1 //! Error Reporting for static impl Traits.
4 ButCallingIntroduces, ButNeedsToSatisfy, DynTraitConstraintSuggestion, MoreTargeted,
5 ReqIntroducedLocations,
7 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
8 use crate::infer::lexical_region_resolve::RegionResolutionError;
9 use crate::infer::{SubregionOrigin, TypeTrace};
10 use crate::traits::{ObligationCauseCode, UnifyReceiverContext};
11 use rustc_data_structures::fx::FxIndexSet;
12 use rustc_errors::{AddToDiagnostic, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan};
13 use rustc_hir::def_id::DefId;
14 use rustc_hir::intravisit::{walk_ty, Visitor};
16 self as hir, GenericBound, GenericParamKind, Item, ItemKind, Lifetime, LifetimeName, Node,
19 use rustc_middle::ty::{
20 self, AssocItemContainer, StaticLifetimeVisitor, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
22 use rustc_span::symbol::Ident;
25 use rustc_span::def_id::LocalDefId;
26 use std::ops::ControlFlow;
28 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
29 /// Print the error message for lifetime errors when the return type is a static `impl Trait`,
30 /// `dyn Trait` or if a method call on a trait object introduces a static requirement.
31 pub(super) fn try_report_static_impl_trait(&self) -> Option<ErrorGuaranteed> {
32 debug!("try_report_static_impl_trait(error={:?})", self.error);
34 let (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans) = match self.error.as_ref()? {
35 RegionResolutionError::SubSupConflict(
43 ) if sub_r.is_static() => (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans),
44 RegionResolutionError::ConcreteFailure(
45 SubregionOrigin::Subtype(box TypeTrace { cause, .. }),
48 ) if sub_r.is_static() => {
49 // This is for an implicit `'static` requirement coming from `impl dyn Trait {}`.
50 if let ObligationCauseCode::UnifyReceiver(ctxt) = cause.code() {
51 // This may have a closure and it would cause ICE
52 // through `find_param_with_region` (#78262).
53 let anon_reg_sup = tcx.is_suitable_region(*sup_r)?;
54 let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);
55 if fn_returns.is_empty() {
59 let param = self.find_param_with_region(*sup_r, *sub_r)?;
60 let simple_ident = param.param.pat.simple_ident();
62 let (has_impl_path, impl_path) = match ctxt.assoc_item.container {
63 AssocItemContainer::TraitContainer => {
64 let id = ctxt.assoc_item.container_id(tcx);
65 (true, tcx.def_path_str(id))
67 AssocItemContainer::ImplContainer => (false, String::new()),
70 let mut err = self.tcx().sess.create_err(ButCallingIntroduces {
71 param_ty_span: param.param_ty_span,
72 cause_span: cause.span,
73 has_param_name: simple_ident.is_some(),
74 param_name: simple_ident.map(|x| x.to_string()).unwrap_or_default(),
75 has_lifetime: sup_r.has_name(),
76 lifetime: sup_r.to_string(),
77 assoc_item: ctxt.assoc_item.name,
81 if self.find_impl_on_dyn_trait(&mut err, param.param_ty, &ctxt) {
82 let reported = err.emit();
83 return Some(reported);
93 "try_report_static_impl_trait(var={:?}, sub={:?} {:?} sup={:?} {:?})",
94 var_origin, sub_origin, sub_r, sup_origin, sup_r
96 let anon_reg_sup = tcx.is_suitable_region(*sup_r)?;
97 debug!("try_report_static_impl_trait: anon_reg_sup={:?}", anon_reg_sup);
98 let sp = var_origin.span();
99 let return_sp = sub_origin.span();
100 let param = self.find_param_with_region(*sup_r, *sub_r)?;
101 let lifetime_name = if sup_r.has_name() { sup_r.to_string() } else { "'_".to_owned() };
103 let (mention_influencer, influencer_point) =
104 if sup_origin.span().overlaps(param.param_ty_span) {
105 // Account for `async fn` like in `async-await/issues/issue-62097.rs`.
106 // The desugaring of `async `fn`s causes `sup_origin` and `param` to point at the same
107 // place (but with different `ctxt`, hence `overlaps` instead of `==` above).
109 // This avoids the following:
111 // LL | pub async fn run_dummy_fn(&self) {
114 // | this data with an anonymous lifetime `'_`...
115 // | ...is captured here...
116 (false, sup_origin.span())
118 (!sup_origin.span().overlaps(return_sp), param.param_ty_span)
121 debug!("try_report_static_impl_trait: param_info={:?}", param);
123 let mut spans = spans.clone();
125 if mention_influencer {
126 spans.push(sup_origin.span());
128 // We dedup the spans *ignoring* expansion context.
