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, ErrorReported};
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_middle::ty::fold::TypeFoldable;
16 use rustc_middle::ty::layout::MAX_SIMD_LANES;
17 use rustc_middle::ty::subst::GenericArgKind;
18 use rustc_middle::ty::util::{Discr, IntTypeExt};
19 use rustc_middle::ty::{self, OpaqueTypeKey, ParamEnv, RegionKind, Ty, TyCtxt};
20 use rustc_session::lint::builtin::{UNINHABITED_STATIC, UNSUPPORTED_CALLING_CONVENTIONS};
21 use rustc_span::symbol::sym;
22 use rustc_span::{self, MultiSpan, Span};
23 use rustc_target::spec::abi::Abi;
24 use rustc_trait_selection::traits;
25 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
26 use rustc_ty_utils::representability::{self, Representability};
29 use std::ops::ControlFlow;
31 pub fn check_wf_new(tcx: TyCtxt<'_>) {
32 let visit = wfcheck::CheckTypeWellFormedVisitor::new(tcx);
33 tcx.hir().par_visit_all_item_likes(&visit);
36 pub(super) fn check_abi(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: Abi) {
37 match tcx.sess.target.is_abi_supported(abi) {
39 Some(false) => struct_span_err!(
43 "`{}` is not a supported ABI for the current target",
48 tcx.struct_span_lint_hir(UNSUPPORTED_CALLING_CONVENTIONS, hir_id, span, |lint| {
49 lint.build("use of calling convention not supported on this target").emit()
54 // This ABI is only allowed on function pointers
55 if abi == Abi::CCmseNonSecureCall {
60 "the `\"C-cmse-nonsecure-call\"` ABI is only allowed on function pointers"
66 /// Helper used for fns and closures. Does the grungy work of checking a function
67 /// body and returns the function context used for that purpose, since in the case of a fn item
68 /// there is still a bit more to do.
71 /// * inherited: other fields inherited from the enclosing fn (if any)
72 #[instrument(skip(inherited, body), level = "debug")]
73 pub(super) fn check_fn<'a, 'tcx>(
74 inherited: &'a Inherited<'a, 'tcx>,
75 param_env: ty::ParamEnv<'tcx>,
76 fn_sig: ty::FnSig<'tcx>,
77 decl: &'tcx hir::FnDecl<'tcx>,
79 body: &'tcx hir::Body<'tcx>,
80 can_be_generator: Option<hir::Movability>,
81 return_type_pre_known: bool,
82 ) -> (FnCtxt<'a, 'tcx>, Option<GeneratorTypes<'tcx>>) {
83 let mut fn_sig = fn_sig;
85 // Create the function context. This is either derived from scratch or,
86 // in the case of closures, based on the outer context.
87 let mut fcx = FnCtxt::new(inherited, param_env, body.value.hir_id);
88 fcx.ps.set(UnsafetyState::function(fn_sig.unsafety, fn_id));
89 fcx.return_type_pre_known = return_type_pre_known;
95 let declared_ret_ty = fn_sig.output();
98 fcx.instantiate_opaque_types_from_value(declared_ret_ty, decl.output.span());
99 debug!("check_fn: declared_ret_ty: {}, revealed_ret_ty: {}", declared_ret_ty, revealed_ret_ty);
100 fcx.ret_coercion = Some(RefCell::new(CoerceMany::new(revealed_ret_ty)));
101 fcx.ret_type_span = Some(decl.output.span());
102 if let ty::Opaque(..) = declared_ret_ty.kind() {
103 fcx.ret_coercion_impl_trait = Some(declared_ret_ty);
105 fn_sig = tcx.mk_fn_sig(
106 fn_sig.inputs().iter().cloned(),
113 let span = body.value.span;
115 fn_maybe_err(tcx, span, fn_sig.abi);
117 if fn_sig.abi == Abi::RustCall {
118 let expected_args = if let ImplicitSelfKind::None = decl.implicit_self { 1 } else { 2 };
121 let item = match tcx.hir().get(fn_id) {
122 Node::Item(hir::Item { kind: ItemKind::Fn(header, ..), .. }) => Some(header),
123 Node::ImplItem(hir::ImplItem {
124 kind: hir::ImplItemKind::Fn(header, ..), ..
126 Node::TraitItem(hir::TraitItem {
127 kind: hir::TraitItemKind::Fn(header, ..),
130 // Closures are RustCall, but they tuple their arguments, so shouldn't be checked
131 Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => None,
132 node => bug!("Item being checked wasn't a function/closure: {:?}", node),
135 if let Some(header) = item {
136 tcx.sess.span_err(header.span, "functions with the \"rust-call\" ABI must take a single non-self argument that is a tuple")
140 if fn_sig.inputs().len() != expected_args {
143 // FIXME(CraftSpider) Add a check on parameter expansion, so we don't just make the ICE happen later on
144 // This will probably require wide-scale changes to support a TupleKind obligation
145 // We can't resolve this without knowing the type of the param
146 if !matches!(fn_sig.inputs()[expected_args - 1].kind(), ty::Tuple(_) | ty::Param(_)) {
152 if body.generator_kind.is_some() && can_be_generator.is_some() {
154 .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span });
155 fcx.require_type_is_sized(yield_ty, span, traits::SizedYieldType);
157 // Resume type defaults to `()` if the generator has no argument.
158 let resume_ty = fn_sig.inputs().get(0).copied().unwrap_or_else(|| tcx.mk_unit());
160 fcx.resume_yield_tys = Some((resume_ty, yield_ty));
163 GatherLocalsVisitor::new(&fcx).visit_body(body);
165 // C-variadic fns also have a `VaList` input that's not listed in `fn_sig`
166 // (as it's created inside the body itself, not passed in from outside).
167 let maybe_va_list = if fn_sig.c_variadic {
168 let span = body.params.last().unwrap().span;
169 let va_list_did = tcx.require_lang_item(LangItem::VaList, Some(span));
170 let region = fcx.next_region_var(RegionVariableOrigin::MiscVariable(span));
172 Some(tcx.type_of(va_list_did).subst(tcx, &[region.into()]))
177 // Add formal parameters.
