2 use rustc_data_structures::fx::FxHashSet;
3 use rustc_errors::{Applicability, DiagnosticBuilder};
5 use rustc_hir::def_id::DefId;
6 use rustc_hir::{AsyncGeneratorKind, GeneratorKind};
7 use rustc_index::vec::Idx;
8 use rustc_middle::mir::{
9 self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, ConstraintCategory,
10 FakeReadCause, Local, LocalDecl, LocalInfo, LocalKind, Location, Operand, Place, PlaceRef,
11 ProjectionElem, Rvalue, Statement, StatementKind, TerminatorKind, VarBindingForm,
13 use rustc_middle::ty::{self, Ty};
14 use rustc_span::source_map::DesugaringKind;
16 use rustc_trait_selection::traits::error_reporting::suggest_constraining_type_param;
18 use crate::dataflow::drop_flag_effects;
19 use crate::dataflow::indexes::{MoveOutIndex, MovePathIndex};
20 use crate::util::borrowck_errors;
22 use crate::borrow_check::{
23 borrow_set::BorrowData, prefixes::IsPrefixOf, InitializationRequiringAction, MirBorrowckCtxt,
28 explain_borrow::BorrowExplanation, IncludingDowncast, RegionName, RegionNameSource, UseSpans,
33 /// Index of the "move out" that we found. The `MoveData` can
34 /// then tell us where the move occurred.
37 /// `true` if we traversed a back edge while walking from the point
38 /// of error to the move site.
39 traversed_back_edge: bool,
42 /// Which case a StorageDeadOrDrop is for.
43 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
44 enum StorageDeadOrDrop<'tcx> {
50 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
51 pub(in crate::borrow_check) fn report_use_of_moved_or_uninitialized(
54 desired_action: InitializationRequiringAction,
55 (moved_place, used_place, span): (PlaceRef<'tcx>, PlaceRef<'tcx>, Span),
59 "report_use_of_moved_or_uninitialized: location={:?} desired_action={:?} \
60 moved_place={:?} used_place={:?} span={:?} mpi={:?}",
61 location, desired_action, moved_place, used_place, span, mpi
65 self.move_spans(moved_place, location).or_else(|| self.borrow_spans(span, location));
66 let span = use_spans.args_or_use();
68 let move_site_vec = self.get_moved_indexes(location, mpi);
69 debug!("report_use_of_moved_or_uninitialized: move_site_vec={:?}", move_site_vec);
70 let move_out_indices: Vec<_> =
71 move_site_vec.iter().map(|move_site| move_site.moi).collect();
73 if move_out_indices.is_empty() {
74 let root_place = PlaceRef { projection: &[], ..used_place };
76 if !self.uninitialized_error_reported.insert(root_place) {
78 "report_use_of_moved_or_uninitialized place: error about {:?} suppressed",
85 match self.describe_place_with_options(used_place, IncludingDowncast(true)) {
86 Some(name) => format!("`{}`", name),
87 None => "value".to_owned(),
89 let mut err = self.cannot_act_on_uninitialized_variable(
91 desired_action.as_noun(),
93 .describe_place_with_options(moved_place, IncludingDowncast(true))
94 .unwrap_or_else(|| "_".to_owned()),
96 err.span_label(span, format!("use of possibly-uninitialized {}", item_msg));
98 use_spans.var_span_label(
100 format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
103 err.buffer(&mut self.errors_buffer);
105 if let Some((reported_place, _)) = self.move_error_reported.get(&move_out_indices) {
106 if self.prefixes(*reported_place, PrefixSet::All).any(|p| p == used_place) {
108 "report_use_of_moved_or_uninitialized place: error suppressed \
116 let msg = ""; //FIXME: add "partially " or "collaterally "
118 let mut err = self.cannot_act_on_moved_value(
120 desired_action.as_noun(),
122 self.describe_place_with_options(moved_place, IncludingDowncast(true)),
125 self.add_moved_or_invoked_closure_note(location, used_place, &mut err);
127 let mut is_loop_move = false;
128 let is_partial_move = move_site_vec.iter().any(|move_site| {
129 let move_out = self.move_data.moves[(*move_site).moi];
130 let moved_place = &self.move_data.move_paths[move_out.path].place;
131 used_place != moved_place.as_ref() && used_place.is_prefix_of(moved_place.as_ref())
133 for move_site in &move_site_vec {
134 let move_out = self.move_data.moves[(*move_site).moi];
135 let moved_place = &self.move_data.move_paths[move_out.path].place;
137 let move_spans = self.move_spans(moved_place.as_ref(), move_out.source);
138 let move_span = move_spans.args_or_use();
140 let move_msg = if move_spans.for_closure() { " into closure" } else { "" };
142 if span == move_span {
145 format!("value moved{} here, in previous iteration of loop", move_msg),
148 } else if move_site.traversed_back_edge {
151 format!("value moved{} here, in previous iteration of loop", move_msg),
154 err.span_label(move_span, format!("value moved{} here", move_msg));
155 move_spans.var_span_label(
157 format!("variable moved due to use{}", move_spans.describe()),
160 if Some(DesugaringKind::ForLoop) == move_span.desugaring_kind() {
161 let sess = self.infcx.tcx.sess;
162 if let Ok(snippet) = sess.source_map().span_to_snippet(move_span) {
165 "consider borrowing to avoid moving into the for loop",
166 format!("&{}", snippet),
167 Applicability::MaybeIncorrect,
173 use_spans.var_span_label(
175 format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
183 desired_action.as_verb_in_past_tense(),
184 if is_partial_move { "after partial move" } else { "after move" },
190 Place::ty_from(used_place.local, used_place.projection, self.body, self.infcx.tcx)
192 let needs_note = match ty.kind {
193 ty::Closure(id, _) => {
194 let tables = self.infcx.tcx.typeck_tables_of(id);
195 let hir_id = self.infcx.tcx.hir().as_local_hir_id(id).unwrap();
197 tables.closure_kind_origins().get(hir_id).is_none()
203 let mpi = self.move_data.moves[move_out_indices[0]].path;
204 let place = &self.move_data.move_paths[mpi].place;
206 let ty = place.ty(self.body, self.infcx.tcx).ty;
208 self.describe_place_with_options(place.as_ref(), IncludingDowncast(true));
209 let note_msg = match opt_name {
210 Some(ref name) => format!("`{}`", name),
211 None => "value".to_owned(),
213 if let ty::Param(param_ty) = ty.kind {
214 let tcx = self.infcx.tcx;
215 let generics = tcx.generics_of(self.mir_def_id);
216 let param = generics.type_param(¶m_ty, tcx);
217 if let Some(generics) =
218 tcx.hir().get_generics(tcx.closure_base_def_id(self.mir_def_id))
220 suggest_constraining_type_param(
224 ¶m.name.as_str(),
230 let span = if let Some(local) = place.as_local() {
231 let decl = &self.body.local_decls[local];
232 Some(decl.source_info.span)
236 self.note_type_does_not_implement_copy(&mut err, ¬e_msg, ty, span);
239 if let Some((_, mut old_err)) =
240 self.move_error_reported.insert(move_out_indices, (used_place, err))
242 // Cancel the old error so it doesn't ICE.
