| //! Error reporting machinery for lifetime errors. |
| |
| use rustc_errors::{Applicability, DiagnosticBuilder}; |
| use rustc_infer::infer::{ |
| error_reporting::nice_region_error::NiceRegionError, |
| error_reporting::unexpected_hidden_region_diagnostic, NllRegionVariableOrigin, |
| }; |
| use rustc_middle::hir::place::PlaceBase; |
| use rustc_middle::mir::{ConstraintCategory, ReturnConstraint}; |
| use rustc_middle::ty::subst::{InternalSubsts, Subst}; |
| use rustc_middle::ty::{self, RegionVid, Ty}; |
| use rustc_span::symbol::{kw, sym}; |
| use rustc_span::{BytePos, Span}; |
| |
| use crate::borrowck_errors; |
| |
| use super::{OutlivesSuggestionBuilder, RegionName}; |
| use crate::region_infer::BlameConstraint; |
| use crate::{ |
| nll::ConstraintDescription, |
| region_infer::{values::RegionElement, TypeTest}, |
| universal_regions::DefiningTy, |
| MirBorrowckCtxt, |
| }; |
| |
| impl ConstraintDescription for ConstraintCategory { |
| 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. |
| crate type RegionErrors<'tcx> = Vec<RegionErrorKind<'tcx>>; |
| |
| #[derive(Clone, Debug)] |
| 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 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 { |
| // 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, |
| 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<ty::Region<'tcx>> { |
| 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<RegionVid> { |
| 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() { |
| if let ty::BoundRegionKind::BrEnv = free_region.bound_region { |
| if let DefiningTy::Closure(_, substs) = |
| self.regioncx.universal_regions().defining_ty |
| { |
| return substs.as_closure().kind() == ty::ClosureKind::FnMut; |
| } |
| } |
| } |
| |
| false |
| } |
| |
| /// 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.locations.span(&self.body); |
| |
| if let Some(lower_bound_region) = lower_bound_region { |
| self.buffer_error(self.infcx.construct_generic_bound_failure( |
| type_test_span, |
| None, |
| 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 univesal 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. |
| self.buffer_error(self.infcx.tcx.sess.struct_span_err( |
| type_test_span, |
| &format!("`{}` does not live long enough", type_test.generic_kind), |
| )); |
| } |
| } |
| |
| RegionErrorKind::UnexpectedHiddenRegion { span, hidden_ty, member_region } => { |
| let named_ty = self.regioncx.name_regions(self.infcx.tcx, hidden_ty); |
| let named_region = self.regioncx.name_regions(self.infcx.tcx, member_region); |
| self.buffer_error(unexpected_hidden_region_diagnostic( |
| self.infcx.tcx, |
| span, |
| named_ty, |
| named_region, |
| )); |
| } |
| |
| 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( |
| &self.body, |
| 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: |
| /// |
| /// ``` |
| /// 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 BlameConstraint { category, cause, variance_info, from_closure: _ } = |
| self.regioncx.best_blame_constraint(&self.body, fr, fr_origin, |r| { |
| self.regioncx.provides_universal_region(r, fr, outlived_fr) |
| }); |
| |
| 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 nice = NiceRegionError::new_from_span(self.infcx, 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) |
| } |
| _ => panic!("Unexpected type {:?}", ty), |
| }; |
| diag.note(&format!("requirement occurs because of {desc}",)); |
| diag.note(¬e); |
| diag.help("see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance"); |
| } |
| } |
| |
| 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, |
| kind: ReturnConstraint, |
| ) -> DiagnosticBuilder<'tcx> { |
| let ErrorConstraintInfo { outlived_fr, span, .. } = errci; |
| |
| let mut diag = self |
| .infcx |
| .tcx |
| .sess |
| .struct_span_err(*span, "captured variable cannot escape `FnMut` closure body"); |
| |
| let mut output_ty = self.regioncx.universal_regions().unnormalized_output_ty; |
| if let ty::Opaque(def_id, _) = *output_ty.kind() { |
| output_ty = self.infcx.tcx.type_of(def_id) |
| }; |
| |
| debug!("report_fnmut_error: output_ty={:?}", output_ty); |
| |
| let message = match output_ty.kind() { |
| ty::Closure(_, _) => { |
| "returns a closure that contains a reference to a captured variable, which then \ |
| escapes the closure body" |
| } |
| ty::Adt(def, _) if self.infcx.tcx.is_diagnostic_item(sym::gen_future, def.did) => { |
| "returns an `async` block that contains a reference to a captured variable, which then \ |
| escapes the closure body" |
| } |
| _ => "returns a reference to a captured variable which escapes the closure body", |
| }; |
| |
| diag.span_label(*span, message); |
| |
| 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 defined_hir.is_some() { |
| let upvars_map = self.infcx.tcx.upvars_mentioned(def_id).unwrap(); |
| let upvar_def_span = self.infcx.tcx.hir().span(defined_hir.unwrap()); |
| let upvar_span = upvars_map.get(&defined_hir.unwrap()).unwrap().span; |
| diag.span_label(upvar_def_span, "variable defined here"); |