178 let inputs_hir = hir.fn_decl_by_hir_id(fn_id).map(|decl| &decl.inputs);
179 let inputs_fn = fn_sig.inputs().iter().copied();
180 for (idx, (param_ty, param)) in inputs_fn.chain(maybe_va_list).zip(body.params).enumerate() {
181 // Check the pattern.
182 let ty_span = try { inputs_hir?.get(idx)?.span };
183 fcx.check_pat_top(¶m.pat, param_ty, ty_span, false);
185 // Check that argument is Sized.
186 // The check for a non-trivial pattern is a hack to avoid duplicate warnings
187 // for simple cases like `fn foo(x: Trait)`,
188 // where we would error once on the parameter as a whole, and once on the binding `x`.
189 if param.pat.simple_ident().is_none() && !tcx.features().unsized_fn_params {
190 fcx.require_type_is_sized(param_ty, param.pat.span, traits::SizedArgumentType(ty_span));
193 fcx.write_ty(param.hir_id, param_ty);
196 inherited.typeck_results.borrow_mut().liberated_fn_sigs_mut().insert(fn_id, fn_sig);
198 fcx.in_tail_expr = true;
199 if let ty::Dynamic(..) = declared_ret_ty.kind() {
200 // FIXME: We need to verify that the return type is `Sized` after the return expression has
201 // been evaluated so that we have types available for all the nodes being returned, but that
202 // requires the coerced evaluated type to be stored. Moving `check_return_expr` before this
203 // causes unsized errors caused by the `declared_ret_ty` to point at the return expression,
204 // while keeping the current ordering we will ignore the tail expression's type because we
205 // don't know it yet. We can't do `check_expr_kind` while keeping `check_return_expr`
206 // because we will trigger "unreachable expression" lints unconditionally.
207 // Because of all of this, we perform a crude check to know whether the simplest `!Sized`
208 // case that a newcomer might make, returning a bare trait, and in that case we populate
209 // the tail expression's type so that the suggestion will be correct, but ignore all other
211 fcx.check_expr(&body.value);
212 fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
214 fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
215 fcx.check_return_expr(&body.value, false);
217 fcx.in_tail_expr = false;
219 // We insert the deferred_generator_interiors entry after visiting the body.
220 // This ensures that all nested generators appear before the entry of this generator.
221 // resolve_generator_interiors relies on this property.
222 let gen_ty = if let (Some(_), Some(gen_kind)) = (can_be_generator, body.generator_kind) {
224 .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::MiscVariable, span });
225 fcx.deferred_generator_interiors.borrow_mut().push((body.id(), interior, gen_kind));
227 let (resume_ty, yield_ty) = fcx.resume_yield_tys.unwrap();
228 Some(GeneratorTypes {
232 movability: can_be_generator.unwrap(),
238 // Finalize the return check by taking the LUB of the return types
239 // we saw and assigning it to the expected return type. This isn't
240 // really expected to fail, since the coercions would have failed
241 // earlier when trying to find a LUB.
242 let coercion = fcx.ret_coercion.take().unwrap().into_inner();
243 let mut actual_return_ty = coercion.complete(&fcx);
244 debug!("actual_return_ty = {:?}", actual_return_ty);
245 if let ty::Dynamic(..) = declared_ret_ty.kind() {
246 // We have special-cased the case where the function is declared
247 // `-> dyn Foo` and we don't actually relate it to the
248 // `fcx.ret_coercion`, so just substitute a type variable.
250 fcx.next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::DynReturnFn, span });
251 debug!("actual_return_ty replaced with {:?}", actual_return_ty);
253 fcx.demand_suptype(span, revealed_ret_ty, actual_return_ty);
255 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
256 if let Some(panic_impl_did) = tcx.lang_items().panic_impl() {
257 if panic_impl_did == hir.local_def_id(fn_id).to_def_id() {
258 if let Some(panic_info_did) = tcx.lang_items().panic_info() {
259 if *declared_ret_ty.kind() != ty::Never {
260 sess.span_err(decl.output.span(), "return type should be `!`");
263 let inputs = fn_sig.inputs();
264 let span = hir.span(fn_id);
265 if inputs.len() == 1 {
266 let arg_is_panic_info = match *inputs[0].kind() {
267 ty::Ref(region, ty, mutbl) => match *ty.kind() {
268 ty::Adt(ref adt, _) => {
269 adt.did == panic_info_did
270 && mutbl == hir::Mutability::Not
271 && *region != RegionKind::ReStatic
278 if !arg_is_panic_info {
279 sess.span_err(decl.inputs[0].span, "argument should be `&PanicInfo`");
282 if let Node::Item(item) = hir.get(fn_id) {
283 if let ItemKind::Fn(_, ref generics, _) = item.kind {
284 if !generics.params.is_empty() {
285 sess.span_err(span, "should have no type parameters");
290 let span = sess.source_map().guess_head_span(span);
291 sess.span_err(span, "function should have one argument");
294 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 if alloc_error_handler_did == hir.local_def_id(fn_id).to_def_id() {
302 if let Some(alloc_layout_did) = tcx.lang_items().alloc_layout() {
303 if *declared_ret_ty.kind() != ty::Never {
304 sess.span_err(decl.output.span(), "return type should be `!`");
307 let inputs = fn_sig.inputs();
308 let span = hir.span(fn_id);
309 if inputs.len() == 1 {
310 let arg_is_alloc_layout = match inputs[0].kind() {
311 ty::Adt(ref adt, _) => adt.did == alloc_layout_did,
315 if !arg_is_alloc_layout {
316 sess.span_err(decl.inputs[0].span, "argument should be `Layout`");
319 if let Node::Item(item) = hir.get(fn_id) {
320 if let ItemKind::Fn(_, ref generics, _) = item.kind {
321 if !generics.params.is_empty() {
324 "`#[alloc_error_handler]` function should have no type \
331 let span = sess.source_map().guess_head_span(span);
332 sess.span_err(span, "function should have one argument");
335 sess.err("language item required, but not found: `alloc_layout`");
343 fn check_struct(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) {
344 let def = tcx.adt_def(def_id);
345 def.destructor(tcx); // force the destructor to be evaluated
346 check_representable(tcx, span, def_id);
349 check_simd(tcx, span, def_id);
352 check_transparent(tcx, span, def);
353 check_packed(tcx, span, def);
356 fn check_union(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) {
357 let def = tcx.adt_def(def_id);
358 def.destructor(tcx); // force the destructor to be evaluated
359 check_representable(tcx, span, def_id);
360 check_transparent(tcx, span, def);
361 check_union_fields(tcx, span, def_id);
362 check_packed(tcx, span, def);
365 /// Check that the fields of the `union` do not need dropping.
