compiler/rustc_typeck/src/collect/type_of.rs

   1 use rustc_data_structures::fx::FxHashSet;
   2 use rustc_errors::{Applicability, ErrorReported, StashKey};
   3 use rustc_hir as hir;
   4 use rustc_hir::def::{DefKind, Res};
   5 use rustc_hir::def_id::{DefId, LocalDefId};
   6 use rustc_hir::intravisit;
   7 use rustc_hir::intravisit::Visitor;
   8 use rustc_hir::{HirId, Node};
   9 use rustc_middle::hir::map::Map;
  10 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
  11 use rustc_middle::ty::util::IntTypeExt;
  12 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt, TypeFoldable};
  13 use rustc_span::symbol::Ident;
  14 use rustc_span::{Span, DUMMY_SP};
  15
  16 use super::ItemCtxt;
  17 use super::{bad_placeholder_type, is_suggestable_infer_ty};
  18
  19 /// Computes the relevant generic parameter for a potential generic const argument.
  20 ///
  21 /// This should be called using the query `tcx.opt_const_param_of`.
  22 pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<DefId> {
  23     use hir::*;
  24     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
  25
  26     if let Node::AnonConst(_) = tcx.hir().get(hir_id) {
  27         let parent_node_id = tcx.hir().get_parent_node(hir_id);
  28         let parent_node = tcx.hir().get(parent_node_id);
  29
  30         match parent_node {
  31             // This match arm is for when the def_id appears in a GAT whose
  32             // path can't be resolved without typechecking e.g.
  33             //
  34             // trait Foo {
  35             //   type Assoc<const N: usize>;
  36             //   fn foo() -> Self::Assoc<3>;
  37             // }
  38             //
  39             // In the above code we would call this query with the def_id of 3 and
  40             // the parent_node we match on would be the hir node for Self::Assoc<3>
  41             //
  42             // `Self::Assoc<3>` cant be resolved without typchecking here as we
  43             // didnt write <Self as Foo>::Assoc<3>. If we did then another match
  44             // arm would handle this.
  45             //
  46             // I believe this match arm is only needed for GAT but I am not 100% sure - BoxyUwU
  47             Node::Ty(hir_ty @ Ty { kind: TyKind::Path(QPath::TypeRelative(_, segment)), .. }) => {
  48                 // Find the Item containing the associated type so we can create an ItemCtxt.
  49                 // Using the ItemCtxt convert the HIR for the unresolved assoc type into a
  50                 // ty which is a fully resolved projection.
  51                 // For the code example above, this would mean converting Self::Assoc<3>
  52                 // into a ty::Projection(<Self as Foo>::Assoc<3>)
  53                 let item_hir_id = tcx
  54                     .hir()
  55                     .parent_iter(hir_id)
  56                     .filter(|(_, node)| matches!(node, Node::Item(_)))
  57                     .map(|(id, _)| id)
  58                     .next()
  59                     .unwrap();
  60                 let item_did = tcx.hir().local_def_id(item_hir_id).to_def_id();
  61                 let item_ctxt = &ItemCtxt::new(tcx, item_did) as &dyn crate::astconv::AstConv<'_>;
  62                 let ty = item_ctxt.ast_ty_to_ty(hir_ty);
  63
  64                 // Iterate through the generics of the projection to find the one that corresponds to
  65                 // the def_id that this query was called with. We filter to only const args here as a
  66                 // precaution for if it's ever allowed to elide lifetimes in GAT's. It currently isn't
  67                 // but it can't hurt to be safe ^^
  68                 if let ty::Projection(projection) = ty.kind() {
  69                     let generics = tcx.generics_of(projection.item_def_id);
  70
  71                     let arg_index = segment
  72                         .args
  73                         .and_then(|args| {
  74                             args.args
  75                                 .iter()
  76                                 .filter(|arg| arg.is_const())
  77                                 .position(|arg| arg.id() == hir_id)
  78                         })
  79                         .unwrap_or_else(|| {
  80                             bug!("no arg matching AnonConst in segment");
  81                         });
  82
  83                     return generics
  84                         .params
  85                         .iter()
  86                         .filter(|param| matches!(param.kind, ty::GenericParamDefKind::Const { .. }))
  87                         .nth(arg_index)
  88                         .map(|param| param.def_id);
  89                 }
  90
  91                 // I dont think it's possible to reach this but I'm not 100% sure - BoxyUwU
  92                 tcx.sess.delay_span_bug(
  93                     tcx.def_span(def_id),
  94                     "unexpected non-GAT usage of an anon const",
  95                 );
  96                 return None;
  97             }
  98             Node::Expr(&Expr {
  99                 kind:
 100                     ExprKind::MethodCall(segment, ..) | ExprKind::Path(QPath::TypeRelative(_, segment)),
 101                 ..
