compiler/rustc_borrowck/src/diagnostics/region_errors.rs

   1 #![deny(rustc::untranslatable_diagnostic)]
   2 #![deny(rustc::diagnostic_outside_of_impl)]
   3 //! Error reporting machinery for lifetime errors.
   4
   5 use rustc_data_structures::fx::FxIndexSet;
   6 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
   7 use rustc_hir::def_id::DefId;
   8 use rustc_hir::intravisit::Visitor;
   9 use rustc_hir::{self as hir, Item, ItemKind, Node};
  10 use rustc_infer::infer::{
  11     error_reporting::nice_region_error::{
  12         self, find_anon_type, find_param_with_region, suggest_adding_lifetime_params,
  13         HirTraitObjectVisitor, NiceRegionError, TraitObjectVisitor,
  14     },
  15     error_reporting::unexpected_hidden_region_diagnostic,
  16     NllRegionVariableOrigin, RelateParamBound,
  17 };
  18 use rustc_middle::hir::place::PlaceBase;
  19 use rustc_middle::mir::{ConstraintCategory, ReturnConstraint};
  20 use rustc_middle::ty::subst::InternalSubsts;
  21 use rustc_middle::ty::Region;
  22 use rustc_middle::ty::TypeVisitor;
  23 use rustc_middle::ty::{self, RegionVid, Ty};
  24 use rustc_span::symbol::{kw, Ident};
  25 use rustc_span::Span;
  26
  27 use crate::borrowck_errors;
  28 use crate::session_diagnostics::{
  29     FnMutError, FnMutReturnTypeErr, GenericDoesNotLiveLongEnough, LifetimeOutliveErr,
  30     LifetimeReturnCategoryErr, RequireStaticErr, VarHereDenote,
  31 };
  32
  33 use super::{OutlivesSuggestionBuilder, RegionName};
  34 use crate::region_infer::{BlameConstraint, ExtraConstraintInfo};
  35 use crate::{
  36     nll::ConstraintDescription,
  37     region_infer::{values::RegionElement, TypeTest},
  38     universal_regions::DefiningTy,
  39     MirBorrowckCtxt,
  40 };
  41
  42 impl<'tcx> ConstraintDescription for ConstraintCategory<'tcx> {
  43     fn description(&self) -> &'static str {
  44         // Must end with a space. Allows for empty names to be provided.
  45         match self {
  46             ConstraintCategory::Assignment => "assignment ",
  47             ConstraintCategory::Return(_) => "returning this value ",
  48             ConstraintCategory::Yield => "yielding this value ",
  49             ConstraintCategory::UseAsConst => "using this value as a constant ",
  50             ConstraintCategory::UseAsStatic => "using this value as a static ",
  51             ConstraintCategory::Cast => "cast ",
  52             ConstraintCategory::CallArgument(_) => "argument ",
  53             ConstraintCategory::TypeAnnotation => "type annotation ",
  54             ConstraintCategory::ClosureBounds => "closure body ",
  55             ConstraintCategory::SizedBound => "proving this value is `Sized` ",
  56             ConstraintCategory::CopyBound => "copying this value ",
  57             ConstraintCategory::OpaqueType => "opaque type ",
  58             ConstraintCategory::ClosureUpvar(_) => "closure capture ",
  59             ConstraintCategory::Usage => "this usage ",
  60             ConstraintCategory::Predicate(_)
  61             | ConstraintCategory::Boring
  62             | ConstraintCategory::BoringNoLocation
  63             | ConstraintCategory::Internal => "",
  64         }
  65     }
  66 }
  67
  68 /// A collection of errors encountered during region inference. This is needed to efficiently
  69 /// report errors after borrow checking.
  70 ///
  71 /// Usually we expect this to either be empty or contain a small number of items, so we can avoid
  72 /// allocation most of the time.
  73 pub(crate) type RegionErrors<'tcx> = Vec<RegionErrorKind<'tcx>>;
  74
  75 #[derive(Clone, Debug)]
  76 pub(crate) enum RegionErrorKind<'tcx> {
  77     /// A generic bound failure for a type test (`T: 'a`).
  78     TypeTestError { type_test: TypeTest<'tcx> },
  79
  80     /// An unexpected hidden region for an opaque type.
  81     UnexpectedHiddenRegion {
  82         /// The span for the member constraint.
  83         span: Span,
  84         /// The hidden type.
  85         hidden_ty: Ty<'tcx>,
  86         /// The opaque type.
  87         key: ty::OpaqueTypeKey<'tcx>,
  88         /// The unexpected region.
  89         member_region: ty::Region<'tcx>,
  90     },
  91
  92     /// Higher-ranked subtyping error.
  93     BoundUniversalRegionError {
  94         /// The placeholder free region.
  95         longer_fr: RegionVid,
  96         /// The region element that erroneously must be outlived by `longer_fr`.
  97         error_element: RegionElement,
  98         /// The placeholder region.
  99         placeholder: ty::PlaceholderRegion,
 100     },
 101
 102     /// Any other lifetime error.
