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, suggest_constraining_type_param, Ty};
14 use rustc_span::source_map::DesugaringKind;
17 use crate::dataflow::drop_flag_effects;
18 use crate::dataflow::indexes::{MoveOutIndex, MovePathIndex};
19 use crate::util::borrowck_errors;
21 use crate::borrow_check::{
22 borrow_set::BorrowData, prefixes::IsPrefixOf, InitializationRequiringAction, MirBorrowckCtxt,
27 explain_borrow::BorrowExplanation, FnSelfUseKind, IncludingDowncast, RegionName,
28 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 is_partial_move = move_site_vec.iter().any(|move_site| {
117 let move_out = self.move_data.moves[(*move_site).moi];
118 let moved_place = &self.move_data.move_paths[move_out.path].place;
119 // `*(_1)` where `_1` is a `Box` is actually a move out.
120 let is_box_move = moved_place.as_ref().projection == &[ProjectionElem::Deref]
121 && self.body.local_decls[moved_place.local].ty.is_box();
124 && used_place != moved_place.as_ref()
125 && used_place.is_prefix_of(moved_place.as_ref())
128 let partial_str = if is_partial_move { "partial " } else { "" };
129 let partially_str = if is_partial_move { "partially " } else { "" };
131 let mut err = self.cannot_act_on_moved_value(
133 desired_action.as_noun(),
135 self.describe_place_with_options(moved_place, IncludingDowncast(true)),
138 self.add_moved_or_invoked_closure_note(location, used_place, &mut err);
140 let mut is_loop_move = false;
142 for move_site in &move_site_vec {
143 let move_out = self.move_data.moves[(*move_site).moi];
144 let moved_place = &self.move_data.move_paths[move_out.path].place;
146 let move_spans = self.move_spans(moved_place.as_ref(), move_out.source);
147 let move_span = move_spans.args_or_use();
149 let move_msg = if move_spans.for_closure() { " into closure" } else { "" };
151 if location == move_out.source {
155 "value {}moved{} here, in previous iteration of loop",
156 partially_str, move_msg
160 } else if move_site.traversed_back_edge {
164 "value {}moved{} here, in previous iteration of loop",
165 partially_str, move_msg
169 if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } =
172 let place_name = self
173 .describe_place(moved_place.as_ref())
174 .map(|n| format!("`{}`", n))
175 .unwrap_or_else(|| "value".to_owned());
177 FnSelfUseKind::FnOnceCall => {
181 "{} {}moved due to this call",
182 place_name, partially_str
187 "this value implements `FnOnce`, which causes it to be moved when called",
190 FnSelfUseKind::Operator { self_arg } => {
194 "{} {}moved due to usage in operator",
195 place_name, partially_str
198 if self.fn_self_span_reported.insert(fn_span) {
201 "calling this operator moves the left-hand side",
205 FnSelfUseKind::Normal { self_arg, implicit_into_iter } => {
206 if implicit_into_iter {
210 "{} {}moved due to this implicit call to `.into_iter()`",
211 place_name, partially_str
218 "{} {}moved due to this method call",
219 place_name, partially_str
223 // Avoid pointing to the same function in multiple different
225 if self.fn_self_span_reported.insert(self_arg.span) {
228 &format!("this function consumes the receiver `self` by taking ownership of it, which moves {}", place_name)
236 format!("value {}moved{} here", partially_str, move_msg),
238 move_spans.var_span_label(
241 "variable {}moved due to use{}",
243 move_spans.describe()
248 if let UseSpans::PatUse(span) = move_spans {
249 err.span_suggestion_verbose(
252 "borrow this field in the pattern to avoid moving {}",
253 self.describe_place(moved_place.as_ref())
254 .map(|n| format!("`{}`", n))
255 .unwrap_or_else(|| "the value".to_string())
258 Applicability::MachineApplicable,
262 if let Some(DesugaringKind::ForLoop(_)) = move_span.desugaring_kind() {
263 let sess = self.infcx.tcx.sess;
264 if let Ok(snippet) = sess.source_map().span_to_snippet(move_span) {
267 "consider borrowing to avoid moving into the for loop",
268 format!("&{}", snippet),
269 Applicability::MaybeIncorrect,
275 use_spans.var_span_label(
277 format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
284 "value {} here after {}move",
285 desired_action.as_verb_in_past_tense(),
292 Place::ty_from(used_place.local, used_place.projection, self.body, self.infcx.tcx)
294 let needs_note = match ty.kind {
295 ty::Closure(id, _) => {
296 let tables = self.infcx.tcx.typeck(id.expect_local());
297 let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(id.expect_local());
299 tables.closure_kind_origins().get(hir_id).is_none()
304 let mpi = self.move_data.moves[move_out_indices[0]].path;
305 let place = &self.move_data.move_paths[mpi].place;
306 let ty = place.ty(self.body, self.infcx.tcx).ty;
309 if let ty::Ref(_, _, hir::Mutability::Mut) = ty.kind {
310 // We have a `&mut` ref, we need to reborrow on each iteration (#62112).
311 err.span_suggestion_verbose(
314 "consider creating a fresh reborrow of {} here",
315 self.describe_place(moved_place)
316 .map(|n| format!("`{}`", n))
317 .unwrap_or_else(|| "the mutable reference".to_string()),
319 "&mut *".to_string(),
320 Applicability::MachineApplicable,
327 self.describe_place_with_options(place.as_ref(), IncludingDowncast(true));
328 let note_msg = match opt_name {
329 Some(ref name) => format!("`{}`", name),
330 None => "value".to_owned(),
332 if let ty::Param(param_ty) = ty.kind {
333 let tcx = self.infcx.tcx;
334 let generics = tcx.generics_of(self.mir_def_id);
335 let param = generics.type_param(¶m_ty, tcx);
336 if let Some(generics) =
337 tcx.hir().get_generics(tcx.closure_base_def_id(self.mir_def_id.to_def_id()))
339 suggest_constraining_type_param(
343 ¶m.name.as_str(),
349 let span = if let Some(local) = place.as_local() {
350 let decl = &self.body.local_decls[local];
351 Some(decl.source_info.span)
355 self.note_type_does_not_implement_copy(&mut err, ¬e_msg, ty, span, partial_str);
358 if let Some((_, mut old_err)) =
359 self.move_error_reported.insert(move_out_indices, (used_place, err))
361 // Cancel the old error so it doesn't ICE.
