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
);
70 "report_use_of_moved_or_uninitialized: move_site_vec={:?} use_spans={:?}",
71 move_site_vec
, use_spans
73 let move_out_indices
: Vec
<_
> =
74 move_site_vec
.iter().map(|move_site
| move_site
.moi
).collect();
76 if move_out_indices
.is_empty() {
77 let root_place
= PlaceRef { projection: &[], ..used_place }
;
79 if !self.uninitialized_error_reported
.insert(root_place
) {
81 "report_use_of_moved_or_uninitialized place: error about {:?} suppressed",
88 match self.describe_place_with_options(used_place
, IncludingDowncast(true)) {
89 Some(name
) => format
!("`{}`", name
),
90 None
=> "value".to_owned(),
92 let mut err
= self.cannot_act_on_uninitialized_variable(
94 desired_action
.as_noun(),
96 .describe_place_with_options(moved_place
, IncludingDowncast(true))
97 .unwrap_or_else(|| "_".to_owned()),
99 err
.span_label(span
, format
!("use of possibly-uninitialized {}", item_msg
));
101 use_spans
.var_span_label(
103 format
!("{} occurs due to use{}", desired_action
.as_noun(), use_spans
.describe()),
106 err
.buffer(&mut self.errors_buffer
);
108 if let Some((reported_place
, _
)) = self.move_error_reported
.get(&move_out_indices
) {
109 if self.prefixes(*reported_place
, PrefixSet
::All
).any(|p
| p
== used_place
) {
111 "report_use_of_moved_or_uninitialized place: error suppressed \
119 let is_partial_move
= move_site_vec
.iter().any(|move_site
| {
120 let move_out
= self.move_data
.moves
[(*move_site
).moi
];
121 let moved_place
= &self.move_data
.move_paths
[move_out
.path
].place
;
122 // `*(_1)` where `_1` is a `Box` is actually a move out.
123 let is_box_move
= moved_place
.as_ref().projection
== &[ProjectionElem
::Deref
]
124 && self.body
.local_decls
[moved_place
.local
].ty
.is_box();
127 && used_place
!= moved_place
.as_ref()
128 && used_place
.is_prefix_of(moved_place
.as_ref())
131 let partial_str
= if is_partial_move { "partial " }
else { "" }
;
132 let partially_str
= if is_partial_move { "partially " }
else { "" }
;
134 let mut err
= self.cannot_act_on_moved_value(
136 desired_action
.as_noun(),
138 self.describe_place_with_options(moved_place
, IncludingDowncast(true)),
141 self.add_moved_or_invoked_closure_note(location
, used_place
, &mut err
);
143 let mut is_loop_move
= false;
145 for move_site
in &move_site_vec
{
146 let move_out
= self.move_data
.moves
[(*move_site
).moi
];
147 let moved_place
= &self.move_data
.move_paths
[move_out
.path
].place
;
149 let move_spans
= self.move_spans(moved_place
.as_ref(), move_out
.source
);
150 let move_span
= move_spans
.args_or_use();
152 let move_msg
= if move_spans
.for_closure() { " into closure" }
else { "" }
;
154 if location
== move_out
.source
{
158 "value {}moved{} here, in previous iteration of loop",
159 partially_str
, move_msg
163 } else if move_site
.traversed_back_edge
{
167 "value {}moved{} here, in previous iteration of loop",
168 partially_str
, move_msg
172 if let UseSpans
::FnSelfUse { var_span, fn_call_span, fn_span, kind }
=
175 let place_name
= self
176 .describe_place(moved_place
.as_ref())
177 .map(|n
| format
!("`{}`", n
))
178 .unwrap_or_else(|| "value".to_owned());
180 FnSelfUseKind
::FnOnceCall
=> {
184 "{} {}moved due to this call",
185 place_name
, partially_str
190 "this value implements `FnOnce`, which causes it to be moved when called",
193 FnSelfUseKind
::Operator { self_arg }
=> {
197 "{} {}moved due to usage in operator",
198 place_name
, partially_str
201 if self.fn_self_span_reported
.insert(fn_span
) {
204 "calling this operator moves the left-hand side",
208 FnSelfUseKind
::Normal { self_arg, implicit_into_iter }
=> {
209 if implicit_into_iter
{
213 "{} {}moved due to this implicit call to `.into_iter()`",
214 place_name
, partially_str
221 "{} {}moved due to this method call",
222 place_name
, partially_str
226 // Avoid pointing to the same function in multiple different
228 if self.fn_self_span_reported
.insert(self_arg
.span
) {
231 &format
!("this function consumes the receiver `self` by taking ownership of it, which moves {}", place_name
)
235 // Deref::deref takes &self, which cannot cause a move
236 FnSelfUseKind
::DerefCoercion { .. }
=> unreachable
!(),
241 format
!("value {}moved{} here", partially_str
, move_msg
),
243 move_spans
.var_span_label(
246 "variable {}moved due to use{}",
248 move_spans
.describe()
253 if let UseSpans
::PatUse(span
) = move_spans
{
254 err
.span_suggestion_verbose(
257 "borrow this field in the pattern to avoid moving {}",
258 self.describe_place(moved_place
.as_ref())
259 .map(|n
| format
!("`{}`", n
))
260 .unwrap_or_else(|| "the value".to_string())
263 Applicability
::MachineApplicable
,
267 if let Some(DesugaringKind
::ForLoop(_
)) = move_span
.desugaring_kind() {
268 let sess
= self.infcx
.tcx
.sess
;
269 if let Ok(snippet
) = sess
.source_map().span_to_snippet(move_span
) {
272 "consider borrowing to avoid moving into the for loop",
273 format
!("&{}", snippet
),
274 Applicability
::MaybeIncorrect
,
280 use_spans
.var_span_label(
282 format
!("{} occurs due to use{}", desired_action
.as_noun(), use_spans
.describe()),
289 "value {} here after {}move",
290 desired_action
.as_verb_in_past_tense(),
297 Place
::ty_from(used_place
.local
, used_place
.projection
, self.body
, self.infcx
.tcx
)
299 let needs_note
= match ty
.kind() {
300 ty
::Closure(id
, _
) => {
301 let tables
= self.infcx
.tcx
.typeck(id
.expect_local());
302 let hir_id
= self.infcx
.tcx
.hir().local_def_id_to_hir_id(id
.expect_local());
304 tables
.closure_kind_origins().get(hir_id
).is_none()
309 let mpi
= self.move_data
.moves
[move_out_indices
[0]].path
;
310 let place
= &self.move_data
.move_paths
[mpi
].place
;
311 let ty
= place
.ty(self.body
, self.infcx
.tcx
).ty
;
314 if let ty
::Ref(_
, _
, hir
::Mutability
::Mut
) = ty
.kind() {
315 // We have a `&mut` ref, we need to reborrow on each iteration (#62112).
