1 use super::coercion::CoerceMany;
2 use super::compare_method::check_type_bounds;
3 use super::compare_method::{compare_const_impl, compare_impl_method, compare_ty_impl};
6 use rustc_attr as attr;
7 use rustc_errors::{Applicability, ErrorGuaranteed, MultiSpan};
9 use rustc_hir::def_id::{DefId, LocalDefId};
10 use rustc_hir::intravisit::Visitor;
11 use rustc_hir::lang_items::LangItem;
12 use rustc_hir::{def::Res, ItemKind, Node, PathSegment};
13 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
14 use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
15 use rustc_infer::traits::Obligation;
16 use rustc_middle::hir::nested_filter;
17 use rustc_middle::ty::fold::TypeFoldable;
18 use rustc_middle::ty::layout::{LayoutError, MAX_SIMD_LANES};
19 use rustc_middle::ty::subst::GenericArgKind;
20 use rustc_middle::ty::util::{Discr, IntTypeExt};
21 use rustc_middle::ty::{self, ParamEnv, ToPredicate, Ty, TyCtxt};
22 use rustc_session::lint::builtin::{UNINHABITED_STATIC, UNSUPPORTED_CALLING_CONVENTIONS};
23 use rustc_span::symbol::sym;
24 use rustc_span::{self, Span};
25 use rustc_target::spec::abi::Abi;
26 use rustc_trait_selection::traits;
27 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
28 use rustc_ty_utils::representability::{self, Representability};
31 use std::ops::ControlFlow;
33 pub fn check_wf_new(tcx: TyCtxt<'_>) {
34 let visit = wfcheck::CheckTypeWellFormedVisitor::new(tcx);
35 tcx.hir().par_visit_all_item_likes(&visit);
38 pub(super) fn check_abi(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: Abi) {
39 match tcx.sess.target.is_abi_supported(abi) {
46 "`{abi}` is not a supported ABI for the current target",
51 tcx.struct_span_lint_hir(UNSUPPORTED_CALLING_CONVENTIONS, hir_id, span, |lint| {
52 lint.build("use of calling convention not supported on this target").emit();
57 // This ABI is only allowed on function pointers
58 if abi == Abi::CCmseNonSecureCall {
63 "the `\"C-cmse-nonsecure-call\"` ABI is only allowed on function pointers"
69 /// Helper used for fns and closures. Does the grungy work of checking a function
70 /// body and returns the function context used for that purpose, since in the case of a fn item
71 /// there is still a bit more to do.
74 /// * inherited: other fields inherited from the enclosing fn (if any)
75 #[instrument(skip(inherited, body), level = "debug")]
76 pub(super) fn check_fn<'a, 'tcx>(
77 inherited: &'a Inherited<'a, 'tcx>,
78 param_env: ty::ParamEnv<'tcx>,
79 fn_sig: ty::FnSig<'tcx>,
80 decl: &'tcx hir::FnDecl<'tcx>,
82 body: &'tcx hir::Body<'tcx>,
83 can_be_generator: Option<hir::Movability>,
84 return_type_pre_known: bool,
85 ) -> (FnCtxt<'a, 'tcx>, Option<GeneratorTypes<'tcx>>) {
86 // Create the function context. This is either derived from scratch or,
87 // in the case of closures, based on the outer context.
88 let mut fcx = FnCtxt::new(inherited, param_env, body.value.hir_id);
89 fcx.ps.set(UnsafetyState::function(fn_sig.unsafety, fn_id));
90 fcx.return_type_pre_known = return_type_pre_known;
96 let declared_ret_ty = fn_sig.output();
99 fcx.register_infer_ok_obligations(fcx.infcx.replace_opaque_types_with_inference_vars(
105 // HACK(oli-obk): we rewrite the declared return type, too, so that we don't end up inferring all
106 // unconstrained RPIT to have `()` as their hidden type. This would happen because further down we
107 // compare the ret_coercion with declared_ret_ty, and anything uninferred would be inferred to the
108 // opaque type itself. That again would cause writeback to assume we have a recursive call site
109 // and do the sadly stabilized fallback to `()`.
110 let declared_ret_ty = ret_ty;
111 fcx.ret_coercion = Some(RefCell::new(CoerceMany::new(ret_ty)));
112 fcx.ret_type_span = Some(decl.output.span());
114 let span = body.value.span;
116 fn_maybe_err(tcx, span, fn_sig.abi);
118 if fn_sig.abi == Abi::RustCall {
119 let expected_args = if let ImplicitSelfKind::None = decl.implicit_self { 1 } else { 2 };
122 let item = match tcx.hir().get(fn_id) {
123 Node::Item(hir::Item { kind: ItemKind::Fn(header, ..), .. }) => Some(header),
124 Node::ImplItem(hir::ImplItem {
125 kind: hir::ImplItemKind::Fn(header, ..), ..
127 Node::TraitItem(hir::TraitItem {
128 kind: hir::TraitItemKind::Fn(header, ..),
131 // Closures are RustCall, but they tuple their arguments, so shouldn't be checked
132 Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => None,
133 node => bug!("Item being checked wasn't a function/closure: {:?}", node),
136 if let Some(header) = item {
137 tcx.sess.span_err(header.span, "functions with the \"rust-call\" ABI must take a single non-self argument that is a tuple");
141 if fn_sig.inputs().len() != expected_args {
144 // FIXME(CraftSpider) Add a check on parameter expansion, so we don't just make the ICE happen later on
145 // This will probably require wide-scale changes to support a TupleKind obligation
146 // We can't resolve this without knowing the type of the param
147 if !matches!(fn_sig.inputs()[expected_args - 1].kind(), ty::Tuple(_) | ty::Param(_)) {
153 if body.generator_kind.is_some() && can_be_generator.is_some() {
155 .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span });
156 fcx.require_type_is_sized(yield_ty, span, traits::SizedYieldType);
158 // Resume type defaults to `()` if the generator has no argument.
159 let resume_ty = fn_sig.inputs().get(0).copied().unwrap_or_else(|| tcx.mk_unit());
161 fcx.resume_yield_tys = Some((resume_ty, yield_ty));
164 GatherLocalsVisitor::new(&fcx).visit_body(body);
166 // C-variadic fns also have a `VaList` input that's not listed in `fn_sig`
167 // (as it's created inside the body itself, not passed in from outside).