 102             }) => {
 103                 let body_owner = tcx.hir().local_def_id(tcx.hir().enclosing_body_owner(hir_id));
 104                 let tables = tcx.typeck(body_owner);
 105                 // This may fail in case the method/path does not actually exist.
 106                 // As there is no relevant param for `def_id`, we simply return
 107                 // `None` here.
 108                 let type_dependent_def = tables.type_dependent_def_id(parent_node_id)?;
 109                 let idx = segment
 110                     .args
 111                     .and_then(|args| {
 112                         args.args
 113                             .iter()
 114                             .filter(|arg| arg.is_const())
 115                             .position(|arg| arg.id() == hir_id)
 116                     })
 117                     .unwrap_or_else(|| {
 118                         bug!("no arg matching AnonConst in segment");
 119                     });
 120
 121                 tcx.generics_of(type_dependent_def)
 122                     .params
 123                     .iter()
 124                     .filter(|param| matches!(param.kind, ty::GenericParamDefKind::Const { .. }))
 125                     .nth(idx)
 126                     .map(|param| param.def_id)
 127             }
 128
 129             Node::Ty(&Ty { kind: TyKind::Path(_), .. })
 130             | Node::Expr(&Expr { kind: ExprKind::Path(_) | ExprKind::Struct(..), .. })
 131             | Node::TraitRef(..)
 132             | Node::Pat(_) => {
 133                 let path = match parent_node {
 134                     Node::Ty(&Ty { kind: TyKind::Path(QPath::Resolved(_, path)), .. })
 135                     | Node::TraitRef(&TraitRef { path, .. }) => &*path,
 136                     Node::Expr(&Expr {
 137                         kind:
 138                             ExprKind::Path(QPath::Resolved(_, path))
 139                             | ExprKind::Struct(&QPath::Resolved(_, path), ..),
 140                         ..
 141                     }) => {
 142                         let body_owner =
 143                             tcx.hir().local_def_id(tcx.hir().enclosing_body_owner(hir_id));
 144                         let _tables = tcx.typeck(body_owner);
 145                         &*path
 146                     }
 147                     Node::Pat(pat) => {
 148                         if let Some(path) = get_path_containing_arg_in_pat(pat, hir_id) {
 149                             path
 150                         } else {
 151                             tcx.sess.delay_span_bug(
 152                                 tcx.def_span(def_id),
 153                                 &format!(
 154                                     "unable to find const parent for {} in pat {:?}",
 155                                     hir_id, pat
 156                                 ),
 157                             );
 158                             return None;
 159                         }
 160                     }
 161                     _ => {
 162                         tcx.sess.delay_span_bug(
 163                             tcx.def_span(def_id),
 164                             &format!("unexpected const parent path {:?}", parent_node),
 165                         );
 166                         return None;
 167                     }
 168                 };
 169
 170                 // We've encountered an `AnonConst` in some path, so we need to
 171                 // figure out which generic parameter it corresponds to and return
 172                 // the relevant type.
 173                 let (arg_index, segment) = path
 174                     .segments
 175                     .iter()
 176                     .filter_map(|seg| seg.args.map(|args| (args.args, seg)))
 177                     .find_map(|(args, seg)| {
 178                         args.iter()
 179                             .filter(|arg| arg.is_const())
 180                             .position(|arg| arg.id() == hir_id)
 181                             .map(|index| (index, seg))
 182                     })
 183                     .unwrap_or_else(|| {
 184                         bug!("no arg matching AnonConst in path");
 185                     });
 186
 187                 // Try to use the segment resolution if it is valid, otherwise we
 188                 // default to the path resolution.
