//! Error reporting machinery for lifetime errors. use rustc_data_structures::fx::FxIndexSet; use rustc_errors::{Applicability, Diag, ErrorGuaranteed, MultiSpan}; use rustc_hir as hir; use rustc_hir::GenericBound::Trait; use rustc_hir::QPath::Resolved; use rustc_hir::WherePredicateKind::BoundPredicate; use rustc_hir::def::Res::Def; use rustc_hir::def_id::DefId; use rustc_hir::intravisit::VisitorExt; use rustc_hir::{PolyTraitRef, TyKind, WhereBoundPredicate}; use rustc_infer::infer::{NllRegionVariableOrigin, SubregionOrigin}; use rustc_middle::bug; use rustc_middle::hir::place::PlaceBase; use rustc_middle::mir::{AnnotationSource, ConstraintCategory, ReturnConstraint}; use rustc_middle::ty::{ self, GenericArgs, Region, RegionVid, Ty, TyCtxt, TypeFoldable, TypeVisitor, fold_regions, }; use rustc_span::{Ident, Span, kw}; use rustc_trait_selection::error_reporting::InferCtxtErrorExt; use rustc_trait_selection::error_reporting::infer::nice_region_error::{ self, HirTraitObjectVisitor, NiceRegionError, TraitObjectVisitor, find_anon_type, find_param_with_region, suggest_adding_lifetime_params, }; use rustc_trait_selection::infer::InferCtxtExt; use rustc_trait_selection::traits::{Obligation, ObligationCtxt}; use tracing::{debug, instrument, trace}; use super::{OutlivesSuggestionBuilder, RegionName, RegionNameSource}; use crate::nll::ConstraintDescription; use crate::region_infer::values::RegionElement; use crate::region_infer::{BlameConstraint, TypeTest}; use crate::session_diagnostics::{ FnMutError, FnMutReturnTypeErr, GenericDoesNotLiveLongEnough, LifetimeOutliveErr, LifetimeReturnCategoryErr, RequireStaticErr, VarHereDenote, }; use crate::universal_regions::DefiningTy; use crate::{MirBorrowckCtxt, borrowck_errors, fluent_generated as fluent}; impl<'tcx> ConstraintDescription for ConstraintCategory<'tcx> { fn description(&self) -> &'static str { // Must end with a space. Allows for empty names to be provided. match self { ConstraintCategory::Assignment => "assignment ", ConstraintCategory::Return(_) => "returning this value ", ConstraintCategory::Yield => "yielding this value ", ConstraintCategory::UseAsConst => "using this value as a constant ", ConstraintCategory::UseAsStatic => "using this value as a static ", ConstraintCategory::Cast { is_implicit_coercion: false, .. } => "cast ", ConstraintCategory::Cast { is_implicit_coercion: true, .. } => "coercion ", ConstraintCategory::CallArgument(_) => "argument ", ConstraintCategory::TypeAnnotation(AnnotationSource::GenericArg) => "generic argument ", ConstraintCategory::TypeAnnotation(_) => "type annotation ", ConstraintCategory::SizedBound => "proving this value is `Sized` ", ConstraintCategory::CopyBound => "copying this value ", ConstraintCategory::OpaqueType => "opaque type ", ConstraintCategory::ClosureUpvar(_) => "closure capture ", ConstraintCategory::Usage => "this usage ", ConstraintCategory::Predicate(_) | ConstraintCategory::Boring | ConstraintCategory::BoringNoLocation | ConstraintCategory::Internal | ConstraintCategory::OutlivesUnnameablePlaceholder(..) => "", } } } /// A collection of errors encountered during region inference. This is needed to efficiently /// report errors after borrow checking. /// /// Usually we expect this to either be empty or contain a small number of items, so we can avoid /// allocation most of the time. pub(crate) struct RegionErrors<'tcx>(Vec<(RegionErrorKind<'tcx>, ErrorGuaranteed)>, TyCtxt<'tcx>); impl<'tcx> RegionErrors<'tcx> { pub(crate) fn new(tcx: TyCtxt<'tcx>) -> Self { Self(vec![], tcx) } #[track_caller] pub(crate) fn push(&mut self, val: impl Into>) { let val = val.into(); let guar = self.1.sess.dcx().delayed_bug(format!("{val:?}")); self.0.push((val, guar)); } pub(crate) fn is_empty(&self) -> bool { self.0.is_empty() } pub(crate) fn into_iter( self, ) -> impl Iterator, ErrorGuaranteed)> { self.0.into_iter() } } impl std::fmt::Debug for RegionErrors<'_> { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { f.debug_tuple("RegionErrors").field(&self.0).finish() } } #[derive(Clone, Debug)] pub(crate) enum RegionErrorKind<'tcx> { /// A generic bound failure for a type test (`T: 'a`). TypeTestError { type_test: TypeTest<'tcx> }, /// Higher-ranked subtyping error. BoundUniversalRegionError { /// The placeholder free region. longer_fr: RegionVid, /// The region element that erroneously must be outlived by `longer_fr`. error_element: RegionElement, /// The placeholder region. placeholder: ty::PlaceholderRegion, }, /// Any other lifetime error. RegionError { /// The origin of the region. fr_origin: NllRegionVariableOrigin, /// The region that should outlive `shorter_fr`. longer_fr: RegionVid, /// The region that should be shorter, but we can't prove it. shorter_fr: RegionVid, /// Indicates whether this is a reported error. We currently only report the first error /// encountered and leave the rest unreported so as not to overwhelm the user. is_reported: bool, }, } /// Information about the various region constraints involved in a borrow checker error. #[derive(Clone, Debug)] pub(crate) struct ErrorConstraintInfo<'tcx> { // fr: outlived_fr pub(super) fr: RegionVid, pub(super) outlived_fr: RegionVid, // Category and span for best blame constraint pub(super) category: ConstraintCategory<'tcx>, pub(super) span: Span, } impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> { /// Converts a region inference variable into a `ty::Region` that /// we can use for error reporting. If `r` is universally bound, /// then we use the name that we have on record for it. If `r` is /// existentially bound, then we check its inferred value and try /// to find a good name from that. Returns `None` if we can't find /// one (e.g., this is just some random part of the CFG). pub(super) fn to_error_region(&self, r: RegionVid) -> Option> { self.to_error_region_vid(r).and_then(|r| self.regioncx.region_definition(r).external_name) } /// Returns the `RegionVid` corresponding to the region returned by /// `to_error_region`. pub(super) fn to_error_region_vid(&self, r: RegionVid) -> Option { if self.regioncx.universal_regions().is_universal_region(r) { Some(r) } else { // We just want something nameable, even if it's not // actually an upper bound. let upper_bound = self.regioncx.approx_universal_upper_bound(r); if self.regioncx.upper_bound_in_region_scc(r, upper_bound) { self.to_error_region_vid(upper_bound) } else { None } } } /// Map the regions in the type to named regions, where possible. fn name_regions(&self, tcx: TyCtxt<'tcx>, ty: T) -> T where T: TypeFoldable>, { fold_regions(tcx, ty, |region, _| match region.kind() { ty::ReVar(vid) => self.to_error_region(vid).unwrap_or(region), _ => region, }) } /// Returns `true` if a closure is inferred to be an `FnMut` closure. fn is_closure_fn_mut(&self, fr: RegionVid) -> bool { if let Some(r) = self.to_error_region(fr) && let ty::ReLateParam(late_param) = r.kind() && let ty::LateParamRegionKind::ClosureEnv = late_param.kind && let DefiningTy::Closure(_, args) = self.regioncx.universal_regions().defining_ty { return args.as_closure().kind() == ty::ClosureKind::FnMut; } false } // For generic associated types (GATs) which implied 'static requirement // from higher-ranked trait bounds (HRTB). Try to locate span of the trait // and the span which bounded to the trait for adding 'static lifetime suggestion #[allow(rustc::diagnostic_outside_of_impl)] fn suggest_static_lifetime_for_gat_from_hrtb( &self, diag: &mut Diag<'_>, lower_bound: RegionVid, ) { let tcx = self.infcx.tcx; // find generic associated types in the given region 'lower_bound' let gat_id_and_generics = self .regioncx .placeholders_contained_in(lower_bound) .map(|placeholder| { if let Some(id) = placeholder.bound.kind.get_id() && let Some(placeholder_id) = id.as_local() && let gat_hir_id = tcx.local_def_id_to_hir_id(placeholder_id) && let Some(generics_impl) = tcx.parent_hir_node(tcx.parent_hir_id(gat_hir_id)).generics() { Some((gat_hir_id, generics_impl)) } else { None } }) .collect::>(); debug!(?gat_id_and_generics); // Look for the where-bound which introduces the placeholder. // As we're using the HIR, we need to handle both `for<'a> T: Trait<'a>` // and `T: for<'a> Trait`<'a>. let mut hrtb_bounds = vec![]; gat_id_and_generics.iter().flatten().for_each(|&(gat_hir_id, generics)| { for pred in generics.predicates { let BoundPredicate(WhereBoundPredicate { bound_generic_params, bounds, .. }) = pred.kind else { continue; }; if bound_generic_params .iter() .rfind(|bgp| tcx.local_def_id_to_hir_id(bgp.def_id) == gat_hir_id) .is_some() { for bound in *bounds { hrtb_bounds.push(bound); } } else { for bound in *bounds { if let Trait(trait_bound) = bound { if trait_bound .bound_generic_params .iter() .rfind(|bgp| tcx.local_def_id_to_hir_id(bgp.def_id) == gat_hir_id) .is_some() { hrtb_bounds.push(bound); return; } } } } } }); debug!