316 err
.span_suggestion_verbose(
319 "consider creating a fresh reborrow of {} here",
320 self.describe_place(moved_place
)
321 .map(|n
| format
!("`{}`", n
))
322 .unwrap_or_else(|| "the mutable reference".to_string()),
324 "&mut *".to_string(),
325 Applicability
::MachineApplicable
,
332 self.describe_place_with_options(place
.as_ref(), IncludingDowncast(true));
333 let note_msg
= match opt_name
{
334 Some(ref name
) => format
!("`{}`", name
),
335 None
=> "value".to_owned(),
337 if let ty
::Param(param_ty
) = ty
.kind() {
338 let tcx
= self.infcx
.tcx
;
339 let generics
= tcx
.generics_of(self.mir_def_id
);
340 let param
= generics
.type_param(¶m_ty
, tcx
);
341 if let Some(generics
) =
342 tcx
.hir().get_generics(tcx
.closure_base_def_id(self.mir_def_id
.to_def_id()))
344 suggest_constraining_type_param(
348 ¶m
.name
.as_str(),
354 let span
= if let Some(local
) = place
.as_local() {
355 let decl
= &self.body
.local_decls
[local
];
356 Some(decl
.source_info
.span
)
360 self.note_type_does_not_implement_copy(&mut err
, ¬e_msg
, ty
, span
, partial_str
);
363 if let UseSpans
::FnSelfUse
{
364 kind
: FnSelfUseKind
::DerefCoercion { deref_target, deref_target_ty }
,
369 "{} occurs due to deref coercion to `{}`",
370 desired_action
.as_noun(),
374 err
.span_note(deref_target
, "deref defined here");
377 if let Some((_
, mut old_err
)) =
378 self.move_error_reported
.insert(move_out_indices
, (used_place
, err
))
380 // Cancel the old error so it doesn't ICE.
386 pub(in crate::borrow_check
) fn report_move_out_while_borrowed(
389 (place
, span
): (Place
<'tcx
>, Span
),
390 borrow
: &BorrowData
<'tcx
>,
393 "report_move_out_while_borrowed: location={:?} place={:?} span={:?} borrow={:?}",
394 location
, place
, span
, borrow
396 let value_msg
= self.describe_any_place(place
.as_ref());
397 let borrow_msg
= self.describe_any_place(borrow
.borrowed_place
.as_ref());
399 let borrow_spans
= self.retrieve_borrow_spans(borrow
);
400 let borrow_span
= borrow_spans
.args_or_use();
402 let move_spans
= self.move_spans(place
.as_ref(), location
);
403 let span
= move_spans
.args_or_use();
406 self.cannot_move_when_borrowed(span
, &self.describe_any_place(place
.as_ref()));
407 err
.span_label(borrow_span
, format
!("borrow of {} occurs here", borrow_msg
));
408 err
.span_label(span
, format
!("move out of {} occurs here", value_msg
));
410 borrow_spans
.var_span_label(
412 format
!("borrow occurs due to use{}", borrow_spans
.describe()),
416 .var_span_label(&mut err
, format
!("move occurs due to use{}", move_spans
.describe()));
418 self.explain_why_borrow_contains_point(location
, borrow
, None
)
419 .add_explanation_to_diagnostic(
427 err
.buffer(&mut self.errors_buffer
);
430 pub(in crate::borrow_check
) fn report_use_while_mutably_borrowed(
433 (place
, _span
): (Place
<'tcx
>, Span
),
434 borrow
: &BorrowData
<'tcx
>,
435 ) -> DiagnosticBuilder
<'cx
> {
436 let borrow_spans
= self.retrieve_borrow_spans(borrow
);
437 let borrow_span
= borrow_spans
.args_or_use();
439 // Conflicting borrows are reported separately, so only check for move
441 let use_spans
= self.move_spans(place
.as_ref(), location
);
442 let span
= use_spans
.var_or_use();
444 let mut err
= self.cannot_use_when_mutably_borrowed(
446 &self.describe_any_place(place
.as_ref()),
448 &self.describe_any_place(borrow
.borrowed_place
.as_ref()),
451 borrow_spans
.var_span_label(&mut err
, {
452 let place
= &borrow
.borrowed_place
;
453 let desc_place
= self.describe_any_place(place
.as_ref());
454 format
!("borrow occurs due to use of {}{}", desc_place
, borrow_spans
.describe())
457 self.explain_why_borrow_contains_point(location
, borrow
, None
)
458 .add_explanation_to_diagnostic(
469 pub(in crate::borrow_check
) fn report_conflicting_borrow(
472 (place
, span
): (Place
<'tcx
>, Span
),
473 gen_borrow_kind
: BorrowKind
,
474 issued_borrow
: &BorrowData
<'tcx
>,
475 ) -> DiagnosticBuilder
<'cx
> {
476 let issued_spans
= self.retrieve_borrow_spans(issued_borrow
);
477 let issued_span
= issued_spans
.args_or_use();
479 let borrow_spans
= self.borrow_spans(span
, location
);
480 let span
= borrow_spans
.args_or_use();
482 let container_name
= if issued_spans
.for_generator() || borrow_spans
.for_generator() {
488 let (desc_place
, msg_place
, msg_borrow
, union_type_name
) =
489 self.describe_place_for_conflicting_borrow(place
, issued_borrow
.borrowed_place
);
491 let explanation
= self.explain_why_borrow_contains_point(location
, issued_borrow
, None
);
492 let second_borrow_desc
= if explanation
.is_explained() { "second " }
else { "" }
;
494 // FIXME: supply non-"" `opt_via` when appropriate
495 let first_borrow_desc
;
496 let mut err
