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::infer::error_reporting::nice_region_error::NiceRegionError;
   4 use crate::infer::lexical_region_resolve::RegionResolutionError;
   5 use crate::infer::{SubregionOrigin, TypeTrace};
   6 use crate::traits::{ObligationCauseCode, UnifyReceiverContext};
   7 use rustc_data_structures::fx::FxHashSet;
   8 use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan};
   9 use rustc_hir::def_id::DefId;
  10 use rustc_hir::intravisit::{walk_ty, Visitor};
  11 use rustc_hir::{self as hir, GenericBound, Item, ItemKind, Lifetime, LifetimeName, Node, TyKind};
  12 use rustc_middle::ty::{
  13     self, AssocItemContainer, StaticLifetimeVisitor, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
  14 };
  15 use rustc_span::symbol::Ident;
  16 use rustc_span::Span;
  17
  18 use std::ops::ControlFlow;
  19
  20 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
  21     /// Print the error message for lifetime errors when the return type is a static `impl Trait`,
  22     /// `dyn Trait` or if a method call on a trait object introduces a static requirement.
  23     pub(super) fn try_report_static_impl_trait(&self) -> Option<ErrorGuaranteed> {
  24         debug!("try_report_static_impl_trait(error={:?})", self.error);
  25         let tcx = self.tcx();
  26         let (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans) = match self.error.as_ref()? {
  27             RegionResolutionError::SubSupConflict(
  28                 _,
  29                 var_origin,
  30                 sub_origin,
  31                 sub_r,
  32                 sup_origin,
  33                 sup_r,
  34                 spans,
  35             ) if sub_r.is_static() => (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans),
  36             RegionResolutionError::ConcreteFailure(
  37                 SubregionOrigin::Subtype(box TypeTrace { cause, .. }),
  38                 sub_r,
  39                 sup_r,
  40             ) if sub_r.is_static() => {
  41                 // This is for an implicit `'static` requirement coming from `impl dyn Trait {}`.
  42                 if let ObligationCauseCode::UnifyReceiver(ctxt) = cause.code() {
  43                     // This may have a closure and it would cause ICE
  44                     // through `find_param_with_region` (#78262).
  45                     let anon_reg_sup = tcx.is_suitable_region(*sup_r)?;
  46                     let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);
  47                     if fn_returns.is_empty() {
  48                         return None;
  49                     }
  50
  51                     let param = self.find_param_with_region(*sup_r, *sub_r)?;
  52                     let lifetime = if sup_r.has_name() {
  53                         format!("lifetime `{}`", sup_r)
  54                     } else {
  55                         "an anonymous lifetime `'_`".to_string()
  56                     };
  57                     let mut err = struct_span_err!(
  58                         tcx.sess,
  59                         cause.span,
  60                         E0772,
  61                         "{} has {} but calling `{}` introduces an implicit `'static` lifetime \
  62                          requirement",
  63                         param
  64                             .param
  65                             .pat
  66                             .simple_ident()
  67                             .map(|s| format!("`{}`", s))
  68                             .unwrap_or_else(|| "`fn` parameter".to_string()),
  69                         lifetime,
  70                         ctxt.assoc_item.name,
  71                     );
  72                     err.span_label(param.param_ty_span, &format!("this data with {}...", lifetime));
  73                     err.span_label(
  74                         cause.span,
  75                         &format!(
  76                             "...is used and required to live as long as `'static` here \
  77                              because of an implicit lifetime bound on the {}",
  78                             match ctxt.assoc_item.container {
  79                                 AssocItemContainer::TraitContainer => {
  80                                     let id = ctxt.assoc_item.container_id(tcx);
  81                                     format!("`impl` of `{}`", tcx.def_path_str(id))
  82                                 }
