| use crate::infer::{InferCtxt, TyOrConstInferVar}; |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_data_structures::obligation_forest::ProcessResult; |
| use rustc_data_structures::obligation_forest::{Error, ForestObligation, Outcome}; |
| use rustc_data_structures::obligation_forest::{ObligationForest, ObligationProcessor}; |
| use rustc_infer::traits::ProjectionCacheKey; |
| use rustc_infer::traits::{SelectionError, TraitEngine, TraitEngineExt as _, TraitObligation}; |
| use rustc_middle::mir::interpret::ErrorHandled; |
| use rustc_middle::ty::abstract_const::NotConstEvaluatable; |
| use rustc_middle::ty::error::{ExpectedFound, TypeError}; |
| use rustc_middle::ty::subst::SubstsRef; |
| use rustc_middle::ty::ToPredicate; |
| use rustc_middle::ty::{self, Binder, Const, Ty, TypeVisitable}; |
| use std::marker::PhantomData; |
| |
| use super::const_evaluatable; |
| use super::project::{self, ProjectAndUnifyResult}; |
| use super::select::SelectionContext; |
| use super::wf; |
| use super::CodeAmbiguity; |
| use super::CodeProjectionError; |
| use super::CodeSelectionError; |
| use super::EvaluationResult; |
| use super::Unimplemented; |
| use super::{FulfillmentError, FulfillmentErrorCode}; |
| use super::{ObligationCause, PredicateObligation}; |
| |
| use crate::traits::error_reporting::InferCtxtExt as _; |
| use crate::traits::project::PolyProjectionObligation; |
| use crate::traits::project::ProjectionCacheKeyExt as _; |
| use crate::traits::query::evaluate_obligation::InferCtxtExt as _; |
| |
| impl<'tcx> ForestObligation for PendingPredicateObligation<'tcx> { |
| /// Note that we include both the `ParamEnv` and the `Predicate`, |
| /// as the `ParamEnv` can influence whether fulfillment succeeds |
| /// or fails. |
| type CacheKey = ty::ParamEnvAnd<'tcx, ty::Predicate<'tcx>>; |
| |
| fn as_cache_key(&self) -> Self::CacheKey { |
| self.obligation.param_env.and(self.obligation.predicate) |
| } |
| } |
| |
| /// The fulfillment context is used to drive trait resolution. It |
| /// consists of a list of obligations that must be (eventually) |
| /// satisfied. The job is to track which are satisfied, which yielded |
| /// errors, and which are still pending. At any point, users can call |
| /// `select_where_possible`, and the fulfillment context will try to do |
| /// selection, retaining only those obligations that remain |
| /// ambiguous. This may be helpful in pushing type inference |
| /// along. Once all type inference constraints have been generated, the |
| /// method `select_all_or_error` can be used to report any remaining |
| /// ambiguous cases as errors. |
| pub struct FulfillmentContext<'tcx> { |
| // A list of all obligations that have been registered with this |
| // fulfillment context. |
| predicates: ObligationForest<PendingPredicateObligation<'tcx>>, |
| |
| relationships: FxHashMap<ty::TyVid, ty::FoundRelationships>, |
| |
| // Is it OK to register obligations into this infcx inside |
| // an infcx snapshot? |
| // |
| // The "primary fulfillment" in many cases in typeck lives |
| // outside of any snapshot, so any use of it inside a snapshot |
| // will lead to trouble and therefore is checked against, but |
| // other fulfillment contexts sometimes do live inside of |
| // a snapshot (they don't *straddle* a snapshot, so there |
| // is no trouble there). |
| usable_in_snapshot: bool, |
| } |
| |
| #[derive(Clone, Debug)] |
| pub struct PendingPredicateObligation<'tcx> { |
| pub obligation: PredicateObligation<'tcx>, |
| // This is far more often read than modified, meaning that we |
| // should mostly optimize for reading speed, while modifying is not as relevant. |