 103     RegionError {
 104         /// The origin of the region.
 105         fr_origin: NllRegionVariableOrigin,
 106         /// The region that should outlive `shorter_fr`.
 107         longer_fr: RegionVid,
 108         /// The region that should be shorter, but we can't prove it.
 109         shorter_fr: RegionVid,
 110         /// Indicates whether this is a reported error. We currently only report the first error
 111         /// encountered and leave the rest unreported so as not to overwhelm the user.
 112         is_reported: bool,
 113     },
 114 }
 115
 116 /// Information about the various region constraints involved in a borrow checker error.
 117 #[derive(Clone, Debug)]
 118 pub struct ErrorConstraintInfo<'tcx> {
 119     // fr: outlived_fr
 120     pub(super) fr: RegionVid,
 121     pub(super) fr_is_local: bool,
 122     pub(super) outlived_fr: RegionVid,
 123     pub(super) outlived_fr_is_local: bool,
 124
 125     // Category and span for best blame constraint
 126     pub(super) category: ConstraintCategory<'tcx>,
 127     pub(super) span: Span,
 128 }
 129
 130 impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
 131     /// Converts a region inference variable into a `ty::Region` that
 132     /// we can use for error reporting. If `r` is universally bound,
 133     /// then we use the name that we have on record for it. If `r` is
 134     /// existentially bound, then we check its inferred value and try
 135     /// to find a good name from that. Returns `None` if we can't find
 136     /// one (e.g., this is just some random part of the CFG).
 137     pub(super) fn to_error_region(&self, r: RegionVid) -> Option<ty::Region<'tcx>> {
 138         self.to_error_region_vid(r).and_then(|r| self.regioncx.region_definition(r).external_name)
 139     }
 140
 141     /// Returns the `RegionVid` corresponding to the region returned by
 142     /// `to_error_region`.
 143     pub(super) fn to_error_region_vid(&self, r: RegionVid) -> Option<RegionVid> {
 144         if self.regioncx.universal_regions().is_universal_region(r) {
 145             Some(r)
 146         } else {
 147             // We just want something nameable, even if it's not
 148             // actually an upper bound.
 149             let upper_bound = self.regioncx.approx_universal_upper_bound(r);
 150
 151             if self.regioncx.upper_bound_in_region_scc(r, upper_bound) {
 152                 self.to_error_region_vid(upper_bound)
 153             } else {
 154                 None
 155             }
 156         }
 157     }
 158
 159     /// Returns `true` if a closure is inferred to be an `FnMut` closure.
 160     fn is_closure_fn_mut(&self, fr: RegionVid) -> bool {
 161         if let Some(ty::ReFree(free_region)) = self.to_error_region(fr).as_deref()
 162             && let ty::BoundRegionKind::BrEnv = free_region.bound_region
 163             && let DefiningTy::Closure(_, substs) = self.regioncx.universal_regions().defining_ty
 164         {
 165             return substs.as_closure().kind() == ty::ClosureKind::FnMut;
 166         }
 167
 168         false
 169     }
 170
 171     /// Produces nice borrowck error diagnostics for all the errors collected in `nll_errors`.
 172     pub(crate) fn report_region_errors(&mut self, nll_errors: RegionErrors<'tcx>) {
 173         // Iterate through all the errors, producing a diagnostic for each one. The diagnostics are
 174         // buffered in the `MirBorrowckCtxt`.
 175
 176         let mut outlives_suggestion = OutlivesSuggestionBuilder::default();
 177
 178         for nll_error in nll_errors.into_iter() {
 179             match nll_error {
 180                 RegionErrorKind::TypeTestError { type_test } => {
 181                     // Try to convert the lower-bound region into something named we can print for the user.
 182                     let lower_bound_region = self.to_error_region(type_test.lower_bound);
 183
 184                     let type_test_span = type_test.span;
 185
 186                     if let Some(lower_bound_region) = lower_bound_region {
 187                         let generic_ty = type_test.generic_kind.to_ty(self.infcx.tcx);
 188                         let origin = RelateParamBound(type_test_span, generic_ty, None);
 189                         self.buffer_error(self.infcx.err_ctxt().construct_generic_bound_failure(
 190                             self.body.source.def_id().expect_local(),
 191                             type_test_span,
 192                             Some(origin),
 193                             type_test.generic_kind,
 194                             lower_bound_region,
 195                         ));
 196                     } else {
 197                         // FIXME. We should handle this case better. It
 198                         // indicates that we have e.g., some region variable
 199                         // whose value is like `'a+'b` where `'a` and `'b` are
 200                         // distinct unrelated universal regions that are not
 201                         // known to outlive one another. It'd be nice to have
 202                         // some examples where this arises to decide how best
 203                         // to report it; we could probably handle it by
 204                         // iterating over the universal regions and reporting
 205                         // an error that multiple bounds are required.
