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::stable_set::FxHashSet;
   8 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorReported};
   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, TypeFoldable, TypeVisitor,
  14 };
  15 use rustc_span::symbol::Ident;
  16 use rustc_span::{MultiSpan, 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<ErrorReported> {
  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(id) =>
  80                                     format!("`impl` of `{}`", tcx.def_path_str(id)),
  81                                 AssocItemContainer::ImplContainer(_) =>
  82                                     "inherent `impl`".to_string(),
  83                             },
  84                         ),
  85                     );
  86                     if self.find_impl_on_dyn_trait(&mut err, param.param_ty, &ctxt) {
  87                         err.emit();
  88                         return Some(ErrorReported);
  89                     } else {
  90                         err.cancel();
  91                     }
  92                 }
  93                 return None;
  94             }
  95             _ => return None,
  96         };
  97         debug!(
  98             "try_report_static_impl_trait(var={:?}, sub={:?} {:?} sup={:?} {:?})",
  99             var_origin, sub_origin, sub_r, sup_origin, sup_r
 100         );
 101         let anon_reg_sup = tcx.is_suitable_region(*sup_r)?;
 102         debug!("try_report_static_impl_trait: anon_reg_sup={:?}", anon_reg_sup);
 103         let sp = var_origin.span();
 104         let return_sp = sub_origin.span();
 105         let param = self.find_param_with_region(*sup_r, *sub_r)?;
 106         let (lifetime_name, lifetime) = if sup_r.has_name() {
 107             (sup_r.to_string(), format!("lifetime `{}`", sup_r))
 108         } else {
 109             ("'_".to_owned(), "an anonymous lifetime `'_`".to_string())
 110         };
 111         let param_name = param
 112             .param
 113             .pat
 114             .simple_ident()
 115             .map(|s| format!("`{}`", s))
 116             .unwrap_or_else(|| "`fn` parameter".to_string());
 117         let mut err = struct_span_err!(
 118             tcx.sess,
 119             sp,
 120             E0759,
 121             "{} has {} but it needs to satisfy a `'static` lifetime requirement",
 122             param_name,
 123             lifetime,
 124         );
 125
 126         let (mention_influencer, influencer_point) =
 127             if sup_origin.span().overlaps(param.param_ty_span) {
 128                 // Account for `async fn` like in `async-await/issues/issue-62097.rs`.
 129                 // The desugaring of `async `fn`s causes `sup_origin` and `param` to point at the same
 130                 // place (but with different `ctxt`, hence `overlaps` instead of `==` above).
 131                 //
 132                 // This avoids the following:
 133                 //
 134                 // LL |     pub async fn run_dummy_fn(&self) {
 135                 //    |                               ^^^^^
 136                 //    |                               |
 137                 //    |                               this data with an anonymous lifetime `'_`...
 138                 //    |                               ...is captured here...
 139                 (false, sup_origin.span())
 140             } else {
 141                 (!sup_origin.span().overlaps(return_sp), param.param_ty_span)
 142             };
 143         err.span_label(influencer_point, &format!("this data with {}...", lifetime));
 144
 145         debug!("try_report_static_impl_trait: param_info={:?}", param);
 146
 147         let mut spans = spans.clone();
 148
 149         if mention_influencer {
 150             spans.push(sup_origin.span());
 151         }
 152         // We dedup the spans *ignoring* expansion context.
 153         spans.sort();
 154         spans.dedup_by_key(|span| (span.lo(), span.hi()));
 155
 156         // We try to make the output have fewer overlapping spans if possible.
 157         let require_msg = if spans.is_empty() {
 158             "...is used and required to live as long as `'static` here"
 159         } else {
 160             "...and is required to live as long as `'static` here"
 161         };
 162         let require_span =
 163             if sup_origin.span().overlaps(return_sp) { sup_origin.span() } else { return_sp };
 164
 165         for span in &spans {
 166             err.span_label(*span, "...is used here...");
 167         }
 168
 169         if spans.iter().any(|sp| sp.overlaps(return_sp) || *sp > return_sp) {
 170             // If any of the "captured here" labels appears on the same line or after
 171             // `require_span`, we put it on a note to ensure the text flows by appearing
 172             // always at the end.
