More robustly reject relaxing non-default trait bounds

Author: fmease

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -204,7 +204,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             //        FIXME(more_maybe_bounds): We don't call this for trait object tys, supertrait
             //                                  bounds, trait alias bounds, assoc type bounds (ATB)!
             let bounds = collect_relaxed_bounds(hir_bounds, self_ty_where_predicates);
-            self.check_and_report_invalid_relaxed_bounds(bounds);
+            self.reject_duplicate_relaxed_bounds(bounds);
         }
 
         let collected = collect_sizedness_bounds(tcx, hir_bounds, self_ty_where_predicates, span);
@@ -308,6 +308,53 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         !self.tcx().has_attr(CRATE_DEF_ID, sym::rustc_no_implicit_bounds) && !collected.any()
     }
 
+    fn reject_duplicate_relaxed_bounds(&self, relaxed_bounds: SmallVec<[&PolyTraitRef<'_>; 1]>) {
+        let tcx = self.tcx();
+
+        let mut grouped_bounds = FxIndexMap::<_, Vec<_>>::default();
+
+        for bound in &relaxed_bounds {
+            if let Res::Def(DefKind::Trait, trait_def_id) = bound.trait_ref.path.res {
+                grouped_bounds.entry(trait_def_id).or_default().push(bound.span);
+            }
+        }
+
+        for (trait_def_id, spans) in grouped_bounds {
+            if spans.len() > 1 {
+                let name = tcx.item_name(trait_def_id);
+                self.dcx()
+                    .struct_span_err(spans, format!("duplicate relaxed `{name}` bounds"))
+                    .with_code(E0203)
+                    .emit();
+            }
+        }
+    }
+
+    pub(crate) fn require_bound_to_relax_default_trait(
+        &self,
+        trait_ref: hir::TraitRef<'_>,
+        span: Span,
+    ) {
+        let tcx = self.tcx();
+
+        if let Res::Def(DefKind::Trait, def_id) = trait_ref.path.res
+            && (tcx.is_lang_item(def_id, hir::LangItem::Sized) || tcx.is_default_trait(def_id))
+        {
+            return;
+        }
+
+        self.dcx().span_err(
+            span,
+            if tcx.sess.opts.unstable_opts.experimental_default_bounds
+                || tcx.features().more_maybe_bounds()
+            {
+                "bound modifier `?` can only be applied to default traits"
+            } else {
+                "bound modifier `?` can only be applied to `Sized`"
+            },
+        );
+    }
+
     /// Lower HIR bounds into `bounds` given the self type `param_ty` and the overarching late-bound vars if any.
     ///
     /// ### Examples

compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs

@@ -8,7 +8,7 @@ use rustc_errors::{
 };
 use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::def_id::DefId;
-use rustc_hir::{self as hir, HirId, PolyTraitRef};
+use rustc_hir::{self as hir, HirId};
 use rustc_middle::bug;
 use rustc_middle::ty::fast_reject::{TreatParams, simplify_type};
 use rustc_middle::ty::print::{PrintPolyTraitRefExt as _, PrintTraitRefExt as _};
@@ -35,52 +35,6 @@ use crate::fluent_generated as fluent;
 use crate::hir_ty_lowering::{AssocItemQSelf, HirTyLowerer};
 
 impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
-    /// Check for duplicate relaxed bounds and relaxed bounds of non-default traits.
-    pub(crate) fn check_and_report_invalid_relaxed_bounds(
-        &self,
-        relaxed_bounds: SmallVec<[&PolyTraitRef<'_>; 1]>,
-    ) {
-        let tcx = self.tcx();
-
-        let mut grouped_bounds = FxIndexMap::<_, Vec<_>>::default();
-
-        for bound in &relaxed_bounds {
-            if let Res::Def(DefKind::Trait, trait_def_id) = bound.trait_ref.path.res {
-                grouped_bounds.entry(trait_def_id).or_default().push(bound.span);
-            }
-        }
-
-        for (trait_def_id, spans) in grouped_bounds {
-            if spans.len() > 1 {
-                let name = tcx.item_name(trait_def_id);
-                self.dcx()
-                    .struct_span_err(spans, format!("duplicate relaxed `{name}` bounds"))
-                    .with_code(E0203)
-                    .emit();
-            }
-        }
-
-        let sized_def_id = tcx.require_lang_item(hir::LangItem::Sized, DUMMY_SP);
-
-        for bound in relaxed_bounds {
-            if let Res::Def(DefKind::Trait, def_id) = bound.trait_ref.path.res
-                && (def_id == sized_def_id || tcx.is_default_trait(def_id))
-            {
-                continue;
-            }
-            self.dcx().span_err(
-                bound.span,
-                if tcx.sess.opts.unstable_opts.experimental_default_bounds
-                    || tcx.features().more_maybe_bounds()
-                {
-                    "bound modifier `?` can only be applied to default traits like `Sized`"
-                } else {
-                    "bound modifier `?` can only be applied to `Sized`"
-                },
-            );
-        }
-    }
-
     /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
     /// the type parameter's name as a placeholder.
     pub(crate) fn report_missing_type_params(

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -767,7 +767,7 @@ impl<'tcx> dyn HirTyLowerer<'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 } =
+        let hir::PolyTraitRef { bound_generic_params: _, modifiers, trait_ref, span } =
             *poly_trait_ref;
         let hir::TraitBoundModifiers { constness, polarity } = modifiers;
 