 206                         self.buffer_error(self.infcx.tcx.sess.create_err(
 207                             GenericDoesNotLiveLongEnough {
 208                                 kind: type_test.generic_kind.to_string(),
 209                                 span: type_test_span,
 210                             },
 211                         ));
 212                     }
 213                 }
 214
 215                 RegionErrorKind::UnexpectedHiddenRegion { span, hidden_ty, key, member_region } => {
 216                     let named_ty = self.regioncx.name_regions(self.infcx.tcx, hidden_ty);
 217                     let named_key = self.regioncx.name_regions(self.infcx.tcx, key);
 218                     let named_region = self.regioncx.name_regions(self.infcx.tcx, member_region);
 219                     self.buffer_error(unexpected_hidden_region_diagnostic(
 220                         self.infcx.tcx,
 221                         span,
 222                         named_ty,
 223                         named_region,
 224                         named_key,
 225                     ));
 226                 }
 227
 228                 RegionErrorKind::BoundUniversalRegionError {
 229                     longer_fr,
 230                     placeholder,
 231                     error_element,
 232                 } => {
 233                     let error_vid = self.regioncx.region_from_element(longer_fr, &error_element);
 234
 235                     // Find the code to blame for the fact that `longer_fr` outlives `error_fr`.
 236                     let (_, cause) = self.regioncx.find_outlives_blame_span(
 237                         longer_fr,
 238                         NllRegionVariableOrigin::Placeholder(placeholder),
 239                         error_vid,
 240                     );
 241
 242                     let universe = placeholder.universe;
 243                     let universe_info = self.regioncx.universe_info(universe);
 244
 245                     universe_info.report_error(self, placeholder, error_element, cause);
 246                 }
 247
 248                 RegionErrorKind::RegionError { fr_origin, longer_fr, shorter_fr, is_reported } => {
 249                     if is_reported {
 250                         self.report_region_error(
 251                             longer_fr,
 252                             fr_origin,
 253                             shorter_fr,
 254                             &mut outlives_suggestion,
 255                         );
 256                     } else {
 257                         // We only report the first error, so as not to overwhelm the user. See
 258                         // `RegRegionErrorKind` docs.
 259                         //
 260                         // FIXME: currently we do nothing with these, but perhaps we can do better?
 261                         // FIXME: try collecting these constraints on the outlives suggestion
 262                         // builder. Does it make the suggestions any better?
 263                         debug!(
 264                             "Unreported region error: can't prove that {:?}: {:?}",
 265                             longer_fr, shorter_fr
 266                         );
 267                     }
 268                 }
 269             }
 270         }
 271
 272         // Emit one outlives suggestions for each MIR def we borrowck
 273         outlives_suggestion.add_suggestion(self);
 274     }
 275
 276     fn get_impl_ident_and_self_ty_from_trait(
 277         &self,
 278         def_id: DefId,
 279         trait_objects: &FxIndexSet<DefId>,
 280     ) -> Option<(Ident, &'tcx hir::Ty<'tcx>)> {
 281         let tcx = self.infcx.tcx;
 282         match tcx.hir().get_if_local(def_id) {
 283             Some(Node::ImplItem(impl_item)) => {
 284                 match tcx.hir().find_by_def_id(tcx.hir().get_parent_item(impl_item.hir_id()).def_id)
 285                 {
 286                     Some(Node::Item(Item {
 287                         kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
 288                         ..
 289                     })) => Some((impl_item.ident, self_ty)),
 290                     _ => None,
 291                 }
 292             }
 293             Some(Node::TraitItem(trait_item)) => {
 294                 let trait_did = tcx.hir().get_parent_item(trait_item.hir_id());
 295                 match tcx.hir().find_by_def_id(trait_did.def_id) {
 296                     Some(Node::Item(Item { kind: ItemKind::Trait(..), .. })) => {
 297                         // The method being called is defined in the `trait`, but the `'static`
 298                         // obligation comes from the `impl`. Find that `impl` so that we can point
 299                         // at it in the suggestion.
 300                         let trait_did = trait_did.to_def_id();
 301                         match tcx
 302                             .hir()
 303                             .trait_impls(trait_did)
 304                             .iter()
 305                             .filter_map(|&impl_did| {
 306                                 match tcx.hir().get_if_local(impl_did.to_def_id()) {
 307                                     Some(Node::Item(Item {
 308                                         kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
 309                                         ..
 310                                     })) if trait_objects.iter().all(|did| {
 311                                         // FIXME: we should check `self_ty` against the receiver
 312                                         // type in the `UnifyReceiver` context, but for now, use
 313                                         // this imperfect proxy. This will fail if there are
 314                                         // multiple `impl`s for the same trait like
 315                                         // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
 316                                         // In that case, only the first one will get suggestions.