(?hrtb_bounds); let mut suggestions = vec![]; hrtb_bounds.iter().for_each(|bound| { let Trait(PolyTraitRef { trait_ref, span: trait_span, .. }) = bound else { return; }; diag.span_note(*trait_span, fluent::borrowck_limitations_implies_static); let Some(generics_fn) = tcx.hir_get_generics(self.body.source.def_id().expect_local()) else { return; }; let Def(_, trait_res_defid) = trait_ref.path.res else { return; }; debug!(?generics_fn); generics_fn.predicates.iter().for_each(|predicate| { let BoundPredicate(WhereBoundPredicate { bounded_ty, bounds, .. }) = predicate.kind else { return; }; bounds.iter().for_each(|bd| { if let Trait(PolyTraitRef { trait_ref: tr_ref, .. }) = bd && let Def(_, res_defid) = tr_ref.path.res && res_defid == trait_res_defid // trait id matches && let TyKind::Path(Resolved(_, path)) = bounded_ty.kind && let Def(_, defid) = path.res && generics_fn.params .iter() .rfind(|param| param.def_id.to_def_id() == defid) .is_some() { suggestions.push((predicate.span.shrink_to_hi(), " + 'static".to_string())); } }); }); }); if suggestions.len() > 0 { suggestions.dedup(); diag.multipart_suggestion_verbose( fluent::borrowck_restrict_to_static, suggestions, Applicability::MaybeIncorrect, ); } } /// Produces nice borrowck error diagnostics for all the errors collected in `nll_errors`. pub(crate) fn report_region_errors(&mut self, nll_errors: RegionErrors<'tcx>) { // Iterate through all the errors, producing a diagnostic for each one. The diagnostics are // buffered in the `MirBorrowckCtxt`. let mut outlives_suggestion = OutlivesSuggestionBuilder::default(); for (nll_error, _) in nll_errors.into_iter() { match nll_error { RegionErrorKind::TypeTestError { type_test } => { // Try to convert the lower-bound region into something named we can print for // the user. let lower_bound_region = self.to_error_region(type_test.lower_bound); let type_test_span = type_test.span; if let Some(lower_bound_region) = lower_bound_region { let generic_ty = self.name_regions( self.infcx.tcx, type_test.generic_kind.to_ty(self.infcx.tcx), ); let origin = SubregionOrigin::RelateParamBound(type_test_span, generic_ty, None); self.buffer_error(self.infcx.err_ctxt().construct_generic_bound_failure( self.body.source.def_id().expect_local(), type_test_span, Some(origin), self.name_regions(self.infcx.tcx, type_test.generic_kind), lower_bound_region, )); } else { // FIXME. We should handle this case better. It // indicates that we have e.g., some region variable // whose value is like `'a+'b` where `'a` and `'b` are // distinct unrelated universal regions that are not // known to outlive one another. It'd be nice to have // some examples where this arises to decide how best // to report it; we could probably handle it by // iterating over the universal regions and reporting // an error that multiple bounds are required. let mut diag = self.dcx().create_err(GenericDoesNotLiveLongEnough { kind: type_test.generic_kind.to_string(), span: type_test_span, }); // Add notes and suggestions for the case of 'static lifetime // implied but not specified when a generic associated types // are from higher-ranked trait bounds self.suggest_static_lifetime_for_gat_from_hrtb( &mut diag, type_test.lower_bound, ); self.buffer_error(diag); } } RegionErrorKind::BoundUniversalRegionError { longer_fr, placeholder, error_element, } => { let error_vid = self.regioncx.region_from_element(longer_fr, &error_element); // Find the code to blame for the fact that `longer_fr` outlives `error_fr`. let cause = self .regioncx .best_blame_constraint( longer_fr, NllRegionVariableOrigin::Placeholder(placeholder), error_vid, ) .0 .cause; let universe = placeholder.universe; let universe_info = self.regioncx.universe_info(universe); universe_info.report_erroneous_element(self, placeholder, error_element, cause); } RegionErrorKind::RegionError { fr_origin, longer_fr, shorter_fr, is_reported } => { if is_reported { self.report_region_error( longer_fr, fr_origin, shorter_fr, &mut outlives_suggestion, ); } else { // We only report the first error, so as not to overwhelm the user. See // `RegRegionErrorKind` docs. // // FIXME: currently we do nothing with these, but perhaps we can do better? // FIXME: try collecting these constraints on the outlives suggestion // builder. Does it make the suggestions any better? debug!( "Unreported region error: can't prove that {:?}: {:?