366 fn check_union_fields(tcx: TyCtxt<'_>, span: Span, item_def_id: LocalDefId) -> bool {
367 let item_type = tcx.type_of(item_def_id);
368 if let ty::Adt(def, substs) = item_type.kind() {
369 assert!(def.is_union());
370 let fields = &def.non_enum_variant().fields;
371 let param_env = tcx.param_env(item_def_id);
372 for field in fields {
373 let field_ty = field.ty(tcx, substs);
374 // We are currently checking the type this field came from, so it must be local.
375 let field_span = tcx.hir().span_if_local(field.did).unwrap();
376 if field_ty.needs_drop(tcx, param_env) {
381 "unions may not contain fields that need dropping"
383 .span_note(field_span, "`std::mem::ManuallyDrop` can be used to wrap the type")
389 span_bug!(span, "unions must be ty::Adt, but got {:?}", item_type.kind());
394 /// Check that a `static` is inhabited.
395 fn check_static_inhabited<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
396 // Make sure statics are inhabited.
397 // Other parts of the compiler assume that there are no uninhabited places. In principle it
398 // would be enough to check this for `extern` statics, as statics with an initializer will
399 // have UB during initialization if they are uninhabited, but there also seems to be no good
400 // reason to allow any statics to be uninhabited.
401 let ty = tcx.type_of(def_id);
402 let layout = match tcx.layout_of(ParamEnv::reveal_all().and(ty)) {
405 // Generic statics are rejected, but we still reach this case.
406 tcx.sess.delay_span_bug(span, "generic static must be rejected");
410 if layout.abi.is_uninhabited() {
411 tcx.struct_span_lint_hir(
413 tcx.hir().local_def_id_to_hir_id(def_id),
416 lint.build("static of uninhabited type")
417 .note("uninhabited statics cannot be initialized, and any access would be an immediate error")
424 /// Checks that an opaque type does not contain cycles and does not use `Self` or `T::Foo`
425 /// projections that would result in "inheriting lifetimes".
426 pub(super) fn check_opaque<'tcx>(
429 substs: SubstsRef<'tcx>,
431 origin: &hir::OpaqueTyOrigin,
433 check_opaque_for_inheriting_lifetimes(tcx, def_id, span);
434 if tcx.type_of(def_id).references_error() {
437 if check_opaque_for_cycles(tcx, def_id, substs, span, origin).is_err() {
440 check_opaque_meets_bounds(tcx, def_id, substs, span, origin);
443 /// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result
444 /// in "inheriting lifetimes".
445 #[instrument(level = "debug", skip(tcx, span))]
446 pub(super) fn check_opaque_for_inheriting_lifetimes(
451 let item = tcx.hir().expect_item(tcx.hir().local_def_id_to_hir_id(def_id));
452 debug!(?item, ?span);
454 struct FoundParentLifetime;
455 struct FindParentLifetimeVisitor<'tcx>(TyCtxt<'tcx>, &'tcx ty::Generics);
456 impl<'tcx> ty::fold::TypeVisitor<'tcx> for FindParentLifetimeVisitor<'tcx> {
457 type BreakTy = FoundParentLifetime;
458 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
462 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
463 debug!("FindParentLifetimeVisitor: r={:?}", r);
464 if let RegionKind::ReEarlyBound(ty::EarlyBoundRegion { index, .. }) = r {
465 if *index < self.1.parent_count as u32 {
466 return ControlFlow::Break(FoundParentLifetime);
468 return ControlFlow::CONTINUE;
472 r.super_visit_with(self)
475 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
476 if let ty::ConstKind::Unevaluated(..) = c.val {
477 // FIXME(#72219) We currently don't detect lifetimes within substs
478 // which would violate this check. Even though the particular substitution is not used
479 // within the const, this should still be fixed.
480 return ControlFlow::CONTINUE;
482 c.super_visit_with(self)
486 struct ProhibitOpaqueVisitor<'tcx> {
488 opaque_identity_ty: Ty<'tcx>,
489 generics: &'tcx ty::Generics,
490 selftys: Vec<(Span, Option<String>)>,
493 impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
494 type BreakTy = Ty<'tcx>;
495 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
499 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
500 debug!("check_opaque_for_inheriting_lifetimes: (visit_ty) t={:?}", t);
501 if t == self.opaque_identity_ty {
502 ControlFlow::CONTINUE
504 t.super_visit_with(&mut FindParentLifetimeVisitor(self.tcx, self.generics))
505 .map_break(|FoundParentLifetime| t)
510 impl Visitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
511 type Map = rustc_middle::hir::map::Map<'tcx>;
513 fn nested_visit_map(&mut self) -> hir::intravisit::NestedVisitorMap<Self::Map> {
514 hir::intravisit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
517 fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
519 hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
520 [PathSegment { res: Some(Res::SelfTy(_, impl_ref)), .. }] => {
522 impl_ref.map(|(def_id, _)| self.tcx.def_path_str(def_id));
523 self.selftys.push((path.span, impl_ty_name));
529 hir::intravisit::walk_ty(self, arg);
533 if let ItemKind::OpaqueTy(hir::OpaqueTy {
534 origin: hir::OpaqueTyOrigin::AsyncFn | hir::OpaqueTyOrigin::FnReturn,
538 let mut visitor = ProhibitOpaqueVisitor {
539 opaque_identity_ty: tcx.mk_opaque(
541 InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
543 generics: tcx.generics_of(def_id),
547 let prohibit_opaque = tcx
548 .explicit_item_bounds(def_id)
550 .try_for_each(|(predicate, _)| predicate.visit_with(&mut visitor));
552 "check_opaque_for_inheriting_lifetimes: prohibit_opaque={:?}, visitor.opaque_identity_ty={:?}, visitor.generics={:?}",
553 prohibit_opaque, visitor.opaque_identity_ty, visitor.generics
556 if let Some(ty) = prohibit_opaque.break_value() {
557 visitor.visit_item(&item);
558 let is_async = match item.kind {
559 ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
560 matches!(origin, hir::OpaqueTyOrigin::AsyncFn)
565 let mut err = struct_span_err!(
569 "`{}` return type cannot contain a projection or `Self` that references lifetimes from \
571 if is_async { "async fn" } else { "impl Trait" },
574 for (span, name) in visitor.selftys {
577 "consider spelling out the type instead",
578 name.unwrap_or_else(|| format!("{:?}", ty)),
579 Applicability::MaybeIncorrect,
587 /// Checks that an opaque type does not contain cycles.
