compiler/rustc_ty_utils/src/ty.rs

   1 use rustc_data_structures::fx::FxIndexSet;
   2 use rustc_hir as hir;
   3 use rustc_hir::def_id::DefId;
   4 use rustc_middle::ty::subst::Subst;
   5 use rustc_middle::ty::{
   6     self, Binder, EarlyBinder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt,
   7 };
   8 use rustc_span::{sym, Span};
   9 use rustc_trait_selection::traits;
  10
  11 fn sized_constraint_for_ty<'tcx>(
  12     tcx: TyCtxt<'tcx>,
  13     adtdef: ty::AdtDef<'tcx>,
  14     ty: Ty<'tcx>,
  15 ) -> Vec<Ty<'tcx>> {
  16     use ty::TyKind::*;
  17
  18     let result = match ty.kind() {
  19         Bool | Char | Int(..) | Uint(..) | Float(..) | RawPtr(..) | Ref(..) | FnDef(..)
  20         | FnPtr(_) | Array(..) | Closure(..) | Generator(..) | Never => vec![],
  21
  22         Str | Dynamic(..) | Slice(_) | Foreign(..) | Error(_) | GeneratorWitness(..) => {
  23             // these are never sized - return the target type
  24             vec![ty]
  25         }
  26
  27         Tuple(ref tys) => match tys.last() {
  28             None => vec![],
  29             Some(&ty) => sized_constraint_for_ty(tcx, adtdef, ty),
  30         },
  31
  32         Adt(adt, substs) => {
  33             // recursive case
  34             let adt_tys = adt.sized_constraint(tcx);
  35             debug!("sized_constraint_for_ty({:?}) intermediate = {:?}", ty, adt_tys);
  36             adt_tys
  37                 .iter()
  38                 .map(|ty| EarlyBinder(*ty).subst(tcx, substs))
  39                 .flat_map(|ty| sized_constraint_for_ty(tcx, adtdef, ty))
  40                 .collect()
  41         }
  42
  43         Projection(..) | Opaque(..) => {
  44             // must calculate explicitly.
  45             // FIXME: consider special-casing always-Sized projections
  46             vec![ty]
  47         }
  48
  49         Param(..) => {
  50             // perf hack: if there is a `T: Sized` bound, then
  51             // we know that `T` is Sized and do not need to check
  52             // it on the impl.
  53
  54             let Some(sized_trait) = tcx.lang_items().sized_trait() else { return vec![ty] };
  55             let sized_predicate = ty::Binder::dummy(ty::TraitRef {
  56                 def_id: sized_trait,
  57                 substs: tcx.mk_substs_trait(ty, &[]),
  58             })
  59             .without_const()
  60             .to_predicate(tcx);
  61             let predicates = tcx.predicates_of(adtdef.did()).predicates;
  62             if predicates.iter().any(|(p, _)| *p == sized_predicate) { vec![] } else { vec![ty] }
  63         }
  64
  65         Placeholder(..) | Bound(..) | Infer(..) => {
  66             bug!("unexpected type `{:?}` in sized_constraint_for_ty", ty)
  67         }
  68     };
  69     debug!("sized_constraint_for_ty({:?}) = {:?}", ty, result);
  70     result
  71 }
  72
  73 fn impl_defaultness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::Defaultness {
  74     let item = tcx.hir().expect_item(def_id.expect_local());
  75     if let hir::ItemKind::Impl(impl_) = &item.kind {
  76         impl_.defaultness
  77     } else {
  78         bug!("`impl_defaultness` called on {:?}", item);
  79     }
  80 }
  81
  82 /// Calculates the `Sized` constraint.
  83 ///
  84 /// In fact, there are only a few options for the types in the constraint:
  85 ///     - an obviously-unsized type
  86 ///     - a type parameter or projection whose Sizedness can't be known
  87 ///     - a tuple of type parameters or projections, if there are multiple
  88 ///       such.
  89 ///     - an Error, if a type contained itself. The representability
  90 ///       check should catch this case.
