1 use crate::check::wfcheck::for_item;
3 use super::coercion::CoerceMany;
4 use super::compare_method::check_type_bounds;
5 use super::compare_method::{compare_const_impl, compare_impl_method, compare_ty_impl};
8 use rustc_attr as attr;
9 use rustc_errors::{Applicability, ErrorGuaranteed, MultiSpan};
11 use rustc_hir::def_id::{DefId, LocalDefId};
12 use rustc_hir::intravisit::Visitor;
13 use rustc_hir::lang_items::LangItem;
14 use rustc_hir::{def::Res, ItemKind, Node, PathSegment};
15 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
16 use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
17 use rustc_infer::traits::Obligation;
18 use rustc_middle::hir::nested_filter;
19 use rustc_middle::ty::fold::TypeFoldable;
20 use rustc_middle::ty::layout::{LayoutError, MAX_SIMD_LANES};
21 use rustc_middle::ty::subst::GenericArgKind;
22 use rustc_middle::ty::util::{Discr, IntTypeExt};
23 use rustc_middle::ty::{self, ParamEnv, ToPredicate, Ty, TyCtxt};
24 use rustc_session::lint::builtin::{UNINHABITED_STATIC, UNSUPPORTED_CALLING_CONVENTIONS};
25 use rustc_span::symbol::sym;
26 use rustc_span::{self, Span};
27 use rustc_target::spec::abi::Abi;
28 use rustc_trait_selection::traits;
29 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
30 use rustc_ty_utils::representability::{self, Representability};
32 use rustc_hir::def::DefKind;
34 use std::ops::ControlFlow;
36 pub fn check_wf_new(tcx: TyCtxt<'_>) {
37 let visit = wfcheck::CheckTypeWellFormedVisitor::new(tcx);
38 tcx.hir().par_visit_all_item_likes(&visit);
41 pub(super) fn check_abi(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: Abi) {
42 match tcx.sess.target.is_abi_supported(abi) {
49 "`{abi}` is not a supported ABI for the current target",
54 tcx.struct_span_lint_hir(UNSUPPORTED_CALLING_CONVENTIONS, hir_id, span, |lint| {
55 lint.build("use of calling convention not supported on this target").emit();
60 // This ABI is only allowed on function pointers
61 if abi == Abi::CCmseNonSecureCall {
66 "the `\"C-cmse-nonsecure-call\"` ABI is only allowed on function pointers"
72 /// Helper used for fns and closures. Does the grungy work of checking a function
73 /// body and returns the function context used for that purpose, since in the case of a fn item
74 /// there is still a bit more to do.
77 /// * inherited: other fields inherited from the enclosing fn (if any)
78 #[instrument(skip(inherited, body), level = "debug")]
79 pub(super) fn check_fn<'a, 'tcx>(
80 inherited: &'a Inherited<'a, 'tcx>,
81 param_env: ty::ParamEnv<'tcx>,
82 fn_sig: ty::FnSig<'tcx>,
83 decl: &'tcx hir::FnDecl<'tcx>,
85 body: &'tcx hir::Body<'tcx>,
86 can_be_generator: Option<hir::Movability>,
87 return_type_pre_known: bool,
88 ) -> (FnCtxt<'a, 'tcx>, Option<GeneratorTypes<'tcx>>) {
89 // Create the function context. This is either derived from scratch or,
90 // in the case of closures, based on the outer context.
91 let mut fcx = FnCtxt::new(inherited, param_env, body.value.hir_id);
92 fcx.ps.set(UnsafetyState::function(fn_sig.unsafety, fn_id));
93 fcx.return_type_pre_known = return_type_pre_known;
99 let declared_ret_ty = fn_sig.output();
102 fcx.register_infer_ok_obligations(fcx.infcx.replace_opaque_types_with_inference_vars(
108 // HACK(oli-obk): we rewrite the declared return type, too, so that we don't end up inferring all
109 // unconstrained RPIT to have `()` as their hidden type. This would happen because further down we
110 // compare the ret_coercion with declared_ret_ty, and anything uninferred would be inferred to the
111 // opaque type itself. That again would cause writeback to assume we have a recursive call site
112 // and do the sadly stabilized fallback to `()`.
113 let declared_ret_ty = ret_ty;
114 fcx.ret_coercion = Some(RefCell::new(CoerceMany::new(ret_ty)));
115 fcx.ret_type_span = Some(decl.output.span());
117 let span = body.value.span;
119 fn_maybe_err(tcx, span, fn_sig.abi);
121 if fn_sig.abi == Abi::RustCall {
122 let expected_args = if let ImplicitSelfKind::None = decl.implicit_self { 1 } else { 2 };
125 let item = match tcx.hir().get(fn_id) {
126 Node::Item(hir::Item { kind: ItemKind::Fn(header, ..), .. }) => Some(header),
127 Node::ImplItem(hir::ImplItem {
128 kind: hir::ImplItemKind::Fn(header, ..), ..
130 Node::TraitItem(hir::TraitItem {
131 kind: hir::TraitItemKind::Fn(header, ..),
134 // Closures are RustCall, but they tuple their arguments, so shouldn't be checked
135 Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => None,
136 node => bug!("Item being checked wasn't a function/closure: {:?}", node),
139 if let Some(header) = item {
140 tcx.sess.span_err(header.span, "functions with the \"rust-call\" ABI must take a single non-self argument that is a tuple");
144 if fn_sig.inputs().len() != expected_args {
147 // FIXME(CraftSpider) Add a check on parameter expansion, so we don't just make the ICE happen later on
148 // This will probably require wide-scale changes to support a TupleKind obligation
149 // We can't resolve this without knowing the type of the param
150 if !matches!(fn_sig.inputs()[expected_args - 1].kind(), ty::Tuple(_) | ty::Param(_)) {
156 if body.generator_kind.is_some() && can_be_generator.is_some() {
158 .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span });
159 fcx.require_type_is_sized(yield_ty, span, traits::SizedYieldType);
161 // Resume type defaults to `()` if the generator has no argument.
162 let resume_ty = fn_sig.inputs().get(0).copied().unwrap_or_else(|| tcx.mk_unit());
164 fcx.resume_yield_tys = Some((resume_ty, yield_ty));
167 GatherLocalsVisitor::new(&fcx).visit_body(body);
169 // C-variadic fns also have a `VaList` input that's not listed in `fn_sig`
170 // (as it's created inside the body itself, not passed in from outside).
