diff options
Diffstat (limited to 'compiler/rustc_hir_analysis/src/astconv/bounds.rs')
| -rw-r--r-- | compiler/rustc_hir_analysis/src/astconv/bounds.rs | 575 |
1 files changed, 575 insertions, 0 deletions
diff --git a/compiler/rustc_hir_analysis/src/astconv/bounds.rs b/compiler/rustc_hir_analysis/src/astconv/bounds.rs new file mode 100644 index 000000000..b13de7701 --- /dev/null +++ b/compiler/rustc_hir_analysis/src/astconv/bounds.rs @@ -0,0 +1,575 @@ +use rustc_data_structures::fx::FxHashMap; +use rustc_errors::struct_span_err; +use rustc_hir as hir; +use rustc_hir::def::{DefKind, Res}; +use rustc_hir::def_id::{DefId, LocalDefId}; +use rustc_lint_defs::Applicability; +use rustc_middle::ty::{self as ty, Ty, TypeVisitableExt}; +use rustc_span::symbol::Ident; +use rustc_span::{ErrorGuaranteed, Span}; +use rustc_trait_selection::traits; + +use crate::astconv::{ + AstConv, ConvertedBinding, ConvertedBindingKind, OnlySelfBounds, PredicateFilter, +}; +use crate::bounds::Bounds; +use crate::errors::{MultipleRelaxedDefaultBounds, ValueOfAssociatedStructAlreadySpecified}; + +impl<'tcx> dyn AstConv<'tcx> + '_ { + /// Sets `implicitly_sized` to true on `Bounds` if necessary + pub(crate) fn add_implicitly_sized( + &self, + bounds: &mut Bounds<'tcx>, + self_ty: Ty<'tcx>, + ast_bounds: &'tcx [hir::GenericBound<'tcx>], + self_ty_where_predicates: Option<(LocalDefId, &'tcx [hir::WherePredicate<'tcx>])>, + span: Span, + ) { + let tcx = self.tcx(); + + // Try to find an unbound in bounds. + let mut unbound = None; + let mut search_bounds = |ast_bounds: &'tcx [hir::GenericBound<'tcx>]| { + for ab in ast_bounds { + if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab { + if unbound.is_none() { + unbound = Some(&ptr.trait_ref); + } else { + tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span }); + } + } + } + }; + search_bounds(ast_bounds); + if let Some((self_ty, where_clause)) = self_ty_where_predicates { + for clause in where_clause { + if let hir::WherePredicate::BoundPredicate(pred) = clause { + if pred.is_param_bound(self_ty.to_def_id()) { + search_bounds(pred.bounds); + } + } + } + } + + let sized_def_id = tcx.lang_items().sized_trait(); + match (&sized_def_id, unbound) { + (Some(sized_def_id), Some(tpb)) + if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) => + { + // There was in fact a `?Sized` bound, return without doing anything + return; + } + (_, Some(_)) => { + // There was a `?Trait` bound, but it was not `?Sized`; warn. + tcx.sess.span_warn( + span, + "default bound relaxed for a type parameter, but \ + this does nothing because the given bound is not \ + a default; only `?Sized` is supported", + ); + // Otherwise, add implicitly sized if `Sized` is available. + } + _ => { + // There was no `?Sized` bound; add implicitly sized if `Sized` is available. + } + } + if sized_def_id.is_none() { + // No lang item for `Sized`, so we can't add it as a bound. + return; + } + bounds.push_sized(tcx, self_ty, span); + } + + /// This helper takes a *converted* parameter type (`param_ty`) + /// and an *unconverted* list of bounds: + /// + /// ```text + /// fn foo<T: Debug> + /// ^ ^^^^^ `ast_bounds` parameter, in HIR form + /// | + /// `param_ty`, in ty form + /// ``` + /// + /// It adds these `ast_bounds` into the `bounds` structure. + /// + /// **A note on binders:** there is an implied binder around + /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref` + /// for more details. + #[instrument(level = "debug", skip(self, ast_bounds, bounds))] + pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>( + &self, + param_ty: Ty<'tcx>, + ast_bounds: I, + bounds: &mut Bounds<'tcx>, + bound_vars: &'tcx ty::List<ty::BoundVariableKind>, + only_self_bounds: OnlySelfBounds, + ) { + for ast_bound in ast_bounds { + match ast_bound { + hir::GenericBound::Trait(poly_trait_ref, modifier) => { + 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, + only_self_bounds, + ); + } + &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => { + self.instantiate_lang_item_trait_ref( + lang_item, + span, + hir_id, + args, + param_ty, + bounds, + only_self_bounds, + ); + } + hir::GenericBound::Outlives(lifetime) => { + let