src/librustc_ty/instance.rs

   1 use rustc_errors::ErrorReported;
   2 use rustc_hir::def_id::DefId;
   3 use rustc_infer::infer::TyCtxtInferExt;
   4 use rustc_middle::ty::subst::SubstsRef;
   5 use rustc_middle::ty::{self, Instance, TyCtxt, TypeFoldable};
   6 use rustc_span::sym;
   7 use rustc_target::spec::abi::Abi;
   8 use rustc_trait_selection::traits;
   9 use traits::{translate_substs, Reveal};
  10
  11 use log::debug;
  12
  13 fn resolve_instance<'tcx>(
  14     tcx: TyCtxt<'tcx>,
  15     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
  16 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  17     let (param_env, (def_id, substs)) = key.into_parts();
  18
  19     debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
  20     let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
  21         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
  22         let item = tcx.associated_item(def_id);
  23         resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
  24     } else {
  25         let ty = tcx.type_of(def_id);
  26         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, &ty);
  27
  28         let def = match item_type.kind {
  29             ty::FnDef(..)
  30                 if {
  31                     let f = item_type.fn_sig(tcx);
  32                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
  33                 } =>
  34             {
  35                 debug!(" => intrinsic");
  36                 ty::InstanceDef::Intrinsic(def_id)
  37             }
  38             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
  39                 let ty = substs.type_at(0);
  40
  41                 if ty.needs_drop(tcx, param_env) {
  42                     // `DropGlue` requires a monomorphic aka concrete type.
  43                     if ty.needs_subst() {
  44                         return Ok(None);
  45                     }
  46
  47                     debug!(" => nontrivial drop glue");
  48                     ty::InstanceDef::DropGlue(def_id, Some(ty))
  49                 } else {
  50                     debug!(" => trivial drop glue");
  51                     ty::InstanceDef::DropGlue(def_id, None)
  52                 }
  53             }
  54             _ => {
  55                 debug!(" => free item");
  56                 ty::InstanceDef::Item(def_id)
  57             }
  58         };
  59         Ok(Some(Instance { def, substs }))
  60     };
  61     debug!("resolve(def_id={:?}, substs={:?}) = {:?}", def_id, substs, result);
  62     result
  63 }
  64
  65 fn resolve_associated_item<'tcx>(
  66     tcx: TyCtxt<'tcx>,
  67     trait_item: &ty::AssocItem,
  68     param_env: ty::ParamEnv<'tcx>,
  69     trait_id: DefId,
  70     rcvr_substs: SubstsRef<'tcx>,
  71 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  72     let def_id = trait_item.def_id;
  73     debug!(
  74         "resolve_associated_item(trait_item={:?}, \
  75             param_env={:?}, \
  76             trait_id={:?}, \
  77             rcvr_substs={:?})",
  78         def_id, param_env, trait_id, rcvr_substs
  79     );
  80
  81     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
  82     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)))?;
  83
  84     // Now that we know which impl is being used, we can dispatch to
  85     // the actual function:
  86     Ok(match vtbl {
  87         traits::VtableImpl(impl_data) => {
  88             debug!(
  89                 "resolving VtableImpl: {:?}, {:?}, {:?}, {:?}",
  90                 param_env, trait_item, rcvr_substs, impl_data
  91             );
  92             assert!(!rcvr_substs.needs_infer());
  93             assert!(!trait_ref.needs_infer());
  94
  95             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
  96             let trait_def = tcx.trait_def(trait_def_id);
  97             let leaf_def = trait_def
  98                 .ancestors(tcx, impl_data.impl_def_id)?
  99                 .leaf_def(tcx, trait_item.ident, trait_item.kind)
 100                 .unwrap_or_else(|| {
 101                     bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
 102                 });
 103
 104             let substs = tcx.infer_ctxt().enter(|infcx| {
 105                 let param_env = param_env.with_reveal_all();
 106                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 107                 let substs = translate_substs(
 108                     &infcx,
 109                     param_env,
 110                     impl_data.impl_def_id,
 111                     substs,
 112                     leaf_def.defining_node,
 113                 );
 114                 infcx.tcx.erase_regions(&substs)
 115             });
 116
 117             // Since this is a trait item, we need to see if the item is either a trait default item
 118             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 119             // NOTE: This should be kept in sync with the similar code in
 120             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 121             let eligible = if leaf_def.is_final() {
 122                 // Non-specializable items are always projectable.