168 let maybe_va_list = if fn_sig.c_variadic {
169 let span = body.params.last().unwrap().span;
170 let va_list_did = tcx.require_lang_item(LangItem::VaList, Some(span));
171 let region = fcx.next_region_var(RegionVariableOrigin::MiscVariable(span));
173 Some(tcx.type_of(va_list_did).subst(tcx, &[region.into()]))
178 // Add formal parameters.
179 let inputs_hir = hir.fn_decl_by_hir_id(fn_id).map(|decl| &decl.inputs);
180 let inputs_fn = fn_sig.inputs().iter().copied();
181 for (idx, (param_ty, param)) in inputs_fn.chain(maybe_va_list).zip(body.params).enumerate() {
182 // Check the pattern.
183 let ty_span = try { inputs_hir?.get(idx)?.span };
184 fcx.check_pat_top(¶m.pat, param_ty, ty_span, false);
186 // Check that argument is Sized.
187 // The check for a non-trivial pattern is a hack to avoid duplicate warnings
188 // for simple cases like `fn foo(x: Trait)`,
189 // where we would error once on the parameter as a whole, and once on the binding `x`.
190 if param.pat.simple_ident().is_none() && !tcx.features().unsized_fn_params {
191 fcx.require_type_is_sized(param_ty, param.pat.span, traits::SizedArgumentType(ty_span));
194 fcx.write_ty(param.hir_id, param_ty);
197 inherited.typeck_results.borrow_mut().liberated_fn_sigs_mut().insert(fn_id, fn_sig);
199 fcx.in_tail_expr = true;
200 if let ty::Dynamic(..) = declared_ret_ty.kind() {
201 // FIXME: We need to verify that the return type is `Sized` after the return expression has
202 // been evaluated so that we have types available for all the nodes being returned, but that
203 // requires the coerced evaluated type to be stored. Moving `check_return_expr` before this
204 // causes unsized errors caused by the `declared_ret_ty` to point at the return expression,
205 // while keeping the current ordering we will ignore the tail expression's type because we
206 // don't know it yet. We can't do `check_expr_kind` while keeping `check_return_expr`
207 // because we will trigger "unreachable expression" lints unconditionally.
208 // Because of all of this, we perform a crude check to know whether the simplest `!Sized`
209 // case that a newcomer might make, returning a bare trait, and in that case we populate
210 // the tail expression's type so that the suggestion will be correct, but ignore all other
212 fcx.check_expr(&body.value);
213 fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
215 fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
216 fcx.check_return_expr(&body.value, false);
218 fcx.in_tail_expr = false;
220 // We insert the deferred_generator_interiors entry after visiting the body.
221 // This ensures that all nested generators appear before the entry of this generator.
222 // resolve_generator_interiors relies on this property.
223 let gen_ty = if let (Some(_), Some(gen_kind)) = (can_be_generator, body.generator_kind) {
225 .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::MiscVariable, span });
226 fcx.deferred_generator_interiors.borrow_mut().push((body.id(), interior, gen_kind));
228 let (resume_ty, yield_ty) = fcx.resume_yield_tys.unwrap();
229 Some(GeneratorTypes {
233 movability: can_be_generator.unwrap(),
239 // Finalize the return check by taking the LUB of the return types
240 // we saw and assigning it to the expected return type. This isn't
241 // really expected to fail, since the coercions would have failed
242 // earlier when trying to find a LUB.
243 let coercion = fcx.ret_coercion.take().unwrap().into_inner();
244 let mut actual_return_ty = coercion.complete(&fcx);
245 debug!("actual_return_ty = {:?}", actual_return_ty);
246 if let ty::Dynamic(..) = declared_ret_ty.kind() {
247 // We have special-cased the case where the function is declared
248 // `-> dyn Foo` and we don't actually relate it to the
249 // `fcx.ret_coercion`, so just substitute a type variable.
251 fcx.next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::DynReturnFn, span });
252 debug!("actual_return_ty replaced with {:?}", actual_return_ty);
254 fcx.demand_suptype(span, declared_ret_ty, actual_return_ty);
256 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
257 if let Some(panic_impl_did) = tcx.lang_items().panic_impl()
258 && panic_impl_did == hir.local_def_id(fn_id).to_def_id()
260 if let Some(panic_info_did) = tcx.lang_items().panic_info() {
261 if *declared_ret_ty.kind() != ty::Never {
262 sess.span_err(decl.output.span(), "return type should be `!`");
265 let inputs = fn_sig.inputs();
266 let span = hir.span(fn_id);
267 if inputs.len() == 1 {
268 let arg_is_panic_info = match *inputs[0].kind() {
269 ty::Ref(region, ty, mutbl) => match *ty.kind() {
270 ty::Adt(ref adt, _) => {
271 adt.did() == panic_info_did
272 && mutbl == hir::Mutability::Not
273 && !region.is_static()
280 if !arg_is_panic_info {
281 sess.span_err(decl.inputs[0].span, "argument should be `&PanicInfo`");
284 if let Node::Item(item) = hir.get(fn_id)
285 && let ItemKind::Fn(_, ref generics, _) = item.kind
286 && !generics.params.is_empty()
288 sess.span_err(span, "should have no type parameters");
291 let span = sess.source_map().guess_head_span(span);
292 sess.span_err(span, "function should have one argument");
295 sess.err("language item required, but not found: `panic_info`");
299 // Check that a function marked as `#[alloc_error_handler]` has signature `fn(Layout) -> !`
300 if let Some(alloc_error_handler_did) = tcx.lang_items().oom()
301 && alloc_error_handler_did == hir.local_def_id(fn_id).to_def_id()
303 if let Some(alloc_layout_did) = tcx.lang_items().alloc_layout() {
304 if *declared_ret_ty.kind() != ty::Never {
305 sess.span_err(decl.output.span(), "return type should be `!`");
308 let inputs = fn_sig.inputs();
309 let span = hir.span(fn_id);
310 if inputs.len() == 1 {
311 let arg_is_alloc_layout = match inputs[0].kind() {
312 ty::Adt(ref adt, _) => adt.did() == alloc_layout_did,
316 if !arg_is_alloc_layout {
317 sess.span_err(decl.inputs[0].span, "argument should be `Layout`");
320 if let Node::Item(item) = hir.get(fn_id)
321 && let ItemKind::Fn(_, ref generics, _) = item.kind
322 && !generics.params.is_empty()
326 "`#[alloc_error_handler]` function should have no type parameters",
330 let span = sess.source_map().guess_head_span(span);
331 sess.span_err(span, "function should have one argument");
334 sess.err("language item required, but not found: `alloc_layout`");
341 fn check_struct(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) {
342 let def = tcx.adt_def(def_id);
343 def.destructor(tcx); // force the destructor to be evaluated
344 check_representable(tcx, span, def_id);
346 if def.repr().simd() {
347 check_simd(tcx, span, def_id);
350 check_transparent(tcx, span, def);
351 check_packed(tcx, span, def);
354 fn check_union(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) {
355 let def = tcx.adt_def(def_id);
356 def.destructor(tcx); // force the destructor to be evaluated
357 check_representable(tcx, span, def_id);
358 check_transparent(tcx, span, def);
359 check_union_fields(tcx, span, def_id);
360 check_packed(tcx, span, def);
363 /// Check that the fields of the `union` do not need dropping.