588 pub(super) fn check_opaque_for_cycles<'tcx>(
591 substs: SubstsRef<'tcx>,
593 origin: &hir::OpaqueTyOrigin,
594 ) -> Result<(), ErrorReported> {
595 if tcx.try_expand_impl_trait_type(def_id.to_def_id(), substs).is_err() {
597 hir::OpaqueTyOrigin::AsyncFn => async_opaque_type_cycle_error(tcx, span),
598 _ => opaque_type_cycle_error(tcx, def_id, span),
606 /// Check that the concrete type behind `impl Trait` actually implements `Trait`.
608 /// This is mostly checked at the places that specify the opaque type, but we
609 /// check those cases in the `param_env` of that function, which may have
610 /// bounds not on this opaque type:
612 /// type X<T> = impl Clone
613 /// fn f<T: Clone>(t: T) -> X<T> {
617 /// Without this check the above code is incorrectly accepted: we would ICE if
618 /// some tried, for example, to clone an `Option<X<&mut ()>>`.
619 fn check_opaque_meets_bounds<'tcx>(
622 substs: SubstsRef<'tcx>,
624 origin: &hir::OpaqueTyOrigin,
627 // Checked when type checking the function containing them.
628 hir::OpaqueTyOrigin::FnReturn | hir::OpaqueTyOrigin::AsyncFn => return,
629 // Can have different predicates to their defining use
630 hir::OpaqueTyOrigin::TyAlias => {}
633 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
634 let param_env = tcx.param_env(def_id);
636 tcx.infer_ctxt().enter(move |infcx| {
637 let inh = Inherited::new(infcx, def_id);
638 let infcx = &inh.infcx;
639 let opaque_ty = tcx.mk_opaque(def_id.to_def_id(), substs);
641 let misc_cause = traits::ObligationCause::misc(span, hir_id);
643 let _ = inh.register_infer_ok_obligations(
644 infcx.instantiate_opaque_types(hir_id, param_env, opaque_ty, span),
647 let opaque_type_map = infcx.inner.borrow().opaque_types.clone();
648 for (OpaqueTypeKey { def_id, substs }, opaque_defn) in opaque_type_map {
650 .at(&misc_cause, param_env)
651 .eq(opaque_defn.concrete_ty, tcx.type_of(def_id).subst(tcx, substs))
653 Ok(infer_ok) => inh.register_infer_ok_obligations(infer_ok),
654 Err(ty_err) => tcx.sess.delay_span_bug(
655 opaque_defn.definition_span,
657 "could not unify `{}` with revealed type:\n{}",
658 opaque_defn.concrete_ty, ty_err,
664 // Check that all obligations are satisfied by the implementation's
666 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
667 infcx.report_fulfillment_errors(errors, None, false);
670 // Finally, resolve all regions. This catches wily misuses of
671 // lifetime parameters.
672 let fcx = FnCtxt::new(&inh, param_env, hir_id);
673 fcx.regionck_item(hir_id, span, FxHashSet::default());
677 pub fn check_item_type<'tcx>(tcx: TyCtxt<'tcx>, it: &'tcx hir::Item<'tcx>) {
679 "check_item_type(it.def_id={:?}, it.name={})",
681 tcx.def_path_str(it.def_id.to_def_id())
683 let _indenter = indenter();
685 // Consts can play a role in type-checking, so they are included here.
686 hir::ItemKind::Static(..) => {
687 tcx.ensure().typeck(it.def_id);
688 maybe_check_static_with_link_section(tcx, it.def_id, it.span);
689 check_static_inhabited(tcx, it.def_id, it.span);
691 hir::ItemKind::Const(..) => {
692 tcx.ensure().typeck(it.def_id);
694 hir::ItemKind::Enum(ref enum_definition, _) => {
695 check_enum(tcx, it.span, &enum_definition.variants, it.def_id);
697 hir::ItemKind::Fn(..) => {} // entirely within check_item_body
698 hir::ItemKind::Impl(ref impl_) => {
699 debug!("ItemKind::Impl {} with id {:?}", it.ident, it.def_id);
700 if let Some(impl_trait_ref) = tcx.impl_trait_ref(it.def_id) {
701 check_impl_items_against_trait(
708 let trait_def_id = impl_trait_ref.def_id;
709 check_on_unimplemented(tcx, trait_def_id, it);
712 hir::ItemKind::Trait(_, _, _, _, ref items) => {
713 check_on_unimplemented(tcx, it.def_id.to_def_id(), it);
715 for item in items.iter() {
716 let item = tcx.hir().trait_item(item.id);
718 hir::TraitItemKind::Fn(ref sig, _) => {
719 let abi = sig.header.abi;
720 fn_maybe_err(tcx, item.ident.span, abi);
722 hir::TraitItemKind::Type(.., Some(_default)) => {
723 let assoc_item = tcx.associated_item(item.def_id);
725 InternalSubsts::identity_for_item(tcx, it.def_id.to_def_id());
726 let _: Result<_, rustc_errors::ErrorReported> = check_type_bounds(
731 ty::TraitRef { def_id: it.def_id.to_def_id(), substs: trait_substs },
738 hir::ItemKind::Struct(..) => {
739 check_struct(tcx, it.def_id, it.span);
741 hir::ItemKind::Union(..) => {
742 check_union(tcx, it.def_id, it.span);
744 hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
745 // HACK(jynelson): trying to infer the type of `impl trait` breaks documenting
746 // `async-std` (and `pub async fn` in general).
