diff options
Diffstat (limited to 'compiler/rustc_ast_lowering/src/lib.rs')
| -rw-r--r-- | compiler/rustc_ast_lowering/src/lib.rs | 142 |
1 files changed, 122 insertions, 20 deletions
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs index 1c96a375035..533ee9bff54 100644 --- a/compiler/rustc_ast_lowering/src/lib.rs +++ b/compiler/rustc_ast_lowering/src/lib.rs @@ -53,8 +53,8 @@ use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res}; use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId}; use rustc_hir::lints::DelayedLint; use rustc_hir::{ - self as hir, AngleBrackets, ConstArg, GenericArg, HirId, ItemLocalMap, LangItem, - LifetimeSource, LifetimeSyntax, ParamName, TraitCandidate, + self as hir, AngleBrackets, ConstArg, GenericArg, HirId, ItemLocalMap, LifetimeSource, + LifetimeSyntax, ParamName, TraitCandidate, }; use rustc_index::{Idx, IndexSlice, IndexVec}; use rustc_macros::extension; @@ -281,6 +281,24 @@ impl ResolverAstLowering { } } +/// How relaxed bounds `?Trait` should be treated. +/// +/// Relaxed bounds should only be allowed in places where we later +/// (namely during HIR ty lowering) perform *sized elaboration*. +#[derive(Clone, Copy, Debug)] +enum RelaxedBoundPolicy<'a> { + Allowed, + AllowedIfOnTyParam(NodeId, &'a [ast::GenericParam]), + Forbidden(RelaxedBoundForbiddenReason), +} + +#[derive(Clone, Copy, Debug)] +enum RelaxedBoundForbiddenReason { + TraitObjectTy, + SuperTrait, + LateBoundVarsInScope, +} + /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree, /// and if so, what meaning it has. #[derive(Debug, Copy, Clone, PartialEq, Eq)] @@ -1084,10 +1102,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { &*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err(guar))); hir::AssocItemConstraintKind::Equality { term: err_ty.into() } } else { - // Desugar `AssocTy: Bounds` into an assoc type binding where the - // later desugars into a trait predicate. - let bounds = self.lower_param_bounds(bounds, itctx); - + // FIXME(#135229): These should be forbidden! + let bounds = + self.lower_param_bounds(bounds, RelaxedBoundPolicy::Allowed, itctx); hir::AssocItemConstraintKind::Bound { bounds } } } @@ -1216,6 +1233,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { span: t.span, parens: ast::Parens::No, }, + RelaxedBoundPolicy::Forbidden(RelaxedBoundForbiddenReason::TraitObjectTy), itctx, ); let bounds = this.arena.alloc_from_iter([bound]); @@ -1271,7 +1289,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { parenthesized: hir::GenericArgsParentheses::No, span_ext: span, }); - let path = self.make_lang_item_qpath(LangItem::Pin, span, Some(args)); + let path = self.make_lang_item_qpath(hir::LangItem::Pin, span, Some(args)); hir::TyKind::Path(path) } TyKind::FnPtr(f) => { @@ -1332,7 +1350,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { // takes care of rejecting invalid modifier combinations and // const trait bounds in trait object types. GenericBound::Trait(ty) => { - let trait_ref = this.lower_poly_trait_ref(ty, itctx); + let trait_ref = this.lower_poly_trait_ref( + ty, + RelaxedBoundPolicy::Forbidden( + RelaxedBoundForbiddenReason::TraitObjectTy, + ), + itctx, + ); Some(trait_ref) } GenericBound::Outlives(lifetime) => { @@ -1387,9 +1411,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { } path } - ImplTraitContext::InBinding => { - hir::TyKind::TraitAscription(self.lower_param_bounds(bounds, itctx)) - } + ImplTraitContext::InBinding => hir::TyKind::TraitAscription( + self.lower_param_bounds(bounds, RelaxedBoundPolicy::Allowed, itctx), + ), ImplTraitContext::FeatureGated(position, feature) => { let guar = self .tcx @@ -1505,7 +1529,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None); self.lower_opaque_inner(opaque_ty_node_id, origin, opaque_ty_span, |this| { - this.lower_param_bounds(bounds, itctx) + this.lower_param_bounds(bounds, RelaxedBoundPolicy::Allowed, itctx) }) } @@ -1799,10 +1823,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { fn lower_param_bound( &mut self, tpb: &GenericBound, + rbp: RelaxedBoundPolicy<'_>, itctx: ImplTraitContext, ) -> hir::GenericBound<'hir> { match tpb { - GenericBound::Trait(p) => hir::GenericBound::Trait(self.lower_poly_trait_ref(p, itctx)), + GenericBound::Trait(p) => { + hir::GenericBound::Trait(self.lower_poly_trait_ref(p, rbp, itctx)) + } GenericBound::Outlives(lifetime) => hir::GenericBound::Outlives(self.lower_lifetime( lifetime, LifetimeSource::OutlivesBound, @@ -2017,19 +2044,91 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { #[instrument(level = "debug", skip(self))] fn lower_poly_trait_ref( &mut self, - p: &PolyTraitRef, + PolyTraitRef { bound_generic_params, modifiers, trait_ref, span, parens: _ }: &PolyTraitRef, + rbp: RelaxedBoundPolicy<'_>, itctx: ImplTraitContext, ) -> hir::PolyTraitRef<'hir> { let bound_generic_params = - self.lower_lifetime_binder(p.trait_ref.ref_id, &p.bound_generic_params); - let trait_ref = self.lower_trait_ref(p.modifiers, &p.trait_ref, itctx); - let modifiers = self.lower_trait_bound_modifiers(p.modifiers); + self.lower_lifetime_binder(trait_ref.ref_id, bound_generic_params); + let trait_ref = self.lower_trait_ref(*modifiers, trait_ref, itctx); + let modifiers = self.lower_trait_bound_modifiers(*modifiers); + + if let ast::BoundPolarity::Maybe(_) = modifiers.polarity { + self.validate_relaxed_bound(trait_ref, *span, rbp); + } + hir::PolyTraitRef { bound_generic_params, modifiers, trait_ref, - span: self.lower_span(p.span), + span: self.lower_span(*span), + } + } + + fn validate_relaxed_bound( + &self, + trait_ref: hir::TraitRef<'_>, + span: Span, + rbp: RelaxedBoundPolicy<'_>, + ) { + // Even though feature `more_maybe_bounds` bypasses the given policy and (currently) enables + // relaxed bounds in every conceivable position[^1], we don't want to advertise it to the user + // (via a feature gate) since it's super internal. Besides this, it'd be quite distracting. + // + // [^1]: Strictly speaking, this is incorrect (at the very least for `Sized`) because it's + // no longer fully consistent with default trait elaboration in HIR ty lowering. + + match rbp { + RelaxedBoundPolicy::Allowed => return, + RelaxedBoundPolicy::AllowedIfOnTyParam(id, params) => { + if let Some(res) = self.resolver.get_partial_res(id).and_then(|r| r.full_res()) + && let Res::Def(DefKind::TyParam, def_id) = res + && params.iter().any(|p| def_id == self.local_def_id(p.id).to_def_id()) + { + return; + } + if self.tcx.features().more_maybe_bounds() { + return; + } + } + RelaxedBoundPolicy::Forbidden(reason) => { + if self.tcx.features().more_maybe_bounds() { + return; + } + + match reason { + RelaxedBoundForbiddenReason::TraitObjectTy => { + self.dcx().span_err( + span, + "relaxed bounds are not permitted in trait object types", + ); + return; + } + RelaxedBoundForbiddenReason::SuperTrait => { + let mut diag = self.dcx().struct_span_err( + span, + "relaxed bounds are not permitted in supertrait bounds", + ); + if let Some(def_id) = trait_ref.trait_def_id() + && self.tcx.is_lang_item(def_id, hir::LangItem::Sized) + { + diag.note("traits are `?Sized` by default"); + } + diag.emit(); + return; + } + RelaxedBoundForbiddenReason::LateBoundVarsInScope => {} + }; + } } + + self.dcx() + .struct_span_err(span, "this relaxed bound is not permitted here") + .with_note( + "in this context, relaxed bounds are only allowed on \ + type parameters defined by the closest item", + ) + .emit(); } fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext) -> hir::MutTy<'hir> { @@ -2040,17 +2139,19 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { fn lower_param_bounds( &mut self, bounds: &[GenericBound], + rbp: RelaxedBoundPolicy<'_>, itctx: ImplTraitContext, ) -> hir::GenericBounds<'hir> { - self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx)) + self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, rbp, itctx)) } fn lower_param_bounds_mut( &mut self, bounds: &[GenericBound], + rbp: RelaxedBoundPolicy<'_>, itctx: ImplTraitContext, ) -> impl Iterator<Item = hir::GenericBound<'hir>> { - bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx)) + bounds.iter().map(move |bound| self.lower_param_bound(bound, rbp, itctx)) } #[instrument(level = "debug", skip(self), ret)] @@ -2084,6 +2185,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { bounds, /* colon_span */ None, span, + RelaxedBoundPolicy::Allowed, ImplTraitContext::Universal, hir::PredicateOrigin::ImplTrait, ); |