use crate::autoderef::Autoderef; use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter}; use hir::def::DefKind; use rustc_ast as ast; use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet}; use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed}; use rustc_hir as hir; use rustc_hir::def_id::{DefId, LocalDefId}; use rustc_hir::lang_items::LangItem; use rustc_hir::ItemKind; use rustc_infer::infer::outlives::env::{OutlivesEnvironment, RegionBoundPairs}; use rustc_infer::infer::outlives::obligations::TypeOutlives; use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt}; use rustc_middle::mir::ConstraintCategory; use rustc_middle::ty::query::Providers; use rustc_middle::ty::trait_def::TraitSpecializationKind; use rustc_middle::ty::{ self, AdtKind, GenericParamDefKind, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor, }; use rustc_middle::ty::{GenericArgKind, InternalSubsts}; use rustc_session::parse::feature_err; use rustc_span::symbol::{sym, Ident, Symbol}; use rustc_span::{Span, DUMMY_SP}; use rustc_target::spec::abi::Abi; use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt; use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _; use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _; use rustc_trait_selection::traits::{ self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc, }; use std::cell::LazyCell; use std::ops::{ControlFlow, Deref}; pub(super) struct WfCheckingCtxt<'a, 'tcx> { pub(super) ocx: ObligationCtxt<'a, 'tcx>, span: Span, body_def_id: LocalDefId, param_env: ty::ParamEnv<'tcx>, } impl<'a, 'tcx> Deref for WfCheckingCtxt<'a, 'tcx> { type Target = ObligationCtxt<'a, 'tcx>; fn deref(&self) -> &Self::Target { &self.ocx } } impl<'tcx> WfCheckingCtxt<'_, 'tcx> { fn tcx(&self) -> TyCtxt<'tcx> { self.ocx.infcx.tcx } // Convenience function to normalize during wfcheck. This performs // `ObligationCtxt::normalize`, but provides a nice `ObligationCauseCode`. fn normalize(&self, span: Span, loc: Option, value: T) -> T where T: TypeFoldable>, { self.ocx.normalize( &ObligationCause::new(span, self.body_def_id, ObligationCauseCode::WellFormed(loc)), self.param_env, value, ) } fn register_wf_obligation( &self, span: Span, loc: Option, arg: ty::GenericArg<'tcx>, ) { let cause = traits::ObligationCause::new( span, self.body_def_id, ObligationCauseCode::WellFormed(loc), ); // for a type to be WF, we do not need to check if const trait predicates satisfy. let param_env = self.param_env.without_const(); self.ocx.register_obligation(traits::Obligation::new( self.tcx(), cause, param_env, ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)), )); } } pub(super) fn enter_wf_checking_ctxt<'tcx, F>( tcx: TyCtxt<'tcx>, span: Span, body_def_id: LocalDefId, f: F, ) where F: for<'a> FnOnce(&WfCheckingCtxt<'a, 'tcx>), { let param_env = tcx.param_env(body_def_id); let infcx = &tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(infcx); let mut wfcx = WfCheckingCtxt { ocx, span, body_def_id, param_env }; if !tcx.features().trivial_bounds { wfcx.check_false_global_bounds() } f(&mut wfcx); let assumed_wf_types = wfcx.ocx.assumed_wf_types(param_env, span, body_def_id); let implied_bounds = infcx.implied_bounds_tys(param_env, body_def_id, assumed_wf_types); let errors = wfcx.select_all_or_error(); if !errors.is_empty() { infcx.err_ctxt().report_fulfillment_errors(&errors, None); return; } let outlives_environment = OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds); let _ = infcx .err_ctxt() .check_region_obligations_and_report_errors(body_def_id, &outlives_environment); } fn check_well_formed(tcx: TyCtxt<'_>, def_id: hir::OwnerId) { let node = tcx.hir().owner(def_id); match node { hir::OwnerNode::Crate(_) => {} hir::OwnerNode::Item(item) => check_item(tcx, item), hir::OwnerNode::TraitItem(item) => check_trait_item(tcx, item), hir::OwnerNode::ImplItem(item) => check_impl_item(tcx, item), hir::OwnerNode::ForeignItem(item) => check_foreign_item(tcx, item), } if let Some(generics) = node.generics() { for param in generics.params { check_param_wf(tcx, param) } } } /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are /// well-formed, meaning that they do not require any constraints not declared in the struct /// definition itself. For example, this definition would be illegal: /// /// ```rust /// struct Ref<'a, T> { x: &'a T } /// ``` /// /// because the type did not declare that `T:'a`. /// /// We do this check as a pre-pass before checking fn bodies because if these constraints are /// not included it frequently leads to confusing errors in fn bodies. So it's better to check /// the types first. #[instrument(skip(tcx), level = "debug")] fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) { let def_id = item.owner_id.def_id; debug!( ?item.owner_id, item.name = ? tcx.def_path_str(def_id.to_def_id()) ); match item.kind { // Right now we check that every default trait implementation // has an implementation of itself. Basically, a case like: // // impl Trait for T {} // // has a requirement of `T: Trait` which was required for default // method implementations. Although this could be improved now that // there's a better infrastructure in place for this, it's being left // for a follow-up work. // // Since there's such a requirement, we need to check *just* positive // implementations, otherwise things like: // // impl !Send for T {} // // won't be allowed unless there's an *explicit* implementation of `Send` // for `T` hir::ItemKind::Impl(impl_) => { let is_auto = tcx .impl_trait_ref(def_id) .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.skip_binder().def_id)); if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) { let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span); let mut err = tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default"); err.span_labels(impl_.defaultness_span, "default because of this"); err.span_label(sp, "auto trait"); err.emit(); } // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span. match (tcx.impl_polarity(def_id), impl_.polarity) { (ty::ImplPolarity::Positive, _) => { check_impl(tcx, item, impl_.self_ty, &impl_.of_trait, impl_.constness); } (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => { // FIXME(#27579): what amount of WF checking do we need for neg impls? if let hir::Defaultness::Default { .. } = impl_.defaultness { let mut spans = vec![span]; spans.extend(impl_.defaultness_span); struct_span_err!( tcx.sess, spans, E0750, "negative impls cannot be default impls" ) .emit(); } } (ty::ImplPolarity::Reservation, _) => { // FIXME: what amount of WF checking do we need for reservation impls? } _ => unreachable!