595 lines
24 KiB
Rust
595 lines
24 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use infer::{InferCtxt, InferOk};
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use ty::{self, Ty, TypeFoldable, ToPolyTraitRef, ToPredicate};
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use ty::error::ExpectedFound;
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use rustc_data_structures::obligation_forest::{ObligationForest, Error};
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use rustc_data_structures::obligation_forest::{ForestObligation, ObligationProcessor};
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use std::marker::PhantomData;
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use syntax::ast;
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use util::nodemap::NodeMap;
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use hir::def_id::DefId;
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use super::CodeAmbiguity;
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use super::CodeProjectionError;
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use super::CodeSelectionError;
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use super::{FulfillmentError, FulfillmentErrorCode};
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use super::{ObligationCause, PredicateObligation, Obligation};
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use super::project;
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use super::select::SelectionContext;
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use super::{Unimplemented, ConstEvalFailure};
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impl<'tcx> ForestObligation for PendingPredicateObligation<'tcx> {
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type Predicate = ty::Predicate<'tcx>;
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fn as_predicate(&self) -> &Self::Predicate { &self.obligation.predicate }
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}
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/// The fulfillment context is used to drive trait resolution. It
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/// consists of a list of obligations that must be (eventually)
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/// satisfied. The job is to track which are satisfied, which yielded
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/// errors, and which are still pending. At any point, users can call
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/// `select_where_possible`, and the fulfillment context will try to do
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/// selection, retaining only those obligations that remain
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/// ambiguous. This may be helpful in pushing type inference
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/// along. Once all type inference constraints have been generated, the
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/// method `select_all_or_error` can be used to report any remaining
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/// ambiguous cases as errors.
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pub struct FulfillmentContext<'tcx> {
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// A list of all obligations that have been registered with this
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// fulfillment context.
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predicates: ObligationForest<PendingPredicateObligation<'tcx>>,
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// A set of constraints that regionck must validate. Each
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// constraint has the form `T:'a`, meaning "some type `T` must
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// outlive the lifetime 'a". These constraints derive from
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// instantiated type parameters. So if you had a struct defined
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// like
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//
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// struct Foo<T:'static> { ... }
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//
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// then in some expression `let x = Foo { ... }` it will
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// instantiate the type parameter `T` with a fresh type `$0`. At
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// the same time, it will record a region obligation of
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// `$0:'static`. This will get checked later by regionck. (We
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// can't generally check these things right away because we have
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// to wait until types are resolved.)
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//
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// These are stored in a map keyed to the id of the innermost
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// enclosing fn body / static initializer expression. This is
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// because the location where the obligation was incurred can be
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// relevant with respect to which sublifetime assumptions are in
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// place. The reason that we store under the fn-id, and not
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// something more fine-grained, is so that it is easier for
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// regionck to be sure that it has found *all* the region
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// obligations (otherwise, it's easy to fail to walk to a
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// particular node-id).
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region_obligations: NodeMap<Vec<RegionObligation<'tcx>>>,
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}
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#[derive(Clone)]
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pub struct RegionObligation<'tcx> {
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pub sub_region: ty::Region<'tcx>,
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pub sup_type: Ty<'tcx>,
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pub cause: ObligationCause<'tcx>,
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}
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#[derive(Clone, Debug)]
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pub struct PendingPredicateObligation<'tcx> {
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pub obligation: PredicateObligation<'tcx>,
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pub stalled_on: Vec<Ty<'tcx>>,
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}
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impl<'a, 'gcx, 'tcx> FulfillmentContext<'tcx> {
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/// Creates a new fulfillment context.
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pub fn new() -> FulfillmentContext<'tcx> {
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FulfillmentContext {
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predicates: ObligationForest::new(),
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region_obligations: NodeMap(),
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}
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}
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/// "Normalize" a projection type `<SomeType as SomeTrait>::X` by
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/// creating a fresh type variable `$0` as well as a projection
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/// predicate `<SomeType as SomeTrait>::X == $0`. When the
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/// inference engine runs, it will attempt to find an impl of
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/// `SomeTrait` or a where clause that lets us unify `$0` with
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/// something concrete. If this fails, we'll unify `$0` with
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/// `projection_ty` again.
