compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs

   1 //! Error Reporting for static impl Traits.
   2
   3 use crate::errors::{
   4     ButCallingIntroduces, ButNeedsToSatisfy, DynTraitConstraintSuggestion, MoreTargeted,
   5     ReqIntroducedLocations,
   6 };
   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};
  15 use rustc_hir::{
  16     self as hir, GenericBound, GenericParamKind, Item, ItemKind, Lifetime, LifetimeName, Node,
  17     TyKind,
  18 };
  19 use rustc_middle::ty::{
  20     self, AssocItemContainer, StaticLifetimeVisitor, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
  21 };
  22 use rustc_span::symbol::Ident;
  23 use rustc_span::Span;
  24
  25 use rustc_span::def_id::LocalDefId;
  26 use std::ops::ControlFlow;
  27
  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);
  33         let tcx = self.tcx();
  34         let (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans) = match self.error.as_ref()? {
  35             RegionResolutionError::SubSupConflict(
  36                 _,
  37                 var_origin,
  38                 sub_origin,
  39                 sub_r,
  40                 sup_origin,
  41                 sup_r,
  42                 spans,
  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, .. }),
  46                 sub_r,
  47                 sup_r,
  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() {
  56                         return None;
  57                     }
  58
  59                     let param = self.find_param_with_region(*sup_r, *sub_r)?;
  60                     let simple_ident = param.param.pat.simple_ident();
  61
  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))
  66                         }
  67                         AssocItemContainer::ImplContainer => (false, String::new()),
  68                     };
  69
  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,
  78                         has_impl_path,
  79                         impl_path,
  80                     });
  81                     if self.find_impl_on_dyn_trait(&mut err, param.param_ty, &ctxt) {
  82                         let reported = err.emit();
  83                         return Some(reported);
  84                     } else {
  85                         err.cancel()
  86                     }
  87                 }
  88                 return None;
  89             }
  90             _ => return None,
  91         };
  92         debug!(
  93             "try_report_static_impl_trait(var={:?}, sub={:?} {:?} sup={:?} {:?})",
  94             var_origin, sub_origin, sub_r, sup_origin, sup_r
  95         );
  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() };
 102
 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).
 108                 //
 109                 // This avoids the following:
 110                 //
 111                 // LL |     pub async fn run_dummy_fn(&self) {
 112                 //    |                               ^^^^^
 113                 //    |                               |
 114                 //    |                               this data with an anonymous lifetime `'_`...
 115                 //    |                               ...is captured here...
 116                 (false, sup_origin.span())
 117             } else {
 118                 (!sup_origin.span().overlaps(return_sp), param.param_ty_span)
 119             };
 120
 121         debug!("try_report_static_impl_trait: param_info={:?}", param);
 122
 123         let mut spans = spans.clone();
 124
 125         if mention_influencer {
 126             spans.push(sup_origin.span());
 127         }
 128         // We dedup the spans *ignoring* expansion context.
 129         spans.sort();
 130         spans.dedup_by_key(|span| (span.lo(), span.hi()));
 131
 132         // We try to make the output have fewer overlapping spans if possible.
 133         let require_span =
 134             if sup_origin.span().overlaps(return_sp) { sup_origin.span() } else { return_sp };
 135
 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 {
 139             Some(*bound)
 140         } else {
 141             None
 142         };
 143
 144         let mut subdiag = None;
 145
 146         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = sub_origin {
 147             if let ObligationCauseCode::ReturnValue(hir_id)
 148             | ObligationCauseCode::BlockTailExpression(hir_id) = cause.code()
 149             {
 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());
 157                         v.visit_ty(ty);
 158                         if !v.0.is_empty() {
 159                             span = v.0.clone().into();
 160                             spans = v.0;
 161                             add_label = false;
 162                         }
 163                     }
 164                     let fn_decl_span = fn_decl.output.span();
 165
 166                     subdiag = Some(ReqIntroducedLocations {
 167                         span,
 168                         spans,
 169                         fn_decl_span,
 170                         cause_span: cause.span,
 171                         add_label,
 172                     });
 173                 }
 174             }
 175         }
 176
 177         let diag = ButNeedsToSatisfy {
 178             sp,
 179             influencer_point,
 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,
 188
 189             has_lifetime: sup_r.has_name(),
 190             lifetime: sup_r.to_string(),
 191             spans_empty,
 192             bound,
 193         };
 194
 195         let mut err = self.tcx().sess.create_err(diag);
 196
 197         let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);
 198
 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)
 205         {
 206             override_error_code = Some(ctxt.assoc_item.name);
 207         }
 208
 209         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = &sub_origin
 210             && let code = match cause.code() {
 211                 ObligationCauseCode::MatchImpl(parent, ..) => parent.code(),
 212                 _ => cause.code(),
 213             }
 214             && let (&ObligationCauseCode::ItemObligation(item_def_id) | &ObligationCauseCode::ExprItemObligation(item_def_id, ..), None) = (code, override_error_code)
 215         {
 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:
 218             // `Foo::qux(bar)`.