130 spans.dedup_by_key(|span| (span.lo(), span.hi()));
132 // We try to make the output have fewer overlapping spans if possible.
134 if sup_origin.span().overlaps(return_sp) { sup_origin.span() } else { return_sp };
136 let spans_empty = spans.is_empty();
137 let require_as_note = spans.iter().any(|sp| sp.overlaps(return_sp) || *sp > return_sp);
138 let bound = if let SubregionOrigin::RelateParamBound(_, _, Some(bound)) = sub_origin {
144 let mut subdiag = None;
146 if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = sub_origin {
147 if let ObligationCauseCode::ReturnValue(hir_id)
148 | ObligationCauseCode::BlockTailExpression(hir_id) = cause.code()
150 let parent_id = tcx.hir().get_parent_item(*hir_id);
151 if let Some(fn_decl) = tcx.hir().fn_decl_by_hir_id(parent_id.into()) {
152 let mut span: MultiSpan = fn_decl.output.span().into();
153 let mut spans = Vec::new();
154 let mut add_label = true;
155 if let hir::FnRetTy::Return(ty) = fn_decl.output {
156 let mut v = StaticLifetimeVisitor(vec![], tcx.hir());
159 span = v.0.clone().into();
164 let fn_decl_span = fn_decl.output.span();
166 subdiag = Some(ReqIntroducedLocations {
170 cause_span: cause.span,
177 let diag = ButNeedsToSatisfy {
180 spans: spans.clone(),
181 // If any of the "captured here" labels appears on the same line or after
182 // `require_span`, we put it on a note to ensure the text flows by appearing
183 // always at the end.
184 require_span_as_note: require_as_note.then_some(require_span),
185 // We don't need a note, it's already at the end, it can be shown as a `span_label`.
186 require_span_as_label: (!require_as_note).then_some(require_span),
187 req_introduces_loc: subdiag,
189 has_lifetime: sup_r.has_name(),
190 lifetime: sup_r.to_string(),
195 let mut err = self.tcx().sess.create_err(diag);
197 let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);
199 let mut override_error_code = None;
200 if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = &sup_origin
201 && let ObligationCauseCode::UnifyReceiver(ctxt) = cause.code()
202 // Handle case of `impl Foo for dyn Bar { fn qux(&self) {} }` introducing a
203 // `'static` lifetime when called as a method on a binding: `bar.qux()`.
204 && self.find_impl_on_dyn_trait(&mut err, param.param_ty, &ctxt)
206 override_error_code = Some(ctxt.assoc_item.name);
209 if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = &sub_origin
210 && let code = match cause.code() {
211 ObligationCauseCode::MatchImpl(parent, ..) => parent.code(),
214 && let (&ObligationCauseCode::ItemObligation(item_def_id) | &ObligationCauseCode::ExprItemObligation(item_def_id, ..), None) = (code, override_error_code)
216 // Same case of `impl Foo for dyn Bar { fn qux(&self) {} }` introducing a `'static`
217 // lifetime as above, but called using a fully-qualified path to the method:
219 let mut v = TraitObjectVisitor(FxIndexSet::default());
220 v.visit_ty(param.param_ty);
221 if let Some((ident, self_ty)) =
222 NiceRegionError::get_impl_ident_and_self_ty_from_trait(tcx, item_def_id, &v.0)
223 && self.suggest_constrain_dyn_trait_in_impl(&mut err, &v.0, ident, self_ty)
225 override_error_code = Some(ident.name);
228 if let (Some(ident), true) = (override_error_code, fn_returns.is_empty()) {
229 // Provide a more targeted error code and description.
230 let retarget_subdiag = MoreTargeted { ident };
231 retarget_subdiag.add_to_diagnostic(&mut err);
234 let arg = match param.param.pat.simple_ident() {
235 Some(simple_ident) => format!("argument `{}`", simple_ident),
236 None => "the argument".to_string(),
238 let captures = format!("captures data from {}", arg);
239 suggest_new_region_bound(
246 Some((param.param_ty_span, param.param_ty.to_string())),
247 Some(anon_reg_sup.def_id),
250 let reported = err.emit();
255 pub fn suggest_new_region_bound(
257 err: &mut Diagnostic,
258 fn_returns: Vec<&rustc_hir::Ty<'_>>,
259 lifetime_name: String,
262 param: Option<(Span, String)>,
263 scope_def_id: Option<LocalDefId>,
265 debug!("try_report_static_impl_trait: fn_return={:?}", fn_returns);
266 // FIXME: account for the need of parens in `&(dyn Trait + '_)`
267 let consider = "consider changing";
268 let declare = "to declare that";
269 let explicit = format!("you can add an explicit `{}` lifetime bound", lifetime_name);
270 let explicit_static =
271 arg.map(|arg| format!("explicit `'static` bound to the lifetime of {}", arg));
272 let add_static_bound = "alternatively, add an explicit `'static` bound to this reference";
273 let plus_lt = format!(" + {}", lifetime_name);
274 for fn_return in fn_returns {
275 if fn_return.span.desugaring_kind().is_some() {
276 // Skip `async` desugaring `impl Future`.