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pub fn normalize_projection_type(&mut self,
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infcx: &InferCtxt<'a, 'gcx, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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projection_ty: ty::ProjectionTy<'tcx>,
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cause: ObligationCause<'tcx>)
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-> Ty<'tcx>
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{
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debug!("normalize_projection_type(projection_ty={:?})",
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projection_ty);
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assert!(!projection_ty.has_escaping_regions());
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// FIXME(#20304) -- cache
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let mut selcx = SelectionContext::new(infcx);
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let normalized = project::normalize_projection_type(&mut selcx,
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param_env,
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projection_ty,
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cause,
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0);
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for obligation in normalized.obligations {
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self.register_predicate_obligation(infcx, obligation);
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}
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debug!("normalize_projection_type: result={:?}", normalized.value);
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normalized.value
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}
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/// Requires that `ty` must implement the trait with `def_id` in
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/// the given environment. This trait must not have any type
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/// parameters (except for `Self`).
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pub fn register_bound(&mut self,
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infcx: &InferCtxt<'a, 'gcx, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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ty: Ty<'tcx>,
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def_id: DefId,
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cause: ObligationCause<'tcx>)
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{
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let trait_ref = ty::TraitRef {
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def_id,
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substs: infcx.tcx.mk_substs_trait(ty, &[]),
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};
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self.register_predicate_obligation(infcx, Obligation {
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cause,
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recursion_depth: 0,
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param_env,
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predicate: trait_ref.to_predicate()
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});
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}
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pub fn register_region_obligation(&mut self,
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t_a: Ty<'tcx>,
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r_b: ty::Region<'tcx>,
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cause: ObligationCause<'tcx>)
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{
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register_region_obligation(t_a, r_b, cause, &mut self.region_obligations);
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}
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pub fn register_predicate_obligation(&mut self,
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infcx: &InferCtxt<'a, 'gcx, 'tcx>,
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obligation: PredicateObligation<'tcx>)
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{
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// this helps to reduce duplicate errors, as well as making
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// debug output much nicer to read and so on.
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let obligation = infcx.resolve_type_vars_if_possible(&obligation);
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debug!("register_predicate_obligation(obligation={:?})", obligation);
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assert!(!infcx.is_in_snapshot());
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self.predicates.register_obligation(PendingPredicateObligation {
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obligation,
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stalled_on: vec![]
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});
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}
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pub fn register_predicate_obligations(&mut self,
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infcx: &InferCtxt<'a, 'gcx, 'tcx>,
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obligations: Vec<PredicateObligation<'tcx>>)
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{
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for obligation in obligations {
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self.register_predicate_obligation(infcx, obligation);
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}
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}
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pub fn region_obligations(&self,
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body_id: ast::NodeId)
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-> &[RegionObligation<'tcx>]
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{
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match self.region_obligations.get(&body_id) {
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None => Default::default(),
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Some(vec) => vec,
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}
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}
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pub fn select_all_or_error(&mut self,
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infcx: &InferCtxt<'a, 'gcx, 'tcx>)
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-> Result<(),Vec<FulfillmentError<'tcx>>>
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{
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self.select_where_possible(infcx)?;
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let errors: Vec<_> =
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self.predicates.to_errors(CodeAmbiguity)
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.into_iter()
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.map(|e| to_fulfillment_error(e))
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.collect();
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if errors.is_empty() {
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Ok(())
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} else {
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Err(errors)
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}
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}
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pub fn select_where_possible(&mut self,
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infcx: &InferCtxt<'a, 'gcx, 'tcx>)
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-> Result<(),Vec<FulfillmentError<'tcx>>>
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{
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let mut selcx = SelectionContext::new(infcx);
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self.select(&mut selcx)
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}
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pub fn pending_obligations(&self) -> Vec<PendingPredicateObligation<'tcx>> {
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self.predicates.pending_obligations()
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}
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/// Attempts to select obligations using `selcx`. If `only_new_obligations` is true, then it
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/// only attempts to select obligations that haven't been seen before.
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fn select(&mut self, selcx: &mut SelectionContext<'a, 'gcx, 'tcx>)
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-> Result<(),Vec<FulfillmentError<'tcx>>> {
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debug!("select(obligation-forest-size={})", self.predicates.len());
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let mut errors = Vec::new();
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loop {
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debug!("select: starting another iteration");
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// Process pending obligations.