= match (gen_borrow_kind
, issued_borrow
.kind
) {
497 (BorrowKind
::Shared
, BorrowKind
::Mut { .. }
) => {
498 first_borrow_desc
= "mutable ";
499 self.cannot_reborrow_already_borrowed(
511 (BorrowKind
::Mut { .. }
, BorrowKind
::Shared
) => {
512 first_borrow_desc
= "immutable ";
513 self.cannot_reborrow_already_borrowed(
526 (BorrowKind
::Mut { .. }
, BorrowKind
::Mut { .. }
) => {
527 first_borrow_desc
= "first ";
528 let mut err
= self.cannot_mutably_borrow_multiply(
536 self.suggest_split_at_mut_if_applicable(
539 issued_borrow
.borrowed_place
,
544 (BorrowKind
::Unique
, BorrowKind
::Unique
) => {
545 first_borrow_desc
= "first ";
546 self.cannot_uniquely_borrow_by_two_closures(span
, &desc_place
, issued_span
, None
)
549 (BorrowKind
::Mut { .. }
| BorrowKind
::Unique
, BorrowKind
::Shallow
) => {
550 if let Some(immutable_section_description
) =
551 self.classify_immutable_section(issued_borrow
.assigned_place
)
553 let mut err
= self.cannot_mutate_in_immutable_section(
557 immutable_section_description
,
560 borrow_spans
.var_span_label(
563 "borrow occurs due to use of {}{}",
565 borrow_spans
.describe(),
571 first_borrow_desc
= "immutable ";
572 self.cannot_reborrow_already_borrowed(
586 (BorrowKind
::Unique
, _
) => {
587 first_borrow_desc
= "first ";
588 self.cannot_uniquely_borrow_by_one_closure(
600 (BorrowKind
::Shared
, BorrowKind
::Unique
) => {
601 first_borrow_desc
= "first ";
602 self.cannot_reborrow_already_uniquely_borrowed(
615 (BorrowKind
::Mut { .. }
, BorrowKind
::Unique
) => {
616 first_borrow_desc
= "first ";
617 self.cannot_reborrow_already_uniquely_borrowed(
630 (BorrowKind
::Shared
, BorrowKind
::Shared
| BorrowKind
::Shallow
)
633 BorrowKind
::Mut { .. }
636 | BorrowKind
::Shallow
,
640 if issued_spans
== borrow_spans
{
641 borrow_spans
.var_span_label(
643 format
!("borrows occur due to use of {}{}", desc_place
, borrow_spans
.describe()),
646 let borrow_place
= &issued_borrow
.borrowed_place
;
647 let borrow_place_desc
= self.describe_any_place(borrow_place
.as_ref());
648 issued_spans
.var_span_label(
651 "first borrow occurs due to use of {}{}",
653 issued_spans
.describe(),
657 borrow_spans
.var_span_label(
660 "second borrow occurs due to use of {}{}",
662 borrow_spans
.describe(),
667 if union_type_name
!= "" {
669 "{} is a field of the union `{}`, so it overlaps the field {}",
670 msg_place
, union_type_name
, msg_borrow
,
674 explanation
.add_explanation_to_diagnostic(
686 fn suggest_split_at_mut_if_applicable(
688 err
: &mut DiagnosticBuilder
<'_
>,
690 borrowed_place
: Place
<'tcx
>,
692 if let ([ProjectionElem
::Index(_
)], [ProjectionElem
::Index(_
)]) =
693 (&place
.projection
[..], &borrowed_place
.projection
[..])
696 "consider using `.split_at_mut(position)` or similar method to obtain \
697 two mutable non-overlapping sub-slices",
702 /// Returns the description of the root place for a conflicting borrow and the full
703 /// descriptions of the places that caused the conflict.
705 /// In the simplest case, where there are no unions involved, if a mutable borrow of `x` is
706 /// attempted while a shared borrow is live, then this function will return:
710 /// In the simple union case, if a mutable borrow of a union field `x.z` is attempted while
711 /// a shared borrow of another field `x.y`, then this function will return:
713 /// ("x", "x.z", "x.y")
715 /// In the more complex union case, where the union is a field of a struct, then if a mutable
716 /// borrow of a union field in a struct `x.u.z` is attempted while a shared borrow of
717 /// another field `x.u.y`, then this function will return:
719 /// ("x.u", "x.u.z", "x.u.y")
721 /// This is used when creating error messages like below:
724 /// cannot borrow `a.u` (via `a.u.z.c`) as immutable because it is also borrowed as
725 /// mutable (via `a.u.s.b`) [E0502]
727 pub(in crate::borrow_check
) fn describe_place_for_conflicting_borrow(
729 first_borrowed_place
: Place
<'tcx
>,
730 second_borrowed_place
: Place
<'tcx
>,
731 ) -> (String
, String
, String
, String
) {
732 // Define a small closure that we can use to check if the type of a place
734 let union_ty
= |place_base
, place_projection
| {
735 let ty
= Place
::ty_from(place_base
, place_projection
, self.body
, self.infcx
.tcx
).ty
;
736 ty
.ty_adt_def().filter(|adt
| adt
.is_union()).map(|_
| ty
)
739 // Start with an empty tuple, so we can use the functions on `Option` to reduce some
740 // code duplication (particularly around returning an empty description in the failure
744 // If we have a conflicting borrow of the same place, then we don't want to add
745 // an extraneous "via x.y" to our diagnostics, so filter out this case.
