#![deny(rustc::untranslatable_diagnostic)] #![deny(rustc::diagnostic_outside_of_impl)] //! Error reporting machinery for lifetime errors. use rustc_data_structures::fx::FxIndexSet; use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan}; use rustc_hir as hir; use rustc_hir::def::Res::Def; use rustc_hir::def_id::DefId; use rustc_hir::intravisit::Visitor; use rustc_hir::GenericBound::Trait; use rustc_hir::QPath::Resolved; use rustc_hir::WherePredicate::BoundPredicate; use rustc_hir::{PolyTraitRef, TyKind, WhereBoundPredicate}; use rustc_infer::infer::{ error_reporting::nice_region_error::{ self, find_anon_type, find_param_with_region, suggest_adding_lifetime_params, HirTraitObjectVisitor, NiceRegionError, TraitObjectVisitor, }, error_reporting::unexpected_hidden_region_diagnostic, NllRegionVariableOrigin, RelateParamBound, }; use rustc_middle::hir::place::PlaceBase; use rustc_middle::mir::{ConstraintCategory, ReturnConstraint}; use rustc_middle::ty::subst::InternalSubsts; use rustc_middle::ty::TypeVisitor; use rustc_middle::ty::{self, RegionVid, Ty}; use rustc_middle::ty::{Region, TyCtxt}; use rustc_span::symbol::{kw, Ident}; use rustc_span::{Span, DUMMY_SP}; use crate::borrowck_errors; use crate::session_diagnostics::{ FnMutError, FnMutReturnTypeErr, GenericDoesNotLiveLongEnough, LifetimeOutliveErr, LifetimeReturnCategoryErr, RequireStaticErr, VarHereDenote, }; use super::{OutlivesSuggestionBuilder, RegionName}; use crate::region_infer::{BlameConstraint, ExtraConstraintInfo}; use crate::{ nll::ConstraintDescription, region_infer::{values::RegionElement, TypeTest}, universal_regions::DefiningTy, MirBorrowckCtxt, }; 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 => "cast ", ConstraintCategory::CallArgument(_) => "argument ", ConstraintCategory::TypeAnnotation => "type annotation ", ConstraintCategory::ClosureBounds => "closure body ", 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 => "", } } } /// 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>, TyCtxt<'tcx>); impl<'tcx> RegionErrors<'tcx> { pub fn new(tcx: TyCtxt<'tcx>) -> Self { Self(vec![], tcx) } #[track_caller] pub fn push(&mut self, val: impl Into>) { let val = val.into(); self.1.sess.delay_span_bug(DUMMY_SP, format!("{val:?}")); self.0.push(val); } pub fn is_empty(&self) -> bool { self.0.is_empty() } pub fn into_iter(self) -> impl Iterator> { self.0.into_iter() } } #[derive(Clone, Debug)] pub(crate) enum RegionErrorKind<'tcx> { /// A generic bound failure for a type test (`T: 'a`). TypeTestError { type_test: TypeTest<'tcx> }, /// An unexpected hidden region for an opaque type. UnexpectedHiddenRegion { /// The span for the member constraint. span: Span, /// The hidden type. hidden_ty: Ty<'tcx>, /// The opaque type. key: ty::OpaqueTypeKey<'tcx>, /// The unexpected region. member_region: ty::Region<'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 struct ErrorConstraintInfo<'tcx> { // fr: outlived_fr pub(super) fr: RegionVid, pub(super) fr_is_local: bool, pub(super) outlived_fr: RegionVid, pub(super) outlived_fr_is_local: bool, // Category and span for best blame constraint pub(super) category: ConstraintCategory<'tcx>, pub(super) span: Span, } impl<'a, 'tcx> MirBorrowckCtxt<'a, '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 } } } /// Returns `true` if a closure is inferred to be an `FnMut` closure. fn is_closure_fn_mut(&self, fr: RegionVid) -> bool { if let Some(ty::ReFree(free_region)) = self.to_error_region(fr).as_deref() && let ty::BoundRegionKind::BrEnv = free_region.bound_region && let DefiningTy::Closure(_, substs) = self.regioncx.universal_regions().defining_ty { return substs.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 fn suggest_static_lifetime_for_gat_from_hrtb( &self, diag: &mut DiagnosticBuilder<'_, ErrorGuaranteed>, lower_bound: RegionVid, ) { let mut suggestions = vec![]; let hir = self.infcx.tcx.hir(); // 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.name.get_id() && let Some(placeholder_id) = id.as_local() && let gat_hir_id = hir.local_def_id_to_hir_id(placeholder_id) && let Some(generics_impl) = hir.get_parent(gat_hir_id).generics() { Some((gat_hir_id, generics_impl)) } else { None } }) .collect::>(); debug!(?gat_id_and_generics); // find higher-ranked trait bounds bounded to the generic associated types 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 else { continue; }; if bound_generic_params .iter() .rfind(|bgp| hir.local_def_id_to_hir_id(bgp.def_id) == *gat_hir_id) .is_some() { for bound in *bounds { hrtb_bounds.push(bound); } } } }); debug!