171 let maybe_va_list = if fn_sig.c_variadic {
172 let span = body.params.last().unwrap().span;
173 let va_list_did = tcx.require_lang_item(LangItem::VaList, Some(span));
174 let region = fcx.next_region_var(RegionVariableOrigin::MiscVariable(span));
176 Some(tcx.bound_type_of(va_list_did).subst(tcx, &[region.into()]))
181 // Add formal parameters.
182 let inputs_hir = hir.fn_decl_by_hir_id(fn_id).map(|decl| &decl.inputs);
183 let inputs_fn = fn_sig.inputs().iter().copied();
184 for (idx, (param_ty, param)) in inputs_fn.chain(maybe_va_list).zip(body.params).enumerate() {
185 // Check the pattern.
186 let ty_span = try { inputs_hir?.get(idx)?.span };
187 fcx.check_pat_top(¶m.pat, param_ty, ty_span, false);
189 // Check that argument is Sized.
190 // The check for a non-trivial pattern is a hack to avoid duplicate warnings
191 // for simple cases like `fn foo(x: Trait)`,
192 // where we would error once on the parameter as a whole, and once on the binding `x`.
193 if param.pat.simple_ident().is_none() && !tcx.features().unsized_fn_params {
194 fcx.require_type_is_sized(param_ty, param.pat.span, traits::SizedArgumentType(ty_span));
197 fcx.write_ty(param.hir_id, param_ty);
200 inherited.typeck_results.borrow_mut().liberated_fn_sigs_mut().insert(fn_id, fn_sig);
202 fcx.in_tail_expr = true;
203 if let ty::Dynamic(..) = declared_ret_ty.kind() {
204 // FIXME: We need to verify that the return type is `Sized` after the return expression has
205 // been evaluated so that we have types available for all the nodes being returned, but that
206 // requires the coerced evaluated type to be stored. Moving `check_return_expr` before this
207 // causes unsized errors caused by the `declared_ret_ty` to point at the return expression,
208 // while keeping the current ordering we will ignore the tail expression's type because we
209 // don't know it yet. We can't do `check_expr_kind` while keeping `check_return_expr`
210 // because we will trigger "unreachable expression" lints unconditionally.
211 // Because of all of this, we perform a crude check to know whether the simplest `!Sized`
212 // case that a newcomer might make, returning a bare trait, and in that case we populate
213 // the tail expression's type so that the suggestion will be correct, but ignore all other
215 fcx.check_expr(&body.value);
216 fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
218 fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
219 fcx.check_return_expr(&body.value, false);
221 fcx.in_tail_expr = false;
223 // We insert the deferred_generator_interiors entry after visiting the body.
224 // This ensures that all nested generators appear before the entry of this generator.
225 // resolve_generator_interiors relies on this property.
226 let gen_ty = if let (Some(_), Some(gen_kind)) = (can_be_generator, body.generator_kind) {
228 .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::MiscVariable, span });
229 fcx.deferred_generator_interiors.borrow_mut().push((body.id(), interior, gen_kind));
231 let (resume_ty, yield_ty) = fcx.resume_yield_tys.unwrap();
232 Some(GeneratorTypes {
236 movability: can_be_generator.unwrap(),
242 // Finalize the return check by taking the LUB of the return types
243 // we saw and assigning it to the expected return type. This isn't
244 // really expected to fail, since the coercions would have failed
245 // earlier when trying to find a LUB.
246 let coercion = fcx.ret_coercion.take().unwrap().into_inner();
247 let mut actual_return_ty = coercion.complete(&fcx);
248 debug!("actual_return_ty = {:?}", actual_return_ty);
249 if let ty::Dynamic(..) = declared_ret_ty.kind() {
250 // We have special-cased the case where the function is declared
251 // `-> dyn Foo` and we don't actually relate it to the
252 // `fcx.ret_coercion`, so just substitute a type variable.
254 fcx.next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::DynReturnFn, span });
255 debug!("actual_return_ty replaced with {:?}", actual_return_ty);
257 fcx.demand_suptype(span, declared_ret_ty, actual_return_ty);
259 // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
260 if let Some(panic_impl_did) = tcx.lang_items().panic_impl()
261 && panic_impl_did == hir.local_def_id(fn_id).to_def_id()
263 if let Some(panic_info_did) = tcx.lang_items().panic_info() {
264 if *declared_ret_ty.kind() != ty::Never {
265 sess.span_err(decl.output.span(), "return type should be `!`");
268 let inputs = fn_sig.inputs();
269 let span = hir.span(fn_id);
270 if inputs.len() == 1 {
271 let arg_is_panic_info = match *inputs[0].kind() {
272 ty::Ref(region, ty, mutbl) => match *ty.kind() {
273 ty::Adt(ref adt, _) => {
274 adt.did() == panic_info_did
275 && mutbl == hir::Mutability::Not
276 && !region.is_static()
283 if !arg_is_panic_info {
284 sess.span_err(decl.inputs[0].span, "argument should be `&PanicInfo`");
287 if let Node::Item(item) = hir.get(fn_id)
288 && let ItemKind::Fn(_, ref generics, _) = item.kind
289 && !generics.params.is_empty()
291 sess.span_err(span, "should have no type parameters");
294 let span = sess.source_map().guess_head_span(span);
295 sess.span_err(span, "function should have one argument");
298 sess.err("language item required, but not found: `panic_info`");
302 // Check that a function marked as `#[alloc_error_handler]` has signature `fn(Layout) -> !`
303 if let Some(alloc_error_handler_did) = tcx.lang_items().oom()
304 && alloc_error_handler_did == hir.local_def_id(fn_id).to_def_id()
306 if let Some(alloc_layout_did) = tcx.lang_items().alloc_layout() {
307 if *declared_ret_ty.kind() != ty::Never {
308 sess.span_err(decl.output.span(), "return type should be `!`");
311 let inputs = fn_sig.inputs();
312 let span = hir.span(fn_id);
313 if inputs.len() == 1 {
314 let arg_is_alloc_layout = match inputs[0].kind() {
315 ty::Adt(ref adt, _) => adt.did() == alloc_layout_did,
319 if !arg_is_alloc_layout {
320 sess.span_err(decl.inputs[0].span, "argument should be `Layout`");
323 if let Node::Item(item) = hir.get(fn_id)
324 && let ItemKind::Fn(_, ref generics, _) = item.kind
325 && !generics.params.is_empty()
329 "`#[alloc_error_handler]` function should have no type parameters",
333 let span = sess.source_map().guess_head_span(span);
334 sess.span_err(span, "function should have one argument");
337 sess.err("language item required, but not found: `alloc_layout`");
344 fn check_struct(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) {
345 let def = tcx.adt_def(def_id);
346 def.destructor(tcx); // force the destructor to be evaluated
347 check_representable(tcx, span, def_id);
349 if def.repr().simd() {
350 check_simd(tcx, span, def_id);
353 check_transparent(tcx, span, def);
354 check_packed(tcx, span, def);
357 fn check_union(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) {
358 let def = tcx.adt_def(def_id);
359 def.destructor(tcx); // force the destructor to be evaluated
360 check_representable(tcx, span, def_id);
361 check_transparent(tcx, span, def);
362 check_union_fields(tcx, span, def_id);
363 check_packed(tcx, span, def);
366 /// Check that the fields of the `union` do not need dropping.