364 fn check_union_fields(tcx: TyCtxt<'_>, span: Span, item_def_id: LocalDefId) -> bool {
365 let item_type = tcx.type_of(item_def_id);
366 if let ty::Adt(def, substs) = item_type.kind() {
367 assert!(def.is_union());
368 let fields = &def.non_enum_variant().fields;
369 let param_env = tcx.param_env(item_def_id);
370 for field in fields {
371 let field_ty = field.ty(tcx, substs);
372 if field_ty.needs_drop(tcx, param_env) {
373 let (field_span, ty_span) = match tcx.hir().get_if_local(field.did) {
374 // We are currently checking the type this field came from, so it must be local.
375 Some(Node::Field(field)) => (field.span, field.ty.span),
376 _ => unreachable!("mir field has to correspond to hir field"),
382 "unions cannot contain fields that may need dropping"
385 "a type is guaranteed not to need dropping \
386 when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type",
388 .multipart_suggestion_verbose(
389 "when the type does not implement `Copy`, \
390 wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped",
392 (ty_span.shrink_to_lo(), "std::mem::ManuallyDrop<".into()),
393 (ty_span.shrink_to_hi(), ">".into()),
395 Applicability::MaybeIncorrect,
402 span_bug!(span, "unions must be ty::Adt, but got {:?}", item_type.kind());
407 /// Check that a `static` is inhabited.
408 fn check_static_inhabited<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
409 // Make sure statics are inhabited.
410 // Other parts of the compiler assume that there are no uninhabited places. In principle it
411 // would be enough to check this for `extern` statics, as statics with an initializer will
412 // have UB during initialization if they are uninhabited, but there also seems to be no good
413 // reason to allow any statics to be uninhabited.
414 let ty = tcx.type_of(def_id);
415 let layout = match tcx.layout_of(ParamEnv::reveal_all().and(ty)) {
417 // Foreign statics that overflow their allowed size should emit an error
418 Err(LayoutError::SizeOverflow(_))
420 let node = tcx.hir().get_by_def_id(def_id);
423 hir::Node::ForeignItem(hir::ForeignItem {
424 kind: hir::ForeignItemKind::Static(..),
431 .struct_span_err(span, "extern static is too large for the current architecture")
435 // Generic statics are rejected, but we still reach this case.
437 tcx.sess.delay_span_bug(span, &e.to_string());
441 if layout.abi.is_uninhabited() {
442 tcx.struct_span_lint_hir(
444 tcx.hir().local_def_id_to_hir_id(def_id),
447 lint.build("static of uninhabited type")
448 .note("uninhabited statics cannot be initialized, and any access would be an immediate error")
455 /// Checks that an opaque type does not contain cycles and does not use `Self` or `T::Foo`
456 /// projections that would result in "inheriting lifetimes".
457 pub(super) fn check_opaque<'tcx>(
460 substs: SubstsRef<'tcx>,
462 origin: &hir::OpaqueTyOrigin,
464 check_opaque_for_inheriting_lifetimes(tcx, def_id, span);
465 if tcx.type_of(def_id).references_error() {
468 if check_opaque_for_cycles(tcx, def_id, substs, span, origin).is_err() {
471 check_opaque_meets_bounds(tcx, def_id, substs, span, origin);
474 /// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result
475 /// in "inheriting lifetimes".
476 #[instrument(level = "debug", skip(tcx, span))]
477 pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
482 let item = tcx.hir().expect_item(def_id);
483 debug!(?item, ?span);
485 struct FoundParentLifetime;
486 struct FindParentLifetimeVisitor<'tcx>(&'tcx ty::Generics);
487 impl<'tcx> ty::fold::TypeVisitor<'tcx> for FindParentLifetimeVisitor<'tcx> {
488 type BreakTy = FoundParentLifetime;
490 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
491 debug!("FindParentLifetimeVisitor: r={:?}", r);
492 if let ty::ReEarlyBound(ty::EarlyBoundRegion { index, .. }) = *r {
493 if index < self.0.parent_count as u32 {
494 return ControlFlow::Break(FoundParentLifetime);
496 return ControlFlow::CONTINUE;
500 r.super_visit_with(self)
503 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
504 if let ty::ConstKind::Unevaluated(..) = c.val() {
505 // FIXME(#72219) We currently don't detect lifetimes within substs
506 // which would violate this check. Even though the particular substitution is not used
507 // within the const, this should still be fixed.
