From 149c2ebabfdb971ee6faa8e3e5d087e23d71ff46 Mon Sep 17 00:00:00 2001
From: "Shane F. Carr" <shane@unicode.org>
Date: Wed, 6 Mar 2024 23:23:26 +0100
Subject: [PATCH 1/2] Require Sized generics in Yokeable derive

---
 utils/yoke/derive/src/lib.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/utils/yoke/derive/src/lib.rs b/utils/yoke/derive/src/lib.rs
index dd1ea90b8d7..57d8d38b206 100644
--- a/utils/yoke/derive/src/lib.rs
+++ b/utils/yoke/derive/src/lib.rs
@@ -53,7 +53,10 @@ fn yokeable_derive_impl(input: &DeriveInput) -> TokenStream2 {
     // the Yokeable impl becomes really unweildy to generate safely
     let static_bounds: Vec<WherePredicate> = typarams
         .iter()
-        .map(|ty| parse_quote!(#ty: 'static))
+        // Yokeable::Output is Sized, so we ask that our generics are Sized, too.
+        // This could be improved to only enforce Sized on the type parameter that
+        // makes this struct a DST (the last field in the struct).
+        .map(|ty| parse_quote!(#ty: 'static + Sized))
         .collect();
     let lts = input.generics.lifetimes().count();
     if lts == 0 {

From e0722be3eb48becbe5a43061f8ed6b18feb42b42 Mon Sep 17 00:00:00 2001
From: "Shane F. Carr" <shane@unicode.org>
Date: Thu, 7 Mar 2024 11:40:11 +0100
Subject: [PATCH 2/2] Review feedback

---
 utils/yoke/derive/examples/yoke_derive.rs | 24 ++++++++++++++++++++++-
 utils/yoke/derive/src/lib.rs              |  9 +++------
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/utils/yoke/derive/examples/yoke_derive.rs b/utils/yoke/derive/examples/yoke_derive.rs
index a011d5c2411..d65ada1bc92 100644
--- a/utils/yoke/derive/examples/yoke_derive.rs
+++ b/utils/yoke/derive/examples/yoke_derive.rs
@@ -4,7 +4,7 @@
 
 #![allow(unused)]
 
-use std::borrow::Cow;
+use std::{borrow::Cow, marker::PhantomData};
 use yoke::{Yoke, Yokeable};
 use zerovec::{maps::ZeroMapKV, ule::AsULE, VarZeroVec, ZeroMap, ZeroVec};
 
@@ -67,6 +67,25 @@ pub struct ZeroMapGenericExample<'a, T: for<'b> ZeroMapKV<'b> + ?Sized> {
     map: ZeroMap<'a, str, T>,
 }
 
+#[derive(Yokeable)]
+pub struct MaybeSizedWrap<T, Q: ?Sized, U: ?Sized> {
+    x: T,
+    y: Option<T>,
+    ignored: PhantomData<U>,
+    q: Q,
+}
+
+// TODO(#4119): Make this example compile
+/*
+#[derive(Yokeable)]
+pub struct MaybeSizedWrapWithLifetime<'a, T, Q: ?Sized, U: ?Sized> {
+    x: T,
+    y: Option<T>,
+    ignored: &'a U,
+    q: Q,
+}
+*/
+
 pub struct AssertYokeable {
     string: Yoke<StringExample, Box<[u8]>>,
     int: Yoke<IntExample, Box<[u8]>>,
@@ -81,6 +100,9 @@ pub struct AssertYokeable {
     map: Yoke<ZeroMapExample<'static>, Box<[u8]>>,
     map_gen1: Yoke<ZeroMapGenericExample<'static, u32>, Box<[u8]>>,
     map_gen2: Yoke<ZeroMapGenericExample<'static, str>, Box<[u8]>>,
+    maybe_sized_wrap: Yoke<MaybeSizedWrap<usize, usize, str>, Box<[u8]>>,
+    // TODO(#4119): Make this example compile
+    // maybe_sized_wrap_with_lt: Yoke<MaybeSizedWrapWithLifetime<'static, usize, usize, str>, Box<[u8]>>,
 }
 
 fn main() {}
diff --git a/utils/yoke/derive/src/lib.rs b/utils/yoke/derive/src/lib.rs
index 57d8d38b206..4d3d8843a4f 100644
--- a/utils/yoke/derive/src/lib.rs
+++ b/utils/yoke/derive/src/lib.rs
@@ -53,17 +53,14 @@ fn yokeable_derive_impl(input: &DeriveInput) -> TokenStream2 {
     // the Yokeable impl becomes really unweildy to generate safely
     let static_bounds: Vec<WherePredicate> = typarams
         .iter()
-        // Yokeable::Output is Sized, so we ask that our generics are Sized, too.
-        // This could be improved to only enforce Sized on the type parameter that
-        // makes this struct a DST (the last field in the struct).
-        .map(|ty| parse_quote!(#ty: 'static + Sized))
+        .map(|ty| parse_quote!(#ty: 'static))
         .collect();
     let lts = input.generics.lifetimes().count();
     if lts == 0 {
         let name = &input.ident;
         quote! {
             // This is safe because there are no lifetime parameters.
-            unsafe impl<'a, #(#tybounds),*> yoke::Yokeable<'a> for #name<#(#typarams),*> where #(#static_bounds),* {
+            unsafe impl<'a, #(#tybounds),*> yoke::Yokeable<'a> for #name<#(#typarams),*> where #(#static_bounds,)* Self: Sized {
                 type Output = Self;
                 #[inline]
                 fn transform(&self) -> &Self::Output {
@@ -223,7 +220,7 @@ fn yokeable_derive_impl(input: &DeriveInput) -> TokenStream2 {
             //
             // This custom derive can be improved to handle this case when
             // necessary
-            unsafe impl<'a, #(#tybounds),*> yoke::Yokeable<'a> for #name<'static, #(#typarams),*> where #(#static_bounds),* {
+            unsafe impl<'a, #(#tybounds),*> yoke::Yokeable<'a> for #name<'static, #(#typarams),*> where #(#static_bounds,)* {
                 type Output = #name<'a, #(#typarams),*>;
                 #[inline]
                 fn transform(&'a self) -> &'a Self::Output {