367 pub(in crate::borrow_check) fn report_move_out_while_borrowed(
370 (place, span): (Place<'tcx>, Span),
371 borrow: &BorrowData<'tcx>,
374 "report_move_out_while_borrowed: location={:?} place={:?} span={:?} borrow={:?}",
375 location, place, span, borrow
377 let value_msg = self.describe_any_place(place.as_ref());
378 let borrow_msg = self.describe_any_place(borrow.borrowed_place.as_ref());
380 let borrow_spans = self.retrieve_borrow_spans(borrow);
381 let borrow_span = borrow_spans.args_or_use();
383 let move_spans = self.move_spans(place.as_ref(), location);
384 let span = move_spans.args_or_use();
387 self.cannot_move_when_borrowed(span, &self.describe_any_place(place.as_ref()));
388 err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
389 err.span_label(span, format!("move out of {} occurs here", value_msg));
391 borrow_spans.var_span_label(
393 format!("borrow occurs due to use{}", borrow_spans.describe()),
397 .var_span_label(&mut err, format!("move occurs due to use{}", move_spans.describe()));
399 self.explain_why_borrow_contains_point(location, borrow, None)
400 .add_explanation_to_diagnostic(
408 err.buffer(&mut self.errors_buffer);
411 pub(in crate::borrow_check) fn report_use_while_mutably_borrowed(
414 (place, _span): (Place<'tcx>, Span),
415 borrow: &BorrowData<'tcx>,
416 ) -> DiagnosticBuilder<'cx> {
417 let borrow_spans = self.retrieve_borrow_spans(borrow);
418 let borrow_span = borrow_spans.args_or_use();
420 // Conflicting borrows are reported separately, so only check for move
422 let use_spans = self.move_spans(place.as_ref(), location);
423 let span = use_spans.var_or_use();
425 let mut err = self.cannot_use_when_mutably_borrowed(
427 &self.describe_any_place(place.as_ref()),
429 &self.describe_any_place(borrow.borrowed_place.as_ref()),
432 borrow_spans.var_span_label(&mut err, {
433 let place = &borrow.borrowed_place;
434 let desc_place = self.describe_any_place(place.as_ref());
435 format!("borrow occurs due to use of {}{}", desc_place, borrow_spans.describe())
438 self.explain_why_borrow_contains_point(location, borrow, None)
439 .add_explanation_to_diagnostic(
450 pub(in crate::borrow_check) fn report_conflicting_borrow(
453 (place, span): (Place<'tcx>, Span),
454 gen_borrow_kind: BorrowKind,
455 issued_borrow: &BorrowData<'tcx>,
456 ) -> DiagnosticBuilder<'cx> {
457 let issued_spans = self.retrieve_borrow_spans(issued_borrow);
458 let issued_span = issued_spans.args_or_use();
460 let borrow_spans = self.borrow_spans(span, location);
461 let span = borrow_spans.args_or_use();
463 let container_name = if issued_spans.for_generator() || borrow_spans.for_generator() {
469 let (desc_place, msg_place, msg_borrow, union_type_name) =
470 self.describe_place_for_conflicting_borrow(place, issued_borrow.borrowed_place);
472 let explanation = self.explain_why_borrow_contains_point(location, issued_borrow, None);
473 let second_borrow_desc = if explanation.is_explained() { "second " } else { "" };
475 // FIXME: supply non-"" `opt_via` when appropriate
476 let first_borrow_desc;
477 let mut err = match (gen_borrow_kind, issued_borrow.kind) {
478 (BorrowKind::Shared, BorrowKind::Mut { .. }) => {
479 first_borrow_desc = "mutable ";
480 self.cannot_reborrow_already_borrowed(
492 (BorrowKind::Mut { .. }, BorrowKind::Shared) => {
493 first_borrow_desc = "immutable ";
494 self.cannot_reborrow_already_borrowed(
507 (BorrowKind::Mut { .. }, BorrowKind::Mut { .. }) => {
508 first_borrow_desc = "first ";
509 let mut err = self.cannot_mutably_borrow_multiply(
517 self.suggest_split_at_mut_if_applicable(
520 issued_borrow.borrowed_place,
525 (BorrowKind::Unique, BorrowKind::Unique) => {
526 first_borrow_desc = "first ";
527 self.cannot_uniquely_borrow_by_two_closures(span, &desc_place, issued_span, None)
530 (BorrowKind::Mut { .. } | BorrowKind::Unique, BorrowKind::Shallow) => {
531 if let Some(immutable_section_description) =
532 self.classify_immutable_section(issued_borrow.assigned_place)
534 let mut err = self.cannot_mutate_in_immutable_section(
538 immutable_section_description,
541 borrow_spans.var_span_label(
544 "borrow occurs due to use of {}{}",
546 borrow_spans.describe(),
552 first_borrow_desc = "immutable ";
553 self.cannot_reborrow_already_borrowed(
567 (BorrowKind::Unique, _) => {
568 first_borrow_desc = "first ";
569 self.cannot_uniquely_borrow_by_one_closure(
581 (BorrowKind::Shared, BorrowKind::Unique) => {
582 first_borrow_desc = "first ";
583 self.cannot_reborrow_already_uniquely_borrowed(
596 (BorrowKind::Mut { .. }, BorrowKind::Unique) => {
597 first_borrow_desc = "first ";
598 self.cannot_reborrow_already_uniquely_borrowed(
611 (BorrowKind::Shared, BorrowKind::Shared | BorrowKind::Shallow)
614 BorrowKind::Mut { .. }
617 | BorrowKind::Shallow,
621 if issued_spans == borrow_spans {
622 borrow_spans.var_span_label(
624 format!("borrows occur due to use of {}{}", desc_place, borrow_spans.describe()),
627 let borrow_place = &issued_borrow.borrowed_place;
628 let borrow_place_desc = self.describe_any_place(borrow_place.as_ref());
629 issued_spans.var_span_label(
632 "first borrow occurs due to use of {}{}",
634 issued_spans.describe(),
638 borrow_spans.var_span_label(
641 "second borrow occurs due to use of {}{}",
643 borrow_spans.describe(),
648 if union_type_name != "" {
650 "{} is a field of the union `{}`, so it overlaps the field {}",
651 msg_place, union_type_name, msg_borrow,
655 explanation.add_explanation_to_diagnostic(
667 fn suggest_split_at_mut_if_applicable(
669 err: &mut DiagnosticBuilder<'_>,
671 borrowed_place: Place<'tcx>,
673 if let ([ProjectionElem::Index(_)], [ProjectionElem::Index(_)]) =
674 (&place.projection[..], &borrowed_place.projection[..])
