| use crate::infer::InferCtxt; |
| use crate::traits; |
| use rustc_hir as hir; |
| use rustc_hir::lang_items::LangItem; |
| use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt}; |
| use rustc_middle::ty::{GenericArg, GenericArgKind, GenericArgsRef}; |
| use rustc_span::def_id::{DefId, LocalDefId, CRATE_DEF_ID}; |
| use rustc_span::{Span, DUMMY_SP}; |
| |
| use std::iter; |
| /// Returns the set of obligations needed to make `arg` well-formed. |
| /// If `arg` contains unresolved inference variables, this may include |
| /// further WF obligations. However, if `arg` IS an unresolved |
| /// inference variable, returns `None`, because we are not able to |
| /// make any progress at all. This is to prevent "livelock" where we |
| /// say "$0 is WF if $0 is WF". |
| pub fn obligations<'tcx>( |
| infcx: &InferCtxt<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| body_id: LocalDefId, |
| recursion_depth: usize, |
| arg: GenericArg<'tcx>, |
| span: Span, |
| ) -> Option<Vec<traits::PredicateObligation<'tcx>>> { |
| // Handle the "livelock" case (see comment above) by bailing out if necessary. |
| let arg = match arg.unpack() { |
| GenericArgKind::Type(ty) => { |
| match ty.kind() { |
| ty::Infer(ty::TyVar(_)) => { |
| let resolved_ty = infcx.shallow_resolve(ty); |
| if resolved_ty == ty { |
| // No progress, bail out to prevent "livelock". |
| return None; |
| } else { |
| resolved_ty |
| } |
| } |
| _ => ty, |
| } |
| .into() |
| } |
| GenericArgKind::Const(ct) => { |
| match ct.kind() { |
| ty::ConstKind::Infer(_) => { |
| let resolved = infcx.shallow_resolve(ct); |
| if resolved == ct { |
| // No progress. |
| return None; |
| } else { |
| resolved |
| } |
| } |
| _ => ct, |
| } |
| .into() |
| } |
| // There is nothing we have to do for lifetimes. |
| GenericArgKind::Lifetime(..) => return Some(Vec::new()), |
| }; |
| |
| let mut wf = |
| WfPredicates { infcx, param_env, body_id, span, out: vec![], recursion_depth, item: None }; |
| wf.compute(arg); |
| debug!("wf::obligations({:?}, body_id={:?}) = {:?}", arg, body_id, wf.out); |
| |
| let result = wf.normalize(infcx); |
| debug!("wf::obligations({:?}, body_id={:?}) ~~> {:?}", arg, body_id, result); |
| Some(result) |
| } |
| |
| /// Compute the predicates that are required for a type to be well-formed. |
| /// |
| /// This is only intended to be used in the new solver, since it does not |
| /// take into account recursion depth or proper error-reporting spans. |
| pub fn unnormalized_obligations<'tcx>( |
| infcx: &InferCtxt<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| arg: GenericArg<'tcx>, |
| ) -> Option<Vec<traits::PredicateObligation<'tcx>>> { |
| debug_assert_eq!(arg, infcx.resolve_vars_if_possible(arg)); |
| |
| // However, if `arg` IS an unresolved inference variable, returns `None`, |
| // because we are not able to make any progress at all. This is to prevent |
| // "livelock" where we say "$0 is WF if $0 is WF". |
| if arg.is_non_region_infer() { |
| return None; |
| } |
| |
| if let ty::GenericArgKind::Lifetime(..) = arg.unpack() { |
| return Some(vec![]); |
| } |
| |
| let mut wf = WfPredicates { |
| infcx, |
| param_env, |
| body_id: CRATE_DEF_ID, |
| span: DUMMY_SP, |
| out: vec![], |
| recursion_depth: 0, |
| item: None, |
| }; |
| wf.compute(arg); |
| Some(wf.out) |
| } |
| |
| /// Returns the obligations that make this trait reference |
| /// well-formed. For example, if there is a trait `Set` defined like |
| /// `trait Set<K:Eq>`, then the trait reference `Foo: Set<Bar>` is WF |
| /// if `Bar: Eq`. |
| pub fn trait_obligations<'tcx>( |
| infcx: &InferCtxt<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| body_id: LocalDefId, |
| trait_pred: &ty::TraitPredicate<'tcx>, |
| span: Span, |
| item: &'tcx hir::Item<'tcx>, |
| ) -> Vec<traits::PredicateObligation<'tcx>> { |
| let mut wf = WfPredicates { |
| infcx, |
| param_env, |
| body_id, |
| span, |
| out: vec![], |
| recursion_depth: 0, |
| item: Some(item), |
| }; |
| wf.compute_trait_pred(trait_pred, Elaborate::All); |
| debug!(obligations = ?wf.out); |
| wf.normalize(infcx) |
| } |
| |
| #[instrument(skip(infcx), ret)] |
| pub fn predicate_obligations<'tcx>( |