 189                 let res = segment.res.filter(|&r| r != Res::Err).unwrap_or(path.res);
 190                 let generics = match res {
 191                     Res::Def(DefKind::Ctor(..), def_id) => {
 192                         tcx.generics_of(tcx.parent(def_id).unwrap())
 193                     }
 194                     Res::Def(_, def_id) => tcx.generics_of(def_id),
 195                     Res::Err => {
 196                         tcx.sess.delay_span_bug(tcx.def_span(def_id), "anon const with Res::Err");
 197                         return None;
 198                     }
 199                     _ => {
 200                         // If the user tries to specify generics on a type that does not take them,
 201                         // e.g. `usize<T>`, we may hit this branch, in which case we treat it as if
 202                         // no arguments have been passed. An error should already have been emitted.
 203                         tcx.sess.delay_span_bug(
 204                             tcx.def_span(def_id),
 205                             &format!("unexpected anon const res {:?} in path: {:?}", res, path),
 206                         );
 207                         return None;
 208                     }
 209                 };
 210
 211                 generics
 212                     .params
 213                     .iter()
 214                     .filter(|param| matches!(param.kind, ty::GenericParamDefKind::Const { .. }))
 215                     .nth(arg_index)
 216                     .map(|param| param.def_id)
 217             }
 218             _ => None,
 219         }
 220     } else {
 221         None
 222     }
 223 }
 224
 225 fn get_path_containing_arg_in_pat<'hir>(
 226     pat: &'hir hir::Pat<'hir>,
 227     arg_id: HirId,
 228 ) -> Option<&'hir hir::Path<'hir>> {
 229     use hir::*;
 230
 231     let is_arg_in_path = |p: &hir::Path<'_>| {
 232         p.segments
 233             .iter()
 234             .filter_map(|seg| seg.args)
 235             .flat_map(|args| args.args)
 236             .any(|arg| arg.id() == arg_id)
 237     };
 238     let mut arg_path = None;
 239     pat.walk(|pat| match pat.kind {
 240         PatKind::Struct(QPath::Resolved(_, path), _, _)
 241         | PatKind::TupleStruct(QPath::Resolved(_, path), _, _)
 242         | PatKind::Path(QPath::Resolved(_, path))
 243             if is_arg_in_path(path) =>
 244         {
 245             arg_path = Some(path);
 246             false
 247         }
 248         _ => true,
 249     });
 250     arg_path
 251 }
 252
 253 pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
 254     let def_id = def_id.expect_local();
 255     use rustc_hir::*;
 256
 257     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 258
 259     let icx = ItemCtxt::new(tcx, def_id.to_def_id());
 260
 261     match tcx.hir().get(hir_id) {
 262         Node::TraitItem(item) => match item.kind {
 263             TraitItemKind::Fn(..) => {
 264                 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
 265                 tcx.mk_fn_def(def_id.to_def_id(), substs)
 266             }
 267             TraitItemKind::Const(ref ty, body_id) => body_id
 268                 .and_then(|body_id| {
 269                     if is_suggestable_infer_ty(ty) {
 270                         Some(infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident))
 271                     } else {
 272                         None
 273                     }
 274                 })
 275                 .unwrap_or_else(|| icx.to_ty(ty)),
 276             TraitItemKind::Type(_, Some(ref ty)) => icx.to_ty(ty),
 277             TraitItemKind::Type(_, None) => {
 278                 span_bug!(item.span, "associated type missing default");
 279             }
 280         },
 281
 282         Node::ImplItem(item) => match item.kind {
 283             ImplItemKind::Fn(..) => {
 284                 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
 285                 tcx.mk_fn_def(def_id.to_def_id(), substs)
 286             }
 287             ImplItemKind::Const(ref ty, body_id) => {
 288                 if is_suggestable_infer_ty(ty) {
 289                     infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident)