677 "consider using `.split_at_mut(position)` or similar method to obtain \
678 two mutable non-overlapping sub-slices",
683 /// Returns the description of the root place for a conflicting borrow and the full
684 /// descriptions of the places that caused the conflict.
686 /// In the simplest case, where there are no unions involved, if a mutable borrow of `x` is
687 /// attempted while a shared borrow is live, then this function will return:
691 /// In the simple union case, if a mutable borrow of a union field `x.z` is attempted while
692 /// a shared borrow of another field `x.y`, then this function will return:
694 /// ("x", "x.z", "x.y")
696 /// In the more complex union case, where the union is a field of a struct, then if a mutable
697 /// borrow of a union field in a struct `x.u.z` is attempted while a shared borrow of
698 /// another field `x.u.y`, then this function will return:
700 /// ("x.u", "x.u.z", "x.u.y")
702 /// This is used when creating error messages like below:
705 /// cannot borrow `a.u` (via `a.u.z.c`) as immutable because it is also borrowed as
706 /// mutable (via `a.u.s.b`) [E0502]
708 pub(in crate::borrow_check) fn describe_place_for_conflicting_borrow(
710 first_borrowed_place: Place<'tcx>,
711 second_borrowed_place: Place<'tcx>,
712 ) -> (String, String, String, String) {
713 // Define a small closure that we can use to check if the type of a place
715 let union_ty = |place_base, place_projection| {
716 let ty = Place::ty_from(place_base, place_projection, self.body, self.infcx.tcx).ty;
717 ty.ty_adt_def().filter(|adt| adt.is_union()).map(|_| ty)
720 // Start with an empty tuple, so we can use the functions on `Option` to reduce some
721 // code duplication (particularly around returning an empty description in the failure
725 // If we have a conflicting borrow of the same place, then we don't want to add
726 // an extraneous "via x.y" to our diagnostics, so filter out this case.
727 first_borrowed_place != second_borrowed_place
730 // We're going to want to traverse the first borrowed place to see if we can find
731 // field access to a union. If we find that, then we will keep the place of the
732 // union being accessed and the field that was being accessed so we can check the
733 // second borrowed place for the same union and a access to a different field.
734 let Place { local, projection } = first_borrowed_place;
736 let mut cursor = projection.as_ref();
737 while let [proj_base @ .., elem] = cursor {
741 ProjectionElem::Field(field, _) if union_ty(local, proj_base).is_some() => {
742 return Some((PlaceRef { local, projection: proj_base }, field));
749 .and_then(|(target_base, target_field)| {
750 // With the place of a union and a field access into it, we traverse the second
751 // borrowed place and look for a access to a different field of the same union.
752 let Place { local, ref projection } = second_borrowed_place;
754 let mut cursor = &projection[..];
755 while let [proj_base @ .., elem] = cursor {
758 if let ProjectionElem::Field(field, _) = elem {
759 if let Some(union_ty) = union_ty(local, proj_base) {
760 if field != target_field
761 && local == target_base.local
762 && proj_base == target_base.projection
765 self.describe_any_place(PlaceRef {
767 projection: proj_base,
769 self.describe_any_place(first_borrowed_place.as_ref()),
770 self.describe_any_place(second_borrowed_place.as_ref()),
771 union_ty.to_string(),
780 // If we didn't find a field access into a union, or both places match, then
781 // only return the description of the first place.
783 self.describe_any_place(first_borrowed_place.as_ref()),
791 /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
793 /// This means that some data referenced by `borrow` needs to live
794 /// past the point where the StorageDeadOrDrop of `place` occurs.
795 /// This is usually interpreted as meaning that `place` has too
796 /// short a lifetime. (But sometimes it is more useful to report
797 /// it as a more direct conflict between the execution of a
798 /// `Drop::drop` with an aliasing borrow.)
799 pub(in crate::borrow_check) fn report_borrowed_value_does_not_live_long_enough(
802 borrow: &BorrowData<'tcx>,
803 place_span: (Place<'tcx>, Span),
804 kind: Option<WriteKind>,
807 "report_borrowed_value_does_not_live_long_enough(\
808 {:?}, {:?}, {:?}, {:?}\
810 location, borrow, place_span, kind
813 let drop_span = place_span.1;
815 self.prefixes(borrow.borrowed_place.as_ref(), PrefixSet::All).last().unwrap();
817 let borrow_spans = self.retrieve_borrow_spans(borrow);
818 let borrow_span = borrow_spans.var_or_use();
820 assert!(root_place.projection.is_empty());
821 let proper_span = self.body.local_decls[root_place.local].source_info.span;
823 let root_place_projection = self.infcx.tcx.intern_place_elems(root_place.projection);
825 if self.access_place_error_reported.contains(&(
826 Place { local: root_place.local, projection: root_place_projection },
830 "suppressing access_place error when borrow doesn't live long enough for {:?}",
836 self.access_place_error_reported.insert((
837 Place { local: root_place.local, projection: root_place_projection },
841 let borrowed_local = borrow.borrowed_place.local;
842 if self.body.local_decls[borrowed_local].is_ref_to_thread_local() {
844 self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span);
845 err.buffer(&mut self.errors_buffer);
849 if let StorageDeadOrDrop::Destructor(dropped_ty) =
850 self.classify_drop_access_kind(borrow.borrowed_place.as_ref())
852 // If a borrow of path `B` conflicts with drop of `D` (and
853 // we're not in the uninteresting case where `B` is a
854 // prefix of `D`), then report this as a more interesting
855 // destructor conflict.