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let outcome = self.predicates.process_obligations(&mut FulfillProcessor {
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selcx,
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region_obligations: &mut self.region_obligations,
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});
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debug!("select: outcome={:?}", outcome);
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// FIXME: if we kept the original cache key, we could mark projection
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// obligations as complete for the projection cache here.
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errors.extend(
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outcome.errors.into_iter()
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.map(|e| to_fulfillment_error(e)));
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// If nothing new was added, no need to keep looping.
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if outcome.stalled {
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break;
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}
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}
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debug!("select({} predicates remaining, {} errors) done",
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self.predicates.len(), errors.len());
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if errors.is_empty() {
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Ok(())
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} else {
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Err(errors)
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}
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}
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}
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struct FulfillProcessor<'a, 'b: 'a, 'gcx: 'tcx, 'tcx: 'b> {
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selcx: &'a mut SelectionContext<'b, 'gcx, 'tcx>,
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region_obligations: &'a mut NodeMap<Vec<RegionObligation<'tcx>>>,
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}
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impl<'a, 'b, 'gcx, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'gcx, 'tcx> {
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type Obligation = PendingPredicateObligation<'tcx>;
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type Error = FulfillmentErrorCode<'tcx>;
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fn process_obligation(&mut self,
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obligation: &mut Self::Obligation)
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-> Result<Option<Vec<Self::Obligation>>, Self::Error>
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{
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process_predicate(self.selcx,
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obligation,
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self.region_obligations)
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.map(|os| os.map(|os| os.into_iter().map(|o| PendingPredicateObligation {
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obligation: o,
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stalled_on: vec![]
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}).collect()))
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}
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fn process_backedge<'c, I>(&mut self, cycle: I,
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_marker: PhantomData<&'c PendingPredicateObligation<'tcx>>)
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where I: Clone + Iterator<Item=&'c PendingPredicateObligation<'tcx>>,
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{
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if self.selcx.coinductive_match(cycle.clone().map(|s| s.obligation.predicate)) {
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debug!("process_child_obligations: coinductive match");
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} else {
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let cycle : Vec<_> = cycle.map(|c| c.obligation.clone()).collect();
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self.selcx.infcx().report_overflow_error_cycle(&cycle);
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}
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}
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}
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/// Return the set of type variables contained in a trait ref
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fn trait_ref_type_vars<'a, 'gcx, 'tcx>(selcx: &mut SelectionContext<'a, 'gcx, 'tcx>,
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t: ty::PolyTraitRef<'tcx>) -> Vec<Ty<'tcx>>
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{
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t.skip_binder() // ok b/c this check doesn't care about regions
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.input_types()
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.map(|t| selcx.infcx().resolve_type_vars_if_possible(&t))
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.filter(|t| t.has_infer_types())
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.flat_map(|t| t.walk())
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.filter(|t| match t.sty { ty::TyInfer(_) => true, _ => false })
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.collect()
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}
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/// Processes a predicate obligation and returns either:
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/// - `Ok(Some(v))` if the predicate is true, presuming that `v` are also true
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/// - `Ok(None)` if we don't have enough info to be sure
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/// - `Err` if the predicate does not hold
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fn process_predicate<'a, 'gcx, 'tcx>(
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selcx: &mut SelectionContext<'a, 'gcx, 'tcx>,
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pending_obligation: &mut PendingPredicateObligation<'tcx>,
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region_obligations: &mut NodeMap<Vec<RegionObligation<'tcx>>>)
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-> Result<Option<Vec<PredicateObligation<'tcx>>>,
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FulfillmentErrorCode<'tcx>>
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{
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// if we were stalled on some unresolved variables, first check
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// whether any of them have been resolved; if not, don't bother
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// doing more work yet
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if !pending_obligation.stalled_on.is_empty() {
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if pending_obligation.stalled_on.iter().all(|&ty| {
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let resolved_ty = selcx.infcx().shallow_resolve(&ty);
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resolved_ty == ty // nothing changed here
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}) {
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debug!("process_predicate: pending obligation {:?} still stalled on {:?}",
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selcx.infcx().resolve_type_vars_if_possible(&pending_obligation.obligation),
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pending_obligation.stalled_on);
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return Ok(None);
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}
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pending_obligation.stalled_on = vec![];
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}
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let obligation = &mut pending_obligation.obligation;
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if obligation.predicate.has_infer_types() {
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obligation.predicate = selcx.infcx().resolve_type_vars_if_possible(&obligation.predicate);
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}
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match obligation.predicate {
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ty::Predicate::Trait(ref data) => {
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let trait_obligation = obligation.with(data.clone());
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if data.is_global() {
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// no type variables present, can use evaluation for better caching.
