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, _) if Some(def_id) == tcx.lang_items().count_code_region_fn() => {
  39                 debug!(" => injected placeholder function to be replaced");
  40                 ty::InstanceDef::InjectedCode(def_id)
  41             }
  42             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
  43                 let ty = substs.type_at(0);
  44
  45                 if ty.needs_drop(tcx, param_env) {
  46                     // `DropGlue` requires a monomorphic aka concrete type.
  47                     if ty.needs_subst() {
  48                         return Ok(None);
  49                     }
  50
  51                     debug!(" => nontrivial drop glue");
  52                     ty::InstanceDef::DropGlue(def_id, Some(ty))
  53                 } else {
  54                     debug!(" => trivial drop glue");
  55                     ty::InstanceDef::DropGlue(def_id, None)
  56                 }
  57             }
  58             _ => {
  59                 debug!(" => free item");
  60                 ty::InstanceDef::Item(def_id)
  61             }
  62         };
  63         Ok(Some(Instance { def, substs }))
  64     };
  65     debug!("resolve(def_id={:?}, substs={:?}) = {:?}", def_id, substs, result);
  66     result
  67 }
  68
  69 fn resolve_associated_item<'tcx>(
  70     tcx: TyCtxt<'tcx>,
  71     trait_item: &ty::AssocItem,
  72     param_env: ty::ParamEnv<'tcx>,
  73     trait_id: DefId,
  74     rcvr_substs: SubstsRef<'tcx>,
  75 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  76     let def_id = trait_item.def_id;
  77     debug!(
  78         "resolve_associated_item(trait_item={:?}, \
  79             param_env={:?}, \
  80             trait_id={:?}, \
  81             rcvr_substs={:?})",
  82         def_id, param_env, trait_id, rcvr_substs
  83     );
  84
  85     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
  86     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)))?;
  87
  88     // Now that we know which impl is being used, we can dispatch to
  89     // the actual function:
  90     Ok(match vtbl {
  91         traits::ImplSourceUserDefined(impl_data) => {
  92             debug!(
  93                 "resolving ImplSourceUserDefined: {:?}, {:?}, {:?}, {:?}",
  94                 param_env, trait_item, rcvr_substs, impl_data
  95             );
  96             assert!(!rcvr_substs.needs_infer());
  97             assert!(!trait_ref.needs_infer());
  98
  99             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 100             let trait_def = tcx.trait_def(trait_def_id);
 101             let leaf_def = trait_def
 102                 .ancestors(tcx, impl_data.impl_def_id)?
 103                 .leaf_def(tcx, trait_item.ident, trait_item.kind)
 104                 .unwrap_or_else(|| {
 105                     bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
 106                 });
 107
 108             let substs = tcx.infer_ctxt().enter(|infcx| {
 109                 let param_env = param_env.with_reveal_all();
 110                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 111                 let substs = translate_substs(
 112                     &infcx,
 113                     param_env,
 114                     impl_data.impl_def_id,
 115                     substs,
 116                     leaf_def.defining_node,
 117                 );
 118                 infcx.tcx.erase_regions(&substs)
 119             });
 120
 121             // Since this is a trait item, we need to see if the item is either a trait default item
 122             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 123             // NOTE: This should be kept in sync with the similar code in
 124             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 125             let eligible = if leaf_def.is_final() {
 126                 // Non-specializable items are always projectable.
 127                 true
 128             } else {
 129                 // Only reveal a specializable default if we're past type-checking
 130                 // and the obligation is monomorphic, otherwise passes such as
 131                 // transmute checking and polymorphic MIR optimizations could
 132                 // get a result which isn't correct for all monomorphizations.
 133                 if param_env.reveal == Reveal::All {
 134                     !trait_ref.still_further_specializable()
 135                 } else {
 136                     false
 137                 }
 138             };
 139
 140             if !eligible {
 141                 return Ok(None);
 142             }
 143
 144             let substs = tcx.erase_regions(&substs);
 145
 146             // Check if we just resolved an associated `const` declaration from
 147             // a `trait` to an associated `const` definition in an `impl`, where
 148             // the definition in the `impl` has the wrong type (for which an
 149             // error has already been/will be emitted elsewhere).