  83                                 AssocItemContainer::ImplContainer => "inherent `impl`".to_string(),
  84                             },
  85                         ),
  86                     );
  87                     if self.find_impl_on_dyn_trait(&mut err, param.param_ty, &ctxt) {
  88                         let reported = err.emit();
  89                         return Some(reported);
  90                     } else {
  91                         err.cancel();
  92                     }
  93                 }
  94                 return None;
  95             }
  96             _ => return None,
  97         };
  98         debug!(
  99             "try_report_static_impl_trait(var={:?}, sub={:?} {:?} sup={:?} {:?})",
 100             var_origin, sub_origin, sub_r, sup_origin, sup_r
 101         );
 102         let anon_reg_sup = tcx.is_suitable_region(*sup_r)?;
 103         debug!("try_report_static_impl_trait: anon_reg_sup={:?}", anon_reg_sup);
 104         let sp = var_origin.span();
 105         let return_sp = sub_origin.span();
 106         let param = self.find_param_with_region(*sup_r, *sub_r)?;
 107         let (lifetime_name, lifetime) = if sup_r.has_name() {
 108             (sup_r.to_string(), format!("lifetime `{}`", sup_r))
 109         } else {
 110             ("'_".to_owned(), "an anonymous lifetime `'_`".to_string())
 111         };
 112         let param_name = param
 113             .param
 114             .pat
 115             .simple_ident()
 116             .map(|s| format!("`{}`", s))
 117             .unwrap_or_else(|| "`fn` parameter".to_string());
 118         let mut err = struct_span_err!(
 119             tcx.sess,
 120             sp,
 121             E0759,
 122             "{} has {} but it needs to satisfy a `'static` lifetime requirement",
 123             param_name,
 124             lifetime,
 125         );
 126
 127         let (mention_influencer, influencer_point) =
 128             if sup_origin.span().overlaps(param.param_ty_span) {
 129                 // Account for `async fn` like in `async-await/issues/issue-62097.rs`.
 130                 // The desugaring of `async `fn`s causes `sup_origin` and `param` to point at the same
 131                 // place (but with different `ctxt`, hence `overlaps` instead of `==` above).
 132                 //
 133                 // This avoids the following:
 134                 //
 135                 // LL |     pub async fn run_dummy_fn(&self) {
 136                 //    |                               ^^^^^
 137                 //    |                               |
 138                 //    |                               this data with an anonymous lifetime `'_`...
 139                 //    |                               ...is captured here...
 140                 (false, sup_origin.span())
 141             } else {
 142                 (!sup_origin.span().overlaps(return_sp), param.param_ty_span)
 143             };
 144         err.span_label(influencer_point, &format!("this data with {}...", lifetime));
 145
 146         debug!("try_report_static_impl_trait: param_info={:?}", param);
 147
 148         let mut spans = spans.clone();
 149
 150         if mention_influencer {
 151             spans.push(sup_origin.span());
 152         }
 153         // We dedup the spans *ignoring* expansion context.
 154         spans.sort();
 155         spans.dedup_by_key(|span| (span.lo(), span.hi()));
 156
 157         // We try to make the output have fewer overlapping spans if possible.
 158         let require_msg = if spans.is_empty() {
 159             "...is used and required to live as long as `'static` here"
 160         } else {
 161             "...and is required to live as long as `'static` here"
 162         };
 163         let require_span =
 164             if sup_origin.span().overlaps(return_sp) { sup_origin.span() } else { return_sp };
 165
 166         for span in &spans {
 167             err.span_label(*span, "...is used here...");
 168         }
 169
 170         if spans.iter().any(|sp| sp.overlaps(return_sp) || *sp > return_sp) {
 171             // If any of the "captured here" labels appears on the same line or after
 172             // `require_span`, we put it on a note to ensure the text flows by appearing
 173             // always at the end.
 174             err.span_note(require_span, require_msg);
 175         } else {
 176             // We don't need a note, it's already at the end, it can be shown as a `span_label`.
