diff options
Diffstat (limited to 'compiler/rustc_borrowck/src/diagnostics/region_errors.rs')
| -rw-r--r-- | compiler/rustc_borrowck/src/diagnostics/region_errors.rs | 904 |
1 files changed, 904 insertions, 0 deletions
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs new file mode 100644 index 000000000..176090c3b --- /dev/null +++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs @@ -0,0 +1,904 @@ +//! Error reporting machinery for lifetime errors. + +use rustc_data_structures::fx::FxHashSet; +use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan}; +use rustc_hir::def_id::DefId; +use rustc_hir::intravisit::Visitor; +use rustc_hir::{self as hir, Item, ItemKind, Node}; +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::Region; +use rustc_middle::ty::TypeVisitor; +use rustc_middle::ty::{self, RegionVid, Ty}; +use rustc_span::symbol::{kw, sym, Ident}; +use rustc_span::Span; + +use crate::borrowck_errors; +use crate::session_diagnostics::GenericDoesNotLiveLongEnough; + +use super::{OutlivesSuggestionBuilder, RegionName}; +use crate::region_infer::BlameConstraint; +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) type RegionErrors<'tcx> = Vec<RegionErrorKind<'tcx>>; + +#[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<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() + && 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 + } + + /// 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 { + 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.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. + self.buffer_error(self.infcx.tcx.sess.create_err( + GenericDoesNotLiveLongEnough { + kind: type_test.generic_kind.to_string(), + span: type_test_span, + }, + )); + } + } + + 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); + self.buffer_error(unexpected_hidden_region_diagnostic( + self.infcx.tcx, + span, + named_ty, + named_region, + named_key, + )); + } + + 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); + } + + fn get_impl_ident_and_self_ty_from_trait( + &self, + def_id: DefId, + trait_objects: &FxHashSet<DefId>, + ) -> Option<(Ident, &'tcx hir::Ty<'tcx>)> { + let tcx = self.infcx.tcx; + match tcx.hir().get_if_local(def_id) { + Some(Node::ImplItem(impl_item)) => { + match tcx.hir().find_by_def_id(tcx.hir().get_parent_item(impl_item.hir_id())) { + Some(Node::Item(Item { + kind: ItemKind::Impl(hir::Impl { self_ty, .. }), + .. + })) => Some((impl_item.ident, self_ty)), + _ => None, + } + } + Some(Node::TraitItem(trait_item)) => { + let trait_did = tcx.hir().get_parent_item(trait_item.hir_id()); + match tcx.hir().find_by_def_id(trait_did) { + Some(Node::Item(Item { kind: ItemKind::Trait(..), .. })) => { + // The method being called is defined in the `trait`, but the `'static` + // obligation comes from the `impl`. Find that `impl` so that we can point + // at it in the suggestion. + let trait_did = trait_did.to_def_id(); + match tcx + .hir() + .trait_impls(trait_did) + .iter() + .filter_map(|&impl_did| { + match tcx.hir().get_if_local(impl_did.to_def_id()) { + Some(Node::Item(Item { + kind: ItemKind::Impl(hir::Impl { self_ty, .. }), + .. + })) if trait_objects.iter().all(|did| { + // FIXME: we should check `self_ty` against the receiver + // type in the `UnifyReceiver` context, but for now, use + // this imperfect proxy. This will fail if there are + // multiple `impl`s for the same trait like + // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`. + // In that case, only the first one will get suggestions. + let mut traits = vec![]; + let mut hir_v = HirTraitObjectVisitor(&mut traits, *did); + hir_v.visit_ty(self_ty); + !traits.is_empty() + }) => + { + Some(self_ty) + } + _ => None, + } + }) + .next() + { + Some(self_ty) => Some((trait_item.ident, self_ty)), + _ => None, + } + } + _ => None, + } + } + _ => None, + } + } + + /// 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,E0312 + /// 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) + } + 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 <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<'tcx>, + kind: ReturnConstraint, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { + 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 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.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<'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 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!( + "{mir_def_name} was supposed to return data with lifetime `{outlived_fr_name}` but it is returning \ + data with lifetime `{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); + self.suggest_adding_lifetime_params(&mut diag, *fr, *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 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())), + ); + } + } + + fn maybe_suggest_constrain_dyn_trait_impl( + &self, + diag: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>, + 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(FxHashSet::default()); + visitor.visit_ty(param.param_ty); + + let Some((ident, self_ty)) = + self.get_impl_ident_and_self_ty_from_trait(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: &FxHashSet<DefId>, + 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.span_note(multi_span, "the used `impl` has a `'static` requirement"); + 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); + } +} |