508 return ControlFlow::CONTINUE;
510 c.super_visit_with(self)
514 struct ProhibitOpaqueVisitor<'tcx> {
516 opaque_identity_ty: Ty<'tcx>,
517 generics: &'tcx ty::Generics,
518 selftys: Vec<(Span, Option<String>)>,
521 impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
522 type BreakTy = Ty<'tcx>;
524 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
525 debug!("check_opaque_for_inheriting_lifetimes: (visit_ty) t={:?}", t);
526 if t == self.opaque_identity_ty {
527 ControlFlow::CONTINUE
529 t.super_visit_with(&mut FindParentLifetimeVisitor(self.generics))
530 .map_break(|FoundParentLifetime| t)
535 impl<'tcx> Visitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
536 type NestedFilter = nested_filter::OnlyBodies;
538 fn nested_visit_map(&mut self) -> Self::Map {
542 fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
544 hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
547 res: Some(Res::SelfTy { trait_: _, alias_to: impl_ref }),
552 impl_ref.map(|(def_id, _)| self.tcx.def_path_str(def_id));
553 self.selftys.push((path.span, impl_ty_name));
559 hir::intravisit::walk_ty(self, arg);
563 if let ItemKind::OpaqueTy(hir::OpaqueTy {
564 origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
568 let mut visitor = ProhibitOpaqueVisitor {
569 opaque_identity_ty: tcx.mk_opaque(
571 InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
573 generics: tcx.generics_of(def_id),
577 let prohibit_opaque = tcx
578 .explicit_item_bounds(def_id)
580 .try_for_each(|(predicate, _)| predicate.visit_with(&mut visitor));
582 "check_opaque_for_inheriting_lifetimes: prohibit_opaque={:?}, visitor.opaque_identity_ty={:?}, visitor.generics={:?}",
583 prohibit_opaque, visitor.opaque_identity_ty, visitor.generics
586 if let Some(ty) = prohibit_opaque.break_value() {
587 visitor.visit_item(&item);
588 let is_async = match item.kind {
589 ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
590 matches!(origin, hir::OpaqueTyOrigin::AsyncFn(..))
595 let mut err = struct_span_err!(
599 "`{}` return type cannot contain a projection or `Self` that references lifetimes from \
601 if is_async { "async fn" } else { "impl Trait" },
604 for (span, name) in visitor.selftys {
607 "consider spelling out the type instead",
608 name.unwrap_or_else(|| format!("{:?}", ty)),
609 Applicability::MaybeIncorrect,
617 /// Checks that an opaque type does not contain cycles.
618 pub(super) fn check_opaque_for_cycles<'tcx>(
621 substs: SubstsRef<'tcx>,
623 origin: &hir::OpaqueTyOrigin,
624 ) -> Result<(), ErrorGuaranteed> {
625 if tcx.try_expand_impl_trait_type(def_id.to_def_id(), substs).is_err() {
626 let reported = match origin {
627 hir::OpaqueTyOrigin::AsyncFn(..) => async_opaque_type_cycle_error(tcx, span),
628 _ => opaque_type_cycle_error(tcx, def_id, span),
636 /// Check that the concrete type behind `impl Trait` actually implements `Trait`.
638 /// This is mostly checked at the places that specify the opaque type, but we
639 /// check those cases in the `param_env` of that function, which may have
640 /// bounds not on this opaque type:
642 /// type X<T> = impl Clone
643 /// fn f<T: Clone>(t: T) -> X<T> {
647 /// Without this check the above code is incorrectly accepted: we would ICE if
648 /// some tried, for example, to clone an `Option<X<&mut ()>>`.
649 #[instrument(level = "debug", skip(tcx))]
650 fn check_opaque_meets_bounds<'tcx>(
653 substs: SubstsRef<'tcx>,
655 origin: &hir::OpaqueTyOrigin,
657 let hidden_type = tcx.type_of(def_id).subst(tcx, substs);
659 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
660 let defining_use_anchor = match *origin {
661 hir::OpaqueTyOrigin::FnReturn(did) | hir::OpaqueTyOrigin::AsyncFn(did) => did,
662 hir::OpaqueTyOrigin::TyAlias => def_id,
664 let param_env = tcx.param_env(defining_use_anchor);
666 tcx.infer_ctxt().with_opaque_type_inference(defining_use_anchor).enter(move |infcx| {
667 let inh = Inherited::new(infcx, def_id);
668 let infcx = &inh.infcx;
669 let opaque_ty = tcx.mk_opaque(def_id.to_def_id(), substs);
671 let misc_cause = traits::ObligationCause::misc(span, hir_id);
673 match infcx.at(&misc_cause, param_env).eq(opaque_ty, hidden_type) {
674 Ok(infer_ok) => inh.register_infer_ok_obligations(infer_ok),
676 tcx.sess.delay_span_bug(
678 &format!("could not unify `{hidden_type}` with revealed type:\n{ty_err}"),
683 // Additionally require the hidden type to be well-formed with only the generics of the opaque type.
684 // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
685 // hidden type is well formed even without those bounds.
687 ty::Binder::dummy(ty::PredicateKind::WellFormed(hidden_type.into())).to_predicate(tcx);
688 inh.register_predicate(Obligation::new(misc_cause, param_env, predicate));
690 // Check that all obligations are satisfied by the implementation's
692 let errors = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx);
693 if !errors.is_empty() {
694 infcx.report_fulfillment_errors(&errors, None, false);
698 // Checked when type checking the function containing them.
699 hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) => {}
700 // Can have different predicates to their defining use
701 hir::OpaqueTyOrigin::TyAlias => {
702 // Finally, resolve all regions. This catches wily misuses of
703 // lifetime parameters.
704 let fcx = FnCtxt::new(&inh, param_env, hir_id);
705 fcx.regionck_item(hir_id, span, FxHashSet::default());
709 // Clean up after ourselves
710 let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
714 pub fn check_item_type<'tcx>(tcx: TyCtxt<'tcx>, it: &'tcx hir::Item<'tcx>) {
716 "check_item_type(it.def_id={:?}, it.name={})",
718 tcx.def_path_str(it.def_id.to_def_id())
720 let _indenter = indenter();
722 // Consts can play a role in type-checking, so they are included here.