| diag.span_label(upvar_span, "variable captured here"); |
| } |
| } |
| |
| if let Some(fr_span) = self.give_region_a_name(*outlived_fr).unwrap().span() { |
| diag.span_label(fr_span, "inferred to be a `FnMut` closure"); |
| } |
| |
| diag.note( |
| "`FnMut` closures only have access to their captured variables while they are \ |
| executing...", |
| ); |
| diag.note("...therefore, they cannot allow references to captured variables to escape"); |
| |
| 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<Fn()+'a>) { |
| /// | - `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 |
| /// ``` |
| fn report_escaping_data_error(&self, errci: &ErrorConstraintInfo) -> DiagnosticBuilder<'tcx> { |
| 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!( |
| "`{}` declared here, outside of the {} body", |
| outlived_fr_name, escapes_from |
| ), |
| ); |
| } |
| |
| if let Some((Some(fr_name), fr_span)) = fr_name_and_span { |
| diag.span_label( |
| fr_span, |
| format!( |
| "`{}` is a reference that is only valid in the {} body", |
| fr_name, escapes_from |
| ), |
| ); |
| |
| diag.span_label(*span, format!("`{}` escapes the {} body here", fr_name, escapes_from)); |
| } |
| |
| // 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. |
| if self.to_error_region(errci.fr).is_some() |
| && self.to_error_region(errci.outlived_fr).is_some() |
| { |
| 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) -> DiagnosticBuilder<'tcx> { |
| let ErrorConstraintInfo { |
| fr, |
| fr_is_local, |
| outlived_fr, |
| outlived_fr_is_local, |
| span, |
| category, |
| .. |
| } = errci; |
| |
| let mut diag = |
| self.infcx.tcx.sess.struct_span_err(*span, "lifetime may not live long enough"); |
| |
| let (_, mir_def_name) = |
| self.infcx.tcx.article_and_description(self.mir_def_id().to_def_id()); |
| |
| 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); |
| |
| match (category, outlived_fr_is_local, fr_is_local) { |
| (ConstraintCategory::Return(_), true, _) => { |
| diag.span_label( |
| *span, |
| format!( |
| "{} was supposed to return data with lifetime `{}` but it is returning \ |
| data with lifetime `{}`", |
| mir_def_name, outlived_fr_name, fr_name |
| ), |
| ); |
| } |
| _ => { |
| diag.span_label( |
| *span, |
| format!( |
| "{}requires that `{}` must outlive `{}`", |
| category.description(), |
| fr_name, |
| outlived_fr_name, |
| ), |
| ); |
| } |
| } |
| |
| self.add_static_impl_trait_suggestion(&mut diag, *fr, fr_name, *outlived_fr); |
| |
| 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<Item=u32> + 'a { |
| /// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| /// ``` |
| fn add_static_impl_trait_suggestion( |
| &self, |
| diag: &mut DiagnosticBuilder<'tcx>, |
| 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(ty::ReStatic)) = |
| (self.to_error_region(fr), self.to_error_region(outlived_fr).as_deref()) |
| { |
| if let Some(&ty::Opaque(did, substs)) = self |
| .infcx |
| .tcx |
| .is_suitable_region(f) |
| .map(|r| r.def_id) |
| .and_then(|id| self.infcx.tcx.return_type_impl_trait(id)) |
| .map(|(ty, _)| ty.kind()) |
| { |
| // Check whether or not the impl trait return type is intended to capture |
| // data with the static lifetime. |
| // |
| // eg. check for `impl Trait + 'static` instead of `impl Trait`. |
| let has_static_predicate = { |
| let bounds = self.infcx.tcx.explicit_item_bounds(did); |
| |
| let mut found = false; |
| for (bound, _) in bounds { |
| if let ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(_, r)) = |
| bound.kind().skip_binder() |
| { |
| let r = r.subst(self.infcx.tcx, substs); |
| if r.is_static() { |
| found = true; |
| break; |
| } else { |
| // If there's already a lifetime bound, don't |
| // suggest anything. |
| return; |
| } |
| } |
| } |
| |
| found |
| }; |
| |
| debug!( |
| "add_static_impl_trait_suggestion: has_static_predicate={:?}", |
| has_static_predicate |
| ); |
| let static_str = kw::StaticLifetime; |
| // If there is a static predicate, then the only sensible suggestion is to replace |
| // fr with `'static`. |
| if has_static_predicate { |
| diag.help(&format!("consider replacing `{}` with `{}`", fr_name, static_str)); |
| } else { |
| // Otherwise, we should suggest adding a constraint on the return type. |
| let span = self.infcx.tcx.def_span(did); |
| if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) { |
| let suggestable_fr_name = if fr_name.was_named() { |
| fr_name.to_string() |
| } else { |
| "'_".to_string() |
| }; |
| let span = if snippet.ends_with(';') { |
| // `type X = impl Trait;` |
| span.with_hi(span.hi() - BytePos(1)) |
| } else { |
| span |
| }; |
| let suggestion = format!(" + {}", suggestable_fr_name); |
| let span = span.shrink_to_hi(); |
| diag.span_suggestion( |
| span, |
| &format!( |
| "to allow this `impl Trait` to capture borrowed data with lifetime \ |
| `{}`, add `{}` as a bound", |
| fr_name, suggestable_fr_name, |
| ), |
| suggestion, |
| Applicability::MachineApplicable, |
| ); |
| } |
| } |
| } |
| } |
| } |
| } |