| infcx: &InferCtxt<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| body_id: LocalDefId, |
| predicate: ty::Predicate<'tcx>, |
| span: Span, |
| ) -> Vec<traits::PredicateObligation<'tcx>> { |
| let mut wf = WfPredicates { |
| infcx, |
| param_env, |
| body_id, |
| span, |
| out: vec![], |
| recursion_depth: 0, |
| item: None, |
| }; |
| |
| // It's ok to skip the binder here because wf code is prepared for it |
| match predicate.kind().skip_binder() { |
| ty::PredicateKind::Clause(ty::ClauseKind::Trait(t)) => { |
| wf.compute_trait_pred(&t, Elaborate::None); |
| } |
| ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(..)) => {} |
| ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate( |
| ty, |
| _reg, |
| ))) => { |
| wf.compute(ty.into()); |
| } |
| ty::PredicateKind::Clause(ty::ClauseKind::Projection(t)) => { |
| wf.compute_projection(t.projection_ty); |
| wf.compute(match t.term.unpack() { |
| ty::TermKind::Ty(ty) => ty.into(), |
| ty::TermKind::Const(c) => c.into(), |
| }) |
| } |
| ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => { |
| wf.compute(ct.into()); |
| wf.compute(ty.into()); |
| } |
| ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => { |
| wf.compute(arg); |
| } |
| |
| ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(ct)) => { |
| wf.compute(ct.into()); |
| } |
| |
| ty::PredicateKind::ObjectSafe(_) |
| | ty::PredicateKind::ClosureKind(..) |
| | ty::PredicateKind::Subtype(..) |
| | ty::PredicateKind::Coerce(..) |
| | ty::PredicateKind::ConstEquate(..) |
| | ty::PredicateKind::Ambiguous |
| | ty::PredicateKind::AliasRelate(..) => { |
| bug!("We should only wf check where clauses, unexpected predicate: {predicate:?}") |
| } |
| } |
| |
| wf.normalize(infcx) |
| } |
| |
| struct WfPredicates<'a, 'tcx> { |
| infcx: &'a InferCtxt<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| body_id: LocalDefId, |
| span: Span, |
| out: Vec<traits::PredicateObligation<'tcx>>, |
| recursion_depth: usize, |
| item: Option<&'tcx hir::Item<'tcx>>, |
| } |
| |
| /// Controls whether we "elaborate" supertraits and so forth on the WF |
| /// predicates. This is a kind of hack to address #43784. The |
| /// underlying problem in that issue was a trait structure like: |
| /// |
| /// ```ignore (illustrative) |
| /// trait Foo: Copy { } |
| /// trait Bar: Foo { } |
| /// impl<T: Bar> Foo for T { } |
| /// impl<T> Bar for T { } |
| /// ``` |
| /// |
| /// Here, in the `Foo` impl, we will check that `T: Copy` holds -- but |
| /// we decide that this is true because `T: Bar` is in the |
| /// where-clauses (and we can elaborate that to include `T: |
| /// Copy`). This wouldn't be a problem, except that when we check the |
| /// `Bar` impl, we decide that `T: Foo` must hold because of the `Foo` |
| /// impl. And so nowhere did we check that `T: Copy` holds! |
| /// |
| /// To resolve this, we elaborate the WF requirements that must be |
| /// proven when checking impls. This means that (e.g.) the `impl Bar |
| /// for T` will be forced to prove not only that `T: Foo` but also `T: |
| /// Copy` (which it won't be able to do, because there is no `Copy` |
| /// impl for `T`). |
| #[derive(Debug, PartialEq, Eq, Copy, Clone)] |
| enum Elaborate { |
| All, |
| None, |
| } |
| |
| fn extend_cause_with_original_assoc_item_obligation<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| trait_ref: &ty::TraitRef<'tcx>, |
| item: Option<&hir::Item<'tcx>>, |
| cause: &mut traits::ObligationCause<'tcx>, |
| pred: ty::Predicate<'tcx>, |
| ) { |
| debug!( |
| "extended_cause_with_original_assoc_item_obligation {:?} {:?} {:?} {:?}", |
| trait_ref, item, cause, pred |
| ); |
| let (items, impl_def_id) = match item { |
| Some(hir::Item { kind: hir::ItemKind::Impl(impl_), owner_id, .. }) => { |
| (impl_.items, *owner_id) |
| } |
| _ => return, |
| }; |
| let fix_span = |
| |impl_item_ref: &hir::ImplItemRef| match tcx.hir().impl_item(impl_item_ref.id).kind { |
| hir::ImplItemKind::Const(ty, _) | hir::ImplItemKind::Type(ty) => ty.span, |
| _ => impl_item_ref.span, |
| }; |
| |
| // It is fine to skip the binder as we don't care about regions here. |
| match pred.kind().skip_binder() { |
| ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj)) => { |
