From b49de3dc5b526fc9f411c1d48cce5c923727bd16 Mon Sep 17 00:00:00 2001
From: Ding Xiang Fei <dingxiangfei2009@protonmail.ch>
Date: Wed, 31 Jul 2024 22:50:45 +0800
Subject: [PATCH] reject pointee without ?Sized

---
 .../src/deriving/smart_ptr.rs                 | 34 +++++++++----------
 .../ui/deriving/deriving-smart-pointer-neg.rs |  7 ++++
 .../deriving-smart-pointer-neg.stderr         |  8 ++++-
 3 files changed, 31 insertions(+), 18 deletions(-)

diff --git a/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs b/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
index 02555bd799c42..640c61b6ab00e 100644
--- a/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs
@@ -154,6 +154,23 @@ pub fn expand_deriving_smart_ptr(
     {
         let pointee = &mut impl_generics.params[pointee_param_idx];
         self_bounds = pointee.bounds.clone();
+        if !contains_maybe_sized_bound(&self_bounds)
+            && !contains_maybe_sized_bound_on_pointee(
+                &generics.where_clause.predicates,
+                pointee_ty_ident.name,
+            )
+        {
+            cx.dcx()
+                .struct_span_err(
+                    pointee_ty_ident.span,
+                    format!(
+                        "`SmartPointer` is meaningless because `{}` is not `?Sized`",
+                        pointee_ty_ident.name
+                    ),
+                )
+                .emit();
+            return;
+        }
         let arg = GenericArg::Type(s_ty.clone());
         let unsize = cx.path_all(span, true, path!(span, core::marker::Unsize), vec![arg]);
         pointee.bounds.push(cx.trait_bound(unsize, false));
@@ -218,23 +235,6 @@ pub fn expand_deriving_smart_ptr(
     //
     // We now insert `__S` with the missing bounds marked with (*) above.
     // We should also write the bounds from `#[pointee]` to `__S` as required by `Unsize<__S>`.
-    let sized = cx.path_global(span, path!(span, core::marker::Sized));
-    // For some reason, we are not allowed to write `?Sized` bound twice like `__S: ?Sized + ?Sized`.
-    if !contains_maybe_sized_bound(&self_bounds)
-        && !contains_maybe_sized_bound_on_pointee(
-            &generics.where_clause.predicates,
-            pointee_ty_ident.name,
-        )
-    {
-        self_bounds.push(GenericBound::Trait(
-            cx.poly_trait_ref(span, sized),
-            TraitBoundModifiers {
-                polarity: ast::BoundPolarity::Maybe(span),
-                constness: ast::BoundConstness::Never,
-                asyncness: ast::BoundAsyncness::Normal,
-            },
-        ));
-    }
     {
         let mut substitution =
             TypeSubstitution { from_name: pointee_ty_ident.name, to_ty: &s_ty, rewritten: false };
diff --git a/tests/ui/deriving/deriving-smart-pointer-neg.rs b/tests/ui/deriving/deriving-smart-pointer-neg.rs
index bfb4e86b39601..10189b28c5792 100644
--- a/tests/ui/deriving/deriving-smart-pointer-neg.rs
+++ b/tests/ui/deriving/deriving-smart-pointer-neg.rs
@@ -35,6 +35,13 @@ struct NotTransparent<'a, #[pointee] T: ?Sized> {
     ptr: &'a T,
 }
 
+#[derive(SmartPointer)]
+#[repr(transparent)]
+struct NoMaybeSized<'a, #[pointee] T> {
+    //~^ ERROR: SmartPointer` is meaningless because `T` is not `?Sized
+    ptr: &'a T,
+}
+
 // However, reordering attributes should work nevertheless.
 #[repr(transparent)]
 #[derive(SmartPointer)]
diff --git a/tests/ui/deriving/deriving-smart-pointer-neg.stderr b/tests/ui/deriving/deriving-smart-pointer-neg.stderr
index d994a6ee376b0..0fdd65583d68c 100644
--- a/tests/ui/deriving/deriving-smart-pointer-neg.stderr
+++ b/tests/ui/deriving/deriving-smart-pointer-neg.stderr
@@ -38,6 +38,12 @@ LL | #[derive(SmartPointer)]
    |
    = note: this error originates in the derive macro `SmartPointer` (in Nightly builds, run with -Z macro-backtrace for more info)
 
+error: `SmartPointer` is meaningless because `T` is not `?Sized`
+  --> $DIR/deriving-smart-pointer-neg.rs:40:36
+   |
+LL | struct NoMaybeSized<'a, #[pointee] T> {
+   |                                    ^
+
 error[E0392]: lifetime parameter `'a` is never used
   --> $DIR/deriving-smart-pointer-neg.rs:21:16
    |
@@ -70,6 +76,6 @@ LL | struct NoFieldUnit<'a, #[pointee] T: ?Sized>();
    |
    = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
 
-error: aborting due to 9 previous errors
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0392`.