1 use rustc_errors::{Applicability, ErrorReported, StashKey};
3 use rustc_hir::def::{DefKind, Res};
4 use rustc_hir::def_id::{DefId, LocalDefId};
5 use rustc_hir::intravisit;
6 use rustc_hir::intravisit::Visitor;
7 use rustc_hir::{HirId, Node};
8 use rustc_middle::hir::map::Map;
9 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
10 use rustc_middle::ty::util::IntTypeExt;
11 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt, TypeFoldable, TypeFolder};
12 use rustc_span::symbol::Ident;
13 use rustc_span::{Span, DUMMY_SP};
16 use super::{bad_placeholder_type, is_suggestable_infer_ty};
18 /// Computes the relevant generic parameter for a potential generic const argument.
20 /// This should be called using the query `tcx.opt_const_param_of`.
21 pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<DefId> {
22 // FIXME(generic_arg_infer): allow for returning DefIds of inference of
23 // GenericArg::Infer below. This may require a change where GenericArg::Infer has some flag
26 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
28 if let Node::AnonConst(_) = tcx.hir().get(hir_id) {
29 let parent_node_id = tcx.hir().get_parent_node(hir_id);
30 let parent_node = tcx.hir().get(parent_node_id);
33 // This match arm is for when the def_id appears in a GAT whose
34 // path can't be resolved without typechecking e.g.
37 // type Assoc<const N: usize>;
38 // fn foo() -> Self::Assoc<3>;
41 // In the above code we would call this query with the def_id of 3 and
42 // the parent_node we match on would be the hir node for Self::Assoc<3>
44 // `Self::Assoc<3>` cant be resolved without typchecking here as we
45 // didnt write <Self as Foo>::Assoc<3>. If we did then another match
46 // arm would handle this.
48 // I believe this match arm is only needed for GAT but I am not 100% sure - BoxyUwU
49 Node::Ty(hir_ty @ Ty { kind: TyKind::Path(QPath::TypeRelative(_, segment)), .. }) => {
50 // Find the Item containing the associated type so we can create an ItemCtxt.
51 // Using the ItemCtxt convert the HIR for the unresolved assoc type into a
52 // ty which is a fully resolved projection.
53 // For the code example above, this would mean converting Self::Assoc<3>
54 // into a ty::Projection(<Self as Foo>::Assoc<3>)
58 .filter(|(_, node)| matches!(node, Node::Item(_)))
62 let item_did = tcx.hir().local_def_id(item_hir_id).to_def_id();
63 let item_ctxt = &ItemCtxt::new(tcx, item_did) as &dyn crate::astconv::AstConv<'_>;
64 let ty = item_ctxt.ast_ty_to_ty(hir_ty);
66 // Iterate through the generics of the projection to find the one that corresponds to
67 // the def_id that this query was called with. We filter to only const args here as a
68 // precaution for if it's ever allowed to elide lifetimes in GAT's. It currently isn't
69 // but it can't hurt to be safe ^^
70 if let ty::Projection(projection) = ty.kind() {
71 let generics = tcx.generics_of(projection.item_def_id);
73 let arg_index = segment
78 .filter(|arg| arg.is_const())
79 .position(|arg| arg.id() == hir_id)
82 bug!("no arg matching AnonConst in segment");
88 .filter(|param| matches!(param.kind, ty::GenericParamDefKind::Const { .. }))
90 .map(|param| param.def_id);
93 // I dont think it's possible to reach this but I'm not 100% sure - BoxyUwU
94 tcx.sess.delay_span_bug(
96 "unexpected non-GAT usage of an anon const",
102 ExprKind::MethodCall(segment, ..) | ExprKind::Path(QPath::TypeRelative(_, segment)),
105 let body_owner = tcx.hir().local_def_id(tcx.hir().enclosing_body_owner(hir_id));
106 let tables = tcx.typeck(body_owner);
107 // This may fail in case the method/path does not actually exist.
