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;
   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             let infcx = tcx.infer_ctxt().build();
 138             let param_env = param_env.with_reveal_all_normalized(tcx);
 139             let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 140             let substs = translate_substs(
 141                 &infcx,
 142                 param_env,
 143                 impl_data.impl_def_id,
 144                 substs,
 145                 leaf_def.defining_node,
 146             );
 147             let substs = infcx.tcx.erase_regions(substs);
 148
 149             // Since this is a trait item, we need to see if the item is either a trait default item
 150             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 151             // NOTE: This should be kept in sync with the similar code in
 152             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 153             let eligible = if leaf_def.is_final() {
 154                 // Non-specializable items are always projectable.
 155                 true
 156             } else {
 157                 // Only reveal a specializable default if we're past type-checking
 158                 // and the obligation is monomorphic, otherwise passes such as
 159                 // transmute checking and polymorphic MIR optimizations could
 160                 // get a result which isn't correct for all monomorphizations.
 161                 if param_env.reveal() == Reveal::All {
 162                     !trait_ref.still_further_specializable()
 163                 } else {
 164                     false
 165                 }
 166             };
 167
 168             if !eligible {
 169                 return Ok(None);
 170             }
 171
 172             // Any final impl is required to define all associated items.
 173             if !leaf_def.item.defaultness(tcx).has_value() {
 174                 let guard = tcx.sess.delay_span_bug(
 175                     tcx.def_span(leaf_def.item.def_id),
 176                     "missing value for assoc item in impl",
 177                 );
 178                 return Err(guard);
 179             }
 180
 181             let substs = tcx.erase_regions(substs);
 182
 183             // Check if we just resolved an associated `const` declaration from
 184             // a `trait` to an associated `const` definition in an `impl`, where
 185             // the definition in the `impl` has the wrong type (for which an
 186             // error has already been/will be emitted elsewhere).
 187             if leaf_def.item.kind == ty::AssocKind::Const
 188                 && trait_item_id != leaf_def.item.def_id
 189                 && let Some(leaf_def_item) = leaf_def.item.def_id.as_local()
 190             {
 191                 tcx.compare_assoc_const_impl_item_with_trait_item((
 192                     leaf_def_item,
 193                     trait_item_id,
 194                 ))?;
 195             }
 196
 197             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 198         }
 199         traits::ImplSource::Generator(generator_data) => Some(Instance {
 200             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 201                 generator_data.generator_def_id,
 202             )),
 203             substs: generator_data.substs,
 204         }),
 205         traits::ImplSource::Future(future_data) => Some(Instance {
 206             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 207                 future_data.generator_def_id,
 208             )),
 209             substs: future_data.substs,
 210         }),
 211         traits::ImplSource::Closure(closure_data) => {
 212             let trait_closure_kind = tcx.fn_trait_kind_from_def_id(trait_id).unwrap();
 213             Instance::resolve_closure(
 214                 tcx,
 215                 closure_data.closure_def_id,
 216                 closure_data.substs,
 217                 trait_closure_kind,
 218             )
 219         }
 220         traits::ImplSource::FnPointer(ref data) => match data.fn_ty.kind() {
 221             ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
 222                 def: ty::InstanceDef::FnPtrShim(trait_item_id, data.fn_ty),
 223                 substs: rcvr_substs,
 224             }),
 225             _ => None,
 226         },
 227         traits::ImplSource::Object(ref data) => {
 228             if let Some(index) = traits::get_vtable_index_of_object_method(tcx, data, trait_item_id)
 229             {
 230                 Some(Instance {
 231                     def: ty::InstanceDef::Virtual(trait_item_id, index),
 232                     substs: rcvr_substs,
 233                 })
 234             } else {
 235                 None
 236             }
 237         }
 238         traits::ImplSource::Builtin(..) => {
 239             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 240                 // FIXME(eddyb) use lang items for methods instead of names.
 241                 let name = tcx.item_name(trait_item_id);
 242                 if name == sym::clone {
 243                     let self_ty = trait_ref.self_ty();
 244
 245                     let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env);
 246                     match self_ty.kind() {
 247                         _ if is_copy => (),
 248                         ty::Generator(..)
 249                         | ty::GeneratorWitness(..)
 250                         | ty::Closure(..)
 251                         | ty::Tuple(..) => {}
 252                         _ => return Ok(None),
 253                     };
 254
 255                     Some(Instance {
 256                         def: ty::InstanceDef::CloneShim(trait_item_id, self_ty),
 257                         substs: rcvr_substs,
 258                     })
 259                 } else {
 260                     assert_eq!(name, sym::clone_from);
 261
 262                     // Use the default `fn clone_from` from `trait Clone`.
 263                     let substs = tcx.erase_regions(rcvr_substs);
 264                     Some(ty::Instance::new(trait_item_id, substs))
 265                 }
 266             } else {
 267                 None
 268             }
 269         }
 270         traits::ImplSource::AutoImpl(..)
 271         | traits::ImplSource::Param(..)
 272         | traits::ImplSource::TraitAlias(..)
 273         | traits::ImplSource::TraitUpcasting(_)
 274         | traits::ImplSource::ConstDestruct(_) => None,
 275     })
 276 }
 277
 278 pub fn provide(providers: &mut ty::query::Providers) {
 279     *providers =
 280         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 281 }