 173             err.span_note(require_span, require_msg);
 174         } else {
 175             // We don't need a note, it's already at the end, it can be shown as a `span_label`.
 176             err.span_label(require_span, require_msg);
 177         }
 178
 179         if let SubregionOrigin::RelateParamBound(_, _, Some(bound)) = sub_origin {
 180             err.span_note(*bound, "`'static` lifetime requirement introduced by this bound");
 181         }
 182         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = sub_origin {
 183             if let ObligationCauseCode::ReturnValue(hir_id)
 184             | ObligationCauseCode::BlockTailExpression(hir_id) = cause.code()
 185             {
 186                 let parent_id = tcx.hir().get_parent_item(*hir_id);
 187                 let parent_id = tcx.hir().local_def_id_to_hir_id(parent_id);
 188                 if let Some(fn_decl) = tcx.hir().fn_decl_by_hir_id(parent_id) {
 189                     let mut span: MultiSpan = fn_decl.output.span().into();
 190                     let mut add_label = true;
 191                     if let hir::FnRetTy::Return(ty) = fn_decl.output {
 192                         let mut v = StaticLifetimeVisitor(vec![], tcx.hir());
 193                         v.visit_ty(ty);
 194                         if !v.0.is_empty() {
 195                             span = v.0.clone().into();
 196                             for sp in v.0 {
 197                                 span.push_span_label(
 198                                     sp,
 199                                     "`'static` requirement introduced here".to_string(),
 200                                 );
 201                             }
 202                             add_label = false;
 203                         }
 204                     }
 205                     if add_label {
 206                         span.push_span_label(
 207                             fn_decl.output.span(),
 208                             "requirement introduced by this return type".to_string(),
 209                         );
 210                     }
 211                     span.push_span_label(
 212                         cause.span,
 213                         "because of this returned expression".to_string(),
 214                     );
 215                     err.span_note(
 216                         span,
 217                         "`'static` lifetime requirement introduced by the return type",
 218                     );
 219                 }
 220             }
 221         }
 222
 223         let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);
 224
 225         let mut override_error_code = None;
 226         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = &sup_origin {
 227             if let ObligationCauseCode::UnifyReceiver(ctxt) = cause.code() {
 228                 // Handle case of `impl Foo for dyn Bar { fn qux(&self) {} }` introducing a
 229                 // `'static` lifetime when called as a method on a binding: `bar.qux()`.
 230                 if self.find_impl_on_dyn_trait(&mut err, param.param_ty, &ctxt) {
 231                     override_error_code = Some(ctxt.assoc_item.name);
 232                 }
 233             }
 234         }
 235         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = &sub_origin {
 236             let code = match cause.code() {
 237                 ObligationCauseCode::MatchImpl(parent, ..) => parent.code(),
 238                 _ => cause.code(),
 239             };
 240             if let (ObligationCauseCode::ItemObligation(item_def_id), None) =
 241                 (code, override_error_code)
 242             {
 243                 // Same case of `impl Foo for dyn Bar { fn qux(&self) {} }` introducing a `'static`
 244                 // lifetime as above, but called using a fully-qualified path to the method:
 245                 // `Foo::qux(bar)`.
 246                 let mut v = TraitObjectVisitor(FxHashSet::default());
 247                 v.visit_ty(param.param_ty);
 248                 if let Some((ident, self_ty)) =
 249                     self.get_impl_ident_and_self_ty_from_trait(*item_def_id, &v.0)
 250                 {
 251                     if self.suggest_constrain_dyn_trait_in_impl(&mut err, &v.0, ident, self_ty) {
 252                         override_error_code = Some(ident.name);
 253                     }
 254                 }
 255             }
 256         }
 257         if let (Some(ident), true) = (override_error_code, fn_returns.is_empty()) {
 258             // Provide a more targeted error code and description.