108 // As there is no relevant param for `def_id`, we simply return
110 let type_dependent_def = tables.type_dependent_def_id(parent_node_id)?;
116 .filter(|arg| arg.is_const())
117 .position(|arg| arg.id() == hir_id)
120 bug!("no arg matching AnonConst in segment");
123 tcx.generics_of(type_dependent_def)
126 .filter(|param| matches!(param.kind, ty::GenericParamDefKind::Const { .. }))
128 .map(|param| param.def_id)
131 Node::Ty(&Ty { kind: TyKind::Path(_), .. })
132 | Node::Expr(&Expr { kind: ExprKind::Path(_) | ExprKind::Struct(..), .. })
135 let path = match parent_node {
136 Node::Ty(&Ty { kind: TyKind::Path(QPath::Resolved(_, path)), .. })
137 | Node::TraitRef(&TraitRef { path, .. }) => &*path,
140 ExprKind::Path(QPath::Resolved(_, path))
141 | ExprKind::Struct(&QPath::Resolved(_, path), ..),
145 tcx.hir().local_def_id(tcx.hir().enclosing_body_owner(hir_id));
146 let _tables = tcx.typeck(body_owner);
150 if let Some(path) = get_path_containing_arg_in_pat(pat, hir_id) {
153 tcx.sess.delay_span_bug(
154 tcx.def_span(def_id),
156 "unable to find const parent for {} in pat {:?}",
164 tcx.sess.delay_span_bug(
165 tcx.def_span(def_id),
166 &format!("unexpected const parent path {:?}", parent_node),
172 // We've encountered an `AnonConst` in some path, so we need to
173 // figure out which generic parameter it corresponds to and return
174 // the relevant type.
175 let (arg_index, segment) = path
178 .filter_map(|seg| seg.args.map(|args| (args.args, seg)))
179 .find_map(|(args, seg)| {
181 .filter(|arg| arg.is_const())
182 .position(|arg| arg.id() == hir_id)
183 .map(|index| (index, seg))
186 bug!("no arg matching AnonConst in path");
189 // Try to use the segment resolution if it is valid, otherwise we
190 // default to the path resolution.
191 let res = segment.res.filter(|&r| r != Res::Err).unwrap_or(path.res);
193 let generics = match res {
194 Res::Def(DefKind::Ctor(CtorOf::Variant, _), def_id) => tcx.generics_of(
195 tcx.parent(def_id).and_then(|def_id| tcx.parent(def_id)).unwrap(),
197 Res::Def(DefKind::Variant | DefKind::Ctor(CtorOf::Struct, _), def_id) => {
198 tcx.generics_of(tcx.parent(def_id).unwrap())
200 // Other `DefKind`s don't have generics and would ICE when calling
210 | DefKind::TraitAlias
214 | DefKind::AssocConst
217 ) => tcx.generics_of(def_id),
219 tcx.sess.delay_span_bug(tcx.def_span(def_id), "anon const with Res::Err");
223 // If the user tries to specify generics on a type that does not take them,
224 // e.g. `usize<T>`, we may hit this branch, in which case we treat it as if
225 // no arguments have been passed. An error should already have been emitted.
226 tcx.sess.delay_span_bug(
227 tcx.def_span(def_id),
228 &format!("unexpected anon const res {:?} in path: {:?}", res, path),
237 .filter(|param| matches!(param.kind, ty::GenericParamDefKind::Const { .. }))
239 .map(|param| param.def_id)
248 fn get_path_containing_arg_in_pat<'hir>(
249 pat: &'hir hir::Pat<'hir>,
251 ) -> Option<&'hir hir::Path<'hir>> {
254 let is_arg_in_path = |p: &hir::Path<'_>| {
257 .filter_map(|seg| seg.args)
258 .flat_map(|args| args.args)
259 .any(|arg| arg.id() == arg_id)
261 let mut arg_path = None;
262 pat.walk(|pat| match pat.kind {
263 PatKind::Struct(QPath::Resolved(_, path), _, _)
264 | PatKind::TupleStruct(QPath::Resolved(_, path), _, _)
265 | PatKind::Path(QPath::Resolved(_, path))
266 if is_arg_in_path(path) =>
268 arg_path = Some(path);
276 pub(super) fn default_anon_const_substs(tcx: TyCtxt<'_>, def_id: DefId) -> SubstsRef<'_> {
277 let generics = tcx.generics_of(def_id);
278 if let Some(parent) = generics.parent {
279 // This is the reason we bother with having optional anon const substs.