746 first_borrowed_place
!= second_borrowed_place
749 // We're going to want to traverse the first borrowed place to see if we can find
750 // field access to a union. If we find that, then we will keep the place of the
751 // union being accessed and the field that was being accessed so we can check the
752 // second borrowed place for the same union and a access to a different field.
753 let Place { local, projection }
= first_borrowed_place
;
755 let mut cursor
= projection
.as_ref();
756 while let [proj_base @
.., elem
] = cursor
{
760 ProjectionElem
::Field(field
, _
) if union_ty(local
, proj_base
).is_some() => {
761 return Some((PlaceRef { local, projection: proj_base }
, field
));
768 .and_then(|(target_base
, target_field
)| {
769 // With the place of a union and a field access into it, we traverse the second
770 // borrowed place and look for a access to a different field of the same union.
771 let Place { local, ref projection }
= second_borrowed_place
;
773 let mut cursor
= &projection
[..];
774 while let [proj_base @
.., elem
] = cursor
{
777 if let ProjectionElem
::Field(field
, _
) = elem
{
778 if let Some(union_ty
) = union_ty(local
, proj_base
) {
779 if field
!= target_field
780 && local
== target_base
.local
781 && proj_base
== target_base
.projection
784 self.describe_any_place(PlaceRef
{
786 projection
: proj_base
,
788 self.describe_any_place(first_borrowed_place
.as_ref()),
789 self.describe_any_place(second_borrowed_place
.as_ref()),
790 union_ty
.to_string(),
799 // If we didn't find a field access into a union, or both places match, then
800 // only return the description of the first place.
802 self.describe_any_place(first_borrowed_place
.as_ref()),
810 /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
812 /// This means that some data referenced by `borrow` needs to live
813 /// past the point where the StorageDeadOrDrop of `place` occurs.
814 /// This is usually interpreted as meaning that `place` has too
815 /// short a lifetime. (But sometimes it is more useful to report
816 /// it as a more direct conflict between the execution of a
817 /// `Drop::drop` with an aliasing borrow.)
818 pub(in crate::borrow_check
) fn report_borrowed_value_does_not_live_long_enough(
821 borrow
: &BorrowData
<'tcx
>,
822 place_span
: (Place
<'tcx
>, Span
),
823 kind
: Option
<WriteKind
>,
826 "report_borrowed_value_does_not_live_long_enough(\
827 {:?}, {:?}, {:?}, {:?}\
829 location
, borrow
, place_span
, kind
832 let drop_span
= place_span
.1;
834 self.prefixes(borrow
.borrowed_place
.as_ref(), PrefixSet
::All
).last().unwrap();
836 let borrow_spans
= self.retrieve_borrow_spans(borrow
);
837 let borrow_span
= borrow_spans
.var_or_use();
839 assert
!(root_place
.projection
.is_empty());
840 let proper_span
= self.body
.local_decls
[root_place
.local
].source_info
.span
;
842 let root_place_projection
= self.infcx
.tcx
.intern_place_elems(root_place
.projection
);
844 if self.access_place_error_reported
.contains(&(
845 Place { local: root_place.local, projection: root_place_projection }
,
849 "suppressing access_place error when borrow doesn't live long enough for {:?}",
855 self.access_place_error_reported
.insert((
856 Place { local: root_place.local, projection: root_place_projection }
,
860 let borrowed_local
= borrow
.borrowed_place
.local
;
861 if self.body
.local_decls
[borrowed_local
].is_ref_to_thread_local() {
863 self.report_thread_local_value_does_not_live_long_enough(drop_span
, borrow_span
);
864 err
.buffer(&mut self.errors_buffer
);
868 if let StorageDeadOrDrop
::Destructor(dropped_ty
) =
869 self.classify_drop_access_kind(borrow
.borrowed_place
.as_ref())
871 // If a borrow of path `B` conflicts with drop of `D` (and
872 // we're not in the uninteresting case where `B` is a
873 // prefix of `D`), then report this as a more interesting
874 // destructor conflict.
875 if !borrow
.borrowed_place
.as_ref().is_prefix_of(place_span
.0.as_ref()) {
876 self.report_borrow_conflicts_with_destructor(
877 location
, borrow
, place_span
, kind
, dropped_ty
,
883 let place_desc
= self.describe_place(borrow
.borrowed_place
.as_ref());
885 let kind_place
= kind
.filter(|_
| place_desc
.is_some()).map(|k
| (k
, place_span
.0));
886 let explanation
= self.explain_why_borrow_contains_point(location
, &borrow
, kind_place
);
889 "report_borrowed_value_does_not_live_long_enough(place_desc: {:?}, explanation: {:?})",
890 place_desc
, explanation
892 let err
= match (place_desc
, explanation
) {
893 // If the outlives constraint comes from inside the closure,
898 // Box::new(|| y) as Box<Fn() -> &'static i32>
900 // then just use the normal error. The closure isn't escaping
901 // and `move` will not help here.
