HIR ty lowering: Validate PointeeSized bounds

fmease · fmease · commit 04dad4ee8a1a · 2025-06-20T23:17:36.000+02:00
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
@@ -6,7 +6,7 @@ use rustc_errors::struct_span_code_err;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_hir::{AmbigArg, LangItem, PolyTraitRef};
+use rustc_hir::{AmbigArg, PolyTraitRef};
 use rustc_middle::bug;
 use rustc_middle::ty::{
     self as ty, IsSuggestable, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt,
@@ -124,13 +124,13 @@ fn collect_sizedness_bounds<'tcx>(
     self_ty_where_predicates: Option<(LocalDefId, &'tcx [hir::WherePredicate<'tcx>])>,
     span: Span,
 ) -> CollectedSizednessBounds {
-    let sized_did = tcx.require_lang_item(LangItem::Sized, span);
+    let sized_did = tcx.require_lang_item(hir::LangItem::Sized, span);
     let sized = collect_bounds(hir_bounds, self_ty_where_predicates, sized_did);
 
-    let meta_sized_did = tcx.require_lang_item(LangItem::MetaSized, span);
+    let meta_sized_did = tcx.require_lang_item(hir::LangItem::MetaSized, span);
     let meta_sized = collect_bounds(hir_bounds, self_ty_where_predicates, meta_sized_did);
 
-    let pointee_sized_did = tcx.require_lang_item(LangItem::PointeeSized, span);
+    let pointee_sized_did = tcx.require_lang_item(hir::LangItem::PointeeSized, span);
     let pointee_sized = collect_bounds(hir_bounds, self_ty_where_predicates, pointee_sized_did);
 
     CollectedSizednessBounds { sized, meta_sized, pointee_sized }
@@ -151,24 +151,6 @@ fn add_trait_bound<'tcx>(
 }
 
 impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
-    /// Skip `PointeeSized` bounds.
-    ///
-    /// `PointeeSized` is a "fake bound" insofar as anywhere a `PointeeSized` bound exists, there
-    /// is actually the absence of any bounds. This avoids limitations around non-global where
-    /// clauses being preferred over item bounds (where `PointeeSized` bounds would be
-    /// proven) - which can result in errors when a `PointeeSized` supertrait/bound/predicate is
-    /// added to some items.
-    pub(crate) fn should_skip_sizedness_bound<'hir>(
-        &self,
-        bound: &'hir hir::GenericBound<'tcx>,
-    ) -> bool {
-        bound
-            .trait_ref()
-            .and_then(|tr| tr.trait_def_id())
-            .map(|did| self.tcx().is_lang_item(did, LangItem::PointeeSized))
-            .unwrap_or(false)
-    }
-
     /// Adds sizedness bounds to a trait, trait alias, parameter, opaque type or associated type.
     ///
     /// - On parameters, opaque type and associated types, add default `Sized` bound if no explicit
@@ -188,8 +170,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     ) {
         let tcx = self.tcx();
 
-        let meta_sized_did = tcx.require_lang_item(LangItem::MetaSized, span);
-        let pointee_sized_did = tcx.require_lang_item(LangItem::PointeeSized, span);
+        let meta_sized_did = tcx.require_lang_item(hir::LangItem::MetaSized, span);
+        let pointee_sized_did = tcx.require_lang_item(hir::LangItem::PointeeSized, span);
 
         // If adding sizedness bounds to a trait, then there are some relevant early exits
         if let Some(trait_did) = trait_did {
@@ -230,7 +212,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             } else {
                 // If there are no explicit sizedness bounds on a parameter then add a default
                 // `Sized` bound.
-                let sized_did = tcx.require_lang_item(LangItem::Sized, span);
+                let sized_did = tcx.require_lang_item(hir::LangItem::Sized, span);
                 add_trait_bound(tcx, bounds, self_ty, sized_did, span);
             }
         }
@@ -465,10 +447,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         'tcx: 'hir,
     {
         for hir_bound in hir_bounds {
-            if self.should_skip_sizedness_bound(hir_bound) {
-                continue;
-            }
-
             // In order to avoid cycles, when we're lowering `SelfTraitThatDefines`,
             // we skip over any traits that don't define the given associated type.
             if let PredicateFilter::SelfTraitThatDefines(assoc_ident) = predicate_filter {
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -758,13 +758,37 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         bounds: &mut Vec<(ty::Clause<'tcx>, Span)>,
         predicate_filter: PredicateFilter,
     ) -> GenericArgCountResult {
+        let tcx = self.tcx();
+
         // We use the *resolved* bound vars later instead of the HIR ones since the former
         // also include the bound vars of the overarching predicate if applicable.
         let hir::PolyTraitRef { bound_generic_params: _, modifiers, ref trait_ref, span } =
             *poly_trait_ref;
         let hir::TraitBoundModifiers { constness, polarity } = modifiers;
 
