src/librustc_ty/instance.rs

   1 use rustc_errors::ErrorReported;
   2 use rustc_hir::def_id::{DefId, LocalDefId};
   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, (did, substs)) = key.into_parts();
  18     if let Some(did) = did.as_local() {
  19         if let Some(param_did) = tcx.opt_const_param_of(did) {
  20             return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
  21         }
  22     }
  23
  24     inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::dummy(did), substs)))
  25 }
  26
  27 fn resolve_instance_of_const_arg<'tcx>(
  28     tcx: TyCtxt<'tcx>,
  29     key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
  30 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  31     let (param_env, (did, const_param_did, substs)) = key.into_parts();
  32     inner_resolve_instance(
  33         tcx,
  34         param_env.and((
  35             ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
  36             substs,
  37         )),
  38     )
  39 }
  40
  41 fn inner_resolve_instance<'tcx>(
  42     tcx: TyCtxt<'tcx>,
  43     key: ty::ParamEnvAnd<'tcx, (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>)>,
  44 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
  45     let (param_env, (def, substs)) = key.into_parts();
  46
  47     debug!("resolve(def={:?}, substs={:?})", def.did, substs);
  48     let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
  49         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
  50         let item = tcx.associated_item(def.did);
  51         resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
  52     } else {
  53         let ty = tcx.type_of(def.ty_def_id());
  54         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, &ty);
  55
  56         let def = match item_type.kind {
  57             ty::FnDef(..)
  58                 if {
  59                     let f = item_type.fn_sig(tcx);
  60                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
  61                 } =>
  62             {
  63                 debug!(" => intrinsic");
  64                 ty::InstanceDef::Intrinsic(def.did)
  65             }
  66             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
  67                 let ty = substs.type_at(0);
  68
  69                 if ty.needs_drop(tcx, param_env) {
  70                     // `DropGlue` requires a monomorphic aka concrete type.
  71                     if ty.needs_subst() {
  72                         return Ok(None);
  73                     }
  74
  75                     debug!(" => nontrivial drop glue");
  76                     ty::InstanceDef::DropGlue(def_id, Some(ty))
  77                 } else {
  78                     debug!(" => trivial drop glue");
  79                     ty::InstanceDef::DropGlue(def_id, None)
  80                 }
  81             }
  82             _ => {
  83                 debug!(" => free item");
  84                 ty::InstanceDef::Item(def)
  85             }
  86         };
  87         Ok(Some(Instance { def, substs }))
  88     };
  89     debug!("resolve(def.did={:?}, substs={:?}) = {:?}", def.did, substs, result);
  90     result
  91 }
  92
  93 fn resolve_associated_item<'tcx>(
  94     tcx: TyCtxt<'tcx>,
  95     trait_item: &ty::AssocItem,
  96     param_env: ty::ParamEnv<'tcx>,
  97     trait_id: DefId,
  98     rcvr_substs: SubstsRef<'tcx>,
  99 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 100     let def_id = trait_item.def_id;
 101     debug!(
 102         "resolve_associated_item(trait_item={:?}, \
 103             param_env={:?}, \
 104             trait_id={:?}, \
 105             rcvr_substs={:?})",
 106         def_id, param_env, trait_id, rcvr_substs
 107     );
 108
 109     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 110     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)))?;
 111
 112     // Now that we know which impl is being used, we can dispatch to
 113     // the actual function:
 114     Ok(match vtbl {
 115         traits::ImplSourceUserDefined(impl_data) => {
 116             debug!(
 117                 "resolving ImplSourceUserDefined: {:?}, {:?}, {:?}, {:?}",
 118                 param_env, trait_item, rcvr_substs, impl_data
 119             );
 120             assert!(!rcvr_substs.needs_infer());
 121             assert!(!trait_ref.needs_infer());
 122
 123             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 124             let trait_def = tcx.trait_def(trait_def_id);
 125             let leaf_def = trait_def
 126                 .ancestors(tcx, impl_data.impl_def_id)?
 127                 .leaf_def(tcx, trait_item.ident, trait_item.kind)
 128                 .unwrap_or_else(|| {
 129                     bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
 130                 });
 131
 132             let substs = tcx.infer_ctxt().enter(|infcx| {
 133                 let param_env = param_env.with_reveal_all();
 134                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 135                 let substs = translate_substs(
 136                     &infcx,
 137                     param_env,
 138                     impl_data.impl_def_id,
 139                     substs,
 140                     leaf_def.defining_node,
 141                 );
 142                 infcx.tcx.erase_regions(&substs)
 143             });
 144
 145             // Since this is a trait item, we need to see if the item is either a trait default item
 146             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 147             // NOTE: This should be kept in sync with the similar code in
 148             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 149             let eligible = if leaf_def.is_final() {
 150                 // Non-specializable items are always projectable.