(), } } hir::ItemKind::Fn(ref sig, ..) => { check_item_fn(tcx, def_id, item.ident, item.span, sig.decl); } hir::ItemKind::Static(ty, ..) => { check_item_type(tcx, def_id, ty.span, false); } hir::ItemKind::Const(ty, ..) => { check_item_type(tcx, def_id, ty.span, false); } hir::ItemKind::Struct(_, ast_generics) => { check_type_defn(tcx, item, false); check_variances_for_type_defn(tcx, item, ast_generics); } hir::ItemKind::Union(_, ast_generics) => { check_type_defn(tcx, item, true); check_variances_for_type_defn(tcx, item, ast_generics); } hir::ItemKind::Enum(_, ast_generics) => { check_type_defn(tcx, item, true); check_variances_for_type_defn(tcx, item, ast_generics); } hir::ItemKind::Trait(..) => { check_trait(tcx, item); } hir::ItemKind::TraitAlias(..) => { check_trait(tcx, item); } // `ForeignItem`s are handled separately. hir::ItemKind::ForeignMod { .. } => {} _ => {} } } fn check_foreign_item(tcx: TyCtxt<'_>, item: &hir::ForeignItem<'_>) { let def_id = item.owner_id.def_id; debug!( ?item.owner_id, item.name = ? tcx.def_path_str(def_id.to_def_id()) ); match item.kind { hir::ForeignItemKind::Fn(decl, ..) => { check_item_fn(tcx, def_id, item.ident, item.span, decl) } hir::ForeignItemKind::Static(ty, ..) => check_item_type(tcx, def_id, ty.span, true), hir::ForeignItemKind::Type => (), } } fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) { let def_id = trait_item.owner_id.def_id; let (method_sig, span) = match trait_item.kind { hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span), hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span), _ => (None, trait_item.span), }; check_object_unsafe_self_trait_by_name(tcx, trait_item); check_associated_item(tcx, def_id, span, method_sig); } /// Require that the user writes where clauses on GATs for the implicit /// outlives bounds involving trait parameters in trait functions and /// lifetimes passed as GAT substs. See `self-outlives-lint` test. /// /// We use the following trait as an example throughout this function: /// ```rust,ignore (this code fails due to this lint) /// trait IntoIter { /// type Iter<'a>: Iterator>; /// type Item<'a>; /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>; /// } /// ``` fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) { // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint. let mut required_bounds_by_item = FxHashMap::default(); // Loop over all GATs together, because if this lint suggests adding a where-clause bound // to one GAT, it might then require us to an additional bound on another GAT. // In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which // then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between // those GATs. loop { let mut should_continue = false; for gat_item in associated_items { let gat_def_id = gat_item.id.owner_id; let gat_item = tcx.associated_item(gat_def_id); // If this item is not an assoc ty, or has no substs, then it's not a GAT if gat_item.kind != ty::AssocKind::Type { continue; } let gat_generics = tcx.generics_of(gat_def_id); // FIXME(jackh726): we can also warn in the more general case if gat_generics.params.is_empty() { continue; } // Gather the bounds with which all other items inside of this trait constrain the GAT. // This is calculated by taking the intersection of the bounds that each item // constrains the GAT with individually. let mut new_required_bounds: Option>> = None; for item in associated_items { let item_def_id = item.id.owner_id; // Skip our own GAT, since it does not constrain itself at all. if item_def_id == gat_def_id { continue; } let param_env = tcx.param_env(item_def_id); let item_required_bounds = match item.kind { // In our example, this corresponds to `into_iter` method hir::AssocItemKind::Fn { .. } => { // For methods, we check the function signature's return type for any GATs // to constrain. In the `into_iter` case, we see that the return type // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from. let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions( item_def_id.to_def_id(), tcx.fn_sig(item_def_id).subst_identity(), ); gather_gat_bounds( tcx, param_env, item_def_id, sig.inputs_and_output, // We also assume that all of the function signature's parameter types // are well formed. &sig.inputs().iter().copied().collect(), gat_def_id.def_id, gat_generics, ) } // In our example, this corresponds to the `Iter` and `Item` associated types hir::AssocItemKind::Type => { // If our associated item is a GAT with missing bounds, add them to // the param-env here. This allows this GAT to propagate missing bounds // to other GATs. let param_env = augment_param_env( tcx, param_env, required_bounds_by_item.get(&item_def_id), ); gather_gat_bounds( tcx, param_env, item_def_id, tcx.explicit_item_bounds(item_def_id).to_vec(), &FxIndexSet::default(), gat_def_id.def_id, gat_generics, ) } hir::AssocItemKind::Const => None, }; if let Some(item_required_bounds) = item_required_bounds { // Take the intersection of the required bounds for this GAT, and // the item_required_bounds which are the ones implied by just // this item alone. // This is why we use an Option<_>, since we need to distinguish // the empty set of bounds from the _uninitialized_ set of bounds. if let Some(new_required_bounds) = &mut new_required_bounds { new_required_bounds.retain(|b| item_required_bounds.contains(b)); } else { new_required_bounds = Some(item_required_bounds); } } } if let Some(new_required_bounds) = new_required_bounds { let required_bounds = required_bounds_by_item.entry(gat_def_id).or_default(); if new_required_bounds.into_iter().any(|p| required_bounds.insert(p)) { // Iterate until our required_bounds no longer change // Since they changed here, we should continue the loop should_continue = true; } } } // We know that this loop will eventually halt, since we only set `should_continue` if the // `required_bounds` for this item grows. Since we are not creating any new region or type // variables, the set of all region and type bounds that we could ever insert are limited // by the number of unique types and regions we observe in a given item. if !should_continue { break; } } for (gat_def_id, required_bounds) in required_bounds_by_item { let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id.def_id); debug!(?required_bounds); let param_env = tcx.param_env(gat_def_id); let mut unsatisfied_bounds: Vec<_> = required_bounds .into_iter() .filter(|clause| match clause.kind().skip_binder() { ty::PredicateKind::Clause(ty::Clause::RegionOutlives(ty::OutlivesPredicate( a, b, ))) => !region_known_to_outlive( tcx, gat_def_id.def_id, param_env, &FxIndexSet::default(), a, b, ), ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate( a, b, ))) => !ty_known_to_outlive( tcx, gat_def_id.def_id, param_env, &FxIndexSet::default(), a, b, ), _ => bug!("Unexpected PredicateKind"), }) .map(|clause| clause.to_string()) .collect(); // We sort so that order is predictable unsatisfied_bounds.sort(); if !unsatisfied_bounds.is_empty() { let plural = pluralize!(unsatisfied_bounds.len()); let mut err = tcx.sess.struct_span_err( gat_item_hir.span, &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident), ); let suggestion = format!