(?hrtb_bounds); hrtb_bounds.iter().for_each(|bound| { let Trait(PolyTraitRef { trait_ref, span: trait_span, .. }, _) = bound else { return; }; diag.span_note( *trait_span, format!("due to current limitations in the borrow checker, this implies a `'static` lifetime") ); let Some(generics_fn) = 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 { span: bounded_span, bounded_ty, bounds, .. } ) = predicate 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((bounded_span.shrink_to_hi(), format!(" + 'static"))); } }); }); }); if suggestions.len() > 0 { suggestions.dedup(); diag.multipart_suggestion_verbose( format!("consider restricting the type parameter to the `'static` lifetime"), 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(); let mut last_unexpected_hidden_region: Option<(Span, Ty<'_>, ty::OpaqueTypeKey<'tcx>)> = None; 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 = type_test.generic_kind.to_ty(self.infcx.tcx); let origin = 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), 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.infcx.tcx.sess.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::UnexpectedHiddenRegion { span, hidden_ty, key, member_region } => { let named_ty = self.regioncx.name_regions(self.infcx.tcx, hidden_ty); let named_key = self.regioncx.name_regions(self.infcx.tcx, key); let named_region = self.regioncx.name_regions(self.infcx.tcx, member_region); let mut diag = unexpected_hidden_region_diagnostic( self.infcx.tcx, span, named_ty, named_region, named_key, ); if last_unexpected_hidden_region != Some((span, named_ty, named_key)) { self.buffer_error(diag); last_unexpected_hidden_region = Some((span, named_ty, named_key)); } else { diag.delay_as_bug(); } } 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.find_outlives_blame_span( longer_fr, NllRegionVariableOrigin::Placeholder(placeholder), error_vid, ); let universe = placeholder.universe; let universe_info = self.regioncx.universe_info(universe); universe_info.report_error(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`. 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, extra_info) = self.regioncx.best_blame_constraint(fr, fr_origin, |r| { self.regioncx.provides_universal_region(r, fr, 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, 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, fr_is_local, outlived_fr_is_local, 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_mut) => { assert_eq!(ty_mut.mutbl, rustc_hir::Mutability::Mut); ( format!("a mutable pointer to `{}`", ty_mut.ty), "mutable pointers are invariant over their type parameter".to_string(), ) } ty::Ref(_, inner_ty, mutbl) => { assert_eq!(*mutbl, rustc_hir::Mutability::Mut); ( format!("a mutable reference to `{inner_ty}`"), "mutable references are invariant over their type parameter" .to_string(), ) } ty::Adt(adt, substs) => { let generic_arg = substs[param_index as usize]; let identity_substs = InternalSubsts::identity_for_item(self.infcx.tcx, adt.did()); let base_ty = self.infcx.tcx.mk_adt(*adt, identity_substs); let base_generic_arg = identity_substs[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_substs = InternalSubsts::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_substs[param_index as usize] ); (desc, note) } _ => panic!("Unexpected type {ty:?}"), }; diag.note(&format!("requirement occurs because of {desc}",)); diag.note(¬e); diag.help("see for more information about variance"); } } for extra in extra_info { match extra { ExtraConstraintInfo::PlaceholderFromPredicate(span) => { diag.span_note(span, "due to current limitations in the borrow checker, this implies a `'static` lifetime"); } } } 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 /// ``` fn report_fnmut_error( &self, errci: &ErrorConstraintInfo<'tcx>, kind: ReturnConstraint, ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { 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) }; debug!("report_fnmut_error: output_ty={:?}", output_ty); let err = FnMutError { span: *span, ty_err: match output_ty.kind() { ty::Closure(_, _) => FnMutReturnTypeErr::ReturnClosure { span: *span }, ty::Generator(def, ..) if self.infcx.tcx.generator_is_async(*def) => { FnMutReturnTypeErr::ReturnAsyncBlock { span: *span } } _ => FnMutReturnTypeErr::ReturnRef { span: *span }, }, }; let mut diag = self.infcx.tcx.sess.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.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>, ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { 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 .article_and_description(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(&ErrorConstraintInfo { fr_is_local: true, outlived_fr_is_local: false, ..