856 if !borrow.borrowed_place.as_ref().is_prefix_of(place_span.0.as_ref()) {
857 self.report_borrow_conflicts_with_destructor(
858 location, borrow, place_span, kind, dropped_ty,
864 let place_desc = self.describe_place(borrow.borrowed_place.as_ref());
866 let kind_place = kind.filter(|_| place_desc.is_some()).map(|k| (k, place_span.0));
867 let explanation = self.explain_why_borrow_contains_point(location, &borrow, kind_place);
870 "report_borrowed_value_does_not_live_long_enough(place_desc: {:?}, explanation: {:?})",
871 place_desc, explanation
873 let err = match (place_desc, explanation) {
874 // If the outlives constraint comes from inside the closure,
879 // Box::new(|| y) as Box<Fn() -> &'static i32>
881 // then just use the normal error. The closure isn't escaping
882 // and `move` will not help here.
885 BorrowExplanation::MustBeValidFor {
889 (ConstraintCategory::Return(_)
890 | ConstraintCategory::CallArgument
891 | ConstraintCategory::OpaqueType),
897 ) if borrow_spans.for_generator() | borrow_spans.for_closure() => self
898 .report_escaping_closure_capture(
904 &format!("`{}`", name),
908 BorrowExplanation::MustBeValidFor {
909 category: ConstraintCategory::Assignment,
914 RegionNameSource::AnonRegionFromUpvar(upvar_span, ref upvar_name),
920 ) => self.report_escaping_data(borrow_span, name, upvar_span, upvar_name, span),
921 (Some(name), explanation) => self.report_local_value_does_not_live_long_enough(
929 (None, explanation) => self.report_temporary_value_does_not_live_long_enough(
939 err.buffer(&mut self.errors_buffer);
942 fn report_local_value_does_not_live_long_enough(
946 borrow: &BorrowData<'tcx>,
948 borrow_spans: UseSpans,
949 explanation: BorrowExplanation,
950 ) -> DiagnosticBuilder<'cx> {
952 "report_local_value_does_not_live_long_enough(\
953 {:?}, {:?}, {:?}, {:?}, {:?}\
955 location, name, borrow, drop_span, borrow_spans
958 let borrow_span = borrow_spans.var_or_use();
959 if let BorrowExplanation::MustBeValidFor {
967 if let Some(diag) = self.try_report_cannot_return_reference_to_local(
972 opt_place_desc.as_ref(),
978 let mut err = self.path_does_not_live_long_enough(borrow_span, &format!("`{}`", name));
980 if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
981 let region_name = annotation.emit(self, &mut err);
985 format!("`{}` would have to be valid for `{}`...", name, region_name),
988 let fn_hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(self.mir_def_id);
992 "...but `{}` will be dropped here, when the {} returns",
998 .map(|name| format!("function `{}`", name))
1000 match &self.infcx.tcx.typeck(self.mir_def_id).node_type(fn_hir_id).kind
1002 ty::Closure(..) => "enclosing closure",
1003 ty::Generator(..) => "enclosing generator",
1004 kind => bug!("expected closure or generator, found {:?}", kind),
1012 "functions cannot return a borrow to data owned within the function's scope, \
1013 functions can only return borrows to data passed as arguments",
1016 "to learn more, visit <https://doc.rust-lang.org/book/ch04-02-\
1017 references-and-borrowing.html#dangling-references>",
1020 if let BorrowExplanation::MustBeValidFor { .. } = explanation {
1022 explanation.add_explanation_to_diagnostic(
1032 err.span_label(borrow_span, "borrowed value does not live long enough");
1033 err.span_label(drop_span, format!("`{}` dropped here while still borrowed", name));
1035 let within = if borrow_spans.for_generator() { " by generator" } else { "" };
1037 borrow_spans.args_span_label(&mut err, format!("value captured here{}", within));
1039 explanation.add_explanation_to_diagnostic(
1052 fn report_borrow_conflicts_with_destructor(
1055 borrow: &BorrowData<'tcx>,
1056 (place, drop_span): (Place<'tcx>, Span),
1057 kind: Option<WriteKind>,
1058 dropped_ty: Ty<'tcx>,
1061 "report_borrow_conflicts_with_destructor(\
1062 {:?}, {:?}, ({:?}, {:?}), {:?}\
1064 location, borrow, place, drop_span, kind,
1067 let borrow_spans = self.retrieve_borrow_spans(borrow);
1068 let borrow_span = borrow_spans.var_or_use();
1070 let mut err = self.cannot_borrow_across_destructor(borrow_span);
1072 let what_was_dropped = match self.describe_place(place.as_ref()) {
1073 Some(name) => format!("`{}`", name),
1074 None => String::from("temporary value"),
1077 let label = match self.describe_place(borrow.borrowed_place.as_ref()) {
1078 Some(borrowed) => format!(
1079 "here, drop of {D} needs exclusive access to `{B}`, \
1080 because the type `{T}` implements the `Drop` trait",
1081 D = what_was_dropped,
1086 "here is drop of {D}; whose type `{T}` implements the `Drop` trait",
1087 D = what_was_dropped,
1091 err.span_label(drop_span, label);
1093 // Only give this note and suggestion if they could be relevant.
1095 self.explain_why_borrow_contains_point(location, borrow, kind.map(|k| (k, place)));
1097 BorrowExplanation::UsedLater { .. }
1098 | BorrowExplanation::UsedLaterWhenDropped { .. } => {
1099 err.note("consider using a `let` binding to create a longer lived value");
1104 explanation.add_explanation_to_diagnostic(
1113 err.buffer(&mut self.errors_buffer);
1116 fn report_thread_local_value_does_not_live_long_enough(
1120 ) -> DiagnosticBuilder<'cx> {
1122 "report_thread_local_value_does_not_live_long_enough(\
1125 drop_span, borrow_span
1128 let mut err = self.thread_local_value_does_not_live_long_enough(borrow_span);
1132 "thread-local variables cannot be borrowed beyond the end of the function",
1134 err.span_label(drop_span, "end of enclosing function is here");
1139 fn report_temporary_value_does_not_live_long_enough(
1142 borrow: &BorrowData<'tcx>,
1144 borrow_spans: UseSpans,
1146 explanation: BorrowExplanation,
1147 ) -> DiagnosticBuilder<'cx> {
1149 "report_temporary_value_does_not_live_long_enough(\
1150 {:?}, {:?}, {:?}, {:?}\
1152 location, borrow, drop_span, proper_span
1155 if let BorrowExplanation::MustBeValidFor { category, span, from_closure: false, .. } =
1158 if let Some(diag) = self.try_report_cannot_return_reference_to_local(
1169 let mut err = self.temporary_value_borrowed_for_too_long(proper_span);
1170 err.span_label(proper_span, "creates a temporary which is freed while still in use");
1171 err.span_label(drop_span, "temporary value is freed at the end of this statement");
1174 BorrowExplanation::UsedLater(..)
1175 | BorrowExplanation::UsedLaterInLoop(..)