279 match fn_return.kind {
280 TyKind::OpaqueDef(item_id, _, _) => {
281 let item = tcx.hir().item(item_id);
282 let ItemKind::OpaqueTy(opaque) = &item.kind else {
286 // Get the identity type for this RPIT
287 let did = item_id.owner_id.to_def_id();
288 let ty = tcx.mk_opaque(did, ty::InternalSubsts::identity_for_item(tcx, did));
290 if let Some(span) = opaque.bounds.iter().find_map(|arg| match arg {
291 GenericBound::Outlives(Lifetime {
292 res: LifetimeName::Static, ident, ..
293 }) => Some(ident.span),
296 if let Some(explicit_static) = &explicit_static {
297 err.span_suggestion_verbose(
299 &format!("{consider} `{ty}`'s {explicit_static}"),
301 Applicability::MaybeIncorrect,
304 if let Some((param_span, ref param_ty)) = param {
305 err.span_suggestion_verbose(
309 Applicability::MaybeIncorrect,
312 } else if opaque.bounds.iter().any(|arg| match arg {
313 GenericBound::Outlives(Lifetime { ident, .. })
314 if ident.name.to_string() == lifetime_name =>
321 // get a lifetime name of existing named lifetimes if any
322 let existing_lt_name = if let Some(id) = scope_def_id
323 && let Some(generics) = tcx.hir().get_generics(id)
324 && let named_lifetimes = generics
327 .filter(|p| matches!(p.kind, GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit }))
328 .map(|p| { if let hir::ParamName::Plain(name) = p.name {Some(name.to_string())} else {None}})
329 .filter(|n| ! matches!(n, None))
331 && named_lifetimes.len() > 0 {
332 named_lifetimes[0].clone()
336 let name = if let Some(name) = &existing_lt_name {
341 // if there are more than one elided lifetimes in inputs, the explicit `'_` lifetime cannot be used.
342 // introducing a new lifetime `'a` or making use of one from existing named lifetimes if any
343 if let Some(id) = scope_def_id
344 && let Some(generics) = tcx.hir().get_generics(id)
345 && let mut spans_suggs = generics
348 .filter(|p| p.is_elided_lifetime())
350 if p.span.hi() - p.span.lo() == rustc_span::BytePos(1) { // Ampersand (elided without '_)
351 (p.span.shrink_to_hi(),format!("{name} "))
352 } else { // Underscore (elided with '_)
353 (p.span, format!("{name}"))
357 && spans_suggs.len() > 1
360 if existing_lt_name == None {
361 spans_suggs.push((generics.span.shrink_to_hi(), format!("<{name}>")));
362 format!("you can introduce a named lifetime parameter `{name}`")
364 // make use the existing named lifetime
365 format!("you can use the named lifetime parameter `{name}`")
368 .push((fn_return.span.shrink_to_hi(), format!(" + {name} ")));
369 err.multipart_suggestion_verbose(
371 "{declare} `{ty}` {captures}, {use_lt}",
374 Applicability::MaybeIncorrect,
377 err.span_suggestion_verbose(
378 fn_return.span.shrink_to_hi(),
379 &format!("{declare} `{ty}` {captures}, {explicit}",),
381 Applicability::MaybeIncorrect,
386 TyKind::TraitObject(_, lt, _) => {
387 if let LifetimeName::ImplicitObjectLifetimeDefault = lt.res {
388 err.span_suggestion_verbose(
389 fn_return.span.shrink_to_hi(),
391 "{declare} the trait object {captures}, {explicit}",
397 Applicability::MaybeIncorrect,
399 } else if lt.ident.name.to_string() != lifetime_name {
400 // With this check we avoid suggesting redundant bounds. This
401 // would happen if there are nested impl/dyn traits and only
402 // one of them has the bound we'd suggest already there, like
403 // in `impl Foo<X = dyn Bar> + '_`.