248 pub(in crate::borrow_check) fn report_move_out_while_borrowed(
251 (place, span): (Place<'tcx>, Span),
252 borrow: &BorrowData<'tcx>,
255 "report_move_out_while_borrowed: location={:?} place={:?} span={:?} borrow={:?}",
256 location, place, span, borrow
258 let value_msg = self.describe_any_place(place.as_ref());
259 let borrow_msg = self.describe_any_place(borrow.borrowed_place.as_ref());
261 let borrow_spans = self.retrieve_borrow_spans(borrow);
262 let borrow_span = borrow_spans.args_or_use();
264 let move_spans = self.move_spans(place.as_ref(), location);
265 let span = move_spans.args_or_use();
268 self.cannot_move_when_borrowed(span, &self.describe_any_place(place.as_ref()));
269 err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
270 err.span_label(span, format!("move out of {} occurs here", value_msg));
272 borrow_spans.var_span_label(
274 format!("borrow occurs due to use{}", borrow_spans.describe()),
278 .var_span_label(&mut err, format!("move occurs due to use{}", move_spans.describe()));
280 self.explain_why_borrow_contains_point(location, borrow, None)
281 .add_explanation_to_diagnostic(
289 err.buffer(&mut self.errors_buffer);
292 pub(in crate::borrow_check) fn report_use_while_mutably_borrowed(
295 (place, _span): (Place<'tcx>, Span),
296 borrow: &BorrowData<'tcx>,
297 ) -> DiagnosticBuilder<'cx> {
298 let borrow_spans = self.retrieve_borrow_spans(borrow);
299 let borrow_span = borrow_spans.args_or_use();
301 // Conflicting borrows are reported separately, so only check for move
303 let use_spans = self.move_spans(place.as_ref(), location);
304 let span = use_spans.var_or_use();
306 let mut err = self.cannot_use_when_mutably_borrowed(
308 &self.describe_any_place(place.as_ref()),
310 &self.describe_any_place(borrow.borrowed_place.as_ref()),
313 borrow_spans.var_span_label(&mut err, {
314 let place = &borrow.borrowed_place;
315 let desc_place = self.describe_any_place(place.as_ref());
316 format!("borrow occurs due to use of {}{}", desc_place, borrow_spans.describe())
319 self.explain_why_borrow_contains_point(location, borrow, None)
320 .add_explanation_to_diagnostic(
331 pub(in crate::borrow_check) fn report_conflicting_borrow(
334 (place, span): (Place<'tcx>, Span),
335 gen_borrow_kind: BorrowKind,
336 issued_borrow: &BorrowData<'tcx>,
337 ) -> DiagnosticBuilder<'cx> {
338 let issued_spans = self.retrieve_borrow_spans(issued_borrow);
339 let issued_span = issued_spans.args_or_use();
341 let borrow_spans = self.borrow_spans(span, location);
342 let span = borrow_spans.args_or_use();
344 let container_name = if issued_spans.for_generator() || borrow_spans.for_generator() {
350 let (desc_place, msg_place, msg_borrow, union_type_name) =
351 self.describe_place_for_conflicting_borrow(place, issued_borrow.borrowed_place);
353 let explanation = self.explain_why_borrow_contains_point(location, issued_borrow, None);
354 let second_borrow_desc = if explanation.is_explained() { "second " } else { "" };
356 // FIXME: supply non-"" `opt_via` when appropriate
357 let first_borrow_desc;
358 let mut err = match (gen_borrow_kind, issued_borrow.kind) {
359 (BorrowKind::Shared, BorrowKind::Mut { .. }) => {
360 first_borrow_desc = "mutable ";
361 self.cannot_reborrow_already_borrowed(
373 (BorrowKind::Mut { .. }, BorrowKind::Shared) => {
374 first_borrow_desc = "immutable ";
375 self.cannot_reborrow_already_borrowed(
388 (BorrowKind::Mut { .. }, BorrowKind::Mut { .. }) => {
389 first_borrow_desc = "first ";
390 let mut err = self.cannot_mutably_borrow_multiply(
398 self.suggest_split_at_mut_if_applicable(
401 issued_borrow.borrowed_place,
406 (BorrowKind::Unique, BorrowKind::Unique) => {
407 first_borrow_desc = "first ";
408 self.cannot_uniquely_borrow_by_two_closures(span, &desc_place, issued_span, None)
411 (BorrowKind::Mut { .. } | BorrowKind::Unique, BorrowKind::Shallow) => {
412 if let Some(immutable_section_description) =
413 self.classify_immutable_section(issued_borrow.assigned_place)
415 let mut err = self.cannot_mutate_in_immutable_section(
419 immutable_section_description,
422 borrow_spans.var_span_label(
425 "borrow occurs due to use of {}{}",
427 borrow_spans.describe(),
433 first_borrow_desc = "immutable ";
434 self.cannot_reborrow_already_borrowed(
448 (BorrowKind::Unique, _) => {
449 first_borrow_desc = "first ";
450 self.cannot_uniquely_borrow_by_one_closure(
462 (BorrowKind::Shared, BorrowKind::Unique) => {
463 first_borrow_desc = "first ";
464 self.cannot_reborrow_already_uniquely_borrowed(
477 (BorrowKind::Mut { .. }, BorrowKind::Unique) => {
478 first_borrow_desc = "first ";
479 self.cannot_reborrow_already_uniquely_borrowed(
492 (BorrowKind::Shared, BorrowKind::Shared | BorrowKind::Shallow)
495 BorrowKind::Mut { .. }
498 | BorrowKind::Shallow,
502 if issued_spans == borrow_spans {
503 borrow_spans.var_span_label(
505 format!("borrows occur due to use of {}{}", desc_place, borrow_spans.describe()),
508 let borrow_place = &issued_borrow.borrowed_place;
509 let borrow_place_desc = self.describe_any_place(borrow_place.as_ref());
510 issued_spans.var_span_label(
513 "first borrow occurs due to use of {}{}",
515 issued_spans.describe(),
519 borrow_spans.var_span_label(
522 "second borrow occurs due to use of {}{}",
524 borrow_spans.describe(),
529 if union_type_name != "" {
531 "{} is a field of the union `{}`, so it overlaps the field {}",
532 msg_place, union_type_name, msg_borrow,
536 explanation.add_explanation_to_diagnostic(
548 fn suggest_split_at_mut_if_applicable(
550 err: &mut DiagnosticBuilder<'_>,
552 borrowed_place: Place<'tcx>,
554 if let ([ProjectionElem::Index(_)], [ProjectionElem::Index(_)]) =
555 (&place.projection[..], &borrowed_place.projection[..])