1176 | BorrowExplanation::UsedLaterWhenDropped { .. } => {
1177 // Only give this note and suggestion if it could be relevant.
1178 err.note("consider using a `let` binding to create a longer lived value");
1182 explanation.add_explanation_to_diagnostic(
1191 let within = if borrow_spans.for_generator() { " by generator" } else { "" };
1193 borrow_spans.args_span_label(&mut err, format!("value captured here{}", within));
1198 fn try_report_cannot_return_reference_to_local(
1200 borrow: &BorrowData<'tcx>,
1203 category: ConstraintCategory,
1204 opt_place_desc: Option<&String>,
1205 ) -> Option<DiagnosticBuilder<'cx>> {
1206 let return_kind = match category {
1207 ConstraintCategory::Return(_) => "return",
1208 ConstraintCategory::Yield => "yield",
1212 // FIXME use a better heuristic than Spans
1213 let reference_desc = if return_span == self.body.source_info(borrow.reserve_location).span {
1219 let (place_desc, note) = if let Some(place_desc) = opt_place_desc {
1220 let local_kind = if let Some(local) = borrow.borrowed_place.as_local() {
1221 match self.body.local_kind(local) {
1222 LocalKind::ReturnPointer | LocalKind::Temp => {
1223 bug!("temporary or return pointer with a name")
1225 LocalKind::Var => "local variable ",
1226 LocalKind::Arg if !self.upvars.is_empty() && local == Local::new(1) => {
1227 "variable captured by `move` "
1229 LocalKind::Arg => "function parameter ",
1235 format!("{}`{}`", local_kind, place_desc),
1236 format!("`{}` is borrowed here", place_desc),
1240 self.prefixes(borrow.borrowed_place.as_ref(), PrefixSet::All).last().unwrap();
1241 let local = root_place.local;
1242 match self.body.local_kind(local) {
1243 LocalKind::ReturnPointer | LocalKind::Temp => {
1244 ("temporary value".to_string(), "temporary value created here".to_string())
1247 "function parameter".to_string(),
1248 "function parameter borrowed here".to_string(),
1251 ("local binding".to_string(), "local binding introduced here".to_string())
1256 let mut err = self.cannot_return_reference_to_local(
1263 if return_span != borrow_span {
1264 err.span_label(borrow_span, note);
1270 fn report_escaping_closure_capture(
1274 fr_name: &RegionName,
1275 category: ConstraintCategory,
1276 constraint_span: Span,
1278 ) -> DiagnosticBuilder<'cx> {
1279 let tcx = self.infcx.tcx;
1280 let args_span = use_span.args_or_use();
1282 let suggestion = match tcx.sess.source_map().span_to_snippet(args_span) {
1284 if string.starts_with("async ") {
1285 string.insert_str(6, "move ");
1286 } else if string.starts_with("async|") {
1287 string.insert_str(5, " move");
1289 string.insert_str(0, "move ");
1293 Err(_) => "move |<args>| <body>".to_string(),
1295 let kind = match use_span.generator_kind() {
1296 Some(generator_kind) => match generator_kind {
1297 GeneratorKind::Async(async_kind) => match async_kind {
1298 AsyncGeneratorKind::Block => "async block",
1299 AsyncGeneratorKind::Closure => "async closure",
1300 _ => bug!("async block/closure expected, but async function found."),
1302 GeneratorKind::Gen => "generator",
1308 self.cannot_capture_in_long_lived_closure(args_span, kind, captured_var, var_span);
1309 err.span_suggestion(
1312 "to force the {} to take ownership of {} (and any \
1313 other referenced variables), use the `move` keyword",
1317 Applicability::MachineApplicable,
1320 let msg = match category {
1321 ConstraintCategory::Return(_) | ConstraintCategory::OpaqueType => {
1322 format!("{} is returned here", kind)
1324 ConstraintCategory::CallArgument => {
1325 fr_name.highlight_region_name(&mut err);
1326 format!("function requires argument type to outlive `{}`", fr_name)
1329 "report_escaping_closure_capture called with unexpected constraint \
1334 err.span_note(constraint_span, &msg);
1338 fn report_escaping_data(
1341 name: &Option<String>,
1345 ) -> DiagnosticBuilder<'cx> {
1346 let tcx = self.infcx.tcx;
1348 let (_, escapes_from) = tcx.article_and_description(self.mir_def_id.to_def_id());
1351 borrowck_errors::borrowed_data_escapes_closure(tcx, escape_span, escapes_from);
1355 format!("`{}` declared here, outside of the {} body", upvar_name, escapes_from),
1358 err.span_label(borrow_span, format!("borrow is only valid in the {} body", escapes_from));
1360 if let Some(name) = name {
1363 format!("reference to `{}` escapes the {} body here", name, escapes_from),
1368 format!("reference escapes the {} body here", escapes_from),
1375 fn get_moved_indexes(&mut self, location: Location, mpi: MovePathIndex) -> Vec<MoveSite> {
1376 fn predecessor_locations(
1377 body: &'a mir::Body<'tcx>,
1379 ) -> impl Iterator<Item = Location> + 'a {
1380 if location.statement_index == 0 {
1381 let predecessors = body.predecessors()[location.block].to_vec();
1382 Either::Left(predecessors.into_iter().map(move |bb| body.terminator_loc(bb)))
1384 Either::Right(std::iter::once(Location {
1385 statement_index: location.statement_index - 1,
1391 let mut stack = Vec::new();
1392 stack.extend(predecessor_locations(self.body, location).map(|predecessor| {
1393 let is_back_edge = location.dominates(predecessor, &self.dominators);
1394 (predecessor, is_back_edge)
1397 let mut visited = FxHashSet::default();
1398 let mut result = vec![];
1400 'dfs: while let Some((location, is_back_edge)) = stack.pop() {
1402 "report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
1403 location, is_back_edge
1406 if !visited.insert(location) {
1412 self.body[location.block].statements.get(location.statement_index).map(|s| &s.kind);
1413 if let Some(StatementKind::StorageDead(..)) = stmt_kind {
1414 // this analysis only tries to find moves explicitly
1415 // written by the user, so we ignore the move-outs
1416 // created by `StorageDead` and at the beginning
1419 // If we are found a use of a.b.c which was in error, then we want to look for
1420 // moves not only of a.b.c but also a.b and a.