region = self.ast_region_to_region(lifetime, None); + bounds.push_region_bound( + self.tcx(), + ty::Binder::bind_with_vars( + ty::OutlivesPredicate(param_ty, region), + bound_vars, + ), + lifetime.ident.span, + ); + } + } + } + } + + /// Translates a list of bounds from the HIR into the `Bounds` data structure. + /// The self-type for the bounds is given by `param_ty`. + /// + /// Example: + /// + /// ```ignore (illustrative) + /// fn foo<T: Bar + Baz>() { } + /// // ^ ^^^^^^^^^ ast_bounds + /// // param_ty + /// ``` + /// + /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be + /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the + /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`. + /// + /// `span` should be the declaration size of the parameter. + pub(crate) fn compute_bounds( + &self, + param_ty: Ty<'tcx>, + ast_bounds: &[hir::GenericBound<'_>], + filter: PredicateFilter, + ) -> Bounds<'tcx> { + let mut bounds = Bounds::default(); + + let only_self_bounds = match filter { + PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => { + OnlySelfBounds(false) + } + PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => OnlySelfBounds(true), + }; + + self.add_bounds( + param_ty, + ast_bounds.iter().filter(|bound| { + match filter { + PredicateFilter::All + | PredicateFilter::SelfOnly + | PredicateFilter::SelfAndAssociatedTypeBounds => true, + PredicateFilter::SelfThatDefines(assoc_name) => { + if let Some(trait_ref) = bound.trait_ref() + && let Some(trait_did) = trait_ref.trait_def_id() + && self.tcx().trait_may_define_assoc_item(trait_did, assoc_name) + { + true + } else { + false + } + } + } + }), + &mut bounds, + ty::List::empty(), + only_self_bounds, + ); + debug!(?bounds); + + bounds + } + + /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates + /// onto `bounds`. + /// + /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the + /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside* + /// the binder (e.g., `&'a u32`) and hence may reference bound regions. + #[instrument(level = "debug", skip(self, bounds, speculative, dup_bindings, path_span))] + pub(super) fn add_predicates_for_ast_type_binding( + &self, + hir_ref_id: hir::HirId, + trait_ref: ty::PolyTraitRef<'tcx>, + binding: &ConvertedBinding<'_, 'tcx>, + bounds: &mut Bounds<'tcx>, + speculative: bool, + dup_bindings: &mut FxHashMap<DefId, Span>, + 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 + // subtle in the event that `T` is defined in a supertrait of + // `SomeTrait`, because in that case we need to upcast. + // + // That is, consider this case: + // + // ``` + // trait SubTrait: SuperTrait<i32> { } + // trait SuperTrait<A> { type T; } + // + // ... B: SubTrait<T = foo> ... + // ``` + // + // We want to produce `<B as SuperTrait<i32>>::T == foo`. + + let tcx = self.tcx(); + + let return_type_notation = + binding.gen_args.parenthesized == hir::GenericArgsParentheses::ReturnTypeNotation; + + let candidate = if return_type_notation { + if self.trait_defines_associated_item_named( + trait_ref.def_id(), + ty::AssocKind::Fn, + binding.item_name, + ) { + trait_ref + } else { + self.one_bound_for_assoc_method( + traits::supertraits(tcx, trait_ref), + trait_ref.print_only_trait_path(), + binding.item_name, + path_span, + )? + } + } else if self.trait_defines_associated_item_named( + trait_ref.def_id(), + ty::AssocKind::Type, + binding.item_name, + ) { + // Simple case: X is defined in the current trait. + trait_ref + } else { + // Otherwise, we have to walk through the supertraits to find + // those that do. + self.one_bound_for_assoc_type( + || traits::supertraits(tcx, trait_ref), + trait_ref.skip_binder().print_only_trait_name(), + binding.item_name, + path_span, + match binding.kind { + ConvertedBindingKind::Equality(term) => Some(term), + _ => None, + }, + )? + }; + + let (assoc_ident, def_scope) = + tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id); + + // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead + // of calling `filter_by_name_and_kind`. + let find_item_of_kind = |kind| { + tcx.associated_items(candidate.def_id()) + .filter_by_name_unhygienic(assoc_ident.name) + .find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident) + }; + let assoc_item = if return_type_notation { + find_item_of_kind(ty::AssocKind::Fn) + } else { + find_item_of_kind(ty::AssocKind::Type) + .or_else(|| find_item_of_kind(ty::AssocKind::Const)) + } + .expect("missing associated type"); + + if !assoc_item.visibility(tcx).is_accessible_from(def_scope, tcx) { + tcx.sess + .struct_span_err( + binding.span, + format!