 290                 } else {
 291                     icx.to_ty(ty)
 292                 }
 293             }
 294             ImplItemKind::TyAlias(ref ty) => {
 295                 if tcx.impl_trait_ref(tcx.hir().get_parent_did(hir_id).to_def_id()).is_none() {
 296                     check_feature_inherent_assoc_ty(tcx, item.span);
 297                 }
 298
 299                 icx.to_ty(ty)
 300             }
 301         },
 302
 303         Node::Item(item) => {
 304             match item.kind {
 305                 ItemKind::Static(ref ty, .., body_id) | ItemKind::Const(ref ty, body_id) => {
 306                     if is_suggestable_infer_ty(ty) {
 307                         infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident)
 308                     } else {
 309                         icx.to_ty(ty)
 310                     }
 311                 }
 312                 ItemKind::TyAlias(ref self_ty, _)
 313                 | ItemKind::Impl(hir::Impl { ref self_ty, .. }) => icx.to_ty(self_ty),
 314                 ItemKind::Fn(..) => {
 315                     let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
 316                     tcx.mk_fn_def(def_id.to_def_id(), substs)
 317                 }
 318                 ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
 319                     let def = tcx.adt_def(def_id);
 320                     let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
 321                     tcx.mk_adt(def, substs)
 322                 }
 323                 ItemKind::OpaqueTy(OpaqueTy { origin: hir::OpaqueTyOrigin::Binding, .. }) => {
 324                     let_position_impl_trait_type(tcx, def_id)
 325                 }
 326                 ItemKind::OpaqueTy(OpaqueTy { impl_trait_fn: None, .. }) => {
 327                     find_opaque_ty_constraints(tcx, def_id)
 328                 }
 329                 // Opaque types desugared from `impl Trait`.
 330                 ItemKind::OpaqueTy(OpaqueTy { impl_trait_fn: Some(owner), .. }) => {
 331                     let concrete_ty = tcx
 332                         .mir_borrowck(owner.expect_local())
 333                         .concrete_opaque_types
 334                         .get(&def_id.to_def_id())
 335                         .map(|opaque| opaque.concrete_type)
 336                         .unwrap_or_else(|| {
 337                             tcx.sess.delay_span_bug(
 338                                 DUMMY_SP,
 339                                 &format!(
 340                                     "owner {:?} has no opaque type for {:?} in its typeck results",
 341                                     owner, def_id,
 342                                 ),
 343                             );
 344                             if let Some(ErrorReported) =
 345                                 tcx.typeck(owner.expect_local()).tainted_by_errors
 346                             {
 347                                 // Some error in the
 348                                 // owner fn prevented us from populating
 349                                 // the `concrete_opaque_types` table.
 350                                 tcx.ty_error()
 351                             } else {
 352                                 // We failed to resolve the opaque type or it
 353                                 // resolves to itself. Return the non-revealed
 354                                 // type, which should result in E0720.
 355                                 tcx.mk_opaque(
 356                                     def_id.to_def_id(),
 357                                     InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
 358                                 )
 359                             }
 360                         });
 361                     debug!("concrete_ty = {:?}", concrete_ty);
 362                     concrete_ty
 363                 }
 364                 ItemKind::Trait(..)
 365                 | ItemKind::TraitAlias(..)
 366                 | ItemKind::Mod(..)
 367                 | ItemKind::ForeignMod { .. }
 368                 | ItemKind::GlobalAsm(..)
 369                 | ItemKind::ExternCrate(..)