904 BorrowExplanation
::MustBeValidFor
{
908 (ConstraintCategory
::Return(_
)
909 | ConstraintCategory
::CallArgument
910 | ConstraintCategory
::OpaqueType
),
916 ) if borrow_spans
.for_generator() | borrow_spans
.for_closure() => self
917 .report_escaping_closure_capture(
923 &format
!("`{}`", name
),
927 BorrowExplanation
::MustBeValidFor
{
928 category
: ConstraintCategory
::Assignment
,
933 RegionNameSource
::AnonRegionFromUpvar(upvar_span
, ref upvar_name
),
939 ) => self.report_escaping_data(borrow_span
, name
, upvar_span
, upvar_name
, span
),
940 (Some(name
), explanation
) => self.report_local_value_does_not_live_long_enough(
948 (None
, explanation
) => self.report_temporary_value_does_not_live_long_enough(
958 err
.buffer(&mut self.errors_buffer
);
961 fn report_local_value_does_not_live_long_enough(
965 borrow
: &BorrowData
<'tcx
>,
967 borrow_spans
: UseSpans
<'tcx
>,
968 explanation
: BorrowExplanation
,
969 ) -> DiagnosticBuilder
<'cx
> {
971 "report_local_value_does_not_live_long_enough(\
972 {:?}, {:?}, {:?}, {:?}, {:?}\
974 location
, name
, borrow
, drop_span
, borrow_spans
977 let borrow_span
= borrow_spans
.var_or_use();
978 if let BorrowExplanation
::MustBeValidFor
{
986 if let Some(diag
) = self.try_report_cannot_return_reference_to_local(
991 opt_place_desc
.as_ref(),
997 let mut err
= self.path_does_not_live_long_enough(borrow_span
, &format
!("`{}`", name
));
999 if let Some(annotation
) = self.annotate_argument_and_return_for_borrow(borrow
) {
1000 let region_name
= annotation
.emit(self, &mut err
);
1004 format
!("`{}` would have to be valid for `{}`...", name
, region_name
),
1007 let fn_hir_id
= self.infcx
.tcx
.hir().local_def_id_to_hir_id(self.mir_def_id
);
1011 "...but `{}` will be dropped here, when the {} returns",
1016 .opt_name(fn_hir_id
)
1017 .map(|name
| format
!("function `{}`", name
))
1018 .unwrap_or_else(|| {
1022 .typeck(self.mir_def_id
)
1023 .node_type(fn_hir_id
)
1026 ty
::Closure(..) => "enclosing closure",
1027 ty
::Generator(..) => "enclosing generator",
1028 kind
=> bug
!("expected closure or generator, found {:?}", kind
),
1036 "functions cannot return a borrow to data owned within the function's scope, \
1037 functions can only return borrows to data passed as arguments",
1040 "to learn more, visit <https://doc.rust-lang.org/book/ch04-02-\
1041 references-and-borrowing.html#dangling-references>",
1044 if let BorrowExplanation
::MustBeValidFor { .. }
= explanation
{
1046 explanation
.add_explanation_to_diagnostic(
1056 err
.span_label(borrow_span
, "borrowed value does not live long enough");
1057 err
.span_label(drop_span
, format
!("`{}` dropped here while still borrowed", name
));
1059 let within
= if borrow_spans
.for_generator() { " by generator" }
else { "" }
;
1061 borrow_spans
.args_span_label(&mut err
, format
!("value captured here{}", within
));
1063 explanation
.add_explanation_to_diagnostic(
1076 fn report_borrow_conflicts_with_destructor(
1079 borrow
: &BorrowData
<'tcx
>,
1080 (place
, drop_span
): (Place
<'tcx
>, Span
),
1081 kind
: Option
<WriteKind
>,
1082 dropped_ty
: Ty
<'tcx
>,
1085 "report_borrow_conflicts_with_destructor(\
1086 {:?}, {:?}, ({:?}, {:?}), {:?}\
1088 location
, borrow
, place
, drop_span
, kind
,
1091 let borrow_spans
= self.retrieve_borrow_spans(borrow
);
1092 let borrow_span
= borrow_spans
.var_or_use();
1094 let mut err
= self.cannot_borrow_across_destructor(borrow_span
);
1096 let what_was_dropped
= match self.describe_place(place
.as_ref()) {
1097 Some(name
) => format
!("`{}`", name
),
1098 None
=> String
::from("temporary value"),
1101 let label
= match self.describe_place(borrow
.borrowed_place
.as_ref()) {
1102 Some(borrowed
) => format
!(
1103 "here, drop of {D} needs exclusive access to `{B}`, \
1104 because the type `{T}` implements the `Drop` trait",
1105 D
= what_was_dropped
,
1110 "here is drop of {D}; whose type `{T}` implements the `Drop` trait",
1111 D
= what_was_dropped
,
1115 err
.span_label(drop_span
, label
);
1117 // Only give this note and suggestion if they could be relevant.
1119 self.explain_why_borrow_contains_point(location
, borrow
, kind
.map(|k
| (k
, place
)));
1121 BorrowExplanation
::UsedLater { .. }
1122 | BorrowExplanation
::UsedLaterWhenDropped { .. }
=> {
1123 err
.note("consider using a `let` binding to create a longer lived value");
1128 explanation
.add_explanation_to_diagnostic(
1137 err
.buffer(&mut self.errors_buffer
);
1140 fn report_thread_local_value_does_not_live_long_enough(
1144 ) -> DiagnosticBuilder
<'cx
> {
1146 "report_thread_local_value_does_not_live_long_enough(\
1149 drop_span
, borrow_span
1152 let mut err
= self.thread_local_value_does_not_live_long_enough(borrow_span
);
1156 "thread-local variables cannot be borrowed beyond the end of the function",
1158 err
.span_label(drop_span
, "end of enclosing function is here");
1163 fn report_temporary_value_does_not_live_long_enough(
1166 borrow
: &BorrowData
<'tcx
>,
1168 borrow_spans
: UseSpans
<'tcx
>,
1170 explanation
: BorrowExplanation
,
1171 ) -> DiagnosticBuilder
<'cx
> {
1173 "report_temporary_value_does_not_live_long_enough(\
1174 {:?}, {:?}, {:?}, {:?}\
1176 location
, borrow
, drop_span
, proper_span
1179 if let BorrowExplanation
::MustBeValidFor { category, span, from_closure: false, .. }
=
1182 if let Some(diag
) = self.try_report_cannot_return_reference_to_local(
1193 let mut err
= self.temporary_value_borrowed_for_too_long(proper_span
);
1194 err
.span_label(proper_span
, "creates a temporary which is freed while still in use");
1195 err
.span_label(drop_span
, "temporary value is freed at the end of this statement");
1198 BorrowExplanation
::UsedLater(..)
1199 | BorrowExplanation
::UsedLaterInLoop(..)
1200 | BorrowExplanation
::UsedLaterWhenDropped { .. }
=> {
1201 // Only give this note and suggestion if it could be relevant.
