compiler/rustc_trait_selection/src/solve/fulfill.rs

   1 use std::mem;
   2
   3 use rustc_data_structures::fx::FxHashMap;
   4 use rustc_infer::{
   5     infer::InferCtxt,
   6     traits::{
   7         query::NoSolution, FulfillmentError, FulfillmentErrorCode, PredicateObligation,
   8         SelectionError, TraitEngine,
   9     },
  10 };
  11 use rustc_middle::ty;
  12
  13 use super::{search_graph, Certainty, EvalCtxt};
  14
  15 /// A trait engine using the new trait solver.
  16 ///
  17 /// This is mostly identical to how `evaluate_all` works inside of the
  18 /// solver, except that the requirements are slightly different.
  19 ///
  20 /// Unlike `evaluate_all` it is possible to add new obligations later on
  21 /// and we also have to track diagnostics information by using `Obligation`
  22 /// instead of `Goal`.
  23 ///
  24 /// It is also likely that we want to use slightly different datastructures
  25 /// here as this will have to deal with far more root goals than `evaluate_all`.
  26 pub struct FulfillmentCtxt<'tcx> {
  27     obligations: Vec<PredicateObligation<'tcx>>,
  28 }
  29
  30 impl<'tcx> FulfillmentCtxt<'tcx> {
  31     pub fn new() -> FulfillmentCtxt<'tcx> {
  32         FulfillmentCtxt { obligations: Vec::new() }
  33     }
  34 }
  35
  36 impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
  37     fn register_predicate_obligation(
  38         &mut self,
  39         _infcx: &InferCtxt<'tcx>,
  40         obligation: PredicateObligation<'tcx>,
  41     ) {
  42         self.obligations.push(obligation);
  43     }
  44
  45     fn select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
  46         let errors = self.select_where_possible(infcx);
  47         if !errors.is_empty() {
  48             return errors;
  49         }
  50
  51         self.obligations
  52             .drain(..)
  53             .map(|obligation| FulfillmentError {
  54                 obligation: obligation.clone(),
  55                 code: FulfillmentErrorCode::CodeAmbiguity,
  56                 root_obligation: obligation,
  57             })
  58             .collect()
  59     }
  60
  61     fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
  62         let mut errors = Vec::new();
  63         for i in 0.. {
  64             if !infcx.tcx.recursion_limit().value_within_limit(i) {
  65                 unimplemented!("overflowed on pending obligations: {:?}", self.obligations);
  66             }
  67
  68             let mut has_changed = false;
  69             for obligation in mem::take(&mut self.obligations) {
  70                 let goal = obligation.clone().into();
  71                 let search_graph = &mut search_graph::SearchGraph::new(infcx.tcx);
  72                 let mut ecx = EvalCtxt::new_outside_solver(infcx, search_graph);
  73                 let (changed, certainty) = match ecx.evaluate_goal(goal) {
  74                     Ok(result) => result,
  75                     Err(NoSolution) => {
  76                         errors.push(FulfillmentError {
  77                             obligation: obligation.clone(),
  78                             code: FulfillmentErrorCode::CodeSelectionError(
  79                                 SelectionError::Unimplemented,
  80                             ),
  81                             root_obligation: obligation,
  82                         });
  83                         continue;
  84                     }
  85                 };
  86
  87                 has_changed |= changed;
  88                 match certainty {
  89                     Certainty::Yes => {}
  90                     Certainty::Maybe(_) => self.obligations.push(obligation),
  91                 }
  92             }
  93
  94             if !has_changed {
  95                 break;
  96             }
  97         }
  98
  99         errors
 100     }
 101
 102     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
 103         self.obligations.clone()
 104     }
 105
 106     fn relationships(&mut self) -> &mut FxHashMap<ty::TyVid, ty::FoundRelationships> {
 107         unimplemented!("Should be moved out of `TraitEngine`")
 108     }
 109 }