723 hir::ItemKind::Static(..) => {
724 tcx.ensure().typeck(it.def_id);
725 maybe_check_static_with_link_section(tcx, it.def_id, it.span);
726 check_static_inhabited(tcx, it.def_id, it.span);
728 hir::ItemKind::Const(..) => {
729 tcx.ensure().typeck(it.def_id);
731 hir::ItemKind::Enum(ref enum_definition, _) => {
732 check_enum(tcx, it.span, &enum_definition.variants, it.def_id);
734 hir::ItemKind::Fn(..) => {} // entirely within check_item_body
735 hir::ItemKind::Impl(ref impl_) => {
736 debug!("ItemKind::Impl {} with id {:?}", it.ident, it.def_id);
737 if let Some(impl_trait_ref) = tcx.impl_trait_ref(it.def_id) {
738 check_impl_items_against_trait(
745 check_on_unimplemented(tcx, it);
748 hir::ItemKind::Trait(_, _, _, _, ref items) => {
749 check_on_unimplemented(tcx, it);
751 for item in items.iter() {
752 let item = tcx.hir().trait_item(item.id);
754 hir::TraitItemKind::Fn(ref sig, _) => {
755 let abi = sig.header.abi;
756 fn_maybe_err(tcx, item.ident.span, abi);
758 hir::TraitItemKind::Type(.., Some(default)) => {
759 let assoc_item = tcx.associated_item(item.def_id);
761 InternalSubsts::identity_for_item(tcx, it.def_id.to_def_id());
762 let _: Result<_, rustc_errors::ErrorGuaranteed> = check_type_bounds(
767 ty::TraitRef { def_id: it.def_id.to_def_id(), substs: trait_substs },
774 hir::ItemKind::Struct(..) => {
775 check_struct(tcx, it.def_id, it.span);
777 hir::ItemKind::Union(..) => {
778 check_union(tcx, it.def_id, it.span);
780 hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
781 // HACK(jynelson): trying to infer the type of `impl trait` breaks documenting
782 // `async-std` (and `pub async fn` in general).
783 // Since rustdoc doesn't care about the concrete type behind `impl Trait`, just don't look at it!
784 // See https://github.com/rust-lang/rust/issues/75100
785 if !tcx.sess.opts.actually_rustdoc {
786 let substs = InternalSubsts::identity_for_item(tcx, it.def_id.to_def_id());
787 check_opaque(tcx, it.def_id, substs, it.span, &origin);
790 hir::ItemKind::TyAlias(..) => {
791 let pty_ty = tcx.type_of(it.def_id);
792 let generics = tcx.generics_of(it.def_id);
793 check_type_params_are_used(tcx, &generics, pty_ty);
795 hir::ItemKind::ForeignMod { abi, items } => {
796 check_abi(tcx, it.hir_id(), it.span, abi);
798 if abi == Abi::RustIntrinsic {
800 let item = tcx.hir().foreign_item(item.id);
801 intrinsic::check_intrinsic_type(tcx, item);
803 } else if abi == Abi::PlatformIntrinsic {
805 let item = tcx.hir().foreign_item(item.id);
806 intrinsic::check_platform_intrinsic_type(tcx, item);
810 let def_id = item.id.def_id;
811 let generics = tcx.generics_of(def_id);
812 let own_counts = generics.own_counts();
813 if generics.params.len() - own_counts.lifetimes != 0 {
814 let (kinds, kinds_pl, egs) = match (own_counts.types, own_counts.consts) {
815 (_, 0) => ("type", "types", Some("u32")),
816 // We don't specify an example value, because we can't generate
817 // a valid value for any type.
818 (0, _) => ("const", "consts", None),
819 _ => ("type or const", "types or consts", None),
825 "foreign items may not have {kinds} parameters",
827 .span_label(item.span, &format!("can't have {kinds} parameters"))
829 // FIXME: once we start storing spans for type arguments, turn this
830 // into a suggestion.
832 "replace the {} parameters with concrete {}{}",
835 egs.map(|egs| format!(" like `{}`", egs)).unwrap_or_default(),
841 let item = tcx.hir().foreign_item(item.id);
843 hir::ForeignItemKind::Fn(ref fn_decl, _, _) => {
844 require_c_abi_if_c_variadic(tcx, fn_decl, abi, item.span);
846 hir::ForeignItemKind::Static(..) => {
847 check_static_inhabited(tcx, def_id, item.span);
854 _ => { /* nothing to do */ }
858 pub(super) fn check_on_unimplemented(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
859 // an error would be reported if this fails.
860 let _ = traits::OnUnimplementedDirective::of_item(tcx, item.def_id.to_def_id());
863 pub(super) fn check_specialization_validity<'tcx>(
865 trait_def: &ty::TraitDef,
866 trait_item: &ty::AssocItem,
868 impl_item: &hir::ImplItemRef,
870 let Ok(ancestors) = trait_def.ancestors(tcx, impl_id) else { return };
871 let mut ancestor_impls = ancestors.skip(1).filter_map(|parent| {
872 if parent.is_from_trait() {
875 Some((parent, parent.item(tcx, trait_item.def_id)))
879 let opt_result = ancestor_impls.find_map(|(parent_impl, parent_item)| {
881 // Parent impl exists, and contains the parent item we're trying to specialize, but
882 // doesn't mark it `default`.
883 Some(parent_item) if traits::impl_item_is_final(tcx, &parent_item) => {
884 Some(Err(parent_impl.def_id()))
887 // Parent impl contains item and makes it specializable.
888 Some(_) => Some(Ok(())),
890 // Parent impl doesn't mention the item. This means it's inherited from the
891 // grandparent. In that case, if parent is a `default impl`, inherited items use the
892 // "defaultness" from the grandparent, else they are final.
894 if tcx.impl_defaultness(parent_impl.def_id()).is_default() {
897 Some(Err(parent_impl.def_id()))
903 // If `opt_result` is `None`, we have only encountered `default impl`s that don't contain the
904 // item. This is allowed, the item isn't actually getting specialized here.
905 let result = opt_result.unwrap_or(Ok(()));
907 if let Err(parent_impl) = result {
908 report_forbidden_specialization(tcx, impl_item, parent_impl);
912 fn check_impl_items_against_trait<'tcx>(
914 full_impl_span: Span,
916 impl_trait_ref: ty::TraitRef<'tcx>,
917 impl_item_refs: &[hir::ImplItemRef],
919 // If the trait reference itself is erroneous (so the compilation is going
920 // to fail), skip checking the items here -- the `impl_item` table in `tcx`
921 // isn't populated for such impls.
