compiler/rustc_ty_utils/src/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, Binder, Instance, Ty, TyCtxt, TypeFoldable, TypeVisitor};
   6 use rustc_span::{sym, DUMMY_SP};
   7 use rustc_target::spec::abi::Abi;
   8 use rustc_trait_selection::traits;
   9 use traits::{translate_substs, Reveal};
  10
  11 use rustc_data_structures::sso::SsoHashSet;
  12 use std::collections::btree_map::Entry;
  13 use std::collections::BTreeMap;
  14 use std::ops::ControlFlow;
  15
  16 use tracing::debug;
  17
  18 // FIXME(#86795): `BoundVarsCollector` here should **NOT** be used
  19 // outside of `resolve_associated_item`. It's just to address #64494,
  20 // #83765, and #85848 which are creating bound types/regions that lose
  21 // their `Binder` *unintentionally*.
  22 // It's ideal to remove `BoundVarsCollector` and just use
  23 // `ty::Binder::*` methods but we use this stopgap until we figure out
  24 // the "real" fix.
  25 struct BoundVarsCollector<'tcx> {
  26     binder_index: ty::DebruijnIndex,
  27     vars: BTreeMap<u32, ty::BoundVariableKind>,
  28     // We may encounter the same variable at different levels of binding, so
  29     // this can't just be `Ty`
  30     visited: SsoHashSet<(ty::DebruijnIndex, Ty<'tcx>)>,
  31 }
  32
  33 impl<'tcx> BoundVarsCollector<'tcx> {
  34     fn new() -> Self {
  35         BoundVarsCollector {
  36             binder_index: ty::INNERMOST,
  37             vars: BTreeMap::new(),
  38             visited: SsoHashSet::default(),
  39         }
  40     }
  41
  42     fn into_vars(self, tcx: TyCtxt<'tcx>) -> &'tcx ty::List<ty::BoundVariableKind> {
  43         let max = self.vars.iter().map(|(k, _)| *k).max().unwrap_or(0);
  44         for i in 0..max {
  45             if let None = self.vars.get(&i) {
  46                 panic!("Unknown variable: {:?}", i);
  47             }
  48         }
  49
  50         tcx.mk_bound_variable_kinds(self.vars.into_iter().map(|(_, v)| v))
  51     }
  52 }
  53
  54 impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
  55     type BreakTy = ();
  56
  57     fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
  58         // Anon const substs do not contain bound vars by default.
  59         None
  60     }
  61     fn visit_binder<T: TypeFoldable<'tcx>>(
  62         &mut self,
  63         t: &Binder<'tcx, T>,
  64     ) -> ControlFlow<Self::BreakTy> {
  65         self.binder_index.shift_in(1);
  66         let result = t.super_visit_with(self);
  67         self.binder_index.shift_out(1);
  68         result
  69     }
  70
  71     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
  72         if t.outer_exclusive_binder() < self.binder_index
  73             || !self.visited.insert((self.binder_index, t))
  74         {
  75             return ControlFlow::CONTINUE;
  76         }
  77         match *t.kind() {
  78             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
  79                 match self.vars.entry(bound_ty.var.as_u32()) {
  80                     Entry::Vacant(entry) => {
  81                         entry.insert(ty::BoundVariableKind::Ty(bound_ty.kind));
  82                     }
  83                     Entry::Occupied(entry) => match entry.get() {
  84                         ty::BoundVariableKind::Ty(_) => {}
  85                         _ => bug!("Conflicting bound vars"),
  86                     },
  87                 }
  88             }
  89
  90             _ => (),
  91         };
  92
  93         t.super_visit_with(self)
  94     }
  95
  96     fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
  97         match r {
  98             ty::ReLateBound(index, br) if *index == self.binder_index => {
  99                 match self.vars.entry(br.var.as_u32()) {
 100                     Entry::Vacant(entry) => {
 101                         entry.insert(ty::BoundVariableKind::Region(br.kind));
 102                     }
 103                     Entry::Occupied(entry) => match entry.get() {
 104                         ty::BoundVariableKind::Region(_) => {}
 105                         _ => bug!("Conflicting bound vars"),
 106                     },
 107                 }
 108             }
 109
 110             _ => (),
 111         };
 112
 113         r.super_visit_with(self)
 114     }
 115 }
 116
 117 #[instrument(level = "debug", skip(tcx))]
 118 fn resolve_instance<'tcx>(
 119     tcx: TyCtxt<'tcx>,
 120     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
 121 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 122     let (param_env, (did, substs)) = key.into_parts();
 123     if let Some(did) = did.as_local() {
 124         if let Some(param_did) = tcx.opt_const_param_of(did) {
 125             return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
 126         }
 127     }
 128
 129     inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::unknown(did), substs)))
 130 }
 131
 132 fn resolve_instance_of_const_arg<'tcx>(
 133     tcx: TyCtxt<'tcx>,
 134     key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
 135 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 136     let (param_env, (did, const_param_did, substs)) = key.into_parts();
 137     inner_resolve_instance(
 138         tcx,
 139         param_env.and((
 140             ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
 141             substs,
 142         )),
 143     )
 144 }
 145
 146 #[instrument(level = "debug", skip(tcx))]
 147 fn inner_resolve_instance<'tcx>(
 148     tcx: TyCtxt<'tcx>,
 149     key: ty::ParamEnvAnd<'tcx, (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>)>,
 150 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 151     let (param_env, (def, substs)) = key.into_parts();
 152
 153     let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
 154         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
 155         resolve_associated_item(tcx, def.did, param_env, trait_def_id, substs)
 156     } else {
 157         let ty = tcx.type_of(def.def_id_for_type_of());
 158         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, ty);
 159
 160         let def = match *item_type.kind() {
 161             ty::FnDef(..)