| // The obligation comes not from the current `impl` nor the `trait` being implemented, |
| // but rather from a "second order" obligation, where an associated type has a |
| // projection coming from another associated type. See |
| // `tests/ui/associated-types/point-at-type-on-obligation-failure.rs` and |
| // `traits-assoc-type-in-supertrait-bad.rs`. |
| if let Some(ty::Alias(ty::Projection, projection_ty)) = proj.term.ty().map(|ty| ty.kind()) |
| && let Some(&impl_item_id) = |
| tcx.impl_item_implementor_ids(impl_def_id).get(&projection_ty.def_id) |
| && let Some(impl_item_span) = items |
| .iter() |
| .find(|item| item.id.owner_id.to_def_id() == impl_item_id) |
| .map(fix_span) |
| { |
| cause.span = impl_item_span; |
| } |
| } |
| ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => { |
| // An associated item obligation born out of the `trait` failed to be met. An example |
| // can be seen in `ui/associated-types/point-at-type-on-obligation-failure-2.rs`. |
| debug!("extended_cause_with_original_assoc_item_obligation trait proj {:?}", pred); |
| if let ty::Alias(ty::Projection, ty::AliasTy { def_id, .. }) = *pred.self_ty().kind() |
| && let Some(&impl_item_id) = |
| tcx.impl_item_implementor_ids(impl_def_id).get(&def_id) |
| && let Some(impl_item_span) = items |
| .iter() |
| .find(|item| item.id.owner_id.to_def_id() == impl_item_id) |
| .map(fix_span) |
| { |
| cause.span = impl_item_span; |
| } |
| } |
| _ => {} |
| } |
| } |
| |
| impl<'a, 'tcx> WfPredicates<'a, 'tcx> { |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.infcx.tcx |
| } |
| |
| fn cause(&self, code: traits::ObligationCauseCode<'tcx>) -> traits::ObligationCause<'tcx> { |
| traits::ObligationCause::new(self.span, self.body_id, code) |
| } |
| |
| fn normalize(self, infcx: &InferCtxt<'tcx>) -> Vec<traits::PredicateObligation<'tcx>> { |
| // Do not normalize `wf` obligations with the new solver. |
| // |
| // The current deep normalization routine with the new solver does not |
| // handle ambiguity and the new solver correctly deals with unnnormalized goals. |
| // If the user relies on normalized types, e.g. for `fn implied_outlives_bounds`, |
| // it is their responsibility to normalize while avoiding ambiguity. |
| if infcx.next_trait_solver() { |
| return self.out; |
| } |
| |
| let cause = self.cause(traits::WellFormed(None)); |
| let param_env = self.param_env; |
| let mut obligations = Vec::with_capacity(self.out.len()); |
| for mut obligation in self.out { |
| assert!(!obligation.has_escaping_bound_vars()); |
| let mut selcx = traits::SelectionContext::new(infcx); |
| // Don't normalize the whole obligation, the param env is either |
| // already normalized, or we're currently normalizing the |
| // param_env. Either way we should only normalize the predicate. |
| let normalized_predicate = traits::project::normalize_with_depth_to( |
| &mut selcx, |
| param_env, |
| cause.clone(), |
| self.recursion_depth, |
| obligation.predicate, |
| &mut obligations, |
| ); |
| obligation.predicate = normalized_predicate; |
| obligations.push(obligation); |
| } |
| obligations |
| } |
| |
| /// Pushes the obligations required for `trait_ref` to be WF into `self.out`. |
| fn compute_trait_pred(&mut self, trait_pred: &ty::TraitPredicate<'tcx>, elaborate: Elaborate) { |
| let tcx = self.tcx(); |
| let trait_ref = &trait_pred.trait_ref; |
| |
| // Negative trait predicates don't require supertraits to hold, just |
| // that their args are WF. |
| if trait_pred.polarity == ty::ImplPolarity::Negative { |
| self.compute_negative_trait_pred(trait_ref); |
| return; |
| } |
| |
| // if the trait predicate is not const, the wf obligations should not be const as well. |
| let obligations = self.nominal_obligations(trait_ref.def_id, trait_ref.args); |
| |
| debug!("compute_trait_pred obligations {:?}", obligations); |
| let param_env = self.param_env; |
| let depth = self.recursion_depth; |
| |
| let item = self.item; |
| |
| let extend = |traits::PredicateObligation { predicate, mut cause, .. }| { |
| if let Some(parent_trait_pred) = predicate.to_opt_poly_trait_pred() { |
| cause = cause.derived_cause( |
| parent_trait_pred, |