| // |
| // For whatever reason using a boxed slice is slower than using a `Vec` here. |
| pub stalled_on: Vec<TyOrConstInferVar<'tcx>>, |
| } |
| |
| // `PendingPredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger. |
| #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))] |
| static_assert_size!(PendingPredicateObligation<'_>, 72); |
| |
| impl<'a, 'tcx> FulfillmentContext<'tcx> { |
| /// Creates a new fulfillment context. |
| pub fn new() -> FulfillmentContext<'tcx> { |
| FulfillmentContext { |
| predicates: ObligationForest::new(), |
| relationships: FxHashMap::default(), |
| usable_in_snapshot: false, |
| } |
| } |
| |
| pub fn new_in_snapshot() -> FulfillmentContext<'tcx> { |
| FulfillmentContext { |
| predicates: ObligationForest::new(), |
| relationships: FxHashMap::default(), |
| usable_in_snapshot: true, |
| } |
| } |
| |
| /// Attempts to select obligations using `selcx`. |
| fn select(&mut self, selcx: &mut SelectionContext<'a, 'tcx>) -> Vec<FulfillmentError<'tcx>> { |
| let span = debug_span!("select", obligation_forest_size = ?self.predicates.len()); |
| let _enter = span.enter(); |
| |
| // Process pending obligations. |
| let outcome: Outcome<_, _> = |
| self.predicates.process_obligations(&mut FulfillProcessor { selcx }); |
| |
| // FIXME: if we kept the original cache key, we could mark projection |
| // obligations as complete for the projection cache here. |
| |
| let errors: Vec<FulfillmentError<'tcx>> = |
| outcome.errors.into_iter().map(to_fulfillment_error).collect(); |
| |
| debug!( |
| "select({} predicates remaining, {} errors) done", |
| self.predicates.len(), |
| errors.len() |
| ); |
| |
| errors |
| } |
| } |
| |
| impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> { |
| /// "Normalize" a projection type `<SomeType as SomeTrait>::X` by |
| /// creating a fresh type variable `$0` as well as a projection |
| /// predicate `<SomeType as SomeTrait>::X == $0`. When the |
| /// inference engine runs, it will attempt to find an impl of |
| /// `SomeTrait` or a where-clause that lets us unify `$0` with |
| /// something concrete. If this fails, we'll unify `$0` with |
| /// `projection_ty` again. |
| #[tracing::instrument(level = "debug", skip(self, infcx, param_env, cause))] |
| fn normalize_projection_type( |
| &mut self, |
| infcx: &InferCtxt<'_, 'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| projection_ty: ty::ProjectionTy<'tcx>, |
| cause: ObligationCause<'tcx>, |
| ) -> Ty<'tcx> { |
| debug_assert!(!projection_ty.has_escaping_bound_vars()); |
| |
| // FIXME(#20304) -- cache |
| |
| let mut selcx = SelectionContext::new(infcx); |
| let mut obligations = vec![]; |
| let normalized_ty = project::normalize_projection_type( |
| &mut selcx, |
| param_env, |
| projection_ty, |
| cause, |
| 0, |
| &mut obligations, |
| ); |
| self.register_predicate_obligations(infcx, obligations); |
| |
| debug!(?normalized_ty); |
| |
| normalized_ty.ty().unwrap() |
| } |
| |
| fn register_predicate_obligation( |
| &mut self, |
| infcx: &InferCtxt<'_, 'tcx>, |
| obligation: PredicateObligation<'tcx>, |
| ) { |
| // this helps to reduce duplicate errors, as well as making |
| // debug output much nicer to read and so on. |
| let obligation = infcx.resolve_vars_if_possible(obligation); |
| |
| debug!(?obligation, "register_predicate_obligation"); |
| |
| assert!(!infcx.is_in_snapshot() || self.usable_in_snapshot); |
| |
| super::relationships::update(self, infcx, &obligation); |
| |
| self.predicates |
| .register_obligation(PendingPredicateObligation { obligation, stalled_on: vec![] }); |
