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, WithConstness};
   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         for &trait_def_id in self.cx.tcx.all_traits(()).iter() {
  23             if !self.cx.cache.access_levels.is_public(trait_def_id)
  24                 || self.cx.generated_synthetics.get(&(ty, 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 = self.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 = self.cx.tcx.impl_trait_ref(impl_def_id).unwrap();
  37                 let is_param = matches!(trait_ref.self_ty().kind(), ty::Param(_));
  38                 let may_apply = is_param && self.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 = 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 = self
  61                             .cx
  62                             .tcx
  63                             .predicates_of(impl_def_id)
  64                             .instantiate(self.cx.tcx, impl_substs)
  65                             .predicates
  66                             .into_iter()
  67                             .chain(Some(trait_ref.without_const().to_predicate(infcx.tcx)));
  68                         for predicate in predicates {
  69                             debug!("testing predicate {:?}", predicate);
  70                             let obligation = traits::Obligation::new(
  71                                 traits::ObligationCause::dummy(),
  72                                 param_env,
  73                                 predicate,
  74                             );
  75                             match infcx.evaluate_obligation(&obligation) {
  76                                 Ok(eval_result) if eval_result.may_apply() => {}
  77                                 Err(traits::OverflowError) => {}
  78                                 _ => {
  79                                     return false;
  80                                 }
  81                             }
  82                         }
  83                         true
  84                     } else {
  85                         false
  86                     }
  87                 });
  88                 debug!(
  89                     "get_blanket_impls: found applicable impl: {} for trait_ref={:?}, ty={:?}",
  90                     may_apply, trait_ref, ty
  91                 );
  92                 if !may_apply {
  93                     continue;
  94                 }
  95
  96                 self.cx.generated_synthetics.insert((ty, trait_def_id));
  97
  98                 impls.push(Item {
  99                     name: None,
 100                     attrs: Default::default(),
 101                     visibility: Inherited,
 102                     def_id: ItemId::Blanket { impl_id: impl_def_id, for_: item_def_id },
 103                     kind: Box::new(ImplItem(Impl {
 104                         span: Span::new(self.cx.tcx.def_span(impl_def_id)),
 105                         unsafety: hir::Unsafety::Normal,
 106                         generics: (
 107                             self.cx.tcx.generics_of(impl_def_id),
 108                             self.cx.tcx.explicit_predicates_of(impl_def_id),
 109                         )
 110                             .clean(self.cx),
 111                         // FIXME(eddyb) compute both `trait_` and `for_` from
 112                         // the post-inference `trait_ref`, as it's more accurate.
 113                         trait_: Some(trait_ref.clean(self.cx).get_trait_type().unwrap()),
 114                         for_: ty.clean(self.cx),
 115                         items: self
 116                             .cx
 117                             .tcx
 118                             .associated_items(impl_def_id)
 119                             .in_definition_order()
 120                             .collect::<Vec<_>>()
 121                             .clean(self.cx),
 122                         negative_polarity: false,
 123                         synthetic: false,
 124                         blanket_impl: Some(Box::new(trait_ref.self_ty().clean(self.cx))),
 125                     })),
 126                     cfg: None,
 127                 });
 128             }
 129         }
 130         impls
 131     }
 132 }