 370                 | ItemKind::Use(..) => {
 371                     span_bug!(
 372                         item.span,
 373                         "compute_type_of_item: unexpected item type: {:?}",
 374                         item.kind
 375                     );
 376                 }
 377             }
 378         }
 379
 380         Node::ForeignItem(foreign_item) => match foreign_item.kind {
 381             ForeignItemKind::Fn(..) => {
 382                 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
 383                 tcx.mk_fn_def(def_id.to_def_id(), substs)
 384             }
 385             ForeignItemKind::Static(ref t, _) => icx.to_ty(t),
 386             ForeignItemKind::Type => tcx.mk_foreign(def_id.to_def_id()),
 387         },
 388
 389         Node::Ctor(&ref def) | Node::Variant(Variant { data: ref def, .. }) => match *def {
 390             VariantData::Unit(..) | VariantData::Struct(..) => {
 391                 tcx.type_of(tcx.hir().get_parent_did(hir_id).to_def_id())
 392             }
 393             VariantData::Tuple(..) => {
 394                 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
 395                 tcx.mk_fn_def(def_id.to_def_id(), substs)
 396             }
 397         },
 398
 399         Node::Field(field) => icx.to_ty(&field.ty),
 400
 401         Node::Expr(&Expr { kind: ExprKind::Closure(.., gen), .. }) => {
 402             let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
 403             if let Some(movability) = gen {
 404                 tcx.mk_generator(def_id.to_def_id(), substs, movability)
 405             } else {
 406                 tcx.mk_closure(def_id.to_def_id(), substs)
 407             }
 408         }
 409
 410         Node::AnonConst(_) => {
 411             if let Some(param) = tcx.opt_const_param_of(def_id) {
 412                 // We defer to `type_of` of the corresponding parameter
 413                 // for generic arguments.
 414                 return tcx.type_of(param);
 415             }
 416
 417             let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
 418             match parent_node {
 419                 Node::Ty(&Ty { kind: TyKind::Array(_, ref constant), .. })
 420                 | Node::Ty(&Ty { kind: TyKind::Typeof(ref constant), .. })
 421                 | Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
 422                     if constant.hir_id == hir_id =>
 423                 {
 424                     tcx.types.usize
 425                 }
 426
 427                 Node::Expr(&Expr { kind: ExprKind::ConstBlock(ref anon_const), .. })
 428                     if anon_const.hir_id == hir_id =>
 429                 {
 430                     tcx.typeck(def_id).node_type(anon_const.hir_id)
 431                 }
 432
 433                 Node::Expr(&Expr { kind: ExprKind::InlineAsm(ia), .. })
 434                     if ia.operands.iter().any(|(op, _op_sp)| match op {
 435                         hir::InlineAsmOperand::Const { anon_const } => anon_const.hir_id == hir_id,
 436                         _ => false,
 437                     }) =>
 438                 {
 439                     tcx.typeck(def_id).node_type(hir_id)
 440                 }
 441
 442                 Node::Variant(Variant { disr_expr: Some(ref e), .. }) if e.hir_id == hir_id => tcx
 443                     .adt_def(tcx.hir().get_parent_did(hir_id).to_def_id())
 444                     .repr
 445                     .discr_type()
 446                     .to_ty(tcx),
 447
 448                 Node::GenericParam(&GenericParam {
 449                     hir_id: param_hir_id,
 450                     kind: GenericParamKind::Const { default: Some(ct), .. },
 451                     ..
 452                 }) if ct.hir_id == hir_id => tcx.type_of(tcx.hir().local_def_id(param_hir_id)),
 453
 454                 x => tcx.ty_error_with_message(
 455                     DUMMY_SP,
 456                     &format!("unexpected const parent in type_of_def_id(): {:?}", x),
 457                 ),
 458             }
 459         }
 460
 461         Node::GenericParam(param) => match &param.kind {
 462             GenericParamKind::Type { default: Some(ty), .. }
 463             | GenericParamKind::Const { ty, .. } => icx.to_ty(ty),
 464             x => bug!("unexpected non-type Node::GenericParam: {:?}", x),
 465         },
 466
 467         x => {
 468             bug!("unexpected sort of node in type_of_def_id(): {:?}", x);
 469         }
 470     }
 471 }
 472
 473 fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
 474     use rustc_hir::{Expr, ImplItem, Item, TraitItem};
 475
 476     debug!("find_opaque_ty_constraints({:?})", def_id);
 477
 478     struct ConstraintLocator<'tcx> {
 479         tcx: TyCtxt<'tcx>,
 480         def_id: DefId,
 481         // (first found type span, actual type)
 482         found: Option<(Span, Ty<'tcx>)>,
 483     }
 484
 485     impl ConstraintLocator<'_> {
 486         fn check(&mut self, def_id: LocalDefId) {
 487             // Don't try to check items that cannot possibly constrain the type.