}", longer_fr, shorter_fr ); } } } } // Emit one outlives suggestions for each MIR def we borrowck outlives_suggestion.add_suggestion(self); } /// Report an error because the universal region `fr` was required to outlive /// `outlived_fr` but it is not known to do so. For example: /// /// ```compile_fail /// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x } /// ``` /// /// Here we would be invoked with `fr = 'a` and `outlived_fr = 'b`. // FIXME: make this translatable #[allow(rustc::diagnostic_outside_of_impl)] #[allow(rustc::untranslatable_diagnostic)] pub(crate) fn report_region_error( &mut self, fr: RegionVid, fr_origin: NllRegionVariableOrigin, outlived_fr: RegionVid, outlives_suggestion: &mut OutlivesSuggestionBuilder, ) { debug!("report_region_error(fr={:?}, outlived_fr={:?})", fr, outlived_fr); let (blame_constraint, path) = self.regioncx.best_blame_constraint(fr, fr_origin, outlived_fr); let BlameConstraint { category, cause, variance_info, .. } = blame_constraint; debug!("report_region_error: category={:?} {:?} {:?}", category, cause, variance_info); // Check if we can use one of the "nice region errors". if let (Some(f), Some(o)) = (self.to_error_region(fr), self.to_error_region(outlived_fr)) { let infer_err = self.infcx.err_ctxt(); let nice = NiceRegionError::new_from_span(&infer_err, self.mir_def_id(), cause.span, o, f); if let Some(diag) = nice.try_report_from_nll() { self.buffer_error(diag); return; } } let (fr_is_local, outlived_fr_is_local): (bool, bool) = ( self.regioncx.universal_regions().is_local_free_region(fr), self.regioncx.universal_regions().is_local_free_region(outlived_fr), ); debug!( "report_region_error: fr_is_local={:?} outlived_fr_is_local={:?} category={:?}", fr_is_local, outlived_fr_is_local, category ); let errci = ErrorConstraintInfo { fr, outlived_fr, category, span: cause.span }; let mut diag = match (category, fr_is_local, outlived_fr_is_local) { (ConstraintCategory::Return(kind), true, false) if self.is_closure_fn_mut(fr) => { self.report_fnmut_error(&errci, kind) } (ConstraintCategory::Assignment, true, false) | (ConstraintCategory::CallArgument(_), true, false) => { let mut db = self.report_escaping_data_error(&errci); outlives_suggestion.intermediate_suggestion(self, &errci, &mut db); outlives_suggestion.collect_constraint(fr, outlived_fr); db } _ => { let mut db = self.report_general_error(&errci); outlives_suggestion.intermediate_suggestion(self, &errci, &mut db); outlives_suggestion.collect_constraint(fr, outlived_fr); db } }; match variance_info { ty::VarianceDiagInfo::None => {} ty::VarianceDiagInfo::Invariant { ty, param_index } => { let (desc, note) = match ty.kind() { ty::RawPtr(ty, mutbl) => { assert_eq!(*mutbl, hir::Mutability::Mut); ( format!("a mutable pointer to `{}`", ty), "mutable pointers are invariant over their type parameter".to_string(), ) } ty::Ref(_, inner_ty, mutbl) => { assert_eq!(*mutbl, hir::Mutability::Mut); ( format!("a mutable reference to `{inner_ty}`"), "mutable references are invariant over their type parameter" .to_string(), ) } ty::Adt(adt, args) => { let generic_arg = args[param_index as usize]; let identity_args = GenericArgs::identity_for_item(self.infcx.tcx, adt.did()); let base_ty = Ty::new_adt(self.infcx.tcx, *adt, identity_args); let base_generic_arg = identity_args[param_index as usize]; let adt_desc = adt.descr(); let desc = format!( "the type `{ty}`, which makes the generic argument `{generic_arg}` invariant" ); let note = format!( "the {adt_desc} `{base_ty}` is invariant over the parameter `{base_generic_arg}`" ); (desc, note) } ty::FnDef(def_id, _) => { let name = self.infcx.tcx.item_name(*def_id); let identity_args = GenericArgs::identity_for_item(self.infcx.tcx, *def_id); let desc = format!("a function pointer to `{name}`"); let note = format!( "the function `{name}` is invariant over the parameter `{}`", identity_args[param_index as usize] ); (desc, note) } _ => panic!("Unexpected type {ty:?}"), }; diag.note(format!