 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)
 224             {
 225                 override_error_code = Some(ident.name);
 226             }
 227         }
 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);
 232         }
 233
 234         let arg = match param.param.pat.simple_ident() {
 235             Some(simple_ident) => format!("argument `{}`", simple_ident),
 236             None => "the argument".to_string(),
 237         };
 238         let captures = format!("captures data from {}", arg);
 239         suggest_new_region_bound(
 240             tcx,
 241             &mut err,
 242             fn_returns,
 243             lifetime_name,
 244             Some(arg),
 245             captures,
 246             Some((param.param_ty_span, param.param_ty.to_string())),
 247             Some(anon_reg_sup.def_id),
 248         );
 249
 250         let reported = err.emit();
 251         Some(reported)
 252     }
 253 }
 254
 255 pub fn suggest_new_region_bound(
 256     tcx: TyCtxt<'_>,
 257     err: &mut Diagnostic,
 258     fn_returns: Vec<&rustc_hir::Ty<'_>>,
 259     lifetime_name: String,
 260     arg: Option<String>,
 261     captures: String,
 262     param: Option<(Span, String)>,
 263     scope_def_id: Option<LocalDefId>,
 264 ) {
 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`.
 277             continue;
 278         }
 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 {
 283                     return;
 284                 };
 285
 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));
 289
 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),
 294                     _ => None,
 295                 }) {
 296                     if let Some(explicit_static) = &explicit_static {
 297                         err.span_suggestion_verbose(
 298                             span,
 299                             &format!("{consider} `{ty}`'s {explicit_static}"),
 300                             &lifetime_name,
 301                             Applicability::MaybeIncorrect,
 302                         );
 303                     }
 304                     if let Some((param_span, ref param_ty)) = param {
 305                         err.span_suggestion_verbose(
 306                             param_span,
 307                             add_static_bound,
 308                             param_ty,
 309                             Applicability::MaybeIncorrect,
 310                         );
 311                     }
 312                 } else if opaque.bounds.iter().any(|arg| match arg {
 313                     GenericBound::Outlives(Lifetime { ident, .. })
 314                         if ident.name.to_string() == lifetime_name =>
 315                     {
 316                         true
 317                     }
 318                     _ => false,
 319                 }) {
 320                 } else {
 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
 325                         .params
 326                         .iter()
 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))
 330                         .collect::<Vec<_>>()
 331                         && named_lifetimes.len() > 0 {
 332                         named_lifetimes[0].clone()
 333                     } else {
 334                         None
 335                     };
 336                     let name = if let Some(name) = &existing_lt_name {
 337                         format!("{}", name)
 338                     } else {
 339                         format!("'a")
 340                     };
 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
 346                             .params
 347                             .iter()
 348                             .filter(|p| p.is_elided_lifetime())
 349                             .map(|p|
 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}"))
 354                                   }
 355                             )
 356                             .collect::<Vec<_>>()
 357                         && spans_suggs.len() > 1
 358                     {
 359                         let use_lt =
 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}`")
 363                         } else {
 364                             // make use the existing named lifetime
 365                             format!("you can use the named lifetime parameter `{name}`")
 366                         };
 367                         spans_suggs
 368                             .push((fn_return.span.shrink_to_hi(), format!(" + {name} ")));
 369                         err.multipart_suggestion_verbose(
 370                             &format!(
 371                                 "{declare} `{ty}` {captures}, {use_lt}",
 372                             ),
 373                             spans_suggs,
 374                             Applicability::MaybeIncorrect,
 375                         );
 376                     } else {
 377                         err.span_suggestion_verbose(
 378                             fn_return.span.shrink_to_hi(),
 379                             &format!("{declare} `{ty}` {captures}, {explicit}",),