558 "consider using `.split_at_mut(position)` or similar method to obtain \
559 two mutable non-overlapping sub-slices",
564 /// Returns the description of the root place for a conflicting borrow and the full
565 /// descriptions of the places that caused the conflict.
567 /// In the simplest case, where there are no unions involved, if a mutable borrow of `x` is
568 /// attempted while a shared borrow is live, then this function will return:
572 /// In the simple union case, if a mutable borrow of a union field `x.z` is attempted while
573 /// a shared borrow of another field `x.y`, then this function will return:
575 /// ("x", "x.z", "x.y")
577 /// In the more complex union case, where the union is a field of a struct, then if a mutable
578 /// borrow of a union field in a struct `x.u.z` is attempted while a shared borrow of
579 /// another field `x.u.y`, then this function will return:
581 /// ("x.u", "x.u.z", "x.u.y")
583 /// This is used when creating error messages like below:
585 /// > cannot borrow `a.u` (via `a.u.z.c`) as immutable because it is also borrowed as
586 /// > mutable (via `a.u.s.b`) [E0502]
587 pub(in crate::borrow_check) fn describe_place_for_conflicting_borrow(
589 first_borrowed_place: Place<'tcx>,
590 second_borrowed_place: Place<'tcx>,
591 ) -> (String, String, String, String) {
592 // Define a small closure that we can use to check if the type of a place
594 let union_ty = |place_base, place_projection| {
595 let ty = Place::ty_from(place_base, place_projection, self.body, self.infcx.tcx).ty;
596 ty.ty_adt_def().filter(|adt| adt.is_union()).map(|_| ty)
599 // Start with an empty tuple, so we can use the functions on `Option` to reduce some
600 // code duplication (particularly around returning an empty description in the failure
604 // If we have a conflicting borrow of the same place, then we don't want to add
605 // an extraneous "via x.y" to our diagnostics, so filter out this case.
606 first_borrowed_place != second_borrowed_place
609 // We're going to want to traverse the first borrowed place to see if we can find
610 // field access to a union. If we find that, then we will keep the place of the
611 // union being accessed and the field that was being accessed so we can check the
612 // second borrowed place for the same union and a access to a different field.
613 let Place { local, projection } = first_borrowed_place;
615 let mut cursor = projection.as_ref();
616 while let [proj_base @ .., elem] = cursor {
620 ProjectionElem::Field(field, _) if union_ty(local, proj_base).is_some() => {
621 return Some((PlaceRef { local, projection: proj_base }, field));
628 .and_then(|(target_base, target_field)| {
629 // With the place of a union and a field access into it, we traverse the second
630 // borrowed place and look for a access to a different field of the same union.
631 let Place { local, ref projection } = second_borrowed_place;
633 let mut cursor = &projection[..];
634 while let [proj_base @ .., elem] = cursor {
637 if let ProjectionElem::Field(field, _) = elem {
638 if let Some(union_ty) = union_ty(local, proj_base) {
639 if field != target_field
640 && local == target_base.local
641 && proj_base == target_base.projection
644 self.describe_any_place(PlaceRef {
646 projection: proj_base,
648 self.describe_any_place(first_borrowed_place.as_ref()),
649 self.describe_any_place(second_borrowed_place.as_ref()),
650 union_ty.to_string(),
659 // If we didn't find a field access into a union, or both places match, then
660 // only return the description of the first place.
662 self.describe_any_place(first_borrowed_place.as_ref()),
670 /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
672 /// This means that some data referenced by `borrow` needs to live
673 /// past the point where the StorageDeadOrDrop of `place` occurs.
674 /// This is usually interpreted as meaning that `place` has too
675 /// short a lifetime. (But sometimes it is more useful to report
676 /// it as a more direct conflict between the execution of a
677 /// `Drop::drop` with an aliasing borrow.)
678 pub(in crate::borrow_check) fn report_borrowed_value_does_not_live_long_enough(
681 borrow: &BorrowData<'tcx>,
682 place_span: (Place<'tcx>, Span),
683 kind: Option<WriteKind>,
686 "report_borrowed_value_does_not_live_long_enough(\
687 {:?}, {:?}, {:?}, {:?}\
689 location, borrow, place_span, kind
692 let drop_span = place_span.1;
694 self.prefixes(borrow.borrowed_place.as_ref(), PrefixSet::All).last().unwrap();
696 let borrow_spans = self.retrieve_borrow_spans(borrow);
697 let borrow_span = borrow_spans.var_or_use();
699 assert!(root_place.projection.is_empty());
700 let proper_span = self.body.local_decls[root_place.local].source_info.span;
702 let root_place_projection = self.infcx.tcx.intern_place_elems(root_place.projection);
704 if self.access_place_error_reported.contains(&(
705 Place { local: root_place.local, projection: root_place_projection },
709 "suppressing access_place error when borrow doesn't live long enough for {:?}",
715 self.access_place_error_reported.insert((
716 Place { local: root_place.local, projection: root_place_projection },
720 let borrowed_local = borrow.borrowed_place.local;
721 if self.body.local_decls[borrowed_local].is_ref_to_thread_local() {
723 self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span);
724 err.buffer(&mut self.errors_buffer);
728 if let StorageDeadOrDrop::Destructor(dropped_ty) =
729 self.classify_drop_access_kind(borrow.borrowed_place.as_ref())
731 // If a borrow of path `B` conflicts with drop of `D` (and
732 // we're not in the uninteresting case where `B` is a
733 // prefix of `D`), then report this as a more interesting
734 // destructor conflict.
