| use crate::infer::{InferCtxt, ShallowResolver}; |
| use crate::mir::interpret::{GlobalId, ErrorHandled}; |
| use crate::ty::{self, Ty, TypeFoldable, ToPolyTraitRef}; |
| use crate::ty::error::ExpectedFound; |
| use rustc_data_structures::obligation_forest::{DoCompleted, Error, ForestObligation}; |
| use rustc_data_structures::obligation_forest::{ObligationForest, ObligationProcessor}; |
| use rustc_data_structures::obligation_forest::{ProcessResult}; |
| use std::marker::PhantomData; |
| |
| use super::CodeAmbiguity; |
| use super::CodeProjectionError; |
| use super::CodeSelectionError; |
| use super::engine::{TraitEngine, TraitEngineExt}; |
| use super::{FulfillmentError, FulfillmentErrorCode}; |
| use super::{ObligationCause, PredicateObligation}; |
| use super::project; |
| use super::select::SelectionContext; |
| use super::{Unimplemented, ConstEvalFailure}; |
| |
| impl<'tcx> ForestObligation for PendingPredicateObligation<'tcx> { |
| type Predicate = ty::Predicate<'tcx>; |
| |
| fn as_predicate(&self) -> &Self::Predicate { &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>>, |
| // Should this fulfillment context register type-lives-for-region |
| // obligations on its parent infcx? In some cases, region |
| // obligations are either already known to hold (normalization) or |
| // hopefully verifed elsewhere (type-impls-bound), and therefore |
| // should not be checked. |
| // |
| // Note that if we are normalizing a type that we already |
| // know is well-formed, there should be no harm setting this |
| // to true - all the region variables should be determinable |
| // using the RFC 447 rules, which don't depend on |
| // type-lives-for-region constraints, and because the type |
| // is well-formed, the constraints should hold. |
| register_region_obligations: bool, |
| // 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>, |
| pub stalled_on: Vec<Ty<'tcx>>, |
| } |
| |
| // `PendingPredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger. |
| #[cfg(target_arch = "x86_64")] |
| static_assert_size!(PendingPredicateObligation<'_>, 136); |
| |
| impl<'a, 'tcx> FulfillmentContext<'tcx> { |
| /// Creates a new fulfillment context. |
| pub fn new() -> FulfillmentContext<'tcx> { |
| FulfillmentContext { |
| predicates: ObligationForest::new(), |
| register_region_obligations: true, |
| usable_in_snapshot: false, |
| } |
| } |
| |
| pub fn new_in_snapshot() -> FulfillmentContext<'tcx> { |
| FulfillmentContext { |
| predicates: ObligationForest::new(), |
| register_region_obligations: true, |
| usable_in_snapshot: true, |
| } |
| } |
| |
| pub fn new_ignoring_regions() -> FulfillmentContext<'tcx> { |
| FulfillmentContext { |
| predicates: ObligationForest::new(), |
| register_region_obligations: false, |
| usable_in_snapshot: false |
| } |
| } |
| |
| /// Attempts to select obligations using `selcx`. |
| fn select( |
| &mut self, |
| selcx: &mut SelectionContext<'a, 'tcx>, |
| ) -> Result<(), Vec<FulfillmentError<'tcx>>> { |
| debug!("select(obligation-forest-size={})", self.predicates.len()); |
| |
| let mut errors = Vec::new(); |
| |
| loop { |
| debug!("select: starting another iteration"); |
| |
| // Process pending obligations. |
| let outcome = self.predicates.process_obligations(&mut FulfillProcessor { |
| selcx, |
| register_region_obligations: self.register_region_obligations |
| }, DoCompleted::No); |
| debug!("select: outcome={:#?}", outcome); |
| |
| // FIXME: if we kept the original cache key, we could mark projection |
| // obligations as complete for the projection cache here. |
