HIR ty lowering: Validate `PointeeSized` bounds

5 files changed, 34 insertions, 72 deletions

diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index 3283ce95ee0..5e75a42e824 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -312,13 +312,6 @@ pub(crate) struct TraitObjectDeclaredWithNoTraits {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_pointee_sized_trait_object)]
-pub(crate) struct PointeeSizedTraitObject {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(hir_analysis_ambiguous_lifetime_bound, code = E0227)]
 pub(crate) struct AmbiguousLifetimeBound {
     #[primary_span]
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
index dbd22fabab8..d7a827c649d 100644
--- 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::{CRATE_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
@@ -193,8 +175,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             return;
         }
 
-        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 {
@@ -244,7 +226,7 @@ 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);
             }
         }
@@ -476,10 +458,6 @@ 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/dyn_compatibility.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
index 813353c12aa..76bb59e3f09 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
@@ -2,7 +2,6 @@ use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_errors::codes::*;
 use rustc_errors::struct_span_code_err;
 use rustc_hir as hir;
-use rustc_hir::LangItem;
 use rustc_hir::def::{DefKind, Res};
 use rustc_lint_defs::builtin::UNUSED_ASSOCIATED_TYPE_BOUNDS;
 use rustc_middle::ty::elaborate::ClauseWithSupertraitSpan;
@@ -70,13 +69,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             let guar = self.report_trait_object_addition_traits(&regular_traits);
             return Ty::new_error(tcx, guar);
         }
-        // We don't support `PointeeSized` principals
-        let pointee_sized_did = tcx.require_lang_item(LangItem::PointeeSized, span);
-        if regular_traits.iter().any(|(pred, _)| pred.def_id() == pointee_sized_did) {
-            let guar = self.report_pointee_sized_trait_object(span);
-            return Ty::new_error(tcx, guar);
-        }
-
         // Don't create a dyn trait if we have errors in the principal.
         if let Err(guar) = regular_traits.error_reported() {
             return Ty::new_error(tcx, guar);
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
index 3db78db931a..287a5532f01 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
@@ -29,7 +29,7 @@ use tracing::debug;
 use super::InherentAssocCandidate;
 use crate::errors::{
     self, AssocItemConstraintsNotAllowedHere, ManualImplementation, MissingTypeParams,
-    ParenthesizedFnTraitExpansion, PointeeSizedTraitObject, TraitObjectDeclaredWithNoTraits,
+    ParenthesizedFnTraitExpansion, TraitObjectDeclaredWithNoTraits,
 };
 use crate::fluent_generated as fluent;
 use crate::hir_ty_lowering::{AssocItemQSelf, HirTyLowerer};
@@ -1405,10 +1405,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         self.dcx().emit_err(TraitObjectDeclaredWithNoTraits { span, trait_alias_span })
     }
-
-    pub(super) fn report_pointee_sized_trait_object(&self, span: Span) -> ErrorGuaranteed {
-        self.dcx().emit_err(PointeeSizedTraitObject { span })
-    }
 }
 
 /// Emit an error for the given associated item constraint.
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 5521f97059b..78794cd8eb6 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -755,6 +755,8 @@ 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 } =
@@ -762,6 +764,29 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let hir::TraitBoundModifiers { constness, polarity } = modifiers;
 
         let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
+
+        // Relaxed bounds `?Trait` and `PointeeSized` bounds aren't represented in the `middle::ty` IR
+        // as they denote the *absence* of a default bound. However, we can't bail out early here since
+        // we still need to perform several validation steps (see below). Instead, simply "pour" all
+        // resulting bounds "down the drain", i.e., into a new `Vec` that just gets dropped at the end.
+        let (polarity, bounds) = match polarity {
+            rustc_ast::BoundPolarity::Positive
+                if tcx.is_lang_item(trait_def_id, hir::LangItem::PointeeSized) =>
+            {
+                // To elaborate on the comment directly above, regarding `PointeeSized` specifically,
+                // we don't "reify" such bounds to avoid trait system limitations -- namely,
+                // 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),
+            rustc_ast::BoundPolarity::Maybe(_) => {
+                (ty::PredicatePolarity::Positive, &mut Vec::new())
+            }
+        };
+
         let trait_segment = trait_ref.path.segments.last().unwrap();
 
         let _ = self.prohibit_generic_args(
@@ -778,7 +803,6 @@ 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);
 
@@ -789,27 +813,6 @@ 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
@@ -912,7 +915,7 @@ 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",