 259             err.code(rustc_errors::error_code!(E0772));
 260             err.set_primary_message(&format!(
 261                 "{} has {} but calling `{}` introduces an implicit `'static` lifetime \
 262                 requirement",
 263                 param_name, lifetime, ident,
 264             ));
 265         }
 266
 267         let arg = match param.param.pat.simple_ident() {
 268             Some(simple_ident) => format!("argument `{}`", simple_ident),
 269             None => "the argument".to_string(),
 270         };
 271         let captures = format!("captures data from {}", arg);
 272         suggest_new_region_bound(
 273             tcx,
 274             &mut err,
 275             fn_returns,
 276             lifetime_name,
 277             Some(arg),
 278             captures,
 279             Some((param.param_ty_span, param.param_ty.to_string())),
 280         );
 281
 282         err.emit();
 283         Some(ErrorReported)
 284     }
 285 }
 286
 287 pub fn suggest_new_region_bound(
 288     tcx: TyCtxt<'_>,
 289     err: &mut DiagnosticBuilder<'_>,
 290     fn_returns: Vec<&rustc_hir::Ty<'_>>,
 291     lifetime_name: String,
 292     arg: Option<String>,
 293     captures: String,
 294     param: Option<(Span, String)>,
 295 ) {
 296     debug!("try_report_static_impl_trait: fn_return={:?}", fn_returns);
 297     // FIXME: account for the need of parens in `&(dyn Trait + '_)`
 298     let consider = "consider changing the";
 299     let declare = "to declare that the";
 300     let explicit = format!("you can add an explicit `{}` lifetime bound", lifetime_name);
 301     let explicit_static =
 302         arg.map(|arg| format!("explicit `'static` bound to the lifetime of {}", arg));
 303     let add_static_bound = "alternatively, add an explicit `'static` bound to this reference";
 304     let plus_lt = format!(" + {}", lifetime_name);
 305     for fn_return in fn_returns {
 306         if fn_return.span.desugaring_kind().is_some() {
 307             // Skip `async` desugaring `impl Future`.
 308             continue;
 309         }
 310         match fn_return.kind {
 311             TyKind::OpaqueDef(item_id, _) => {
 312                 let item = tcx.hir().item(item_id);
 313                 let ItemKind::OpaqueTy(opaque) = &item.kind else {
 314                     return;
 315                 };
 316
 317                 if let Some(span) = opaque
 318                     .bounds
 319                     .iter()
 320                     .filter_map(|arg| match arg {
 321                         GenericBound::Outlives(Lifetime {
 322                             name: LifetimeName::Static,
 323                             span,
 324                             ..
 325                         }) => Some(*span),
 326                         _ => None,
 327                     })
 328                     .next()
 329                 {
 330                     if let Some(explicit_static) = &explicit_static {
 331                         err.span_suggestion_verbose(
 332                             span,
 333                             &format!("{} `impl Trait`'s {}", consider, explicit_static),
 334                             lifetime_name.clone(),
 335                             Applicability::MaybeIncorrect,
 336                         );
 337                     }
 338                     if let Some((param_span, param_ty)) = param.clone() {
 339                         err.span_suggestion_verbose(
 340                             param_span,
 341                             add_static_bound,
 342                             param_ty,
 343                             Applicability::MaybeIncorrect,
 344                         );
 345                     }
 346                 } else if opaque
 347                     .bounds
 348                     .iter()
 349                     .filter_map(|arg| match arg {
 350                         GenericBound::Outlives(Lifetime { name, span, .. })
 351                             if name.ident().to_string() == lifetime_name =>
 352                         {
 353                             Some(*span)
 354                         }
 355                         _ => None,
 356                     })
 357                     .next()
 358                     .is_some()
 359                 {
 360                 } else {
 361                     err.span_suggestion_verbose(
 362                         fn_return.span.shrink_to_hi(),
 363                         &format!(
 364                             "{declare} `impl Trait` {captures}, {explicit}",
 365                             declare = declare,
 366                             captures = captures,
 367                             explicit = explicit,
 368                         ),
 369                         plus_lt.clone(),
 370                         Applicability::MaybeIncorrect,
 371                     );
 372                 }
 373             }
 374             TyKind::TraitObject(_, lt, _) => match lt.name {
 375                 LifetimeName::ImplicitObjectLifetimeDefault => {
 376                     err.span_suggestion_verbose(
 377                         fn_return.span.shrink_to_hi(),
 378                         &format!(
 379                             "{declare} trait object {captures}, {explicit}",
 380                             declare = declare,
 381                             captures = captures,
 382                             explicit = explicit,
 383                         ),
 384                         plus_lt.clone(),
 385                         Applicability::MaybeIncorrect,
 386                     );
 387                 }
 388                 name if name.ident().to_string() != lifetime_name => {
 389                     // With this check we avoid suggesting redundant bounds. This
 390                     // would happen if there are nested impl/dyn traits and only
 391                     // one of them has the bound we'd suggest already there, like
 392                     // in `impl Foo<X = dyn Bar> + '_`.