| |
| errors.extend( |
| outcome.errors.into_iter() |
| .map(|e| to_fulfillment_error(e))); |
| |
| // If nothing new was added, no need to keep looping. |
| if outcome.stalled { |
| break; |
| } |
| } |
| |
| debug!("select({} predicates remaining, {} errors) done", |
| self.predicates.len(), errors.len()); |
| |
| if errors.is_empty() { |
| Ok(()) |
| } else { |
| Err(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. |
| 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!("normalize_projection_type(projection_ty={:?})", |
| projection_ty); |
| |
| 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!("normalize_projection_type: result={:?}", normalized_ty); |
| |
| normalized_ty |
| } |
| |
| 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!("register_predicate_obligation(obligation={:?})", obligation); |
| |
| assert!(!infcx.is_in_snapshot() || self.usable_in_snapshot); |
| |
| self.predicates.register_obligation(PendingPredicateObligation { |
| obligation, |
| stalled_on: vec![] |
| }); |
| } |
| |
| fn select_all_or_error( |
| &mut self, |
| infcx: &InferCtxt<'_, 'tcx>, |
| ) -> Result<(), Vec<FulfillmentError<'tcx>>> { |
| self.select_where_possible(infcx)?; |
| |
| let errors: Vec<_> = |
| self.predicates.to_errors(CodeAmbiguity) |
| .into_iter() |
| .map(|e| to_fulfillment_error(e)) |
| .collect(); |
| if errors.is_empty() { |
| Ok(()) |
| } else { |
| Err(errors) |
| } |
| } |
| |
| fn select_where_possible( |
| &mut self, |
| infcx: &InferCtxt<'_, 'tcx>, |
| ) -> Result<(), 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()) |
| } |
| } |
| |
| struct FulfillProcessor<'a, 'b, 'tcx> { |
| selcx: &'a mut SelectionContext<'b, 'tcx>, |
| register_region_obligations: bool, |
| } |
| |
| fn mk_pending(os: Vec<PredicateObligation<'tcx>>) -> Vec<PendingPredicateObligation<'tcx>> { |
| 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>; |
| |
| /// 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 always inlined, despite its size, because it has a single |
| /// callsite and it is called *very* frequently. |
| #[inline(always)] |
| fn process_obligation( |
| &mut self, |
| pending_obligation: &mut Self::Obligation, |
| ) -> ProcessResult<Self::Obligation, Self::Error> { |
| // 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 |
| if !pending_obligation.stalled_on.is_empty() { |
| let mut changed = false; |
| // This `for` loop was once a call to `all()`, but this lower-level |
| // form was a perf win. See #64545 for details. |
| for &ty in &pending_obligation.stalled_on { |
| if ShallowResolver::new(self.selcx.infcx()).shallow_resolve_changed(ty) { |
| changed = true; |
| break; |
| } |
| } |
| if !changed { |
| debug!("process_predicate: pending obligation {:?} still stalled on {:?}", |
| self.selcx.infcx() |
| .resolve_vars_if_possible(&pending_obligation.obligation), |
| pending_obligation.stalled_on); |
| return ProcessResult::Unchanged; |
| } |
| pending_obligation.stalled_on = vec![]; |
| } |
| |
| let obligation = &mut pending_obligation.obligation; |
| |
| if obligation.predicate.has_infer_types() { |
| obligation.predicate = |
| self.selcx.infcx().resolve_vars_if_possible(&obligation.predicate); |
| } |
| |
| debug!("process_obligation: obligation = {:?} cause = {:?}", obligation, obligation.cause); |
| |
| match obligation.predicate { |
| ty::Predicate::Trait(ref data) => { |
| let trait_obligation = obligation.with(data.clone()); |
| |
| if data.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) { |
| debug!("selecting trait `{:?}` at depth {} evaluated to holds", |
