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, Binder, Instance, Ty, TyCtxt, TypeFoldable, TypeVisitor};
   7 use rustc_span::{sym, DUMMY_SP};
   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 visit_binder<T: TypeFoldable<'tcx>>(
  58         &mut self,
  59         t: &Binder<'tcx, T>,
  60     ) -> ControlFlow<Self::BreakTy> {
  61         self.binder_index.shift_in(1);
  62         let result = t.super_visit_with(self);
  63         self.binder_index.shift_out(1);
  64         result
  65     }
  66
  67     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
  68         if t.outer_exclusive_binder() < self.binder_index
  69             || !self.visited.insert((self.binder_index, t))
  70         {
  71             return ControlFlow::CONTINUE;
  72         }
  73         match *t.kind() {
  74             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
  75                 match self.vars.entry(bound_ty.var.as_u32()) {
  76                     Entry::Vacant(entry) => {
  77                         entry.insert(ty::BoundVariableKind::Ty(bound_ty.kind));
  78                     }
  79                     Entry::Occupied(entry) => match entry.get() {
  80                         ty::BoundVariableKind::Ty(_) => {}
  81                         _ => bug!("Conflicting bound vars"),
  82                     },
  83                 }
  84             }
  85
  86             _ => (),
  87         };
  88
  89         t.super_visit_with(self)
  90     }
  91
  92     fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
  93         match *r {
  94             ty::ReLateBound(index, br) if index == self.binder_index => {
  95                 match self.vars.entry(br.var.as_u32()) {
  96                     Entry::Vacant(entry) => {
  97                         entry.insert(ty::BoundVariableKind::Region(br.kind));
  98                     }
  99                     Entry::Occupied(entry) => match entry.get() {
 100                         ty::BoundVariableKind::Region(_) => {}
 101                         _ => bug!("Conflicting bound vars"),
 102                     },
 103                 }
 104             }
 105
 106             _ => (),
 107         };
 108
 109         r.super_visit_with(self)
 110     }
 111 }
 112
 113 #[instrument(level = "debug", skip(tcx))]
 114 fn resolve_instance<'tcx>(
 115     tcx: TyCtxt<'tcx>,
 116     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
 117 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
 118     let (param_env, (did, substs)) = key.into_parts();
 119     if let Some(did) = did.as_local() {
 120         if let Some(param_did) = tcx.opt_const_param_of(did) {
 121             return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
 122         }
 123     }
 124
 125     inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::unknown(did), substs)))
 126 }
 127
 128 fn resolve_instance_of_const_arg<'tcx>(
 129     tcx: TyCtxt<'tcx>,
 130     key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
 131 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
 132     let (param_env, (did, const_param_did, substs)) = key.into_parts();
 133     inner_resolve_instance(
 134         tcx,
 135         param_env.and((
 136             ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
 137             substs,
 138         )),
 139     )
 140 }
 141
 142 #[instrument(level = "debug", skip(tcx))]
 143 fn inner_resolve_instance<'tcx>(
 144     tcx: TyCtxt<'tcx>,
 145     key: ty::ParamEnvAnd<'tcx, (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>)>,
 146 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
 147     let (param_env, (def, substs)) = key.into_parts();
 148
 149     let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
 150         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
 151         resolve_associated_item(tcx, def.did, param_env, trait_def_id, substs)
 152     } else {
 153         let ty = tcx.type_of(def.def_id_for_type_of());
 154         let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, ty);
 155
 156         let def = match *item_type.kind() {
 157             ty::FnDef(def_id, ..) if tcx.is_intrinsic(def_id) => {
 158                 debug!(" => intrinsic");
 159                 ty::InstanceDef::Intrinsic(def.did)
 160             }
 161             ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
 162                 let ty = substs.type_at(0);
 163
 164                 if ty.needs_drop(tcx, param_env) {
 165                     debug!(" => nontrivial drop glue");
 166                     match *ty.kind() {
 167                         ty::Closure(..)
 168                         | ty::Generator(..)
 169                         | ty::Tuple(..)
 170                         | ty::Adt(..)
 171                         | ty::Dynamic(..)
 172                         | ty::Array(..)
 173                         | ty::Slice(..) => {}
 174                         // Drop shims can only be built from ADTs.