 317                                         let mut traits = vec![];
 318                                         let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
 319                                         hir_v.visit_ty(self_ty);
 320                                         !traits.is_empty()
 321                                     }) =>
 322                                     {
 323                                         Some(self_ty)
 324                                     }
 325                                     _ => None,
 326                                 }
 327                             })
 328                             .next()
 329                         {
 330                             Some(self_ty) => Some((trait_item.ident, self_ty)),
 331                             _ => None,
 332                         }
 333                     }
 334                     _ => None,
 335                 }
 336             }
 337             _ => None,
 338         }
 339     }
 340
 341     /// Report an error because the universal region `fr` was required to outlive
 342     /// `outlived_fr` but it is not known to do so. For example:
 343     ///
 344     /// ```compile_fail
 345     /// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
 346     /// ```
 347     ///
 348     /// Here we would be invoked with `fr = 'a` and `outlived_fr = `'b`.
 349     pub(crate) fn report_region_error(
 350         &mut self,
 351         fr: RegionVid,
 352         fr_origin: NllRegionVariableOrigin,
 353         outlived_fr: RegionVid,
 354         outlives_suggestion: &mut OutlivesSuggestionBuilder,
 355     ) {
 356         debug!("report_region_error(fr={:?}, outlived_fr={:?})", fr, outlived_fr);
 357
 358         let (blame_constraint, extra_info) =
 359             self.regioncx.best_blame_constraint(fr, fr_origin, |r| {
 360                 self.regioncx.provides_universal_region(r, fr, outlived_fr)
 361             });
 362         let BlameConstraint { category, cause, variance_info, .. } = blame_constraint;
 363
 364         debug!("report_region_error: category={:?} {:?} {:?}", category, cause, variance_info);
 365
 366         // Check if we can use one of the "nice region errors".
 367         if let (Some(f), Some(o)) = (self.to_error_region(fr), self.to_error_region(outlived_fr)) {
 368             let infer_err = self.infcx.err_ctxt();
 369             let nice = NiceRegionError::new_from_span(&infer_err, cause.span, o, f);
 370             if let Some(diag) = nice.try_report_from_nll() {
 371                 self.buffer_error(diag);
 372                 return;
 373             }
 374         }
 375
 376         let (fr_is_local, outlived_fr_is_local): (bool, bool) = (
 377             self.regioncx.universal_regions().is_local_free_region(fr),
 378             self.regioncx.universal_regions().is_local_free_region(outlived_fr),
 379         );
 380
 381         debug!(
 382             "report_region_error: fr_is_local={:?} outlived_fr_is_local={:?} category={:?}",
 383             fr_is_local, outlived_fr_is_local, category
 384         );
 385
 386         let errci = ErrorConstraintInfo {
 387             fr,
 388             outlived_fr,
 389             fr_is_local,
 390             outlived_fr_is_local,
 391             category,
 392             span: cause.span,
 393         };
 394
 395         let mut diag = match (category, fr_is_local, outlived_fr_is_local) {
 396             (ConstraintCategory::Return(kind), true, false) if self.is_closure_fn_mut(fr) => {
 397                 self.report_fnmut_error(&errci, kind)
 398             }
 399             (ConstraintCategory::Assignment, true, false)
 400             | (ConstraintCategory::CallArgument(_), true, false) => {
 401                 let mut db = self.report_escaping_data_error(&errci);
 402
 403                 outlives_suggestion.intermediate_suggestion(self, &errci, &mut db);
 404                 outlives_suggestion.collect_constraint(fr, outlived_fr);
 405
 406                 db
 407             }
 408             _ => {
 409                 let mut db = self.report_general_error(&errci);
 410
 411                 outlives_suggestion.intermediate_suggestion(self, &errci, &mut db);
 412                 outlives_suggestion.collect_constraint(fr, outlived_fr);
 413
 414                 db
 415             }
 416         };
 417
 418         match variance_info {
 419             ty::VarianceDiagInfo::None => {}
 420             ty::VarianceDiagInfo::Invariant { ty, param_index } => {
 421                 let (desc, note) = match ty.kind() {
 422                     ty::RawPtr(ty_mut) => {
 423                         assert_eq!(ty_mut.mutbl, rustc_hir::Mutability::Mut);
 424                         (
 425                             format!("a mutable pointer to `{}`", ty_mut.ty),
 426                             "mutable pointers are invariant over their type parameter".to_string(),
 427                         )
 428                     }
 429                     ty::Ref(_, inner_ty, mutbl) => {
 430                         assert_eq!(*mutbl, rustc_hir::Mutability::Mut);
 431                         (
 432                             format!("a mutable reference to `{inner_ty}`"),
 433                             "mutable references are invariant over their type parameter"
 434                                 .to_string(),
 435                         )
 436                     }
 437                     ty::Adt(adt, substs) => {
 438                         let generic_arg = substs[param_index as usize];
 439                         let identity_substs =
 440                             InternalSubsts::identity_for_item(self.infcx.tcx, adt.did());
 441                         let base_ty = self.infcx.tcx.mk_adt(*adt, identity_substs);
 442                         let base_generic_arg = identity_substs[param_index as usize];
 443                         let adt_desc = adt.descr();
 444
 445                         let desc = format!(
 446                             "the type `{ty}`, which makes the generic argument `{generic_arg}` invariant"
 447                         );
 448                         let note = format!(
 449                             "the {adt_desc} `{base_ty}` is invariant over the parameter `{base_generic_arg}`"
 450                         );
 451                         (desc, note)
 452                     }
 453                     ty::FnDef(def_id, _) => {
 454                         let name = self.infcx.tcx.item_name(*def_id);
 455                         let identity_substs =
 456                             InternalSubsts::identity_for_item(self.infcx.tcx, *def_id);
 457                         let desc = format!("a function pointer to `{name}`");
 458                         let note = format!(
 459                             "the function `{name}` is invariant over the parameter `{}`",
 460                             identity_substs[param_index as usize]
 461                         );
 462                         (desc, note)
 463                     }
 464                     _ => panic!("Unexpected type {:?}", ty),
 465                 };
 466                 diag.note(&format!("requirement occurs because of {desc}",));
 467                 diag.note(&note);
 468                 diag.help("see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance");
 469             }
 470         }
 471
 472         for extra in extra_info {
 473             match extra {
 474                 ExtraConstraintInfo::PlaceholderFromPredicate(span) => {
 475                     diag.span_note(span, format!("due to current limitations in the borrow checker, this implies a `'static` lifetime"));
 476                 }
 477             }
 478         }
 479
 480         self.buffer_error(diag);
 481     }
 482
 483     /// Report a specialized error when `FnMut` closures return a reference to a captured variable.