("requirement occurs because of {desc}",)); diag.note(note); diag.help("see for more information about variance"); } } self.add_placeholder_from_predicate_note(&mut diag, &path); self.add_sized_or_copy_bound_info(&mut diag, category, &path); self.buffer_error(diag); } /// Report a specialized error when `FnMut` closures return a reference to a captured variable. /// This function expects `fr` to be local and `outlived_fr` to not be local. /// /// ```text /// error: captured variable cannot escape `FnMut` closure body /// --> $DIR/issue-53040.rs:15:8 /// | /// LL | || &mut v; /// | -- ^^^^^^ creates a reference to a captured variable which escapes the closure body /// | | /// | inferred to be a `FnMut` closure /// | /// = note: `FnMut` closures only have access to their captured variables while they are /// executing... /// = note: ...therefore, returned references to captured variables will escape the closure /// ``` #[allow(rustc::diagnostic_outside_of_impl)] // FIXME fn report_fnmut_error( &self, errci: &ErrorConstraintInfo<'tcx>, kind: ReturnConstraint, ) -> Diag<'infcx> { let ErrorConstraintInfo { outlived_fr, span, .. } = errci; let mut output_ty = self.regioncx.universal_regions().unnormalized_output_ty; if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) = *output_ty.kind() { output_ty = self.infcx.tcx.type_of(def_id).instantiate_identity() }; debug!("report_fnmut_error: output_ty={:?}", output_ty); let err = FnMutError { span: *span, ty_err: match output_ty.kind() { ty::Coroutine(def, ..) if self.infcx.tcx.coroutine_is_async(*def) => { FnMutReturnTypeErr::ReturnAsyncBlock { span: *span } } _ if output_ty.contains_closure() => { FnMutReturnTypeErr::ReturnClosure { span: *span } } _ => FnMutReturnTypeErr::ReturnRef { span: *span }, }, }; let mut diag = self.dcx().create_err(err); if let ReturnConstraint::ClosureUpvar(upvar_field) = kind { let def_id = match self.regioncx.universal_regions().defining_ty { DefiningTy::Closure(def_id, _) => def_id, ty => bug!("unexpected DefiningTy {:?}", ty), }; let captured_place = &self.upvars[upvar_field.index()].place; let defined_hir = match captured_place.base { PlaceBase::Local(hirid) => Some(hirid), PlaceBase::Upvar(upvar) => Some(upvar.var_path.hir_id), _ => None, }; if let Some(def_hir) = defined_hir { let upvars_map = self.infcx.tcx.upvars_mentioned(def_id).unwrap(); let upvar_def_span = self.infcx.tcx.hir_span(def_hir); let upvar_span = upvars_map.get(&def_hir).unwrap().span; diag.subdiagnostic(VarHereDenote::Defined { span: upvar_def_span }); diag.subdiagnostic(VarHereDenote::Captured { span: upvar_span }); } } if let Some(fr_span) = self.give_region_a_name(*outlived_fr).unwrap().span() { diag.subdiagnostic(VarHereDenote::FnMutInferred { span: fr_span }); } self.suggest_move_on_borrowing_closure(&mut diag); diag } /// Reports an error specifically for when data is escaping a closure. /// /// ```text /// error: borrowed data escapes outside of function /// --> $DIR/lifetime-bound-will-change-warning.rs:44:5 /// | /// LL | fn test2<'a>(x: &'a Box) { /// | - `x` is a reference that is only valid in the function body /// LL | // but ref_obj will not, so warn. /// LL | ref_obj(x) /// | ^^^^^^^^^^ `x` escapes the function body here /// ``` #[instrument(level = "debug", skip(self))] fn report_escaping_data_error(&self, errci: &ErrorConstraintInfo<'tcx>) -> Diag<'infcx> { let ErrorConstraintInfo { span, category, .. } = errci; let fr_name_and_span = self.regioncx.get_var_name_and_span_for_region( self.infcx.tcx, self.body, &self.local_names(), &self.upvars, errci.fr, ); let outlived_fr_name_and_span = self.regioncx.get_var_name_and_span_for_region( self.infcx.tcx, self.body, &self.local_names(), &self.upvars, errci.outlived_fr, ); let escapes_from = self.infcx.tcx.def_descr(self.regioncx.universal_regions().defining_ty.def_id()); // Revert to the normal error in these cases. // Assignments aren't "escapes" in function items. if (fr_name_and_span.is_none() && outlived_fr_name_and_span.is_none()) || (*category == ConstraintCategory::Assignment && self.regioncx.universal_regions().defining_ty.is_fn_def()) || self.regioncx.universal_regions().defining_ty.is_const() { return self.report_general_error(errci); } let mut diag = borrowck_errors::borrowed_data_escapes_closure(self.infcx.tcx, *span, escapes_from); if let Some((Some(outlived_fr_name), outlived_fr_span)) = outlived_fr_name_and_span { // FIXME: make this translatable #[allow(rustc::diagnostic_outside_of_impl)] #[allow(rustc::untranslatable_diagnostic)] diag.span_label( outlived_fr_span, format!("`{outlived_fr_name}` declared here, outside of the {escapes_from} body",), ); } // FIXME: make this translatable #[allow(rustc::diagnostic_outside_of_impl)] #[allow(rustc::untranslatable_diagnostic)] if let Some((Some(fr_name), fr_span)) = fr_name_and_span { diag.span_label( fr_span, format!( "`{fr_name}` is a reference that is only valid in the {escapes_from} body", ), ); diag.span_label(*span, format!