367 fn check_union_fields(tcx: TyCtxt<'_>, span: Span, item_def_id: LocalDefId) -> bool {
368 let item_type = tcx.type_of(item_def_id);
369 if let ty::Adt(def, substs) = item_type.kind() {
370 assert!(def.is_union());
371 let fields = &def.non_enum_variant().fields;
372 let param_env = tcx.param_env(item_def_id);
373 for field in fields {
374 let field_ty = field.ty(tcx, substs);
375 if field_ty.needs_drop(tcx, param_env) {
376 let (field_span, ty_span) = match tcx.hir().get_if_local(field.did) {
377 // We are currently checking the type this field came from, so it must be local.
378 Some(Node::Field(field)) => (field.span, field.ty.span),
379 _ => unreachable!("mir field has to correspond to hir field"),
385 "unions cannot contain fields that may need dropping"
388 "a type is guaranteed not to need dropping \
389 when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type",
391 .multipart_suggestion_verbose(
392 "when the type does not implement `Copy`, \
393 wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped",
395 (ty_span.shrink_to_lo(), "std::mem::ManuallyDrop<".into()),
396 (ty_span.shrink_to_hi(), ">".into()),
398 Applicability::MaybeIncorrect,
405 span_bug!(span, "unions must be ty::Adt, but got {:?}", item_type.kind());
410 /// Check that a `static` is inhabited.
411 fn check_static_inhabited<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
412 // Make sure statics are inhabited.
413 // Other parts of the compiler assume that there are no uninhabited places. In principle it
414 // would be enough to check this for `extern` statics, as statics with an initializer will
415 // have UB during initialization if they are uninhabited, but there also seems to be no good
416 // reason to allow any statics to be uninhabited.
417 let ty = tcx.type_of(def_id);
418 let layout = match tcx.layout_of(ParamEnv::reveal_all().and(ty)) {
420 // Foreign statics that overflow their allowed size should emit an error
421 Err(LayoutError::SizeOverflow(_))
423 let node = tcx.hir().get_by_def_id(def_id);
426 hir::Node::ForeignItem(hir::ForeignItem {
427 kind: hir::ForeignItemKind::Static(..),
434 .struct_span_err(span, "extern static is too large for the current architecture")
438 // Generic statics are rejected, but we still reach this case.
440 tcx.sess.delay_span_bug(span, &e.to_string());
444 if layout.abi.is_uninhabited() {
445 tcx.struct_span_lint_hir(
447 tcx.hir().local_def_id_to_hir_id(def_id),
450 lint.build("static of uninhabited type")
451 .note("uninhabited statics cannot be initialized, and any access would be an immediate error")
458 /// Checks that an opaque type does not contain cycles and does not use `Self` or `T::Foo`
459 /// projections that would result in "inheriting lifetimes".
460 pub(super) fn check_opaque<'tcx>(
463 substs: SubstsRef<'tcx>,
465 origin: &hir::OpaqueTyOrigin,
467 check_opaque_for_inheriting_lifetimes(tcx, def_id, span);
468 if tcx.type_of(def_id).references_error() {
471 if check_opaque_for_cycles(tcx, def_id, substs, span, origin).is_err() {
474 check_opaque_meets_bounds(tcx, def_id, substs, span, origin);
477 /// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result
478 /// in "inheriting lifetimes".
479 #[instrument(level = "debug", skip(tcx, span))]
480 pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
485 let item = tcx.hir().expect_item(def_id);
486 debug!(?item, ?span);
488 struct FoundParentLifetime;
489 struct FindParentLifetimeVisitor<'tcx>(&'tcx ty::Generics);
490 impl<'tcx> ty::fold::TypeVisitor<'tcx> for FindParentLifetimeVisitor<'tcx> {
491 type BreakTy = FoundParentLifetime;
493 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
494 debug!("FindParentLifetimeVisitor: r={:?}", r);
495 if let ty::ReEarlyBound(ty::EarlyBoundRegion { index, .. }) = *r {
496 if index < self.0.parent_count as u32 {
497 return ControlFlow::Break(FoundParentLifetime);
499 return ControlFlow::CONTINUE;
503 r.super_visit_with(self)
506 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
507 if let ty::ConstKind::Unevaluated(..) = c.val() {
508 // FIXME(#72219) We currently don't detect lifetimes within substs
509 // which would violate this check. Even though the particular substitution is not used
510 // within the const, this should still be fixed.