 488             if !self.tcx.has_typeck_results(def_id) {
 489                 debug!(
 490                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`: no typeck results",
 491                     self.def_id, def_id,
 492                 );
 493                 return;
 494             }
 495             // Calling `mir_borrowck` can lead to cycle errors through
 496             // const-checking, avoid calling it if we don't have to.
 497             if !self.tcx.typeck(def_id).concrete_opaque_types.contains_key(&self.def_id) {
 498                 debug!(
 499                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`",
 500                     self.def_id, def_id,
 501                 );
 502                 return;
 503             }
 504             // Use borrowck to get the type with unerased regions.
 505             let ty = self.tcx.mir_borrowck(def_id).concrete_opaque_types.get(&self.def_id);
 506             if let Some(ty::ResolvedOpaqueTy { concrete_type, substs }) = ty {
 507                 debug!(
 508                     "find_opaque_ty_constraints: found constraint for `{:?}` at `{:?}`: {:?}",
 509                     self.def_id, def_id, ty,
 510                 );
 511
 512                 // FIXME(oli-obk): trace the actual span from inference to improve errors.
 513                 let span = self.tcx.def_span(def_id);
 514
 515                 // HACK(eddyb) this check shouldn't be needed, as `wfcheck`
 516                 // performs the same checks, in theory, but I've kept it here
 517                 // using `delay_span_bug`, just in case `wfcheck` slips up.
 518                 let opaque_generics = self.tcx.generics_of(self.def_id);
 519                 let mut used_params: FxHashSet<_> = FxHashSet::default();
 520                 for (i, arg) in substs.iter().enumerate() {
 521                     let arg_is_param = match arg.unpack() {
 522                         GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
 523                         GenericArgKind::Lifetime(lt) => {
 524                             matches!(lt, ty::ReEarlyBound(_) | ty::ReFree(_))
 525                         }
 526                         GenericArgKind::Const(ct) => matches!(ct.val, ty::ConstKind::Param(_)),
 527                     };
 528
 529                     if arg_is_param {
 530                         if !used_params.insert(arg) {
 531                             // There was already an entry for `arg`, meaning a generic parameter
 532                             // was used twice.
 533                             self.tcx.sess.delay_span_bug(
 534                                 span,
 535                                 &format!(
 536                                     "defining opaque type use restricts opaque \
 537                                      type by using the generic parameter `{}` twice",
 538                                     arg,
 539                                 ),
 540                             );
 541                         }
 542                     } else {
 543                         let param = opaque_generics.param_at(i, self.tcx);
 544                         self.tcx.sess.delay_span_bug(
 545                             span,
 546                             &format!(
 547                                 "defining opaque type use does not fully define opaque type: \
 548                                  generic parameter `{}` is specified as concrete {} `{}`",
 549                                 param.name,
 550                                 param.kind.descr(),
 551                                 arg,
 552                             ),
 553                         );
 554                     }
 555                 }
 556
 557                 if let Some((prev_span, prev_ty)) = self.found {
 558                     if *concrete_type != prev_ty {
 559                         debug!("find_opaque_ty_constraints: span={:?}", span);
 560                         // Found different concrete types for the opaque type.