( "{} {}", gat_item_hir.generics.add_where_or_trailing_comma(), unsatisfied_bounds.join(", "), ); err.span_suggestion( gat_item_hir.generics.tail_span_for_predicate_suggestion(), &format!("add the required where clause{plural}"), suggestion, Applicability::MachineApplicable, ); let bound = if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" }; err.note(&format!( "{} currently required to ensure that impls have maximum flexibility", bound )); err.note( "we are soliciting feedback, see issue #87479 \ \ for more information", ); err.emit(); } } } /// Add a new set of predicates to the caller_bounds of an existing param_env. fn augment_param_env<'tcx>( tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, new_predicates: Option<&FxHashSet>>, ) -> ty::ParamEnv<'tcx> { let Some(new_predicates) = new_predicates else { return param_env; }; if new_predicates.is_empty() { return param_env; } let bounds = tcx.mk_predicates_from_iter( param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()), ); // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this // i.e. traits::normalize_param_env_or_error ty::ParamEnv::new(bounds, param_env.reveal(), param_env.constness()) } /// We use the following trait as an example throughout this function. /// Specifically, let's assume that `to_check` here is the return type /// of `into_iter`, and the GAT we are checking this for is `Iter`. /// ```rust,ignore (this code fails due to this lint) /// trait IntoIter { /// type Iter<'a>: Iterator>; /// type Item<'a>; /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>; /// } /// ``` fn gather_gat_bounds<'tcx, T: TypeFoldable>>( tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, item_def_id: hir::OwnerId, to_check: T, wf_tys: &FxIndexSet>, gat_def_id: LocalDefId, gat_generics: &'tcx ty::Generics, ) -> Option>> { // The bounds we that we would require from `to_check` let mut bounds = FxHashSet::default(); let (regions, types) = GATSubstCollector::visit(gat_def_id.to_def_id(), to_check); // If both regions and types are empty, then this GAT isn't in the // set of types we are checking, and we shouldn't try to do clause analysis // (particularly, doing so would end up with an empty set of clauses, // since the current method would require none, and we take the // intersection of requirements of all methods) if types.is_empty() && regions.is_empty() { return None; } for (region_a, region_a_idx) in ®ions { // Ignore `'static` lifetimes for the purpose of this lint: it's // because we know it outlives everything and so doesn't give meaningful // clues if let ty::ReStatic = **region_a { continue; } // For each region argument (e.g., `'a` in our example), check for a // relationship to the type arguments (e.g., `Self`). If there is an // outlives relationship (`Self: 'a`), then we want to ensure that is // reflected in a where clause on the GAT itself. for (ty, ty_idx) in &types { // In our example, requires that `Self: 'a` if ty_known_to_outlive(tcx, item_def_id.def_id, param_env, &wf_tys, *ty, *region_a) { debug!(?ty_idx, ?region_a_idx); debug!("required clause: {ty} must outlive {region_a}"); // Translate into the generic parameters of the GAT. In // our example, the type was `Self`, which will also be // `Self` in the GAT. let ty_param = gat_generics.param_at(*ty_idx, tcx); let ty_param = tcx.mk_ty_param(ty_param.index, ty_param.name); // Same for the region. In our example, 'a corresponds // to the 'me parameter. let region_param = gat_generics.param_at(*region_a_idx, tcx); let region_param = tcx.mk_re_early_bound(ty::EarlyBoundRegion { def_id: region_param.def_id, index: region_param.index, name: region_param.name, }); // The predicate we expect to see. (In our example, // `Self: 'me`.) let clause = ty::PredicateKind::Clause(ty::Clause::TypeOutlives( ty::OutlivesPredicate(ty_param, region_param), )); let clause = tcx.mk_predicate(ty::Binder::dummy(clause)); bounds.insert(clause); } } // For each region argument (e.g., `'a` in our example), also check for a // relationship to the other region arguments. If there is an outlives // relationship, then we want to ensure that is reflected in the where clause // on the GAT itself. for (region_b, region_b_idx) in ®ions { // Again, skip `'static` because it outlives everything. Also, we trivially // know that a region outlives itself. if ty::ReStatic == **region_b || region_a == region_b { continue; } if region_known_to_outlive( tcx, item_def_id.def_id, param_env, &wf_tys, *region_a, *region_b, ) { debug!(?region_a_idx, ?region_b_idx); debug!("required clause: {region_a} must outlive {region_b}"); // Translate into the generic parameters of the GAT. let region_a_param = gat_generics.param_at(*region_a_idx, tcx); let region_a_param = tcx.mk_re_early_bound(ty::EarlyBoundRegion { def_id: region_a_param.def_id, index: region_a_param.index, name: region_a_param.name, }); // Same for the region. let region_b_param = gat_generics.param_at(*region_b_idx, tcx); let region_b_param = tcx.mk_re_early_bound(ty::EarlyBoundRegion { def_id: region_b_param.def_id, index: region_b_param.index, name: region_b_param.name, }); // The predicate we expect to see. let clause = ty::PredicateKind::Clause(ty::Clause::RegionOutlives( ty::OutlivesPredicate(region_a_param, region_b_param), )); let clause = tcx.mk_predicate(ty::Binder::dummy(clause)); bounds.insert(clause); } } } Some(bounds) } /// Given a known `param_env` and a set of well formed types, can we prove that /// `ty` outlives `region`. fn ty_known_to_outlive<'tcx>( tcx: TyCtxt<'tcx>, id: LocalDefId, param_env: ty::ParamEnv<'tcx>, wf_tys: &FxIndexSet>, ty: Ty<'tcx>, region: ty::Region<'tcx>, ) -> bool { resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |infcx, region_bound_pairs| { let origin = infer::RelateParamBound(DUMMY_SP, ty, None); let outlives = &mut TypeOutlives::new(infcx, tcx, region_bound_pairs, None, param_env); outlives.type_must_outlive(origin, ty, region, ConstraintCategory::BoringNoLocation); }) } /// Given a known `param_env` and a set of well formed types, can we prove that /// `region_a` outlives `region_b` fn region_known_to_outlive<'tcx>( tcx: TyCtxt<'tcx>, id: LocalDefId, param_env: ty::ParamEnv<'tcx>, wf_tys: &FxIndexSet>, region_a: ty::Region<'tcx>, region_b: ty::Region<'tcx>, ) -> bool { resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |mut infcx, _| { use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate; let origin = infer::RelateRegionParamBound(DUMMY_SP); // `region_a: region_b` -> `region_b <= region_a` infcx.push_sub_region_constraint( origin, region_b, region_a, ConstraintCategory::BoringNoLocation, ); }) } /// Given a known `param_env` and a set of well formed types, set up an /// `InferCtxt`, call the passed function (to e.g. set up region constraints /// to be tested), then resolve region and return errors fn resolve_regions_with_wf_tys<'tcx>( tcx: TyCtxt<'tcx>, id: LocalDefId, param_env: ty::ParamEnv<'tcx>, wf_tys: &FxIndexSet>, add_constraints: impl for<'a> FnOnce(&'a InferCtxt<'tcx>, &'a RegionBoundPairs<'tcx>), ) -> bool { // Unfortunately, we have to use a new `InferCtxt` each call, because // region constraints get added and solved there and we need to test each // call individually. let infcx = tcx.infer_ctxt().build(); let outlives_environment = OutlivesEnvironment::with_bounds( param_env, Some(&infcx), infcx.implied_bounds_tys(param_env, id, wf_tys.clone()), ); let region_bound_pairs = outlives_environment.region_bound_pairs(); add_constraints(&infcx, region_bound_pairs); infcx.process_registered_region_obligations( outlives_environment.region_bound_pairs(), param_env, ); let errors = infcx.resolve_regions(&outlives_environment); debug!