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, PredicateObligation,
   8     SelectionError, TraitEngine,
   9 };
  10 use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
  11 use rustc_middle::ty::{self, TypeVisitable};
  12
  13 pub struct FulfillmentContext<'tcx> {
  14     obligations: FxIndexSet<PredicateObligation<'tcx>>,
  15
  16     relationships: FxHashMap<ty::TyVid, ty::FoundRelationships>,
  17
  18     usable_in_snapshot: bool,
  19 }
  20
  21 impl FulfillmentContext<'_> {
  22     pub(super) fn new() -> Self {
  23         FulfillmentContext {
  24             obligations: FxIndexSet::default(),
  25             relationships: FxHashMap::default(),
  26             usable_in_snapshot: false,
  27         }
  28     }
  29
  30     pub(crate) fn new_in_snapshot() -> Self {
  31         FulfillmentContext { usable_in_snapshot: true, ..Self::new() }
  32     }
  33 }
  34
  35 impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
  36     fn register_predicate_obligation(
  37         &mut self,
  38         infcx: &InferCtxt<'tcx>,
  39         obligation: PredicateObligation<'tcx>,
  40     ) {
  41         if !self.usable_in_snapshot {
  42             assert!(!infcx.is_in_snapshot());
  43         }
  44         let obligation = infcx.resolve_vars_if_possible(obligation);
  45
  46         super::relationships::update(self, infcx, &obligation);
  47
  48         self.obligations.insert(obligation);
  49     }
  50
  51     fn select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
  52         {
  53             let errors = self.select_where_possible(infcx);
  54
  55             if !errors.is_empty() {
  56                 return errors;
  57             }
  58         }
  59
  60         // any remaining obligations are errors
  61         self.obligations
  62             .iter()
  63             .map(|obligation| FulfillmentError {
  64                 obligation: obligation.clone(),
  65                 code: FulfillmentErrorCode::CodeAmbiguity,
  66                 // FIXME - does Chalk have a notation of 'root obligation'?
  67                 // This is just for diagnostics, so it's okay if this is wrong
  68                 root_obligation: obligation.clone(),
  69             })
  70             .collect()
  71     }
  72
  73     fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
  74         if !self.usable_in_snapshot {
  75             assert!(!infcx.is_in_snapshot());
  76         }
  77
  78         let mut errors = Vec::new();
  79         let mut next_round = FxIndexSet::default();
  80         let mut making_progress;
  81
  82         loop {
  83             making_progress = false;
  84
  85             // We iterate over all obligations, and record if we are able
  86             // to unambiguously prove at least one obligation.
  87             for obligation in self.obligations.drain(..) {
  88                 let obligation = infcx.resolve_vars_if_possible(obligation);
  89                 let environment = obligation.param_env.caller_bounds();
  90                 let goal = ChalkEnvironmentAndGoal { environment, goal: obligation.predicate };
  91                 let mut orig_values = OriginalQueryValues::default();
  92                 if goal.references_error() {
  93                     continue;
  94                 }
  95
  96                 let canonical_goal =
  97                     infcx.canonicalize_query_preserving_universes(goal, &mut orig_values);
  98
  99                 match infcx.tcx.evaluate_goal(canonical_goal) {
 100                     Ok(response) => {
 101                         if response.is_proven() {
 102                             making_progress = true;
 103
 104                             match infcx.instantiate_query_response_and_region_obligations(
 105                                 &obligation.cause,
 106                                 obligation.param_env,
 107                                 &orig_values,
 108                                 &response,
 109                             ) {
 110                                 Ok(infer_ok) => next_round.extend(
 111                                     infer_ok.obligations.into_iter().map(|obligation| {
 112                                         assert!(!infcx.is_in_snapshot());
 113                                         infcx.resolve_vars_if_possible(obligation)
 114                                     }),
 115                                 ),
 116
 117                                 Err(_err) => errors.push(FulfillmentError {
 118                                     obligation: obligation.clone(),
 119                                     code: FulfillmentErrorCode::CodeSelectionError(
 120                                         SelectionError::Unimplemented,
 121                                     ),
 122                                     // FIXME - does Chalk have a notation of 'root obligation'?
 123                                     // This is just for diagnostics, so it's okay if this is wrong
 124                                     root_obligation: obligation,
 125                                 }),
 126                             }
 127                         } else {
 128                             // Ambiguous: retry at next round.
 129                             next_round.insert(obligation);
 130                         }
 131                     }
 132
 133                     Err(NoSolution) => errors.push(FulfillmentError {
 134                         obligation: obligation.clone(),
 135                         code: FulfillmentErrorCode::CodeSelectionError(
 136                             SelectionError::Unimplemented,
 137                         ),
 138                         // FIXME - does Chalk have a notation of 'root obligation'?
 139                         // This is just for diagnostics, so it's okay if this is wrong
 140                         root_obligation: obligation,
 141                     }),
 142                 }
 143             }
 144             next_round = std::mem::replace(&mut self.obligations, next_round);
 145
 146             if !making_progress {
 147                 break;
 148             }
 149         }
 150
 151         errors
 152     }
 153
 154     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
 155         self.obligations.iter().cloned().collect()
 156     }
 157
 158     fn relationships(&mut self) -> &mut FxHashMap<ty::TyVid, ty::FoundRelationships> {
 159         &mut self.relationships
 160     }
 161 }