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_hir::def_id::LOCAL_CRATE;
   4 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
   5 use rustc_infer::traits;
   6 use rustc_middle::ty::subst::Subst;
   7 use rustc_middle::ty::{ToPredicate, WithConstness};
   8 use rustc_span::DUMMY_SP;
   9
  10 use super::*;
  11
  12 crate struct BlanketImplFinder<'a, 'tcx> {
  13     crate cx: &'a core::DocContext<'tcx>,
  14 }
  15
  16 impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
  17     crate fn new(cx: &'a core::DocContext<'tcx>) -> Self {
  18         BlanketImplFinder { cx }
  19     }
  20
  21     // FIXME(eddyb) figure out a better way to pass information about
  22     // parametrization of `ty` than `param_env_def_id`.
  23     crate fn get_blanket_impls(&self, ty: Ty<'tcx>, param_env_def_id: DefId) -> Vec<Item> {
  24         let param_env = self.cx.tcx.param_env(param_env_def_id);
  25
  26         debug!("get_blanket_impls({:?})", ty);
  27         let mut impls = Vec::new();
  28         for &trait_def_id in self.cx.tcx.all_traits(LOCAL_CRATE).iter() {
  29             if !self.cx.renderinfo.borrow().access_levels.is_public(trait_def_id)
  30                 || self.cx.generated_synthetics.borrow_mut().get(&(ty, trait_def_id)).is_some()
  31             {
  32                 continue;
  33             }
  34             self.cx.tcx.for_each_relevant_impl(trait_def_id, ty, |impl_def_id| {
  35                 debug!(
  36                     "get_blanket_impls: Considering impl for trait '{:?}' {:?}",
  37                     trait_def_id, impl_def_id
  38                 );
  39                 let trait_ref = self.cx.tcx.impl_trait_ref(impl_def_id).unwrap();
  40                 let may_apply = self.cx.tcx.infer_ctxt().enter(|infcx| {
  41                     match trait_ref.self_ty().kind() {
  42                         ty::Param(_) => {}
  43                         _ => return false,
  44                     }
  45
  46                     let substs = infcx.fresh_substs_for_item(DUMMY_SP, param_env_def_id);
  47                     let ty = ty.subst(infcx.tcx, substs);
  48                     let param_env = param_env.subst(infcx.tcx, substs);
  49
  50                     let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
  51                     let trait_ref = trait_ref.subst(infcx.tcx, impl_substs);
  52
  53                     // Require the type the impl is implemented on to match
  54                     // our type, and ignore the impl if there was a mismatch.
  55                     let cause = traits::ObligationCause::dummy();
  56                     let eq_result = infcx.at(&cause, param_env).eq(trait_ref.self_ty(), ty);
  57                     if let Ok(InferOk { value: (), obligations }) = eq_result {
  58                         // FIXME(eddyb) ignoring `obligations` might cause false positives.
  59                         drop(obligations);
  60
  61                         debug!(
  62                             "invoking predicate_may_hold: param_env={:?}, trait_ref={:?}, ty={:?}",
  63                             param_env, trait_ref, ty
  64                         );
  65                         let predicates = self
  66                             .cx
  67                             .tcx
  68                             .predicates_of(impl_def_id)
  69                             .instantiate(self.cx.tcx, impl_substs)
  70                             .predicates
  71                             .into_iter()
  72                             .chain(Some(trait_ref.without_const().to_predicate(infcx.tcx)));
  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) => {}
  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                     return;
  99                 }
 100
 101                 self.cx.generated_synthetics.borrow_mut().insert((ty, trait_def_id));
 102                 let provided_trait_methods = self
 103                     .cx
 104                     .tcx
 105                     .provided_trait_methods(trait_def_id)
 106                     .map(|meth| meth.ident.name)
 107                     .collect();
 108
 109                 impls.push(Item {
 110                     source: self.cx.tcx.def_span(impl_def_id).clean(self.cx),
 111                     name: None,
 112                     attrs: Default::default(),
 113                     visibility: Inherited,
 114                     def_id: self.cx.next_def_id(impl_def_id.krate),
 115                     kind: box ImplItem(Impl {
 116                         unsafety: hir::Unsafety::Normal,
 117                         generics: (
 118                             self.cx.tcx.generics_of(impl_def_id),
 119                             self.cx.tcx.explicit_predicates_of(impl_def_id),
 120                         )
 121                             .clean(self.cx),
 122                         provided_trait_methods,
 123                         // FIXME(eddyb) compute both `trait_` and `for_` from
 124                         // the post-inference `trait_ref`, as it's more accurate.
 125                         trait_: Some(trait_ref.clean(self.cx).get_trait_type().unwrap()),
 126                         for_: ty.clean(self.cx),
 127                         items: self
 128                             .cx
 129                             .tcx
 130                             .associated_items(impl_def_id)
 131                             .in_definition_order()
 132                             .collect::<Vec<_>>()
 133                             .clean(self.cx),
 134                         negative_polarity: false,
 135                         synthetic: false,
 136                         blanket_impl: Some(trait_ref.self_ty().clean(self.cx)),
 137                     }),
 138                 });
 139             });
 140         }
 141         impls
 142     }
 143 }