(?errors, "errors"); // If we were able to prove that the type outlives the region without // an error, it must be because of the implied or explicit bounds... errors.is_empty() } /// TypeVisitor that looks for uses of GATs like /// `>::GAT` and adds the arguments `P0..Pm` into /// the two vectors, `regions` and `types` (depending on their kind). For each /// parameter `Pi` also track the index `i`. struct GATSubstCollector<'tcx> { gat: DefId, // Which region appears and which parameter index its substituted for regions: FxHashSet<(ty::Region<'tcx>, usize)>, // Which params appears and which parameter index its substituted for types: FxHashSet<(Ty<'tcx>, usize)>, } impl<'tcx> GATSubstCollector<'tcx> { fn visit>>( gat: DefId, t: T, ) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) { let mut visitor = GATSubstCollector { gat, regions: FxHashSet::default(), types: FxHashSet::default() }; t.visit_with(&mut visitor); (visitor.regions, visitor.types) } } impl<'tcx> TypeVisitor> for GATSubstCollector<'tcx> { type BreakTy = !; fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow { match t.kind() { ty::Alias(ty::Projection, p) if p.def_id == self.gat => { for (idx, subst) in p.substs.iter().enumerate() { match subst.unpack() { GenericArgKind::Lifetime(lt) if !lt.is_late_bound() => { self.regions.insert((lt, idx)); } GenericArgKind::Type(t) => { self.types.insert((t, idx)); } _ => {} } } } _ => {} } t.super_visit_with(self) } } fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool { match ty.kind { hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments { [s] => s.res.opt_def_id() == Some(trait_def_id.to_def_id()), _ => false, }, _ => false, } } /// Detect when an object unsafe trait is referring to itself in one of its associated items. /// When this is done, suggest using `Self` instead. fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) { let (trait_name, trait_def_id) = match tcx.hir().get_by_def_id(tcx.hir().get_parent_item(item.hir_id()).def_id) { hir::Node::Item(item) => match item.kind { hir::ItemKind::Trait(..) => (item.ident, item.owner_id), _ => return, }, _ => return, }; let mut trait_should_be_self = vec![]; match &item.kind { hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty)) if could_be_self(trait_def_id.def_id, ty) => { trait_should_be_self.push(ty.span) } hir::TraitItemKind::Fn(sig, _) => { for ty in sig.decl.inputs { if could_be_self(trait_def_id.def_id, ty) { trait_should_be_self.push(ty.span); } } match sig.decl.output { hir::FnRetTy::Return(ty) if could_be_self(trait_def_id.def_id, ty) => { trait_should_be_self.push(ty.span); } _ => {} } } _ => {} } if !trait_should_be_self.is_empty() { if tcx.check_is_object_safe(trait_def_id) { return; } let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect(); tcx.sess .struct_span_err( trait_should_be_self, "associated item referring to unboxed trait object for its own trait", ) .span_label(trait_name.span, "in this trait") .multipart_suggestion( "you might have meant to use `Self` to refer to the implementing type", sugg, Applicability::MachineApplicable, ) .emit(); } } fn check_impl_item(tcx: TyCtxt<'_>, impl_item: &hir::ImplItem<'_>) { let (method_sig, span) = match impl_item.kind { hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span), // Constrain binding and overflow error spans to `` in `type foo = `. hir::ImplItemKind::Type(ty) if ty.span != DUMMY_SP => (None, ty.span), _ => (None, impl_item.span), }; check_associated_item(tcx, impl_item.owner_id.def_id, span, method_sig); } fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) { match param.kind { // We currently only check wf of const params here. hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (), // Const parameters are well formed if their type is structural match. hir::GenericParamKind::Const { ty: hir_ty, default: _ } => { let ty = tcx.type_of(param.def_id).subst_identity(); if tcx.features().adt_const_params { if let Some(non_structural_match_ty) = traits::search_for_adt_const_param_violation(param.span, tcx, ty) { // We use the same error code in both branches, because this is really the same // issue: we just special-case the message for type parameters to make it // clearer. match non_structural_match_ty.kind() { ty::Param(_) => { // Const parameters may not have type parameters as their types, // because we cannot be sure that the type parameter derives `PartialEq` // and `Eq` (just implementing them is not enough for `structural_match`). struct_span_err!( tcx.sess, hir_ty.span, E0741, "`{ty}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \ used as the type of a const parameter", ) .span_label( hir_ty.span, format!("`{ty}` may not derive both `PartialEq` and `Eq`"), ) .note( "it is not currently possible to use a type parameter as the type of a \ const parameter", ) .emit(); } ty::Float(_) => { struct_span_err!( tcx.sess, hir_ty.span, E0741, "`{ty}` is forbidden as the type of a const generic parameter", ) .note("floats do not derive `Eq` or `Ord`, which are required for const parameters") .emit(); } ty::FnPtr(_) => { struct_span_err!( tcx.sess, hir_ty.span, E0741, "using function pointers as const generic parameters is forbidden", ) .emit(); } ty::RawPtr(_) => { struct_span_err!( tcx.sess, hir_ty.span, E0741, "using raw pointers as const generic parameters is forbidden", ) .emit(); } _ => { let mut diag = struct_span_err!( tcx.sess, hir_ty.span, E0741, "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \ the type of a const parameter", non_structural_match_ty, ); if ty == non_structural_match_ty { diag.span_label( hir_ty.span, format!("`{ty}` doesn't derive both `PartialEq` and `Eq`"), ); } diag.emit(); } } } } else { let err_ty_str; let mut is_ptr = true; let err = match ty.kind() { ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None, ty::FnPtr(_) => Some("function pointers"), ty::RawPtr(_) => Some("raw pointers"), _ => { is_ptr = false; err_ty_str = format!("`{ty}`"); Some(err_ty_str.as_str()) } }; if let Some(unsupported_type) = err { if is_ptr { tcx.sess.span_err( hir_ty.span, &format!( "using {unsupported_type} as const generic parameters is forbidden", ), ); } else { let mut err = tcx.sess.struct_span_err( hir_ty.span, &format!