  91 fn adt_sized_constraint(tcx: TyCtxt<'_>, def_id: DefId) -> ty::AdtSizedConstraint<'_> {
  92     let def = tcx.adt_def(def_id);
  93
  94     let result = tcx.mk_type_list(
  95         def.variants()
  96             .iter()
  97             .flat_map(|v| v.fields.last())
  98             .flat_map(|f| sized_constraint_for_ty(tcx, def, tcx.type_of(f.did))),
  99     );
 100
 101     debug!("adt_sized_constraint: {:?} => {:?}", def, result);
 102
 103     ty::AdtSizedConstraint(result)
 104 }
 105
 106 fn def_ident_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
 107     tcx.hir()
 108         .get_if_local(def_id)
 109         .and_then(|node| match node {
 110             // A `Ctor` doesn't have an identifier itself, but its parent
 111             // struct/variant does. Compare with `hir::Map::opt_span`.
 112             hir::Node::Ctor(ctor) => ctor
 113                 .ctor_hir_id()
 114                 .and_then(|ctor_id| tcx.hir().find(tcx.hir().get_parent_node(ctor_id)))
 115                 .and_then(|parent| parent.ident()),
 116             _ => node.ident(),
 117         })
 118         .map(|ident| ident.span)
 119 }
 120
 121 /// See `ParamEnv` struct definition for details.
 122 #[instrument(level = "debug", skip(tcx))]
 123 fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
 124     // The param_env of an impl Trait type is its defining function's param_env
 125     if let Some(parent) = ty::is_impl_trait_defn(tcx, def_id) {
 126         return param_env(tcx, parent.to_def_id());
 127     }
 128     // Compute the bounds on Self and the type parameters.
 129
 130     let ty::InstantiatedPredicates { mut predicates, .. } =
 131         tcx.predicates_of(def_id).instantiate_identity(tcx);
 132
 133     // Finally, we have to normalize the bounds in the environment, in
 134     // case they contain any associated type projections. This process
 135     // can yield errors if the put in illegal associated types, like
 136     // `<i32 as Foo>::Bar` where `i32` does not implement `Foo`. We
 137     // report these errors right here; this doesn't actually feel
 138     // right to me, because constructing the environment feels like a
 139     // kind of an "idempotent" action, but I'm not sure where would be
 140     // a better place. In practice, we construct environments for
 141     // every fn once during type checking, and we'll abort if there
 142     // are any errors at that point, so outside of type inference you can be
 143     // sure that this will succeed without errors anyway.
 144
 145     if tcx.sess.opts.debugging_opts.chalk {
 146         let environment = well_formed_types_in_env(tcx, def_id);
 147         predicates.extend(environment);
 148     }
 149
 150     let local_did = def_id.as_local();
 151     let hir_id = local_did.map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id));
 152
 153     let constness = match hir_id {
 154         Some(hir_id) => match tcx.hir().get(hir_id) {
 155             hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. })
 156                 if tcx.has_attr(def_id, sym::default_method_body_is_const) =>
 157             {
 158                 hir::Constness::Const
 159             }
 160
 161             hir::Node::Item(hir::Item { kind: hir::ItemKind::Const(..), .. })
 162             | hir::Node::Item(hir::Item { kind: hir::ItemKind::Static(..), .. })
 163             | hir::Node::TraitItem(hir::TraitItem {
 164                 kind: hir::TraitItemKind::Const(..), ..
 165             })
 166             | hir::Node::AnonConst(_)
 167             | hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. })
 168             | hir::Node::ImplItem(hir::ImplItem {
 169                 kind:
 170                     hir::ImplItemKind::Fn(
 171                         hir::FnSig {
 172                             header: hir::FnHeader { constness: hir::Constness::Const, .. },
 173                             ..
 174                         },
 175                         ..,
 176                     ),
 177                 ..
 178             }) => hir::Constness::Const,
 179
 180             hir::Node::ImplItem(hir::ImplItem {
 181                 kind: hir::ImplItemKind::TyAlias(..) | hir::ImplItemKind::Fn(..),
 182                 ..
 183             }) => {
 184                 let parent_hir_id = tcx.hir().get_parent_node(hir_id);
 185                 match tcx.hir().get(parent_hir_id) {
 186                     hir::Node::Item(hir::Item {
 187                         kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
 188                         ..