511 return ControlFlow::CONTINUE;
513 c.super_visit_with(self)
517 struct ProhibitOpaqueVisitor<'tcx> {
519 opaque_identity_ty: Ty<'tcx>,
520 generics: &'tcx ty::Generics,
521 selftys: Vec<(Span, Option<String>)>,
524 impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
525 type BreakTy = Ty<'tcx>;
527 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
528 debug!("check_opaque_for_inheriting_lifetimes: (visit_ty) t={:?}", t);
529 if t == self.opaque_identity_ty {
530 ControlFlow::CONTINUE
532 t.super_visit_with(&mut FindParentLifetimeVisitor(self.generics))
533 .map_break(|FoundParentLifetime| t)
538 impl<'tcx> Visitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
539 type NestedFilter = nested_filter::OnlyBodies;
541 fn nested_visit_map(&mut self) -> Self::Map {
545 fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
547 hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
550 res: Some(Res::SelfTy { trait_: _, alias_to: impl_ref }),
555 impl_ref.map(|(def_id, _)| self.tcx.def_path_str(def_id));
556 self.selftys.push((path.span, impl_ty_name));
562 hir::intravisit::walk_ty(self, arg);
566 if let ItemKind::OpaqueTy(hir::OpaqueTy {
567 origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
571 let mut visitor = ProhibitOpaqueVisitor {
572 opaque_identity_ty: tcx.mk_opaque(
574 InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
576 generics: tcx.generics_of(def_id),
580 let prohibit_opaque = tcx
581 .explicit_item_bounds(def_id)
583 .try_for_each(|(predicate, _)| predicate.visit_with(&mut visitor));
585 "check_opaque_for_inheriting_lifetimes: prohibit_opaque={:?}, visitor.opaque_identity_ty={:?}, visitor.generics={:?}",
586 prohibit_opaque, visitor.opaque_identity_ty, visitor.generics
589 if let Some(ty) = prohibit_opaque.break_value() {
590 visitor.visit_item(&item);
591 let is_async = match item.kind {
592 ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
593 matches!(origin, hir::OpaqueTyOrigin::AsyncFn(..))
598 let mut err = struct_span_err!(
602 "`{}` return type cannot contain a projection or `Self` that references lifetimes from \
604 if is_async { "async fn" } else { "impl Trait" },
607 for (span, name) in visitor.selftys {
610 "consider spelling out the type instead",
611 name.unwrap_or_else(|| format!("{:?}", ty)),
612 Applicability::MaybeIncorrect,
620 /// Checks that an opaque type does not contain cycles.
621 pub(super) fn check_opaque_for_cycles<'tcx>(
624 substs: SubstsRef<'tcx>,
626 origin: &hir::OpaqueTyOrigin,
627 ) -> Result<(), ErrorGuaranteed> {
628 if tcx.try_expand_impl_trait_type(def_id.to_def_id(), substs).is_err() {
629 let reported = match origin {
630 hir::OpaqueTyOrigin::AsyncFn(..) => async_opaque_type_cycle_error(tcx, span),
631 _ => opaque_type_cycle_error(tcx, def_id, span),
639 /// Check that the concrete type behind `impl Trait` actually implements `Trait`.
641 /// This is mostly checked at the places that specify the opaque type, but we
642 /// check those cases in the `param_env` of that function, which may have
643 /// bounds not on this opaque type:
645 /// type X<T> = impl Clone
646 /// fn f<T: Clone>(t: T) -> X<T> {
650 /// Without this check the above code is incorrectly accepted: we would ICE if
651 /// some tried, for example, to clone an `Option<X<&mut ()>>`.
652 #[instrument(level = "debug", skip(tcx))]
653 fn check_opaque_meets_bounds<'tcx>(
656 substs: SubstsRef<'tcx>,
658 origin: &hir::OpaqueTyOrigin,
660 let hidden_type = tcx.bound_type_of(def_id.to_def_id()).subst(tcx, substs);
662 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
663 let defining_use_anchor = match *origin {
664 hir::OpaqueTyOrigin::FnReturn(did) | hir::OpaqueTyOrigin::AsyncFn(did) => did,
665 hir::OpaqueTyOrigin::TyAlias => def_id,
667 let param_env = tcx.param_env(defining_use_anchor);
669 tcx.infer_ctxt().with_opaque_type_inference(defining_use_anchor).enter(move |infcx| {
670 let inh = Inherited::new(infcx, def_id);
671 let infcx = &inh.infcx;
672 let opaque_ty = tcx.mk_opaque(def_id.to_def_id(), substs);
674 let misc_cause = traits::ObligationCause::misc(span, hir_id);
676 match infcx.at(&misc_cause, param_env).eq(opaque_ty, hidden_type) {
677 Ok(infer_ok) => inh.register_infer_ok_obligations(infer_ok),
679 tcx.sess.delay_span_bug(
681 &format!("could not unify `{hidden_type}` with revealed type:\n{ty_err}"),
686 // Additionally require the hidden type to be well-formed with only the generics of the opaque type.
687 // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
688 // hidden type is well formed even without those bounds.
690 ty::Binder::dummy(ty::PredicateKind::WellFormed(hidden_type.into())).to_predicate(tcx);
691 inh.register_predicate(Obligation::new(misc_cause, param_env, predicate));
693 // Check that all obligations are satisfied by the implementation's
695 let errors = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx);
696 if !errors.is_empty() {
697 infcx.report_fulfillment_errors(&errors, None, false);
701 // Checked when type checking the function containing them.
702 hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) => {}
703 // Can have different predicates to their defining use
704 hir::OpaqueTyOrigin::TyAlias => {
705 // Finally, resolve all regions. This catches wily misuses of
706 // lifetime parameters.
707 let fcx = FnCtxt::new(&inh, param_env, hir_id);
708 fcx.regionck_item(hir_id, span, FxHashSet::default());
712 // Clean up after ourselves
713 let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
717 pub fn check_item_type<'tcx>(tcx: TyCtxt<'tcx>, id: hir::ItemId) {
719 "check_item_type(it.def_id={:?}, it.name={})",
721 tcx.def_path_str(id.def_id.to_def_id())
723 let _indenter = indenter();
724 match tcx.def_kind(id.def_id) {
725 DefKind::Static(..) => {
726 tcx.ensure().typeck(id.def_id);
727 maybe_check_static_with_link_section(tcx, id.def_id, tcx.def_span(id.def_id));
728 check_static_inhabited(tcx, id.def_id, tcx.def_span(id.def_id));
731 tcx.ensure().typeck(id.def_id);
734 let item = tcx.hir().item(id);
735 let hir::ItemKind::Enum(ref enum_definition, _) = item.kind else {
738 check_enum(tcx, item.span, &enum_definition.variants, item.def_id);
740 DefKind::Fn => {} // entirely within check_item_body
742 let it = tcx.hir().item(id);
743 let hir::ItemKind::Impl(ref impl_) = it.kind else {
746 debug!("ItemKind::Impl {} with id {:?}", it.ident, it.def_id);
747 if let Some(impl_trait_ref) = tcx.impl_trait_ref(it.def_id) {
748 check_impl_items_against_trait(
755 check_on_unimplemented(tcx, it);
759 let it = tcx.hir().item(id);
760 let hir::ItemKind::Trait(_, _, _, _, ref items) = it.kind else {
763 check_on_unimplemented(tcx, it);
765 for item in items.iter() {
766 let item = tcx.hir().trait_item(item.id);
768 hir::TraitItemKind::Fn(ref sig, _) => {
769 let abi = sig.header.abi;
770 fn_maybe_err(tcx, item.ident.span, abi);
772 hir::TraitItemKind::Type(.., Some(default)) => {
773 let assoc_item = tcx.associated_item(item.def_id);
775 InternalSubsts::identity_for_item(tcx, it.def_id.to_def_id());
776 let _: Result<_, rustc_errors::ErrorGuaranteed> = check_type_bounds(
781 ty::TraitRef { def_id: it.def_id.to_def_id(), substs: trait_substs },
789 check_struct(tcx, id.def_id, tcx.def_span(id.def_id));
792 check_union(tcx, id.def_id, tcx.def_span(id.def_id));
794 DefKind::OpaqueTy => {
795 let item = tcx.hir().item(id);
796 let hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) = item.kind else {
799 // HACK(jynelson): trying to infer the type of `impl trait` breaks documenting
800 // `async-std` (and `pub async fn` in general).