("`{fr_name}` escapes the {escapes_from} body here")); } // Only show an extra note if we can find an 'error region' for both of the region // variables. This avoids showing a noisy note that just mentions 'synthetic' regions // that don't help the user understand the error. match (self.to_error_region(errci.fr), self.to_error_region(errci.outlived_fr)) { (Some(f), Some(o)) => { self.maybe_suggest_constrain_dyn_trait_impl(&mut diag, f, o, category); let fr_region_name = self.give_region_a_name(errci.fr).unwrap(); fr_region_name.highlight_region_name(&mut diag); let outlived_fr_region_name = self.give_region_a_name(errci.outlived_fr).unwrap(); outlived_fr_region_name.highlight_region_name(&mut diag); // FIXME: make this translatable #[allow(rustc::diagnostic_outside_of_impl)] #[allow(rustc::untranslatable_diagnostic)] diag.span_label( *span, format!( "{}requires that `{}` must outlive `{}`", category.description(), fr_region_name, outlived_fr_region_name, ), ); } _ => {} } diag } /// Reports a region inference error for the general case with named/synthesized lifetimes to /// explain what is happening. /// /// ```text /// error: unsatisfied lifetime constraints /// --> $DIR/regions-creating-enums3.rs:17:5 /// | /// LL | fn mk_add_bad1<'a,'b>(x: &'a ast<'a>, y: &'b ast<'b>) -> ast<'a> { /// | -- -- lifetime `'b` defined here /// | | /// | lifetime `'a` defined here /// LL | ast::add(x, y) /// | ^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'a` but it /// | is returning data with lifetime `'b` /// ``` #[allow(rustc::diagnostic_outside_of_impl)] // FIXME fn report_general_error(&self, errci: &ErrorConstraintInfo<'tcx>) -> Diag<'infcx> { let ErrorConstraintInfo { fr, outlived_fr, span, category, .. } = errci; let mir_def_name = self.infcx.tcx.def_descr(self.mir_def_id().to_def_id()); let err = LifetimeOutliveErr { span: *span }; let mut diag = self.dcx().create_err(err); // In certain scenarios, such as the one described in issue #118021, // we might encounter a lifetime that cannot be named. // These situations are bound to result in errors. // To prevent an immediate ICE, we opt to create a dummy name instead. let fr_name = self.give_region_a_name(*fr).unwrap_or(RegionName { name: kw::UnderscoreLifetime, source: RegionNameSource::Static, }); fr_name.highlight_region_name(&mut diag); let outlived_fr_name = self.give_region_a_name(*outlived_fr).unwrap(); outlived_fr_name.highlight_region_name(&mut diag); let err_category = if matches!(category, ConstraintCategory::Return(_)) && self.regioncx.universal_regions().is_local_free_region(*outlived_fr) { LifetimeReturnCategoryErr::WrongReturn { span: *span, mir_def_name, outlived_fr_name, fr_name: &fr_name, } } else { LifetimeReturnCategoryErr::ShortReturn { span: *span, category_desc: category.description(), free_region_name: &fr_name, outlived_fr_name, } }; diag.subdiagnostic(err_category); self.add_static_impl_trait_suggestion(&mut diag, *fr, fr_name, *outlived_fr); self.suggest_adding_lifetime_params(&mut diag, *fr, *outlived_fr); self.suggest_move_on_borrowing_closure(&mut diag); self.suggest_deref_closure_return(&mut diag); diag } /// Adds a suggestion to errors where an `impl Trait` is returned. /// /// ```text /// help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as /// a constraint /// | /// LL | fn iter_values_anon(&self) -> impl Iterator + 'a { /// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ /// ``` #[allow(rustc::diagnostic_outside_of_impl)] #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable fn add_static_impl_trait_suggestion( &self, diag: &mut Diag<'_>, fr: RegionVid, // We need to pass `fr_name` - computing it again will label it twice. fr_name: RegionName, outlived_fr: RegionVid, ) { if let (Some(f), Some(outlived_f)) = (self.to_error_region(fr), self.to_error_region(outlived_fr)) { if outlived_f.kind() != ty::ReStatic { return; } let suitable_region = self.infcx.tcx.is_suitable_region(self.mir_def_id(), f); let Some(suitable_region) = suitable_region else { return; }; let fn_returns = self.infcx.tcx.return_type_impl_or_dyn_traits(suitable_region.scope); let param = if let Some(param) = find_param_with_region(self.infcx.tcx, self.mir_def_id(), f, outlived_f) { param } else { return; }; let lifetime = if f.is_named(self.infcx.tcx) { fr_name.name } else { kw::UnderscoreLifetime }; let arg = match param.param.pat.simple_ident() { Some(simple_ident) => format!("argument `{simple_ident}`"), None => "the argument".to_string(), }; let captures = format!