747 // Since rustdoc doesn't care about the concrete type behind `impl Trait`, just don't look at it!
748 // See https://github.com/rust-lang/rust/issues/75100
749 if !tcx.sess.opts.actually_rustdoc {
750 let substs = InternalSubsts::identity_for_item(tcx, it.def_id.to_def_id());
751 check_opaque(tcx, it.def_id, substs, it.span, &origin);
754 hir::ItemKind::TyAlias(..) => {
755 let pty_ty = tcx.type_of(it.def_id);
756 let generics = tcx.generics_of(it.def_id);
757 check_type_params_are_used(tcx, &generics, pty_ty);
759 hir::ItemKind::ForeignMod { abi, items } => {
760 check_abi(tcx, it.hir_id(), it.span, abi);
762 if abi == Abi::RustIntrinsic {
764 let item = tcx.hir().foreign_item(item.id);
765 intrinsic::check_intrinsic_type(tcx, item);
767 } else if abi == Abi::PlatformIntrinsic {
769 let item = tcx.hir().foreign_item(item.id);
770 intrinsic::check_platform_intrinsic_type(tcx, item);
774 let def_id = item.id.def_id;
775 let generics = tcx.generics_of(def_id);
776 let own_counts = generics.own_counts();
777 if generics.params.len() - own_counts.lifetimes != 0 {
778 let (kinds, kinds_pl, egs) = match (own_counts.types, own_counts.consts) {
779 (_, 0) => ("type", "types", Some("u32")),
780 // We don't specify an example value, because we can't generate
781 // a valid value for any type.
782 (0, _) => ("const", "consts", None),
783 _ => ("type or const", "types or consts", None),
789 "foreign items may not have {} parameters",
792 .span_label(item.span, &format!("can't have {} parameters", kinds))
794 // FIXME: once we start storing spans for type arguments, turn this
795 // into a suggestion.
797 "replace the {} parameters with concrete {}{}",
800 egs.map(|egs| format!(" like `{}`", egs)).unwrap_or_default(),
806 let item = tcx.hir().foreign_item(item.id);
808 hir::ForeignItemKind::Fn(ref fn_decl, _, _) => {
809 require_c_abi_if_c_variadic(tcx, fn_decl, abi, item.span);
811 hir::ForeignItemKind::Static(..) => {
812 check_static_inhabited(tcx, def_id, item.span);
819 _ => { /* nothing to do */ }
823 pub(super) fn check_on_unimplemented(tcx: TyCtxt<'_>, trait_def_id: DefId, item: &hir::Item<'_>) {
824 // an error would be reported if this fails.
825 let _ = traits::OnUnimplementedDirective::of_item(tcx, trait_def_id, item.def_id.to_def_id());
828 pub(super) fn check_specialization_validity<'tcx>(
830 trait_def: &ty::TraitDef,
831 trait_item: &ty::AssocItem,
833 impl_item: &hir::ImplItem<'_>,
835 let kind = match impl_item.kind {
836 hir::ImplItemKind::Const(..) => ty::AssocKind::Const,
837 hir::ImplItemKind::Fn(..) => ty::AssocKind::Fn,
838 hir::ImplItemKind::TyAlias(_) => ty::AssocKind::Type,
841 let ancestors = match trait_def.ancestors(tcx, impl_id) {
842 Ok(ancestors) => ancestors,
845 let mut ancestor_impls = ancestors.skip(1).filter_map(|parent| {
846 if parent.is_from_trait() {
849 Some((parent, parent.item(tcx, trait_item.ident, kind, trait_def.def_id)))
853 let opt_result = ancestor_impls.find_map(|(parent_impl, parent_item)| {
855 // Parent impl exists, and contains the parent item we're trying to specialize, but
856 // doesn't mark it `default`.
857 Some(parent_item) if traits::impl_item_is_final(tcx, &parent_item) => {
858 Some(Err(parent_impl.def_id()))
861 // Parent impl contains item and makes it specializable.
862 Some(_) => Some(Ok(())),
864 // Parent impl doesn't mention the item. This means it's inherited from the
865 // grandparent. In that case, if parent is a `default impl`, inherited items use the
866 // "defaultness" from the grandparent, else they are final.
868 if tcx.impl_defaultness(parent_impl.def_id()).is_default() {
871 Some(Err(parent_impl.def_id()))
877 // If `opt_result` is `None`, we have only encountered `default impl`s that don't contain the
878 // item. This is allowed, the item isn't actually getting specialized here.
879 let result = opt_result.unwrap_or(Ok(()));
881 if let Err(parent_impl) = result {
882 report_forbidden_specialization(tcx, impl_item, parent_impl);
886 pub(super) fn check_impl_items_against_trait<'tcx>(
888 full_impl_span: Span,
890 impl_trait_ref: ty::TraitRef<'tcx>,
891 impl_item_refs: &[hir::ImplItemRef],
893 // If the trait reference itself is erroneous (so the compilation is going
894 // to fail), skip checking the items here -- the `impl_item` table in `tcx`
895 // isn't populated for such impls.
896 if impl_trait_ref.references_error() {
900 // Negative impls are not expected to have any items
901 match tcx.impl_polarity(impl_id) {
902 ty::ImplPolarity::Reservation | ty::ImplPolarity::Positive => {}
903 ty::ImplPolarity::Negative => {
904 if let [first_item_ref, ..] = impl_item_refs {
905 let first_item_span = tcx.hir().impl_item(first_item_ref.id).span;
910 "negative impls cannot have any items"
918 // Locate trait definition and items
919 let trait_def = tcx.trait_def(impl_trait_ref.def_id);
920 let impl_items = impl_item_refs.iter().map(|iiref| tcx.hir().impl_item(iiref.id));
921 let associated_items = tcx.associated_items(impl_trait_ref.def_id);
923 // Check existing impl methods to see if they are both present in trait
924 // and compatible with trait signature
925 for impl_item in impl_items {
926 let ty_impl_item = tcx.associated_item(impl_item.def_id);
929 associated_items.filter_by_name(tcx, ty_impl_item.ident, impl_trait_ref.def_id);
931 let (compatible_kind, ty_trait_item) = if let Some(ty_trait_item) = items.next() {
932 let is_compatible = |ty: &&ty::AssocItem| match (ty.kind, &impl_item.kind) {
933 (ty::AssocKind::Const, hir::ImplItemKind::Const(..)) => true,
934 (ty::AssocKind::Fn, hir::ImplItemKind::Fn(..)) => true,
935 (ty::AssocKind::Type, hir::ImplItemKind::TyAlias(..)) => true,
939 // If we don't have a compatible item, we'll use the first one whose name matches
940 // to report an error.