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// FIXME: consider caching errors too.
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if
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// make defaulted unit go through the slow path for better warnings,
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// please remove this when the warnings are removed.
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!trait_obligation.predicate.skip_binder().self_ty().is_defaulted_unit() &&
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selcx.evaluate_obligation_conservatively(&obligation) {
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debug!("selecting trait `{:?}` at depth {} evaluated to holds",
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data, obligation.recursion_depth);
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return Ok(Some(vec![]))
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}
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}
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match selcx.select(&trait_obligation) {
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Ok(Some(vtable)) => {
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debug!("selecting trait `{:?}` at depth {} yielded Ok(Some)",
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data, obligation.recursion_depth);
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Ok(Some(vtable.nested_obligations()))
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}
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Ok(None) => {
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debug!("selecting trait `{:?}` at depth {} yielded Ok(None)",
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data, obligation.recursion_depth);
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// This is a bit subtle: for the most part, the
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// only reason we can fail to make progress on
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// trait selection is because we don't have enough
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// information about the types in the trait. One
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// exception is that we sometimes haven't decided
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// what kind of closure a closure is. *But*, in
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// that case, it turns out, the type of the
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// closure will also change, because the closure
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// also includes references to its upvars as part
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// of its type, and those types are resolved at
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// the same time.
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//
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// FIXME(#32286) logic seems false if no upvars
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pending_obligation.stalled_on =
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trait_ref_type_vars(selcx, data.to_poly_trait_ref());
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debug!("process_predicate: pending obligation {:?} now stalled on {:?}",
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selcx.infcx().resolve_type_vars_if_possible(obligation),
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pending_obligation.stalled_on);
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Ok(None)
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}
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Err(selection_err) => {
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info!("selecting trait `{:?}` at depth {} yielded Err",
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data, obligation.recursion_depth);
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Err(CodeSelectionError(selection_err))
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}
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}
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}
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ty::Predicate::Equate(ref binder) => {
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match selcx.infcx().equality_predicate(&obligation.cause,
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obligation.param_env,
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binder) {
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Ok(InferOk { obligations, value: () }) => {
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Ok(Some(obligations))
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},
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Err(_) => Err(CodeSelectionError(Unimplemented)),
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}
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}
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ty::Predicate::RegionOutlives(ref binder) => {
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match selcx.infcx().region_outlives_predicate(&obligation.cause, binder) {
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Ok(()) => Ok(Some(Vec::new())),
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Err(_) => Err(CodeSelectionError(Unimplemented)),
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}
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}
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ty::Predicate::TypeOutlives(ref binder) => {
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// Check if there are higher-ranked regions.
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match selcx.tcx().no_late_bound_regions(binder) {
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// If there are, inspect the underlying type further.
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None => {
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// Convert from `Binder<OutlivesPredicate<Ty, Region>>` to `Binder<Ty>`.
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let binder = binder.map_bound_ref(|pred| pred.0);
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// Check if the type has any bound regions.
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match selcx.tcx().no_late_bound_regions(&binder) {
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// If so, this obligation is an error (for now). Eventually we should be
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// able to support additional cases here, like `for<'a> &'a str: 'a`.
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None => {
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Err(CodeSelectionError(Unimplemented))
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}
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// Otherwise, we have something of the form
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// `for<'a> T: 'a where 'a not in T`, which we can treat as `T: 'static`.
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Some(t_a) => {
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let r_static = selcx.tcx().types.re_static;
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register_region_obligation(t_a, r_static,
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obligation.cause.clone(),
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region_obligations);
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Ok(Some(vec![]))
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}
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}
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}
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// If there aren't, register the obligation.