*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 { diag.span_label( outlived_fr_span, format!("`{outlived_fr_name}` declared here, outside of the {escapes_from} body",), ); } 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); 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` /// ``` fn report_general_error( &self, errci: &ErrorConstraintInfo<'tcx>, ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { let ErrorConstraintInfo { fr, fr_is_local, outlived_fr, outlived_fr_is_local, span, category, .. } = errci; let (_, mir_def_name) = self.infcx.tcx.article_and_description(self.mir_def_id().to_def_id()); let err = LifetimeOutliveErr { span: *span }; let mut diag = self.infcx.tcx.sess.create_err(err); let fr_name = self.give_region_a_name(*fr).unwrap(); 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 = match (category, outlived_fr_is_local, fr_is_local) { (ConstraintCategory::Return(_), true, _) => LifetimeReturnCategoryErr::WrongReturn { span: *span, mir_def_name, outlived_fr_name, fr_name: &fr_name, }, _ => 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); 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 { /// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ /// ``` fn add_static_impl_trait_suggestion( &self, diag: &mut Diagnostic, 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 != ty::ReStatic { return; } let fn_returns = self .infcx .tcx .is_suitable_region(f) .map(|r| self.infcx.tcx.return_type_impl_or_dyn_traits(r.def_id)) .unwrap_or_default(); if fn_returns.is_empty() { return; } let param = if let Some(param) = find_param_with_region(self.infcx.tcx, f, outlived_f) { param } else { return; }; let lifetime = if f.has_name() { 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}"); return 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())), self.infcx.tcx.is_suitable_region(f).map(|r| r.def_id), ); } } fn maybe_suggest_constrain_dyn_trait_impl( &self, diag: &mut Diagnostic, 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, substs) = match func_ty.kind() { ty::FnDef(fn_did, substs) => (fn_did, substs), _ => return, }; debug!(?fn_did, ?substs); // Only suggest this on function calls, not closures let ty = tcx.type_of(fn_did); debug!("ty: {:?}, ty.kind: {:?}", ty, ty.kind()); if let ty::Closure(_, _) = ty.kind() { return; } if let Ok(Some(instance)) = ty::Instance::resolve( tcx, self.param_env, *fn_did, self.infcx.resolve_vars_if_possible(substs), ) { instance } else { return; } } else { return; }; let param = match find_param_with_region(tcx, 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); } #[instrument(skip(self, err), level = "debug")] fn suggest_constrain_dyn_trait_in_impl( &self, err: &mut Diagnostic, 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(&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, "this has an implicit `'static` lifetime requirement"); multi_span.push_span_label( ident.span, "calling this method introduces the `impl`'s 'static` requirement", ); err.subdiagnostic(RequireStaticErr::UsedImpl { multi_span }); err.span_suggestion_verbose( span.shrink_to_hi(), "consider relaxing the implicit `'static` requirement", " + '_", Applicability::MaybeIncorrect, ); suggested = true; } } suggested } fn suggest_adding_lifetime_params( &self, diag: &mut Diagnostic, 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(sub) .and_then(|anon_reg| find_anon_type(self.infcx.tcx, sub, &anon_reg.boundregion)) else { return }; let Some((ty_sup, _)) = self .infcx .tcx .is_suitable_region(sup) .and_then(|anon_reg| find_anon_type(self.infcx.tcx, sup, &anon_reg.boundregion)) else { return }; suggest_adding_lifetime_params(self.infcx.tcx, sub, ty_sup, ty_sub, diag); } fn suggest_move_on_borrowing_closure(&self, diag: &mut Diagnostic) { let map = self.infcx.tcx.hir(); let body_id = map.body_owned_by(self.mir_def_id()); let expr = &map.body(body_id).value; 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::Block(blk, _) => { if let Some(expr) = blk.expr { // only when the block is a closure if let hir::ExprKind::Closure(hir::Closure { capture_clause: hir::CaptureBy::Ref, body, .. }) = expr.kind { let body = map.body(*body); if !matches!(body.generator_kind, Some(hir::GeneratorKind::Async(..))) { closure_span = Some(expr.span.shrink_to_lo()); } } } } _ => {} } if let Some(closure_span) = closure_span { diag.span_suggestion_verbose( closure_span, "consider adding 'move' keyword before the nested closure", "move ", Applicability::MaybeIncorrect, ); } } }