281 // In the future the substs of an anon const will depend on its parents predicates
282 // at which point eagerly looking at them will cause a query cycle.
284 // So for now this is only an assurance that this approach won't cause cycle errors in
286 let _cycle_check = tcx.predicates_of(parent);
289 let substs = InternalSubsts::identity_for_item(tcx, def_id);
290 // We only expect substs with the following type flags as default substs.
292 // Getting this wrong can lead to ICE and unsoundness, so we assert it here.
293 for arg in substs.iter() {
294 let allowed_flags = ty::TypeFlags::MAY_NEED_DEFAULT_CONST_SUBSTS
295 | ty::TypeFlags::STILL_FURTHER_SPECIALIZABLE
296 | ty::TypeFlags::HAS_ERROR;
297 assert!(!arg.has_type_flags(!allowed_flags));
302 pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
303 let def_id = def_id.expect_local();
306 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
308 let icx = ItemCtxt::new(tcx, def_id.to_def_id());
310 match tcx.hir().get(hir_id) {
311 Node::TraitItem(item) => match item.kind {
312 TraitItemKind::Fn(..) => {
313 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
314 tcx.mk_fn_def(def_id.to_def_id(), substs)
316 TraitItemKind::Const(ty, body_id) => body_id
317 .and_then(|body_id| {
318 if is_suggestable_infer_ty(ty) {
319 Some(infer_placeholder_type(
320 tcx, def_id, body_id, ty.span, item.ident, "constant",
326 .unwrap_or_else(|| icx.to_ty(ty)),
327 TraitItemKind::Type(_, Some(ty)) => icx.to_ty(ty),
328 TraitItemKind::Type(_, None) => {
329 span_bug!(item.span, "associated type missing default");
333 Node::ImplItem(item) => match item.kind {
334 ImplItemKind::Fn(..) => {
335 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
336 tcx.mk_fn_def(def_id.to_def_id(), substs)
338 ImplItemKind::Const(ty, body_id) => {
339 if is_suggestable_infer_ty(ty) {
340 infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident, "constant")
345 ImplItemKind::TyAlias(ty) => {
346 if tcx.impl_trait_ref(tcx.hir().get_parent_did(hir_id).to_def_id()).is_none() {
347 check_feature_inherent_assoc_ty(tcx, item.span);
354 Node::Item(item) => {
356 ItemKind::Static(ty, .., body_id) => {
357 if is_suggestable_infer_ty(ty) {
358 infer_placeholder_type(
370 ItemKind::Const(ty, body_id) => {
371 if is_suggestable_infer_ty(ty) {
372 infer_placeholder_type(
373 tcx, def_id, body_id, ty.span, item.ident, "constant",
379 ItemKind::TyAlias(self_ty, _)
380 | ItemKind::Impl(hir::Impl { self_ty, .. }) => icx.to_ty(self_ty),
381 ItemKind::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)
385 ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
386 let def = tcx.adt_def(def_id);
387 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
388 tcx.mk_adt(def, substs)
390 ItemKind::OpaqueTy(OpaqueTy { impl_trait_fn: None, .. }) => {
391 find_opaque_ty_constraints(tcx, def_id)
393 // Opaque types desugared from `impl Trait`.
394 ItemKind::OpaqueTy(OpaqueTy { impl_trait_fn: Some(owner), .. }) => {
395 let concrete_ty = tcx
396 .mir_borrowck(owner.expect_local())
397 .concrete_opaque_types
398 .get_value_matching(|(key, _)| key.def_id == def_id.to_def_id())
401 tcx.sess.delay_span_bug(
404 "owner {:?} has no opaque type for {:?} in its typeck results",
408 if let Some(ErrorReported) =
409 tcx.typeck(owner.expect_local()).tainted_by_errors
412 // owner fn prevented us from populating
413 // the `concrete_opaque_types` table.
416 // We failed to resolve the opaque type or it
417 // resolves to itself. Return the non-revealed
418 // type, which should result in E0720.