 189                     }) => *constness,
 190                     _ => span_bug!(
 191                         tcx.def_span(parent_hir_id.owner),
 192                         "impl item's parent node is not an impl",
 193                     ),
 194                 }
 195             }
 196
 197             hir::Node::Item(hir::Item {
 198                 kind:
 199                     hir::ItemKind::Fn(hir::FnSig { header: hir::FnHeader { constness, .. }, .. }, ..),
 200                 ..
 201             })
 202             | hir::Node::TraitItem(hir::TraitItem {
 203                 kind:
 204                     hir::TraitItemKind::Fn(
 205                         hir::FnSig { header: hir::FnHeader { constness, .. }, .. },
 206                         ..,
 207                     ),
 208                 ..
 209             })
 210             | hir::Node::Item(hir::Item {
 211                 kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
 212                 ..
 213             }) => *constness,
 214
 215             _ => hir::Constness::NotConst,
 216         },
 217         None => hir::Constness::NotConst,
 218     };
 219
 220     let unnormalized_env = ty::ParamEnv::new(
 221         tcx.intern_predicates(&predicates),
 222         traits::Reveal::UserFacing,
 223         constness,
 224     );
 225
 226     let body_id = hir_id.map_or(hir::CRATE_HIR_ID, |id| {
 227         tcx.hir().maybe_body_owned_by(id).map_or(id, |body| body.hir_id)
 228     });
 229     let cause = traits::ObligationCause::misc(tcx.def_span(def_id), body_id);
 230     traits::normalize_param_env_or_error(tcx, def_id, unnormalized_env, cause)
 231 }
 232
 233 /// Elaborate the environment.
 234 ///
 235 /// Collect a list of `Predicate`'s used for building the `ParamEnv`. Adds `TypeWellFormedFromEnv`'s
 236 /// that are assumed to be well-formed (because they come from the environment).
 237 ///
 238 /// Used only in chalk mode.
 239 fn well_formed_types_in_env<'tcx>(
 240     tcx: TyCtxt<'tcx>,
 241     def_id: DefId,
 242 ) -> &'tcx ty::List<Predicate<'tcx>> {
 243     use rustc_hir::{ForeignItemKind, ImplItemKind, ItemKind, Node, TraitItemKind};
 244     use rustc_middle::ty::subst::GenericArgKind;
 245
 246     debug!("environment(def_id = {:?})", def_id);
 247
 248     // The environment of an impl Trait type is its defining function's environment.
 249     if let Some(parent) = ty::is_impl_trait_defn(tcx, def_id) {
 250         return well_formed_types_in_env(tcx, parent.to_def_id());
 251     }
 252
 253     // Compute the bounds on `Self` and the type parameters.
 254     let ty::InstantiatedPredicates { predicates, .. } =
 255         tcx.predicates_of(def_id).instantiate_identity(tcx);
 256
 257     let clauses = predicates.into_iter();
 258
 259     if !def_id.is_local() {
 260         return ty::List::empty();
 261     }
 262     let node = tcx.hir().get_by_def_id(def_id.expect_local());
 263
 264     enum NodeKind {
 265         TraitImpl,
 266         InherentImpl,
 267         Fn,
 268         Other,
 269     }
 270
 271     let node_kind = match node {
 272         Node::TraitItem(item) => match item.kind {
 273             TraitItemKind::Fn(..) => NodeKind::Fn,
 274             _ => NodeKind::Other,
 275         },
 276
 277         Node::ImplItem(item) => match item.kind {
 278             ImplItemKind::Fn(..) => NodeKind::Fn,
 279             _ => NodeKind::Other,
 280         },
 281
 282         Node::Item(item) => match item.kind {
 283             ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => NodeKind::TraitImpl,
 284             ItemKind::Impl(hir::Impl { of_trait: None, .. }) => NodeKind::InherentImpl,
 285             ItemKind::Fn(..) => NodeKind::Fn,
 286             _ => NodeKind::Other,
 287         },
 288
 289         Node::ForeignItem(item) => match item.kind {
 290             ForeignItemKind::Fn(..) => NodeKind::Fn,
 291             _ => NodeKind::Other,
 292         },
 293
 294         // FIXME: closures?
