compiler/rustc_ty_utils/src/instance.rs

   1 use rustc_errors::ErrorGuaranteed;
   2 use rustc_hir::def_id::{DefId, LocalDefId};
   3 use rustc_infer::infer::TyCtxtInferExt;
   4 use rustc_middle::traits::CodegenObligationError;
   5 use rustc_middle::ty::subst::SubstsRef;
   6 use rustc_middle::ty::{self, Instance, TyCtxt, TypeVisitable};
   7 use rustc_span::{sym, DUMMY_SP};
   8 use rustc_trait_selection::traits;
   9 use traits::{translate_substs, Reveal};
  10
  11 fn resolve_instance<'tcx>(
  12     tcx: TyCtxt<'tcx>,
  13     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
  14 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
  15     let (param_env, (did, substs)) = key.into_parts();
  16     if let Some(did) = did.as_local() {
  17         if let Some(param_did) = tcx.opt_const_param_of(did) {
  18             return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
  19         }
  20     }
  21
  22     inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::unknown(did), substs)))
  23 }
  24
  25 fn resolve_instance_of_const_arg<'tcx>(
  26     tcx: TyCtxt<'tcx>,
  27     key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
  28 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
  29     let (param_env, (did, const_param_did, substs)) = key.into_parts();
  30     inner_resolve_instance(
  31         tcx,
  32         param_env.and((
  33             ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
  34             substs,
  35         )),
  36     )
  37 }
  38
  39 fn inner_resolve_instance<'tcx>(
  40     tcx: TyCtxt<'tcx>,
  41     key: ty::ParamEnvAnd<'tcx, (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>)>,
  42 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
  43     let (param_env, (def, substs)) = key.into_parts();
  44
  45     let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
  46         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
  47         resolve_associated_item(tcx, def.did, param_env, trait_def_id, substs)
  48     } else {
  49         let ty = tcx.type_of(def.def_id_for_type_of());
  50         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, ty);
  51
  52         let def = match *item_type.kind() {
  53             ty::FnDef(def_id, ..) if tcx.is_intrinsic(def_id) => {
  54                 debug!(" => intrinsic");
  55                 ty::InstanceDef::Intrinsic(def.did)
  56             }
  57             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
  58                 let ty = substs.type_at(0);
  59
  60                 if ty.needs_drop(tcx, param_env) {
  61                     debug!(" => nontrivial drop glue");
  62                     match *ty.kind() {
  63                         ty::Closure(..)
  64                         | ty::Generator(..)
  65                         | ty::Tuple(..)
  66                         | ty::Adt(..)
  67                         | ty::Dynamic(..)
  68                         | ty::Array(..)
  69                         | ty::Slice(..) => {}
  70                         // Drop shims can only be built from ADTs.
  71                         _ => return Ok(None),
  72                     }
  73
  74                     ty::InstanceDef::DropGlue(def_id, Some(ty))
  75                 } else {
  76                     debug!(" => trivial drop glue");
  77                     ty::InstanceDef::DropGlue(def_id, None)
  78                 }
  79             }
  80             _ => {
  81                 debug!(" => free item");
  82                 ty::InstanceDef::Item(def)
  83             }
  84         };
  85         Ok(Some(Instance { def, substs }))
  86     };
  87     debug!("inner_resolve_instance: result={:?}", result);
  88     result
  89 }
  90
  91 fn resolve_associated_item<'tcx>(
  92     tcx: TyCtxt<'tcx>,
  93     trait_item_id: DefId,
  94     param_env: ty::ParamEnv<'tcx>,
  95     trait_id: DefId,
  96     rcvr_substs: SubstsRef<'tcx>,
  97 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
  98     debug!(?trait_item_id, ?param_env, ?trait_id, ?rcvr_substs, "resolve_associated_item");
  99
 100     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 101
 102     let vtbl = match tcx.codegen_select_candidate((param_env, ty::Binder::dummy(trait_ref))) {
 103         Ok(vtbl) => vtbl,
 104         Err(CodegenObligationError::Ambiguity) => {
 105             let reported = tcx.sess.delay_span_bug(