1202 err
.note("consider using a `let` binding to create a longer lived value");
1206 explanation
.add_explanation_to_diagnostic(
1215 let within
= if borrow_spans
.for_generator() { " by generator" }
else { "" }
;
1217 borrow_spans
.args_span_label(&mut err
, format
!("value captured here{}", within
));
1222 fn try_report_cannot_return_reference_to_local(
1224 borrow
: &BorrowData
<'tcx
>,
1227 category
: ConstraintCategory
,
1228 opt_place_desc
: Option
<&String
>,
1229 ) -> Option
<DiagnosticBuilder
<'cx
>> {
1230 let return_kind
= match category
{
1231 ConstraintCategory
::Return(_
) => "return",
1232 ConstraintCategory
::Yield
=> "yield",
1236 // FIXME use a better heuristic than Spans
1237 let reference_desc
= if return_span
== self.body
.source_info(borrow
.reserve_location
).span
{
1243 let (place_desc
, note
) = if let Some(place_desc
) = opt_place_desc
{
1244 let local_kind
= if let Some(local
) = borrow
.borrowed_place
.as_local() {
1245 match self.body
.local_kind(local
) {
1246 LocalKind
::ReturnPointer
| LocalKind
::Temp
=> {
1247 bug
!("temporary or return pointer with a name")
1249 LocalKind
::Var
=> "local variable ",
1250 LocalKind
::Arg
if !self.upvars
.is_empty() && local
== Local
::new(1) => {
1251 "variable captured by `move` "
1253 LocalKind
::Arg
=> "function parameter ",
1259 format
!("{}`{}`", local_kind
, place_desc
),
1260 format
!("`{}` is borrowed here", place_desc
),
1264 self.prefixes(borrow
.borrowed_place
.as_ref(), PrefixSet
::All
).last().unwrap();
1265 let local
= root_place
.local
;
1266 match self.body
.local_kind(local
) {
1267 LocalKind
::ReturnPointer
| LocalKind
::Temp
=> {
1268 ("temporary value".to_string(), "temporary value created here".to_string())
1271 "function parameter".to_string(),
1272 "function parameter borrowed here".to_string(),
1275 ("local binding".to_string(), "local binding introduced here".to_string())
1280 let mut err
= self.cannot_return_reference_to_local(
1287 if return_span
!= borrow_span
{
1288 err
.span_label(borrow_span
, note
);
1294 fn report_escaping_closure_capture(
1296 use_span
: UseSpans
<'tcx
>,
1298 fr_name
: &RegionName
,
1299 category
: ConstraintCategory
,
1300 constraint_span
: Span
,
1302 ) -> DiagnosticBuilder
<'cx
> {
1303 let tcx
= self.infcx
.tcx
;
1304 let args_span
= use_span
.args_or_use();
1306 let suggestion
= match tcx
.sess
.source_map().span_to_snippet(args_span
) {
1308 if string
.starts_with("async ") {
1309 string
.insert_str(6, "move ");
1310 } else if string
.starts_with("async|") {
1311 string
.insert_str(5, " move");
1313 string
.insert_str(0, "move ");
1317 Err(_
) => "move |<args>| <body>".to_string(),
1319 let kind
= match use_span
.generator_kind() {
1320 Some(generator_kind
) => match generator_kind
{
1321 GeneratorKind
::Async(async_kind
) => match async_kind
{
1322 AsyncGeneratorKind
::Block
=> "async block",
1323 AsyncGeneratorKind
::Closure
=> "async closure",
1324 _
=> bug
!("async block/closure expected, but async function found."),
1326 GeneratorKind
::Gen
=> "generator",
1332 self.cannot_capture_in_long_lived_closure(args_span
, kind
, captured_var
, var_span
);
1333 err
.span_suggestion(
1336 "to force the {} to take ownership of {} (and any \
1337 other referenced variables), use the `move` keyword",
1341 Applicability
::MachineApplicable
,
1344 let msg
= match category
{
1345 ConstraintCategory
::Return(_
) | ConstraintCategory
::OpaqueType
=> {
1346 format
!("{} is returned here", kind
)
1348 ConstraintCategory
::CallArgument
=> {
1349 fr_name
.highlight_region_name(&mut err
);
1350 format
!("function requires argument type to outlive `{}`", fr_name
)
1353 "report_escaping_closure_capture called with unexpected constraint \
1358 err
.span_note(constraint_span
, &msg
);
1362 fn report_escaping_data(
1365 name
: &Option
<String
>,
1369 ) -> DiagnosticBuilder
<'cx
> {
1370 let tcx
= self.infcx
.tcx
;
1372 let (_
, escapes_from
) = tcx
.article_and_description(self.mir_def_id
.to_def_id());
1375 borrowck_errors
::borrowed_data_escapes_closure(tcx
, escape_span
, escapes_from
);
1379 format
!("`{}` declared here, outside of the {} body", upvar_name
, escapes_from
),
1382 err
.span_label(borrow_span
, format
!("borrow is only valid in the {} body", escapes_from
));
1384 if let Some(name
) = name
{
1387 format
!("reference to `{}` escapes the {} body here", name
, escapes_from
),
1392 format
!("reference escapes the {} body here", escapes_from
),
1399 fn get_moved_indexes(&mut self, location
: Location
, mpi
: MovePathIndex
) -> Vec
<MoveSite
> {
1400 fn predecessor_locations(
1401 body
: &'a mir
::Body
<'tcx
>,
1403 ) -> impl Iterator
<Item
= Location
> + 'a
{
1404 if location
.statement_index
== 0 {
1405 let predecessors
= body
.predecessors()[location
.block
].to_vec();
1406 Either
::Left(predecessors
.into_iter().map(move |bb
| body
.terminator_loc(bb
)))
1408 Either
::Right(std
::iter
::once(Location
{
1409 statement_index
: location
.statement_index
- 1,
1415 let mut stack
= Vec
::new();
1416 stack
.extend(predecessor_locations(self.body
, location
).map(|predecessor
| {
1417 let is_back_edge
= location
.dominates(predecessor
, &self.dominators
);
1418 (predecessor
, is_back_edge
)
1421 let mut visited
= FxHashSet
::default();
1422 let mut result
= vec
![];
1424 'dfs
: while let Some((location
, is_back_edge
)) = stack
.pop() {
1426 "report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
1427 location
, is_back_edge
1430 if !visited
.insert(location
) {
1436 self.body
[location
.block
].statements
.get(location
.statement_index
).map(|s
| &s
.kind
);
1437 if let Some(StatementKind
::StorageDead(..)) = stmt_kind
{
1438 // this analysis only tries to find moves explicitly
1439 // written by the user, so we ignore the move-outs
1440 // created by `StorageDead` and at the beginning
1443 // If we are found a use of a.b.c which was in error, then we want to look for
1444 // moves not only of a.b.c but also a.b and a.