( "{unsupported_type} is forbidden as the type of a const generic parameter", ), ); err.note("the only supported types are integers, `bool` and `char`"); if tcx.sess.is_nightly_build() { err.help( "more complex types are supported with `#![feature(adt_const_params)]`", ); } err.emit(); } } } } } } #[instrument(level = "debug", skip(tcx, span, sig_if_method))] fn check_associated_item( tcx: TyCtxt<'_>, item_id: LocalDefId, span: Span, sig_if_method: Option<&hir::FnSig<'_>>, ) { let loc = Some(WellFormedLoc::Ty(item_id)); enter_wf_checking_ctxt(tcx, span, item_id, |wfcx| { let item = tcx.associated_item(item_id); let self_ty = match item.container { ty::TraitContainer => tcx.types.self_param, ty::ImplContainer => tcx.type_of(item.container_id(tcx)).subst_identity(), }; match item.kind { ty::AssocKind::Const => { let ty = tcx.type_of(item.def_id).subst_identity(); let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty); wfcx.register_wf_obligation(span, loc, ty.into()); } ty::AssocKind::Fn => { let sig = tcx.fn_sig(item.def_id).subst_identity(); let hir_sig = sig_if_method.expect("bad signature for method"); check_fn_or_method( wfcx, item.ident(tcx).span, sig, hir_sig.decl, item.def_id.expect_local(), ); check_method_receiver(wfcx, hir_sig, item, self_ty); } ty::AssocKind::Type => { if let ty::AssocItemContainer::TraitContainer = item.container { check_associated_type_bounds(wfcx, item, span) } if item.defaultness(tcx).has_value() { let ty = tcx.type_of(item.def_id).subst_identity(); let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty); wfcx.register_wf_obligation(span, loc, ty.into()); } } } }) } fn item_adt_kind(kind: &ItemKind<'_>) -> Option { match kind { ItemKind::Struct(..) => Some(AdtKind::Struct), ItemKind::Union(..) => Some(AdtKind::Union), ItemKind::Enum(..) => Some(AdtKind::Enum), _ => None, } } /// In a type definition, we check that to ensure that the types of the fields are well-formed. fn check_type_defn<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'tcx>, all_sized: bool) { let _ = tcx.representability(item.owner_id.def_id); let adt_def = tcx.adt_def(item.owner_id); enter_wf_checking_ctxt(tcx, item.span, item.owner_id.def_id, |wfcx| { let variants = adt_def.variants(); let packed = adt_def.repr().packed(); for variant in variants.iter() { // All field types must be well-formed. for field in &variant.fields { let field_id = field.did.expect_local(); let hir::FieldDef { ty: hir_ty, .. } = tcx.hir().get_by_def_id(field_id).expect_field(); let ty = wfcx.normalize(hir_ty.span, None, tcx.type_of(field.did).subst_identity()); wfcx.register_wf_obligation( hir_ty.span, Some(WellFormedLoc::Ty(field_id)), ty.into(), ) } // For DST, or when drop needs to copy things around, all // intermediate types must be sized. let needs_drop_copy = || { packed && { let ty = tcx.type_of(variant.fields.last().unwrap().did).subst_identity(); let ty = tcx.erase_regions(ty); if ty.needs_infer() { tcx.sess .delay_span_bug(item.span, &format!("inference variables in {:?}", ty)); // Just treat unresolved type expression as if it needs drop. true } else { ty.needs_drop(tcx, tcx.param_env(item.owner_id)) } } }; // All fields (except for possibly the last) should be sized. let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy(); let unsized_len = if all_sized { 0 } else { 1 }; for (idx, field) in variant.fields[..variant.fields.len() - unsized_len].iter().enumerate() { let last = idx == variant.fields.len() - 1; let field_id = field.did.expect_local(); let hir::FieldDef { ty: hir_ty, .. } = tcx.hir().get_by_def_id(field_id).expect_field(); let ty = wfcx.normalize(hir_ty.span, None, tcx.type_of(field.did).subst_identity()); wfcx.register_bound( traits::ObligationCause::new( hir_ty.span, wfcx.body_def_id, traits::FieldSized { adt_kind: match item_adt_kind(&item.kind) { Some(i) => i, None => bug!(), }, span: hir_ty.span, last, }, ), wfcx.param_env, ty, tcx.require_lang_item(LangItem::Sized, None), ); } // Explicit `enum` discriminant values must const-evaluate successfully. if let ty::VariantDiscr::Explicit(discr_def_id) = variant.discr { let cause = traits::ObligationCause::new( tcx.def_span(discr_def_id), wfcx.body_def_id, traits::MiscObligation, ); wfcx.register_obligation(traits::Obligation::new( tcx, cause, wfcx.param_env, ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable( ty::Const::from_anon_const(tcx, discr_def_id.expect_local()), )), )); } } check_where_clauses(wfcx, item.span, item.owner_id.def_id); }); } #[instrument(skip(tcx, item))] fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) { debug!(?item.owner_id); let def_id = item.owner_id.def_id; let trait_def = tcx.trait_def(def_id); if trait_def.is_marker || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker) { for associated_def_id in &*tcx.associated_item_def_ids(def_id) { struct_span_err!( tcx.sess, tcx.def_span(*associated_def_id), E0714, "marker traits cannot have associated items", ) .emit(); } } enter_wf_checking_ctxt(tcx, item.span, def_id, |wfcx| { check_where_clauses(wfcx, item.span, def_id) }); // Only check traits, don't check trait aliases if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind { check_gat_where_clauses(tcx, items); } } /// Checks all associated type defaults of trait `trait_def_id`. /// /// Assuming the defaults are used, check that all predicates (bounds on the /// assoc type and where clauses on the trait) hold. fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: ty::AssocItem, span: Span) { let bounds = wfcx.tcx().explicit_item_bounds(item.def_id); debug!("check_associated_type_bounds: bounds={:?}", bounds); let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| { let normalized_bound = wfcx.normalize(span, None, bound); traits::wf::predicate_obligations( wfcx.infcx, wfcx.param_env, wfcx.body_def_id, normalized_bound, bound_span, ) }); wfcx.register_obligations(wf_obligations); } fn check_item_fn( tcx: TyCtxt<'_>, def_id: LocalDefId, ident: Ident, span: Span, decl: &hir::FnDecl<'_>, ) { enter_wf_checking_ctxt(tcx, span, def_id, |wfcx| { let sig = tcx.fn_sig(def_id).subst_identity(); check_fn_or_method(wfcx, ident.span, sig, decl, def_id); }) } fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) { debug!("check_item_type: {:?