941 let mut compatible_kind = is_compatible(&ty_trait_item);
942 let mut trait_item = ty_trait_item;
944 if !compatible_kind {
945 if let Some(ty_trait_item) = items.find(is_compatible) {
946 compatible_kind = true;
947 trait_item = ty_trait_item;
951 (compatible_kind, trait_item)
957 match impl_item.kind {
958 hir::ImplItemKind::Const(..) => {
959 // Find associated const definition.
968 hir::ImplItemKind::Fn(..) => {
969 let opt_trait_span = tcx.hir().span_if_local(ty_trait_item.def_id);
979 hir::ImplItemKind::TyAlias(_) => {
980 let opt_trait_span = tcx.hir().span_if_local(ty_trait_item.def_id);
992 check_specialization_validity(
1000 report_mismatch_error(
1002 ty_trait_item.def_id,
1010 if let Ok(ancestors) = trait_def.ancestors(tcx, impl_id.to_def_id()) {
1011 let impl_span = tcx.sess.source_map().guess_head_span(full_impl_span);
1013 // Check for missing items from trait
1014 let mut missing_items = Vec::new();
1015 for trait_item in tcx.associated_items(impl_trait_ref.def_id).in_definition_order() {
1016 let is_implemented = ancestors
1017 .leaf_def(tcx, trait_item.ident, trait_item.kind)
1018 .map(|node_item| !node_item.defining_node.is_from_trait())
1021 if !is_implemented && tcx.impl_defaultness(impl_id).is_final() {
1022 if !trait_item.defaultness.has_value() {
1023 missing_items.push(*trait_item);
1028 if !missing_items.is_empty() {
1029 missing_items_err(tcx, impl_span, &missing_items, full_impl_span);
1036 fn report_mismatch_error<'tcx>(
1038 trait_item_def_id: DefId,
1039 impl_trait_ref: ty::TraitRef<'tcx>,
1040 impl_item: &hir::ImplItem<'_>,
1041 ty_impl_item: &ty::AssocItem,
1043 let mut err = match impl_item.kind {
1044 hir::ImplItemKind::Const(..) => {
1045 // Find associated const definition.
1050 "item `{}` is an associated const, which doesn't match its trait `{}`",
1052 impl_trait_ref.print_only_trait_path()
1056 hir::ImplItemKind::Fn(..) => {
1061 "item `{}` is an associated method, which doesn't match its trait `{}`",
1063 impl_trait_ref.print_only_trait_path()
1067 hir::ImplItemKind::TyAlias(_) => {
1072 "item `{}` is an associated type, which doesn't match its trait `{}`",
1074 impl_trait_ref.print_only_trait_path()
1079 err.span_label(impl_item.span, "does not match trait");
1080 if let Some(trait_span) = tcx.hir().span_if_local(trait_item_def_id) {
1081 err.span_label(trait_span, "item in trait");
1086 /// Checks whether a type can be represented in memory. In particular, it
1087 /// identifies types that contain themselves without indirection through a
1088 /// pointer, which would mean their size is unbounded.
1089 pub(super) fn check_representable(tcx: TyCtxt<'_>, sp: Span, item_def_id: LocalDefId) -> bool {
1090 let rty = tcx.type_of(item_def_id);
1092 // Check that it is possible to represent this type. This call identifies
1093 // (1) types that contain themselves and (2) types that contain a different
1094 // recursive type. It is only necessary to throw an error on those that
1095 // contain themselves. For case 2, there must be an inner type that will be
1096 // caught by case 1.
1097 match representability::ty_is_representable(tcx, rty, sp) {
1098 Representability::SelfRecursive(spans) => {
1099 recursive_type_with_infinite_size_error(tcx, item_def_id.to_def_id(), spans);
1102 Representability::Representable | Representability::ContainsRecursive => (),
1107 pub fn check_simd(tcx: TyCtxt<'_>, sp: Span, def_id: LocalDefId) {
1108 let t = tcx.type_of(def_id);
1109 if let ty::Adt(def, substs) = t.kind() {
1110 if def.is_struct() {
1111 let fields = &def.non_enum_variant().fields;
1112 if fields.is_empty() {
1113 struct_span_err!(tcx.sess, sp, E0075, "SIMD vector cannot be empty").emit();
1116 let e = fields[0].ty(tcx, substs);
1117 if !fields.iter().all(|f| f.ty(tcx, substs) == e) {
1118 struct_span_err!(tcx.sess, sp, E0076, "SIMD vector should be homogeneous")
1119 .span_label(sp, "SIMD elements must have the same type")
1124 let len = if let ty::Array(_ty, c) = e.kind() {
1125 c.try_eval_usize(tcx, tcx.param_env(def.did))
1127 Some(fields.len() as u64)
1129 if let Some(len) = len {
1131 struct_span_err!(tcx.sess, sp, E0075, "SIMD vector cannot be empty").emit();
1133 } else if len > MAX_SIMD_LANES {
1138 "SIMD vector cannot have more than {} elements",
1146 // Check that we use types valid for use in the lanes of a SIMD "vector register"
1147 // These are scalar types which directly match a "machine" type
1148 // Yes: Integers, floats, "thin" pointers
1149 // No: char, "fat" pointers, compound types
1151 ty::Param(_) => (), // pass struct<T>(T, T, T, T) through, let monomorphization catch errors
1152 ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::RawPtr(_) => (), // struct(u8, u8, u8, u8) is ok
1153 ty::Array(t, _) if matches!(t.kind(), ty::Param(_)) => (), // pass struct<T>([T; N]) through, let monomorphization catch errors
1157 ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::RawPtr(_)
1159 { /* struct([f32; 4]) is ok */ }
1165 "SIMD vector element type should be a \
1166 primitive scalar (integer/float/pointer) type"
1176 pub(super) fn check_packed(tcx: TyCtxt<'_>, sp: Span, def: &ty::AdtDef) {
1177 let repr = def.repr;
1179 for attr in tcx.get_attrs(def.did).iter() {
1180 for r in attr::find_repr_attrs(&tcx.sess, attr) {
1181 if let attr::ReprPacked(pack) = r {
1182 if let Some(repr_pack) = repr.pack {
1183 if pack as u64 != repr_pack.bytes() {
1188 "type has conflicting packed representation hints"