 561                         let mut err = self.tcx.sess.struct_span_err(
 562                             span,
 563                             "concrete type differs from previous defining opaque type use",
 564                         );
 565                         err.span_label(
 566                             span,
 567                             format!("expected `{}`, got `{}`", prev_ty, concrete_type),
 568                         );
 569                         err.span_note(prev_span, "previous use here");
 570                         err.emit();
 571                     }
 572                 } else {
 573                     self.found = Some((span, concrete_type));
 574                 }
 575             } else {
 576                 debug!(
 577                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`",
 578                     self.def_id, def_id,
 579                 );
 580             }
 581         }
 582     }
 583
 584     impl<'tcx> intravisit::Visitor<'tcx> for ConstraintLocator<'tcx> {
 585         type Map = Map<'tcx>;
 586
 587         fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 588             intravisit::NestedVisitorMap::All(self.tcx.hir())
 589         }
 590         fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
 591             if let hir::ExprKind::Closure(..) = ex.kind {
 592                 let def_id = self.tcx.hir().local_def_id(ex.hir_id);
 593                 self.check(def_id);
 594             }
 595             intravisit::walk_expr(self, ex);
 596         }
 597         fn visit_item(&mut self, it: &'tcx Item<'tcx>) {
 598             debug!("find_existential_constraints: visiting {:?}", it);
 599             // The opaque type itself or its children are not within its reveal scope.
 600             if it.def_id.to_def_id() != self.def_id {
 601                 self.check(it.def_id);
 602                 intravisit::walk_item(self, it);
 603             }
 604         }
 605         fn visit_impl_item(&mut self, it: &'tcx ImplItem<'tcx>) {
 606             debug!("find_existential_constraints: visiting {:?}", it);
 607             // The opaque type itself or its children are not within its reveal scope.
 608             if it.def_id.to_def_id() != self.def_id {
 609                 self.check(it.def_id);
 610                 intravisit::walk_impl_item(self, it);
 611             }
 612         }
 613         fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
 614             debug!("find_existential_constraints: visiting {:?}", it);
 615             self.check(it.def_id);
 616             intravisit::walk_trait_item(self, it);
 617         }
 618     }
 619
 620     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 621     let scope = tcx.hir().get_defining_scope(hir_id);
 622     let mut locator = ConstraintLocator { def_id: def_id.to_def_id(), tcx, found: None };
 623
 624     debug!("find_opaque_ty_constraints: scope={:?}", scope);
 625
 626     if scope == hir::CRATE_HIR_ID {
 627         intravisit::walk_crate(&mut locator, tcx.hir().krate());
 628     } else {
 629         debug!("find_opaque_ty_constraints: scope={:?}", tcx.hir().get(scope));
 630         match tcx.hir().get(scope) {
 631             // We explicitly call `visit_*` methods, instead of using `intravisit::walk_*` methods
 632             // This allows our visitor to process the defining item itself, causing
 633             // it to pick up any 'sibling' defining uses.
 634             //
 635             // For example, this code:
 636             // ```
 637             // fn foo() {
 638             //     type Blah = impl Debug;
 639             //     let my_closure = || -> Blah { true };
 640             // }
 641             // ```
 642             //
 643             // requires us to explicitly process `foo()` in order
 644             // to notice the defining usage of `Blah`.
 645             Node::Item(ref it) => locator.visit_item(it),
 646             Node::ImplItem(ref it) => locator.visit_impl_item(it),
 647             Node::TraitItem(ref it) => locator.visit_trait_item(it),
 648             other => bug!("{:?} is not a valid scope for an opaque type item", other),
 649         }
 650     }
 651
 652     match locator.found {
 653         Some((_, ty)) => ty,
 654         None => {
 655             let span = tcx.def_span(def_id);
 656             tcx.sess.span_err(span, "could not find defining uses");
 657             tcx.ty_error()
 658         }
 659     }
 660 }
 661
 662 /// Retrieve the inferred concrete type for let position impl trait.
 663 ///
 664 /// This is different to other kinds of impl trait because:
 665 ///
 666 /// 1. We know which function contains the defining use (the function that
 667 ///    contains the let statement)
 668 /// 2. We do not currently allow (free) lifetimes in the return type. `let`
 669 ///    statements in some statically unreachable code are removed from the MIR
 670 ///    by the time we borrow check, and it's not clear how we should handle
 671 ///    those.