922 if impl_trait_ref.references_error() {
926 // Negative impls are not expected to have any items
927 match tcx.impl_polarity(impl_id) {
928 ty::ImplPolarity::Reservation | ty::ImplPolarity::Positive => {}
929 ty::ImplPolarity::Negative => {
930 if let [first_item_ref, ..] = impl_item_refs {
931 let first_item_span = tcx.hir().impl_item(first_item_ref.id).span;
936 "negative impls cannot have any items"
944 let trait_def = tcx.trait_def(impl_trait_ref.def_id);
946 for impl_item in impl_item_refs {
947 let ty_impl_item = tcx.associated_item(impl_item.id.def_id);
948 let ty_trait_item = if let Some(trait_item_id) = ty_impl_item.trait_item_def_id {
949 tcx.associated_item(trait_item_id)
951 // Checked in `associated_item`.
952 tcx.sess.delay_span_bug(impl_item.span, "missing associated item in trait");
955 let impl_item_full = tcx.hir().impl_item(impl_item.id);
956 match impl_item_full.kind {
957 hir::ImplItemKind::Const(..) => {
958 // Find associated const definition.
967 hir::ImplItemKind::Fn(..) => {
968 let opt_trait_span = tcx.hir().span_if_local(ty_trait_item.def_id);
978 hir::ImplItemKind::TyAlias(impl_ty) => {
979 let opt_trait_span = tcx.hir().span_if_local(ty_trait_item.def_id);
991 check_specialization_validity(
1000 if let Ok(ancestors) = trait_def.ancestors(tcx, impl_id.to_def_id()) {
1001 // Check for missing items from trait
1002 let mut missing_items = Vec::new();
1004 let mut must_implement_one_of: Option<&[Ident]> =
1005 trait_def.must_implement_one_of.as_deref();
1007 for &trait_item_id in tcx.associated_item_def_ids(impl_trait_ref.def_id) {
1008 let is_implemented = ancestors
1009 .leaf_def(tcx, trait_item_id)
1010 .map_or(false, |node_item| node_item.item.defaultness.has_value());
1012 if !is_implemented && tcx.impl_defaultness(impl_id).is_final() {
1013 missing_items.push(tcx.associated_item(trait_item_id));
1016 if let Some(required_items) = &must_implement_one_of {
1017 // true if this item is specifically implemented in this impl
1018 let is_implemented_here = ancestors
1019 .leaf_def(tcx, trait_item_id)
1020 .map_or(false, |node_item| !node_item.defining_node.is_from_trait());
1022 if is_implemented_here {
1023 let trait_item = tcx.associated_item(trait_item_id);
1024 if required_items.contains(&trait_item.ident(tcx)) {
1025 must_implement_one_of = None;
1031 if !missing_items.is_empty() {
1032 let impl_span = tcx.sess.source_map().guess_head_span(full_impl_span);
1033 missing_items_err(tcx, impl_span, &missing_items, full_impl_span);
1036 if let Some(missing_items) = must_implement_one_of {
1037 let impl_span = tcx.sess.source_map().guess_head_span(full_impl_span);
1039 .get_attrs(impl_trait_ref.def_id)
1041 .find(|attr| attr.has_name(sym::rustc_must_implement_one_of))
1042 .map(|attr| attr.span);
1044 missing_items_must_implement_one_of_err(tcx, impl_span, missing_items, attr_span);
1049 /// Checks whether a type can be represented in memory. In particular, it
1050 /// identifies types that contain themselves without indirection through a
1051 /// pointer, which would mean their size is unbounded.
1052 pub(super) fn check_representable(tcx: TyCtxt<'_>, sp: Span, item_def_id: LocalDefId) -> bool {
1053 let rty = tcx.type_of(item_def_id);
1055 // Check that it is possible to represent this type. This call identifies
1056 // (1) types that contain themselves and (2) types that contain a different
1057 // recursive type. It is only necessary to throw an error on those that
1058 // contain themselves. For case 2, there must be an inner type that will be
1059 // caught by case 1.
1060 match representability::ty_is_representable(tcx, rty, sp, None) {
1061 Representability::SelfRecursive(spans) => {
1062 recursive_type_with_infinite_size_error(tcx, item_def_id.to_def_id(), spans);
1065 Representability::Representable | Representability::ContainsRecursive => (),
1070 pub fn check_simd(tcx: TyCtxt<'_>, sp: Span, def_id: LocalDefId) {
1071 let t = tcx.type_of(def_id);
1072 if let ty::Adt(def, substs) = t.kind()
1075 let fields = &def.non_enum_variant().fields;
1076 if fields.is_empty() {
1077 struct_span_err!(tcx.sess, sp, E0075, "SIMD vector cannot be empty").emit();
1080 let e = fields[0].ty(tcx, substs);
1081 if !fields.iter().all(|f| f.ty(tcx, substs) == e) {
1082 struct_span_err!(tcx.sess, sp, E0076, "SIMD vector should be homogeneous")
1083 .span_label(sp, "SIMD elements must have the same type")
1088 let len = if let ty::Array(_ty, c) = e.kind() {
1089 c.try_eval_usize(tcx, tcx.param_env(def.did()))
1091 Some(fields.len() as u64)
1093 if let Some(len) = len {
1095 struct_span_err!(tcx.sess, sp, E0075, "SIMD vector cannot be empty").emit();
1097 } else if len > MAX_SIMD_LANES {
1102 "SIMD vector cannot have more than {MAX_SIMD_LANES} elements",
1109 // Check that we use types valid for use in the lanes of a SIMD "vector register"
1110 // These are scalar types which directly match a "machine" type
1111 // Yes: Integers, floats, "thin" pointers
1112 // No: char, "fat" pointers, compound types
1114 ty::Param(_) => (), // pass struct<T>(T, T, T, T) through, let monomorphization catch errors
1115 ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::RawPtr(_) => (), // struct(u8, u8, u8, u8) is ok
1116 ty::Array(t, _) if matches!(t.kind(), ty::Param(_)) => (), // pass struct<T>([T; N]) through, let monomorphization catch errors
1120 ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::RawPtr(_)
1122 { /* struct([f32; 4]) is ok */ }
1128 "SIMD vector element type should be a \
1129 primitive scalar (integer/float/pointer) type"
1138 pub(super) fn check_packed(tcx: TyCtxt<'_>, sp: Span, def: ty::AdtDef<'_>) {
1139 let repr = def.repr();
1141 for attr in tcx.get_attrs(def.did()).iter() {