| traits::ObligationCauseCode::DerivedObligation, |
| ); |
| } |
| extend_cause_with_original_assoc_item_obligation( |
| tcx, trait_ref, item, &mut cause, predicate, |
| ); |
| traits::Obligation::with_depth(tcx, cause, depth, param_env, predicate) |
| }; |
| |
| if let Elaborate::All = elaborate { |
| let implied_obligations = traits::util::elaborate(tcx, obligations); |
| let implied_obligations = implied_obligations.map(extend); |
| self.out.extend(implied_obligations); |
| } else { |
| self.out.extend(obligations); |
| } |
| |
| self.out.extend( |
| trait_ref |
| .args |
| .iter() |
| .enumerate() |
| .filter(|(_, arg)| { |
| matches!(arg.unpack(), GenericArgKind::Type(..) | GenericArgKind::Const(..)) |
| }) |
| .filter(|(_, arg)| !arg.has_escaping_bound_vars()) |
| .map(|(i, arg)| { |
| let mut cause = traits::ObligationCause::misc(self.span, self.body_id); |
| // The first subst is the self ty - use the correct span for it. |
| if i == 0 { |
| if let Some(hir::ItemKind::Impl(hir::Impl { self_ty, .. })) = |
| item.map(|i| &i.kind) |
| { |
| cause.span = self_ty.span; |
| } |
| } |
| traits::Obligation::with_depth( |
| tcx, |
| cause, |
| depth, |
| param_env, |
| ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed( |
| arg, |
| ))), |
| ) |
| }), |
| ); |
| } |
| |
| // Compute the obligations that are required for `trait_ref` to be WF, |
| // given that it is a *negative* trait predicate. |
| fn compute_negative_trait_pred(&mut self, trait_ref: &ty::TraitRef<'tcx>) { |
| for arg in trait_ref.args { |
| self.compute(arg); |
| } |
| } |
| |
| /// Pushes the obligations required for `trait_ref::Item` to be WF |
| /// into `self.out`. |
| fn compute_projection(&mut self, data: ty::AliasTy<'tcx>) { |
| // A projection is well-formed if |
| // |
| // (a) its predicates hold (*) |
| // (b) its args are wf |
| // |
| // (*) The predicates of an associated type include the predicates of |
| // the trait that it's contained in. For example, given |
| // |
| // trait A<T>: Clone { |
| // type X where T: Copy; |
| // } |
| // |
| // The predicates of `<() as A<i32>>::X` are: |
| // [ |
| // `(): Sized` |
| // `(): Clone` |
| // `(): A<i32>` |
| // `i32: Sized` |
| // `i32: Clone` |
| // `i32: Copy` |
| // ] |
| let obligations = self.nominal_obligations(data.def_id, data.args); |
| self.out.extend(obligations); |
| |
| self.compute_projection_args(data.args); |
| } |
| |
| fn compute_inherent_projection(&mut self, data: ty::AliasTy<'tcx>) { |
| // An inherent projection is well-formed if |
| // |
| // (a) its predicates hold (*) |
| // (b) its args are wf |
| // |
| // (*) The predicates of an inherent associated type include the |
| // predicates of the impl that it's contained in. |
| |
| if !data.self_ty().has_escaping_bound_vars() { |
| // FIXME(inherent_associated_types): Should this happen inside of a snapshot? |
| // FIXME(inherent_associated_types): This is incompatible with the new solver and lazy norm! |
| let args = traits::project::compute_inherent_assoc_ty_args( |
| &mut traits::SelectionContext::new(self.infcx), |
| self.param_env, |
| data, |
| self.cause(traits::WellFormed(None)), |
| self.recursion_depth, |
| &mut self.out, |
| ); |
| let obligations = self.nominal_obligations(data.def_id, args); |
| self.out.extend(obligations); |
| } |
| |
| self.compute_projection_args(data.args); |
| } |
| |
| fn compute_projection_args(&mut self, args: GenericArgsRef<'tcx>) { |
| let tcx = self.tcx(); |
| let cause = self.cause(traits::WellFormed(None)); |
| let param_env = self.param_env; |
| let depth = self.recursion_depth; |
| |
| self.out.extend( |
| args.iter() |
| .filter(|arg| { |
| matches!(arg.unpack(), GenericArgKind::Type(..) | GenericArgKind::Const(..)) |
| }) |
| .filter(|arg| !arg.has_escaping_bound_vars()) |
| .map(|arg| { |
| traits::Obligation::with_depth( |
| tcx, |
| cause.clone(), |
| depth, |
| param_env, |
| ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed( |
| arg, |
| ))), |
| ) |
| }), |
| ); |
| } |
| |
| fn require_sized(&mut self, subty: Ty<'tcx>, cause: traits::ObligationCauseCode<'tcx>) { |
| if !subty.has_escaping_bound_vars() { |
| let cause = self.cause(cause); |