404 if let Some(explicit_static) = &explicit_static {
405 err.span_suggestion_verbose(
407 &format!("{} the trait object's {}", consider, explicit_static),
409 Applicability::MaybeIncorrect,
412 if let Some((param_span, param_ty)) = param.clone() {
413 err.span_suggestion_verbose(
417 Applicability::MaybeIncorrect,
427 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
428 pub fn get_impl_ident_and_self_ty_from_trait(
431 trait_objects: &FxIndexSet<DefId>,
432 ) -> Option<(Ident, &'tcx hir::Ty<'tcx>)> {
433 match tcx.hir().get_if_local(def_id)? {
434 Node::ImplItem(impl_item) => {
435 let impl_did = tcx.hir().get_parent_item(impl_item.hir_id());
436 if let hir::OwnerNode::Item(Item {
437 kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
439 }) = tcx.hir().owner(impl_did)
441 Some((impl_item.ident, self_ty))
446 Node::TraitItem(trait_item) => {
447 let trait_id = tcx.hir().get_parent_item(trait_item.hir_id());
448 debug_assert_eq!(tcx.def_kind(trait_id.def_id), hir::def::DefKind::Trait);
449 // The method being called is defined in the `trait`, but the `'static`
450 // obligation comes from the `impl`. Find that `impl` so that we can point
451 // at it in the suggestion.
452 let trait_did = trait_id.to_def_id();
453 tcx.hir().trait_impls(trait_did).iter().find_map(|&impl_did| {
454 if let Node::Item(Item {
455 kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
457 }) = tcx.hir().find_by_def_id(impl_did)?
458 && trait_objects.iter().all(|did| {
459 // FIXME: we should check `self_ty` against the receiver
460 // type in the `UnifyReceiver` context, but for now, use
461 // this imperfect proxy. This will fail if there are
462 // multiple `impl`s for the same trait like
463 // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
464 // In that case, only the first one will get suggestions.
465 let mut traits = vec![];
466 let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
467 hir_v.visit_ty(self_ty);
471 Some((trait_item.ident, *self_ty))
481 /// When we call a method coming from an `impl Foo for dyn Bar`, `dyn Bar` introduces a default
482 /// `'static` obligation. Suggest relaxing that implicit bound.
483 fn find_impl_on_dyn_trait(
485 err: &mut Diagnostic,
487 ctxt: &UnifyReceiverContext<'tcx>,
489 let tcx = self.tcx();
491 // Find the method being called.
492 let Ok(Some(instance)) = ty::Instance::resolve(
495 ctxt.assoc_item.def_id,
496 self.cx.resolve_vars_if_possible(ctxt.substs),
501 let mut v = TraitObjectVisitor(FxIndexSet::default());
504 // Get the `Ident` of the method being called and the corresponding `impl` (to point at
505 // `Bar` in `impl Foo for dyn Bar {}` and the definition of the method being called).
506 let Some((ident, self_ty)) = NiceRegionError::get_impl_ident_and_self_ty_from_trait(tcx, instance.def_id(), &v.0) else {
510 // Find the trait object types in the argument, so we point at *only* the trait object.
511 self.suggest_constrain_dyn_trait_in_impl(err, &v.0, ident, self_ty)
514 fn suggest_constrain_dyn_trait_in_impl(
516 err: &mut Diagnostic,
517 found_dids: &FxIndexSet<DefId>,
519 self_ty: &hir::Ty<'_>,
521 let mut suggested = false;
522 for found_did in found_dids {
523 let mut traits = vec![];
524 let mut hir_v = HirTraitObjectVisitor(&mut traits, *found_did);
525 hir_v.visit_ty(&self_ty);
526 for &span in &traits {
527 let subdiag = DynTraitConstraintSuggestion { span, ident };
528 subdiag.add_to_diagnostic(err);
536 /// Collect all the trait objects in a type that could have received an implicit `'static` lifetime.
537 pub struct TraitObjectVisitor(pub FxIndexSet<DefId>);
539 impl<'tcx> TypeVisitor<'tcx> for TraitObjectVisitor {
540 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
542 ty::Dynamic(preds, re, _) if re.is_static() => {
543 if let Some(def_id) = preds.principal_def_id() {
544 self.0.insert(def_id);
546 ControlFlow::Continue(())
548 _ => t.super_visit_with(self),
553 /// Collect all `hir::Ty<'_>` `Span`s for trait objects with an implicit lifetime.
554 pub struct HirTraitObjectVisitor<'a>(pub &'a mut Vec<Span>, pub DefId);
556 impl<'a, 'tcx> Visitor<'tcx> for HirTraitObjectVisitor<'a> {
557 fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx>) {
558 if let TyKind::TraitObject(
560 Lifetime { res: LifetimeName::ImplicitObjectLifetimeDefault, .. },
564 for ptr in poly_trait_refs {
565 if Some(self.1) == ptr.trait_ref.trait_def_id() {
566 self.0.push(ptr.span);