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                 'blanket_impls: 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                     if !matches!(trait_ref.0.self_ty().kind(), ty::Param(_)) {
  38                         continue;
  39                     }
  40                     let infcx = cx.tcx.infer_ctxt().build();
  41                     let substs = infcx.fresh_substs_for_item(DUMMY_SP, item_def_id);
  42                     let impl_ty = ty.subst(infcx.tcx, substs);
  43                     let param_env = EarlyBinder(param_env).subst(infcx.tcx, substs);
  44
  45                     let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
  46                     let impl_trait_ref = trait_ref.subst(infcx.tcx, impl_substs);
  47
  48                     // Require the type the impl is implemented on to match
  49                     // our type, and ignore the impl if there was a mismatch.
  50                     let cause = traits::ObligationCause::dummy();
  51                     let Ok(eq_result) = infcx.at(&cause, param_env).eq(impl_trait_ref.self_ty(), impl_ty) else {
  52                         continue
  53                     };
  54                     let InferOk { value: (), obligations } = eq_result;
  55                     // FIXME(eddyb) ignoring `obligations` might cause false positives.
  56                     drop(obligations);
  57
  58                     trace!(
  59                         "invoking predicate_may_hold: param_env={:?}, impl_trait_ref={:?}, impl_ty={:?}",
  60                         param_env,
  61                         impl_trait_ref,
  62                         impl_ty
  63                     );
  64                     let predicates = cx
  65                         .tcx
  66                         .predicates_of(impl_def_id)
  67                         .instantiate(cx.tcx, impl_substs)
  68                         .predicates
  69                         .into_iter()
  70                         .chain(Some(
  71                             ty::Binder::dummy(impl_trait_ref)
  72                                 .to_poly_trait_predicate()
  73                                 .map_bound(ty::PredicateKind::Trait)
  74                                 .to_predicate(infcx.tcx),
  75                         ));
  76                     for predicate in predicates {
  77                         debug!("testing predicate {:?}", predicate);
  78                         let obligation = traits::Obligation::new(
  79                             traits::ObligationCause::dummy(),
  80                             param_env,
  81                             predicate,
  82                         );
  83                         match infcx.evaluate_obligation(&obligation) {
  84                             Ok(eval_result) if eval_result.may_apply() => {}
  85                             Err(traits::OverflowError::Canonical) => {}
  86                             Err(traits::OverflowError::ErrorReporting) => {}
  87                             _ => continue 'blanket_impls,
  88                         }
  89                     }
  90                     debug!(
  91                         "get_blanket_impls: found applicable impl for trait_ref={:?}, ty={:?}",
  92                         trait_ref, ty
  93                     );
  94
  95                     cx.generated_synthetics.insert((ty.0, trait_def_id));
  96
  97                     impls.push(Item {
  98                         name: None,
  99                         attrs: Default::default(),
 100                         visibility: Inherited,
 101                         item_id: ItemId::Blanket { impl_id: impl_def_id, for_: item_def_id },
 102                         kind: Box::new(ImplItem(Box::new(Impl {
 103                             unsafety: hir::Unsafety::Normal,
 104                             generics: clean_ty_generics(
 105                                 cx,
 106                                 cx.tcx.generics_of(impl_def_id),
 107                                 cx.tcx.explicit_predicates_of(impl_def_id),
 108                             ),
 109                             // FIXME(eddyb) compute both `trait_` and `for_` from
 110                             // the post-inference `trait_ref`, as it's more accurate.
 111                             trait_: Some(clean_trait_ref_with_bindings(cx, trait_ref.0, ThinVec::new())),
 112                             for_: clean_middle_ty(ty.0, cx, None),
 113                             items: cx.tcx
 114                                 .associated_items(impl_def_id)
 115                                 .in_definition_order()
 116                                 .map(|x| clean_middle_assoc_item(x, cx))
 117                                 .collect::<Vec<_>>(),
 118                             polarity: ty::ImplPolarity::Positive,
 119                             kind: ImplKind::Blanket(Box::new(clean_middle_ty(trait_ref.0.self_ty(), cx, None))),
 120                         }))),
 121                         cfg: None,
 122                     });
 123                 }
 124             }
 125         });
 126
 127         impls
 128     }
 129 }