reject pointee without ?Sized

rust-lang · Jul 31, 2024 · b49de3d · b49de3d
1 parent e7f89a7
commit b49de3d
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Showing 3 changed files with 31 additions and 18 deletions.
diff --git 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
@@ -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
@@ -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`.