| } |
| |
| fn select_all_or_error(&mut self, infcx: &InferCtxt<'_, 'tcx>) -> Vec<FulfillmentError<'tcx>> { |
| { |
| let errors = self.select_where_possible(infcx); |
| if !errors.is_empty() { |
| return errors; |
| } |
| } |
| |
| self.predicates.to_errors(CodeAmbiguity).into_iter().map(to_fulfillment_error).collect() |
| } |
| |
| fn select_where_possible( |
| &mut self, |
| infcx: &InferCtxt<'_, 'tcx>, |
| ) -> Vec<FulfillmentError<'tcx>> { |
| let mut selcx = SelectionContext::new(infcx); |
| self.select(&mut selcx) |
| } |
| |
| fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> { |
| self.predicates.map_pending_obligations(|o| o.obligation.clone()) |
| } |
| |
| fn relationships(&mut self) -> &mut FxHashMap<ty::TyVid, ty::FoundRelationships> { |
| &mut self.relationships |
| } |
| } |
| |
| struct FulfillProcessor<'a, 'b, 'tcx> { |
| selcx: &'a mut SelectionContext<'b, 'tcx>, |
| } |
| |
| fn mk_pending(os: Vec<PredicateObligation<'_>>) -> Vec<PendingPredicateObligation<'_>> { |
| os.into_iter() |
| .map(|o| PendingPredicateObligation { obligation: o, stalled_on: vec![] }) |
| .collect() |
| } |
| |
| impl<'a, 'b, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'tcx> { |
| type Obligation = PendingPredicateObligation<'tcx>; |
| type Error = FulfillmentErrorCode<'tcx>; |
| |
| /// Identifies whether a predicate obligation needs processing. |
| /// |
| /// This is always inlined, despite its size, because it has a single |
| /// callsite and it is called *very* frequently. |
| #[inline(always)] |
| fn needs_process_obligation(&self, pending_obligation: &Self::Obligation) -> bool { |
| // If we were stalled on some unresolved variables, first check whether |
| // any of them have been resolved; if not, don't bother doing more work |
| // yet. |
| match pending_obligation.stalled_on.len() { |
| // Match arms are in order of frequency, which matters because this |
| // code is so hot. 1 and 0 dominate; 2+ is fairly rare. |
| 1 => { |
| let infer_var = pending_obligation.stalled_on[0]; |
| self.selcx.infcx().ty_or_const_infer_var_changed(infer_var) |
| } |
| 0 => { |
| // In this case we haven't changed, but wish to make a change. |
| true |
| } |
| _ => { |
| // This `for` loop was once a call to `all()`, but this lower-level |
| // form was a perf win. See #64545 for details. |
| (|| { |
| for &infer_var in &pending_obligation.stalled_on { |
| if self.selcx.infcx().ty_or_const_infer_var_changed(infer_var) { |
| return true; |
| } |
| } |
| false |
| })() |
| } |
| } |
| } |
| |
| /// Processes a predicate obligation and returns either: |
| /// - `Changed(v)` if the predicate is true, presuming that `v` are also true |
| /// - `Unchanged` if we don't have enough info to be sure |
| /// - `Error(e)` if the predicate does not hold |
| /// |
| /// This is called much less often than `needs_process_obligation`, so we |
| /// never inline it. |
| #[inline(never)] |
| #[instrument(level = "debug", skip(self, pending_obligation))] |
| fn process_obligation( |
| &mut self, |
| pending_obligation: &mut PendingPredicateObligation<'tcx>, |
| ) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> { |
| pending_obligation.stalled_on.truncate(0); |
| |
| let obligation = &mut pending_obligation.obligation; |
| |
| debug!(?obligation, "pre-resolve"); |
| |
| if obligation.predicate.has_infer_types_or_consts() { |
| obligation.predicate = |
| self.selcx.infcx().resolve_vars_if_possible(obligation.predicate); |
| } |
| |
| let obligation = &pending_obligation.obligation; |
| |
| let infcx = self.selcx.infcx(); |
| |
| if obligation.predicate.has_projections() { |