735 if !borrow.borrowed_place.as_ref().is_prefix_of(place_span.0.as_ref()) {
736 self.report_borrow_conflicts_with_destructor(
737 location, borrow, place_span, kind, dropped_ty,
743 let place_desc = self.describe_place(borrow.borrowed_place.as_ref());
745 let kind_place = kind.filter(|_| place_desc.is_some()).map(|k| (k, place_span.0));
746 let explanation = self.explain_why_borrow_contains_point(location, &borrow, kind_place);
749 "report_borrowed_value_does_not_live_long_enough(place_desc: {:?}, explanation: {:?})",
750 place_desc, explanation
752 let err = match (place_desc, explanation) {
753 // If the outlives constraint comes from inside the closure,
758 // Box::new(|| y) as Box<Fn() -> &'static i32>
760 // then just use the normal error. The closure isn't escaping
761 // and `move` will not help here.
764 BorrowExplanation::MustBeValidFor {
768 (ConstraintCategory::Return
769 | ConstraintCategory::CallArgument
770 | ConstraintCategory::OpaqueType),
776 ) if borrow_spans.for_generator() | borrow_spans.for_closure() => self
777 .report_escaping_closure_capture(
783 &format!("`{}`", name),
787 BorrowExplanation::MustBeValidFor {
788 category: ConstraintCategory::Assignment,
793 RegionNameSource::AnonRegionFromUpvar(upvar_span, ref upvar_name),
799 ) => self.report_escaping_data(borrow_span, name, upvar_span, upvar_name, span),
800 (Some(name), explanation) => self.report_local_value_does_not_live_long_enough(
808 (None, explanation) => self.report_temporary_value_does_not_live_long_enough(
818 err.buffer(&mut self.errors_buffer);
821 fn report_local_value_does_not_live_long_enough(
825 borrow: &BorrowData<'tcx>,
827 borrow_spans: UseSpans,
828 explanation: BorrowExplanation,
829 ) -> DiagnosticBuilder<'cx> {
831 "report_local_value_does_not_live_long_enough(\
832 {:?}, {:?}, {:?}, {:?}, {:?}\
834 location, name, borrow, drop_span, borrow_spans
837 let borrow_span = borrow_spans.var_or_use();
838 if let BorrowExplanation::MustBeValidFor {
846 if let Some(diag) = self.try_report_cannot_return_reference_to_local(
851 opt_place_desc.as_ref(),
857 let mut err = self.path_does_not_live_long_enough(borrow_span, &format!("`{}`", name));
859 if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
860 let region_name = annotation.emit(self, &mut err);
864 format!("`{}` would have to be valid for `{}`...", name, region_name),
867 if let Some(fn_hir_id) = self.infcx.tcx.hir().as_local_hir_id(self.mir_def_id) {
871 "...but `{}` will be dropped here, when the {} returns",
877 .map(|name| format!("function `{}`", name))
882 .typeck_tables_of(self.mir_def_id)
883 .node_type(fn_hir_id)
886 ty::Closure(..) => "enclosing closure",
887 ty::Generator(..) => "enclosing generator",
888 kind => bug!("expected closure or generator, found {:?}", kind),
896 "functions cannot return a borrow to data owned within the function's scope, \
897 functions can only return borrows to data passed as arguments",
900 "to learn more, visit <https://doc.rust-lang.org/book/ch04-02-\
901 references-and-borrowing.html#dangling-references>",
906 format!("...but `{}` dropped here while still borrowed", name),
910 if let BorrowExplanation::MustBeValidFor { .. } = explanation {
912 explanation.add_explanation_to_diagnostic(
922 err.span_label(borrow_span, "borrowed value does not live long enough");
923 err.span_label(drop_span, format!("`{}` dropped here while still borrowed", name));
925 let within = if borrow_spans.for_generator() { " by generator" } else { "" };
927 borrow_spans.args_span_label(&mut err, format!("value captured here{}", within));
929 explanation.add_explanation_to_diagnostic(
942 fn report_borrow_conflicts_with_destructor(
945 borrow: &BorrowData<'tcx>,
946 (place, drop_span): (Place<'tcx>, Span),
947 kind: Option<WriteKind>,
948 dropped_ty: Ty<'tcx>,
951 "report_borrow_conflicts_with_destructor(\
952 {:?}, {:?}, ({:?}, {:?}), {:?}\
954 location, borrow, place, drop_span, kind,
957 let borrow_spans = self.retrieve_borrow_spans(borrow);
958 let borrow_span = borrow_spans.var_or_use();
960 let mut err = self.cannot_borrow_across_destructor(borrow_span);
962 let what_was_dropped = match self.describe_place(place.as_ref()) {
963 Some(name) => format!("`{}`", name),
964 None => String::from("temporary value"),
967 let label = match self.describe_place(borrow.borrowed_place.as_ref()) {
968 Some(borrowed) => format!(
969 "here, drop of {D} needs exclusive access to `{B}`, \
970 because the type `{T}` implements the `Drop` trait",
971 D = what_was_dropped,
976 "here is drop of {D}; whose type `{T}` implements the `Drop` trait",
977 D = what_was_dropped,
981 err.span_label(drop_span, label);
983 // Only give this note and suggestion if they could be relevant.
985 self.explain_why_borrow_contains_point(location, borrow, kind.map(|k| (k, place)));
987 BorrowExplanation::UsedLater { .. }
988 | BorrowExplanation::UsedLaterWhenDropped { .. } => {
989 err.note("consider using a `let` binding to create a longer lived value");
994 explanation.add_explanation_to_diagnostic(
1003 err.buffer(&mut self.errors_buffer);
1006 fn report_thread_local_value_does_not_live_long_enough(
1010 ) -> DiagnosticBuilder<'cx> {
1012 "report_thread_local_value_does_not_live_long_enough(\
1015 drop_span, borrow_span
1018 let mut err = self.thread_local_value_does_not_live_long_enough(borrow_span);
1022 "thread-local variables cannot be borrowed beyond the end of the function",
1024 err.span_label(drop_span, "end of enclosing function is here");
1029 fn report_temporary_value_does_not_live_long_enough(
1032 borrow: &BorrowData<'tcx>,
1034 borrow_spans: UseSpans,
1036 explanation: BorrowExplanation,
1037 ) -> DiagnosticBuilder<'cx> {
1039 "report_temporary_value_does_not_live_long_enough(\
1040 {:?}, {:?}, {:?}, {:?}\
1042 location, borrow, drop_span, proper_span
1045 if let BorrowExplanation::MustBeValidFor { category, span, from_closure: false, .. } =
1048 if let Some(diag) = self.try_report_cannot_return_reference_to_local(
1059 let mut err = self.temporary_value_borrowed_for_too_long(proper_span);
1060 err.span_label(proper_span, "creates a temporary which is freed while still in use");
1061 err.span_label(drop_span, "temporary value is freed at the end of this statement");
1064 BorrowExplanation::UsedLater(..)
1065 | BorrowExplanation::UsedLaterInLoop(..)