 484     /// This function expects `fr` to be local and `outlived_fr` to not be local.
 485     ///
 486     /// ```text
 487     /// error: captured variable cannot escape `FnMut` closure body
 488     ///   --> $DIR/issue-53040.rs:15:8
 489     ///    |
 490     /// LL |     || &mut v;
 491     ///    |     -- ^^^^^^ creates a reference to a captured variable which escapes the closure body
 492     ///    |     |
 493     ///    |     inferred to be a `FnMut` closure
 494     ///    |
 495     ///    = note: `FnMut` closures only have access to their captured variables while they are
 496     ///            executing...
 497     ///    = note: ...therefore, returned references to captured variables will escape the closure
 498     /// ```
 499     fn report_fnmut_error(
 500         &self,
 501         errci: &ErrorConstraintInfo<'tcx>,
 502         kind: ReturnConstraint,
 503     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
 504         let ErrorConstraintInfo { outlived_fr, span, .. } = errci;
 505
 506         let mut output_ty = self.regioncx.universal_regions().unnormalized_output_ty;
 507         if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) = *output_ty.kind() {
 508             output_ty = self.infcx.tcx.type_of(def_id)
 509         };
 510
 511         debug!("report_fnmut_error: output_ty={:?}", output_ty);
 512
 513         let err = FnMutError {
 514             span: *span,
 515             ty_err: match output_ty.kind() {
 516                 ty::Closure(_, _) => FnMutReturnTypeErr::ReturnClosure { span: *span },
 517                 ty::Generator(def, ..) if self.infcx.tcx.generator_is_async(*def) => {
 518                     FnMutReturnTypeErr::ReturnAsyncBlock { span: *span }
 519                 }
 520                 _ => FnMutReturnTypeErr::ReturnRef { span: *span },
 521             },
 522         };
 523
 524         let mut diag = self.infcx.tcx.sess.create_err(err);
 525
 526         if let ReturnConstraint::ClosureUpvar(upvar_field) = kind {
 527             let def_id = match self.regioncx.universal_regions().defining_ty {
 528                 DefiningTy::Closure(def_id, _) => def_id,
 529                 ty => bug!("unexpected DefiningTy {:?}", ty),
 530             };
 531
 532             let captured_place = &self.upvars[upvar_field.index()].place;
 533             let defined_hir = match captured_place.place.base {
 534                 PlaceBase::Local(hirid) => Some(hirid),
 535                 PlaceBase::Upvar(upvar) => Some(upvar.var_path.hir_id),
 536                 _ => None,
 537             };
 538
 539             if let Some(def_hir) = defined_hir {
 540                 let upvars_map = self.infcx.tcx.upvars_mentioned(def_id).unwrap();
 541                 let upvar_def_span = self.infcx.tcx.hir().span(def_hir);
 542                 let upvar_span = upvars_map.get(&def_hir).unwrap().span;
 543                 diag.subdiagnostic(VarHereDenote::Defined { span: upvar_def_span });
 544                 diag.subdiagnostic(VarHereDenote::Captured { span: upvar_span });
 545             }
 546         }
 547
 548         if let Some(fr_span) = self.give_region_a_name(*outlived_fr).unwrap().span() {
 549             diag.subdiagnostic(VarHereDenote::FnMutInferred { span: fr_span });
 550         }
 551
 552         self.suggest_move_on_borrowing_closure(&mut diag);
 553
 554         diag
 555     }
 556
 557     /// Reports an error specifically for when data is escaping a closure.