("{} `{}` is private", assoc_item.kind, binding.item_name), + ) + .span_label(binding.span, format!("private {}", assoc_item.kind)) + .emit(); + } + tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None); + + if !speculative { + dup_bindings + .entry(assoc_item.def_id) + .and_modify(|prev_span| { + tcx.sess.emit_err(ValueOfAssociatedStructAlreadySpecified { + span: binding.span, + prev_span: *prev_span, + item_name: binding.item_name, + def_path: tcx.def_path_str(assoc_item.container_id(tcx)), + }); + }) + .or_insert(binding.span); + } + + let projection_ty = if return_type_notation { + let mut emitted_bad_param_err = false; + // If we have an method return type bound, then we need to substitute + // the method's early bound params with suitable late-bound params. + let mut num_bound_vars = candidate.bound_vars().len(); + let substs = + candidate.skip_binder().substs.extend_to(tcx, assoc_item.def_id, |param, _| { + let subst = match param.kind { + ty::GenericParamDefKind::Lifetime => ty::Region::new_late_bound( + tcx, + ty::INNERMOST, + ty::BoundRegion { + var: ty::BoundVar::from_usize(num_bound_vars), + kind: ty::BoundRegionKind::BrNamed(param.def_id, param.name), + }, + ) + .into(), + ty::GenericParamDefKind::Type { .. } => { + if !emitted_bad_param_err { + tcx.sess.emit_err( + crate::errors::ReturnTypeNotationIllegalParam::Type { + span: path_span, + param_span: tcx.def_span(param.def_id), + }, + ); + emitted_bad_param_err = true; + } + Ty::new_bound( + tcx, + ty::INNERMOST, + ty::BoundTy { + var: ty::BoundVar::from_usize(num_bound_vars), + kind: ty::BoundTyKind::Param(param.def_id, param.name), + }, + ) + .into() + } + ty::GenericParamDefKind::Const { .. } => { + if !emitted_bad_param_err { + tcx.sess.emit_err( + crate::errors::ReturnTypeNotationIllegalParam::Const { + span: path_span, + param_span: tcx.def_span(param.def_id), + }, + ); + emitted_bad_param_err = true; + } + let ty = tcx + .type_of(param.def_id) + .no_bound_vars() + .expect("ct params cannot have early bound vars"); + ty::Const::new_bound( + tcx, + ty::INNERMOST, + ty::BoundVar::from_usize(num_bound_vars), + ty, + ) + .into() + } + }; + num_bound_vars += 1; + subst + }); + + // Next, we need to check that the return-type notation is being used on + // an RPITIT (return-position impl trait in trait) or AFIT (async fn in trait). + let output = tcx.fn_sig(assoc_item.def_id).skip_binder().output(); + let output = if let ty::Alias(ty::Projection, alias_ty) = *output.skip_binder().kind() + && tcx.is_impl_trait_in_trait(alias_ty.def_id) + { + alias_ty + } else { + return Err(self.tcx().sess.emit_err( + crate::errors::ReturnTypeNotationOnNonRpitit { + span: binding.span, + ty: tcx.liberate_late_bound_regions(assoc_item.def_id, output), + fn_span: tcx.hir().span_if_local(assoc_item.def_id), + note: (), + }, + )); + }; + + // Finally, move the fn return type's bound vars over to account for the early bound + // params (and trait ref's late bound params). This logic is very similar to + // `Predicate::subst_supertrait`, and it's no coincidence why. + let shifted_output = tcx.shift_bound_var_indices(num_bound_vars, output); + let subst_output = ty::EarlyBinder::bind(shifted_output).subst(tcx, substs); + + let bound_vars = tcx.late_bound_vars(binding.hir_id); + ty::Binder::bind_with_vars(subst_output, bound_vars) + } else { + // Include substitutions for generic parameters of associated types + candidate.map_bound(|trait_ref| { + let ident = Ident::new(assoc_item.name, binding.item_name.span); + let item_segment = hir::PathSegment { + ident, + hir_id: binding.hir_id, + res: Res::Err, + args: Some(binding.gen_args), + infer_args: false, + }; + + let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item( + path_span, + assoc_item.def_id, + &item_segment, + trait_ref.substs, + ); + + debug!