1066 | BorrowExplanation::UsedLaterWhenDropped { .. } => {
1067 // Only give this note and suggestion if it could be relevant.
1068 err.note("consider using a `let` binding to create a longer lived value");
1072 explanation.add_explanation_to_diagnostic(
1081 let within = if borrow_spans.for_generator() { " by generator" } else { "" };
1083 borrow_spans.args_span_label(&mut err, format!("value captured here{}", within));
1088 fn try_report_cannot_return_reference_to_local(
1090 borrow: &BorrowData<'tcx>,
1093 category: ConstraintCategory,
1094 opt_place_desc: Option<&String>,
1095 ) -> Option<DiagnosticBuilder<'cx>> {
1096 let return_kind = match category {
1097 ConstraintCategory::Return => "return",
1098 ConstraintCategory::Yield => "yield",
1102 // FIXME use a better heuristic than Spans
1103 let reference_desc = if return_span == self.body.source_info(borrow.reserve_location).span {
1109 let (place_desc, note) = if let Some(place_desc) = opt_place_desc {
1110 let local_kind = if let Some(local) = borrow.borrowed_place.as_local() {
1111 match self.body.local_kind(local) {
1112 LocalKind::ReturnPointer | LocalKind::Temp => {
1113 bug!("temporary or return pointer with a name")
1115 LocalKind::Var => "local variable ",
1116 LocalKind::Arg if !self.upvars.is_empty() && local == Local::new(1) => {
1117 "variable captured by `move` "
1119 LocalKind::Arg => "function parameter ",
1125 format!("{}`{}`", local_kind, place_desc),
1126 format!("`{}` is borrowed here", place_desc),
1130 self.prefixes(borrow.borrowed_place.as_ref(), PrefixSet::All).last().unwrap();
1131 let local = root_place.local;
1132 match self.body.local_kind(local) {
1133 LocalKind::ReturnPointer | LocalKind::Temp => {
1134 ("temporary value".to_string(), "temporary value created here".to_string())
1137 "function parameter".to_string(),
1138 "function parameter borrowed here".to_string(),
1141 ("local binding".to_string(), "local binding introduced here".to_string())
1146 let mut err = self.cannot_return_reference_to_local(
1153 if return_span != borrow_span {
1154 err.span_label(borrow_span, note);
1160 fn report_escaping_closure_capture(
1164 fr_name: &RegionName,
1165 category: ConstraintCategory,
1166 constraint_span: Span,
1168 ) -> DiagnosticBuilder<'cx> {
1169 let tcx = self.infcx.tcx;
1170 let args_span = use_span.args_or_use();
1172 let suggestion = match tcx.sess.source_map().span_to_snippet(args_span) {
1174 if string.starts_with("async ") {
1175 string.insert_str(6, "move ");
1176 } else if string.starts_with("async|") {
1177 string.insert_str(5, " move");
1179 string.insert_str(0, "move ");
1183 Err(_) => "move |<args>| <body>".to_string(),
1185 let kind = match use_span.generator_kind() {
1186 Some(generator_kind) => match generator_kind {
1187 GeneratorKind::Async(async_kind) => match async_kind {
1188 AsyncGeneratorKind::Block => "async block",
1189 AsyncGeneratorKind::Closure => "async closure",
1190 _ => bug!("async block/closure expected, but async function found."),
1192 GeneratorKind::Gen => "generator",
1198 self.cannot_capture_in_long_lived_closure(args_span, kind, captured_var, var_span);
1199 err.span_suggestion(
1202 "to force the {} to take ownership of {} (and any \
1203 other referenced variables), use the `move` keyword",
1207 Applicability::MachineApplicable,
1210 let msg = match category {
1211 ConstraintCategory::Return | ConstraintCategory::OpaqueType => {
1212 format!("{} is returned here", kind)
1214 ConstraintCategory::CallArgument => {
1215 fr_name.highlight_region_name(&mut err);
1216 format!("function requires argument type to outlive `{}`", fr_name)
1219 "report_escaping_closure_capture called with unexpected constraint \
1224 err.span_note(constraint_span, &msg);
1228 fn report_escaping_data(
1231 name: &Option<String>,
1235 ) -> DiagnosticBuilder<'cx> {
1236 let tcx = self.infcx.tcx;
1238 let (_, escapes_from) = tcx.article_and_description(self.mir_def_id);
1241 borrowck_errors::borrowed_data_escapes_closure(tcx, escape_span, escapes_from);
1245 format!("`{}` declared here, outside of the {} body", upvar_name, escapes_from),
1248 err.span_label(borrow_span, format!("borrow is only valid in the {} body", escapes_from));
1250 if let Some(name) = name {
1253 format!("reference to `{}` escapes the {} body here", name, escapes_from),
1258 format!("reference escapes the {} body here", escapes_from),
1265 fn get_moved_indexes(&mut self, location: Location, mpi: MovePathIndex) -> Vec<MoveSite> {
1266 fn predecessor_locations(
1267 body: &'a mir::Body<'tcx>,
1269 ) -> impl Iterator<Item = Location> + 'a {
1270 if location.statement_index == 0 {
1271 let predecessors = body.predecessors_for(location.block).to_vec();
1272 Either::Left(predecessors.into_iter().map(move |bb| body.terminator_loc(bb)))
1274 Either::Right(std::iter::once(Location {
1275 statement_index: location.statement_index - 1,
1281 let mut stack = Vec::new();
1282 stack.extend(predecessor_locations(self.body, location).map(|predecessor| {
1283 let is_back_edge = location.dominates(predecessor, &self.dominators);
1284 (predecessor, is_back_edge)
1287 let mut visited = FxHashSet::default();
1288 let mut result = vec![];
1290 'dfs: while let Some((location, is_back_edge)) = stack.pop() {
1292 "report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
1293 location, is_back_edge
1296 if !visited.insert(location) {
1302 self.body[location.block].statements.get(location.statement_index).map(|s| &s.kind);
1303 if let Some(StatementKind::StorageDead(..)) = stmt_kind {
1304 // this analysis only tries to find moves explicitly
1305 // written by the user, so we ignore the move-outs
1306 // created by `StorageDead` and at the beginning
1309 // If we are found a use of a.b.c which was in error, then we want to look for
1310 // moves not only of a.b.c but also a.b and a.