 558     ///
 559     /// ```text
 560     /// error: borrowed data escapes outside of function
 561     ///   --> $DIR/lifetime-bound-will-change-warning.rs:44:5
 562     ///    |
 563     /// LL | fn test2<'a>(x: &'a Box<Fn()+'a>) {
 564     ///    |              - `x` is a reference that is only valid in the function body
 565     /// LL |     // but ref_obj will not, so warn.
 566     /// LL |     ref_obj(x)
 567     ///    |     ^^^^^^^^^^ `x` escapes the function body here
 568     /// ```
 569     #[instrument(level = "debug", skip(self))]
 570     fn report_escaping_data_error(
 571         &self,
 572         errci: &ErrorConstraintInfo<'tcx>,
 573     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
 574         let ErrorConstraintInfo { span, category, .. } = errci;
 575
 576         let fr_name_and_span = self.regioncx.get_var_name_and_span_for_region(
 577             self.infcx.tcx,
 578             &self.body,
 579             &self.local_names,
 580             &self.upvars,
 581             errci.fr,
 582         );
 583         let outlived_fr_name_and_span = self.regioncx.get_var_name_and_span_for_region(
 584             self.infcx.tcx,
 585             &self.body,
 586             &self.local_names,
 587             &self.upvars,
 588             errci.outlived_fr,
 589         );
 590
 591         let (_, escapes_from) = self
 592             .infcx
 593             .tcx
 594             .article_and_description(self.regioncx.universal_regions().defining_ty.def_id());
 595
 596         // Revert to the normal error in these cases.
 597         // Assignments aren't "escapes" in function items.
 598         if (fr_name_and_span.is_none() && outlived_fr_name_and_span.is_none())
 599             || (*category == ConstraintCategory::Assignment
 600                 && self.regioncx.universal_regions().defining_ty.is_fn_def())
 601             || self.regioncx.universal_regions().defining_ty.is_const()
 602         {
 603             return self.report_general_error(&ErrorConstraintInfo {
 604                 fr_is_local: true,
 605                 outlived_fr_is_local: false,
 606                 ..*errci
 607             });
 608         }
 609
 610         let mut diag =
 611             borrowck_errors::borrowed_data_escapes_closure(self.infcx.tcx, *span, escapes_from);
 612
 613         if let Some((Some(outlived_fr_name), outlived_fr_span)) = outlived_fr_name_and_span {
 614             diag.span_label(
 615                 outlived_fr_span,
 616                 format!("`{outlived_fr_name}` declared here, outside of the {escapes_from} body",),
 617             );
 618         }
 619
 620         if let Some((Some(fr_name), fr_span)) = fr_name_and_span {
 621             diag.span_label(
 622                 fr_span,
 623                 format!(
 624                     "`{fr_name}` is a reference that is only valid in the {escapes_from} body",
 625                 ),
 626             );
 627
 628             diag.span_label(*span, format!("`{fr_name}` escapes the {escapes_from} body here"));
 629         }
 630
 631         // Only show an extra note if we can find an 'error region' for both of the region
 632         // variables. This avoids showing a noisy note that just mentions 'synthetic' regions
 633         // that don't help the user understand the error.
 634         match (self.to_error_region(errci.fr), self.to_error_region(errci.outlived_fr)) {
 635             (Some(f), Some(o)) => {
 636                 self.maybe_suggest_constrain_dyn_trait_impl(&mut diag, f, o, category);
 637
 638                 let fr_region_name = self.give_region_a_name(errci.fr).unwrap();
 639                 fr_region_name.highlight_region_name(&mut diag);
 640                 let outlived_fr_region_name = self.give_region_a_name(errci.outlived_fr).unwrap();
 641                 outlived_fr_region_name.highlight_region_name(&mut diag);
 642
 643                 diag.span_label(
 644                     *span,
 645                     format!(
 646                         "{}requires that `{}` must outlive `{}`",
 647                         category.description(),
 648                         fr_region_name,
 649                         outlived_fr_region_name,
 650                     ),
 651                 );
 652             }
 653             _ => {}
 654         }
 655
 656         diag
 657     }
 658
 659     /// Reports a region inference error for the general case with named/synthesized lifetimes to
 660     /// explain what is happening.
 661     ///
 662     /// ```text
 663     /// error: unsatisfied lifetime constraints
 664     ///   --> $DIR/regions-creating-enums3.rs:17:5
 665     ///    |
 666     /// LL | fn mk_add_bad1<'a,'b>(x: &'a ast<'a>, y: &'b ast<'b>) -> ast<'a> {
 667     ///    |                -- -- lifetime `'b` defined here
 668     ///    |                |
 669     ///    |                lifetime `'a` defined here
 670     /// LL |     ast::add(x, y)
 671     ///    |     ^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'a` but it
 672     ///    |                    is returning data with lifetime `'b`
 673     /// ```
 674     fn report_general_error(
 675         &self,
 676         errci: &ErrorConstraintInfo<'tcx>,
 677     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
 678         let ErrorConstraintInfo {
 679             fr,
 680             fr_is_local,
 681             outlived_fr,
 682             outlived_fr_is_local,
 683             span,
 684             category,
 685             ..