 380                             &plus_lt,
 381                             Applicability::MaybeIncorrect,
 382                         );
 383                     }
 384                 }
 385             }
 386             TyKind::TraitObject(_, lt, _) => {
 387                 if let LifetimeName::ImplicitObjectLifetimeDefault = lt.res {
 388                     err.span_suggestion_verbose(
 389                         fn_return.span.shrink_to_hi(),
 390                         &format!(
 391                             "{declare} the trait object {captures}, {explicit}",
 392                             declare = declare,
 393                             captures = captures,
 394                             explicit = explicit,
 395                         ),
 396                         &plus_lt,
 397                         Applicability::MaybeIncorrect,
 398                     );
 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(
 406                             lt.ident.span,
 407                             &format!("{} the trait object's {}", consider, explicit_static),
 408                             &lifetime_name,
 409                             Applicability::MaybeIncorrect,
 410                         );
 411                     }
 412                     if let Some((param_span, param_ty)) = param.clone() {
 413                         err.span_suggestion_verbose(
 414                             param_span,
 415                             add_static_bound,
 416                             param_ty,
 417                             Applicability::MaybeIncorrect,
 418                         );
 419                     }
 420                 }
 421             }
 422             _ => {}
 423         }
 424     }
 425 }
 426
 427 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 428     pub fn get_impl_ident_and_self_ty_from_trait(
 429         tcx: TyCtxt<'tcx>,
 430         def_id: DefId,
 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, .. }),
 438                     ..
 439                 }) = tcx.hir().owner(impl_did)
 440                 {
 441                     Some((impl_item.ident, self_ty))
 442                 } else {
 443                     None
 444                 }
 445             }
 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, .. }),
 456                         ..
 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);
 468                             !traits.is_empty()
 469                         })
 470                     {
 471                         Some((trait_item.ident, *self_ty))
 472                     } else {
 473                         None
 474                     }
 475                 })
 476             }
 477             _ => None,
 478         }
 479     }
 480
 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(
 484         &self,
 485         err: &mut Diagnostic,
 486         ty: Ty<'_>,
 487         ctxt: &UnifyReceiverContext<'tcx>,
 488     ) -> bool {
 489         let tcx = self.tcx();
 490
 491         // Find the method being called.
 492         let Ok(Some(instance)) = ty::Instance::resolve(
 493             tcx,
 494             ctxt.param_env,
 495             ctxt.assoc_item.def_id,
 496             self.cx.resolve_vars_if_possible(ctxt.substs),
 497         ) else {
 498             return false;
 499         };
 500
 501         let mut v = TraitObjectVisitor(FxIndexSet::default());
 502         v.visit_ty(ty);
 503
 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 {
 507             return false;
 508         };
 509
 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)
 512     }
 513
 514     fn suggest_constrain_dyn_trait_in_impl(
 515         &self,
 516         err: &mut Diagnostic,
 517         found_dids: &FxIndexSet<DefId>,
 518         ident: Ident,
 519         self_ty: &hir::Ty<'_>,
 520     ) -> bool {
 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);
 529                 suggested = true;
 530             }
 531         }
 532         suggested
 533     }
 534 }
 535
 536 /// Collect all the trait objects in a type that could have received an implicit `'static` lifetime.
 537 pub struct TraitObjectVisitor(pub FxIndexSet<DefId>);
 538
 539 impl<'tcx> TypeVisitor<'tcx> for TraitObjectVisitor {
 540     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 541         match t.kind() {
 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);
 545                 }
 546                 ControlFlow::Continue(())
 547             }
 548             _ => t.super_visit_with(self),
 549         }
 550     }
 551 }
 552
 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);
 555
 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(
 559             poly_trait_refs,
 560             Lifetime { res: LifetimeName::ImplicitObjectLifetimeDefault, .. },
 561             _,
 562         ) = t.kind
 563         {
 564             for ptr in poly_trait_refs {
 565                 if Some(self.1) == ptr.trait_ref.trait_def_id() {
 566                     self.0.push(ptr.span);
 567                 }
 568             }
 569         }
 570         walk_ty(self, t);
 571     }
 572 }