| let trait_ref = |
| ty::TraitRef::from_lang_item(self.tcx(), LangItem::Sized, cause.span, [subty]); |
| self.out.push(traits::Obligation::with_depth( |
| self.tcx(), |
| cause, |
| self.recursion_depth, |
| self.param_env, |
| ty::Binder::dummy(trait_ref), |
| )); |
| } |
| } |
| |
| /// Pushes all the predicates needed to validate that `ty` is WF into `out`. |
| #[instrument(level = "debug", skip(self))] |
| fn compute(&mut self, arg: GenericArg<'tcx>) { |
| let mut walker = arg.walk(); |
| let param_env = self.param_env; |
| let depth = self.recursion_depth; |
| while let Some(arg) = walker.next() { |
| debug!(?arg, ?self.out); |
| let ty = match arg.unpack() { |
| GenericArgKind::Type(ty) => ty, |
| |
| // No WF constraints for lifetimes being present, any outlives |
| // obligations are handled by the parent (e.g. `ty::Ref`). |
| GenericArgKind::Lifetime(_) => continue, |
| |
| GenericArgKind::Const(ct) => { |
| match ct.kind() { |
| ty::ConstKind::Unevaluated(uv) => { |
| if !ct.has_escaping_bound_vars() { |
| let obligations = self.nominal_obligations(uv.def, uv.args); |
| self.out.extend(obligations); |
| |
| let predicate = ty::Binder::dummy(ty::PredicateKind::Clause( |
| ty::ClauseKind::ConstEvaluatable(ct), |
| )); |
| let cause = self.cause(traits::WellFormed(None)); |
| self.out.push(traits::Obligation::with_depth( |
| self.tcx(), |
| cause, |
| self.recursion_depth, |
| self.param_env, |
| predicate, |
| )); |
| } |
| } |
| ty::ConstKind::Infer(_) => { |
| let cause = self.cause(traits::WellFormed(None)); |
| |
| self.out.push(traits::Obligation::with_depth( |
| self.tcx(), |
| cause, |
| self.recursion_depth, |
| self.param_env, |
| ty::Binder::dummy(ty::PredicateKind::Clause( |
| ty::ClauseKind::WellFormed(ct.into()), |
| )), |
| )); |
| } |
| ty::ConstKind::Expr(_) => { |
| // FIXME(generic_const_exprs): this doesn't verify that given `Expr(N + 1)` the |
| // trait bound `typeof(N): Add<typeof(1)>` holds. This is currently unnecessary |
| // as `ConstKind::Expr` is only produced via normalization of `ConstKind::Unevaluated` |
| // which means that the `DefId` would have been typeck'd elsewhere. However in |
| // the future we may allow directly lowering to `ConstKind::Expr` in which case |
| // we would not be proving bounds we should. |
| |
| let predicate = ty::Binder::dummy(ty::PredicateKind::Clause( |
| ty::ClauseKind::ConstEvaluatable(ct), |
| )); |
| let cause = self.cause(traits::WellFormed(None)); |
| self.out.push(traits::Obligation::with_depth( |
| self.tcx(), |
| cause, |
| self.recursion_depth, |
| self.param_env, |
| predicate, |
| )); |
| } |
| |
| ty::ConstKind::Error(_) |
| | ty::ConstKind::Param(_) |
| | ty::ConstKind::Bound(..) |
| | ty::ConstKind::Placeholder(..) => { |
| // These variants are trivially WF, so nothing to do here. |
| } |
| ty::ConstKind::Value(..) => { |
| // FIXME: Enforce that values are structurally-matchable. |
| } |
| } |
| continue; |
| } |
| }; |
| |
| debug!("wf bounds for ty={:?} ty.kind={:#?}", ty, ty.kind()); |
| |
| match *ty.kind() { |
| ty::Bool |
| | ty::Char |
| | ty::Int(..) |
| | ty::Uint(..) |
| | ty::Float(..) |
| | ty::Error(_) |
| | ty::Str |
| | ty::GeneratorWitness(..) |
| | ty::GeneratorWitnessMIR(..) |
| | ty::Never |
| | ty::Param(_) |
| | ty::Bound(..) |
| | ty::Placeholder(..) |
| | ty::Foreign(..) => { |
| // WfScalar, WfParameter, etc |
| } |
| |
| // Can only infer to `ty::Int(_) | ty::Uint(_)`. |
| ty::Infer(ty::IntVar(_)) => {} |
| |
| // Can only infer to `ty::Float(_)`. |
| ty::Infer(ty::FloatVar(_)) => {} |
| |
| ty::Slice(subty) => { |
| self.require_sized(subty, traits::SliceOrArrayElem); |
| } |
| |
| ty::Array(subty, _) => { |
| self.require_sized(subty, traits::SliceOrArrayElem); |
| // Note that we handle the len is implicitly checked while walking `arg`. |
| } |
| |
| ty::Tuple(ref tys) => { |
| if let Some((_last, rest)) = tys.split_last() { |
| for &elem in rest { |
| self.require_sized(elem, traits::TupleElem); |
| } |
| } |
| } |
| |
| ty::RawPtr(_) => { |
| // Simple cases that are WF if their type args are WF. |
| } |
| |
| ty::Alias(ty::Projection, data) => { |
| walker.skip_current_subtree(); // Subtree handled by compute_projection. |