| let mut obligations = Vec::new(); |
| let predicate = crate::traits::project::try_normalize_with_depth_to( |
| self.selcx, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| obligation.predicate, |
| &mut obligations, |
| ); |
| if predicate != obligation.predicate { |
| obligations.push(obligation.with(predicate)); |
| return ProcessResult::Changed(mk_pending(obligations)); |
| } |
| } |
| let binder = obligation.predicate.kind(); |
| match binder.no_bound_vars() { |
| None => match binder.skip_binder() { |
| // Evaluation will discard candidates using the leak check. |
| // This means we need to pass it the bound version of our |
| // predicate. |
| ty::PredicateKind::Trait(trait_ref) => { |
| let trait_obligation = obligation.with(binder.rebind(trait_ref)); |
| |
| self.process_trait_obligation( |
| obligation, |
| trait_obligation, |
| &mut pending_obligation.stalled_on, |
| ) |
| } |
| ty::PredicateKind::Projection(data) => { |
| let project_obligation = obligation.with(binder.rebind(data)); |
| |
| self.process_projection_obligation( |
| obligation, |
| project_obligation, |
| &mut pending_obligation.stalled_on, |
| ) |
| } |
| ty::PredicateKind::RegionOutlives(_) |
| | ty::PredicateKind::TypeOutlives(_) |
| | ty::PredicateKind::WellFormed(_) |
| | ty::PredicateKind::ObjectSafe(_) |
| | ty::PredicateKind::ClosureKind(..) |
| | ty::PredicateKind::Subtype(_) |
| | ty::PredicateKind::Coerce(_) |
| | ty::PredicateKind::ConstEvaluatable(..) |
| | ty::PredicateKind::ConstEquate(..) => { |
| let pred = |
| ty::Binder::dummy(infcx.replace_bound_vars_with_placeholders(binder)); |
| ProcessResult::Changed(mk_pending(vec![ |
| obligation.with(pred.to_predicate(self.selcx.tcx())), |
| ])) |
| } |
| ty::PredicateKind::TypeWellFormedFromEnv(..) => { |
| bug!("TypeWellFormedFromEnv is only used for Chalk") |
| } |
| }, |
| Some(pred) => match pred { |
| ty::PredicateKind::Trait(data) => { |
| let trait_obligation = obligation.with(Binder::dummy(data)); |
| |
| self.process_trait_obligation( |
| obligation, |
| trait_obligation, |
| &mut pending_obligation.stalled_on, |
| ) |
| } |
| |
| ty::PredicateKind::RegionOutlives(data) => { |
| if infcx.considering_regions || data.has_placeholders() { |
| infcx.region_outlives_predicate(&obligation.cause, Binder::dummy(data)); |
| } |
| |
| ProcessResult::Changed(vec![]) |
| } |
| |
| ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(t_a, r_b)) => { |
| if infcx.considering_regions { |
| infcx.register_region_obligation_with_cause(t_a, r_b, &obligation.cause); |
| } |
| ProcessResult::Changed(vec![]) |
| } |
| |
| ty::PredicateKind::Projection(ref data) => { |
| let project_obligation = obligation.with(Binder::dummy(*data)); |
| |
| self.process_projection_obligation( |
| obligation, |
| project_obligation, |
| &mut pending_obligation.stalled_on, |
| ) |
| } |
| |
| ty::PredicateKind::ObjectSafe(trait_def_id) => { |
| if !self.selcx.tcx().is_object_safe(trait_def_id) { |
| ProcessResult::Error(CodeSelectionError(Unimplemented)) |
| } else { |
| ProcessResult::Changed(vec![]) |
| } |
| } |
| |
| ty::PredicateKind::ClosureKind(_, closure_substs, kind) => { |
| match self.selcx.infcx().closure_kind(closure_substs) { |
| Some(closure_kind) => { |
| if closure_kind.extends(kind) { |
| ProcessResult::Changed(vec![]) |
| } else { |
| ProcessResult::Error(CodeSelectionError(Unimplemented)) |
| } |
| } |
| None => ProcessResult::Unchanged, |
| } |
| } |
| |
| ty::PredicateKind::WellFormed(arg) => { |
| match wf::obligations( |
| self.selcx.infcx(), |
| obligation.param_env, |
| obligation.cause.body_id, |