1142 for r in attr::find_repr_attrs(&tcx.sess, attr) {
1143 if let attr::ReprPacked(pack) = r
1144 && let Some(repr_pack) = repr.pack
1145 && pack as u64 != repr_pack.bytes()
1151 "type has conflicting packed representation hints"
1157 if repr.align.is_some() {
1162 "type has conflicting packed and align representation hints"
1166 if let Some(def_spans) = check_packed_inner(tcx, def.did(), &mut vec![]) {
1167 let mut err = struct_span_err!(
1171 "packed type cannot transitively contain a `#[repr(align)]` type"
1175 tcx.def_span(def_spans[0].0),
1177 "`{}` has a `#[repr(align)]` attribute",
1178 tcx.item_name(def_spans[0].0)
1182 if def_spans.len() > 2 {
1183 let mut first = true;
1184 for (adt_def, span) in def_spans.iter().skip(1).rev() {
1185 let ident = tcx.item_name(*adt_def);
1190 "`{}` contains a field of type `{}`",
1191 tcx.type_of(def.did()),
1195 format!("...which contains a field of type `{ident}`")
1208 pub(super) fn check_packed_inner(
1211 stack: &mut Vec<DefId>,
1212 ) -> Option<Vec<(DefId, Span)>> {
1213 if let ty::Adt(def, substs) = tcx.type_of(def_id).kind() {
1214 if def.is_struct() || def.is_union() {
1215 if def.repr().align.is_some() {
1216 return Some(vec![(def.did(), DUMMY_SP)]);
1220 for field in &def.non_enum_variant().fields {
1221 if let ty::Adt(def, _) = field.ty(tcx, substs).kind()
1222 && !stack.contains(&def.did())
1223 && let Some(mut defs) = check_packed_inner(tcx, def.did(), stack)
1225 defs.push((def.did(), field.ident(tcx).span));
1236 pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, sp: Span, adt: ty::AdtDef<'tcx>) {
1237 if !adt.repr().transparent() {
1240 let sp = tcx.sess.source_map().guess_head_span(sp);
1242 if adt.is_union() && !tcx.features().transparent_unions {
1244 &tcx.sess.parse_sess,
1245 sym::transparent_unions,
1247 "transparent unions are unstable",
1252 if adt.variants().len() != 1 {
1253 bad_variant_count(tcx, adt, sp, adt.did());
1254 if adt.variants().is_empty() {
1255 // Don't bother checking the fields. No variants (and thus no fields) exist.
1260 // For each field, figure out if it's known to be a ZST and align(1)
1261 let field_infos = adt.all_fields().map(|field| {
1262 let ty = field.ty(tcx, InternalSubsts::identity_for_item(tcx, field.did));
1263 let param_env = tcx.param_env(field.did);
1264 let layout = tcx.layout_of(param_env.and(ty));
1265 // We are currently checking the type this field came from, so it must be local
1266 let span = tcx.hir().span_if_local(field.did).unwrap();
1267 let zst = layout.map_or(false, |layout| layout.is_zst());
1268 let align1 = layout.map_or(false, |layout| layout.align.abi.bytes() == 1);
1272 let non_zst_fields =
1273 field_infos.clone().filter_map(|(span, zst, _align1)| if !zst { Some(span) } else { None });
1274 let non_zst_count = non_zst_fields.clone().count();
1275 if non_zst_count >= 2 {
1276 bad_non_zero_sized_fields(tcx, adt, non_zst_count, non_zst_fields, sp);
1278 for (span, zst, align1) in field_infos {
1284 "zero-sized field in transparent {} has alignment larger than 1",
1287 .span_label(span, "has alignment larger than 1")
1293 #[allow(trivial_numeric_casts)]
1294 fn check_enum<'tcx>(
1297 vs: &'tcx [hir::Variant<'tcx>],
1300 let def = tcx.adt_def(def_id);
1301 def.destructor(tcx); // force the destructor to be evaluated
1304 let attributes = tcx.get_attrs(def_id.to_def_id());
1305 if let Some(attr) = tcx.sess.find_by_name(&attributes, sym::repr) {
1310 "unsupported representation for zero-variant enum"
1312 .span_label(sp, "zero-variant enum")
1317 let repr_type_ty = def.repr().discr_type().to_ty(tcx);
1318 if repr_type_ty == tcx.types.i128 || repr_type_ty == tcx.types.u128 {
1319 if !tcx.features().repr128 {
1321 &tcx.sess.parse_sess,
1324 "repr with 128-bit type is unstable",
1331 if let Some(ref e) = v.disr_expr {
1332 tcx.ensure().typeck(tcx.hir().local_def_id(e.hir_id));
1336 if tcx.adt_def(def_id).repr().int.is_none() && tcx.features().arbitrary_enum_discriminant {
1337 let is_unit = |var: &hir::Variant<'_>| matches!(var.data, hir::VariantData::Unit(..));
1339 let has_disr = |var: &hir::Variant<'_>| var.disr_expr.is_some();
1340 let has_non_units = vs.iter().any(|var| !is_unit(var));
1341 let disr_units = vs.iter().any(|var| is_unit(&var) && has_disr(&var));
1342 let disr_non_unit = vs.iter().any(|var| !is_unit(&var) && has_disr(&var));
1344 if disr_non_unit || (disr_units && has_non_units) {
1346 struct_span_err!(tcx.sess, sp, E0732, "`#[repr(inttype)]` must be specified");
1351 let mut disr_vals: Vec<Discr<'tcx>> = Vec::with_capacity(vs.len());
1352 for ((_, discr), v) in iter::zip(def.discriminants(tcx), vs) {
1353 // Check for duplicate discriminant values
1354 if let Some(i) = disr_vals.iter().position(|&x| x.val == discr.val) {
1355 let variant_did = def.variant(VariantIdx::new(i)).def_id;
1356 let variant_i_hir_id = tcx.hir().local_def_id_to_hir_id(variant_did.expect_local());
1357 let variant_i = tcx.hir().expect_variant(variant_i_hir_id);
1358 let i_span = match variant_i.disr_expr {
1359 Some(ref expr) => tcx.hir().span(expr.hir_id),
1360 None => tcx.def_span(variant_did),
1362 let span = match v.disr_expr {
1363 Some(ref expr) => tcx.hir().span(expr.hir_id),
1366 let display_discr = display_discriminant_value(tcx, v, discr.val);
1367 let display_discr_i = display_discriminant_value(tcx, variant_i, disr_vals[i].val);
1372 "discriminant value `{}` already exists",
1375 .span_label(i_span, format!("first use of {display_discr_i}"))
1376 .span_label(span, format!("enum already has {display_discr}"))
1379 disr_vals.push(discr);
1382 check_representable(tcx, sp, def_id);
1383 check_transparent(tcx, sp, def);
1386 /// Format an enum discriminant value for use in a diagnostic message.
