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     ) -> Vec<FulfillmentError<'tcx>> {
  56         {
  57             let errors = self.select_where_possible(infcx);
  58
  59             if !errors.is_empty() {
  60                 return errors;
  61             }
  62         }
  63
  64         // any remaining obligations are errors
  65         self
  66             .obligations
  67             .iter()
  68             .map(|obligation| FulfillmentError {
  69                 obligation: obligation.clone(),
  70                 code: FulfillmentErrorCode::CodeAmbiguity,
  71                 // FIXME - does Chalk have a notation of 'root obligation'?
  72                 // This is just for diagnostics, so it's okay if this is wrong
  73                 root_obligation: obligation.clone(),
  74             })
  75             .collect()
  76     }
  77
  78     fn select_where_possible(
  79         &mut self,
  80         infcx: &InferCtxt<'_, 'tcx>,
  81     ) -> Vec<FulfillmentError<'tcx>> {
  82         assert!(!infcx.is_in_snapshot());
  83
  84         let mut errors = Vec::new();
  85         let mut next_round = FxIndexSet::default();
  86         let mut making_progress;
  87
  88         loop {
  89             making_progress = false;
  90
  91             // We iterate over all obligations, and record if we are able
  92             // to unambiguously prove at least one obligation.
  93             for obligation in self.obligations.drain(..) {
  94                 let obligation = infcx.resolve_vars_if_possible(obligation);
  95                 let environment = obligation.param_env.caller_bounds();
  96                 let goal = ChalkEnvironmentAndGoal { environment, goal: obligation.predicate };
  97                 let mut orig_values = OriginalQueryValues::default();
  98                 let canonical_goal = infcx.canonicalize_query(goal, &mut orig_values);
  99
 100                 match infcx.tcx.evaluate_goal(canonical_goal) {
 101                     Ok(response) => {
 102                         if response.is_proven() {
 103                             making_progress = true;
 104
 105                             match infcx.instantiate_query_response_and_region_obligations(
 106                                 &obligation.cause,
 107                                 obligation.param_env,
 108                                 &orig_values,
 109                                 &response,
 110                             ) {
 111                                 Ok(infer_ok) => next_round.extend(
 112                                     infer_ok.obligations.into_iter().map(|obligation| {
 113                                         assert!(!infcx.is_in_snapshot());
 114                                         infcx.resolve_vars_if_possible(obligation)
 115                                     }),
 116                                 ),
 117
 118                                 Err(_err) => errors.push(FulfillmentError {
 119                                     obligation: obligation.clone(),
 120                                     code: FulfillmentErrorCode::CodeSelectionError(
 121                                         SelectionError::Unimplemented,
 122                                     ),
 123                                     // FIXME - does Chalk have a notation of 'root obligation'?
 124                                     // This is just for diagnostics, so it's okay if this is wrong
 125                                     root_obligation: obligation,
 126                                 }),
 127                             }
 128                         } else {
 129                             // Ambiguous: retry at next round.
 130                             next_round.insert(obligation);
 131                         }
 132                     }
 133
 134                     Err(NoSolution) => errors.push(FulfillmentError {
 135                         obligation: obligation.clone(),
 136                         code: FulfillmentErrorCode::CodeSelectionError(
 137                             SelectionError::Unimplemented,
 138                         ),
 139                         // FIXME - does Chalk have a notation of 'root obligation'?
 140                         // This is just for diagnostics, so it's okay if this is wrong
 141                         root_obligation: obligation,
 142                     }),
 143                 }
 144             }
 145             next_round = std::mem::replace(&mut self.obligations, next_round);
 146
 147             if !making_progress {
 148                 break;
 149             }
 150         }
 151
 152         errors
 153     }
 154
 155     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
 156         self.obligations.iter().cloned().collect()
 157     }
 158
 159     fn relationships(&mut self) -> &mut FxHashMap<ty::TyVid, ty::FoundRelationships> {
 160         &mut self.relationships
 161     }
 162 }