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 select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
  44         let errors = self.select_where_possible(infcx);
  45         if !errors.is_empty() {
  46             return errors;
  47         }
  48
  49         self.obligations
  50             .drain(..)
  51             .map(|obligation| FulfillmentError {
  52                 obligation: obligation.clone(),
  53                 code: FulfillmentErrorCode::CodeAmbiguity,
  54                 root_obligation: obligation,
  55             })
  56             .collect()
  57     }
  58
  59     fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
  60         let mut errors = Vec::new();
  61         for i in 0.. {
  62             if !infcx.tcx.recursion_limit().value_within_limit(i) {
  63                 unimplemented!("overflowed on pending obligations: {:?}", self.obligations);
  64             }
  65
  66             let mut has_changed = false;
  67             for obligation in mem::take(&mut self.obligations) {
  68                 let goal = obligation.clone().into();
  69                 let (changed, certainty) = match infcx.evaluate_root_goal(goal) {
  70                     Ok(result) => result,
  71                     Err(NoSolution) => {
  72                         errors.push(FulfillmentError {
  73                             obligation: obligation.clone(),
  74                             code: match goal.predicate.kind().skip_binder() {
  75                                 ty::PredicateKind::Clause(ty::Clause::Projection(_)) => {
  76                                     FulfillmentErrorCode::CodeProjectionError(
  77                                         // FIXME: This could be a `Sorts` if the term is a type
  78                                         MismatchedProjectionTypes { err: TypeError::Mismatch },
  79                                     )
  80                                 }
  81                                 ty::PredicateKind::Subtype(pred) => {
  82                                     let (a, b) = infcx.replace_bound_vars_with_placeholders(
  83                                         goal.predicate.kind().rebind((pred.a, pred.b)),
  84                                     );
  85                                     let expected_found = ExpectedFound::new(true, a, b);
  86                                     FulfillmentErrorCode::CodeSubtypeError(
  87                                         expected_found,
  88                                         TypeError::Sorts(expected_found),
  89                                     )
  90                                 }
  91                                 ty::PredicateKind::Coerce(pred) => {
  92                                     let (a, b) = infcx.replace_bound_vars_with_placeholders(
  93                                         goal.predicate.kind().rebind((pred.a, pred.b)),
  94                                     );
  95                                     let expected_found = ExpectedFound::new(false, a, b);
  96                                     FulfillmentErrorCode::CodeSubtypeError(
  97                                         expected_found,
  98                                         TypeError::Sorts(expected_found),
  99                                     )
 100                                 }
 101                                 ty::PredicateKind::ConstEquate(a, b) => {
 102                                     let (a, b) = infcx.replace_bound_vars_with_placeholders(
 103                                         goal.predicate.kind().rebind((a, b)),
 104                                     );
 105                                     let expected_found = ExpectedFound::new(true, a, b);
 106                                     FulfillmentErrorCode::CodeConstEquateError(
 107                                         expected_found,
 108                                         TypeError::ConstMismatch(expected_found),
 109                                     )
 110                                 }
 111                                 ty::PredicateKind::Clause(_)
 112                                 | ty::PredicateKind::WellFormed(_)
 113                                 | ty::PredicateKind::ObjectSafe(_)
 114                                 | ty::PredicateKind::ClosureKind(_, _, _)
 115                                 | ty::PredicateKind::ConstEvaluatable(_)
 116                                 | ty::PredicateKind::TypeWellFormedFromEnv(_)
 117                                 | ty::PredicateKind::Ambiguous => {
 118                                     FulfillmentErrorCode::CodeSelectionError(
 119                                         SelectionError::Unimplemented,
 120                                     )
 121                                 }
 122                             },
 123                             root_obligation: obligation,
 124                         });
 125                         continue;
 126                     }
 127                 };
 128
 129                 has_changed |= changed;
 130                 match certainty {
 131                     Certainty::Yes => {}
 132                     Certainty::Maybe(_) => self.obligations.push(obligation),
 133                 }
 134             }
 135
 136             if !has_changed {
 137                 break;
 138             }
 139         }
 140
 141         errors
 142     }
 143
 144     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
 145         self.obligations.clone()
 146     }
 147 }