 686         } = errci;
 687
 688         let (_, mir_def_name) =
 689             self.infcx.tcx.article_and_description(self.mir_def_id().to_def_id());
 690
 691         let err = LifetimeOutliveErr { span: *span };
 692         let mut diag = self.infcx.tcx.sess.create_err(err);
 693
 694         let fr_name = self.give_region_a_name(*fr).unwrap();
 695         fr_name.highlight_region_name(&mut diag);
 696         let outlived_fr_name = self.give_region_a_name(*outlived_fr).unwrap();
 697         outlived_fr_name.highlight_region_name(&mut diag);
 698
 699         let err_category = match (category, outlived_fr_is_local, fr_is_local) {
 700             (ConstraintCategory::Return(_), true, _) => LifetimeReturnCategoryErr::WrongReturn {
 701                 span: *span,
 702                 mir_def_name,
 703                 outlived_fr_name,
 704                 fr_name: &fr_name,
 705             },
 706             _ => LifetimeReturnCategoryErr::ShortReturn {
 707                 span: *span,
 708                 category_desc: category.description(),
 709                 free_region_name: &fr_name,
 710                 outlived_fr_name,
 711             },
 712         };
 713
 714         diag.subdiagnostic(err_category);
 715
 716         self.add_static_impl_trait_suggestion(&mut diag, *fr, fr_name, *outlived_fr);
 717         self.suggest_adding_lifetime_params(&mut diag, *fr, *outlived_fr);
 718         self.suggest_move_on_borrowing_closure(&mut diag);
 719
 720         diag
 721     }
 722
 723     /// Adds a suggestion to errors where an `impl Trait` is returned.
 724     ///
 725     /// ```text
 726     /// help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as
 727     ///       a constraint
 728     ///    |
 729     /// LL |     fn iter_values_anon(&self) -> impl Iterator<Item=u32> + 'a {
 730     ///    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 731     /// ```
 732     fn add_static_impl_trait_suggestion(
 733         &self,
 734         diag: &mut Diagnostic,
 735         fr: RegionVid,
 736         // We need to pass `fr_name` - computing it again will label it twice.
 737         fr_name: RegionName,
 738         outlived_fr: RegionVid,
 739     ) {
 740         if let (Some(f), Some(outlived_f)) =
 741             (self.to_error_region(fr), self.to_error_region(outlived_fr))
 742         {
 743             if *outlived_f != ty::ReStatic {
 744                 return;
 745             }
 746
 747             let fn_returns = self
 748                 .infcx
 749                 .tcx
 750                 .is_suitable_region(f)
 751                 .map(|r| self.infcx.tcx.return_type_impl_or_dyn_traits(r.def_id))
 752                 .unwrap_or_default();
 753
 754             if fn_returns.is_empty() {
 755                 return;
 756             }
 757
 758             let param = if let Some(param) = find_param_with_region(self.infcx.tcx, f, outlived_f) {
 759                 param
 760             } else {
 761                 return;
 762             };
 763
 764             let lifetime = if f.has_name() { fr_name.name } else { kw::UnderscoreLifetime };
 765
 766             let arg = match param.param.pat.simple_ident() {
 767                 Some(simple_ident) => format!("argument `{}`", simple_ident),
 768                 None => "the argument".to_string(),
 769             };
 770             let captures = format!("captures data from {}", arg);
 771
 772             return nice_region_error::suggest_new_region_bound(
 773                 self.infcx.tcx,
 774                 diag,
 775                 fn_returns,
 776                 lifetime.to_string(),
 777                 Some(arg),
 778                 captures,
 779                 Some((param.param_ty_span, param.param_ty.to_string())),
 780             );
 781         }
 782     }
 783
 784     fn maybe_suggest_constrain_dyn_trait_impl(
 785         &self,
 786         diag: &mut Diagnostic,
 787         f: Region<'tcx>,
 788         o: Region<'tcx>,
 789         category: &ConstraintCategory<'tcx>,
 790     ) {
 791         if !o.is_static() {
 792             return;
 793         }
 794
 795         let tcx = self.infcx.tcx;
 796
 797         let instance = if let ConstraintCategory::CallArgument(Some(func_ty)) = category {
 798             let (fn_did, substs) = match func_ty.kind() {
 799                 ty::FnDef(fn_did, substs) => (fn_did, substs),
 800                 _ => return,
 801             };
 802             debug!(?fn_did, ?substs);
 803
 804             // Only suggest this on function calls, not closures
 805             let ty = tcx.type_of(fn_did);
 806             debug!("ty: {:?}, ty.kind: {:?}", ty, ty.kind());
 807             if let ty::Closure(_, _) = ty.kind() {
 808                 return;
 809             }
 810
 811             if let Ok(Some(instance)) = ty::Instance::resolve(
 812                 tcx,
 813                 self.param_env,
 814                 *fn_did,
 815                 self.infcx.resolve_vars_if_possible(substs),
 816             ) {
 817                 instance
 818             } else {
 819                 return;
 820             }