1312 // Note that the moves data already includes "parent" paths, so we don't have to
1313 // worry about the other case: that is, if there is a move of a.b.c, it is already
1314 // marked as a move of a.b and a as well, so we will generate the correct errors
1316 let mut mpis = vec![mpi];
1317 let move_paths = &self.move_data.move_paths;
1318 mpis.extend(move_paths[mpi].parents(move_paths).map(|(mpi, _)| mpi));
1320 for moi in &self.move_data.loc_map[location] {
1321 debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
1322 if mpis.contains(&self.move_data.moves[*moi].path) {
1323 debug!("report_use_of_moved_or_uninitialized: found");
1324 result.push(MoveSite { moi: *moi, traversed_back_edge: is_back_edge });
1326 // Strictly speaking, we could continue our DFS here. There may be
1327 // other moves that can reach the point of error. But it is kind of
1328 // confusing to highlight them.
1336 // drop(a); // <-- current point of error
1339 // Because we stop the DFS here, we only highlight `let c = a`,
1340 // and not `let b = a`. We will of course also report an error at
1341 // `let c = a` which highlights `let b = a` as the move.
1348 let mut any_match = false;
1349 drop_flag_effects::for_location_inits(
1364 stack.extend(predecessor_locations(self.body, location).map(|predecessor| {
1365 let back_edge = location.dominates(predecessor, &self.dominators);
1366 (predecessor, is_back_edge || back_edge)
1373 pub(in crate::borrow_check) fn report_illegal_mutation_of_borrowed(
1376 (place, span): (Place<'tcx>, Span),
1377 loan: &BorrowData<'tcx>,
1379 let loan_spans = self.retrieve_borrow_spans(loan);
1380 let loan_span = loan_spans.args_or_use();
1382 let descr_place = self.describe_any_place(place.as_ref());
1383 if loan.kind == BorrowKind::Shallow {
1384 if let Some(section) = self.classify_immutable_section(loan.assigned_place) {
1385 let mut err = self.cannot_mutate_in_immutable_section(
1392 loan_spans.var_span_label(
1394 format!("borrow occurs due to use{}", loan_spans.describe()),
1397 err.buffer(&mut self.errors_buffer);
1403 let mut err = self.cannot_assign_to_borrowed(span, loan_span, &descr_place);
1406 .var_span_label(&mut err, format!("borrow occurs due to use{}", loan_spans.describe()));
1408 self.explain_why_borrow_contains_point(location, loan, None).add_explanation_to_diagnostic(
1417 err.buffer(&mut self.errors_buffer);
1420 /// Reports an illegal reassignment; for example, an assignment to
1421 /// (part of) a non-`mut` local that occurs potentially after that
1422 /// local has already been initialized. `place` is the path being
1423 /// assigned; `err_place` is a place providing a reason why
1424 /// `place` is not mutable (e.g., the non-`mut` local `x` in an
1425 /// assignment to `x.f`).
1426 pub(in crate::borrow_check) fn report_illegal_reassignment(
1428 _location: Location,
1429 (place, span): (Place<'tcx>, Span),
1430 assigned_span: Span,
1431 err_place: Place<'tcx>,
1433 let (from_arg, local_decl, local_name) = match err_place.as_local() {
1435 self.body.local_kind(local) == LocalKind::Arg,
1436 Some(&self.body.local_decls[local]),
1437 self.local_names[local],
1439 None => (false, None, None),
1442 // If root local is initialized immediately (everything apart from let
1443 // PATTERN;) then make the error refer to that local, rather than the
1444 // place being assigned later.
1445 let (place_description, assigned_span) = match local_decl {
1449 ClearCrossCrate::Clear
1450 | ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
1451 opt_match_place: None,
1455 | LocalInfo::StaticRef { .. }
1459 | None => (self.describe_any_place(place.as_ref()), assigned_span),
1460 Some(decl) => (self.describe_any_place(err_place.as_ref()), decl.source_info.span),
1463 let mut err = self.cannot_reassign_immutable(span, &place_description, from_arg);
1464 let msg = if from_arg {
1465 "cannot assign to immutable argument"
1467 "cannot assign twice to immutable variable"
1469 if span != assigned_span {
1471 err.span_label(assigned_span, format!("first assignment to {}", place_description));
1474 if let Some(decl) = local_decl {
1475 if let Some(name) = local_name {
1476 if decl.can_be_made_mutable() {
1477 err.span_suggestion(
1478 decl.source_info.span,
1479 "make this binding mutable",
1480 format!("mut {}", name),
1481 Applicability::MachineApplicable,
1486 err.span_label(span, msg);
1487 err.buffer(&mut self.errors_buffer);
1490 fn classify_drop_access_kind(&self, place: PlaceRef<'tcx>) -> StorageDeadOrDrop<'tcx> {
1491 let tcx = self.infcx.tcx;
1492 match place.projection {
1493 [] => StorageDeadOrDrop::LocalStorageDead,
1494 [proj_base @ .., elem] => {
1495 // FIXME(spastorino) make this iterate
1496 let base_access = self.classify_drop_access_kind(PlaceRef {
1498 projection: proj_base,
1501 ProjectionElem::Deref => match base_access {
1502 StorageDeadOrDrop::LocalStorageDead
1503 | StorageDeadOrDrop::BoxedStorageDead => {
1505 Place::ty_from(place.local, proj_base, self.body, tcx).ty.is_box(),
1506 "Drop of value behind a reference or raw pointer"
1508 StorageDeadOrDrop::BoxedStorageDead
1510 StorageDeadOrDrop::Destructor(_) => base_access,
1512 ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
1513 let base_ty = Place::ty_from(place.local, proj_base, self.body, tcx).ty;
1514 match base_ty.kind {
1515 ty::Adt(def, _) if def.has_dtor(tcx) => {
1516 // Report the outermost adt with a destructor
1518 StorageDeadOrDrop::Destructor(_) => base_access,
1519 StorageDeadOrDrop::LocalStorageDead
1520 | StorageDeadOrDrop::BoxedStorageDead => {
1521 StorageDeadOrDrop::Destructor(base_ty)
1529 ProjectionElem::ConstantIndex { .. }
1530 | ProjectionElem::Subslice { .. }
1531 | ProjectionElem::Index(_) => base_access,
1537 /// Describe the reason for the fake borrow that was assigned to `place`.