1422 // Note that the moves data already includes "parent" paths, so we don't have to
1423 // worry about the other case: that is, if there is a move of a.b.c, it is already
1424 // marked as a move of a.b and a as well, so we will generate the correct errors
1426 let mut mpis = vec![mpi];
1427 let move_paths = &self.move_data.move_paths;
1428 mpis.extend(move_paths[mpi].parents(move_paths).map(|(mpi, _)| mpi));
1430 for moi in &self.move_data.loc_map[location] {
1431 debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
1432 let path = self.move_data.moves[*moi].path;
1433 if mpis.contains(&path) {
1435 "report_use_of_moved_or_uninitialized: found {:?}",
1436 move_paths[path].place
1438 result.push(MoveSite { moi: *moi, traversed_back_edge: is_back_edge });
1440 // Strictly speaking, we could continue our DFS here. There may be
1441 // other moves that can reach the point of error. But it is kind of
1442 // confusing to highlight them.
1450 // drop(a); // <-- current point of error
1453 // Because we stop the DFS here, we only highlight `let c = a`,
1454 // and not `let b = a`. We will of course also report an error at
1455 // `let c = a` which highlights `let b = a` as the move.
1462 let mut any_match = false;
1463 drop_flag_effects::for_location_inits(
1478 stack.extend(predecessor_locations(self.body, location).map(|predecessor| {
1479 let back_edge = location.dominates(predecessor, &self.dominators);
1480 (predecessor, is_back_edge || back_edge)
1487 pub(in crate::borrow_check) fn report_illegal_mutation_of_borrowed(
1490 (place, span): (Place<'tcx>, Span),
1491 loan: &BorrowData<'tcx>,
1493 let loan_spans = self.retrieve_borrow_spans(loan);
1494 let loan_span = loan_spans.args_or_use();
1496 let descr_place = self.describe_any_place(place.as_ref());
1497 if loan.kind == BorrowKind::Shallow {
1498 if let Some(section) = self.classify_immutable_section(loan.assigned_place) {
1499 let mut err = self.cannot_mutate_in_immutable_section(
1506 loan_spans.var_span_label(
1508 format!("borrow occurs due to use{}", loan_spans.describe()),
1511 err.buffer(&mut self.errors_buffer);
1517 let mut err = self.cannot_assign_to_borrowed(span, loan_span, &descr_place);
1520 .var_span_label(&mut err, format!("borrow occurs due to use{}", loan_spans.describe()));
1522 self.explain_why_borrow_contains_point(location, loan, None).add_explanation_to_diagnostic(
1531 err.buffer(&mut self.errors_buffer);
1534 /// Reports an illegal reassignment; for example, an assignment to
1535 /// (part of) a non-`mut` local that occurs potentially after that
1536 /// local has already been initialized. `place` is the path being
1537 /// assigned; `err_place` is a place providing a reason why
1538 /// `place` is not mutable (e.g., the non-`mut` local `x` in an
1539 /// assignment to `x.f`).
1540 pub(in crate::borrow_check) fn report_illegal_reassignment(
1542 _location: Location,
1543 (place, span): (Place<'tcx>, Span),
1544 assigned_span: Span,
1545 err_place: Place<'tcx>,
1547 let (from_arg, local_decl, local_name) = match err_place.as_local() {
1549 self.body.local_kind(local) == LocalKind::Arg,
1550 Some(&self.body.local_decls[local]),
1551 self.local_names[local],
1553 None => (false, None, None),
1556 // If root local is initialized immediately (everything apart from let
1557 // PATTERN;) then make the error refer to that local, rather than the
1558 // place being assigned later.
1559 let (place_description, assigned_span) = match local_decl {
1562 Some(box LocalInfo::User(
1563 ClearCrossCrate::Clear
1564 | ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
1565 opt_match_place: None,
1569 | Some(box LocalInfo::StaticRef { .. })
1573 | None => (self.describe_any_place(place.as_ref()), assigned_span),
1574 Some(decl) => (self.describe_any_place(err_place.as_ref()), decl.source_info.span),
1577 let mut err = self.cannot_reassign_immutable(span, &place_description, from_arg);
1578 let msg = if from_arg {
1579 "cannot assign to immutable argument"
1581 "cannot assign twice to immutable variable"
1583 if span != assigned_span {
1585 err.span_label(assigned_span, format!("first assignment to {}", place_description));
1588 if let Some(decl) = local_decl {
1589 if let Some(name) = local_name {
1590 if decl.can_be_made_mutable() {
1591 err.span_suggestion(
1592 decl.source_info.span,
1593 "make this binding mutable",
1594 format!("mut {}", name),
1595 Applicability::MachineApplicable,
1600 err.span_label(span, msg);
1601 err.buffer(&mut self.errors_buffer);
1604 fn classify_drop_access_kind(&self, place: PlaceRef<'tcx>) -> StorageDeadOrDrop<'tcx> {
1605 let tcx = self.infcx.tcx;
1606 match place.projection {
1607 [] => StorageDeadOrDrop::LocalStorageDead,
1608 [proj_base @ .., elem] => {
1609 // FIXME(spastorino) make this iterate
1610 let base_access = self.classify_drop_access_kind(PlaceRef {
1612 projection: proj_base,
1615 ProjectionElem::Deref => match base_access {
1616 StorageDeadOrDrop::LocalStorageDead
1617 | StorageDeadOrDrop::BoxedStorageDead => {
1619 Place::ty_from(place.local, proj_base, self.body, tcx).ty.is_box(),
1620 "Drop of value behind a reference or raw pointer"
1622 StorageDeadOrDrop::BoxedStorageDead
1624 StorageDeadOrDrop::Destructor(_) => base_access,
1626 ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
1627 let base_ty = Place::ty_from(place.local, proj_base, self.body, tcx).ty;
1628 match base_ty.kind {
1629 ty::Adt(def, _) if def.has_dtor(tcx) => {
1630 // Report the outermost adt with a destructor
1632 StorageDeadOrDrop::Destructor(_) => base_access,
1633 StorageDeadOrDrop::LocalStorageDead
1634 | StorageDeadOrDrop::BoxedStorageDead => {
1635 StorageDeadOrDrop::Destructor(base_ty)
1643 ProjectionElem::ConstantIndex { .. }
1644 | ProjectionElem::Subslice { .. }
1645 | ProjectionElem::Index(_) => base_access,
1651 /// Describe the reason for the fake borrow that was assigned to `place`.