 123                 true
 124             } else {
 125                 // Only reveal a specializable default if we're past type-checking
 126                 // and the obligation is monomorphic, otherwise passes such as
 127                 // transmute checking and polymorphic MIR optimizations could
 128                 // get a result which isn't correct for all monomorphizations.
 129                 if param_env.reveal == Reveal::All {
 130                     !trait_ref.still_further_specializable()
 131                 } else {
 132                     false
 133                 }
 134             };
 135
 136             if !eligible {
 137                 return Ok(None);
 138             }
 139
 140             let substs = tcx.erase_regions(&substs);
 141
 142             // Check if we just resolved an associated `const` declaration from
 143             // a `trait` to an associated `const` definition in an `impl`, where
 144             // the definition in the `impl` has the wrong type (for which an
 145             // error has already been/will be emitted elsewhere).
 146             //
 147             // NB: this may be expensive, we try to skip it in all the cases where
 148             // we know the error would've been caught (e.g. in an upstream crate).
 149             //
 150             // A better approach might be to just introduce a query (returning
 151             // `Result<(), ErrorReported>`) for the check that `rustc_typeck`
 152             // performs (i.e. that the definition's type in the `impl` matches
 153             // the declaration in the `trait`), so that we can cheaply check
 154             // here if it failed, instead of approximating it.
 155             if trait_item.kind == ty::AssocKind::Const
 156                 && trait_item.def_id != leaf_def.item.def_id
 157                 && leaf_def.item.def_id.is_local()
 158             {
 159                 let normalized_type_of = |def_id, substs| {
 160                     tcx.subst_and_normalize_erasing_regions(substs, param_env, &tcx.type_of(def_id))
 161                 };
 162
 163                 let original_ty = normalized_type_of(trait_item.def_id, rcvr_substs);
 164                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 165
 166                 if original_ty != resolved_ty {
 167                     let msg = format!(
 168                         "Instance::resolve: inconsistent associated `const` type: \
 169                          was `{}: {}` but resolved to `{}: {}`",
 170                         tcx.def_path_str_with_substs(trait_item.def_id, rcvr_substs),
 171                         original_ty,
 172                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 173                         resolved_ty,
 174                     );
 175                     let span = tcx.def_span(leaf_def.item.def_id);
 176                     tcx.sess.delay_span_bug(span, &msg);
 177
 178                     return Err(ErrorReported);
 179                 }
 180             }
 181
 182             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 183         }
 184         traits::VtableGenerator(generator_data) => Some(Instance {
 185             def: ty::InstanceDef::Item(generator_data.generator_def_id),
 186             substs: generator_data.substs,
 187         }),
 188         traits::VtableClosure(closure_data) => {
 189             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 190             Some(Instance::resolve_closure(
 191                 tcx,
 192                 closure_data.closure_def_id,
 193                 closure_data.substs,
 194                 trait_closure_kind,
 195             ))
 196         }
 197         traits::VtableFnPointer(ref data) => {
 198             // `FnPtrShim` requires a monomorphic aka concrete type.
 199             if data.fn_ty.needs_subst() {
 200                 return Ok(None);
 201             }
 202
 203             Some(Instance {
 204                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 205                 substs: rcvr_substs,
 206             })
 207         }
 208         traits::VtableObject(ref data) => {
 209             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 210             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 211         }
 212         traits::VtableBuiltin(..) => {
 213             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 214                 // FIXME(eddyb) use lang items for methods instead of names.
 215                 let name = tcx.item_name(def_id);
 216                 if name == sym::clone {
 217                     let self_ty = trait_ref.self_ty();
 218
 219                     // `CloneShim` requires a monomorphic aka concrete type.
 220                     if self_ty.needs_subst() {
 221                         return Ok(None);
 222                     }
 223
 224                     Some(Instance {
 225                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 226                         substs: rcvr_substs,
 227                     })
 228                 } else {
 229                     assert_eq!(name, sym::clone_from);
 230
 231                     // Use the default `fn clone_from` from `trait Clone`.
 232                     let substs = tcx.erase_regions(&rcvr_substs);
 233                     Some(ty::Instance::new(def_id, substs))
 234                 }
 235             } else {
 236                 None
 237             }
 238         }
 239         traits::VtableAutoImpl(..) | traits::VtableParam(..) | traits::VtableTraitAlias(..) => None,
 240     })
 241 }
 242
 243 pub fn provide(providers: &mut ty::query::Providers<'_>) {
 244     *providers = ty::query::Providers { resolve_instance, ..*providers };
 245 }