| data, obligation.recursion_depth); |
| return ProcessResult::Changed(vec![]) |
| } |
| } |
| |
| match self.selcx.select(&trait_obligation) { |
| Ok(Some(vtable)) => { |
| debug!("selecting trait `{:?}` at depth {} yielded Ok(Some)", |
| data, obligation.recursion_depth); |
| ProcessResult::Changed(mk_pending(vtable.nested_obligations())) |
| } |
| Ok(None) => { |
| debug!("selecting trait `{:?}` at depth {} yielded Ok(None)", |
| data, 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. One |
| // exception is that we sometimes haven't decided |
| // what kind of closure a closure is. *But*, in |
| // that case, it turns out, the type of the |
| // closure will also change, because the closure |
| // also includes references to its upvars as part |
| // of its type, and those types are resolved at |
| // the same time. |
| // |
| // FIXME(#32286) logic seems false if no upvars |
| pending_obligation.stalled_on = |
| trait_ref_type_vars(self.selcx, data.to_poly_trait_ref()); |
| |
| debug!("process_predicate: pending obligation {:?} now stalled on {:?}", |
| self.selcx.infcx().resolve_vars_if_possible(obligation), |
| pending_obligation.stalled_on); |
| |
| ProcessResult::Unchanged |
| } |
| Err(selection_err) => { |
| info!("selecting trait `{:?}` at depth {} yielded Err", |
| data, obligation.recursion_depth); |
| |
| ProcessResult::Error(CodeSelectionError(selection_err)) |
| } |
| } |
| } |
| |
| ty::Predicate::RegionOutlives(ref binder) => { |
| match self.selcx.infcx().region_outlives_predicate(&obligation.cause, binder) { |
| Ok(()) => ProcessResult::Changed(vec![]), |
| Err(_) => ProcessResult::Error(CodeSelectionError(Unimplemented)), |
| } |
| } |
| |
| ty::Predicate::TypeOutlives(ref binder) => { |
| // Check if there are higher-ranked vars. |
| match binder.no_bound_vars() { |
| // If there are, inspect the underlying type further. |
| None => { |
| // Convert from `Binder<OutlivesPredicate<Ty, Region>>` to `Binder<Ty>`. |
| let binder = binder.map_bound_ref(|pred| pred.0); |
| |
| // Check if the type has any bound vars. |
| match binder.no_bound_vars() { |
| // If so, this obligation is an error (for now). Eventually we should be |
| // able to support additional cases here, like `for<'a> &'a str: 'a`. |
| // NOTE: this is duplicate-implemented between here and fulfillment. |
| None => { |
| ProcessResult::Error(CodeSelectionError(Unimplemented)) |
| } |
| // Otherwise, we have something of the form |
| // `for<'a> T: 'a where 'a not in T`, which we can treat as |
| // `T: 'static`. |
| Some(t_a) => { |
| let r_static = self.selcx.tcx().lifetimes.re_static; |
| if self.register_region_obligations { |
| self.selcx.infcx().register_region_obligation_with_cause( |
| t_a, |
| r_static, |
| &obligation.cause, |
| ); |
| } |
| ProcessResult::Changed(vec![]) |
| } |
| } |
| } |
| // If there aren't, register the obligation. |
| Some(ty::OutlivesPredicate(t_a, r_b)) => { |
| if self.register_region_obligations { |
| self.selcx.infcx().register_region_obligation_with_cause( |
| t_a, |
| r_b, |
| &obligation.cause, |
| ); |
| } |
| ProcessResult::Changed(vec![]) |
| } |
| } |
| } |
| |
| ty::Predicate::Projection(ref data) => { |
| let project_obligation = obligation.with(data.clone()); |
| match project::poly_project_and_unify_type(self.selcx, &project_obligation) { |
| Ok(None) => { |
| let tcx = self.selcx.tcx(); |
| pending_obligation.stalled_on = |
| trait_ref_type_vars(self.selcx, data.to_poly_trait_ref(tcx)); |
| ProcessResult::Unchanged |
| } |
