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