1538 fn classify_immutable_section(&self, place: Place<'tcx>) -> Option<&'static str> {
1539 use rustc_middle::mir::visit::Visitor;
1540 struct FakeReadCauseFinder<'tcx> {
1542 cause: Option<FakeReadCause>,
1544 impl<'tcx> Visitor<'tcx> for FakeReadCauseFinder<'tcx> {
1545 fn visit_statement(&mut self, statement: &Statement<'tcx>, _: Location) {
1547 Statement { kind: StatementKind::FakeRead(cause, box place), .. }
1548 if *place == self.place =>
1550 self.cause = Some(*cause);
1556 let mut visitor = FakeReadCauseFinder { place, cause: None };
1557 visitor.visit_body(&self.body);
1558 match visitor.cause {
1559 Some(FakeReadCause::ForMatchGuard) => Some("match guard"),
1560 Some(FakeReadCause::ForIndex) => Some("indexing expression"),
1565 /// Annotate argument and return type of function and closure with (synthesized) lifetime for
1566 /// borrow of local value that does not live long enough.
1567 fn annotate_argument_and_return_for_borrow(
1569 borrow: &BorrowData<'tcx>,
1570 ) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
1571 // Define a fallback for when we can't match a closure.
1573 let is_closure = self.infcx.tcx.is_closure(self.mir_def_id);
1577 let ty = self.infcx.tcx.type_of(self.mir_def_id);
1579 ty::FnDef(_, _) | ty::FnPtr(_) => self
1580 .annotate_fn_sig(self.mir_def_id, self.infcx.tcx.fn_sig(self.mir_def_id)),
1586 // In order to determine whether we need to annotate, we need to check whether the reserve
1587 // place was an assignment into a temporary.
1589 // If it was, we check whether or not that temporary is eventually assigned into the return
1590 // place. If it was, we can add annotations about the function's return type and arguments
1591 // and it'll make sense.
1592 let location = borrow.reserve_location;
1593 debug!("annotate_argument_and_return_for_borrow: location={:?}", location);
1594 if let Some(&Statement { kind: StatementKind::Assign(box (ref reservation, _)), .. }) =
1595 &self.body[location.block].statements.get(location.statement_index)
1597 debug!("annotate_argument_and_return_for_borrow: reservation={:?}", reservation);
1598 // Check that the initial assignment of the reserve location is into a temporary.
1599 let mut target = match reservation.as_local() {
1600 Some(local) if self.body.local_kind(local) == LocalKind::Temp => local,
1604 // Next, look through the rest of the block, checking if we are assigning the
1605 // `target` (that is, the place that contains our borrow) to anything.
1606 let mut annotated_closure = None;
1607 for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
1609 "annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
1612 if let StatementKind::Assign(box (place, rvalue)) = &stmt.kind {
1613 if let Some(assigned_to) = place.as_local() {
1615 "annotate_argument_and_return_for_borrow: assigned_to={:?} \
1619 // Check if our `target` was captured by a closure.
1620 if let Rvalue::Aggregate(
1621 box AggregateKind::Closure(def_id, substs),
1625 for operand in operands {
1626 let assigned_from = match operand {
1627 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1633 "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1637 // Find the local from the operand.
1638 let assigned_from_local = match assigned_from.local_or_deref_local()
1640 Some(local) => local,
1644 if assigned_from_local != target {
1648 // If a closure captured our `target` and then assigned
1649 // into a place then we should annotate the closure in
1650 // case it ends up being assigned into the return place.
1652 self.annotate_fn_sig(*def_id, substs.as_closure().sig());
1654 "annotate_argument_and_return_for_borrow: \
1655 annotated_closure={:?} assigned_from_local={:?} \
1657 annotated_closure, assigned_from_local, assigned_to
1660 if assigned_to == mir::RETURN_PLACE {
1661 // If it was assigned directly into the return place, then
1663 return annotated_closure;
1665 // Otherwise, update the target.
1666 target = assigned_to;
1670 // If none of our closure's operands matched, then skip to the next
1675 // Otherwise, look at other types of assignment.
1676 let assigned_from = match rvalue {
1677 Rvalue::Ref(_, _, assigned_from) => assigned_from,
1678 Rvalue::Use(operand) => match operand {
1679 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1687 "annotate_argument_and_return_for_borrow: \
1688 assigned_from={:?}",
1692 // Find the local from the rvalue.
1693 let assigned_from_local = match assigned_from.local_or_deref_local() {
1694 Some(local) => local,
1698 "annotate_argument_and_return_for_borrow: \
1699 assigned_from_local={:?}",
1700 assigned_from_local,
1703 // Check if our local matches the target - if so, we've assigned our
1704 // borrow to a new place.
1705 if assigned_from_local != target {
1709 // If we assigned our `target` into a new place, then we should
1710 // check if it was the return place.
1712 "annotate_argument_and_return_for_borrow: \
1713 assigned_from_local={:?} assigned_to={:?}",
1714 assigned_from_local, assigned_to
1716 if assigned_to == mir::RETURN_PLACE {
1717 // If it was then return the annotated closure if there was one,
1718 // else, annotate this function.
1719 return annotated_closure.or_else(fallback);
1722 // If we didn't assign into the return place, then we just update
1724 target = assigned_to;
1729 // Check the terminator if we didn't find anything in the statements.