 821         } else {
 822             return;
 823         };
 824
 825         let param = match find_param_with_region(tcx, f, o) {
 826             Some(param) => param,
 827             None => return,
 828         };
 829         debug!(?param);
 830
 831         let mut visitor = TraitObjectVisitor(FxIndexSet::default());
 832         visitor.visit_ty(param.param_ty);
 833
 834         let Some((ident, self_ty)) =
 835             self.get_impl_ident_and_self_ty_from_trait(instance.def_id(), &visitor.0) else {return};
 836
 837         self.suggest_constrain_dyn_trait_in_impl(diag, &visitor.0, ident, self_ty);
 838     }
 839
 840     #[instrument(skip(self, err), level = "debug")]
 841     fn suggest_constrain_dyn_trait_in_impl(
 842         &self,
 843         err: &mut Diagnostic,
 844         found_dids: &FxIndexSet<DefId>,
 845         ident: Ident,
 846         self_ty: &hir::Ty<'_>,
 847     ) -> bool {
 848         debug!("err: {:#?}", err);
 849         let mut suggested = false;
 850         for found_did in found_dids {
 851             let mut traits = vec![];
 852             let mut hir_v = HirTraitObjectVisitor(&mut traits, *found_did);
 853             hir_v.visit_ty(&self_ty);
 854             debug!("trait spans found: {:?}", traits);
 855             for span in &traits {
 856                 let mut multi_span: MultiSpan = vec![*span].into();
 857                 multi_span
 858                     .push_span_label(*span, "this has an implicit `'static` lifetime requirement");
 859                 multi_span.push_span_label(
 860                     ident.span,
 861                     "calling this method introduces the `impl`'s 'static` requirement",
 862                 );
 863                 err.subdiagnostic(RequireStaticErr::UsedImpl { multi_span });
 864                 err.span_suggestion_verbose(
 865                     span.shrink_to_hi(),
 866                     "consider relaxing the implicit `'static` requirement",
 867                     " + '_",
 868                     Applicability::MaybeIncorrect,
 869                 );
 870                 suggested = true;
 871             }
 872         }
 873         suggested
 874     }
 875
 876     fn suggest_adding_lifetime_params(
 877         &self,
 878         diag: &mut Diagnostic,
 879         sub: RegionVid,
 880         sup: RegionVid,
 881     ) {
 882         let (Some(sub), Some(sup)) = (self.to_error_region(sub), self.to_error_region(sup)) else {
 883             return
 884         };
 885
 886         let Some((ty_sub, _)) = self
 887             .infcx
 888             .tcx
 889             .is_suitable_region(sub)
 890             .and_then(|anon_reg| find_anon_type(self.infcx.tcx, sub, &anon_reg.boundregion)) else {
 891             return
 892         };
 893
 894         let Some((ty_sup, _)) = self
 895             .infcx
 896             .tcx
 897             .is_suitable_region(sup)
 898             .and_then(|anon_reg| find_anon_type(self.infcx.tcx, sup, &anon_reg.boundregion)) else {
 899             return
 900         };
 901
 902         suggest_adding_lifetime_params(self.infcx.tcx, sub, ty_sup, ty_sub, diag);
 903     }
 904
 905     fn suggest_move_on_borrowing_closure(&self, diag: &mut Diagnostic) {
 906         let map = self.infcx.tcx.hir();
 907         let body_id = map.body_owned_by(self.mir_def_id());
 908         let expr = &map.body(body_id).value;
 909         let mut closure_span = None::<rustc_span::Span>;
 910         match expr.kind {
 911             hir::ExprKind::MethodCall(.., args, _) => {
 912                 for arg in args {
 913                     if let hir::ExprKind::Closure(hir::Closure {
 914                         capture_clause: hir::CaptureBy::Ref,
 915                         ..
 916                     }) = arg.kind
 917                     {
 918                         closure_span = Some(arg.span.shrink_to_lo());
 919                         break;
 920                     }
 921                 }
 922             }
 923             hir::ExprKind::Block(blk, _) => {
 924                 if let Some(expr) = blk.expr {
 925                     // only when the block is a closure
 926                     if let hir::ExprKind::Closure(hir::Closure {
 927                         capture_clause: hir::CaptureBy::Ref,
 928                         body,
 929                         ..
 930                     }) = expr.kind
 931                     {
 932                         let body = map.body(*body);
 933                         if !matches!(body.generator_kind, Some(hir::GeneratorKind::Async(..))) {
 934                             closure_span = Some(expr.span.shrink_to_lo());
 935                         }
 936                     }
 937                 }
 938             }
 939             _ => {}
 940         }
 941         if let Some(closure_span) = closure_span {
 942             diag.span_suggestion_verbose(
 943                 closure_span,
 944                 "consider adding 'move' keyword before the nested closure",
 945                 "move ",
 946                 Applicability::MaybeIncorrect,
 947             );
 948         }
 949     }
 950 }