 295         _ => NodeKind::Other,
 296     };
 297
 298     // FIXME(eddyb) isn't the unordered nature of this a hazard?
 299     let mut inputs = FxIndexSet::default();
 300
 301     match node_kind {
 302         // In a trait impl, we assume that the header trait ref and all its
 303         // constituents are well-formed.
 304         NodeKind::TraitImpl => {
 305             let trait_ref = tcx.impl_trait_ref(def_id).expect("not an impl");
 306
 307             // FIXME(chalk): this has problems because of late-bound regions
 308             //inputs.extend(trait_ref.substs.iter().flat_map(|arg| arg.walk()));
 309             inputs.extend(trait_ref.substs.iter());
 310         }
 311
 312         // In an inherent impl, we assume that the receiver type and all its
 313         // constituents are well-formed.
 314         NodeKind::InherentImpl => {
 315             let self_ty = tcx.type_of(def_id);
 316             inputs.extend(self_ty.walk());
 317         }
 318
 319         // In an fn, we assume that the arguments and all their constituents are
 320         // well-formed.
 321         NodeKind::Fn => {
 322             let fn_sig = tcx.fn_sig(def_id);
 323             let fn_sig = tcx.liberate_late_bound_regions(def_id, fn_sig);
 324
 325             inputs.extend(fn_sig.inputs().iter().flat_map(|ty| ty.walk()));
 326         }
 327
 328         NodeKind::Other => (),
 329     }
 330     let input_clauses = inputs.into_iter().filter_map(|arg| {
 331         match arg.unpack() {
 332             GenericArgKind::Type(ty) => {
 333                 let binder = Binder::dummy(PredicateKind::TypeWellFormedFromEnv(ty));
 334                 Some(tcx.mk_predicate(binder))
 335             }
 336
 337             // FIXME(eddyb) no WF conditions from lifetimes?
 338             GenericArgKind::Lifetime(_) => None,
 339
 340             // FIXME(eddyb) support const generics in Chalk
 341             GenericArgKind::Const(_) => None,
 342         }
 343     });
 344
 345     tcx.mk_predicates(clauses.chain(input_clauses))
 346 }
 347
 348 fn param_env_reveal_all_normalized(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
 349     tcx.param_env(def_id).with_reveal_all_normalized(tcx)
 350 }
 351
 352 fn instance_def_size_estimate<'tcx>(
 353     tcx: TyCtxt<'tcx>,
 354     instance_def: ty::InstanceDef<'tcx>,
 355 ) -> usize {
 356     use ty::InstanceDef;
 357
 358     match instance_def {
 359         InstanceDef::Item(..) | InstanceDef::DropGlue(..) => {
 360             let mir = tcx.instance_mir(instance_def);
 361             mir.basic_blocks().iter().map(|bb| bb.statements.len() + 1).sum()
 362         }
 363         // Estimate the size of other compiler-generated shims to be 1.
 364         _ => 1,
 365     }
 366 }
 367
 368 /// If `def_id` is an issue 33140 hack impl, returns its self type; otherwise, returns `None`.
 369 ///
 370 /// See [`ty::ImplOverlapKind::Issue33140`] for more details.
 371 fn issue33140_self_ty(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Ty<'_>> {
 372     debug!("issue33140_self_ty({:?})", def_id);
 373
 374     let trait_ref = tcx
 375         .impl_trait_ref(def_id)
 376         .unwrap_or_else(|| bug!("issue33140_self_ty called on inherent impl {:?}", def_id));
 377
 378     debug!("issue33140_self_ty({:?}), trait-ref={:?}", def_id, trait_ref);
 379
 380     let is_marker_like = tcx.impl_polarity(def_id) == ty::ImplPolarity::Positive
 381         && tcx.associated_item_def_ids(trait_ref.def_id).is_empty();
 382
 383     // Check whether these impls would be ok for a marker trait.