801 // Since rustdoc doesn't care about the concrete type behind `impl Trait`, just don't look at it!
802 // See https://github.com/rust-lang/rust/issues/75100
803 if !tcx.sess.opts.actually_rustdoc {
804 let substs = InternalSubsts::identity_for_item(tcx, item.def_id.to_def_id());
805 check_opaque(tcx, item.def_id, substs, item.span, &origin);
808 DefKind::TyAlias => {
809 let pty_ty = tcx.type_of(id.def_id);
810 let generics = tcx.generics_of(id.def_id);
811 check_type_params_are_used(tcx, &generics, pty_ty);
813 DefKind::ForeignMod => {
814 let it = tcx.hir().item(id);
815 let hir::ItemKind::ForeignMod { abi, items } = it.kind else {
818 check_abi(tcx, it.hir_id(), it.span, abi);
820 if abi == Abi::RustIntrinsic {
822 let item = tcx.hir().foreign_item(item.id);
823 intrinsic::check_intrinsic_type(tcx, item);
825 } else if abi == Abi::PlatformIntrinsic {
827 let item = tcx.hir().foreign_item(item.id);
828 intrinsic::check_platform_intrinsic_type(tcx, item);
832 let def_id = item.id.def_id;
833 let generics = tcx.generics_of(def_id);
834 let own_counts = generics.own_counts();
835 if generics.params.len() - own_counts.lifetimes != 0 {
836 let (kinds, kinds_pl, egs) = match (own_counts.types, own_counts.consts) {
837 (_, 0) => ("type", "types", Some("u32")),
838 // We don't specify an example value, because we can't generate
839 // a valid value for any type.
840 (0, _) => ("const", "consts", None),
841 _ => ("type or const", "types or consts", None),
847 "foreign items may not have {kinds} parameters",
849 .span_label(item.span, &format!("can't have {kinds} parameters"))
851 // FIXME: once we start storing spans for type arguments, turn this
852 // into a suggestion.
854 "replace the {} parameters with concrete {}{}",
857 egs.map(|egs| format!(" like `{}`", egs)).unwrap_or_default(),
863 let item = tcx.hir().foreign_item(item.id);
865 hir::ForeignItemKind::Fn(ref fn_decl, _, _) => {
866 require_c_abi_if_c_variadic(tcx, fn_decl, abi, item.span);
868 hir::ForeignItemKind::Static(..) => {
869 check_static_inhabited(tcx, def_id, item.span);
876 DefKind::GlobalAsm => {
877 let it = tcx.hir().item(id);
878 let hir::ItemKind::GlobalAsm(asm) = it.kind else { span_bug!(it.span, "DefKind::GlobalAsm but got {:#?}", it) };
879 for_item(tcx, it).with_fcx(|fcx| {
880 fcx.check_asm(asm, it.hir_id());
888 pub(super) fn check_on_unimplemented(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
889 // an error would be reported if this fails.
890 let _ = traits::OnUnimplementedDirective::of_item(tcx, item.def_id.to_def_id());
893 pub(super) fn check_specialization_validity<'tcx>(
895 trait_def: &ty::TraitDef,
896 trait_item: &ty::AssocItem,
898 impl_item: &hir::ImplItemRef,
900 let Ok(ancestors) = trait_def.ancestors(tcx, impl_id) else { return };
901 let mut ancestor_impls = ancestors.skip(1).filter_map(|parent| {
902 if parent.is_from_trait() {
905 Some((parent, parent.item(tcx, trait_item.def_id)))
909 let opt_result = ancestor_impls.find_map(|(parent_impl, parent_item)| {
911 // Parent impl exists, and contains the parent item we're trying to specialize, but
912 // doesn't mark it `default`.
913 Some(parent_item) if traits::impl_item_is_final(tcx, &parent_item) => {
914 Some(Err(parent_impl.def_id()))
917 // Parent impl contains item and makes it specializable.
918 Some(_) => Some(Ok(())),
920 // Parent impl doesn't mention the item. This means it's inherited from the
921 // grandparent. In that case, if parent is a `default impl`, inherited items use the
922 // "defaultness" from the grandparent, else they are final.
924 if tcx.impl_defaultness(parent_impl.def_id()).is_default() {
927 Some(Err(parent_impl.def_id()))
933 // If `opt_result` is `None`, we have only encountered `default impl`s that don't contain the
934 // item. This is allowed, the item isn't actually getting specialized here.
935 let result = opt_result.unwrap_or(Ok(()));
937 if let Err(parent_impl) = result {
938 report_forbidden_specialization(tcx, impl_item, parent_impl);
942 fn check_impl_items_against_trait<'tcx>(
944 full_impl_span: Span,
946 impl_trait_ref: ty::TraitRef<'tcx>,
947 impl_item_refs: &[hir::ImplItemRef],
949 // If the trait reference itself is erroneous (so the compilation is going
950 // to fail), skip checking the items here -- the `impl_item` table in `tcx`
951 // isn't populated for such impls.