 106                 tcx.def_span(trait_item_id),
 107                 &format!(
 108                     "encountered ambiguity selecting `{trait_ref:?}` during codegen, presuming due to \
 109                      overflow or prior type error",
 110                 ),
 111             );
 112             return Err(reported);
 113         }
 114         Err(CodegenObligationError::Unimplemented) => return Ok(None),
 115         Err(CodegenObligationError::FulfillmentError) => return Ok(None),
 116     };
 117
 118     // Now that we know which impl is being used, we can dispatch to
 119     // the actual function:
 120     Ok(match vtbl {
 121         traits::ImplSource::UserDefined(impl_data) => {
 122             debug!(
 123                 "resolving ImplSource::UserDefined: {:?}, {:?}, {:?}, {:?}",
 124                 param_env, trait_item_id, rcvr_substs, impl_data
 125             );
 126             assert!(!rcvr_substs.needs_infer());
 127             assert!(!trait_ref.needs_infer());
 128
 129             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 130             let trait_def = tcx.trait_def(trait_def_id);
 131             let leaf_def = trait_def
 132                 .ancestors(tcx, impl_data.impl_def_id)?
 133                 .leaf_def(tcx, trait_item_id)
 134                 .unwrap_or_else(|| {
 135                     bug!("{:?} not found in {:?}", trait_item_id, impl_data.impl_def_id);
 136                 });
 137
 138             let substs = tcx.infer_ctxt().enter(|infcx| {
 139                 let param_env = param_env.with_reveal_all_normalized(tcx);
 140                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 141                 let substs = translate_substs(
 142                     &infcx,
 143                     param_env,
 144                     impl_data.impl_def_id,
 145                     substs,
 146                     leaf_def.defining_node,
 147                 );
 148                 infcx.tcx.erase_regions(substs)
 149             });
 150
 151             // Since this is a trait item, we need to see if the item is either a trait default item
 152             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 153             // NOTE: This should be kept in sync with the similar code in
 154             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 155             let eligible = if leaf_def.is_final() {
 156                 // Non-specializable items are always projectable.
 157                 true
 158             } else {
 159                 // Only reveal a specializable default if we're past type-checking
 160                 // and the obligation is monomorphic, otherwise passes such as
 161                 // transmute checking and polymorphic MIR optimizations could
 162                 // get a result which isn't correct for all monomorphizations.
 163                 if param_env.reveal() == Reveal::All {
 164                     !trait_ref.still_further_specializable()
 165                 } else {
 166                     false
 167                 }
 168             };
 169
 170             if !eligible {
 171                 return Ok(None);
 172             }
 173
 174             // If the item does not have a value, then we cannot return an instance.
 175             if !leaf_def.item.defaultness(tcx).has_value() {
 176                 return Ok(None);
 177             }
 178
 179             let substs = tcx.erase_regions(substs);
 180
 181             // Check if we just resolved an associated `const` declaration from
 182             // a `trait` to an associated `const` definition in an `impl`, where
 183             // the definition in the `impl` has the wrong type (for which an
 184             // error has already been/will be emitted elsewhere).
 185             //
 186             // NB: this may be expensive, we try to skip it in all the cases where
 187             // we know the error would've been caught (e.g. in an upstream crate).
 188             //
 189             // A better approach might be to just introduce a query (returning
 190             // `Result<(), ErrorGuaranteed>`) for the check that `rustc_hir_analysis`
 191             // performs (i.e. that the definition's type in the `impl` matches
 192             // the declaration in the `trait`), so that we can cheaply check
 193             // here if it failed, instead of approximating it.
