diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/wf.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/wf.rs | 139 |
1 files changed, 72 insertions, 67 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs index 54b6c22b2d8..62bd8e1af05 100644 --- a/compiler/rustc_trait_selection/src/traits/wf.rs +++ b/compiler/rustc_trait_selection/src/traits/wf.rs @@ -1,3 +1,8 @@ +//! Core logic responsible for determining what it means for various type system +//! primitives to be "well formed". Actually checking whether these primitives are +//! well formed is performed elsewhere (e.g. during type checking or item well formedness +//! checking). + use std::iter; use rustc_hir as hir; @@ -5,8 +10,8 @@ use rustc_hir::lang_items::LangItem; use rustc_infer::traits::{ObligationCauseCode, PredicateObligations}; use rustc_middle::bug; use rustc_middle::ty::{ - self, GenericArg, GenericArgKind, GenericArgsRef, Ty, TyCtxt, TypeSuperVisitable, - TypeVisitable, TypeVisitableExt, TypeVisitor, + self, GenericArgsRef, Term, TermKind, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, + TypeVisitableExt, TypeVisitor, }; use rustc_session::parse::feature_err; use rustc_span::def_id::{DefId, LocalDefId}; @@ -15,28 +20,29 @@ use tracing::{debug, instrument, trace}; use crate::infer::InferCtxt; use crate::traits; + /// 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". +/// make any progress at all. This is to prevent cycles 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>, + term: Term<'tcx>, span: Span, ) -> Option<PredicateObligations<'tcx>> { - // Handle the "livelock" case (see comment above) by bailing out if necessary. - let arg = match arg.unpack() { - GenericArgKind::Type(ty) => { + // Handle the "cycle" case (see comment above) by bailing out if necessary. + let term = match term.unpack() { + TermKind::Ty(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". + // No progress, bail out to prevent cycles. return None; } else { resolved_ty @@ -46,12 +52,12 @@ pub fn obligations<'tcx>( } .into() } - GenericArgKind::Const(ct) => { + TermKind::Const(ct) => { match ct.kind() { ty::ConstKind::Infer(_) => { let resolved = infcx.shallow_resolve_const(ct); if resolved == ct { - // No progress. + // No progress, bail out to prevent cycles. return None; } else { resolved @@ -61,8 +67,6 @@ pub fn obligations<'tcx>( } .into() } - // There is nothing we have to do for lifetimes. - GenericArgKind::Lifetime(..) => return Some(PredicateObligations::new()), }; let mut wf = WfPredicates { @@ -74,11 +78,11 @@ pub fn obligations<'tcx>( recursion_depth, item: None, }; - wf.compute(arg); - debug!("wf::obligations({:?}, body_id={:?}) = {:?}", arg, body_id, wf.out); + wf.add_wf_preds_for_term(term); + debug!("wf::obligations({:?}, body_id={:?}) = {:?}", term, body_id, wf.out); let result = wf.normalize(infcx); - debug!("wf::obligations({:?}, body_id={:?}) ~~> {:?}", arg, body_id, result); + debug!("wf::obligations({:?}, body_id={:?}) ~~> {:?}", term, body_id, result); Some(result) } @@ -89,23 +93,19 @@ pub fn obligations<'tcx>( pub fn unnormalized_obligations<'tcx>( infcx: &InferCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, - arg: GenericArg<'tcx>, + term: Term<'tcx>, span: Span, body_id: LocalDefId, ) -> Option<PredicateObligations<'tcx>> { - debug_assert_eq!(arg, infcx.resolve_vars_if_possible(arg)); + debug_assert_eq!(term, infcx.resolve_vars_if_possible(term)); // 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() { + // cycles where we say "?0 is WF if ?0 is WF". + if term.is_infer() { return None; } - if let ty::GenericArgKind::Lifetime(..) = arg.unpack() { - return Some(PredicateObligations::new()); - } - let mut wf = WfPredicates { infcx, param_env, @@ -115,7 +115,7 @@ pub fn unnormalized_obligations<'tcx>( recursion_depth: 0, item: None, }; - wf.compute(arg); + wf.add_wf_preds_for_term(term); Some(wf.out) } @@ -140,7 +140,7 @@ pub fn trait_obligations<'tcx>( recursion_depth: 0, item: Some(item), }; - wf.compute_trait_pred(trait_pred, Elaborate::All); + wf.add_wf_preds_for_trait_pred(trait_pred, Elaborate::All); debug!(obligations = ?wf.out); wf.normalize(infcx) } @@ -171,7 +171,7 @@ pub fn clause_obligations<'tcx>( // It's ok to skip the binder here because wf code is prepared for it match clause.kind().skip_binder() { ty::ClauseKind::Trait(t) => { - wf.compute_trait_pred(t, Elaborate::None); + wf.add_wf_preds_for_trait_pred(t, Elaborate::None); } ty::ClauseKind::HostEffect(..) => { // Technically the well-formedness of this predicate is implied by @@ -179,22 +179,22 @@ pub fn clause_obligations<'tcx>( } ty::ClauseKind::RegionOutlives(..) => {} ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty, _reg)) => { - wf.compute(ty.into()); + wf.add_wf_preds_for_term(ty.into()); } ty::ClauseKind::Projection(t) => { - wf.compute_alias_term(t.projection_term); - wf.compute(t.term.into_arg()); + wf.add_wf_preds_for_alias_term(t.projection_term); + wf.add_wf_preds_for_term(t.term); } ty::ClauseKind::ConstArgHasType(ct, ty) => { - wf.compute(ct.into()); - wf.compute(ty.into()); + wf.add_wf_preds_for_term(ct.into()); + wf.add_wf_preds_for_term(ty.into()); } - ty::ClauseKind::WellFormed(arg) => { - wf.compute(arg); + ty::ClauseKind::WellFormed(term) => { + wf.add_wf_preds_for_term(term); } ty::ClauseKind::ConstEvaluatable(ct) => { - wf.compute(ct.into()); + wf.add_wf_preds_for_term(ct.into()); } } @@ -372,14 +372,18 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { } /// 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) { + fn add_wf_preds_for_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::PredicatePolarity::Negative { - self.compute_negative_trait_pred(trait_ref); + self.add_wf_preds_for_negative_trait_pred(trait_ref); return; } @@ -416,11 +420,9 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { .args .iter() .enumerate() - .filter(|(_, arg)| { - matches!