}", item_id); enter_wf_checking_ctxt(tcx, ty_span, item_id, |wfcx| { let ty = tcx.type_of(item_id).subst_identity(); let item_ty = wfcx.normalize(ty_span, Some(WellFormedLoc::Ty(item_id)), ty); let mut forbid_unsized = true; if allow_foreign_ty { let tail = tcx.struct_tail_erasing_lifetimes(item_ty, wfcx.param_env); if let ty::Foreign(_) = tail.kind() { forbid_unsized = false; } } wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(item_id)), item_ty.into()); if forbid_unsized { wfcx.register_bound( traits::ObligationCause::new(ty_span, wfcx.body_def_id, traits::WellFormed(None)), wfcx.param_env, item_ty, tcx.require_lang_item(LangItem::Sized, None), ); } // Ensure that the end result is `Sync` in a non-thread local `static`. let should_check_for_sync = tcx.static_mutability(item_id.to_def_id()) == Some(hir::Mutability::Not) && !tcx.is_foreign_item(item_id.to_def_id()) && !tcx.is_thread_local_static(item_id.to_def_id()); if should_check_for_sync { wfcx.register_bound( traits::ObligationCause::new(ty_span, wfcx.body_def_id, traits::SharedStatic), wfcx.param_env, item_ty, tcx.require_lang_item(LangItem::Sync, Some(ty_span)), ); } }); } #[instrument(level = "debug", skip(tcx, ast_self_ty, ast_trait_ref))] fn check_impl<'tcx>( tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>, ast_self_ty: &hir::Ty<'_>, ast_trait_ref: &Option>, constness: hir::Constness, ) { enter_wf_checking_ctxt(tcx, item.span, item.owner_id.def_id, |wfcx| { match ast_trait_ref { Some(ast_trait_ref) => { // `#[rustc_reservation_impl]` impls are not real impls and // therefore don't need to be WF (the trait's `Self: Trait` predicate // won't hold). let trait_ref = tcx.impl_trait_ref(item.owner_id).unwrap().subst_identity(); let trait_ref = wfcx.normalize( ast_trait_ref.path.span, Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)), trait_ref, ); let trait_pred = ty::TraitPredicate { trait_ref, constness: match constness { hir::Constness::Const => ty::BoundConstness::ConstIfConst, hir::Constness::NotConst => ty::BoundConstness::NotConst, }, polarity: ty::ImplPolarity::Positive, }; let mut obligations = traits::wf::trait_obligations( wfcx.infcx, wfcx.param_env, wfcx.body_def_id, &trait_pred, ast_trait_ref.path.span, item, ); for obligation in &mut obligations { if let Some(pred) = obligation.predicate.to_opt_poly_trait_pred() && pred.self_ty().skip_binder() == trait_ref.self_ty() { obligation.cause.span = ast_self_ty.span; } } debug!(?obligations); wfcx.register_obligations(obligations); } None => { let self_ty = tcx.type_of(item.owner_id).subst_identity(); let self_ty = wfcx.normalize( item.span, Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)), self_ty, ); wfcx.register_wf_obligation( ast_self_ty.span, Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)), self_ty.into(), ); } } check_where_clauses(wfcx, item.span, item.owner_id.def_id); }); } /// Checks where-clauses and inline bounds that are declared on `def_id`. #[instrument(level = "debug", skip(wfcx))] fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id: LocalDefId) { let infcx = wfcx.infcx; let tcx = wfcx.tcx(); let predicates = tcx.predicates_of(def_id.to_def_id()); let generics = tcx.generics_of(def_id); let is_our_default = |def: &ty::GenericParamDef| match def.kind { GenericParamDefKind::Type { has_default, .. } | GenericParamDefKind::Const { has_default } => { has_default && def.index >= generics.parent_count as u32 } GenericParamDefKind::Lifetime => unreachable!(), }; // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`. // For example, this forbids the declaration: // // struct Foo> { .. } // // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold. for param in &generics.params { match param.kind { GenericParamDefKind::Type { .. } => { if is_our_default(param) { let ty = tcx.type_of(param.def_id).subst_identity(); // Ignore dependent defaults -- that is, where the default of one type // parameter includes another (e.g., ``). In those cases, we can't // be sure if it will error or not as user might always specify the other. if !ty.needs_subst() { wfcx.register_wf_obligation( tcx.def_span(param.def_id), Some(WellFormedLoc::Ty(param.def_id.expect_local())), ty.into(), ); } } } GenericParamDefKind::Const { .. } => { if is_our_default(param) { // FIXME(const_generics_defaults): This // is incorrect when dealing with unused substs, for example // for `struct Foo` // we should eagerly error. let default_ct = tcx.const_param_default(param.def_id).subst_identity(); if !default_ct.needs_subst() { wfcx.register_wf_obligation( tcx.def_span(param.def_id), None, default_ct.into(), ); } } } // Doesn't have defaults. GenericParamDefKind::Lifetime => {} } } // Check that trait predicates are WF when params are substituted by their defaults. // We don't want to overly constrain the predicates that may be written but we want to // catch cases where a default my never be applied such as `struct Foo`. // Therefore we check if a predicate which contains a single type param // with a concrete default is WF with that default substituted. // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`. // // First we build the defaulted substitution. let substs = InternalSubsts::for_item(tcx, def_id.to_def_id(), |param, _| { match param.kind { GenericParamDefKind::Lifetime => { // All regions are identity. tcx.mk_param_from_def(param) } GenericParamDefKind::Type { .. } => { // If the param has a default, ... if is_our_default(param) { let default_ty = tcx.type_of(param.def_id).subst_identity(); // ... and it's not a dependent default, ... if !default_ty.needs_subst() { // ... then substitute it with the default. return default_ty.into(); } } tcx.mk_param_from_def(param) } GenericParamDefKind::Const { .. } => { // If the param has a default, ... if is_our_default(param) { let default_ct = tcx.const_param_default(param.def_id).subst_identity(); // ... and it's not a dependent default, ... if !default_ct.needs_subst() { // ... then substitute it with the default. return default_ct.into(); } } tcx.mk_param_from_def(param) } } }); // Now we build the substituted predicates. let default_obligations = predicates .predicates .iter() .flat_map(|&(pred, sp)| { #[derive(Default)] struct CountParams { params: FxHashSet, } impl<'tcx> ty::visit::TypeVisitor> for CountParams { type BreakTy = (); fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow { if let ty::Param(param) = t.kind() { self.params.insert(param.index); } t.super_visit_with(self) } fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow { ControlFlow::Break(()) } fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow { if let ty::ConstKind::Param(param) = c.kind() { self.params.insert(param.index); } c.super_visit_with(self) } } let mut param_count = CountParams::default(); let has_region = pred.visit_with(&mut param_count).is_break(); let substituted_pred = ty::EarlyBinder(pred).subst(tcx, substs); // Don't check non-defaulted params, dependent defaults (including lifetimes) // or preds with multiple params. if substituted_pred.has_non_region_param() || param_count.params.len() > 1 || has_region { None } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) { // Avoid duplication of predicates that contain no parameters, for example. None } else { Some((substituted_pred, sp)) } }) .map(|(pred, sp)| { // Convert each of those into an obligation. So if you have // something like `struct Foo`, we would // take that predicate `T: Copy`, substitute to `String: Copy` // (actually that happens in the previous `flat_map` call), // and then try to prove it (in this case, we'll fail). // // Note the subtle difference from how we handle `predicates` // below: there, we are not trying to prove those predicates // to be *true* but merely *well-formed*. let pred = wfcx.normalize(sp, None, pred); let cause = traits::ObligationCause::new( sp, wfcx.body_def_id, traits::ItemObligation(def_id.to_def_id()), ); traits::Obligation::new(tcx, cause, wfcx.param_env, pred) }); let predicates = predicates.instantiate_identity(tcx); let predicates = wfcx.normalize(span, None, predicates); debug!