 672 fn let_position_impl_trait_type(tcx: TyCtxt<'_>, opaque_ty_id: LocalDefId) -> Ty<'_> {
 673     let scope = tcx.hir().get_defining_scope(tcx.hir().local_def_id_to_hir_id(opaque_ty_id));
 674     let scope_def_id = tcx.hir().local_def_id(scope);
 675
 676     let opaque_ty_def_id = opaque_ty_id.to_def_id();
 677
 678     let owner_typeck_results = tcx.typeck(scope_def_id);
 679     let concrete_ty = owner_typeck_results
 680         .concrete_opaque_types
 681         .get(&opaque_ty_def_id)
 682         .map(|opaque| opaque.concrete_type)
 683         .unwrap_or_else(|| {
 684             tcx.sess.delay_span_bug(
 685                 DUMMY_SP,
 686                 &format!(
 687                     "owner {:?} has no opaque type for {:?} in its typeck results",
 688                     scope_def_id, opaque_ty_id
 689                 ),
 690             );
 691             if let Some(ErrorReported) = owner_typeck_results.tainted_by_errors {
 692                 // Some error in the owner fn prevented us from populating the
 693                 // `concrete_opaque_types` table.
 694                 tcx.ty_error()
 695             } else {
 696                 // We failed to resolve the opaque type or it resolves to
 697                 // itself. Return the non-revealed type, which should result in
 698                 // E0720.
 699                 tcx.mk_opaque(
 700                     opaque_ty_def_id,
 701                     InternalSubsts::identity_for_item(tcx, opaque_ty_def_id),
 702                 )
 703             }
 704         });
 705     debug!("concrete_ty = {:?}", concrete_ty);
 706     if concrete_ty.has_erased_regions() {
 707         // FIXME(impl_trait_in_bindings) Handle this case.
 708         tcx.sess.span_fatal(
 709             tcx.hir().span(tcx.hir().local_def_id_to_hir_id(opaque_ty_id)),
 710             "lifetimes in impl Trait types in bindings are not currently supported",
 711         );
 712     }
 713     concrete_ty
 714 }
 715
 716 fn infer_placeholder_type(
 717     tcx: TyCtxt<'_>,
 718     def_id: LocalDefId,
 719     body_id: hir::BodyId,
 720     span: Span,
 721     item_ident: Ident,
 722 ) -> Ty<'_> {
 723     let ty = tcx.diagnostic_only_typeck(def_id).node_type(body_id.hir_id);
 724
 725     // If this came from a free `const` or `static mut?` item,
 726     // then the user may have written e.g. `const A = 42;`.
 727     // In this case, the parser has stashed a diagnostic for
 728     // us to improve in typeck so we do that now.
 729     match tcx.sess.diagnostic().steal_diagnostic(span, StashKey::ItemNoType) {
 730         Some(mut err) => {
 731             // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type.
 732             // We are typeck and have the real type, so remove that and suggest the actual type.
 733             err.suggestions.clear();
 734             err.span_suggestion(
 735                 span,
 736                 "provide a type for the item",
 737                 format!("{}: {}", item_ident, ty),
 738                 Applicability::MachineApplicable,
 739             )
 740             .emit_unless(ty.references_error());
 741         }
 742         None => {
 743             let mut diag = bad_placeholder_type(tcx, vec![span]);
 744
 745             if !ty.references_error() {
 746                 diag.span_suggestion(
 747                     span,
 748                     "replace `_` with the correct type",
 749                     ty.to_string(),
 750                     Applicability::MaybeIncorrect,
 751                 );
 752             }
 753
 754             diag.emit();
 755         }
 756     }
 757
 758     // Typeck doesn't expect erased regions to be returned from `type_of`.
 759     tcx.fold_regions(ty, &mut false, |r, _| match r {
 760         ty::ReErased => tcx.lifetimes.re_static,
 761         _ => r,
 762     })
 763 }
 764
 765 fn check_feature_inherent_assoc_ty(tcx: TyCtxt<'_>, span: Span) {
 766     if !tcx.features().inherent_associated_types {
 767         use rustc_session::parse::feature_err;
 768         use rustc_span::symbol::sym;
 769         feature_err(
 770             &tcx.sess.parse_sess,
 771             sym::inherent_associated_types,
 772             span,
 773             "inherent associated types are unstable",
 774         )
 775         .emit();
 776     }
 777 }