compiler/rustc_trait_selection/src/solve/fulfill.rs

   1 use std::mem;
   2
   3 use rustc_infer::infer::InferCtxt;
   4 use rustc_infer::traits::{
   5     query::NoSolution, FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes,
   6     PredicateObligation, SelectionError, TraitEngine,
   7 };
   8 use rustc_middle::ty;
   9 use rustc_middle::ty::error::{ExpectedFound, TypeError};
  10
  11 use super::{Certainty, InferCtxtEvalExt};
  12
  13 /// A trait engine using the new trait solver.
  14 ///
  15 /// This is mostly identical to how `evaluate_all` works inside of the
  16 /// solver, except that the requirements are slightly different.
  17 ///
  18 /// Unlike `evaluate_all` it is possible to add new obligations later on
  19 /// and we also have to track diagnostics information by using `Obligation`
  20 /// instead of `Goal`.
  21 ///
  22 /// It is also likely that we want to use slightly different datastructures
  23 /// here as this will have to deal with far more root goals than `evaluate_all`.
  24 pub struct FulfillmentCtxt<'tcx> {
  25     obligations: Vec<PredicateObligation<'tcx>>,
  26 }
  27
  28 impl<'tcx> FulfillmentCtxt<'tcx> {
  29     pub fn new() -> FulfillmentCtxt<'tcx> {
  30         FulfillmentCtxt { obligations: Vec::new() }
  31     }
  32 }
  33
  34 impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
  35     fn register_predicate_obligation(
  36         &mut self,
  37         _infcx: &InferCtxt<'tcx>,
  38         obligation: PredicateObligation<'tcx>,
  39     ) {
  40         self.obligations.push(obligation);
  41     }
  42
  43     fn collect_remaining_errors(&mut self) -> Vec<FulfillmentError<'tcx>> {
  44         self.obligations
  45             .drain(..)
  46             .map(|obligation| FulfillmentError {
  47                 obligation: obligation.clone(),
  48                 code: FulfillmentErrorCode::CodeAmbiguity,
  49                 root_obligation: obligation,
  50             })
  51             .collect()
  52     }
  53
  54     fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
  55         let mut errors = Vec::new();
  56         for i in 0.. {
  57             if !infcx.tcx.recursion_limit().value_within_limit(i) {
  58                 unimplemented!("overflowed on pending obligations: {:?}", self.obligations);
  59             }
  60
  61             let mut has_changed = false;
  62             for obligation in mem::take(&mut self.obligations) {
  63                 let goal = obligation.clone().into();
  64                 let (changed, certainty) = match infcx.evaluate_root_goal(goal) {
  65                     Ok(result) => result,
  66                     Err(NoSolution) => {
  67                         errors.push(FulfillmentError {
  68                             obligation: obligation.clone(),
  69                             code: match goal.predicate.kind().skip_binder() {
  70                                 ty::PredicateKind::Clause(ty::Clause::Projection(_)) => {
  71                                     FulfillmentErrorCode::CodeProjectionError(
  72                                         // FIXME: This could be a `Sorts` if the term is a type
  73                                         MismatchedProjectionTypes { err: TypeError::Mismatch },
  74                                     )
  75                                 }
  76                                 ty::PredicateKind::Subtype(pred) => {
  77                                     let (a, b) = infcx.instantiate_binder_with_placeholders(
  78                                         goal.predicate.kind().rebind((pred.a, pred.b)),
  79                                     );
  80                                     let expected_found = ExpectedFound::new(true, a, b);
  81                                     FulfillmentErrorCode::CodeSubtypeError(
  82                                         expected_found,
  83                                         TypeError::Sorts(expected_found),
  84                                     )
  85                                 }
  86                                 ty::PredicateKind::Coerce(pred) => {
  87                                     let (a, b) = infcx.instantiate_binder_with_placeholders(
  88                                         goal.predicate.kind().rebind((pred.a, pred.b)),
  89                                     );
  90                                     let expected_found = ExpectedFound::new(false, a, b);
  91                                     FulfillmentErrorCode::CodeSubtypeError(
  92                                         expected_found,
  93                                         TypeError::Sorts(expected_found),
  94                                     )
  95                                 }
  96                                 ty::PredicateKind::ConstEquate(a, b) => {
  97                                     let (a, b) = infcx.instantiate_binder_with_placeholders(
  98                                         goal.predicate.kind().rebind((a, b)),
  99                                     );
 100                                     let expected_found = ExpectedFound::new(true, a, b);
 101                                     FulfillmentErrorCode::CodeConstEquateError(
 102                                         expected_found,
 103                                         TypeError::ConstMismatch(expected_found),
 104                                     )
 105                                 }
 106                                 ty::PredicateKind::Clause(_)
 107                                 | ty::PredicateKind::WellFormed(_)
 108                                 | ty::PredicateKind::ObjectSafe(_)
 109                                 | ty::PredicateKind::ClosureKind(_, _, _)
 110                                 | ty::PredicateKind::ConstEvaluatable(_)
 111                                 | ty::PredicateKind::TypeWellFormedFromEnv(_)
 112                                 | ty::PredicateKind::Ambiguous => {
 113                                     FulfillmentErrorCode::CodeSelectionError(
 114                                         SelectionError::Unimplemented,
 115                                     )
 116                                 }
 117                             },
 118                             root_obligation: obligation,
 119                         });
 120                         continue;
 121                     }
 122                 };
 123
 124                 has_changed |= changed;
 125                 match certainty {
 126                     Certainty::Yes => {}
 127                     Certainty::Maybe(_) => self.obligations.push(obligation),
 128                 }
 129             }
 130
 131             if !has_changed {
 132                 break;
 133             }
 134         }
 135
 136         errors
 137     }
 138
 139     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
 140         self.obligations.clone()
 141     }
 142
 143     fn drain_unstalled_obligations(
 144         &mut self,
 145         _: &InferCtxt<'tcx>,
 146     ) -> Vec<PredicateObligation<'tcx>> {
 147         unimplemented!()
 148     }
 149 }