1652 fn classify_immutable_section(&self, place: Place<'tcx>) -> Option<&'static str> {
1653 use rustc_middle::mir::visit::Visitor;
1654 struct FakeReadCauseFinder<'tcx> {
1656 cause: Option<FakeReadCause>,
1658 impl<'tcx> Visitor<'tcx> for FakeReadCauseFinder<'tcx> {
1659 fn visit_statement(&mut self, statement: &Statement<'tcx>, _: Location) {
1661 Statement { kind: StatementKind::FakeRead(cause, box place), .. }
1662 if *place == self.place =>
1664 self.cause = Some(*cause);
1670 let mut visitor = FakeReadCauseFinder { place, cause: None };
1671 visitor.visit_body(&self.body);
1672 match visitor.cause {
1673 Some(FakeReadCause::ForMatchGuard) => Some("match guard"),
1674 Some(FakeReadCause::ForIndex) => Some("indexing expression"),
1679 /// Annotate argument and return type of function and closure with (synthesized) lifetime for
1680 /// borrow of local value that does not live long enough.
1681 fn annotate_argument_and_return_for_borrow(
1683 borrow: &BorrowData<'tcx>,
1684 ) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
1685 // Define a fallback for when we can't match a closure.
1687 let is_closure = self.infcx.tcx.is_closure(self.mir_def_id.to_def_id());
1691 let ty = self.infcx.tcx.type_of(self.mir_def_id);
1693 ty::FnDef(_, _) | ty::FnPtr(_) => self.annotate_fn_sig(
1694 self.mir_def_id.to_def_id(),
1695 self.infcx.tcx.fn_sig(self.mir_def_id),
1702 // In order to determine whether we need to annotate, we need to check whether the reserve
1703 // place was an assignment into a temporary.
1705 // If it was, we check whether or not that temporary is eventually assigned into the return
1706 // place. If it was, we can add annotations about the function's return type and arguments
1707 // and it'll make sense.
1708 let location = borrow.reserve_location;
1709 debug!("annotate_argument_and_return_for_borrow: location={:?}", location);
1710 if let Some(&Statement { kind: StatementKind::Assign(box (ref reservation, _)), .. }) =
1711 &self.body[location.block].statements.get(location.statement_index)
1713 debug!("annotate_argument_and_return_for_borrow: reservation={:?}", reservation);
1714 // Check that the initial assignment of the reserve location is into a temporary.
1715 let mut target = match reservation.as_local() {
1716 Some(local) if self.body.local_kind(local) == LocalKind::Temp => local,
1720 // Next, look through the rest of the block, checking if we are assigning the
1721 // `target` (that is, the place that contains our borrow) to anything.
1722 let mut annotated_closure = None;
1723 for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
1725 "annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
1728 if let StatementKind::Assign(box (place, rvalue)) = &stmt.kind {
1729 if let Some(assigned_to) = place.as_local() {
1731 "annotate_argument_and_return_for_borrow: assigned_to={:?} \
1735 // Check if our `target` was captured by a closure.
1736 if let Rvalue::Aggregate(
1737 box AggregateKind::Closure(def_id, substs),
1741 for operand in operands {
1742 let assigned_from = match operand {
1743 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1749 "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1753 // Find the local from the operand.
1754 let assigned_from_local = match assigned_from.local_or_deref_local()
1756 Some(local) => local,
1760 if assigned_from_local != target {
1764 // If a closure captured our `target` and then assigned
1765 // into a place then we should annotate the closure in
1766 // case it ends up being assigned into the return place.
1768 self.annotate_fn_sig(*def_id, substs.as_closure().sig());
1770 "annotate_argument_and_return_for_borrow: \
1771 annotated_closure={:?} assigned_from_local={:?} \
1773 annotated_closure, assigned_from_local, assigned_to
1776 if assigned_to == mir::RETURN_PLACE {
1777 // If it was assigned directly into the return place, then
1779 return annotated_closure;
1781 // Otherwise, update the target.
1782 target = assigned_to;
1786 // If none of our closure's operands matched, then skip to the next
1791 // Otherwise, look at other types of assignment.
1792 let assigned_from = match rvalue {
1793 Rvalue::Ref(_, _, assigned_from) => assigned_from,
1794 Rvalue::Use(operand) => match operand {
1795 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1803 "annotate_argument_and_return_for_borrow: \
1804 assigned_from={:?}",
1808 // Find the local from the rvalue.
1809 let assigned_from_local = match assigned_from.local_or_deref_local() {
1810 Some(local) => local,
1814 "annotate_argument_and_return_for_borrow: \
1815 assigned_from_local={:?}",
1816 assigned_from_local,
1819 // Check if our local matches the target - if so, we've assigned our
1820 // borrow to a new place.
1821 if assigned_from_local != target {
1825 // If we assigned our `target` into a new place, then we should
1826 // check if it was the return place.
1828 "annotate_argument_and_return_for_borrow: \
1829 assigned_from_local={:?} assigned_to={:?}",
1830 assigned_from_local, assigned_to
1832 if assigned_to == mir::RETURN_PLACE {
1833 // If it was then return the annotated closure if there was one,
1834 // else, annotate this function.
1835 return annotated_closure.or_else(fallback);
1838 // If we didn't assign into the return place, then we just update
1840 target = assigned_to;
1845 // Check the terminator if we didn't find anything in the statements.