 162                 if {
 163                     let f = item_type.fn_sig(tcx);
 164                     f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
 165                 } =>
 166             {
 167                 debug!(" => intrinsic");
 168                 ty::InstanceDef::Intrinsic(def.did)
 169             }
 170             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
 171                 let ty = substs.type_at(0);
 172
 173                 if ty.needs_drop(tcx, param_env) {
 174                     debug!(" => nontrivial drop glue");
 175                     match *ty.kind() {
 176                         ty::Closure(..)
 177                         | ty::Generator(..)
 178                         | ty::Tuple(..)
 179                         | ty::Adt(..)
 180                         | ty::Dynamic(..)
 181                         | ty::Array(..)
 182                         | ty::Slice(..) => {}
 183                         // Drop shims can only be built from ADTs.
 184                         _ => return Ok(None),
 185                     }
 186
 187                     ty::InstanceDef::DropGlue(def_id, Some(ty))
 188                 } else {
 189                     debug!(" => trivial drop glue");
 190                     ty::InstanceDef::DropGlue(def_id, None)
 191                 }
 192             }
 193             _ => {
 194                 debug!(" => free item");
 195                 ty::InstanceDef::Item(def)
 196             }
 197         };
 198         Ok(Some(Instance { def, substs }))
 199     };
 200     debug!("inner_resolve_instance: result={:?}", result);
 201     result
 202 }
 203
 204 fn resolve_associated_item<'tcx>(
 205     tcx: TyCtxt<'tcx>,
 206     trait_item_id: DefId,
 207     param_env: ty::ParamEnv<'tcx>,
 208     trait_id: DefId,
 209     rcvr_substs: SubstsRef<'tcx>,
 210 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
 211     debug!(?trait_item_id, ?param_env, ?trait_id, ?rcvr_substs, "resolve_associated_item");
 212
 213     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 214
 215     // See FIXME on `BoundVarsCollector`.
 216     let mut bound_vars_collector = BoundVarsCollector::new();
 217     trait_ref.visit_with(&mut bound_vars_collector);
 218     let trait_binder = ty::Binder::bind_with_vars(trait_ref, bound_vars_collector.into_vars(tcx));
 219     let vtbl = tcx.codegen_fulfill_obligation((param_env, trait_binder))?;
 220
 221     // Now that we know which impl is being used, we can dispatch to
 222     // the actual function:
 223     Ok(match vtbl {
 224         traits::ImplSource::UserDefined(impl_data) => {
 225             debug!(
 226                 "resolving ImplSource::UserDefined: {:?}, {:?}, {:?}, {:?}",
 227                 param_env, trait_item_id, rcvr_substs, impl_data
 228             );
 229             assert!(!rcvr_substs.needs_infer());
 230             assert!(!trait_ref.needs_infer());
 231
 232             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 233             let trait_def = tcx.trait_def(trait_def_id);
 234             let leaf_def = trait_def
 235                 .ancestors(tcx, impl_data.impl_def_id)?
 236                 .leaf_def(tcx, trait_item_id)
 237                 .unwrap_or_else(|| {
 238                     bug!("{:?} not found in {:?}", trait_item_id, impl_data.impl_def_id);
 239                 });
 240
 241             let substs = tcx.infer_ctxt().enter(|infcx| {
 242                 let param_env = param_env.with_reveal_all_normalized(tcx);
 243                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 244                 let substs = translate_substs(
 245                     &infcx,
 246                     param_env,
 247                     impl_data.impl_def_id,
 248                     substs,
 249                     leaf_def.defining_node,
 250                 );
 251                 infcx.tcx.erase_regions(substs)
 252             });
 253
 254             // Since this is a trait item, we need to see if the item is either a trait default item
 255             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 256             // NOTE: This should be kept in sync with the similar code in
 257             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 258             let eligible = if leaf_def.is_final() {
 259                 // Non-specializable items are always projectable.
 260                 true
 261             } else {
 262                 // Only reveal a specializable default if we're past type-checking
 263                 // and the obligation is monomorphic, otherwise passes such as
 264                 // transmute checking and polymorphic MIR optimizations could
 265                 // get a result which isn't correct for all monomorphizations.