| self.compute_projection(data); |
| } |
| ty::Alias(ty::Inherent, data) => { |
| walker.skip_current_subtree(); // Subtree handled by compute_inherent_projection. |
| self.compute_inherent_projection(data); |
| } |
| |
| ty::Adt(def, args) => { |
| // WfNominalType |
| let obligations = self.nominal_obligations(def.did(), args); |
| self.out.extend(obligations); |
| } |
| |
| ty::FnDef(did, args) => { |
| let obligations = self.nominal_obligations(did, args); |
| self.out.extend(obligations); |
| } |
| |
| ty::Ref(r, rty, _) => { |
| // WfReference |
| if !r.has_escaping_bound_vars() && !rty.has_escaping_bound_vars() { |
| let cause = self.cause(traits::ReferenceOutlivesReferent(ty)); |
| self.out.push(traits::Obligation::with_depth( |
| self.tcx(), |
| cause, |
| depth, |
| param_env, |
| ty::Binder::dummy(ty::PredicateKind::Clause( |
| ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(rty, r)), |
| )), |
| )); |
| } |
| } |
| |
| ty::Generator(did, args, ..) => { |
| // Walk ALL the types in the generator: this will |
| // include the upvar types as well as the yield |
| // type. Note that this is mildly distinct from |
| // the closure case, where we have to be careful |
| // about the signature of the closure. We don't |
| // have the problem of implied bounds here since |
| // generators don't take arguments. |
| let obligations = self.nominal_obligations(did, args); |
| self.out.extend(obligations); |
| } |
| |
| ty::Closure(did, args) => { |
| // Only check the upvar types for WF, not the rest |
| // of the types within. This is needed because we |
| // capture the signature and it may not be WF |
| // without the implied bounds. Consider a closure |
| // like `|x: &'a T|` -- it may be that `T: 'a` is |
| // not known to hold in the creator's context (and |
| // indeed the closure may not be invoked by its |
| // creator, but rather turned to someone who *can* |
| // verify that). |
| // |
| // The special treatment of closures here really |
| // ought not to be necessary either; the problem |
| // is related to #25860 -- there is no way for us |
| // to express a fn type complete with the implied |
| // bounds that it is assuming. I think in reality |
| // the WF rules around fn are a bit messed up, and |
| // that is the rot problem: `fn(&'a T)` should |
| // probably always be WF, because it should be |
| // shorthand for something like `where(T: 'a) { |
| // fn(&'a T) }`, as discussed in #25860. |
| walker.skip_current_subtree(); // subtree handled below |
| // FIXME(eddyb) add the type to `walker` instead of recursing. |
| self.compute(args.as_closure().tupled_upvars_ty().into()); |
| // Note that we cannot skip the generic types |
| // types. Normally, within the fn |
| // body where they are created, the generics will |
| // always be WF, and outside of that fn body we |
| // are not directly inspecting closure types |
| // anyway, except via auto trait matching (which |
| // only inspects the upvar types). |
| // But when a closure is part of a type-alias-impl-trait |
| // then the function that created the defining site may |
| // have had more bounds available than the type alias |
| // specifies. This may cause us to have a closure in the |
| // hidden type that is not actually well formed and |
| // can cause compiler crashes when the user abuses unsafe |
| // code to procure such a closure. |
| // See tests/ui/type-alias-impl-trait/wf_check_closures.rs |
| let obligations = self.nominal_obligations(did, args); |
| self.out.extend(obligations); |
| } |
| |
| ty::FnPtr(_) => { |
| // let the loop iterate into the argument/return |
| // types appearing in the fn signature |
| } |
| |
| ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => { |
| // All of the requirements on type parameters |
| // have already been checked for `impl Trait` in |
| // return position. We do need to check type-alias-impl-trait though. |
| if self.tcx().is_type_alias_impl_trait(def_id) { |
| let obligations = self.nominal_obligations(def_id, args); |
| self.out.extend(obligations); |
| } |
| } |
| |
| ty::Alias(ty::Weak, ty::AliasTy { def_id, args, .. }) => { |
