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::ToPredicate;
   6 use rustc_span::DUMMY_SP;
   7
   8 use super::*;
   9
  10 pub(crate) struct BlanketImplFinder<'a, 'tcx> {
  11     pub(crate) cx: &'a mut core::DocContext<'tcx>,
  12 }
  13
  14 impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
  15     pub(crate) fn get_blanket_impls(&mut self, item_def_id: DefId) -> Vec<Item> {
  16         let param_env = self.cx.tcx.param_env(item_def_id);
  17         let ty = self.cx.tcx.bound_type_of(item_def_id);
  18
  19         trace!("get_blanket_impls({:?})", ty);
  20         let mut impls = Vec::new();
  21         self.cx.with_all_traits(|cx, all_traits| {
  22             for &trait_def_id in all_traits {
  23                 if !cx.cache.access_levels.is_public(trait_def_id)
  24                     || cx.generated_synthetics.get(&(ty.0, trait_def_id)).is_some()
  25                 {
  26                     continue;
  27                 }
  28                 // NOTE: doesn't use `for_each_relevant_impl` to avoid looking at anything besides blanket impls
  29                 let trait_impls = cx.tcx.trait_impls_of(trait_def_id);
  30                 for &impl_def_id in trait_impls.blanket_impls() {
  31                     trace!(
  32                         "get_blanket_impls: Considering impl for trait '{:?}' {:?}",
  33                         trait_def_id,
  34                         impl_def_id
  35                     );
  36                     let trait_ref = cx.tcx.bound_impl_trait_ref(impl_def_id).unwrap();
  37                     let is_param = matches!(trait_ref.0.self_ty().kind(), ty::Param(_));
  38                     let may_apply = is_param && cx.tcx.infer_ctxt().enter(|infcx| {
  39                         let substs = infcx.fresh_substs_for_item(DUMMY_SP, item_def_id);
  40                         let ty = ty.subst(infcx.tcx, substs);
  41                         let param_env = EarlyBinder(param_env).subst(infcx.tcx, substs);
  42
  43                         let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
  44                         let trait_ref = trait_ref.subst(infcx.tcx, impl_substs);
  45
  46                         // Require the type the impl is implemented on to match
  47                         // our type, and ignore the impl if there was a mismatch.
  48                         let cause = traits::ObligationCause::dummy();
  49                         let eq_result = infcx.at(&cause, param_env).eq(trait_ref.self_ty(), ty);
  50                         if let Ok(InferOk { value: (), obligations }) = eq_result {
  51                             // FIXME(eddyb) ignoring `obligations` might cause false positives.
  52                             drop(obligations);
  53
  54                             trace!(
  55                                 "invoking predicate_may_hold: param_env={:?}, trait_ref={:?}, ty={:?}",
  56                                 param_env,
  57                                 trait_ref,
  58                                 ty
  59                             );
  60                             let predicates = cx
  61                                 .tcx
  62                                 .predicates_of(impl_def_id)
  63                                 .instantiate(cx.tcx, impl_substs)
  64                                 .predicates
  65                                 .into_iter()
  66                                 .chain(Some(
  67                                     ty::Binder::dummy(trait_ref)
  68                                         .to_poly_trait_predicate()
  69                                         .map_bound(ty::PredicateKind::Trait)
  70                                         .to_predicate(infcx.tcx),
  71                                 ));
  72                             for predicate in predicates {
  73                                 debug!("testing predicate {:?}", predicate);
  74                                 let obligation = traits::Obligation::new(
  75                                     traits::ObligationCause::dummy(),
  76                                     param_env,
  77                                     predicate,
  78                                 );
  79                                 match infcx.evaluate_obligation(&obligation) {
  80                                     Ok(eval_result) if eval_result.may_apply() => {}
  81                                     Err(traits::OverflowError::Canonical) => {}
  82                                     Err(traits::OverflowError::ErrorReporting) => {}
  83                                     _ => {
  84                                         return false;
  85                                     }
  86                                 }
  87                             }
  88                             true
  89                         } else {
  90                             false
  91                         }
  92                     });
  93                     debug!(
  94                         "get_blanket_impls: found applicable impl: {} for trait_ref={:?}, ty={:?}",
  95                         may_apply, trait_ref, ty
  96                     );
  97                     if !may_apply {
  98                         continue;
  99                     }
 100
 101                     cx.generated_synthetics.insert((ty.0, trait_def_id));
 102
 103                     impls.push(Item {
 104                         name: None,
 105                         attrs: Default::default(),
 106                         visibility: Inherited,
 107                         item_id: ItemId::Blanket { impl_id: impl_def_id, for_: item_def_id },
 108                         kind: Box::new(ImplItem(Box::new(Impl {
 109                             unsafety: hir::Unsafety::Normal,
 110                             generics: clean_ty_generics(
 111                                 cx,
 112                                 cx.tcx.generics_of(impl_def_id),
 113                                 cx.tcx.explicit_predicates_of(impl_def_id),
 114                             ),
 115                             // FIXME(eddyb) compute both `trait_` and `for_` from
 116                             // the post-inference `trait_ref`, as it's more accurate.
 117                             trait_: Some(clean_trait_ref_with_bindings(cx, trait_ref.0, ThinVec::new())),
 118                             for_: clean_middle_ty(ty.0, cx, None),
 119                             items: cx.tcx
 120                                 .associated_items(impl_def_id)
 121                                 .in_definition_order()
 122                                 .map(|x| clean_middle_assoc_item(x, cx))
 123                                 .collect::<Vec<_>>(),
 124                             polarity: ty::ImplPolarity::Positive,
 125                             kind: ImplKind::Blanket(Box::new(clean_middle_ty(trait_ref.0.self_ty(), cx, None))),
 126                         }))),
 127                         cfg: None,
 128                     });
 129                 }
 130             }
 131         });
 132
 133         impls
 134     }
 135 }