 177             err.span_label(require_span, require_msg);
 178         }
 179
 180         if let SubregionOrigin::RelateParamBound(_, _, Some(bound)) = sub_origin {
 181             err.span_note(*bound, "`'static` lifetime requirement introduced by this bound");
 182         }
 183         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = sub_origin {
 184             if let ObligationCauseCode::ReturnValue(hir_id)
 185             | ObligationCauseCode::BlockTailExpression(hir_id) = cause.code()
 186             {
 187                 let parent_id = tcx.hir().get_parent_item(*hir_id);
 188                 let parent_id = tcx.hir().local_def_id_to_hir_id(parent_id);
 189                 if let Some(fn_decl) = tcx.hir().fn_decl_by_hir_id(parent_id) {
 190                     let mut span: MultiSpan = fn_decl.output.span().into();
 191                     let mut add_label = true;
 192                     if let hir::FnRetTy::Return(ty) = fn_decl.output {
 193                         let mut v = StaticLifetimeVisitor(vec![], tcx.hir());
 194                         v.visit_ty(ty);
 195                         if !v.0.is_empty() {
 196                             span = v.0.clone().into();
 197                             for sp in v.0 {
 198                                 span.push_span_label(sp, "`'static` requirement introduced here");
 199                             }
 200                             add_label = false;
 201                         }
 202                     }
 203                     if add_label {
 204                         span.push_span_label(
 205                             fn_decl.output.span(),
 206                             "requirement introduced by this return type",
 207                         );
 208                     }
 209                     span.push_span_label(cause.span, "because of this returned expression");
 210                     err.span_note(
 211                         span,
 212                         "`'static` lifetime requirement introduced by the return type",
 213                     );
 214                 }
 215             }
 216         }
 217
 218         let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);
 219
 220         let mut override_error_code = None;
 221         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = &sup_origin
 222             && let ObligationCauseCode::UnifyReceiver(ctxt) = cause.code()
 223             // Handle case of `impl Foo for dyn Bar { fn qux(&self) {} }` introducing a
 224             // `'static` lifetime when called as a method on a binding: `bar.qux()`.
 225             && self.find_impl_on_dyn_trait(&mut err, param.param_ty, &ctxt)
 226         {
 227             override_error_code = Some(ctxt.assoc_item.name);
 228         }
 229
 230         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = &sub_origin
 231             && let code = match cause.code() {
 232                 ObligationCauseCode::MatchImpl(parent, ..) => parent.code(),
 233                 _ => cause.code(),
 234             }
 235             && let (&ObligationCauseCode::ItemObligation(item_def_id) | &ObligationCauseCode::ExprItemObligation(item_def_id, ..), None) = (code, override_error_code)
 236         {
 237             // Same case of `impl Foo for dyn Bar { fn qux(&self) {} }` introducing a `'static`
 238             // lifetime as above, but called using a fully-qualified path to the method:
 239             // `Foo::qux(bar)`.
 240             let mut v = TraitObjectVisitor(FxHashSet::default());
 241             v.visit_ty(param.param_ty);
 242             if let Some((ident, self_ty)) =
 243                 self.get_impl_ident_and_self_ty_from_trait(item_def_id, &v.0)
 244                 && self.suggest_constrain_dyn_trait_in_impl(&mut err, &v.0, ident, self_ty)
 245             {
 246                 override_error_code = Some(ident.name);
 247             }
 248         }
 249         if let (Some(ident), true) = (override_error_code, fn_returns.is_empty()) {
 250             // Provide a more targeted error code and description.