@@ -791,6 +791,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             rustc_ast::BoundPolarity::Positive => (ty::PredicatePolarity::Positive, bounds),
             rustc_ast::BoundPolarity::Negative(_) => (ty::PredicatePolarity::Negative, bounds),
             rustc_ast::BoundPolarity::Maybe(_) => {
+                self.require_bound_to_relax_default_trait(trait_ref, span);
+
                 (ty::PredicatePolarity::Positive, &mut Vec::new())
             }
         };

compiler/rustc_middle/src/ty/context.rs

@@ -1782,9 +1782,7 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     pub fn is_default_trait(self, def_id: DefId) -> bool {
-        self.default_traits()
-            .iter()
-            .any(|&default_trait| self.lang_items().get(default_trait) == Some(def_id))
+        self.default_traits().iter().any(|&default_trait| self.is_lang_item(def_id, default_trait))
     }
 
     /// Returns a range of the start/end indices specified with the

tests/ui/feature-gates/feature-gate-more-maybe-bounds.rs

@@ -1,12 +1,17 @@
-#![feature(auto_traits)]
+#![feature(auto_traits, lang_items)]
 
-trait Trait1 {}
-auto trait Trait2 {}
-trait Trait3: ?Trait1 {} //~ ERROR relaxed bounds are not permitted in supertrait bounds
-trait Trait4 where Self: ?Trait1 {} //~ ERROR this relaxed bound is not permitted here
+#[lang = "default_trait1"] trait Trait1 {}
+#[lang = "default_trait2"] auto trait Trait2 {}
+
+trait Trait3: ?Trait1 {}
+//~^ ERROR relaxed bounds are not permitted in supertrait bounds
+//~| ERROR bound modifier `?` can only be applied to `Sized`
+//~| ERROR bound modifier `?` can only be applied to `Sized`
+//~| ERROR bound modifier `?` can only be applied to `Sized`
 
 fn foo(_: Box<dyn Trait1 + ?Trait2>) {}
 //~^  ERROR relaxed bounds are not permitted in trait object types
+//~| ERROR bound modifier `?` can only be applied to `Sized`
 fn bar<T: ?Trait1 + ?Trait2>(_: T) {}
 //~^ ERROR bound modifier `?` can only be applied to `Sized`
 //~| ERROR bound modifier `?` can only be applied to `Sized`

tests/ui/feature-gates/feature-gate-more-maybe-bounds.stderr

@@ -1,34 +1,54 @@
 error: relaxed bounds are not permitted in supertrait bounds
-  --> $DIR/feature-gate-more-maybe-bounds.rs:5:15
+  --> $DIR/feature-gate-more-maybe-bounds.rs:6:15
    |
 LL | trait Trait3: ?Trait1 {}
    |               ^^^^^^^
 
-error: this relaxed bound is not permitted here
-  --> $DIR/feature-gate-more-maybe-bounds.rs:6:26
+error: relaxed bounds are not permitted in trait object types
+  --> $DIR/feature-gate-more-maybe-bounds.rs:12:28
    |
-LL | trait Trait4 where Self: ?Trait1 {}
-   |                          ^^^^^^^
+LL | fn foo(_: Box<dyn Trait1 + ?Trait2>) {}
+   |                            ^^^^^^^
+
+error: bound modifier `?` can only be applied to `Sized`
+  --> $DIR/feature-gate-more-maybe-bounds.rs:6:15
    |
-   = note: in this context, relaxed bounds are only allowed on type parameters defined on the closest item
+LL | trait Trait3: ?Trait1 {}
+   |               ^^^^^^^
 
-error: relaxed bounds are not permitted in trait object types
-  --> $DIR/feature-gate-more-maybe-bounds.rs:8:28
+error: bound modifier `?` can only be applied to `Sized`
+  --> $DIR/feature-gate-more-maybe-bounds.rs:6:15
+   |
+LL | trait Trait3: ?Trait1 {}
+   |               ^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: bound modifier `?` can only be applied to `Sized`
+  --> $DIR/feature-gate-more-maybe-bounds.rs:6:15
+   |
+LL | trait Trait3: ?Trait1 {}
+   |               ^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: bound modifier `?` can only be applied to `Sized`
+  --> $DIR/feature-gate-more-maybe-bounds.rs:12:28
    |
 LL | fn foo(_: Box<dyn Trait1 + ?Trait2>) {}
    |                            ^^^^^^^
 
 error: bound modifier `?` can only be applied to `Sized`
-  --> $DIR/feature-gate-more-maybe-bounds.rs:10:11
+  --> $DIR/feature-gate-more-maybe-bounds.rs:15:11
    |
 LL | fn bar<T: ?Trait1 + ?Trait2>(_: T) {}
    |           ^^^^^^^
 
 error: bound modifier `?` can only be applied to `Sized`
-  --> $DIR/feature-gate-more-maybe-bounds.rs:10:21
+  --> $DIR/feature-gate-more-maybe-bounds.rs:15:21
    |
 LL | fn bar<T: ?Trait1 + ?Trait2>(_: T) {}
    |                     ^^^^^^^
 
-error: aborting due to 5 previous errors
+error: aborting due to 8 previous errors
 

tests/ui/sized-hierarchy/default-supertrait.rs

@@ -12,12 +12,17 @@ trait MetaSized_: MetaSized { }
 
 trait NegMetaSized: ?MetaSized { }
 //~^ ERROR relaxed bounds are not permitted in supertrait bounds
-
+//~| ERROR bound modifier `?` can only be applied to `Sized`
+//~| ERROR bound modifier `?` can only be applied to `Sized`
+//~| ERROR bound modifier `?` can only be applied to `Sized`
 
 trait PointeeSized_: PointeeSized { }
 
 trait NegPointeeSized: ?PointeeSized { }
 //~^ ERROR relaxed bounds are not permitted in supertrait bounds
+//~| ERROR bound modifier `?` can only be applied to `Sized`
+//~| ERROR bound modifier `?` can only be applied to `Sized`
+//~| ERROR bound modifier `?` can only be applied to `Sized`
 
 trait Bare {}