(arg.unpack(), GenericArgKind::Type(..) | GenericArgKind::Const(..)) - }) - .filter(|(_, arg)| !arg.has_escaping_bound_vars()) - .map(|(i, arg)| { + .filter_map(|(i, arg)| arg.as_term().map(|t| (i, t))) + .filter(|(_, term)| !term.has_escaping_bound_vars()) + .map(|(i, term)| { let mut cause = traits::ObligationCause::misc(self.span, self.body_id); // The first arg is the self ty - use the correct span for it. if i == 0 { @@ -435,9 +437,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { cause, depth, param_env, - ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed( - arg, - ))), + ty::ClauseKind::WellFormed(term), ) }), ); @@ -445,15 +445,17 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { // 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>) { + fn add_wf_preds_for_negative_trait_pred(&mut self, trait_ref: ty::TraitRef<'tcx>) { for arg in trait_ref.args { - self.compute(arg); + if let Some(term) = arg.as_term() { + self.add_wf_preds_for_term(term); + } } } /// Pushes the obligations required for an alias (except inherent) to be WF /// into `self.out`. - fn compute_alias_term(&mut self, data: ty::AliasTerm<'tcx>) { + fn add_wf_preds_for_alias_term(&mut self, data: ty::AliasTerm<'tcx>) { // A projection is well-formed if // // (a) its predicates hold (*) @@ -478,13 +480,13 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { let obligations = self.nominal_obligations(data.def_id, data.args); self.out.extend(obligations); - self.compute_projection_args(data.args); + self.add_wf_preds_for_projection_args(data.args); } /// Pushes the obligations required for an inherent alias to be WF /// into `self.out`. // FIXME(inherent_associated_types): Merge this function with `fn compute_alias`. - fn compute_inherent_projection(&mut self, data: ty::AliasTy<'tcx>) { + fn add_wf_preds_for_inherent_projection(&mut self, data: ty::AliasTy<'tcx>) { // An inherent projection is well-formed if // // (a) its predicates hold (*) @@ -511,7 +513,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { data.args.visit_with(self); } - fn compute_projection_args(&mut self, args: GenericArgsRef<'tcx>) { + fn add_wf_preds_for_projection_args(&mut self, args: GenericArgsRef<'tcx>) { let tcx = self.tcx(); let cause = self.cause(ObligationCauseCode::WellFormed(None)); let param_env = self.param_env; @@ -519,19 +521,15 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { self.out.extend( args.iter() - .filter(|arg| { - matches!(arg.unpack(), GenericArgKind::Type(..) | GenericArgKind::Const(..)) - }) - .filter(|arg| !arg.has_escaping_bound_vars()) - .map(|arg| { + .filter_map(|arg| arg.as_term()) + .filter(|term| !term.has_escaping_bound_vars()) + .map(|term| { traits::Obligation::with_depth( tcx, cause.clone(), depth, param_env, - ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed( - arg, - ))), + ty::ClauseKind::WellFormed(term), ) }), ); @@ -555,10 +553,10 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { } } - /// Pushes all the predicates needed to validate that `ty` is WF into `out`. + /// Pushes all the predicates needed to validate that `term` is WF into `out`. #[instrument(level = "debug", skip(self))] - fn compute(&mut self, arg: GenericArg<'tcx>) { - arg.visit_with(self); + fn add_wf_preds_for_term(&mut self, term: Term<'tcx>) { + term.visit_with(self); debug!(?self.out); } @@ -596,7 +594,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { .collect() } - fn from_object_ty( + fn add_wf_preds_for_dyn_ty( &mut self, ty: Ty<'tcx>, data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>, @@ -651,6 +649,13 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> { outlives, )); } + + // We don't add any wf predicates corresponding to the trait ref's generic arguments + // which allows code like this to compile: + // ```rust + // trait Trait<T: Sized> {} + // fn foo(_: &dyn Trait<[u32]>) {} + // ``` } } } @@ -761,7 +766,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> { self.out.extend(obligations); } ty::Alias(ty::Inherent, data) => { - self.compute_inherent_projection(data); + self.add_wf_preds_for_inherent_projection(data); return; // Subtree handled by compute_inherent_projection. } @@ -895,7 +900,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> { // // Here, we defer WF checking due to higher-ranked // regions. This is perhaps not ideal. - self.from_object_ty(t, data, r); + self.add_wf_preds_for_dyn_ty(t, data, r); // FIXME(#27579) RFC also considers adding trait // obligations that don't refer to Self and @@ -917,11 +922,11 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> { // 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 + // 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" + // See also the comment on `fn obligations`, describing cycle // prevention, which happens before this can be reached. ty::Infer(_) => { let cause = self.cause(ObligationCauseCode::WellFormed(None)); |