 194             if leaf_def.item.kind == ty::AssocKind::Const
 195                 && trait_item_id != leaf_def.item.def_id
 196                 && leaf_def.item.def_id.is_local()
 197             {
 198                 let normalized_type_of = |def_id, substs| {
 199                     tcx.subst_and_normalize_erasing_regions(substs, param_env, tcx.type_of(def_id))
 200                 };
 201
 202                 let original_ty = normalized_type_of(trait_item_id, rcvr_substs);
 203                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 204
 205                 if original_ty != resolved_ty {
 206                     let msg = format!(
 207                         "Instance::resolve: inconsistent associated `const` type: \
 208                          was `{}: {}` but resolved to `{}: {}`",
 209                         tcx.def_path_str_with_substs(trait_item_id, rcvr_substs),
 210                         original_ty,
 211                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 212                         resolved_ty,
 213                     );
 214                     let span = tcx.def_span(leaf_def.item.def_id);
 215                     let reported = tcx.sess.delay_span_bug(span, &msg);
 216
 217                     return Err(reported);
 218                 }
 219             }
 220
 221             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 222         }
 223         traits::ImplSource::Generator(generator_data) => Some(Instance {
 224             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 225                 generator_data.generator_def_id,
 226             )),
 227             substs: generator_data.substs,
 228         }),
 229         traits::ImplSource::Closure(closure_data) => {
 230             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 231             Instance::resolve_closure(
 232                 tcx,
 233                 closure_data.closure_def_id,
 234                 closure_data.substs,
 235                 trait_closure_kind,
 236             )
 237         }
 238         traits::ImplSource::FnPointer(ref data) => match data.fn_ty.kind() {
 239             ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
 240                 def: ty::InstanceDef::FnPtrShim(trait_item_id, data.fn_ty),
 241                 substs: rcvr_substs,
 242             }),
 243             _ => None,
 244         },
 245         traits::ImplSource::Object(ref data) => {
 246             if let Some(index) = traits::get_vtable_index_of_object_method(tcx, data, trait_item_id)
 247             {
 248                 Some(Instance {
 249                     def: ty::InstanceDef::Virtual(trait_item_id, index),
 250                     substs: rcvr_substs,
 251                 })
 252             } else {
 253                 None
 254             }
 255         }
 256         traits::ImplSource::Builtin(..) => {
 257             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 258                 // FIXME(eddyb) use lang items for methods instead of names.
 259                 let name = tcx.item_name(trait_item_id);
 260                 if name == sym::clone {
 261                     let self_ty = trait_ref.self_ty();
 262
 263                     let is_copy = self_ty.is_copy_modulo_regions(tcx.at(DUMMY_SP), param_env);
 264                     match self_ty.kind() {
 265                         _ if is_copy => (),
 266                         ty::Generator(..)
 267                         | ty::GeneratorWitness(..)
 268                         | ty::Closure(..)
 269                         | ty::Tuple(..) => {}
 270                         _ => return Ok(None),
 271                     };
 272
 273                     Some(Instance {
 274                         def: ty::InstanceDef::CloneShim(trait_item_id, self_ty),
 275                         substs: rcvr_substs,
 276                     })
 277                 } else {
 278                     assert_eq!(name, sym::clone_from);
 279
 280                     // Use the default `fn clone_from` from `trait Clone`.
 281                     let substs = tcx.erase_regions(rcvr_substs);
 282                     Some(ty::Instance::new(trait_item_id, substs))
 283                 }
 284             } else {
 285                 None
 286             }
 287         }
 288         traits::ImplSource::AutoImpl(..)
 289         | traits::ImplSource::Param(..)
 290         | traits::ImplSource::TraitAlias(..)
 291         | traits::ImplSource::DiscriminantKind(..)
 292         | traits::ImplSource::Pointee(..)
 293         | traits::ImplSource::TraitUpcasting(_)
 294         | traits::ImplSource::ConstDestruct(_)
 295         | traits::ImplSource::Tuple => None,
 296     })
 297 }
 298
 299 pub fn provide(providers: &mut ty::query::Providers) {
 300     *providers =
 301         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 302 }