 393                     if let Some(explicit_static) = &explicit_static {
 394                         err.span_suggestion_verbose(
 395                             lt.span,
 396                             &format!("{} trait object's {}", consider, explicit_static),
 397                             lifetime_name.clone(),
 398                             Applicability::MaybeIncorrect,
 399                         );
 400                     }
 401                     if let Some((param_span, param_ty)) = param.clone() {
 402                         err.span_suggestion_verbose(
 403                             param_span,
 404                             add_static_bound,
 405                             param_ty,
 406                             Applicability::MaybeIncorrect,
 407                         );
 408                     }
 409                 }
 410                 _ => {}
 411             },
 412             _ => {}
 413         }
 414     }
 415 }
 416
 417 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 418     fn get_impl_ident_and_self_ty_from_trait(
 419         &self,
 420         def_id: DefId,
 421         trait_objects: &FxHashSet<DefId>,
 422     ) -> Option<(Ident, &'tcx hir::Ty<'tcx>)> {
 423         let tcx = self.tcx();
 424         match tcx.hir().get_if_local(def_id) {
 425             Some(Node::ImplItem(impl_item)) => {
 426                 match tcx.hir().find_by_def_id(tcx.hir().get_parent_item(impl_item.hir_id())) {
 427                     Some(Node::Item(Item {
 428                         kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
 429                         ..
 430                     })) => Some((impl_item.ident, self_ty)),
 431                     _ => None,
 432                 }
 433             }
 434             Some(Node::TraitItem(trait_item)) => {
 435                 let trait_did = tcx.hir().get_parent_item(trait_item.hir_id());
 436                 match tcx.hir().find_by_def_id(trait_did) {
 437                     Some(Node::Item(Item { kind: ItemKind::Trait(..), .. })) => {
 438                         // The method being called is defined in the `trait`, but the `'static`
 439                         // obligation comes from the `impl`. Find that `impl` so that we can point
 440                         // at it in the suggestion.
 441                         let trait_did = trait_did.to_def_id();
 442                         match tcx
 443                             .hir()
 444                             .trait_impls(trait_did)
 445                             .iter()
 446                             .filter_map(|&impl_did| {
 447                                 match tcx.hir().get_if_local(impl_did.to_def_id()) {
 448                                     Some(Node::Item(Item {
 449                                         kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
 450                                         ..
 451                                     })) if trait_objects.iter().all(|did| {
 452                                         // FIXME: we should check `self_ty` against the receiver
 453                                         // type in the `UnifyReceiver` context, but for now, use
 454                                         // this imperfect proxy. This will fail if there are
 455                                         // multiple `impl`s for the same trait like
 456                                         // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
 457                                         // In that case, only the first one will get suggestions.
 458                                         let mut traits = vec![];
 459                                         let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
 460                                         hir_v.visit_ty(self_ty);
 461                                         !traits.is_empty()
 462                                     }) =>
 463                                     {
 464                                         Some(self_ty)
 465                                     }
 466                                     _ => None,
 467                                 }
 468                             })
 469                             .next()
 470                         {
 471                             Some(self_ty) => Some((trait_item.ident, self_ty)),
 472                             _ => None,
 473                         }
 474                     }
 475                     _ => None,
 476                 }
 477             }
 478             _ => None,
 479         }
 480     }
 481
 482     /// When we call a method coming from an `impl Foo for dyn Bar`, `dyn Bar` introduces a default
 483     /// `'static` obligation. Suggest relaxing that implicit bound.
 484     fn find_impl_on_dyn_trait(
 485         &self,
 486         err: &mut DiagnosticBuilder<'_>,
 487         ty: Ty<'_>,
 488         ctxt: &UnifyReceiverContext<'tcx>,
 489     ) -> bool {
 490         let tcx = self.tcx();
 491
 492         // Find the method being called.