 150             //
 151             // NB: this may be expensive, we try to skip it in all the cases where
 152             // we know the error would've been caught (e.g. in an upstream crate).
 153             //
 154             // A better approach might be to just introduce a query (returning
 155             // `Result<(), ErrorReported>`) for the check that `rustc_typeck`
 156             // performs (i.e. that the definition's type in the `impl` matches
 157             // the declaration in the `trait`), so that we can cheaply check
 158             // here if it failed, instead of approximating it.
 159             if trait_item.kind == ty::AssocKind::Const
 160                 && trait_item.def_id != leaf_def.item.def_id
 161                 && leaf_def.item.def_id.is_local()
 162             {
 163                 let normalized_type_of = |def_id, substs| {
 164                     tcx.subst_and_normalize_erasing_regions(substs, param_env, &tcx.type_of(def_id))
 165                 };
 166
 167                 let original_ty = normalized_type_of(trait_item.def_id, rcvr_substs);
 168                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 169
 170                 if original_ty != resolved_ty {
 171                     let msg = format!(
 172                         "Instance::resolve: inconsistent associated `const` type: \
 173                          was `{}: {}` but resolved to `{}: {}`",
 174                         tcx.def_path_str_with_substs(trait_item.def_id, rcvr_substs),
 175                         original_ty,
 176                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 177                         resolved_ty,
 178                     );
 179                     let span = tcx.def_span(leaf_def.item.def_id);
 180                     tcx.sess.delay_span_bug(span, &msg);
 181
 182                     return Err(ErrorReported);
 183                 }
 184             }
 185
 186             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 187         }
 188         traits::ImplSourceGenerator(generator_data) => Some(Instance {
 189             def: ty::InstanceDef::Item(generator_data.generator_def_id),
 190             substs: generator_data.substs,
 191         }),
 192         traits::ImplSourceClosure(closure_data) => {
 193             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 194             Some(Instance::resolve_closure(
 195                 tcx,
 196                 closure_data.closure_def_id,
 197                 closure_data.substs,
 198                 trait_closure_kind,
 199             ))
 200         }
 201         traits::ImplSourceFnPointer(ref data) => {
 202             // `FnPtrShim` requires a monomorphic aka concrete type.
 203             if data.fn_ty.needs_subst() {
 204                 return Ok(None);
 205             }
 206
 207             Some(Instance {
 208                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 209                 substs: rcvr_substs,
 210             })
 211         }
 212         traits::ImplSourceObject(ref data) => {
 213             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 214             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 215         }
 216         traits::ImplSourceBuiltin(..) => {
 217             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 218                 // FIXME(eddyb) use lang items for methods instead of names.
 219                 let name = tcx.item_name(def_id);
 220                 if name == sym::clone {
 221                     let self_ty = trait_ref.self_ty();
 222
 223                     // `CloneShim` requires a monomorphic aka concrete type.
 224                     if self_ty.needs_subst() {
 225                         return Ok(None);
 226                     }
 227
 228                     Some(Instance {
 229                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 230                         substs: rcvr_substs,
 231                     })
 232                 } else {
 233                     assert_eq!(name, sym::clone_from);
 234
 235                     // Use the default `fn clone_from` from `trait Clone`.
 236                     let substs = tcx.erase_regions(&rcvr_substs);
 237                     Some(ty::Instance::new(def_id, substs))
 238                 }
 239             } else {
 240                 None
 241             }
 242         }
 243         traits::ImplSourceAutoImpl(..)
 244         | traits::ImplSourceParam(..)
 245         | traits::ImplSourceTraitAlias(..)
 246         | traits::ImplSourceDiscriminantKind(..) => None,
 247     })
 248 }
 249
 250 pub fn provide(providers: &mut ty::query::Providers<'_>) {
 251     *providers = ty::query::Providers { resolve_instance, ..*providers };
 252 }