1846 let terminator = &self.body[location.block].terminator();
1848 "annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
1851 if let TerminatorKind::Call { destination: Some((place, _)), args, .. } =
1854 if let Some(assigned_to) = place.as_local() {
1856 "annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
1859 for operand in args {
1860 let assigned_from = match operand {
1861 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1867 "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1871 if let Some(assigned_from_local) = assigned_from.local_or_deref_local() {
1873 "annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
1874 assigned_from_local,
1877 if assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
1878 return annotated_closure.or_else(fallback);
1886 // If we haven't found an assignment into the return place, then we need not add
1888 debug!("annotate_argument_and_return_for_borrow: none found");
1892 /// Annotate the first argument and return type of a function signature if they are
1897 sig: ty::PolyFnSig<'tcx>,
1898 ) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
1899 debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
1900 let is_closure = self.infcx.tcx.is_closure(did);
1901 let fn_hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did.as_local()?);
1902 let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(fn_hir_id)?;
1904 // We need to work out which arguments to highlight. We do this by looking
1905 // at the return type, where there are three cases:
1907 // 1. If there are named arguments, then we should highlight the return type and
1908 // highlight any of the arguments that are also references with that lifetime.
1909 // If there are no arguments that have the same lifetime as the return type,
1910 // then don't highlight anything.
1911 // 2. The return type is a reference with an anonymous lifetime. If this is
1912 // the case, then we can take advantage of (and teach) the lifetime elision
1915 // We know that an error is being reported. So the arguments and return type
1916 // must satisfy the elision rules. Therefore, if there is a single argument
1917 // then that means the return type and first (and only) argument have the same
1918 // lifetime and the borrow isn't meeting that, we can highlight the argument
1921 // If there are multiple arguments then the first argument must be self (else
1922 // it would not satisfy the elision rules), so we can highlight self and the
1924 // 3. The return type is not a reference. In this case, we don't highlight
1926 let return_ty = sig.output();
1927 match return_ty.skip_binder().kind {
1928 ty::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
1929 // This is case 1 from above, return type is a named reference so we need to
1930 // search for relevant arguments.
1931 let mut arguments = Vec::new();
1932 for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
1933 if let ty::Ref(argument_region, _, _) = argument.kind {
1934 if argument_region == return_region {
1935 // Need to use the `rustc_middle::ty` types to compare against the
1936 // `return_region`. Then use the `rustc_hir` type to get only
1937 // the lifetime span.
1938 if let hir::TyKind::Rptr(lifetime, _) = &fn_decl.inputs[index].kind {
1939 // With access to the lifetime, we can get
1941 arguments.push((*argument, lifetime.span));
1943 bug!("ty type is a ref but hir type is not");
1949 // We need to have arguments. This shouldn't happen, but it's worth checking.
1950 if arguments.is_empty() {
1954 // We use a mix of the HIR and the Ty types to get information
1955 // as the HIR doesn't have full types for closure arguments.
1956 let return_ty = sig.output().skip_binder();
1957 let mut return_span = fn_decl.output.span();
1958 if let hir::FnRetTy::Return(ty) = &fn_decl.output {
1959 if let hir::TyKind::Rptr(lifetime, _) = ty.kind {
1960 return_span = lifetime.span;
1964 Some(AnnotatedBorrowFnSignature::NamedFunction {
1970 ty::Ref(_, _, _) if is_closure => {
1971 // This is case 2 from above but only for closures, return type is anonymous
1972 // reference so we select
1973 // the first argument.
1974 let argument_span = fn_decl.inputs.first()?.span;
1975 let argument_ty = sig.inputs().skip_binder().first()?;
1977 // Closure arguments are wrapped in a tuple, so we need to get the first
1979 if let ty::Tuple(elems) = argument_ty.kind {
1980 let argument_ty = elems.first()?.expect_ty();
1981 if let ty::Ref(_, _, _) = argument_ty.kind {
1982 return Some(AnnotatedBorrowFnSignature::Closure {
1991 ty::Ref(_, _, _) => {
1992 // This is also case 2 from above but for functions, return type is still an
1993 // anonymous reference so we select the first argument.
1994 let argument_span = fn_decl.inputs.first()?.span;
1995 let argument_ty = sig.inputs().skip_binder().first()?;
1997 let return_span = fn_decl.output.span();
1998 let return_ty = sig.output().skip_binder();
2000 // We expect the first argument to be a reference.
2001 match argument_ty.kind {
2002 ty::Ref(_, _, _) => {}
2006 Some(AnnotatedBorrowFnSignature::AnonymousFunction {
2014 // This is case 3 from above, return type is not a reference so don't highlight
2023 enum AnnotatedBorrowFnSignature<'tcx> {
2025 arguments: Vec<(Ty<'tcx>, Span)>,
2026 return_ty: Ty<'tcx>,
2030 argument_ty: Ty<'tcx>,
2031 argument_span: Span,
2032 return_ty: Ty<'tcx>,
2036 argument_ty: Ty<'tcx>,
2037 argument_span: Span,
2041 impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
2042 /// Annotate the provided diagnostic with information about borrow from the fn signature that
2044 pub(in crate::borrow_check) fn emit(
2046 cx: &mut MirBorrowckCtxt<'_, 'tcx>,
2047 diag: &mut DiagnosticBuilder<'_>,
2050 AnnotatedBorrowFnSignature::Closure { argument_ty, argument_span } => {
2053 format!("has type `{}`", cx.get_name_for_ty(argument_ty, 0)),
2056 cx.get_region_name_for_ty(argument_ty, 0)
2058 AnnotatedBorrowFnSignature::AnonymousFunction {
2064 let argument_ty_name = cx.get_name_for_ty(argument_ty, 0);
2065 diag.span_label(*argument_span, format!("has type `{}`", argument_ty_name));
2067 let return_ty_name = cx.get_name_for_ty(return_ty, 0);
2068 let types_equal = return_ty_name == argument_ty_name;
2073 if types_equal { "also " } else { "" },
2079 "argument and return type have the same lifetime due to lifetime elision rules",
2082 "to learn more, visit <https://doc.rust-lang.org/book/ch10-03-\
2083 lifetime-syntax.html#lifetime-elision>",
2086 cx.get_region_name_for_ty(return_ty, 0)
2088 AnnotatedBorrowFnSignature::NamedFunction { arguments, return_ty, return_span } => {
2089 // Region of return type and arguments checked to be the same earlier.
2090 let region_name = cx.get_region_name_for_ty(return_ty, 0);
2091 for (_, argument_span) in arguments {
2092 diag.span_label(*argument_span, format!("has lifetime `{}`", region_name));
2095 diag.span_label(*return_span, format!("also has lifetime `{}`", region_name,));
2098 "use data from the highlighted arguments which match the `{}` lifetime of \