 266                 if param_env.reveal() == Reveal::All {
 267                     !trait_ref.still_further_specializable()
 268                 } else {
 269                     false
 270                 }
 271             };
 272
 273             if !eligible {
 274                 return Ok(None);
 275             }
 276
 277             let substs = tcx.erase_regions(substs);
 278
 279             // Check if we just resolved an associated `const` declaration from
 280             // a `trait` to an associated `const` definition in an `impl`, where
 281             // the definition in the `impl` has the wrong type (for which an
 282             // error has already been/will be emitted elsewhere).
 283             //
 284             // NB: this may be expensive, we try to skip it in all the cases where
 285             // we know the error would've been caught (e.g. in an upstream crate).
 286             //
 287             // A better approach might be to just introduce a query (returning
 288             // `Result<(), ErrorReported>`) for the check that `rustc_typeck`
 289             // performs (i.e. that the definition's type in the `impl` matches
 290             // the declaration in the `trait`), so that we can cheaply check
 291             // here if it failed, instead of approximating it.
 292             if leaf_def.item.kind == ty::AssocKind::Const
 293                 && trait_item_id != leaf_def.item.def_id
 294                 && leaf_def.item.def_id.is_local()
 295             {
 296                 let normalized_type_of = |def_id, substs| {
 297                     tcx.subst_and_normalize_erasing_regions(substs, param_env, tcx.type_of(def_id))
 298                 };
 299
 300                 let original_ty = normalized_type_of(trait_item_id, rcvr_substs);
 301                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 302
 303                 if original_ty != resolved_ty {
 304                     let msg = format!(
 305                         "Instance::resolve: inconsistent associated `const` type: \
 306                          was `{}: {}` but resolved to `{}: {}`",
 307                         tcx.def_path_str_with_substs(trait_item_id, rcvr_substs),
 308                         original_ty,
 309                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 310                         resolved_ty,
 311                     );
 312                     let span = tcx.def_span(leaf_def.item.def_id);
 313                     tcx.sess.delay_span_bug(span, &msg);
 314
 315                     return Err(ErrorReported);
 316                 }
 317             }
 318
 319             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 320         }
 321         traits::ImplSource::Generator(generator_data) => Some(Instance {
 322             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 323                 generator_data.generator_def_id,
 324             )),
 325             substs: generator_data.substs,
 326         }),
 327         traits::ImplSource::Closure(closure_data) => {
 328             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 329             Some(Instance::resolve_closure(
 330                 tcx,
 331                 closure_data.closure_def_id,
 332                 closure_data.substs,
 333                 trait_closure_kind,
 334             ))
 335         }
 336         traits::ImplSource::FnPointer(ref data) => match data.fn_ty.kind() {
 337             ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
 338                 def: ty::InstanceDef::FnPtrShim(trait_item_id, data.fn_ty),
 339                 substs: rcvr_substs,
 340             }),
 341             _ => None,
 342         },
 343         traits::ImplSource::Object(ref data) => {
 344             let index = traits::get_vtable_index_of_object_method(tcx, data, trait_item_id);
 345             Some(Instance {
 346                 def: ty::InstanceDef::Virtual(trait_item_id, index),
 347                 substs: rcvr_substs,
 348             })
 349         }
 350         traits::ImplSource::Builtin(..) => {
 351             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 352                 // FIXME(eddyb) use lang items for methods instead of names.
 353                 let name = tcx.item_name(trait_item_id);
 354                 if name == sym::clone {
 355                     let self_ty = trait_ref.self_ty();
 356
 357                     let is_copy = self_ty.is_copy_modulo_regions(tcx.at(DUMMY_SP), param_env);
 358                     match self_ty.kind() {
 359                         _ if is_copy => (),
 360                         ty::Closure(..) | ty::Tuple(..) => {}
 361                         _ => return Ok(None),
 362                     };
 363
 364                     Some(Instance {
 365                         def: ty::InstanceDef::CloneShim(trait_item_id, self_ty),
 366                         substs: rcvr_substs,
 367                     })
 368                 } else {
 369                     assert_eq!(name, sym::clone_from);
 370
 371                     // Use the default `fn clone_from` from `trait Clone`.
 372                     let substs = tcx.erase_regions(rcvr_substs);
 373                     Some(ty::Instance::new(trait_item_id, substs))
 374                 }
 375             } else {
 376                 None
 377             }
 378         }
 379         traits::ImplSource::AutoImpl(..)
 380         | traits::ImplSource::Param(..)
 381         | traits::ImplSource::TraitAlias(..)
 382         | traits::ImplSource::DiscriminantKind(..)
 383         | traits::ImplSource::Pointee(..)
 384         | traits::ImplSource::TraitUpcasting(_)
 385         | traits::ImplSource::ConstDrop(_) => None,
 386     })
 387 }
 388
 389 pub fn provide(providers: &mut ty::query::Providers) {
 390     *providers =
 391         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 392 }