| obligation.recursion_depth + 1, |
| arg, |
| obligation.cause.span, |
| ) { |
| None => { |
| pending_obligation.stalled_on = |
| vec![TyOrConstInferVar::maybe_from_generic_arg(arg).unwrap()]; |
| ProcessResult::Unchanged |
| } |
| Some(os) => ProcessResult::Changed(mk_pending(os)), |
| } |
| } |
| |
| ty::PredicateKind::Subtype(subtype) => { |
| match self.selcx.infcx().subtype_predicate( |
| &obligation.cause, |
| obligation.param_env, |
| Binder::dummy(subtype), |
| ) { |
| None => { |
| // None means that both are unresolved. |
| pending_obligation.stalled_on = vec![ |
| TyOrConstInferVar::maybe_from_ty(subtype.a).unwrap(), |
| TyOrConstInferVar::maybe_from_ty(subtype.b).unwrap(), |
| ]; |
| ProcessResult::Unchanged |
| } |
| Some(Ok(ok)) => ProcessResult::Changed(mk_pending(ok.obligations)), |
| Some(Err(err)) => { |
| let expected_found = |
| ExpectedFound::new(subtype.a_is_expected, subtype.a, subtype.b); |
| ProcessResult::Error(FulfillmentErrorCode::CodeSubtypeError( |
| expected_found, |
| err, |
| )) |
| } |
| } |
| } |
| |
| ty::PredicateKind::Coerce(coerce) => { |
| match self.selcx.infcx().coerce_predicate( |
| &obligation.cause, |
| obligation.param_env, |
| Binder::dummy(coerce), |
| ) { |
| None => { |
| // None means that both are unresolved. |
| pending_obligation.stalled_on = vec![ |
| TyOrConstInferVar::maybe_from_ty(coerce.a).unwrap(), |
| TyOrConstInferVar::maybe_from_ty(coerce.b).unwrap(), |
| ]; |
| ProcessResult::Unchanged |
| } |
| Some(Ok(ok)) => ProcessResult::Changed(mk_pending(ok.obligations)), |
| Some(Err(err)) => { |
| let expected_found = ExpectedFound::new(false, coerce.a, coerce.b); |
| ProcessResult::Error(FulfillmentErrorCode::CodeSubtypeError( |
| expected_found, |
| err, |
| )) |
| } |
| } |
| } |
| |
| ty::PredicateKind::ConstEvaluatable(uv) => { |
| match const_evaluatable::is_const_evaluatable( |
| self.selcx.infcx(), |
| uv, |
| obligation.param_env, |
| obligation.cause.span, |
| ) { |
| Ok(()) => ProcessResult::Changed(vec![]), |
| Err(NotConstEvaluatable::MentionsInfer) => { |
| pending_obligation.stalled_on.clear(); |
| pending_obligation.stalled_on.extend( |
| uv.substs |
| .iter() |
| .filter_map(TyOrConstInferVar::maybe_from_generic_arg), |
| ); |
| ProcessResult::Unchanged |
| } |
| Err( |
| e @ NotConstEvaluatable::MentionsParam |
| | e @ NotConstEvaluatable::Error(_), |
| ) => ProcessResult::Error(CodeSelectionError( |
| SelectionError::NotConstEvaluatable(e), |
| )), |
| } |
| } |
| |
| ty::PredicateKind::ConstEquate(c1, c2) => { |
| debug!(?c1, ?c2, "equating consts"); |
| let tcx = self.selcx.tcx(); |
| if tcx.features().generic_const_exprs { |
| // FIXME: we probably should only try to unify abstract constants |
| // if the constants depend on generic parameters. |
| // |
| // Let's just see where this breaks :shrug: |
| if let (ty::ConstKind::Unevaluated(a), ty::ConstKind::Unevaluated(b)) = |
| (c1.kind(), c2.kind()) |
| { |
| if infcx.try_unify_abstract_consts( |
| a.shrink(), |
| b.shrink(), |
| obligation.param_env, |
| ) { |
| return ProcessResult::Changed(vec![]); |
| } |
| } |
| } |
| |
| let stalled_on = &mut pending_obligation.stalled_on; |
| |
| let mut evaluate = |c: Const<'tcx>| { |
| if let ty::ConstKind::Unevaluated(unevaluated) = c.kind() { |
| match self.selcx.infcx().try_const_eval_resolve( |
| obligation.param_env, |
| unevaluated, |
| c.ty(), |
| Some(obligation.cause.span), |
| ) { |
| Ok(val) => Ok(val), |
| Err(e) => match e { |
| ErrorHandled::TooGeneric => { |
| stalled_on.extend( |
| unevaluated.substs.iter().filter_map( |
| TyOrConstInferVar::maybe_from_generic_arg, |
| ), |
| ); |