 384     if !is_marker_like {
 385         debug!("issue33140_self_ty - not marker-like!");
 386         return None;
 387     }
 388
 389     // impl must be `impl Trait for dyn Marker1 + Marker2 + ...`
 390     if trait_ref.substs.len() != 1 {
 391         debug!("issue33140_self_ty - impl has substs!");
 392         return None;
 393     }
 394
 395     let predicates = tcx.predicates_of(def_id);
 396     if predicates.parent.is_some() || !predicates.predicates.is_empty() {
 397         debug!("issue33140_self_ty - impl has predicates {:?}!", predicates);
 398         return None;
 399     }
 400
 401     let self_ty = trait_ref.self_ty();
 402     let self_ty_matches = match self_ty.kind() {
 403         ty::Dynamic(ref data, re) if re.is_static() => data.principal().is_none(),
 404         _ => false,
 405     };
 406
 407     if self_ty_matches {
 408         debug!("issue33140_self_ty - MATCHES!");
 409         Some(self_ty)
 410     } else {
 411         debug!("issue33140_self_ty - non-matching self type");
 412         None
 413     }
 414 }
 415
 416 /// Check if a function is async.
 417 fn asyncness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::IsAsync {
 418     let node = tcx.hir().get_by_def_id(def_id.expect_local());
 419     if let Some(fn_kind) = node.fn_kind() { fn_kind.asyncness() } else { hir::IsAsync::NotAsync }
 420 }
 421
 422 /// Don't call this directly: use ``tcx.conservative_is_privately_uninhabited`` instead.
 423 #[instrument(level = "debug", skip(tcx))]
 424 pub fn conservative_is_privately_uninhabited_raw<'tcx>(
 425     tcx: TyCtxt<'tcx>,
 426     param_env_and: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
 427 ) -> bool {
 428     let (param_env, ty) = param_env_and.into_parts();
 429     match ty.kind() {
 430         ty::Never => {
 431             debug!("ty::Never =>");
 432             true
 433         }
 434         ty::Adt(def, _) if def.is_union() => {
 435             debug!("ty::Adt(def, _) if def.is_union() =>");
 436             // For now, `union`s are never considered uninhabited.
 437             false
 438         }
 439         ty::Adt(def, substs) => {
 440             debug!("ty::Adt(def, _) if def.is_not_union() =>");
 441             // Any ADT is uninhabited if either:
 442             // (a) It has no variants (i.e. an empty `enum`);
 443             // (b) Each of its variants (a single one in the case of a `struct`) has at least
 444             //     one uninhabited field.
 445             def.variants().iter().all(|var| {
 446                 var.fields.iter().any(|field| {
 447                     let ty = tcx.bound_type_of(field.did).subst(tcx, substs);
 448                     tcx.conservative_is_privately_uninhabited(param_env.and(ty))
 449                 })
 450             })
 451         }
 452         ty::Tuple(fields) => {
 453             debug!("ty::Tuple(..) =>");
 454             fields.iter().any(|ty| tcx.conservative_is_privately_uninhabited(param_env.and(ty)))
 455         }
 456         ty::Array(ty, len) => {
 457             debug!("ty::Array(ty, len) =>");
 458             match len.try_eval_usize(tcx, param_env) {
 459                 Some(0) | None => false,
 460                 // If the array is definitely non-empty, it's uninhabited if
 461                 // the type of its elements is uninhabited.
 462                 Some(1..) => tcx.conservative_is_privately_uninhabited(param_env.and(*ty)),
 463             }
 464         }
 465         ty::Ref(..) => {
 466             debug!("ty::Ref(..) =>");
 467             // References to uninitialised memory is valid for any type, including
 468             // uninhabited types, in unsafe code, so we treat all references as
 469             // inhabited.
 470             false
 471         }
 472         _ => {
 473             debug!("_ =>");
 474             false
 475         }
 476     }
 477 }
 478
 479 pub fn provide(providers: &mut ty::query::Providers) {
 480     *providers = ty::query::Providers {
 481         asyncness,
 482         adt_sized_constraint,
 483         def_ident_span,
 484         param_env,
 485         param_env_reveal_all_normalized,
 486         instance_def_size_estimate,
 487         issue33140_self_ty,
 488         impl_defaultness,
 489         conservative_is_privately_uninhabited: conservative_is_privately_uninhabited_raw,
 490         ..*providers
 491     };
 492 }