src/librustdoc/clean/blanket_impl.rs

   1 use crate::rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
   2 use rustc_hir as hir;
   3 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
   4 use rustc_infer::traits;
   5 use rustc_middle::ty::subst::Subst;
   6 use rustc_middle::ty::ToPredicate;
   7 use rustc_span::DUMMY_SP;
   8
   9 use super::*;
  10
  11 crate struct BlanketImplFinder<'a, 'tcx> {
  12     crate cx: &'a mut core::DocContext<'tcx>,
  13 }
  14
  15 impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
  16     crate fn get_blanket_impls(&mut self, item_def_id: DefId) -> Vec<Item> {
  17         let param_env = self.cx.tcx.param_env(item_def_id);
  18         let ty = self.cx.tcx.type_of(item_def_id);
  19
  20         trace!("get_blanket_impls({:?})", ty);
  21         let mut impls = Vec::new();
  22         self.cx.with_all_traits(|cx, all_traits| {
  23             for &trait_def_id in all_traits {
  24                 if !cx.cache.access_levels.is_public(trait_def_id)
  25                     || cx.generated_synthetics.get(&(ty, trait_def_id)).is_some()
  26                 {
  27                     continue;
  28                 }
  29                 // NOTE: doesn't use `for_each_relevant_impl` to avoid looking at anything besides blanket impls
  30                 let trait_impls = cx.tcx.trait_impls_of(trait_def_id);
  31                 for &impl_def_id in trait_impls.blanket_impls() {
  32                     trace!(
  33                         "get_blanket_impls: Considering impl for trait '{:?}' {:?}",
  34                         trait_def_id,
  35                         impl_def_id
  36                     );
  37                     let trait_ref = cx.tcx.impl_trait_ref(impl_def_id).unwrap();
  38                     let is_param = matches!(trait_ref.self_ty().kind(), ty::Param(_));
  39                     let may_apply = is_param && cx.tcx.infer_ctxt().enter(|infcx| {
  40                         let substs = infcx.fresh_substs_for_item(DUMMY_SP, item_def_id);
  41                         let ty = ty.subst(infcx.tcx, substs);
  42                         let param_env = param_env.subst(infcx.tcx, substs);
  43
  44                         let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
  45                         let trait_ref = trait_ref.subst(infcx.tcx, impl_substs);
  46
  47                         // Require the type the impl is implemented on to match
  48                         // our type, and ignore the impl if there was a mismatch.
  49                         let cause = traits::ObligationCause::dummy();
  50                         let eq_result = infcx.at(&cause, param_env).eq(trait_ref.self_ty(), ty);
  51                         if let Ok(InferOk { value: (), obligations }) = eq_result {
  52                             // FIXME(eddyb) ignoring `obligations` might cause false positives.
  53                             drop(obligations);
  54
  55                             trace!(
  56                                 "invoking predicate_may_hold: param_env={:?}, trait_ref={:?}, ty={:?}",
  57                                 param_env,
  58                                 trait_ref,
  59                                 ty
  60                             );
  61                             let predicates = cx
  62                                 .tcx
  63                                 .predicates_of(impl_def_id)
  64                                 .instantiate(cx.tcx, impl_substs)
  65                                 .predicates
  66                                 .into_iter()
  67                                 .chain(Some(
  68                                     ty::Binder::dummy(trait_ref)
  69                                         .to_poly_trait_predicate()
  70                                         .map_bound(ty::PredicateKind::Trait)
  71                                         .to_predicate(infcx.tcx),
  72                                 ));
  73                             for predicate in predicates {
  74                                 debug!("testing predicate {:?}", predicate);
  75                                 let obligation = traits::Obligation::new(
  76                                     traits::ObligationCause::dummy(),
  77                                     param_env,
  78                                     predicate,
  79                                 );
  80                                 match infcx.evaluate_obligation(&obligation) {
  81                                     Ok(eval_result) if eval_result.may_apply() => {}
  82                                     Err(traits::OverflowError::Canonical) => {}
  83                                     Err(traits::OverflowError::ErrorReporting) => {}
  84                                     _ => {
  85                                         return false;
  86                                     }
  87                                 }
  88                             }
  89                             true
  90                         } else {
  91                             false
  92                         }
  93                     });
  94                     debug!(
  95                         "get_blanket_impls: found applicable impl: {} for trait_ref={:?}, ty={:?}",
  96                         may_apply, trait_ref, ty
  97                     );
  98                     if !may_apply {
  99                         continue;
 100                     }
 101
 102                     cx.generated_synthetics.insert((ty, trait_def_id));
 103
 104                     impls.push(Item {
 105                         name: None,
 106                         attrs: Default::default(),
 107                         visibility: Inherited,
 108                         def_id: ItemId::Blanket { impl_id: impl_def_id, for_: item_def_id },
 109                         kind: box ImplItem(Impl {
 110                             unsafety: hir::Unsafety::Normal,
 111                             generics: clean_ty_generics(
 112                                 cx,
 113                                 cx.tcx.generics_of(impl_def_id),
 114                                 cx.tcx.explicit_predicates_of(impl_def_id),
 115                             ),
 116                             // FIXME(eddyb) compute both `trait_` and `for_` from
 117                             // the post-inference `trait_ref`, as it's more accurate.
 118                             trait_: Some(trait_ref.clean(cx)),
 119                             for_: ty.clean(cx),
 120                             items: cx.tcx
 121                                 .associated_items(impl_def_id)
 122                                 .in_definition_order()
 123                                 .map(|x| x.clean(cx))
 124                                 .collect::<Vec<_>>(),
 125                             polarity: ty::ImplPolarity::Positive,
 126                             kind: ImplKind::Blanket(box trait_ref.self_ty().clean(cx)),
 127                         }),
 128                         cfg: None,
 129                     });
 130                 }
 131             }
 132         });
 133
 134         impls
 135     }
 136 }