952 if impl_trait_ref.references_error() {
956 // Negative impls are not expected to have any items
957 match tcx.impl_polarity(impl_id) {
958 ty::ImplPolarity::Reservation | ty::ImplPolarity::Positive => {}
959 ty::ImplPolarity::Negative => {
960 if let [first_item_ref, ..] = impl_item_refs {
961 let first_item_span = tcx.hir().impl_item(first_item_ref.id).span;
966 "negative impls cannot have any items"
974 let trait_def = tcx.trait_def(impl_trait_ref.def_id);
976 for impl_item in impl_item_refs {
977 let ty_impl_item = tcx.associated_item(impl_item.id.def_id);
978 let ty_trait_item = if let Some(trait_item_id) = ty_impl_item.trait_item_def_id {
979 tcx.associated_item(trait_item_id)
981 // Checked in `associated_item`.
982 tcx.sess.delay_span_bug(impl_item.span, "missing associated item in trait");
985 let impl_item_full = tcx.hir().impl_item(impl_item.id);
986 match impl_item_full.kind {
987 hir::ImplItemKind::Const(..) => {
988 // Find associated const definition.
997 hir::ImplItemKind::Fn(..) => {
998 let opt_trait_span = tcx.hir().span_if_local(ty_trait_item.def_id);
1008 hir::ImplItemKind::TyAlias(impl_ty) => {
1009 let opt_trait_span = tcx.hir().span_if_local(ty_trait_item.def_id);
1021 check_specialization_validity(
1025 impl_id.to_def_id(),
1030 if let Ok(ancestors) = trait_def.ancestors(tcx, impl_id.to_def_id()) {
1031 // Check for missing items from trait
1032 let mut missing_items = Vec::new();
1034 let mut must_implement_one_of: Option<&[Ident]> =
1035 trait_def.must_implement_one_of.as_deref();
1037 for &trait_item_id in tcx.associated_item_def_ids(impl_trait_ref.def_id) {
1038 let is_implemented = ancestors
1039 .leaf_def(tcx, trait_item_id)
1040 .map_or(false, |node_item| node_item.item.defaultness.has_value());
1042 if !is_implemented && tcx.impl_defaultness(impl_id).is_final() {
1043 missing_items.push(tcx.associated_item(trait_item_id));
1046 if let Some(required_items) = &must_implement_one_of {
1047 // true if this item is specifically implemented in this impl
1048 let is_implemented_here = ancestors
1049 .leaf_def(tcx, trait_item_id)
1050 .map_or(false, |node_item| !node_item.defining_node.is_from_trait());
1052 if is_implemented_here {
1053 let trait_item = tcx.associated_item(trait_item_id);
1054 if required_items.contains(&trait_item.ident(tcx)) {
1055 must_implement_one_of = None;
1061 if !missing_items.is_empty() {
1062 let impl_span = tcx.sess.source_map().guess_head_span(full_impl_span);
1063 missing_items_err(tcx, impl_span, &missing_items, full_impl_span);
1066 if let Some(missing_items) = must_implement_one_of {
1067 let impl_span = tcx.sess.source_map().guess_head_span(full_impl_span);
1069 .get_attr(impl_trait_ref.def_id, sym::rustc_must_implement_one_of)
1070 .map(|attr| attr.span);
1072 missing_items_must_implement_one_of_err(tcx, impl_span, missing_items, attr_span);
1077 /// Checks whether a type can be represented in memory. In particular, it
1078 /// identifies types that contain themselves without indirection through a
1079 /// pointer, which would mean their size is unbounded.
1080 pub(super) fn check_representable(tcx: TyCtxt<'_>, sp: Span, item_def_id: LocalDefId) -> bool {
1081 let rty = tcx.type_of(item_def_id);
1083 // Check that it is possible to represent this type. This call identifies
1084 // (1) types that contain themselves and (2) types that contain a different
1085 // recursive type. It is only necessary to throw an error on those that
1086 // contain themselves. For case 2, there must be an inner type that will be
1087 // caught by case 1.
1088 match representability::ty_is_representable(tcx, rty, sp, None) {
1089 Representability::SelfRecursive(spans) => {
1090 recursive_type_with_infinite_size_error(tcx, item_def_id.to_def_id(), spans);
1093 Representability::Representable | Representability::ContainsRecursive => (),
1098 pub fn check_simd(tcx: TyCtxt<'_>, sp: Span, def_id: LocalDefId) {
1099 let t = tcx.type_of(def_id);
1100 if let ty::Adt(def, substs) = t.kind()
1103 let fields = &def.non_enum_variant().fields;
1104 if fields.is_empty() {
1105 struct_span_err!(tcx.sess, sp, E0075, "SIMD vector cannot be empty").emit();
1108 let e = fields[0].ty(tcx, substs);
1109 if !fields.iter().all(|f| f.ty(tcx, substs) == e) {
1110 struct_span_err!(tcx.sess, sp, E0076, "SIMD vector should be homogeneous")
1111 .span_label(sp, "SIMD elements must have the same type")
1116 let len = if let ty::Array(_ty, c) = e.kind() {
1117 c.try_eval_usize(tcx, tcx.param_env(def.did()))
1119 Some(fields.len() as u64)
1121 if let Some(len) = len {
1123 struct_span_err!(tcx.sess, sp, E0075, "SIMD vector cannot be empty").emit();
1125 } else if len > MAX_SIMD_LANES {
1130 "SIMD vector cannot have more than {MAX_SIMD_LANES} elements",
1137 // Check that we use types valid for use in the lanes of a SIMD "vector register"
1138 // These are scalar types which directly match a "machine" type
1139 // Yes: Integers, floats, "thin" pointers
1140 // No: char, "fat" pointers, compound types
1142 ty::Param(_) => (), // pass struct<T>(T, T, T, T) through, let monomorphization catch errors
1143 ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::RawPtr(_) => (), // struct(u8, u8, u8, u8) is ok
1144 ty::Array(t, _) if matches!(t.kind(), ty::Param(_)) => (), // pass struct<T>([T; N]) through, let monomorphization catch errors
1148 ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::RawPtr(_)
1150 { /* struct([f32; 4]) is ok */ }
1156 "SIMD vector element type should be a \
1157 primitive scalar (integer/float/pointer) type"
1166 pub(super) fn check_packed(tcx: TyCtxt<'_>, sp: Span, def: ty::AdtDef<'_>) {
1167 let repr = def.repr();
1169 for attr in tcx.get_attrs(def.did(), sym::repr) {
1170 for r in attr::parse_repr_attr(&tcx.sess, attr) {
1171 if let attr::ReprPacked(pack) = r
1172 && let Some(repr_pack) = repr.pack
1173 && pack as u64 != repr_pack.bytes()
1179 "type has conflicting packed representation hints"