(?predicates.predicates); assert_eq!(predicates.predicates.len(), predicates.spans.len()); let wf_obligations = predicates.into_iter().flat_map(|(p, sp)| { traits::wf::predicate_obligations( infcx, wfcx.param_env.without_const(), wfcx.body_def_id, p, sp, ) }); let obligations: Vec<_> = wf_obligations.chain(default_obligations).collect(); wfcx.register_obligations(obligations); } #[instrument(level = "debug", skip(wfcx, span, hir_decl))] fn check_fn_or_method<'tcx>( wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, sig: ty::PolyFnSig<'tcx>, hir_decl: &hir::FnDecl<'_>, def_id: LocalDefId, ) { let tcx = wfcx.tcx(); let mut sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig); // Normalize the input and output types one at a time, using a different // `WellFormedLoc` for each. We cannot call `normalize_associated_types` // on the entire `FnSig`, since this would use the same `WellFormedLoc` // for each type, preventing the HIR wf check from generating // a nice error message. let arg_span = |idx| hir_decl.inputs.get(idx).map_or(hir_decl.output.span(), |arg: &hir::Ty<'_>| arg.span); sig.inputs_and_output = tcx.mk_type_list_from_iter(sig.inputs_and_output.iter().enumerate().map(|(idx, ty)| { wfcx.normalize( arg_span(idx), Some(WellFormedLoc::Param { function: def_id, // Note that the `param_idx` of the output type is // one greater than the index of the last input type. param_idx: idx.try_into().unwrap(), }), ty, ) })); for (idx, ty) in sig.inputs_and_output.iter().enumerate() { wfcx.register_wf_obligation( arg_span(idx), Some(WellFormedLoc::Param { function: def_id, param_idx: idx.try_into().unwrap() }), ty.into(), ); } check_where_clauses(wfcx, span, def_id); check_return_position_impl_trait_in_trait_bounds( wfcx, def_id, sig.output(), hir_decl.output.span(), ); if sig.abi == Abi::RustCall { let span = tcx.def_span(def_id); let has_implicit_self = hir_decl.implicit_self != hir::ImplicitSelfKind::None; let mut inputs = sig.inputs().iter().skip(if has_implicit_self { 1 } else { 0 }); // Check that the argument is a tuple if let Some(ty) = inputs.next() { wfcx.register_bound( ObligationCause::new(span, wfcx.body_def_id, ObligationCauseCode::RustCall), wfcx.param_env, *ty, tcx.require_lang_item(hir::LangItem::Tuple, Some(span)), ); } else { tcx.sess.span_err( hir_decl.inputs.last().map_or(span, |input| input.span), "functions with the \"rust-call\" ABI must take a single non-self tuple argument", ); } // No more inputs other than the `self` type and the tuple type if inputs.next().is_some() { tcx.sess.span_err( hir_decl.inputs.last().map_or(span, |input| input.span), "functions with the \"rust-call\" ABI must take a single non-self tuple argument", ); } } } /// Basically `check_associated_type_bounds`, but separated for now and should be /// deduplicated when RPITITs get lowered into real associated items. #[tracing::instrument(level = "trace", skip(wfcx))] fn check_return_position_impl_trait_in_trait_bounds<'tcx>( wfcx: &WfCheckingCtxt<'_, 'tcx>, fn_def_id: LocalDefId, fn_output: Ty<'tcx>, span: Span, ) { let tcx = wfcx.tcx(); if let Some(assoc_item) = tcx.opt_associated_item(fn_def_id.to_def_id()) && assoc_item.container == ty::AssocItemContainer::TraitContainer { for arg in fn_output.walk() { if let ty::GenericArgKind::Type(ty) = arg.unpack() && let ty::Alias(ty::Opaque, proj) = ty.kind() && tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder && tcx.impl_trait_in_trait_parent(proj.def_id) == fn_def_id.to_def_id() { let span = tcx.def_span(proj.def_id); let bounds = wfcx.tcx().explicit_item_bounds(proj.def_id); let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| { let bound = ty::EarlyBinder(bound).subst(tcx, proj.substs); let normalized_bound = wfcx.normalize(span, None, bound); traits::wf::predicate_obligations( wfcx.infcx, wfcx.param_env, wfcx.body_def_id, normalized_bound, bound_span, ) }); wfcx.register_obligations(wf_obligations); } } } } const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box`, \ `self: Rc`, `self: Arc`, or `self: Pin

` (where P is one \ of the previous types except `Self`)"; #[instrument(level = "debug", skip(wfcx))] fn check_method_receiver<'tcx>( wfcx: &WfCheckingCtxt<'_, 'tcx>, fn_sig: &hir::FnSig<'_>, method: ty::AssocItem, self_ty: Ty<'tcx>, ) { let tcx = wfcx.tcx(); if !method.fn_has_self_parameter { return; } let span = fn_sig.decl.inputs[0].span; let sig = tcx.fn_sig(method.def_id).subst_identity(); let sig = tcx.liberate_late_bound_regions(method.def_id, sig); let sig = wfcx.normalize(span, None, sig); debug!("check_method_receiver: sig={:?}", sig); let self_ty = wfcx.normalize(span, None, self_ty); let receiver_ty = sig.inputs()[0]; let receiver_ty = wfcx.normalize(span, None, receiver_ty); if tcx.features().arbitrary_self_types { if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) { // Report error; `arbitrary_self_types` was enabled. e0307(tcx, span, receiver_ty); } } else { if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, false) { if receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) { // Report error; would have worked with `arbitrary_self_types`. feature_err( &tcx.sess.parse_sess, sym::arbitrary_self_types, span, &format!( "`{receiver_ty}` cannot be used as the type of `self` without \ the `arbitrary_self_types` feature", ), ) .help(HELP_FOR_SELF_TYPE) .emit(); } else { // Report error; would not have worked with `arbitrary_self_types`. e0307(tcx, span, receiver_ty); } } } } fn e0307(tcx: TyCtxt<'_>, span: Span, receiver_ty: Ty<'_>) { struct_span_err!( tcx.sess.diagnostic(), span, E0307, "invalid `self` parameter type: {receiver_ty}" ) .note("type of `self` must be `Self` or a type that dereferences to it") .help(HELP_FOR_SELF_TYPE) .emit(); } /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more /// strict: `receiver_ty` must implement `Receiver` and directly implement /// `Deref`. /// /// N.B., there are cases this function returns `true` but causes an error to be emitted, /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the /// wrong lifetime. Be careful of this if you are calling this function speculatively. fn receiver_is_valid<'tcx>( wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, receiver_ty: Ty<'tcx>, self_ty: Ty<'tcx>, arbitrary_self_types_enabled: bool, ) -> bool { let infcx = wfcx.infcx; let tcx = wfcx.tcx(); let cause = ObligationCause::new(span, wfcx.body_def_id, traits::ObligationCauseCode::MethodReceiver); let can_eq_self = |ty| infcx.can_eq(wfcx.param_env, self_ty, ty); // `self: Self` is always valid. if can_eq_self(receiver_ty) { if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, receiver_ty) { infcx.err_ctxt().report_mismatched_types(&cause, self_ty, receiver_ty, err).emit(); } return true; } let mut autoderef = Autoderef::new(infcx, wfcx.param_env, wfcx.body_def_id, span, receiver_ty); // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`. if arbitrary_self_types_enabled { autoderef = autoderef.include_raw_pointers(); } // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it. autoderef.next(); let receiver_trait_def_id = tcx.require_lang_item(LangItem::Receiver, Some(span)); // Keep dereferencing `receiver_ty` until we get to `self_ty`. loop { if let Some((potential_self_ty, _)) = autoderef.next() { debug!