1446 // Note that the moves data already includes "parent" paths, so we don't have to
1447 // worry about the other case: that is, if there is a move of a.b.c, it is already
1448 // marked as a move of a.b and a as well, so we will generate the correct errors
1450 let mut mpis
= vec
![mpi
];
1451 let move_paths
= &self.move_data
.move_paths
;
1452 mpis
.extend(move_paths
[mpi
].parents(move_paths
).map(|(mpi
, _
)| mpi
));
1454 for moi
in &self.move_data
.loc_map
[location
] {
1455 debug
!("report_use_of_moved_or_uninitialized: moi={:?}", moi
);
1456 let path
= self.move_data
.moves
[*moi
].path
;
1457 if mpis
.contains(&path
) {
1459 "report_use_of_moved_or_uninitialized: found {:?}",
1460 move_paths
[path
].place
1462 result
.push(MoveSite { moi: *moi, traversed_back_edge: is_back_edge }
);
1464 // Strictly speaking, we could continue our DFS here. There may be
1465 // other moves that can reach the point of error. But it is kind of
1466 // confusing to highlight them.
1474 // drop(a); // <-- current point of error
1477 // Because we stop the DFS here, we only highlight `let c = a`,
1478 // and not `let b = a`. We will of course also report an error at
1479 // `let c = a` which highlights `let b = a` as the move.
1486 let mut any_match
= false;
1487 drop_flag_effects
::for_location_inits(
1502 stack
.extend(predecessor_locations(self.body
, location
).map(|predecessor
| {
1503 let back_edge
= location
.dominates(predecessor
, &self.dominators
);
1504 (predecessor
, is_back_edge
|| back_edge
)
1511 pub(in crate::borrow_check
) fn report_illegal_mutation_of_borrowed(
1514 (place
, span
): (Place
<'tcx
>, Span
),
1515 loan
: &BorrowData
<'tcx
>,
1517 let loan_spans
= self.retrieve_borrow_spans(loan
);
1518 let loan_span
= loan_spans
.args_or_use();
1520 let descr_place
= self.describe_any_place(place
.as_ref());
1521 if loan
.kind
== BorrowKind
::Shallow
{
1522 if let Some(section
) = self.classify_immutable_section(loan
.assigned_place
) {
1523 let mut err
= self.cannot_mutate_in_immutable_section(
1530 loan_spans
.var_span_label(
1532 format
!("borrow occurs due to use{}", loan_spans
.describe()),
1535 err
.buffer(&mut self.errors_buffer
);
1541 let mut err
= self.cannot_assign_to_borrowed(span
, loan_span
, &descr_place
);
1544 .var_span_label(&mut err
, format
!("borrow occurs due to use{}", loan_spans
.describe()));
1546 self.explain_why_borrow_contains_point(location
, loan
, None
).add_explanation_to_diagnostic(
1555 err
.buffer(&mut self.errors_buffer
);
1558 /// Reports an illegal reassignment; for example, an assignment to
1559 /// (part of) a non-`mut` local that occurs potentially after that
1560 /// local has already been initialized. `place` is the path being
1561 /// assigned; `err_place` is a place providing a reason why
1562 /// `place` is not mutable (e.g., the non-`mut` local `x` in an
1563 /// assignment to `x.f`).
1564 pub(in crate::borrow_check
) fn report_illegal_reassignment(
1566 _location
: Location
,
1567 (place
, span
): (Place
<'tcx
>, Span
),
1568 assigned_span
: Span
,
1569 err_place
: Place
<'tcx
>,
1571 let (from_arg
, local_decl
, local_name
) = match err_place
.as_local() {
1573 self.body
.local_kind(local
) == LocalKind
::Arg
,
1574 Some(&self.body
.local_decls
[local
]),
1575 self.local_names
[local
],
1577 None
=> (false, None
, None
),
1580 // If root local is initialized immediately (everything apart from let
1581 // PATTERN;) then make the error refer to that local, rather than the
1582 // place being assigned later.
