Implement negative bounds

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -665,6 +665,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         span: Span,
         binding_span: Option<Span>,
         constness: ty::BoundConstness,
+        polarity: ty::ImplPolarity,
         bounds: &mut Bounds<'tcx>,
         speculative: bool,
         trait_ref_span: Span,
@@ -696,10 +697,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             ty::Binder::bind_with_vars(tcx.mk_trait_ref(trait_def_id, substs), bound_vars);
 
         debug!(?poly_trait_ref, ?assoc_bindings);
-        bounds.push_trait_bound(tcx, poly_trait_ref, span, constness);
+        bounds.push_trait_bound(tcx, poly_trait_ref, span, constness, polarity);
 
         let mut dup_bindings = FxHashMap::default();
         for binding in &assoc_bindings {
+            // TODO: negative polarity can't have associated type bindings!
+
             // Specify type to assert that error was already reported in `Err` case.
             let _: Result<_, ErrorGuaranteed> = self.add_predicates_for_ast_type_binding(
                 hir_id,
@@ -711,6 +714,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 binding_span.unwrap_or(binding.span),
                 constness,
                 only_self_bounds,
+                polarity,
             );
             // Okay to ignore `Err` because of `ErrorGuaranteed` (see above).
         }
@@ -743,6 +747,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         trait_ref: &hir::TraitRef<'_>,
         span: Span,
         constness: ty::BoundConstness,
+        polarity: ty::ImplPolarity,
         self_ty: Ty<'tcx>,
         bounds: &mut Bounds<'tcx>,
         speculative: bool,
@@ -764,6 +769,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             span,
             binding_span,
             constness,
+            polarity,
             bounds,
             speculative,
             trait_ref_span,
@@ -799,6 +805,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             span,
             binding_span,
             constness,
+            ty::ImplPolarity::Positive,
             bounds,
             speculative,
             trait_ref_span,
@@ -961,16 +968,23 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         for ast_bound in ast_bounds {
             match ast_bound {
                 hir::GenericBound::Trait(poly_trait_ref, modifier) => {
-                    let constness = match modifier {
-                        hir::TraitBoundModifier::MaybeConst => ty::BoundConstness::ConstIfConst,
-                        hir::TraitBoundModifier::None => ty::BoundConstness::NotConst,
+                    let (constness, polarity) = match modifier {
+                        hir::TraitBoundModifier::MaybeConst => {
+                            (ty::BoundConstness::ConstIfConst, ty::ImplPolarity::Positive)
+                        }
+                        hir::TraitBoundModifier::None => {
+                            (ty::BoundConstness::NotConst, ty::ImplPolarity::Positive)
+                        }
+                        hir::TraitBoundModifier::Negative => {
+                            (ty::BoundConstness::NotConst, ty::ImplPolarity::Negative)
+                        }
                         hir::TraitBoundModifier::Maybe => continue,
                     };
-
                     let _ = self.instantiate_poly_trait_ref(
                         &poly_trait_ref.trait_ref,
                         poly_trait_ref.span,
                         constness,
+                        polarity,
                         param_ty,
                         bounds,
                         false,
@@ -1088,6 +1102,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         path_span: Span,
         constness: ty::BoundConstness,
         only_self_bounds: OnlySelfBounds,
+        polarity: ty::ImplPolarity,
     ) -> Result<(), ErrorGuaranteed> {
         // Given something like `U: SomeTrait<T = X>`, we want to produce a
         // predicate like `<U as SomeTrait>::T = X`. This is somewhat
@@ -1438,6 +1453,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 &trait_bound.trait_ref,
                 trait_bound.span,
                 ty::BoundConstness::NotConst,
+                ty::ImplPolarity::Positive,
                 dummy_self,
                 &mut bounds,
                 false,

compiler/rustc_hir_analysis/src/bounds.rs

@@ -42,8 +42,14 @@ impl<'tcx> Bounds<'tcx> {
         trait_ref: ty::PolyTraitRef<'tcx>,
         span: Span,
         constness: ty::BoundConstness,
+        polarity: ty::ImplPolarity,
     ) {
-        self.predicates.push((trait_ref.with_constness(constness).to_predicate(tcx), span));
+        self.predicates.push((
+            trait_ref
+                .map_bound(|trait_ref| ty::TraitPredicate { trait_ref, constness, polarity })
+                .to_predicate(tcx),
+            span,
+        ));
     }
 
     pub fn push_projection_bound(

compiler/rustc_hir_analysis/src/lib.rs

@@ -528,6 +528,7 @@ pub fn hir_trait_to_predicates<'tcx>(
         hir_trait,
         DUMMY_SP,
         ty::BoundConstness::NotConst,
+        ty::ImplPolarity::Positive,
         self_ty,
         &mut bounds,
         true,