( "receiver_is_valid: potential self type `{:?}` to match `{:?}`", potential_self_ty, self_ty ); if can_eq_self(potential_self_ty) { wfcx.register_obligations(autoderef.into_obligations()); if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, potential_self_ty) { infcx .err_ctxt() .report_mismatched_types(&cause, self_ty, potential_self_ty, err) .emit(); } break; } else { // Without `feature(arbitrary_self_types)`, we require that each step in the // deref chain implement `receiver` if !arbitrary_self_types_enabled && !receiver_is_implemented( wfcx, receiver_trait_def_id, cause.clone(), potential_self_ty, ) { return false; } } } else { debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty); // If the receiver already has errors reported due to it, consider it valid to avoid // unnecessary errors (#58712). return receiver_ty.references_error(); } } // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`. if !arbitrary_self_types_enabled && !receiver_is_implemented(wfcx, receiver_trait_def_id, cause.clone(), receiver_ty) { return false; } true } fn receiver_is_implemented<'tcx>( wfcx: &WfCheckingCtxt<'_, 'tcx>, receiver_trait_def_id: DefId, cause: ObligationCause<'tcx>, receiver_ty: Ty<'tcx>, ) -> bool { let tcx = wfcx.tcx(); let trait_ref = ty::Binder::dummy(tcx.mk_trait_ref(receiver_trait_def_id, [receiver_ty])); let obligation = traits::Obligation::new(tcx, cause, wfcx.param_env, trait_ref); if wfcx.infcx.predicate_must_hold_modulo_regions(&obligation) { true } else { debug!( "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait", receiver_ty ); false } } fn check_variances_for_type_defn<'tcx>( tcx: TyCtxt<'tcx>, item: &hir::Item<'tcx>, hir_generics: &hir::Generics<'_>, ) { let ty = tcx.type_of(item.owner_id).subst_identity(); if tcx.has_error_field(ty) { return; } let ty_predicates = tcx.predicates_of(item.owner_id); assert_eq!(ty_predicates.parent, None); let variances = tcx.variances_of(item.owner_id); let mut constrained_parameters: FxHashSet<_> = variances .iter() .enumerate() .filter(|&(_, &variance)| variance != ty::Bivariant) .map(|(index, _)| Parameter(index as u32)) .collect(); identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters); // Lazily calculated because it is only needed in case of an error. let explicitly_bounded_params = LazyCell::new(|| { let icx = crate::collect::ItemCtxt::new(tcx, item.owner_id.to_def_id()); hir_generics .predicates .iter() .filter_map(|predicate| match predicate { hir::WherePredicate::BoundPredicate(predicate) => { match icx.to_ty(predicate.bounded_ty).kind() { ty::Param(data) => Some(Parameter(data.index)), _ => None, } } _ => None, }) .collect::>() }); for (index, _) in variances.iter().enumerate() { let parameter = Parameter(index as u32); if constrained_parameters.contains(¶meter) { continue; } let param = &hir_generics.params[index]; match param.name { hir::ParamName::Error => {} _ => { let has_explicit_bounds = explicitly_bounded_params.contains(¶meter); report_bivariance(tcx, param, has_explicit_bounds); } } } } fn report_bivariance( tcx: TyCtxt<'_>, param: &rustc_hir::GenericParam<'_>, has_explicit_bounds: bool, ) -> ErrorGuaranteed { let span = param.span; let param_name = param.name.ident().name; let mut err = error_392(tcx, span, param_name); let suggested_marker_id = tcx.lang_items().phantom_data(); // Help is available only in presence of lang items. let msg = if let Some(def_id) = suggested_marker_id { format!( "consider removing `{}`, referring to it in a field, or using a marker such as `{}`", param_name, tcx.def_path_str(def_id), ) } else { format!("consider removing `{param_name}` or referring to it in a field") }; err.help(&msg); if matches!(param.kind, hir::GenericParamKind::Type { .. }) && !has_explicit_bounds { err.help(&format!( "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead", param_name )); } err.emit() } impl<'tcx> WfCheckingCtxt<'_, 'tcx> { /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that /// aren't true. #[instrument(level = "debug", skip(self))] fn check_false_global_bounds(&mut self) { let tcx = self.ocx.infcx.tcx; let mut span = self.span; let empty_env = ty::ParamEnv::empty(); let predicates_with_span = tcx.predicates_of(self.body_def_id).predicates.iter().copied(); // Check elaborated bounds. let implied_obligations = traits::elaborate_predicates_with_span(tcx, predicates_with_span); for obligation in implied_obligations { // We lower empty bounds like `Vec:` as // `WellFormed(Vec)`, which will later get checked by // regular WF checking if let ty::PredicateKind::WellFormed(..) = obligation.predicate.kind().skip_binder() { continue; } let pred = obligation.predicate; // Match the existing behavior. if pred.is_global() && !pred.has_late_bound_vars() { let pred = self.normalize(span, None, pred); let hir_node = tcx.hir().find_by_def_id(self.body_def_id); // only use the span of the predicate clause (#90869) if let Some(hir::Generics { predicates, .. }) = hir_node.and_then(|node| node.generics()) { let obligation_span = obligation.cause.span(); span = predicates .iter() // There seems to be no better way to find out which predicate we are in .find(|pred| pred.span().contains(obligation_span)) .map(|pred| pred.span()) .unwrap_or(obligation_span); } let obligation = traits::Obligation::new( tcx, traits::ObligationCause::new(span, self.body_def_id, traits::TrivialBound), empty_env, pred, ); self.ocx.register_obligation(obligation); } } } } fn check_mod_type_wf(tcx: TyCtxt<'_>, module: LocalDefId) { let items = tcx.hir_module_items(module); items.par_items(|item| tcx.ensure().check_well_formed(item.owner_id)); items.par_impl_items(|item| tcx.ensure().check_well_formed(item.owner_id)); items.par_trait_items(|item| tcx.ensure().check_well_formed(item.owner_id)); items.par_foreign_items(|item| tcx.ensure().check_well_formed(item.owner_id)); } fn error_392( tcx: TyCtxt<'_>, span: Span, param_name: Symbol, ) -> DiagnosticBuilder<'_, ErrorGuaranteed> { let mut err = struct_span_err!(tcx.sess, span, E0392, "parameter `{param_name}` is never used"); err.span_label(span, "unused parameter"); err } pub fn provide(providers: &mut Providers) { *providers = Providers { check_mod_type_wf, check_well_formed, ..*providers }; }