421 InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
425 debug!("concrete_ty = {:?}", concrete_ty);
429 | ItemKind::TraitAlias(..)
430 | ItemKind::Macro(..)
432 | ItemKind::ForeignMod { .. }
433 | ItemKind::GlobalAsm(..)
434 | ItemKind::ExternCrate(..)
435 | ItemKind::Use(..) => {
438 "compute_type_of_item: unexpected item type: {:?}",
445 Node::ForeignItem(foreign_item) => match foreign_item.kind {
446 ForeignItemKind::Fn(..) => {
447 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
448 tcx.mk_fn_def(def_id.to_def_id(), substs)
450 ForeignItemKind::Static(t, _) => icx.to_ty(t),
451 ForeignItemKind::Type => tcx.mk_foreign(def_id.to_def_id()),
454 Node::Ctor(&ref def) | Node::Variant(Variant { data: ref def, .. }) => match *def {
455 VariantData::Unit(..) | VariantData::Struct(..) => {
456 tcx.type_of(tcx.hir().get_parent_did(hir_id).to_def_id())
458 VariantData::Tuple(..) => {
459 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
460 tcx.mk_fn_def(def_id.to_def_id(), substs)
464 Node::Field(field) => icx.to_ty(field.ty),
466 Node::Expr(&Expr { kind: ExprKind::Closure(.., gen), .. }) => {
467 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
468 if let Some(movability) = gen {
469 tcx.mk_generator(def_id.to_def_id(), substs, movability)
471 tcx.mk_closure(def_id.to_def_id(), substs)
475 Node::AnonConst(_) if let Some(param) = tcx.opt_const_param_of(def_id) => {
476 // We defer to `type_of` of the corresponding parameter
477 // for generic arguments.
481 Node::AnonConst(_) => {
482 let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
484 Node::Ty(&Ty { kind: TyKind::Array(_, ref constant), .. })
485 | Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
486 if constant.hir_id == hir_id =>
490 Node::Ty(&Ty { kind: TyKind::Typeof(ref e), .. }) if e.hir_id == hir_id => {
491 tcx.typeck(def_id).node_type(e.hir_id)
494 Node::Expr(&Expr { kind: ExprKind::ConstBlock(ref anon_const), .. })
495 if anon_const.hir_id == hir_id =>
497 tcx.typeck(def_id).node_type(anon_const.hir_id)
500 Node::Expr(&Expr { kind: ExprKind::InlineAsm(asm), .. })
501 | Node::Item(&Item { kind: ItemKind::GlobalAsm(asm), .. })
502 if asm.operands.iter().any(|(op, _op_sp)| match op {
503 hir::InlineAsmOperand::Const { anon_const } => anon_const.hir_id == hir_id,
507 tcx.typeck(def_id).node_type(hir_id)
510 Node::Variant(Variant { disr_expr: Some(ref e), .. }) if e.hir_id == hir_id => tcx
511 .adt_def(tcx.hir().get_parent_did(hir_id).to_def_id())
516 Node::GenericParam(&GenericParam {
517 hir_id: param_hir_id,
518 kind: GenericParamKind::Const { default: Some(ct), .. },
520 }) if ct.hir_id == hir_id => tcx.type_of(tcx.hir().local_def_id(param_hir_id)),
522 x => tcx.ty_error_with_message(
524 &format!("unexpected const parent in type_of(): {:?}", x),
529 Node::GenericParam(param) => match ¶m.kind {
530 GenericParamKind::Type { default: Some(ty), .. }
531 | GenericParamKind::Const { ty, .. } => icx.to_ty(ty),
532 x => bug!("unexpected non-type Node::GenericParam: {:?}", x),
536 bug!("unexpected sort of node in type_of(): {:?}", x);
541 #[instrument(skip(tcx), level = "debug")]
542 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
543 /// laid for "higher-order pattern unification".
544 /// This ensures that inference is tractable.
545 /// In particular, definitions of opaque types can only use other generics as arguments,
546 /// and they cannot repeat an argument. Example:
549 /// type Foo<A, B> = impl Bar<A, B>;
551 /// // Okay -- `Foo` is applied to two distinct, generic types.