1185 if repr.align.is_some() {
1190 "type has conflicting packed and align representation hints"
1194 if let Some(def_spans) = check_packed_inner(tcx, def.did(), &mut vec![]) {
1195 let mut err = struct_span_err!(
1199 "packed type cannot transitively contain a `#[repr(align)]` type"
1203 tcx.def_span(def_spans[0].0),
1205 "`{}` has a `#[repr(align)]` attribute",
1206 tcx.item_name(def_spans[0].0)
1210 if def_spans.len() > 2 {
1211 let mut first = true;
1212 for (adt_def, span) in def_spans.iter().skip(1).rev() {
1213 let ident = tcx.item_name(*adt_def);
1218 "`{}` contains a field of type `{}`",
1219 tcx.type_of(def.did()),
1223 format!("...which contains a field of type `{ident}`")
1236 pub(super) fn check_packed_inner(
1239 stack: &mut Vec<DefId>,
1240 ) -> Option<Vec<(DefId, Span)>> {
1241 if let ty::Adt(def, substs) = tcx.type_of(def_id).kind() {
1242 if def.is_struct() || def.is_union() {
1243 if def.repr().align.is_some() {
1244 return Some(vec![(def.did(), DUMMY_SP)]);
1248 for field in &def.non_enum_variant().fields {
1249 if let ty::Adt(def, _) = field.ty(tcx, substs).kind()
1250 && !stack.contains(&def.did())
1251 && let Some(mut defs) = check_packed_inner(tcx, def.did(), stack)
1253 defs.push((def.did(), field.ident(tcx).span));
1264 pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, sp: Span, adt: ty::AdtDef<'tcx>) {
1265 if !adt.repr().transparent() {
1268 let sp = tcx.sess.source_map().guess_head_span(sp);
1270 if adt.is_union() && !tcx.features().transparent_unions {
1272 &tcx.sess.parse_sess,
1273 sym::transparent_unions,
1275 "transparent unions are unstable",
1280 if adt.variants().len() != 1 {
1281 bad_variant_count(tcx, adt, sp, adt.did());
1282 if adt.variants().is_empty() {
1283 // Don't bother checking the fields. No variants (and thus no fields) exist.
1288 // For each field, figure out if it's known to be a ZST and align(1)
1289 let field_infos = adt.all_fields().map(|field| {
1290 let ty = field.ty(tcx, InternalSubsts::identity_for_item(tcx, field.did));
1291 let param_env = tcx.param_env(field.did);
1292 let layout = tcx.layout_of(param_env.and(ty));
1293 // We are currently checking the type this field came from, so it must be local
1294 let span = tcx.hir().span_if_local(field.did).unwrap();
1295 let zst = layout.map_or(false, |layout| layout.is_zst());
1296 let align1 = layout.map_or(false, |layout| layout.align.abi.bytes() == 1);
1300 let non_zst_fields =
1301 field_infos.clone().filter_map(|(span, zst, _align1)| if !zst { Some(span) } else { None });
1302 let non_zst_count = non_zst_fields.clone().count();
1303 if non_zst_count >= 2 {
1304 bad_non_zero_sized_fields(tcx, adt, non_zst_count, non_zst_fields, sp);
1306 for (span, zst, align1) in field_infos {
1312 "zero-sized field in transparent {} has alignment larger than 1",
1315 .span_label(span, "has alignment larger than 1")
1321 #[allow(trivial_numeric_casts)]
1322 fn check_enum<'tcx>(
1325 vs: &'tcx [hir::Variant<'tcx>],
1328 let def = tcx.adt_def(def_id);
1329 def.destructor(tcx); // force the destructor to be evaluated
1332 if let Some(attr) = tcx.get_attr(def_id.to_def_id(), sym::repr) {
1337 "unsupported representation for zero-variant enum"
1339 .span_label(sp, "zero-variant enum")
1344 let repr_type_ty = def.repr().discr_type().to_ty(tcx);
1345 if repr_type_ty == tcx.types.i128 || repr_type_ty == tcx.types.u128 {
1346 if !tcx.features().repr128 {
1348 &tcx.sess.parse_sess,
1351 "repr with 128-bit type is unstable",
1358 if let Some(ref e) = v.disr_expr {
1359 tcx.ensure().typeck(tcx.hir().local_def_id(e.hir_id));
1363 if tcx.adt_def(def_id).repr().int.is_none() && tcx.features().arbitrary_enum_discriminant {
1364 let is_unit = |var: &hir::Variant<'_>| matches!(var.data, hir::VariantData::Unit(..));
1366 let has_disr = |var: &hir::Variant<'_>| var.disr_expr.is_some();
1367 let has_non_units = vs.iter().any(|var| !is_unit(var));
1368 let disr_units = vs.iter().any(|var| is_unit(&var) && has_disr(&var));
1369 let disr_non_unit = vs.iter().any(|var| !is_unit(&var) && has_disr(&var));
1371 if disr_non_unit || (disr_units && has_non_units) {
1373 struct_span_err!(tcx.sess, sp, E0732, "`#[repr(inttype)]` must be specified");
1378 let mut disr_vals: Vec<Discr<'tcx>> = Vec::with_capacity(vs.len());
1379 // This tracks the previous variant span (in the loop) incase we need it for diagnostics
1380 let mut prev_variant_span: Span = DUMMY_SP;
1381 for ((_, discr), v) in iter::zip(def.discriminants(tcx), vs) {
1382 // Check for duplicate discriminant values
1383 if let Some(i) = disr_vals.iter().position(|&x| x.val == discr.val) {
1384 let variant_did = def.variant(VariantIdx::new(i)).def_id;
1385 let variant_i_hir_id = tcx.hir().local_def_id_to_hir_id(variant_did.expect_local());
1386 let variant_i = tcx.hir().expect_variant(variant_i_hir_id);
1387 let i_span = match variant_i.disr_expr {
1388 Some(ref expr) => tcx.hir().span(expr.hir_id),
1389 None => tcx.def_span(variant_did),
1391 let span = match v.disr_expr {
1392 Some(ref expr) => tcx.hir().span(expr.hir_id),
1395 let display_discr = format_discriminant_overflow(tcx, v, discr);
1396 let display_discr_i = format_discriminant_overflow(tcx, variant_i, disr_vals[i]);
1397 let no_disr = v.disr_expr.is_none();
1398 let mut err = struct_span_err!(
1402 "discriminant value `{}` assigned more than once",
1406 err.span_label(i_span, format!("first assignment of {display_discr_i}"));
1407 err.span_label(span, format!("second assignment of {display_discr}"));
1413 "assigned discriminant for `{}` was incremented from this discriminant",
1421 disr_vals.push(discr);
1422 prev_variant_span = v.span;
1425 check_representable(tcx, sp, def_id);
1426 check_transparent(tcx, sp, def);
1429 /// In the case that a discriminant is both a duplicate and an overflowing literal,
1430 /// we insert both the assigned discriminant and the literal it overflowed from into the formatted
1431 /// output. Otherwise we format the discriminant normally.