 251             err.code(rustc_errors::error_code!(E0772));
 252             err.set_primary_message(&format!(
 253                 "{} has {} but calling `{}` introduces an implicit `'static` lifetime \
 254                 requirement",
 255                 param_name, lifetime, ident,
 256             ));
 257         }
 258
 259         let arg = match param.param.pat.simple_ident() {
 260             Some(simple_ident) => format!("argument `{}`", simple_ident),
 261             None => "the argument".to_string(),
 262         };
 263         let captures = format!("captures data from {}", arg);
 264         suggest_new_region_bound(
 265             tcx,
 266             &mut err,
 267             fn_returns,
 268             lifetime_name,
 269             Some(arg),
 270             captures,
 271             Some((param.param_ty_span, param.param_ty.to_string())),
 272         );
 273
 274         let reported = err.emit();
 275         Some(reported)
 276     }
 277 }
 278
 279 pub fn suggest_new_region_bound(
 280     tcx: TyCtxt<'_>,
 281     err: &mut Diagnostic,
 282     fn_returns: Vec<&rustc_hir::Ty<'_>>,
 283     lifetime_name: String,
 284     arg: Option<String>,
 285     captures: String,
 286     param: Option<(Span, String)>,
 287 ) {
 288     debug!("try_report_static_impl_trait: fn_return={:?}", fn_returns);
 289     // FIXME: account for the need of parens in `&(dyn Trait + '_)`
 290     let consider = "consider changing the";
 291     let declare = "to declare that the";
 292     let explicit = format!("you can add an explicit `{}` lifetime bound", lifetime_name);
 293     let explicit_static =
 294         arg.map(|arg| format!("explicit `'static` bound to the lifetime of {}", arg));
 295     let add_static_bound = "alternatively, add an explicit `'static` bound to this reference";
 296     let plus_lt = format!(" + {}", lifetime_name);
 297     for fn_return in fn_returns {
 298         if fn_return.span.desugaring_kind().is_some() {
 299             // Skip `async` desugaring `impl Future`.
 300             continue;
 301         }
 302         match fn_return.kind {
 303             TyKind::OpaqueDef(item_id, _) => {
 304                 let item = tcx.hir().item(item_id);
 305                 let ItemKind::OpaqueTy(opaque) = &item.kind else {
 306                     return;
 307                 };
 308
 309                 if let Some(span) = opaque
 310                     .bounds
 311                     .iter()
 312                     .filter_map(|arg| match arg {
 313                         GenericBound::Outlives(Lifetime {
 314                             name: LifetimeName::Static,
 315                             span,
 316                             ..
 317                         }) => Some(*span),
 318                         _ => None,
 319                     })
 320                     .next()
 321                 {
 322                     if let Some(explicit_static) = &explicit_static {
 323                         err.span_suggestion_verbose(
 324                             span,
 325                             &format!("{} `impl Trait`'s {}", consider, explicit_static),
 326                             &lifetime_name,
 327                             Applicability::MaybeIncorrect,
 328                         );
 329                     }
 330                     if let Some((param_span, param_ty)) = param.clone() {
 331                         err.span_suggestion_verbose(
 332                             param_span,
 333                             add_static_bound,
 334                             param_ty,
 335                             Applicability::MaybeIncorrect,
 336                         );
 337                     }
 338                 } else if opaque
 339                     .bounds
 340                     .iter()
 341                     .filter_map(|arg| match arg {
 342                         GenericBound::Outlives(Lifetime { name, span, .. })
 343                             if name.ident().to_string() == lifetime_name =>
 344                         {
 345                             Some(*span)
 346                         }
 347                         _ => None,
 348                     })
 349                     .next()
 350                     .is_some()
 351                 {
 352                 } else {
 353                     err.span_suggestion_verbose(
 354                         fn_return.span.shrink_to_hi(),
 355                         &format!(
 356                             "{declare} `impl Trait` {captures}, {explicit}",
 357                             declare = declare,
 358                             captures = captures,
 359                             explicit = explicit,
 360                         ),
 361                         &plus_lt,
 362                         Applicability::MaybeIncorrect,
 363                     );
 364                 }
 365             }
 366             TyKind::TraitObject(_, lt, _) => match lt.name {
 367                 LifetimeName::ImplicitObjectLifetimeDefault => {
 368                     err.span_suggestion_verbose(
 369                         fn_return.span.shrink_to_hi(),
 370                         &format!(
 371                             "{declare} trait object {captures}, {explicit}",
 372                             declare = declare,
 373                             captures = captures,
 374                             explicit = explicit,
 375                         ),
 376                         &plus_lt,
 377                         Applicability::MaybeIncorrect,
 378                     );
 379                 }
 380                 name if name.ident().to_string() != lifetime_name => {
 381                     // With this check we avoid suggesting redundant bounds. This
 382                     // would happen if there are nested impl/dyn traits and only
 383                     // one of them has the bound we'd suggest already there, like
 384                     // in `impl Foo<X = dyn Bar> + '_`.