 175                         _ => return Ok(None),
 176                     }
 177
 178                     ty::InstanceDef::DropGlue(def_id, Some(ty))
 179                 } else {
 180                     debug!(" => trivial drop glue");
 181                     ty::InstanceDef::DropGlue(def_id, None)
 182                 }
 183             }
 184             _ => {
 185                 debug!(" => free item");
 186                 ty::InstanceDef::Item(def)
 187             }
 188         };
 189         Ok(Some(Instance { def, substs }))
 190     };
 191     debug!("inner_resolve_instance: result={:?}", result);
 192     result
 193 }
 194
 195 fn resolve_associated_item<'tcx>(
 196     tcx: TyCtxt<'tcx>,
 197     trait_item_id: DefId,
 198     param_env: ty::ParamEnv<'tcx>,
 199     trait_id: DefId,
 200     rcvr_substs: SubstsRef<'tcx>,
 201 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
 202     debug!(?trait_item_id, ?param_env, ?trait_id, ?rcvr_substs, "resolve_associated_item");
 203
 204     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 205
 206     // See FIXME on `BoundVarsCollector`.
 207     let mut bound_vars_collector = BoundVarsCollector::new();
 208     trait_ref.visit_with(&mut bound_vars_collector);
 209     let trait_binder = ty::Binder::bind_with_vars(trait_ref, bound_vars_collector.into_vars(tcx));
 210     let vtbl = match tcx.codegen_fulfill_obligation((param_env, trait_binder)) {
 211         Ok(vtbl) => vtbl,
 212         Err(CodegenObligationError::Ambiguity) => {
 213             let reported = tcx.sess.delay_span_bug(
 214                 tcx.def_span(trait_item_id),
 215                 &format!(
 216                     "encountered ambiguity selecting `{:?}` during codegen, presuming due to \
 217                      overflow or prior type error",
 218                     trait_binder
 219                 ),
 220             );
 221             return Err(reported);
 222         }
 223         Err(CodegenObligationError::Unimplemented) => return Ok(None),
 224         Err(CodegenObligationError::FulfillmentError) => return Ok(None),
 225     };
 226
 227     // Now that we know which impl is being used, we can dispatch to
 228     // the actual function:
 229     Ok(match vtbl {
 230         traits::ImplSource::UserDefined(impl_data) => {
 231             debug!(
 232                 "resolving ImplSource::UserDefined: {:?}, {:?}, {:?}, {:?}",
 233                 param_env, trait_item_id, rcvr_substs, impl_data
 234             );
 235             assert!(!rcvr_substs.needs_infer());
 236             assert!(!trait_ref.needs_infer());
 237
 238             let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
 239             let trait_def = tcx.trait_def(trait_def_id);
 240             let leaf_def = trait_def
 241                 .ancestors(tcx, impl_data.impl_def_id)?
 242                 .leaf_def(tcx, trait_item_id)
 243                 .unwrap_or_else(|| {
 244                     bug!("{:?} not found in {:?}", trait_item_id, impl_data.impl_def_id);
 245                 });
 246
 247             let substs = tcx.infer_ctxt().enter(|infcx| {
 248                 let param_env = param_env.with_reveal_all_normalized(tcx);
 249                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
 250                 let substs = translate_substs(
 251                     &infcx,
 252                     param_env,
 253                     impl_data.impl_def_id,
 254                     substs,
 255                     leaf_def.defining_node,
 256                 );
 257                 infcx.tcx.erase_regions(substs)
 258             });
 259
 260             // Since this is a trait item, we need to see if the item is either a trait default item
 261             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 262             // NOTE: This should be kept in sync with the similar code in
 263             // `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
 264             let eligible = if leaf_def.is_final() {
 265                 // Non-specializable items are always projectable.
 266                 true
 267             } else {
 268                 // Only reveal a specializable default if we're past type-checking
 269                 // and the obligation is monomorphic, otherwise passes such as
 270                 // transmute checking and polymorphic MIR optimizations could
 271                 // get a result which isn't correct for all monomorphizations.
 272                 if param_env.reveal() == Reveal::All {
 273                     !trait_ref.still_further_specializable()
 274                 } else {
 275                     false
 276                 }
 277             };
 278
 279             if !eligible {
 280                 return Ok(None);
 281             }
 282
 283             let substs = tcx.erase_regions(substs);
 284
 285             // Check if we just resolved an associated `const` declaration from
 286             // a `trait` to an associated `const` definition in an `impl`, where
 287             // the definition in the `impl` has the wrong type (for which an
 288             // error has already been/will be emitted elsewhere).