1196 if repr.align.is_some() {
1201 "type has conflicting packed and align representation hints"
1205 if let Some(def_spans) = check_packed_inner(tcx, def.did, &mut vec![]) {
1206 let mut err = struct_span_err!(
1210 "packed type cannot transitively contain a `#[repr(align)]` type"
1214 tcx.def_span(def_spans[0].0),
1216 "`{}` has a `#[repr(align)]` attribute",
1217 tcx.item_name(def_spans[0].0)
1221 if def_spans.len() > 2 {
1222 let mut first = true;
1223 for (adt_def, span) in def_spans.iter().skip(1).rev() {
1224 let ident = tcx.item_name(*adt_def);
1229 "`{}` contains a field of type `{}`",
1230 tcx.type_of(def.did),
1234 format!("...which contains a field of type `{}`", ident)
1247 pub(super) fn check_packed_inner(
1250 stack: &mut Vec<DefId>,
1251 ) -> Option<Vec<(DefId, Span)>> {
1252 if let ty::Adt(def, substs) = tcx.type_of(def_id).kind() {
1253 if def.is_struct() || def.is_union() {
1254 if def.repr.align.is_some() {
1255 return Some(vec![(def.did, DUMMY_SP)]);
1259 for field in &def.non_enum_variant().fields {
1260 if let ty::Adt(def, _) = field.ty(tcx, substs).kind() {
1261 if !stack.contains(&def.did) {
1262 if let Some(mut defs) = check_packed_inner(tcx, def.did, stack) {
1263 defs.push((def.did, field.ident.span));
1276 pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, sp: Span, adt: &'tcx ty::AdtDef) {
1277 if !adt.repr.transparent() {
1280 let sp = tcx.sess.source_map().guess_head_span(sp);
1282 if adt.is_union() && !tcx.features().transparent_unions {
1284 &tcx.sess.parse_sess,
1285 sym::transparent_unions,
1287 "transparent unions are unstable",
1292 if adt.variants.len() != 1 {
1293 bad_variant_count(tcx, adt, sp, adt.did);
1294 if adt.variants.is_empty() {
1295 // Don't bother checking the fields. No variants (and thus no fields) exist.
1300 // For each field, figure out if it's known to be a ZST and align(1)
1301 let field_infos = adt.all_fields().map(|field| {
1302 let ty = field.ty(tcx, InternalSubsts::identity_for_item(tcx, field.did));
1303 let param_env = tcx.param_env(field.did);
1304 let layout = tcx.layout_of(param_env.and(ty));
1305 // We are currently checking the type this field came from, so it must be local
1306 let span = tcx.hir().span_if_local(field.did).unwrap();
1307 let zst = layout.map_or(false, |layout| layout.is_zst());
1308 let align1 = layout.map_or(false, |layout| layout.align.abi.bytes() == 1);
1312 let non_zst_fields =
1313 field_infos.clone().filter_map(|(span, zst, _align1)| if !zst { Some(span) } else { None });
1314 let non_zst_count = non_zst_fields.clone().count();
1315 if non_zst_count >= 2 {
1316 bad_non_zero_sized_fields(tcx, adt, non_zst_count, non_zst_fields, sp);
1318 for (span, zst, align1) in field_infos {
1324 "zero-sized field in transparent {} has alignment larger than 1",
1327 .span_label(span, "has alignment larger than 1")
1333 #[allow(trivial_numeric_casts)]
1334 fn check_enum<'tcx>(
1337 vs: &'tcx [hir::Variant<'tcx>],
1340 let def = tcx.adt_def(def_id);
1341 def.destructor(tcx); // force the destructor to be evaluated
1344 let attributes = tcx.get_attrs(def_id.to_def_id());
1345 if let Some(attr) = tcx.sess.find_by_name(&attributes, sym::repr) {
1350 "unsupported representation for zero-variant enum"
1352 .span_label(sp, "zero-variant enum")
1357 let repr_type_ty = def.repr.discr_type().to_ty(tcx);
1358 if repr_type_ty == tcx.types.i128 || repr_type_ty == tcx.types.u128 {
1359 if !tcx.features().repr128 {
1361 &tcx.sess.parse_sess,
1364 "repr with 128-bit type is unstable",
1371 if let Some(ref e) = v.disr_expr {
1372 tcx.ensure().typeck(tcx.hir().local_def_id(e.hir_id));
1376 if tcx.adt_def(def_id).repr.int.is_none() && tcx.features().arbitrary_enum_discriminant {
1377 let is_unit = |var: &hir::Variant<'_>| matches!(var.data, hir::VariantData::Unit(..));
1379 let has_disr = |var: &hir::Variant<'_>| var.disr_expr.is_some();
1380 let has_non_units = vs.iter().any(|var| !is_unit(var));
1381 let disr_units = vs.iter().any(|var| is_unit(&var) && has_disr(&var));
1382 let disr_non_unit = vs.iter().any(|var| !is_unit(&var) && has_disr(&var));
1384 if disr_non_unit || (disr_units && has_non_units) {
1386 struct_span_err!(tcx.sess, sp, E0732, "`#[repr(inttype)]` must be specified");
1391 let mut disr_vals: Vec<Discr<'tcx>> = Vec::with_capacity(vs.len());
1392 for ((_, discr), v) in iter::zip(def.discriminants(tcx), vs) {
1393 // Check for duplicate discriminant values
1394 if let Some(i) = disr_vals.iter().position(|&x| x.val == discr.val) {
1395 let variant_did = def.variants[VariantIdx::new(i)].def_id;
1396 let variant_i_hir_id = tcx.hir().local_def_id_to_hir_id(variant_did.expect_local());
1397 let variant_i = tcx.hir().expect_variant(variant_i_hir_id);
1398 let i_span = match variant_i.disr_expr {
1399 Some(ref expr) => tcx.hir().span(expr.hir_id),
1400 None => tcx.hir().span(variant_i_hir_id),
1402 let span = match v.disr_expr {
1403 Some(ref expr) => tcx.hir().span(expr.hir_id),
1406 let display_discr = display_discriminant_value(tcx, v, discr.val);
1407 let display_discr_i = display_discriminant_value(tcx, variant_i, disr_vals[i].val);
1412 "discriminant value `{}` already exists",
1415 .span_label(i_span, format!("first use of {}", display_discr_i))
1416 .span_label(span, format!("enum already has {}", display_discr))
1419 disr_vals.push(discr);
1422 check_representable(tcx, sp, def_id);
1423 check_transparent(tcx, sp, def);
1426 /// Format an enum discriminant value for use in a diagnostic message.