         let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
+
+        let (polarity, bounds) = match polarity {
+            rustc_ast::BoundPolarity::Positive
+                if tcx.is_lang_item(trait_def_id, hir::LangItem::PointeeSized) =>
+            {
+                // Skip `PointeeSized` bounds.
+                //
+                // `PointeeSized` is a "fake bound" insofar as anywhere a `PointeeSized` bound exists, there
+                // is actually the absence of any bounds. This avoids limitations around non-global where
+                // clauses being preferred over item bounds (where `PointeeSized` bounds would be
+                // proven) - which can result in errors when a `PointeeSized` supertrait/bound/predicate is
+                // added to some items.
+                (ty::PredicatePolarity::Positive, &mut Vec::new())
+            }
+            rustc_ast::BoundPolarity::Positive => (ty::PredicatePolarity::Positive, bounds),
+            rustc_ast::BoundPolarity::Negative(_) => (ty::PredicatePolarity::Negative, bounds),
+            // FIXME(fmease): This is super hacky! `Option<Polarity>` is also sad.
+            rustc_ast::BoundPolarity::Maybe(_) => {
+                (ty::PredicatePolarity::Positive, &mut Vec::new())
+            }
+        };
+
         let trait_segment = trait_ref.path.segments.last().unwrap();
 
         let _ = self.prohibit_generic_args(
@@ -781,7 +805,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             Some(self_ty),
         );
 
-        let tcx = self.tcx();
         let bound_vars = tcx.late_bound_vars(trait_ref.hir_ref_id);
         debug!(?bound_vars);
 
@@ -792,27 +815,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         debug!(?poly_trait_ref);
 
-        let polarity = match polarity {
-            rustc_ast::BoundPolarity::Positive => ty::PredicatePolarity::Positive,
-            rustc_ast::BoundPolarity::Negative(_) => ty::PredicatePolarity::Negative,
-            rustc_ast::BoundPolarity::Maybe(_) => {
-                // Validate associated type at least. We may want to reject these
-                // outright in the future...
-                for constraint in trait_segment.args().constraints {
-                    let _ = self.lower_assoc_item_constraint(
-                        trait_ref.hir_ref_id,
-                        poly_trait_ref,
-                        constraint,
-                        &mut Default::default(),
-                        &mut Default::default(),
-                        constraint.span,
-                        predicate_filter,
-                    );
-                }
-                return arg_count;
-            }
-        };
-
         // We deal with const conditions later.
         match predicate_filter {
             PredicateFilter::All
@@ -915,7 +917,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             // Don't register any associated item constraints for negative bounds,
             // since we should have emitted an error for them earlier, and they
             // would not be well-formed!
-            if polarity != ty::PredicatePolarity::Positive {
+            if polarity == ty::PredicatePolarity::Negative {
                 self.dcx().span_delayed_bug(
                     constraint.span,
                     "negative trait bounds should not have assoc item constraints",
diff --git a/tests/ui/sized-hierarchy/pointee-validation.rs b/tests/ui/sized-hierarchy/pointee-validation.rs
@@ -0,0 +1,14 @@
+// Test that despite us dropping `PointeeSized` bounds during HIR ty lowering
+// we still validate it first.
+// issue: <https://github.com/rust-lang/rust/issues/142718>
+#![feature(sized_hierarchy)]
+
+use std::marker::PointeeSized;
+
+struct Test where (): const PointeeSized<(), Undefined = ()>;
+//~^ ERROR trait takes 0 generic arguments but 1 generic argument was supplied
+//~| ERROR associated type `Undefined` not found for `PointeeSized`
+//~| ERROR `const` can only be applied to `#[const_trait]` traits
+//~| ERROR const trait impls are experimental
+
+fn main() {}
diff --git a/tests/ui/sized-hierarchy/pointee-validation.stderr b/tests/ui/sized-hierarchy/pointee-validation.stderr
@@ -0,0 +1,37 @@
+error[E0658]: const trait impls are experimental
+  --> $DIR/pointee-validation.rs:8:23
+   |
+LL | struct Test where (): const PointeeSized<(), Undefined = ()>;
+   |                       ^^^^^
+   |
+   = note: see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information
+   = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0107]: trait takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/pointee-validation.rs:8:29
+   |
+LL | struct Test where (): const PointeeSized<(), Undefined = ()>;
+   |                             ^^^^^^^^^^^^-------------------- help: remove the unnecessary generics
+   |                             |
+   |                             expected 0 generic arguments
+
+error: `const` can only be applied to `#[const_trait]` traits
+  --> $DIR/pointee-validation.rs:8:23
+   |
+LL | struct Test where (): const PointeeSized<(), Undefined = ()>;
+   |                       ^^^^^ can't be applied to `PointeeSized`
+   |
+note: `PointeeSized` can't be used with `const` because it isn't annotated with `#[const_trait]`
+  --> $SRC_DIR/core/src/marker.rs:LL:COL
+
+error[E0220]: associated type `Undefined` not found for `PointeeSized`
+  --> $DIR/pointee-validation.rs:8:46
+   |
+LL | struct Test where (): const PointeeSized<(), Undefined = ()>;
+   |                                              ^^^^^^^^^ associated type `Undefined` not found
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0107, E0220, E0658.
+For more information about an error, try `rustc --explain E0107`.