552 /// fn a<T, U>() -> Foo<T, U> { .. }
554 /// // Not okay -- `Foo` is applied to `T` twice.
555 /// fn b<T>() -> Foo<T, T> { .. }
557 /// // Not okay -- `Foo` is applied to a non-generic type.
558 /// fn b<T>() -> Foo<T, u32> { .. }
561 fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
562 use rustc_hir::{Expr, ImplItem, Item, TraitItem};
564 struct ConstraintLocator<'tcx> {
567 /// def_id of the opaque type whose defining uses are being checked
570 /// as we walk the defining uses, we are checking that all of them
571 /// define the same hidden type. This variable is set to `Some`
572 /// with the first type that we find, and then later types are
573 /// checked against it (we also carry the span of that first
575 found: Option<(Span, Ty<'tcx>)>,
578 impl ConstraintLocator<'_> {
579 #[instrument(skip(self), level = "debug")]
580 fn check(&mut self, def_id: LocalDefId) {
581 // Don't try to check items that cannot possibly constrain the type.
582 if !self.tcx.has_typeck_results(def_id) {
583 debug!("no constraint: no typeck results");
586 // Calling `mir_borrowck` can lead to cycle errors through
587 // const-checking, avoid calling it if we don't have to.
588 if !self.tcx.typeck(def_id).concrete_opaque_types.contains(&self.def_id) {
589 debug!("no constraints in typeck results");
592 // Use borrowck to get the type with unerased regions.
593 let concrete_opaque_types = &self.tcx.mir_borrowck(def_id).concrete_opaque_types;
594 debug!(?concrete_opaque_types);
595 for (opaque_type_key, concrete_type) in concrete_opaque_types {
596 if opaque_type_key.def_id != self.def_id {
597 // Ignore constraints for other opaque types.
601 debug!(?concrete_type, ?opaque_type_key.substs, "found constraint");
603 // FIXME(oli-obk): trace the actual span from inference to improve errors.
604 let span = self.tcx.def_span(def_id);
606 if let Some((prev_span, prev_ty)) = self.found {
607 if *concrete_type != prev_ty && !(*concrete_type, prev_ty).references_error() {
609 // Found different concrete types for the opaque type.
610 let mut err = self.tcx.sess.struct_span_err(
612 "concrete type differs from previous defining opaque type use",
616 format!("expected `{}`, got `{}`", prev_ty, concrete_type),
618 err.span_note(prev_span, "previous use here");
622 self.found = Some((span, concrete_type));
628 impl<'tcx> intravisit::Visitor<'tcx> for ConstraintLocator<'tcx> {
629 type Map = Map<'tcx>;
631 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
632 intravisit::NestedVisitorMap::All(self.tcx.hir())
634 fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
635 if let hir::ExprKind::Closure(..) = ex.kind {
636 let def_id = self.tcx.hir().local_def_id(ex.hir_id);
639 intravisit::walk_expr(self, ex);
641 fn visit_item(&mut self, it: &'tcx Item<'tcx>) {
642 debug!("find_existential_constraints: visiting {:?}", it);
643 // The opaque type itself or its children are not within its reveal scope.
644 if it.def_id.to_def_id() != self.def_id {
645 self.check(it.def_id);
646 intravisit::walk_item(self, it);
649 fn visit_impl_item(&mut self, it: &'tcx ImplItem<'tcx>) {
650 debug!("find_existential_constraints: visiting {:?}", it);
651 // The opaque type itself or its children are not within its reveal scope.
652 if it.def_id.to_def_id() != self.def_id {
653 self.check(it.def_id);
654 intravisit::walk_impl_item(self, it);
657 fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
658 debug!("find_existential_constraints: visiting {:?}", it);
659 self.check(it.def_id);
660 intravisit::walk_trait_item(self, it);
664 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
665 let scope = tcx.hir().get_defining_scope(hir_id);
666 let mut locator = ConstraintLocator { def_id: def_id.to_def_id(), tcx, found: None };
668 debug!("find_opaque_ty_constraints: scope={:?}", scope);
670 if scope == hir::CRATE_HIR_ID {
671 tcx.hir().walk_toplevel_module(&mut locator);
673 debug!("find_opaque_ty_constraints: scope={:?}", tcx.hir().get(scope));
674 match tcx.hir().get(scope) {
675 // We explicitly call `visit_*` methods, instead of using `intravisit::walk_*` methods
676 // This allows our visitor to process the defining item itself, causing
677 // it to pick up any 'sibling' defining uses.