1427 fn display_discriminant_value<'tcx>(
1429 variant: &hir::Variant<'_>,
1432 if let Some(expr) = &variant.disr_expr {
1433 let body = &tcx.hir().body(expr.body).value;
1434 if let hir::ExprKind::Lit(lit) = &body.kind {
1435 if let rustc_ast::LitKind::Int(lit_value, _int_kind) = &lit.node {
1436 if evaluated != *lit_value {
1437 return format!("`{}` (overflowed from `{}`)", evaluated, lit_value);
1442 format!("`{}`", evaluated)
1445 pub(super) fn check_type_params_are_used<'tcx>(
1447 generics: &ty::Generics,
1450 debug!("check_type_params_are_used(generics={:?}, ty={:?})", generics, ty);
1452 assert_eq!(generics.parent, None);
1454 if generics.own_counts().types == 0 {
1458 let mut params_used = BitSet::new_empty(generics.params.len());
1460 if ty.references_error() {
1461 // If there is already another error, do not emit
1462 // an error for not using a type parameter.
1463 assert!(tcx.sess.has_errors());
1467 for leaf in ty.walk(tcx) {
1468 if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
1469 if let ty::Param(param) = leaf_ty.kind() {
1470 debug!("found use of ty param {:?}", param);
1471 params_used.insert(param.index);
1476 for param in &generics.params {
1477 if !params_used.contains(param.index) {
1478 if let ty::GenericParamDefKind::Type { .. } = param.kind {
1479 let span = tcx.def_span(param.def_id);
1484 "type parameter `{}` is unused",
1487 .span_label(span, "unused type parameter")
1494 pub(super) fn check_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
1495 tcx.hir().visit_item_likes_in_module(module_def_id, &mut CheckItemTypesVisitor { tcx });
1498 pub(super) fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
1499 wfcheck::check_item_well_formed(tcx, def_id);
1502 pub(super) fn check_trait_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
1503 wfcheck::check_trait_item(tcx, def_id);
1506 pub(super) fn check_impl_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
1507 wfcheck::check_impl_item(tcx, def_id);
1510 fn async_opaque_type_cycle_error(tcx: TyCtxt<'tcx>, span: Span) {
1511 struct_span_err!(tcx.sess, span, E0733, "recursion in an `async fn` requires boxing")
1512 .span_label(span, "recursive `async fn`")
1513 .note("a recursive `async fn` must be rewritten to return a boxed `dyn Future`")
1515 "consider using the `async_recursion` crate: https://crates.io/crates/async_recursion",
1520 /// Emit an error for recursive opaque types.
1522 /// If this is a return `impl Trait`, find the item's return expressions and point at them. For
1523 /// direct recursion this is enough, but for indirect recursion also point at the last intermediary
1526 /// If all the return expressions evaluate to `!`, then we explain that the error will go away
1527 /// after changing it. This can happen when a user uses `panic!()` or similar as a placeholder.
1528 fn opaque_type_cycle_error(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
1529 let mut err = struct_span_err!(tcx.sess, span, E0720, "cannot resolve opaque type");
1531 let mut label = false;
1532 if let Some((hir_id, visitor)) = get_owner_return_paths(tcx, def_id) {
1533 let typeck_results = tcx.typeck(tcx.hir().local_def_id(hir_id));
1537 .filter_map(|expr| typeck_results.node_type_opt(expr.hir_id))
1538 .all(|ty| matches!(ty.kind(), ty::Never))
1543 .filter(|expr| typeck_results.node_type_opt(expr.hir_id).is_some())
1544 .map(|expr| expr.span)
1545 .collect::<Vec<Span>>();
1546 let span_len = spans.len();
1548 err.span_label(spans[0], "this returned value is of `!` type");
1550 let mut multispan: MultiSpan = spans.clone().into();
1553 .push_span_label(span, "this returned value is of `!` type".to_string());
1555 err.span_note(multispan, "these returned values have a concrete \"never\" type");
1557 err.help("this error will resolve once the item's body returns a concrete type");
1559 let mut seen = FxHashSet::default();
1561 err.span_label(span, "recursive opaque type");
1563 for (sp, ty) in visitor
1566 .filter_map(|e| typeck_results.node_type_opt(e.hir_id).map(|t| (e.span, t)))
1567 .filter(|(_, ty)| !matches!(ty.kind(), ty::Never))
1569 struct OpaqueTypeCollector(Vec<DefId>);
1570 impl<'tcx> ty::fold::TypeVisitor<'tcx> for OpaqueTypeCollector {
1571 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
1572 // Default anon const substs cannot contain opaque types.
1575 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1577 ty::Opaque(def, _) => {
1579 ControlFlow::CONTINUE
1581 _ => t.super_visit_with(self),
1585 let mut visitor = OpaqueTypeCollector(vec![]);
1586 ty.visit_with(&mut visitor);
1587 for def_id in visitor.0 {
1588 let ty_span = tcx.def_span(def_id);
1589 if !seen.contains(&ty_span) {
1590 err.span_label(ty_span, &format!("returning this opaque type `{}`", ty));
1591 seen.insert(ty_span);
1593 err.span_label(sp, &format!("returning here with type `{}`", ty));
1599 err.span_label(span, "cannot resolve opaque type");