| Ok(Some(os)) => ProcessResult::Changed(mk_pending(os)), |
| Err(e) => ProcessResult::Error(CodeProjectionError(e)) |
| } |
| } |
| |
| ty::Predicate::ObjectSafe(trait_def_id) => { |
| if !self.selcx.tcx().is_object_safe(trait_def_id) { |
| ProcessResult::Error(CodeSelectionError(Unimplemented)) |
| } else { |
| ProcessResult::Changed(vec![]) |
| } |
| } |
| |
| ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => { |
| match self.selcx.infcx().closure_kind(closure_def_id, closure_substs) { |
| Some(closure_kind) => { |
| if closure_kind.extends(kind) { |
| ProcessResult::Changed(vec![]) |
| } else { |
| ProcessResult::Error(CodeSelectionError(Unimplemented)) |
| } |
| } |
| None => { |
| ProcessResult::Unchanged |
| } |
| } |
| } |
| |
| ty::Predicate::WellFormed(ty) => { |
| match ty::wf::obligations( |
| self.selcx.infcx(), |
| obligation.param_env, |
| obligation.cause.body_id, |
| ty, |
| obligation.cause.span, |
| ) { |
| None => { |
| pending_obligation.stalled_on = vec![ty]; |
| ProcessResult::Unchanged |
| } |
| Some(os) => ProcessResult::Changed(mk_pending(os)) |
| } |
| } |
| |
| ty::Predicate::Subtype(ref subtype) => { |
| match self.selcx.infcx().subtype_predicate(&obligation.cause, |
| obligation.param_env, |
| subtype) { |
| None => { |
| // None means that both are unresolved. |
| pending_obligation.stalled_on = vec![subtype.skip_binder().a, |
| subtype.skip_binder().b]; |
| ProcessResult::Unchanged |
| } |
| Some(Ok(ok)) => { |
| ProcessResult::Changed(mk_pending(ok.obligations)) |
| } |
| Some(Err(err)) => { |
| let expected_found = ExpectedFound::new(subtype.skip_binder().a_is_expected, |
| subtype.skip_binder().a, |
| subtype.skip_binder().b); |
| ProcessResult::Error( |
| FulfillmentErrorCode::CodeSubtypeError(expected_found, err)) |
| } |
| } |
| } |
| |
| ty::Predicate::ConstEvaluatable(def_id, substs) => { |
| if obligation.param_env.has_local_value() { |
| ProcessResult::Unchanged |
| } else { |
| if !substs.has_local_value() { |
| let instance = ty::Instance::resolve( |
| self.selcx.tcx().global_tcx(), |
| obligation.param_env, |
| def_id, |
| substs, |
| ); |
| if let Some(instance) = instance { |
| let cid = GlobalId { |
| instance, |
| promoted: None, |
| }; |
| match self.selcx.tcx().at(obligation.cause.span) |
| .const_eval(obligation.param_env.and(cid)) { |
| Ok(_) => ProcessResult::Changed(vec![]), |
| Err(err) => ProcessResult::Error( |
| CodeSelectionError(ConstEvalFailure(err))) |
| } |
| } else { |
| ProcessResult::Error(CodeSelectionError( |
| ConstEvalFailure(ErrorHandled::TooGeneric) |
| )) |
| } |
| } else { |
| pending_obligation.stalled_on = substs.types().collect(); |
| ProcessResult::Unchanged |
| } |
| } |
| } |
| } |
| } |
| |
| 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); |
| } |
| } |
| } |
| |
| /// Returns the set of type variables contained in a trait ref |
| fn trait_ref_type_vars<'a, 'tcx>( |
| selcx: &mut SelectionContext<'a, 'tcx>, |
| t: ty::PolyTraitRef<'tcx>, |
| ) -> Vec<Ty<'tcx>> { |
| t.skip_binder() // ok b/c this check doesn't care about regions |
| .input_types() |
| .map(|t| selcx.infcx().resolve_vars_if_possible(&t)) |
| .filter(|t| t.has_infer_types()) |
| .flat_map(|t| t.walk()) |
| .filter(|t| match t.sty { ty::Infer(_) => true, _ => false }) |
| .collect() |
| } |
| |
| fn to_fulfillment_error<'tcx>( |
| error: Error<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>>) |
| -> FulfillmentError<'tcx> |
| { |
| let obligation = error.backtrace.into_iter().next().unwrap().obligation; |
| FulfillmentError::new(obligation, error.error) |
| } |