 289             //
 290             // NB: this may be expensive, we try to skip it in all the cases where
 291             // we know the error would've been caught (e.g. in an upstream crate).
 292             //
 293             // A better approach might be to just introduce a query (returning
 294             // `Result<(), ErrorGuaranteed>`) for the check that `rustc_typeck`
 295             // performs (i.e. that the definition's type in the `impl` matches
 296             // the declaration in the `trait`), so that we can cheaply check
 297             // here if it failed, instead of approximating it.
 298             if leaf_def.item.kind == ty::AssocKind::Const
 299                 && trait_item_id != leaf_def.item.def_id
 300                 && leaf_def.item.def_id.is_local()
 301             {
 302                 let normalized_type_of = |def_id, substs| {
 303                     tcx.subst_and_normalize_erasing_regions(substs, param_env, tcx.type_of(def_id))
 304                 };
 305
 306                 let original_ty = normalized_type_of(trait_item_id, rcvr_substs);
 307                 let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
 308
 309                 if original_ty != resolved_ty {
 310                     let msg = format!(
 311                         "Instance::resolve: inconsistent associated `const` type: \
 312                          was `{}: {}` but resolved to `{}: {}`",
 313                         tcx.def_path_str_with_substs(trait_item_id, rcvr_substs),
 314                         original_ty,
 315                         tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
 316                         resolved_ty,
 317                     );
 318                     let span = tcx.def_span(leaf_def.item.def_id);
 319                     let reported = tcx.sess.delay_span_bug(span, &msg);
 320
 321                     return Err(reported);
 322                 }
 323             }
 324
 325             Some(ty::Instance::new(leaf_def.item.def_id, substs))
 326         }
 327         traits::ImplSource::Generator(generator_data) => Some(Instance {
 328             def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
 329                 generator_data.generator_def_id,
 330             )),
 331             substs: generator_data.substs,
 332         }),
 333         traits::ImplSource::Closure(closure_data) => {
 334             let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
 335             Some(Instance::resolve_closure(
 336                 tcx,
 337                 closure_data.closure_def_id,
 338                 closure_data.substs,
 339                 trait_closure_kind,
 340             ))
 341         }
 342         traits::ImplSource::FnPointer(ref data) => match data.fn_ty.kind() {
 343             ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
 344                 def: ty::InstanceDef::FnPtrShim(trait_item_id, data.fn_ty),
 345                 substs: rcvr_substs,
 346             }),
 347             _ => None,
 348         },
 349         traits::ImplSource::Object(ref data) => {
 350             let index = traits::get_vtable_index_of_object_method(tcx, data, trait_item_id);
 351             Some(Instance {
 352                 def: ty::InstanceDef::Virtual(trait_item_id, index),
 353                 substs: rcvr_substs,
 354             })
 355         }
 356         traits::ImplSource::Builtin(..) => {
 357             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
 358                 // FIXME(eddyb) use lang items for methods instead of names.
 359                 let name = tcx.item_name(trait_item_id);
 360                 if name == sym::clone {
 361                     let self_ty = trait_ref.self_ty();
 362
 363                     let is_copy = self_ty.is_copy_modulo_regions(tcx.at(DUMMY_SP), param_env);
 364                     match self_ty.kind() {
 365                         _ if is_copy => (),
 366                         ty::Closure(..) | ty::Tuple(..) => {}
 367                         _ => return Ok(None),
 368                     };
 369
 370                     Some(Instance {
 371                         def: ty::InstanceDef::CloneShim(trait_item_id, self_ty),
 372                         substs: rcvr_substs,
 373                     })
 374                 } else {
 375                     assert_eq!(name, sym::clone_from);
 376
 377                     // Use the default `fn clone_from` from `trait Clone`.
 378                     let substs = tcx.erase_regions(rcvr_substs);
 379                     Some(ty::Instance::new(trait_item_id, substs))
 380                 }
 381             } else {
 382                 None
 383             }
 384         }
 385         traits::ImplSource::AutoImpl(..)
 386         | traits::ImplSource::Param(..)
 387         | traits::ImplSource::TraitAlias(..)
 388         | traits::ImplSource::DiscriminantKind(..)
 389         | traits::ImplSource::Pointee(..)
 390         | traits::ImplSource::TraitUpcasting(_)
 391         | traits::ImplSource::ConstDestruct(_) => None,
 392     })
 393 }
 394
 395 pub fn provide(providers: &mut ty::query::Providers) {
 396     *providers =
 397         ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
 398 }