 385                     if let Some(explicit_static) = &explicit_static {
 386                         err.span_suggestion_verbose(
 387                             lt.span,
 388                             &format!("{} trait object's {}", consider, explicit_static),
 389                             &lifetime_name,
 390                             Applicability::MaybeIncorrect,
 391                         );
 392                     }
 393                     if let Some((param_span, param_ty)) = param.clone() {
 394                         err.span_suggestion_verbose(
 395                             param_span,
 396                             add_static_bound,
 397                             param_ty,
 398                             Applicability::MaybeIncorrect,
 399                         );
 400                     }
 401                 }
 402                 _ => {}
 403             },
 404             _ => {}
 405         }
 406     }
 407 }
 408
 409 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 410     fn get_impl_ident_and_self_ty_from_trait(
 411         &self,
 412         def_id: DefId,
 413         trait_objects: &FxHashSet<DefId>,
 414     ) -> Option<(Ident, &'tcx hir::Ty<'tcx>)> {
 415         let tcx = self.tcx();
 416         match tcx.hir().get_if_local(def_id) {
 417             Some(Node::ImplItem(impl_item)) => {
 418                 match tcx.hir().find_by_def_id(tcx.hir().get_parent_item(impl_item.hir_id())) {
 419                     Some(Node::Item(Item {
 420                         kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
 421                         ..
 422                     })) => Some((impl_item.ident, self_ty)),
 423                     _ => None,
 424                 }
 425             }
 426             Some(Node::TraitItem(trait_item)) => {
 427                 let trait_did = tcx.hir().get_parent_item(trait_item.hir_id());
 428                 match tcx.hir().find_by_def_id(trait_did) {
 429                     Some(Node::Item(Item { kind: ItemKind::Trait(..), .. })) => {
 430                         // The method being called is defined in the `trait`, but the `'static`
 431                         // obligation comes from the `impl`. Find that `impl` so that we can point
 432                         // at it in the suggestion.
 433                         let trait_did = trait_did.to_def_id();
 434                         match tcx
 435                             .hir()
 436                             .trait_impls(trait_did)
 437                             .iter()
 438                             .filter_map(|&impl_did| {
 439                                 match tcx.hir().get_if_local(impl_did.to_def_id()) {
 440                                     Some(Node::Item(Item {
 441                                         kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
 442                                         ..
 443                                     })) if trait_objects.iter().all(|did| {
 444                                         // FIXME: we should check `self_ty` against the receiver
 445                                         // type in the `UnifyReceiver` context, but for now, use
 446                                         // this imperfect proxy. This will fail if there are
 447                                         // multiple `impl`s for the same trait like
 448                                         // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
 449                                         // In that case, only the first one will get suggestions.
 450                                         let mut traits = vec![];
 451                                         let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
 452                                         hir_v.visit_ty(self_ty);
 453                                         !traits.is_empty()
 454                                     }) =>
 455                                     {
 456                                         Some(self_ty)
 457                                     }
 458                                     _ => None,
 459                                 }
 460                             })
 461                             .next()
 462                         {
 463                             Some(self_ty) => Some((trait_item.ident, self_ty)),
 464                             _ => None,
 465                         }
 466                     }
 467                     _ => None,
 468                 }
 469             }
 470             _ => None,
 471         }
 472     }
 473
 474     /// When we call a method coming from an `impl Foo for dyn Bar`, `dyn Bar` introduces a default
 475     /// `'static` obligation. Suggest relaxing that implicit bound.