679 // For example, this code:
682 // type Blah = impl Debug;
683 // let my_closure = || -> Blah { true };
687 // requires us to explicitly process `foo()` in order
688 // to notice the defining usage of `Blah`.
689 Node::Item(it) => locator.visit_item(it),
690 Node::ImplItem(it) => locator.visit_impl_item(it),
691 Node::TraitItem(it) => locator.visit_trait_item(it),
692 other => bug!("{:?} is not a valid scope for an opaque type item", other),
696 match locator.found {
699 let span = tcx.def_span(def_id);
700 tcx.sess.span_err(span, "could not find defining uses");
706 fn infer_placeholder_type<'a>(
709 body_id: hir::BodyId,
714 // Attempts to make the type nameable by turning FnDefs into FnPtrs.
715 struct MakeNameable<'tcx> {
720 impl<'tcx> MakeNameable<'tcx> {
721 fn new(tcx: TyCtxt<'tcx>) -> Self {
722 MakeNameable { success: true, tcx }
726 impl TypeFolder<'tcx> for MakeNameable<'tcx> {
727 fn tcx(&self) -> TyCtxt<'tcx> {
731 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
737 ty::FnDef(def_id, _) => self.tcx.mk_fn_ptr(self.tcx.fn_sig(*def_id)),
738 // FIXME: non-capturing closures should also suggest a function pointer
739 ty::Closure(..) | ty::Generator(..) => {
740 self.success = false;
743 _ => ty.super_fold_with(self),
748 let ty = tcx.diagnostic_only_typeck(def_id).node_type(body_id.hir_id);
750 // If this came from a free `const` or `static mut?` item,
751 // then the user may have written e.g. `const A = 42;`.
752 // In this case, the parser has stashed a diagnostic for
753 // us to improve in typeck so we do that now.
754 match tcx.sess.diagnostic().steal_diagnostic(span, StashKey::ItemNoType) {
756 if !ty.references_error() {
757 // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type.
758 // We are typeck and have the real type, so remove that and suggest the actual type.
759 err.suggestions.clear();
761 // Suggesting unnameable types won't help.
762 let mut mk_nameable = MakeNameable::new(tcx);
763 let ty = mk_nameable.fold_ty(ty);
764 let sugg_ty = if mk_nameable.success { Some(ty) } else { None };
765 if let Some(sugg_ty) = sugg_ty {
768 &format!("provide a type for the {item}", item = kind),
769 format!("{}: {}", item_ident, sugg_ty),
770 Applicability::MachineApplicable,
774 tcx.hir().body(body_id).value.span,
775 &format!("however, the inferred type `{}` cannot be named", ty),
783 let mut diag = bad_placeholder_type(tcx, vec![span], kind);
785 if !ty.references_error() {
786 let mut mk_nameable = MakeNameable::new(tcx);
787 let ty = mk_nameable.fold_ty(ty);
788 let sugg_ty = if mk_nameable.success { Some(ty) } else { None };
789 if let Some(sugg_ty) = sugg_ty {
790 diag.span_suggestion(
792 "replace with the correct type",
794 Applicability::MaybeIncorrect,
798 tcx.hir().body(body_id).value.span,
799 &format!("however, the inferred type `{}` cannot be named", ty),
808 // Typeck doesn't expect erased regions to be returned from `type_of`.
809 tcx.fold_regions(ty, &mut false, |r, _| match r {
810 ty::ReErased => tcx.lifetimes.re_static,
815 fn check_feature_inherent_assoc_ty(tcx: TyCtxt<'_>, span: Span) {
816 if !tcx.features().inherent_associated_types {
817 use rustc_session::parse::feature_err;
818 use rustc_span::symbol::sym;
820 &tcx.sess.parse_sess,
821 sym::inherent_associated_types,
823 "inherent associated types are unstable",