("captures data from {arg}"); if !fn_returns.is_empty() { nice_region_error::suggest_new_region_bound( self.infcx.tcx, diag, fn_returns, lifetime.to_string(), Some(arg), captures, Some((param.param_ty_span, param.param_ty.to_string())), Some(suitable_region.scope), ); return; } let Some((alias_tys, alias_span, lt_addition_span)) = self .infcx .tcx .return_type_impl_or_dyn_traits_with_type_alias(suitable_region.scope) else { return; }; // in case the return type of the method is a type alias let mut spans_suggs: Vec<_> = Vec::new(); for alias_ty in alias_tys { if alias_ty.span.desugaring_kind().is_some() { // Skip `async` desugaring `impl Future`. } if let TyKind::TraitObject(_, lt) = alias_ty.kind { if lt.kind == hir::LifetimeKind::ImplicitObjectLifetimeDefault { spans_suggs.push((lt.ident.span.shrink_to_hi(), " + 'a".to_string())); } else { spans_suggs.push((lt.ident.span, "'a".to_string())); } } } if let Some(lt_addition_span) = lt_addition_span { spans_suggs.push((lt_addition_span, "'a, ".to_string())); } else { spans_suggs.push((alias_span.shrink_to_hi(), "<'a>".to_string())); } diag.multipart_suggestion_verbose( format!( "to declare that the trait object {captures}, you can add a lifetime parameter `'a` in the type alias" ), spans_suggs, Applicability::MaybeIncorrect, ); } } fn maybe_suggest_constrain_dyn_trait_impl( &self, diag: &mut Diag<'_>, f: Region<'tcx>, o: Region<'tcx>, category: &ConstraintCategory<'tcx>, ) { if !o.is_static() { return; } let tcx = self.infcx.tcx; let instance = if let ConstraintCategory::CallArgument(Some(func_ty)) = category { let (fn_did, args) = match func_ty.kind() { ty::FnDef(fn_did, args) => (fn_did, args), _ => return, }; debug!(?fn_did, ?args); // Only suggest this on function calls, not closures let ty = tcx.type_of(fn_did).instantiate_identity(); debug!("ty: {:?}, ty.kind: {:?}", ty, ty.kind()); if let ty::Closure(_, _) = ty.kind() { return; } if let Ok(Some(instance)) = ty::Instance::try_resolve( tcx, self.infcx.typing_env(self.infcx.param_env), *fn_did, self.infcx.resolve_vars_if_possible(args), ) { instance } else { return; } } else { return; }; let param = match find_param_with_region(tcx, self.mir_def_id(), f, o) { Some(param) => param, None => return, }; debug!(?param); let mut visitor = TraitObjectVisitor(FxIndexSet::default()); visitor.visit_ty(param.param_ty); let Some((ident, self_ty)) = NiceRegionError::get_impl_ident_and_self_ty_from_trait( tcx, instance.def_id(), &visitor.0, ) else { return; }; self.suggest_constrain_dyn_trait_in_impl(diag, &visitor.0, ident, self_ty); } #[allow(rustc::diagnostic_outside_of_impl)] #[instrument(skip(self, err), level = "debug")] fn suggest_constrain_dyn_trait_in_impl( &self, err: &mut Diag<'_>, found_dids: &FxIndexSet, ident: Ident, self_ty: &hir::Ty<'_>, ) -> bool { debug!("err: {:#?}", err); let mut suggested = false; for found_did in found_dids { let mut traits = vec![]; let mut hir_v = HirTraitObjectVisitor(&mut traits, *found_did); hir_v.visit_ty_unambig(self_ty); debug!("trait spans found: {:?}", traits); for span in &traits { let mut multi_span: MultiSpan = vec![*span].into(); multi_span.push_span_label(*span, fluent::borrowck_implicit_static); multi_span.push_span_label(ident.span, fluent::borrowck_implicit_static_introduced); err.subdiagnostic(RequireStaticErr::UsedImpl { multi_span }); err.span_suggestion_verbose( span.shrink_to_hi(), fluent::borrowck_implicit_static_relax, " + '_", Applicability::MaybeIncorrect, ); suggested = true; } } suggested } fn suggest_adding_lifetime_params(&self, diag: &mut Diag<'_>, sub: RegionVid, sup: RegionVid) { let (Some(sub), Some(sup)) = (self.to_error_region(sub), self.to_error_region(sup)) else { return; }; let Some((ty_sub, _)) = self .infcx .tcx .is_suitable_region(self.mir_def_id(), sub) .and_then(|_| find_anon_type(self.infcx.tcx, self.mir_def_id(), sub)) else { return; }; let Some((ty_sup, _)) = self .infcx .tcx .is_suitable_region(self.mir_def_id(), sup) .and_then(|_| find_anon_type(self.infcx.tcx, self.mir_def_id(), sup)) else { return; }; suggest_adding_lifetime_params( self.infcx.tcx, diag, self.mir_def_id(), sub, ty_sup, ty_sub, ); } #[allow(rustc::diagnostic_outside_of_impl)] /// When encountering a lifetime error caused by the return type of a closure, check the /// corresponding trait bound and see if dereferencing the closure return value would satisfy /// them. If so, we produce a structured suggestion. fn suggest_deref_closure_return(&self, diag: &mut Diag<'_>) { let tcx = self.infcx.tcx; // Get the closure return value and type. let closure_def_id = self.mir_def_id(); let hir::Node::Expr( closure_expr @ hir::Expr { kind: hir::ExprKind::Closure(hir::Closure { body, .. }), .. }, ) = tcx.hir_node_by_def_id(closure_def_id) else { return; }; let ty::Closure(_, args) = *tcx.type_of(closure_def_id).instantiate_identity().kind() else { return; }; let args = args.as_closure(); // Make sure that the parent expression is a method call. let parent_expr_id = tcx.parent_hir_id(self.mir_hir_id()); let hir::Node::Expr( parent_expr @ hir::Expr { kind: hir::ExprKind::MethodCall(_, rcvr, call_args, _), .. }, ) = tcx.hir_node(parent_expr_id) else { return; }; let typeck_results = tcx.typeck(self.mir_def_id()); // We don't use `ty.peel_refs()` to get the number of `*`s needed to get the root type. let liberated_sig = tcx.liberate_late_bound_regions(closure_def_id.to_def_id(), args.sig()); let mut peeled_ty = liberated_sig.output(); let mut count = 0; while let ty::Ref(_, ref_ty, _) = *peeled_ty.kind() { peeled_ty = ref_ty; count += 1; } if !self.infcx.type_is_copy_modulo_regions(self.infcx.param_env, peeled_ty) { return; } // Build a new closure where the return type is an owned value, instead of a ref. let closure_sig_as_fn_ptr_ty = Ty::new_fn_ptr( tcx, ty::Binder::dummy(tcx.mk_fn_sig( liberated_sig.inputs().iter().copied(), peeled_ty, liberated_sig.c_variadic, hir::Safety::Safe, rustc_abi::ExternAbi::Rust, )), ); let closure_ty = Ty::new_closure( tcx, closure_def_id.to_def_id(), ty::ClosureArgs::new( tcx, ty::ClosureArgsParts { parent_args: args.parent_args(), closure_kind_ty: args.kind_ty(), tupled_upvars_ty: args.tupled_upvars_ty(), closure_sig_as_fn_ptr_ty, }, ) .args, ); let Some((closure_arg_pos, _)) = call_args.iter().enumerate().find(|(_, arg)| arg.hir_id == closure_expr.hir_id) else { return; }; // Get the type for the parameter corresponding to the argument the closure with the // lifetime error we had. let Some(method_def_id) = typeck_results.type_dependent_def_id(parent_expr.hir_id) else { return; }; let Some(input_arg) = tcx .fn_sig(method_def_id) .skip_binder() .inputs() .skip_binder() // Methods have a `self` arg, so `pos` is actually `+ 1` to match the method call arg. .get(closure_arg_pos + 1) else { return; }; // If this isn't a param, then we can't substitute a new closure. let ty::Param(closure_param) = input_arg.kind() else { return }; // Get the arguments for the found method, only specifying that `Self` is the receiver type. let Some(possible_rcvr_ty) = typeck_results.node_type_opt(rcvr.hir_id) else { return }; let args = GenericArgs::for_item(tcx, method_def_id, |param, _| { if let ty::GenericParamDefKind::Lifetime = param.kind { tcx.lifetimes.re_erased.into() } else if param.index == 0 && param.name == kw::SelfUpper { possible_rcvr_ty.into() } else if param.index == closure_param.index { closure_ty.into() } else { self.infcx.var_for_def(parent_expr.span, param) } }); let preds = tcx.predicates_of(method_def_id).instantiate(tcx, args); let ocx = ObligationCtxt::new(&self.infcx); ocx.register_obligations(preds.iter().map(|(pred, span)| { trace!(?pred); Obligation::misc(tcx, span, self.mir_def_id(), self.infcx.param_env, pred) })); if ocx.select_all_or_error().is_empty() && count > 0 { diag.span_suggestion_verbose( tcx.hir_body(*body).value.peel_blocks().span.shrink_to_lo(), fluent::borrowck_dereference_suggestion, "*".repeat(count), Applicability::MachineApplicable, ); } } #[allow(rustc::diagnostic_outside_of_impl)] fn suggest_move_on_borrowing_closure(&self, diag: &mut Diag<'_>) { let body = self.infcx.tcx.hir_body_owned_by(self.mir_def_id()); let expr = &body.value.peel_blocks(); let mut closure_span = None::; match expr.kind { hir::ExprKind::MethodCall(.., args, _) => { for arg in args { if let hir::ExprKind::Closure(hir::Closure { capture_clause: hir::CaptureBy::Ref, .. }) = arg.kind { closure_span = Some(arg.span.shrink_to_lo()); break; } } } hir::ExprKind::Closure(hir::Closure { capture_clause: hir::CaptureBy::Ref, kind, .. }) => { if !matches!( kind, hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared( hir::CoroutineDesugaring::Async, _ ),) ) { closure_span = Some(expr.span.shrink_to_lo()); } } _ => {} } if let Some(closure_span) = closure_span { diag.span_suggestion_verbose( closure_span, fluent::borrowck_move_closure_suggestion, "move ", Applicability::MaybeIncorrect, ); } } }