| let obligations = self.nominal_obligations(def_id, args); |
| self.out.extend(obligations); |
| } |
| |
| ty::Dynamic(data, r, _) => { |
| // WfObject |
| // |
| // Here, we defer WF checking due to higher-ranked |
| // regions. This is perhaps not ideal. |
| self.from_object_ty(ty, data, r); |
| |
| // FIXME(#27579) RFC also considers adding trait |
| // obligations that don't refer to Self and |
| // checking those |
| |
| let defer_to_coercion = self.tcx().features().object_safe_for_dispatch; |
| |
| if !defer_to_coercion { |
| let cause = self.cause(traits::WellFormed(None)); |
| let component_traits = data.auto_traits().chain(data.principal_def_id()); |
| let tcx = self.tcx(); |
| self.out.extend(component_traits.map(|did| { |
| traits::Obligation::with_depth( |
| tcx, |
| cause.clone(), |
| depth, |
| param_env, |
| ty::Binder::dummy(ty::PredicateKind::ObjectSafe(did)), |
| ) |
| })); |
| } |
| } |
| |
| // Inference variables are the complicated case, since we don't |
| // know what type they are. We do two things: |
| // |
| // 1. Check if they have been resolved, and if so proceed with |
| // THAT type. |
| // 2. If not, we've at least simplified things (e.g., we went |
| // from `Vec<$0>: WF` to `$0: WF`), so we can |
| // register a pending obligation and keep |
| // moving. (Goal is that an "inductive hypothesis" |
| // is satisfied to ensure termination.) |
| // See also the comment on `fn obligations`, describing "livelock" |
| // prevention, which happens before this can be reached. |
| ty::Infer(_) => { |
| let cause = self.cause(traits::WellFormed(None)); |
| self.out.push(traits::Obligation::with_depth( |
| self.tcx(), |
| cause, |
| self.recursion_depth, |
| param_env, |
| ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed( |
| ty.into(), |
| ))), |
| )); |
| } |
| } |
| |
| debug!(?self.out); |
| } |
| } |
| |
| #[instrument(level = "debug", skip(self))] |
| fn nominal_obligations( |
| &mut self, |
| def_id: DefId, |
| args: GenericArgsRef<'tcx>, |
| ) -> Vec<traits::PredicateObligation<'tcx>> { |
| let predicates = self.tcx().predicates_of(def_id); |
| let mut origins = vec![def_id; predicates.predicates.len()]; |
| let mut head = predicates; |
| while let Some(parent) = head.parent { |
| head = self.tcx().predicates_of(parent); |
| origins.extend(iter::repeat(parent).take(head.predicates.len())); |
| } |
| |
| let predicates = predicates.instantiate(self.tcx(), args); |
| trace!("{:#?}", predicates); |
| debug_assert_eq!(predicates.predicates.len(), origins.len()); |
| |
| iter::zip(predicates, origins.into_iter().rev()) |
| .map(|((pred, span), origin_def_id)| { |
| let code = if span.is_dummy() { |
| traits::ItemObligation(origin_def_id) |
| } else { |
| traits::BindingObligation(origin_def_id, span) |
| }; |
| let cause = self.cause(code); |
| traits::Obligation::with_depth( |
| self.tcx(), |
| cause, |
| self.recursion_depth, |
| self.param_env, |
| pred, |
| ) |
| }) |
| .filter(|pred| !pred.has_escaping_bound_vars()) |
| .collect() |
| } |
| |
| fn from_object_ty( |
| &mut self, |
| ty: Ty<'tcx>, |
| data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>, |
| region: ty::Region<'tcx>, |
| ) { |
| // Imagine a type like this: |
| // |
| // trait Foo { } |
| // trait Bar<'c> : 'c { } |
| // |
| // &'b (Foo+'c+Bar<'d>) |
| // ^ |
| // |
| // In this case, the following relationships must hold: |
| // |
| // 'b <= 'c |
| // 'd <= 'c |
| // |
| // The first conditions is due to the normal region pointer |
| // rules, which say that a reference cannot outlive its |
| // referent. |
| // |
| // The final condition may be a bit surprising. In particular, |
| // you may expect that it would have been `'c <= 'd`, since |
| // usually lifetimes of outer things are conservative |
| // approximations for inner things. However, it works somewhat |
| // differently with trait objects: here the idea is that if the |
| // user specifies a region bound (`'c`, in this case) it is the |
| // "master bound" that *implies* that bounds from other traits are |
| // all met. (Remember that *all bounds* in a type like |
| // `Foo+Bar+Zed` must be met, not just one, hence if we write |
| // `Foo<'x>+Bar<'y>`, we know that the type outlives *both* 'x and |