 151                 true
 152             } else {
 153                 // Only reveal a specializable default if we're past type-checking
 154                 // and the obligation is monomorphic, otherwise passes such as
 155                 // transmute checking and polymorphic MIR optimizations could
 156                 // get a result which isn't correct for all monomorphizations.
 157                 if param_env.reveal() == Reveal::All {
 158                     !trait_ref.still_further_specializable()
 159                 } else {
 160                     false
 161                 }
 162             };
 163
 164             if !eligible {
 165                 return Ok(None);
 166             }
 167
 168             let substs = tcx.erase_regions(&substs);
 169
 170             // Check if we just resolved an associated `const` declaration from
 171             // a `trait` to an associated `const` definition in an `impl`, where
 172             // the definition in the `impl` has the wrong type (for which an
 173             // error has already been/will be emitted elsewhere).
 174             //
 175             // NB: this may be expensive, we try to skip it in all the cases where
 176             // we know the error would've been caught (e.g. in an upstream crate).
 177             //
 178             // A better approach might be to just introduce a query (returning
 179             // `Result<(), ErrorReported>`) for the check that `rustc_typeck`
 180             // performs (i.e. that the definition's type in the `impl` matches
 181             // the declaration in the `trait`), so that we can cheaply check
 182             // here if it failed, instead of approximating it.
 183             if trait_item.kind == ty::AssocKind::Const
 184                 && trait_item.def_id != leaf_def.item.def_id
 185                 && leaf_def.item.def_id.is_local()
 186             {
 187                 let normalized_type_of = |def_id, substs| {
 188                     tcx.subst_and_normalize_erasing_regions(substs, param_env, &tcx.type_of(def_id))
 189                 };
 190
 191                 let original_ty = normalized_type_of(trait_item.def_id, rcvr_substs);
 192                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 193
 194                 if original_ty != resolved_ty {
 195                     let msg = format!(
 196                         "Instance::resolve: inconsistent associated `const` type: \
 197                          was `{}: {}` but resolved to `{}: {}`",
 198                         tcx.def_path_str_with_substs(trait_item.def_id, rcvr_substs),
 199                         original_ty,
 200                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 201                         resolved_ty,
 202                     );
 203                     let span = tcx.def_span(leaf_def.item.def_id);
 204                     tcx.sess.delay_span_bug(span, &msg);
 205
 206                     return Err(ErrorReported);
 207                 }
 208             }
 209
 210             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 211         }
 212         traits::ImplSourceGenerator(generator_data) => Some(Instance {
 213             def: ty::InstanceDef::Item(ty::WithOptConstParam::dummy(
 214                 generator_data.generator_def_id,
 215             )),
 216             substs: generator_data.substs,
 217         }),
 218         traits::ImplSourceClosure(closure_data) => {
 219             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 220             Some(Instance::resolve_closure(
 221                 tcx,
 222                 closure_data.closure_def_id,
 223                 closure_data.substs,
 224                 trait_closure_kind,
 225             ))
 226         }
 227         traits::ImplSourceFnPointer(ref data) => {
 228             // `FnPtrShim` requires a monomorphic aka concrete type.
 229             if data.fn_ty.needs_subst() {
 230                 return Ok(None);
 231             }
 232
 233             Some(Instance {
 234                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 235                 substs: rcvr_substs,
 236             })
 237         }
 238         traits::ImplSourceObject(ref data) => {
 239             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 240             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 241         }
 242         traits::ImplSourceBuiltin(..) => {
 243             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 244                 // FIXME(eddyb) use lang items for methods instead of names.
 245                 let name = tcx.item_name(def_id);
 246                 if name == sym::clone {
 247                     let self_ty = trait_ref.self_ty();
 248
 249                     // `CloneShim` requires a monomorphic aka concrete type.
 250                     if self_ty.needs_subst() {
 251                         return Ok(None);
 252                     }
 253
 254                     Some(Instance {
 255                         def: ty::InstanceDef::CloneShim(def_id, self_ty),
 256                         substs: rcvr_substs,
 257                     })
 258                 } else {
 259                     assert_eq!(name, sym::clone_from);
 260
 261                     // Use the default `fn clone_from` from `trait Clone`.
 262                     let substs = tcx.erase_regions(&rcvr_substs);
 263                     Some(ty::Instance::new(def_id, substs))
 264                 }
 265             } else {
 266                 None
 267             }
 268         }
 269         traits::ImplSourceAutoImpl(..)
 270         | traits::ImplSourceParam(..)
 271         | traits::ImplSourceTraitAlias(..)
 272         | traits::ImplSourceDiscriminantKind(..) => None,
 273     })
 274 }
 275
 276 pub fn provide(providers: &mut ty::query::Providers) {
 277     *providers =
 278         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 279 }