 476     fn find_impl_on_dyn_trait(
 477         &self,
 478         err: &mut Diagnostic,
 479         ty: Ty<'_>,
 480         ctxt: &UnifyReceiverContext<'tcx>,
 481     ) -> bool {
 482         let tcx = self.tcx();
 483
 484         // Find the method being called.
 485         let Ok(Some(instance)) = ty::Instance::resolve(
 486             tcx,
 487             ctxt.param_env,
 488             ctxt.assoc_item.def_id,
 489             self.infcx.resolve_vars_if_possible(ctxt.substs),
 490         ) else {
 491             return false;
 492         };
 493
 494         let mut v = TraitObjectVisitor(FxHashSet::default());
 495         v.visit_ty(ty);
 496
 497         // Get the `Ident` of the method being called and the corresponding `impl` (to point at
 498         // `Bar` in `impl Foo for dyn Bar {}` and the definition of the method being called).
 499         let Some((ident, self_ty)) = self.get_impl_ident_and_self_ty_from_trait(instance.def_id(), &v.0) else {
 500             return false;
 501         };
 502
 503         // Find the trait object types in the argument, so we point at *only* the trait object.
 504         self.suggest_constrain_dyn_trait_in_impl(err, &v.0, ident, self_ty)
 505     }
 506
 507     fn suggest_constrain_dyn_trait_in_impl(
 508         &self,
 509         err: &mut Diagnostic,
 510         found_dids: &FxHashSet<DefId>,
 511         ident: Ident,
 512         self_ty: &hir::Ty<'_>,
 513     ) -> bool {
 514         let mut suggested = false;
 515         for found_did in found_dids {
 516             let mut traits = vec![];
 517             let mut hir_v = HirTraitObjectVisitor(&mut traits, *found_did);
 518             hir_v.visit_ty(&self_ty);
 519             for span in &traits {
 520                 let mut multi_span: MultiSpan = vec![*span].into();
 521                 multi_span
 522                     .push_span_label(*span, "this has an implicit `'static` lifetime requirement");
 523                 multi_span.push_span_label(
 524                     ident.span,
 525                     "calling this method introduces the `impl`'s 'static` requirement",
 526                 );
 527                 err.span_note(multi_span, "the used `impl` has a `'static` requirement");
 528                 err.span_suggestion_verbose(
 529                     span.shrink_to_hi(),
 530                     "consider relaxing the implicit `'static` requirement",
 531                     " + '_",
 532                     Applicability::MaybeIncorrect,
 533                 );
 534                 suggested = true;
 535             }
 536         }
 537         suggested
 538     }
 539 }
 540
 541 /// Collect all the trait objects in a type that could have received an implicit `'static` lifetime.
 542 pub struct TraitObjectVisitor(pub FxHashSet<DefId>);
 543
 544 impl<'tcx> TypeVisitor<'tcx> for TraitObjectVisitor {
 545     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 546         match t.kind() {
 547             ty::Dynamic(preds, re) if re.is_static() => {
 548                 if let Some(def_id) = preds.principal_def_id() {
 549                     self.0.insert(def_id);
 550                 }
 551                 ControlFlow::CONTINUE
 552             }
 553             _ => t.super_visit_with(self),
 554         }
 555     }
 556 }
 557
 558 /// Collect all `hir::Ty<'_>` `Span`s for trait objects with an implicit lifetime.
 559 pub struct HirTraitObjectVisitor<'a>(pub &'a mut Vec<Span>, pub DefId);
 560
 561 impl<'a, 'tcx> Visitor<'tcx> for HirTraitObjectVisitor<'a> {
 562     fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx>) {
 563         if let TyKind::TraitObject(
 564             poly_trait_refs,
 565             Lifetime { name: LifetimeName::ImplicitObjectLifetimeDefault, .. },
 566             _,
 567         ) = t.kind
 568         {
 569             for ptr in poly_trait_refs {
 570                 if Some(self.1) == ptr.trait_ref.trait_def_id() {
 571                     self.0.push(ptr.span);
 572                 }
 573             }
 574         }
 575         walk_ty(self, t);
 576     }
 577 }