| // 'y.) |
| // |
| // Note: in fact we only permit builtin traits, not `Bar<'d>`, I |
| // am looking forward to the future here. |
| if !data.has_escaping_bound_vars() && !region.has_escaping_bound_vars() { |
| let implicit_bounds = object_region_bounds(self.tcx(), data); |
| |
| let explicit_bound = region; |
| |
| self.out.reserve(implicit_bounds.len()); |
| for implicit_bound in implicit_bounds { |
| let cause = self.cause(traits::ObjectTypeBound(ty, explicit_bound)); |
| let outlives = |
| ty::Binder::dummy(ty::OutlivesPredicate(explicit_bound, implicit_bound)); |
| self.out.push(traits::Obligation::with_depth( |
| self.tcx(), |
| cause, |
| self.recursion_depth, |
| self.param_env, |
| outlives, |
| )); |
| } |
| } |
| } |
| } |
| |
| /// Given an object type like `SomeTrait + Send`, computes the lifetime |
| /// bounds that must hold on the elided self type. These are derived |
| /// from the declarations of `SomeTrait`, `Send`, and friends -- if |
| /// they declare `trait SomeTrait : 'static`, for example, then |
| /// `'static` would appear in the list. The hard work is done by |
| /// `infer::required_region_bounds`, see that for more information. |
| pub fn object_region_bounds<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| existential_predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>, |
| ) -> Vec<ty::Region<'tcx>> { |
| // Since we don't actually *know* the self type for an object, |
| // this "open(err)" serves as a kind of dummy standin -- basically |
| // a placeholder type. |
| let open_ty = Ty::new_fresh(tcx, 0); |
| |
| let predicates = existential_predicates.iter().filter_map(|predicate| { |
| if let ty::ExistentialPredicate::Projection(_) = predicate.skip_binder() { |
| None |
| } else { |
| Some(predicate.with_self_ty(tcx, open_ty)) |
| } |
| }); |
| |
| required_region_bounds(tcx, open_ty, predicates) |
| } |
| |
| /// Given a set of predicates that apply to an object type, returns |
| /// the region bounds that the (erased) `Self` type must |
| /// outlive. Precisely *because* the `Self` type is erased, the |
| /// parameter `erased_self_ty` must be supplied to indicate what type |
| /// has been used to represent `Self` in the predicates |
| /// themselves. This should really be a unique type; `FreshTy(0)` is a |
| /// popular choice. |
| /// |
| /// N.B., in some cases, particularly around higher-ranked bounds, |
| /// this function returns a kind of conservative approximation. |
| /// That is, all regions returned by this function are definitely |
| /// required, but there may be other region bounds that are not |
| /// returned, as well as requirements like `for<'a> T: 'a`. |
| /// |
| /// Requires that trait definitions have been processed so that we can |
| /// elaborate predicates and walk supertraits. |
| #[instrument(skip(tcx, predicates), level = "debug", ret)] |
| pub(crate) fn required_region_bounds<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| erased_self_ty: Ty<'tcx>, |
| predicates: impl Iterator<Item = ty::Clause<'tcx>>, |
| ) -> Vec<ty::Region<'tcx>> { |
| assert!(!erased_self_ty.has_escaping_bound_vars()); |
| |
| traits::elaborate(tcx, predicates) |
| .filter_map(|pred| { |
| debug!(?pred); |
| match pred.kind().skip_binder() { |
| ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ref t, ref r)) => { |
| // Search for a bound of the form `erased_self_ty |
| // : 'a`, but be wary of something like `for<'a> |
| // erased_self_ty : 'a` (we interpret a |
| // higher-ranked bound like that as 'static, |
| // though at present the code in `fulfill.rs` |
| // considers such bounds to be unsatisfiable, so |
| // it's kind of a moot point since you could never |
| // construct such an object, but this seems |
| // correct even if that code changes). |
| if t == &erased_self_ty && !r.has_escaping_bound_vars() { |
| Some(*r) |
| } else { |
| None |
| } |
| } |
| ty::ClauseKind::Trait(_) |
| | ty::ClauseKind::RegionOutlives(_) |
| | ty::ClauseKind::Projection(_) |
| | ty::ClauseKind::ConstArgHasType(_, _) |
| | ty::ClauseKind::WellFormed(_) |
| | ty::ClauseKind::ConstEvaluatable(_) => None, |
| } |
| }) |
| .collect() |
| } |