(?substs_trait_ref_and_assoc_item); + + tcx.mk_alias_ty(assoc_item.def_id, substs_trait_ref_and_assoc_item) + }) + }; + + if !speculative { + // Find any late-bound regions declared in `ty` that are not + // declared in the trait-ref or assoc_item. These are not well-formed. + // + // Example: + // + // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad + // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok + if let ConvertedBindingKind::Equality(ty) = binding.kind { + let late_bound_in_trait_ref = + tcx.collect_constrained_late_bound_regions(&projection_ty); + let late_bound_in_ty = + tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty)); + debug!(?late_bound_in_trait_ref); + debug!(?late_bound_in_ty); + + // FIXME: point at the type params that don't have appropriate lifetimes: + // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F); + // ---- ---- ^^^^^^^ + self.validate_late_bound_regions( + late_bound_in_trait_ref, + late_bound_in_ty, + |br_name| { + struct_span_err!( + tcx.sess, + binding.span, + E0582, + "binding for associated type `{}` references {}, \ + which does not appear in the trait input types", + binding.item_name, + br_name + ) + }, + ); + } + } + + match binding.kind { + ConvertedBindingKind::Equality(..) if return_type_notation => { + return Err(self.tcx().sess.emit_err( + crate::errors::ReturnTypeNotationEqualityBound { span: binding.span }, + )); + } + ConvertedBindingKind::Equality(mut term) => { + // "Desugar" a constraint like `T: Iterator<Item = u32>` this to + // the "projection predicate" for: + // + // `<T as Iterator>::Item = u32` + let assoc_item_def_id = projection_ty.skip_binder().def_id; + let def_kind = tcx.def_kind(assoc_item_def_id); + match (def_kind, term.unpack()) { + (hir::def::DefKind::AssocTy, ty::TermKind::Ty(_)) + | (hir::def::DefKind::AssocConst, ty::TermKind::Const(_)) => (), + (_, _) => { + let got = if let Some(_) = term.ty() { "type" } else { "constant" }; + let expected = tcx.def_descr(assoc_item_def_id); + let mut err = tcx.sess.struct_span_err( + binding.span, + format!("expected {expected} bound, found {got}"), + ); + err.span_note( + tcx.def_span(assoc_item_def_id), + format!("{expected} defined here"), + ); + + if let hir::def::DefKind::AssocConst = def_kind + && let Some(t) = term.ty() && (t.is_enum() || t.references_error()) + && tcx.features().associated_const_equality { + err.span_suggestion( + binding.span, + "if equating a const, try wrapping with braces", + format!("{} = {{ const }}", binding.item_name), + Applicability::HasPlaceholders, + ); + } + let reported = err.emit(); + term = match def_kind { + hir::def::DefKind::AssocTy => Ty::new_error(tcx, reported).into(), + hir::def::DefKind::AssocConst => ty::Const::new_error( + tcx, + reported, + tcx.type_of(assoc_item_def_id) + .subst(tcx, projection_ty.skip_binder().substs), + ) + .into(), + _ => unreachable!(), + }; + } + } + bounds.push_projection_bound( + tcx, + projection_ty + .map_bound(|projection_ty| ty::ProjectionPredicate { projection_ty, term }), + binding.span, + ); + } + ConvertedBindingKind::Constraint(ast_bounds) => { + // "Desugar" a constraint like `T: Iterator<Item: Debug>` to + // + // `<T as Iterator>::Item: Debug` + // + // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty` + // parameter to have a skipped binder. + // + // NOTE: If `only_self_bounds` is true, do NOT expand this associated + // type bound into a trait predicate, since we only want to add predicates + // for the `Self` type. + if !only_self_bounds.0 { + let param_ty = Ty::new_alias(tcx, ty::Projection, projection_ty.skip_binder()); + self.add_bounds( + param_ty, + ast_bounds.iter(), + bounds, + projection_ty.bound_vars(), + only_self_bounds, + ); + } + } + } + Ok(()) + } +} |