1387 fn display_discriminant_value<'tcx>(
1389 variant: &hir::Variant<'_>,
1392 if let Some(expr) = &variant.disr_expr {
1393 let body = &tcx.hir().body(expr.body).value;
1394 if let hir::ExprKind::Lit(lit) = &body.kind
1395 && let rustc_ast::LitKind::Int(lit_value, _int_kind) = &lit.node
1396 && evaluated != *lit_value
1398 return format!("`{evaluated}` (overflowed from `{lit_value}`)");
1401 format!("`{}`", evaluated)
1404 pub(super) fn check_type_params_are_used<'tcx>(
1406 generics: &ty::Generics,
1409 debug!("check_type_params_are_used(generics={:?}, ty={:?})", generics, ty);
1411 assert_eq!(generics.parent, None);
1413 if generics.own_counts().types == 0 {
1417 let mut params_used = BitSet::new_empty(generics.params.len());
1419 if ty.references_error() {
1420 // If there is already another error, do not emit
1421 // an error for not using a type parameter.
1422 assert!(tcx.sess.has_errors().is_some());
1426 for leaf in ty.walk() {
1427 if let GenericArgKind::Type(leaf_ty) = leaf.unpack()
1428 && let ty::Param(param) = leaf_ty.kind()
1430 debug!("found use of ty param {:?}", param);
1431 params_used.insert(param.index);
1435 for param in &generics.params {
1436 if !params_used.contains(param.index)
1437 && let ty::GenericParamDefKind::Type { .. } = param.kind
1439 let span = tcx.def_span(param.def_id);
1444 "type parameter `{}` is unused",
1447 .span_label(span, "unused type parameter")
1453 pub(super) fn check_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
1454 tcx.hir().visit_item_likes_in_module(module_def_id, &mut CheckItemTypesVisitor { tcx });
1457 pub(super) use wfcheck::check_item_well_formed;
1459 pub(super) use wfcheck::check_trait_item as check_trait_item_well_formed;
1461 pub(super) use wfcheck::check_impl_item as check_impl_item_well_formed;
1463 fn async_opaque_type_cycle_error(tcx: TyCtxt<'_>, span: Span) -> ErrorGuaranteed {
1464 struct_span_err!(tcx.sess, span, E0733, "recursion in an `async fn` requires boxing")
1465 .span_label(span, "recursive `async fn`")
1466 .note("a recursive `async fn` must be rewritten to return a boxed `dyn Future`")
1468 "consider using the `async_recursion` crate: https://crates.io/crates/async_recursion",
1473 /// Emit an error for recursive opaque types.
1475 /// If this is a return `impl Trait`, find the item's return expressions and point at them. For
1476 /// direct recursion this is enough, but for indirect recursion also point at the last intermediary
1479 /// If all the return expressions evaluate to `!`, then we explain that the error will go away
1480 /// after changing it. This can happen when a user uses `panic!()` or similar as a placeholder.
1481 fn opaque_type_cycle_error(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) -> ErrorGuaranteed {
1482 let mut err = struct_span_err!(tcx.sess, span, E0720, "cannot resolve opaque type");
1484 let mut label = false;
1485 if let Some((def_id, visitor)) = get_owner_return_paths(tcx, def_id) {
1486 let typeck_results = tcx.typeck(def_id);
1490 .filter_map(|expr| typeck_results.node_type_opt(expr.hir_id))
1491 .all(|ty| matches!(ty.kind(), ty::Never))
1496 .filter(|expr| typeck_results.node_type_opt(expr.hir_id).is_some())
1497 .map(|expr| expr.span)
1498 .collect::<Vec<Span>>();
1499 let span_len = spans.len();
1501 err.span_label(spans[0], "this returned value is of `!` type");
1503 let mut multispan: MultiSpan = spans.clone().into();
1506 .push_span_label(span, "this returned value is of `!` type".to_string());
1508 err.span_note(multispan, "these returned values have a concrete \"never\" type");
1510 err.help("this error will resolve once the item's body returns a concrete type");
1512 let mut seen = FxHashSet::default();
1514 err.span_label(span, "recursive opaque type");
1516 for (sp, ty) in visitor
1519 .filter_map(|e| typeck_results.node_type_opt(e.hir_id).map(|t| (e.span, t)))
1520 .filter(|(_, ty)| !matches!(ty.kind(), ty::Never))
1522 struct OpaqueTypeCollector(Vec<DefId>);
1523 impl<'tcx> ty::fold::TypeVisitor<'tcx> for OpaqueTypeCollector {
1524 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1526 ty::Opaque(def, _) => {
1528 ControlFlow::CONTINUE
1530 _ => t.super_visit_with(self),
1534 let mut visitor = OpaqueTypeCollector(vec![]);
1535 ty.visit_with(&mut visitor);
1536 for def_id in visitor.0 {
1537 let ty_span = tcx.def_span(def_id);
1538 if !seen.contains(&ty_span) {
1539 err.span_label(ty_span, &format!("returning this opaque type `{ty}`"));
1540 seen.insert(ty_span);
1542 err.span_label(sp, &format!("returning here with type `{ty}`"));
1548 err.span_label(span, "cannot resolve opaque type");