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Some(ty::OutlivesPredicate(t_a, r_b)) => {
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register_region_obligation(t_a, r_b,
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obligation.cause.clone(),
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region_obligations);
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Ok(Some(vec![]))
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}
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|
}
|
|
}
|
|
|
|
ty::Predicate::Projection(ref data) => {
|
|
let project_obligation = obligation.with(data.clone());
|
|
match project::poly_project_and_unify_type(selcx, &project_obligation) {
|
|
Ok(None) => {
|
|
let tcx = selcx.tcx();
|
|
pending_obligation.stalled_on =
|
|
trait_ref_type_vars(selcx, data.to_poly_trait_ref(tcx));
|
|
Ok(None)
|
|
}
|
|
Ok(v) => Ok(v),
|
|
Err(e) => Err(CodeProjectionError(e))
|
|
}
|
|
}
|
|
|
|
ty::Predicate::ObjectSafe(trait_def_id) => {
|
|
if !selcx.tcx().is_object_safe(trait_def_id) {
|
|
Err(CodeSelectionError(Unimplemented))
|
|
} else {
|
|
Ok(Some(Vec::new()))
|
|
}
|
|
}
|
|
|
|
ty::Predicate::ClosureKind(closure_def_id, kind) => {
|
|
match selcx.infcx().closure_kind(closure_def_id) {
|
|
Some(closure_kind) => {
|
|
if closure_kind.extends(kind) {
|
|
Ok(Some(vec![]))
|
|
} else {
|
|
Err(CodeSelectionError(Unimplemented))
|
|
}
|
|
}
|
|
None => {
|
|
Ok(None)
|
|
}
|
|
}
|
|
}
|
|
|
|
ty::Predicate::WellFormed(ty) => {
|
|
match ty::wf::obligations(selcx.infcx(),
|
|
obligation.param_env,
|
|
obligation.cause.body_id,
|
|
ty, obligation.cause.span) {
|
|
None => {
|
|
pending_obligation.stalled_on = vec![ty];
|
|
Ok(None)
|
|
}
|
|
s => Ok(s)
|
|
}
|
|
}
|
|
|
|
ty::Predicate::Subtype(ref subtype) => {
|
|
match 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];
|
|
Ok(None)
|
|
}
|
|
Some(Ok(ok)) => {
|
|
Ok(Some(ok.obligations))
|
|
}
|
|
Some(Err(err)) => {
|
|
let expected_found = ExpectedFound::new(subtype.skip_binder().a_is_expected,
|
|
subtype.skip_binder().a,
|
|
subtype.skip_binder().b);
|
|
Err(FulfillmentErrorCode::CodeSubtypeError(expected_found, err))
|
|
}
|
|
}
|
|
}
|
|
|
|
ty::Predicate::ConstEvaluatable(def_id, substs) => {
|
|
match selcx.tcx().lift_to_global(&obligation.param_env) {
|
|
None => {
|
|
Ok(None)
|
|
}
|
|
Some(param_env) => {
|
|
match selcx.tcx().lift_to_global(&substs) {
|
|
None => {
|
|
pending_obligation.stalled_on = substs.types().collect();
|
|
Ok(None)
|
|
}
|
|
Some(substs) => {
|
|
match selcx.tcx().at(obligation.cause.span)
|
|
.const_eval(param_env.and((def_id, substs))) {
|
|
Ok(_) => Ok(Some(vec![])),
|
|
Err(e) => Err(CodeSelectionError(ConstEvalFailure(e)))
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
fn register_region_obligation<'tcx>(t_a: Ty<'tcx>,
|
|
r_b: ty::Region<'tcx>,
|
|
cause: ObligationCause<'tcx>,
|
|
region_obligations: &mut NodeMap<Vec<RegionObligation<'tcx>>>)
|
|
{
|
|
let region_obligation = RegionObligation { sup_type: t_a,
|
|
sub_region: r_b,
|
|
cause: cause };
|
|
|
|
debug!("register_region_obligation({:?}, cause={:?})",
|
|
region_obligation, region_obligation.cause);
|
|
|
|
region_obligations.entry(region_obligation.cause.body_id)
|
|
.or_insert(vec![])
|
|
.push(region_obligation);
|
|
|
|
}
|
|
|
|
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)
|
|
}
|