(#[$meta:meta])* $(($n:tt, $T:ident)),*) => {
+        $(#[$meta])*
         impl<$($T: StableInterpolate),*> StableInterpolate for ($($T,)*) {
             fn interpolate_stable(&self, other: &Self, t: f32) -> Self {
                 (
@@ -430,68 +409,12 @@ macro_rules! impl_stable_interpolate_tuple {
     };
 }
 
-// (See `macro_metavar_expr`, which might make this better.)
-// This currently implements `StableInterpolate` for tuples of up to 11 elements.
-impl_stable_interpolate_tuple!((T, 0));
-impl_stable_interpolate_tuple!((T0, 0), (T1, 1));
-impl_stable_interpolate_tuple!((T0, 0), (T1, 1), (T2, 2));
-impl_stable_interpolate_tuple!((T0, 0), (T1, 1), (T2, 2), (T3, 3));
-impl_stable_interpolate_tuple!((T0, 0), (T1, 1), (T2, 2), (T3, 3), (T4, 4));
-impl_stable_interpolate_tuple!((T0, 0), (T1, 1), (T2, 2), (T3, 3), (T4, 4), (T5, 5));
-impl_stable_interpolate_tuple!(
-    (T0, 0),
-    (T1, 1),
-    (T2, 2),
-    (T3, 3),
-    (T4, 4),
-    (T5, 5),
-    (T6, 6)
-);
-impl_stable_interpolate_tuple!(
-    (T0, 0),
-    (T1, 1),
-    (T2, 2),
-    (T3, 3),
-    (T4, 4),
-    (T5, 5),
-    (T6, 6),
-    (T7, 7)
-);
-impl_stable_interpolate_tuple!(
-    (T0, 0),
-    (T1, 1),
-    (T2, 2),
-    (T3, 3),
-    (T4, 4),
-    (T5, 5),
-    (T6, 6),
-    (T7, 7),
-    (T8, 8)
-);
-impl_stable_interpolate_tuple!(
-    (T0, 0),
-    (T1, 1),
-    (T2, 2),
-    (T3, 3),
-    (T4, 4),
-    (T5, 5),
-    (T6, 6),
-    (T7, 7),
-    (T8, 8),
-    (T9, 9)
-);
-impl_stable_interpolate_tuple!(
-    (T0, 0),
-    (T1, 1),
-    (T2, 2),
-    (T3, 3),
-    (T4, 4),
-    (T5, 5),
-    (T6, 6),
-    (T7, 7),
-    (T8, 8),
-    (T9, 9),
-    (T10, 10)
+all_tuples_enumerated!(
+    #[doc(fake_variadic)]
+    impl_stable_interpolate_tuple,
+    1,
+    11,
+    T
 );
 
 /// A type that has tangents.