1432 fn format_discriminant_overflow<'tcx>(
1434 variant: &hir::Variant<'_>,
1437 if let Some(expr) = &variant.disr_expr {
1438 let body = &tcx.hir().body(expr.body).value;
1439 if let hir::ExprKind::Lit(lit) = &body.kind
1440 && let rustc_ast::LitKind::Int(lit_value, _int_kind) = &lit.node
1441 && dis.val != *lit_value
1443 return format!("`{dis}` (overflowed from `{lit_value}`)");
1450 pub(super) fn check_type_params_are_used<'tcx>(
1452 generics: &ty::Generics,
1455 debug!("check_type_params_are_used(generics={:?}, ty={:?})", generics, ty);
1457 assert_eq!(generics.parent, None);
1459 if generics.own_counts().types == 0 {
1463 let mut params_used = BitSet::new_empty(generics.params.len());
1465 if ty.references_error() {
1466 // If there is already another error, do not emit
1467 // an error for not using a type parameter.
1468 assert!(tcx.sess.has_errors().is_some());
1472 for leaf in ty.walk() {
1473 if let GenericArgKind::Type(leaf_ty) = leaf.unpack()
1474 && let ty::Param(param) = leaf_ty.kind()
1476 debug!("found use of ty param {:?}", param);
1477 params_used.insert(param.index);
1481 for param in &generics.params {
1482 if !params_used.contains(param.index)
1483 && let ty::GenericParamDefKind::Type { .. } = param.kind
1485 let span = tcx.def_span(param.def_id);
1490 "type parameter `{}` is unused",
1493 .span_label(span, "unused type parameter")
1499 pub(super) fn check_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
1500 let module = tcx.hir_module_items(module_def_id);
1501 for id in module.items() {
1502 check_item_type(tcx, id);
1506 pub(super) use wfcheck::check_item_well_formed;
1508 pub(super) use wfcheck::check_trait_item as check_trait_item_well_formed;
1510 pub(super) use wfcheck::check_impl_item as check_impl_item_well_formed;
1512 fn async_opaque_type_cycle_error(tcx: TyCtxt<'_>, span: Span) -> ErrorGuaranteed {
1513 struct_span_err!(tcx.sess, span, E0733, "recursion in an `async fn` requires boxing")
1514 .span_label(span, "recursive `async fn`")
1515 .note("a recursive `async fn` must be rewritten to return a boxed `dyn Future`")
1517 "consider using the `async_recursion` crate: https://crates.io/crates/async_recursion",
1522 /// Emit an error for recursive opaque types.
1524 /// If this is a return `impl Trait`, find the item's return expressions and point at them. For
1525 /// direct recursion this is enough, but for indirect recursion also point at the last intermediary
1528 /// If all the return expressions evaluate to `!`, then we explain that the error will go away
1529 /// after changing it. This can happen when a user uses `panic!()` or similar as a placeholder.
1530 fn opaque_type_cycle_error(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) -> ErrorGuaranteed {
1531 let mut err = struct_span_err!(tcx.sess, span, E0720, "cannot resolve opaque type");
1533 let mut label = false;
1534 if let Some((def_id, visitor)) = get_owner_return_paths(tcx, def_id) {
1535 let typeck_results = tcx.typeck(def_id);
1539 .filter_map(|expr| typeck_results.node_type_opt(expr.hir_id))
1540 .all(|ty| matches!(ty.kind(), ty::Never))
1545 .filter(|expr| typeck_results.node_type_opt(expr.hir_id).is_some())
1546 .map(|expr| expr.span)
1547 .collect::<Vec<Span>>();
1548 let span_len = spans.len();
1550 err.span_label(spans[0], "this returned value is of `!` type");
1552 let mut multispan: MultiSpan = spans.clone().into();
1555 .push_span_label(span, "this returned value is of `!` type".to_string());
1557 err.span_note(multispan, "these returned values have a concrete \"never\" type");
1559 err.help("this error will resolve once the item's body returns a concrete type");
1561 let mut seen = FxHashSet::default();
1563 err.span_label(span, "recursive opaque type");
1565 for (sp, ty) in visitor
1568 .filter_map(|e| typeck_results.node_type_opt(e.hir_id).map(|t| (e.span, t)))
1569 .filter(|(_, ty)| !matches!(ty.kind(), ty::Never))
1571 struct OpaqueTypeCollector(Vec<DefId>);
1572 impl<'tcx> ty::fold::TypeVisitor<'tcx> for OpaqueTypeCollector {
1573 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1575 ty::Opaque(def, _) => {
1577 ControlFlow::CONTINUE
1579 _ => t.super_visit_with(self),
1583 let mut visitor = OpaqueTypeCollector(vec![]);
1584 ty.visit_with(&mut visitor);
1585 for def_id in visitor.0 {
1586 let ty_span = tcx.def_span(def_id);
1587 if !seen.contains(&ty_span) {
1588 err.span_label(ty_span, &format!("returning this opaque type `{ty}`"));
1589 seen.insert(ty_span);
1591 err.span_label(sp, &format!("returning here with type `{ty}`"));
1597 err.span_label(span, "cannot resolve opaque type");