| Err(ErrorHandled::TooGeneric) |
| } |
| _ => Err(e), |
| }, |
| } |
| } else { |
| Ok(c) |
| } |
| }; |
| |
| match (evaluate(c1), evaluate(c2)) { |
| (Ok(c1), Ok(c2)) => { |
| match self |
| .selcx |
| .infcx() |
| .at(&obligation.cause, obligation.param_env) |
| .eq(c1, c2) |
| { |
| Ok(_) => ProcessResult::Changed(vec![]), |
| Err(err) => ProcessResult::Error( |
| FulfillmentErrorCode::CodeConstEquateError( |
| ExpectedFound::new(true, c1, c2), |
| err, |
| ), |
| ), |
| } |
| } |
| (Err(ErrorHandled::Reported(reported)), _) |
| | (_, Err(ErrorHandled::Reported(reported))) => ProcessResult::Error( |
| CodeSelectionError(SelectionError::NotConstEvaluatable( |
| NotConstEvaluatable::Error(reported), |
| )), |
| ), |
| (Err(ErrorHandled::Linted), _) | (_, Err(ErrorHandled::Linted)) => { |
| span_bug!( |
| obligation.cause.span(), |
| "ConstEquate: const_eval_resolve returned an unexpected error" |
| ) |
| } |
| (Err(ErrorHandled::TooGeneric), _) | (_, Err(ErrorHandled::TooGeneric)) => { |
| if c1.has_infer_types_or_consts() || c2.has_infer_types_or_consts() { |
| ProcessResult::Unchanged |
| } else { |
| // Two different constants using generic parameters ~> error. |
| let expected_found = ExpectedFound::new(true, c1, c2); |
| ProcessResult::Error(FulfillmentErrorCode::CodeConstEquateError( |
| expected_found, |
| TypeError::ConstMismatch(expected_found), |
| )) |
| } |
| } |
| } |
| } |
| ty::PredicateKind::TypeWellFormedFromEnv(..) => { |
| bug!("TypeWellFormedFromEnv is only used for Chalk") |
| } |
| }, |
| } |
| } |
| |
| fn process_backedge<'c, I>( |
| &mut self, |
| cycle: I, |
| _marker: PhantomData<&'c PendingPredicateObligation<'tcx>>, |
| ) where |
| I: Clone + Iterator<Item = &'c PendingPredicateObligation<'tcx>>, |
| { |
| if self.selcx.coinductive_match(cycle.clone().map(|s| s.obligation.predicate)) { |
| debug!("process_child_obligations: coinductive match"); |
| } else { |
| let cycle: Vec<_> = cycle.map(|c| c.obligation.clone()).collect(); |
| self.selcx.infcx().report_overflow_error_cycle(&cycle); |
| } |
| } |
| } |
| |
| impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> { |
| #[instrument(level = "debug", skip(self, obligation, stalled_on))] |
| fn process_trait_obligation( |
| &mut self, |
| obligation: &PredicateObligation<'tcx>, |
| trait_obligation: TraitObligation<'tcx>, |
| stalled_on: &mut Vec<TyOrConstInferVar<'tcx>>, |
| ) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> { |
| let infcx = self.selcx.infcx(); |
| if obligation.predicate.is_global() { |
| // no type variables present, can use evaluation for better caching. |
| // FIXME: consider caching errors too. |
| if infcx.predicate_must_hold_considering_regions(obligation) { |
| debug!( |
| "selecting trait at depth {} evaluated to holds", |
| obligation.recursion_depth |
| ); |
| return ProcessResult::Changed(vec![]); |
| } |
| } |
| |
| match self.selcx.select(&trait_obligation) { |
| Ok(Some(impl_source)) => { |
| debug!("selecting trait at depth {} yielded Ok(Some)", obligation.recursion_depth); |
| ProcessResult::Changed(mk_pending(impl_source.nested_obligations())) |
| } |
| Ok(None) => { |
| debug!("selecting trait at depth {} yielded Ok(None)", obligation.recursion_depth); |
| |
| // This is a bit subtle: for the most part, the |
| // only reason we can fail to make progress on |
| // trait selection is because we don't have enough |
| // information about the types in the trait. |
| stalled_on.clear(); |
| stalled_on.extend(substs_infer_vars( |
| self.selcx, |
| trait_obligation.predicate.map_bound(|pred| pred.trait_ref.substs), |
| )); |
| |
| debug!( |