 493         let instance = match ty::Instance::resolve(
 494             tcx,
 495             ctxt.param_env,
 496             ctxt.assoc_item.def_id,
 497             self.infcx.resolve_vars_if_possible(ctxt.substs),
 498         ) {
 499             Ok(Some(instance)) => instance,
 500             _ => return false,
 501         };
 502
 503         let mut v = TraitObjectVisitor(FxHashSet::default());
 504         v.visit_ty(ty);
 505
 506         // Get the `Ident` of the method being called and the corresponding `impl` (to point at
 507         // `Bar` in `impl Foo for dyn Bar {}` and the definition of the method being called).
 508         let (ident, self_ty) =
 509             match self.get_impl_ident_and_self_ty_from_trait(instance.def_id(), &v.0) {
 510                 Some((ident, self_ty)) => (ident, self_ty),
 511                 None => return false,
 512             };
 513
 514         // Find the trait object types in the argument, so we point at *only* the trait object.
 515         self.suggest_constrain_dyn_trait_in_impl(err, &v.0, ident, self_ty)
 516     }
 517
 518     fn suggest_constrain_dyn_trait_in_impl(
 519         &self,
 520         err: &mut DiagnosticBuilder<'_>,
 521         found_dids: &FxHashSet<DefId>,
 522         ident: Ident,
 523         self_ty: &hir::Ty<'_>,
 524     ) -> bool {
 525         let mut suggested = false;
 526         for found_did in found_dids {
 527             let mut traits = vec![];
 528             let mut hir_v = HirTraitObjectVisitor(&mut traits, *found_did);
 529             hir_v.visit_ty(&self_ty);
 530             for span in &traits {
 531                 let mut multi_span: MultiSpan = vec![*span].into();
 532                 multi_span.push_span_label(
 533                     *span,
 534                     "this has an implicit `'static` lifetime requirement".to_string(),
 535                 );
 536                 multi_span.push_span_label(
 537                     ident.span,
 538                     "calling this method introduces the `impl`'s 'static` requirement".to_string(),
 539                 );
 540                 err.span_note(multi_span, "the used `impl` has a `'static` requirement");
 541                 err.span_suggestion_verbose(
 542                     span.shrink_to_hi(),
 543                     "consider relaxing the implicit `'static` requirement",
 544                     " + '_".to_string(),
 545                     Applicability::MaybeIncorrect,
 546                 );
 547                 suggested = true;
 548             }
 549         }
 550         suggested
 551     }
 552 }
 553
 554 /// Collect all the trait objects in a type that could have received an implicit `'static` lifetime.
 555 pub(super) struct TraitObjectVisitor(pub(super) FxHashSet<DefId>);
 556
 557 impl<'tcx> TypeVisitor<'tcx> for TraitObjectVisitor {
 558     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 559         match t.kind() {
 560             ty::Dynamic(preds, re) if re.is_static() => {
 561                 if let Some(def_id) = preds.principal_def_id() {
 562                     self.0.insert(def_id);
 563                 }
 564                 ControlFlow::CONTINUE
 565             }
 566             _ => t.super_visit_with(self),
 567         }
 568     }
 569 }
 570
 571 /// Collect all `hir::Ty<'_>` `Span`s for trait objects with an implicit lifetime.
 572 pub(super) struct HirTraitObjectVisitor<'a>(pub(super) &'a mut Vec<Span>, pub(super) DefId);
 573
 574 impl<'a, 'tcx> Visitor<'tcx> for HirTraitObjectVisitor<'a> {
 575     fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx>) {
 576         if let TyKind::TraitObject(
 577             poly_trait_refs,
 578             Lifetime { name: LifetimeName::ImplicitObjectLifetimeDefault, .. },
 579             _,
 580         ) = t.kind
 581         {
 582             for ptr in poly_trait_refs {
 583                 if Some(self.1) == ptr.trait_ref.trait_def_id() {
 584                     self.0.push(ptr.span);
 585                 }
 586             }
 587         }
 588         walk_ty(self, t);
 589     }
 590 }