1730 let terminator = &self.body[location.block].terminator();
1732 "annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
1735 if let TerminatorKind::Call { destination: Some((place, _)), args, .. } =
1738 if let Some(assigned_to) = place.as_local() {
1740 "annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
1743 for operand in args {
1744 let assigned_from = match operand {
1745 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1751 "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1755 if let Some(assigned_from_local) = assigned_from.local_or_deref_local() {
1757 "annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
1758 assigned_from_local,
1761 if assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
1762 return annotated_closure.or_else(fallback);
1770 // If we haven't found an assignment into the return place, then we need not add
1772 debug!("annotate_argument_and_return_for_borrow: none found");
1776 /// Annotate the first argument and return type of a function signature if they are
1781 sig: ty::PolyFnSig<'tcx>,
1782 ) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
1783 debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
1784 let is_closure = self.infcx.tcx.is_closure(did);
1785 let fn_hir_id = self.infcx.tcx.hir().as_local_hir_id(did)?;
1786 let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(fn_hir_id)?;
1788 // We need to work out which arguments to highlight. We do this by looking
1789 // at the return type, where there are three cases:
1791 // 1. If there are named arguments, then we should highlight the return type and
1792 // highlight any of the arguments that are also references with that lifetime.
1793 // If there are no arguments that have the same lifetime as the return type,
1794 // then don't highlight anything.
1795 // 2. The return type is a reference with an anonymous lifetime. If this is
1796 // the case, then we can take advantage of (and teach) the lifetime elision
1799 // We know that an error is being reported. So the arguments and return type
1800 // must satisfy the elision rules. Therefore, if there is a single argument
1801 // then that means the return type and first (and only) argument have the same
1802 // lifetime and the borrow isn't meeting that, we can highlight the argument
1805 // If there are multiple arguments then the first argument must be self (else
1806 // it would not satisfy the elision rules), so we can highlight self and the
1808 // 3. The return type is not a reference. In this case, we don't highlight
1810 let return_ty = sig.output();
1811 match return_ty.skip_binder().kind {
1812 ty::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
1813 // This is case 1 from above, return type is a named reference so we need to
1814 // search for relevant arguments.
1815 let mut arguments = Vec::new();
1816 for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
1817 if let ty::Ref(argument_region, _, _) = argument.kind {
1818 if argument_region == return_region {
1819 // Need to use the `rustc_middle::ty` types to compare against the
1820 // `return_region`. Then use the `rustc_hir` type to get only
1821 // the lifetime span.
1822 if let hir::TyKind::Rptr(lifetime, _) = &fn_decl.inputs[index].kind {
1823 // With access to the lifetime, we can get
1825 arguments.push((*argument, lifetime.span));
1827 bug!("ty type is a ref but hir type is not");
1833 // We need to have arguments. This shouldn't happen, but it's worth checking.
1834 if arguments.is_empty() {
1838 // We use a mix of the HIR and the Ty types to get information
1839 // as the HIR doesn't have full types for closure arguments.
1840 let return_ty = *sig.output().skip_binder();
1841 let mut return_span = fn_decl.output.span();
1842 if let hir::FnRetTy::Return(ty) = &fn_decl.output {
1843 if let hir::TyKind::Rptr(lifetime, _) = ty.kind {
1844 return_span = lifetime.span;
1848 Some(AnnotatedBorrowFnSignature::NamedFunction {
1854 ty::Ref(_, _, _) if is_closure => {
1855 // This is case 2 from above but only for closures, return type is anonymous
1856 // reference so we select
1857 // the first argument.
1858 let argument_span = fn_decl.inputs.first()?.span;
1859 let argument_ty = sig.inputs().skip_binder().first()?;
1861 // Closure arguments are wrapped in a tuple, so we need to get the first
1863 if let ty::Tuple(elems) = argument_ty.kind {
1864 let argument_ty = elems.first()?.expect_ty();
1865 if let ty::Ref(_, _, _) = argument_ty.kind {
1866 return Some(AnnotatedBorrowFnSignature::Closure {
1875 ty::Ref(_, _, _) => {
1876 // This is also case 2 from above but for functions, return type is still an
1877 // anonymous reference so we select the first argument.
1878 let argument_span = fn_decl.inputs.first()?.span;
1879 let argument_ty = sig.inputs().skip_binder().first()?;
1881 let return_span = fn_decl.output.span();
1882 let return_ty = *sig.output().skip_binder();
1884 // We expect the first argument to be a reference.
1885 match argument_ty.kind {
1886 ty::Ref(_, _, _) => {}
1890 Some(AnnotatedBorrowFnSignature::AnonymousFunction {
1898 // This is case 3 from above, return type is not a reference so don't highlight
1907 enum AnnotatedBorrowFnSignature<'tcx> {
1909 arguments: Vec<(Ty<'tcx>, Span)>,
1910 return_ty: Ty<'tcx>,
1914 argument_ty: Ty<'tcx>,
1915 argument_span: Span,
1916 return_ty: Ty<'tcx>,
1920 argument_ty: Ty<'tcx>,
1921 argument_span: Span,
1925 impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
1926 /// Annotate the provided diagnostic with information about borrow from the fn signature that
1928 pub(in crate::borrow_check) fn emit(
1930 cx: &mut MirBorrowckCtxt<'_, 'tcx>,
1931 diag: &mut DiagnosticBuilder<'_>,
1934 AnnotatedBorrowFnSignature::Closure { argument_ty, argument_span } => {
1937 format!("has type `{}`", cx.get_name_for_ty(argument_ty, 0)),
1940 cx.get_region_name_for_ty(argument_ty, 0)
1942 AnnotatedBorrowFnSignature::AnonymousFunction {
1948 let argument_ty_name = cx.get_name_for_ty(argument_ty, 0);
1949 diag.span_label(*argument_span, format!("has type `{}`", argument_ty_name));
1951 let return_ty_name = cx.get_name_for_ty(return_ty, 0);
1952 let types_equal = return_ty_name == argument_ty_name;
1957 if types_equal { "also " } else { "" },
1963 "argument and return type have the same lifetime due to lifetime elision rules",
1966 "to learn more, visit <https://doc.rust-lang.org/book/ch10-03-\
1967 lifetime-syntax.html#lifetime-elision>",
1970 cx.get_region_name_for_ty(return_ty, 0)
1972 AnnotatedBorrowFnSignature::NamedFunction { arguments, return_ty, return_span } => {
1973 // Region of return type and arguments checked to be the same earlier.
1974 let region_name = cx.get_region_name_for_ty(return_ty, 0);
1975 for (_, argument_span) in arguments {
1976 diag.span_label(*argument_span, format!("has lifetime `{}`", region_name));
1979 diag.span_label(*return_span, format!("also has lifetime `{}`", region_name,));
1982 "use data from the highlighted arguments which match the `{}` lifetime of \