compiler/rustc_trait_selection/src/traits/chalk_fulfill.rs

   1 //! Defines a Chalk-based `TraitEngine`
   2
   3 use crate::infer::canonical::OriginalQueryValues;
   4 use crate::infer::InferCtxt;
   5 use crate::traits::query::NoSolution;
   6 use crate::traits::{
   7     ChalkEnvironmentAndGoal, FulfillmentError, FulfillmentErrorCode, ObligationCause,
   8     PredicateObligation, SelectionError, TraitEngine,
   9 };
  10 use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
  11 use rustc_middle::ty::{self, Ty};
  12
  13 pub struct FulfillmentContext<'tcx> {
  14     obligations: FxIndexSet<PredicateObligation<'tcx>>,
  15
  16     relationships: FxHashMap<ty::TyVid, ty::FoundRelationships>,
  17 }
  18
  19 impl FulfillmentContext<'tcx> {
  20     crate fn new() -> Self {
  21         FulfillmentContext {
  22             obligations: FxIndexSet::default(),
  23             relationships: FxHashMap::default(),
  24         }
  25     }
  26 }
  27
  28 impl TraitEngine<'tcx> for FulfillmentContext<'tcx> {
  29     fn normalize_projection_type(
  30         &mut self,
  31         infcx: &InferCtxt<'_, 'tcx>,
  32         _param_env: ty::ParamEnv<'tcx>,
  33         projection_ty: ty::ProjectionTy<'tcx>,
  34         _cause: ObligationCause<'tcx>,
  35     ) -> Ty<'tcx> {
  36         infcx.tcx.mk_ty(ty::Projection(projection_ty))
  37     }
  38
  39     fn register_predicate_obligation(
  40         &mut self,
  41         infcx: &InferCtxt<'_, 'tcx>,
  42         obligation: PredicateObligation<'tcx>,
  43     ) {
  44         assert!(!infcx.is_in_snapshot());
  45         let obligation = infcx.resolve_vars_if_possible(obligation);
  46
  47         super::relationships::update(self, infcx, &obligation);
  48
  49         self.obligations.insert(obligation);
  50     }
  51
  52     fn select_all_or_error(
  53         &mut self,
  54         infcx: &InferCtxt<'_, 'tcx>,
  55     ) -> Result<(), Vec<FulfillmentError<'tcx>>> {
  56         self.select_where_possible(infcx)?;
  57
  58         if self.obligations.is_empty() {
  59             Ok(())
  60         } else {
  61             let errors = self
  62                 .obligations
  63                 .iter()
  64                 .map(|obligation| FulfillmentError {
  65                     obligation: obligation.clone(),
  66                     code: FulfillmentErrorCode::CodeAmbiguity,
  67                     // FIXME - does Chalk have a notation of 'root obligation'?
  68                     // This is just for diagnostics, so it's okay if this is wrong
  69                     root_obligation: obligation.clone(),
  70                 })
  71                 .collect();
  72             Err(errors)
  73         }
  74     }
  75
  76     fn select_where_possible(
  77         &mut self,
  78         infcx: &InferCtxt<'_, 'tcx>,
  79     ) -> Result<(), Vec<FulfillmentError<'tcx>>> {
  80         assert!(!infcx.is_in_snapshot());
  81
  82         let mut errors = Vec::new();
  83         let mut next_round = FxIndexSet::default();
  84         let mut making_progress;
  85
  86         loop {
  87             making_progress = false;
  88
  89             // We iterate over all obligations, and record if we are able
  90             // to unambiguously prove at least one obligation.
  91             for obligation in self.obligations.drain(..) {
  92                 let obligation = infcx.resolve_vars_if_possible(obligation);
  93                 let environment = obligation.param_env.caller_bounds();
  94                 let goal = ChalkEnvironmentAndGoal { environment, goal: obligation.predicate };
  95                 let mut orig_values = OriginalQueryValues::default();
  96                 let canonical_goal = infcx.canonicalize_query(goal, &mut orig_values);
  97
  98                 match infcx.tcx.evaluate_goal(canonical_goal) {
  99                     Ok(response) => {
 100                         if response.is_proven() {
 101                             making_progress = true;
 102
 103                             match infcx.instantiate_query_response_and_region_obligations(
 104                                 &obligation.cause,
 105                                 obligation.param_env,
 106                                 &orig_values,
 107                                 &response,
 108                             ) {
 109                                 Ok(infer_ok) => next_round.extend(
 110                                     infer_ok.obligations.into_iter().map(|obligation| {
 111                                         assert!(!infcx.is_in_snapshot());
 112                                         infcx.resolve_vars_if_possible(obligation)
 113                                     }),
 114                                 ),
 115
 116                                 Err(_err) => errors.push(FulfillmentError {
 117                                     obligation: obligation.clone(),
 118                                     code: FulfillmentErrorCode::CodeSelectionError(
 119                                         SelectionError::Unimplemented,
 120                                     ),
 121                                     // FIXME - does Chalk have a notation of 'root obligation'?
 122                                     // This is just for diagnostics, so it's okay if this is wrong
 123                                     root_obligation: obligation,
 124                                 }),
 125                             }
 126                         } else {
 127                             // Ambiguous: retry at next round.
 128                             next_round.insert(obligation);
 129                         }
 130                     }
 131
 132                     Err(NoSolution) => errors.push(FulfillmentError {
 133                         obligation: obligation.clone(),
 134                         code: FulfillmentErrorCode::CodeSelectionError(
 135                             SelectionError::Unimplemented,
 136                         ),
 137                         // FIXME - does Chalk have a notation of 'root obligation'?
 138                         // This is just for diagnostics, so it's okay if this is wrong
 139                         root_obligation: obligation,
 140                     }),
 141                 }
 142             }
 143             next_round = std::mem::replace(&mut self.obligations, next_round);
 144
 145             if !making_progress {
 146                 break;
 147             }
 148         }
 149
 150         if errors.is_empty() { Ok(()) } else { Err(errors) }
 151     }
 152
 153     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
 154         self.obligations.iter().cloned().collect()
 155     }
 156
 157     fn relationships(&mut self) -> &mut FxHashMap<ty::TyVid, ty::FoundRelationships> {
 158         &mut self.relationships
 159     }
 160 }