From d7814e72ebe3b4a293a5f91fa1648d2ef72639d3 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Mon, 6 May 2024 15:36:46 +1000
Subject: [PATCH] Document `Pu128`.

And move the `repr` line after the `derive` line, where it's harder to
overlook. (I overlooked it initially, and didn't understand how this
type worked.)
---
 compiler/rustc_data_structures/src/packed.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_data_structures/src/packed.rs b/compiler/rustc_data_structures/src/packed.rs
index b8d4b295dfa..0a392d91988 100644
--- a/compiler/rustc_data_structures/src/packed.rs
+++ b/compiler/rustc_data_structures/src/packed.rs
@@ -3,8 +3,10 @@ use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use std::cmp::Ordering;
 use std::fmt;
 
-#[repr(packed(8))]
+/// A packed 128-bit integer. Useful for reducing the size of structures in
+/// some cases.
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
+#[repr(packed(8))]
 pub struct Pu128(pub u128);
 
 impl Pu128 {