| "process_predicate: pending obligation {:?} now stalled on {:?}", |
| infcx.resolve_vars_if_possible(obligation.clone()), |
| stalled_on |
| ); |
| |
| ProcessResult::Unchanged |
| } |
| Err(selection_err) => { |
| debug!("selecting trait at depth {} yielded Err", obligation.recursion_depth); |
| |
| ProcessResult::Error(CodeSelectionError(selection_err)) |
| } |
| } |
| } |
| |
| fn process_projection_obligation( |
| &mut self, |
| obligation: &PredicateObligation<'tcx>, |
| project_obligation: PolyProjectionObligation<'tcx>, |
| stalled_on: &mut Vec<TyOrConstInferVar<'tcx>>, |
| ) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> { |
| let tcx = self.selcx.tcx(); |
| |
| if obligation.predicate.is_global() { |
| // no type variables present, can use evaluation for better caching. |
| // FIXME: consider caching errors too. |
| if self.selcx.infcx().predicate_must_hold_considering_regions(obligation) { |
| if let Some(key) = ProjectionCacheKey::from_poly_projection_predicate( |
| &mut self.selcx, |
| project_obligation.predicate, |
| ) { |
| // If `predicate_must_hold_considering_regions` succeeds, then we've |
| // evaluated all sub-obligations. We can therefore mark the 'root' |
| // obligation as complete, and skip evaluating sub-obligations. |
| self.selcx |
| .infcx() |
| .inner |
| .borrow_mut() |
| .projection_cache() |
| .complete(key, EvaluationResult::EvaluatedToOk); |
| } |
| return ProcessResult::Changed(vec![]); |
| } else { |
| debug!("Does NOT hold: {:?}", obligation); |
| } |
| } |
| |
| match project::poly_project_and_unify_type(self.selcx, &project_obligation) { |
| ProjectAndUnifyResult::Holds(os) => ProcessResult::Changed(mk_pending(os)), |
| ProjectAndUnifyResult::FailedNormalization => { |
| stalled_on.clear(); |
| stalled_on.extend(substs_infer_vars( |
| self.selcx, |
| project_obligation.predicate.map_bound(|pred| pred.projection_ty.substs), |
| )); |
| ProcessResult::Unchanged |
| } |
| // Let the caller handle the recursion |
| ProjectAndUnifyResult::Recursive => ProcessResult::Changed(mk_pending(vec![ |
| project_obligation.with(project_obligation.predicate.to_predicate(tcx)), |
| ])), |
| ProjectAndUnifyResult::MismatchedProjectionTypes(e) => { |
| ProcessResult::Error(CodeProjectionError(e)) |
| } |
| } |
| } |
| } |
| |
| /// Returns the set of inference variables contained in `substs`. |
| fn substs_infer_vars<'a, 'tcx>( |
| selcx: &mut SelectionContext<'a, 'tcx>, |
| substs: ty::Binder<'tcx, SubstsRef<'tcx>>, |
| ) -> impl Iterator<Item = TyOrConstInferVar<'tcx>> { |
| selcx |
| .infcx() |
| .resolve_vars_if_possible(substs) |
| .skip_binder() // ok because this check doesn't care about regions |
| .iter() |
| .filter(|arg| arg.has_infer_types_or_consts()) |
| .flat_map(|arg| { |
| let mut walker = arg.walk(); |
| while let Some(c) = walker.next() { |
| if !c.has_infer_types_or_consts() { |
| walker.visited.remove(&c); |
| walker.skip_current_subtree(); |
| } |
| } |
| walker.visited.into_iter() |
| }) |
| .filter_map(TyOrConstInferVar::maybe_from_generic_arg) |
| } |
| |
| fn to_fulfillment_error<'tcx>( |
| error: Error<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>>, |
| ) -> FulfillmentError<'tcx> { |
| let mut iter = error.backtrace.into_iter(); |
| let obligation = iter.next().unwrap().obligation; |
| // The root obligation is the last item in the backtrace - if there's only |
| // one item, then it's the same as the main obligation |
| let root_obligation = iter.next_back().map_or_else(|| obligation.clone(), |e| e.obligation); |
| FulfillmentError::new(obligation, error.error, root_obligation) |
| } |