1583 let (place_description
, assigned_span
) = match local_decl
{
1586 Some(box LocalInfo
::User(
1587 ClearCrossCrate
::Clear
1588 | ClearCrossCrate
::Set(BindingForm
::Var(VarBindingForm
{
1589 opt_match_place
: None
,
1593 | Some(box LocalInfo
::StaticRef { .. }
)
1597 | None
=> (self.describe_any_place(place
.as_ref()), assigned_span
),
1598 Some(decl
) => (self.describe_any_place(err_place
.as_ref()), decl
.source_info
.span
),
1601 let mut err
= self.cannot_reassign_immutable(span
, &place_description
, from_arg
);
1602 let msg
= if from_arg
{
1603 "cannot assign to immutable argument"
1605 "cannot assign twice to immutable variable"
1607 if span
!= assigned_span
{
1609 err
.span_label(assigned_span
, format
!("first assignment to {}", place_description
));
1612 if let Some(decl
) = local_decl
{
1613 if let Some(name
) = local_name
{
1614 if decl
.can_be_made_mutable() {
1615 err
.span_suggestion(
1616 decl
.source_info
.span
,
1617 "make this binding mutable",
1618 format
!("mut {}", name
),
1619 Applicability
::MachineApplicable
,
1624 err
.span_label(span
, msg
);
1625 err
.buffer(&mut self.errors_buffer
);
1628 fn classify_drop_access_kind(&self, place
: PlaceRef
<'tcx
>) -> StorageDeadOrDrop
<'tcx
> {
1629 let tcx
= self.infcx
.tcx
;
1630 match place
.projection
{
1631 [] => StorageDeadOrDrop
::LocalStorageDead
,
1632 [proj_base @
.., elem
] => {
1633 // FIXME(spastorino) make this iterate
1634 let base_access
= self.classify_drop_access_kind(PlaceRef
{
1636 projection
: proj_base
,
1639 ProjectionElem
::Deref
=> match base_access
{
1640 StorageDeadOrDrop
::LocalStorageDead
1641 | StorageDeadOrDrop
::BoxedStorageDead
=> {
1643 Place
::ty_from(place
.local
, proj_base
, self.body
, tcx
).ty
.is_box(),
1644 "Drop of value behind a reference or raw pointer"
1646 StorageDeadOrDrop
::BoxedStorageDead
1648 StorageDeadOrDrop
::Destructor(_
) => base_access
,
1650 ProjectionElem
::Field(..) | ProjectionElem
::Downcast(..) => {
1651 let base_ty
= Place
::ty_from(place
.local
, proj_base
, self.body
, tcx
).ty
;
1652 match base_ty
.kind() {
1653 ty
::Adt(def
, _
) if def
.has_dtor(tcx
) => {
1654 // Report the outermost adt with a destructor
1656 StorageDeadOrDrop
::Destructor(_
) => base_access
,
1657 StorageDeadOrDrop
::LocalStorageDead
1658 | StorageDeadOrDrop
::BoxedStorageDead
=> {
1659 StorageDeadOrDrop
::Destructor(base_ty
)
1667 ProjectionElem
::ConstantIndex { .. }
1668 | ProjectionElem
::Subslice { .. }
1669 | ProjectionElem
::Index(_
) => base_access
,
1675 /// Describe the reason for the fake borrow that was assigned to `place`.
1676 fn classify_immutable_section(&self, place
: Place
<'tcx
>) -> Option
<&'
static str> {
1677 use rustc_middle
::mir
::visit
::Visitor
;
1678 struct FakeReadCauseFinder
<'tcx
> {
1680 cause
: Option
<FakeReadCause
>,
1682 impl<'tcx
> Visitor
<'tcx
> for FakeReadCauseFinder
<'tcx
> {
1683 fn visit_statement(&mut self, statement
: &Statement
<'tcx
>, _
: Location
) {
1685 Statement { kind: StatementKind::FakeRead(cause, box place), .. }
1686 if *place
== self.place
=>
1688 self.cause
= Some(*cause
);
1694 let mut visitor
= FakeReadCauseFinder { place, cause: None }
;
1695 visitor
.visit_body(&self.body
);
1696 match visitor
.cause
{
1697 Some(FakeReadCause
::ForMatchGuard
) => Some("match guard"),
1698 Some(FakeReadCause
::ForIndex
) => Some("indexing expression"),
1703 /// Annotate argument and return type of function and closure with (synthesized) lifetime for
1704 /// borrow of local value that does not live long enough.
1705 fn annotate_argument_and_return_for_borrow(
1707 borrow
: &BorrowData
<'tcx
>,
1708 ) -> Option
<AnnotatedBorrowFnSignature
<'tcx
>> {
1709 // Define a fallback for when we can't match a closure.
1711 let is_closure
= self.infcx
.tcx
.is_closure(self.mir_def_id
.to_def_id());
1715 let ty
= self.infcx
.tcx
.type_of(self.mir_def_id
);
1717 ty
::FnDef(_
, _
) | ty
::FnPtr(_
) => self.annotate_fn_sig(
1718 self.mir_def_id
.to_def_id(),
1719 self.infcx
.tcx
.fn_sig(self.mir_def_id
),
1726 // In order to determine whether we need to annotate, we need to check whether the reserve
1727 // place was an assignment into a temporary.
1729 // If it was, we check whether or not that temporary is eventually assigned into the return
1730 // place. If it was, we can add annotations about the function's return type and arguments
1731 // and it'll make sense.
1732 let location
= borrow
.reserve_location
;
1733 debug
!("annotate_argument_and_return_for_borrow: location={:?}", location
);
1734 if let Some(&Statement { kind: StatementKind::Assign(box (ref reservation, _)), .. }
) =
1735 &self.body
[location
.block
].statements
.get(location
.statement_index
)
1737 debug
!("annotate_argument_and_return_for_borrow: reservation={:?}", reservation
);
1738 // Check that the initial assignment of the reserve location is into a temporary.
1739 let mut target
= match reservation
.as_local() {
1740 Some(local
) if self.body
.local_kind(local
) == LocalKind
::Temp
=> local
,
1744 // Next, look through the rest of the block, checking if we are assigning the
1745 // `target` (that is, the place that contains our borrow) to anything.
1746 let mut annotated_closure
= None
;
1747 for stmt
in &self.body
[location
.block
].statements
[location
.statement_index
+ 1..] {
1749 "annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
1752 if let StatementKind
::Assign(box (place
, rvalue
)) = &stmt
.kind
{
1753 if let Some(assigned_to
) = place
.as_local() {
1755 "annotate_argument_and_return_for_borrow: assigned_to={:?} \
1759 // Check if our `target` was captured by a closure.
1760 if let Rvalue
::Aggregate(
1761 box AggregateKind
::Closure(def_id
, substs
),
1765 for operand
in operands
{
1766 let assigned_from
= match operand
{
1767 Operand
::Copy(assigned_from
) | Operand
::Move(assigned_from
) => {
1773 "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1777 // Find the local from the operand.
1778 let assigned_from_local
= match assigned_from
.local_or_deref_local()
1780 Some(local
) => local
,
1784 if assigned_from_local
!= target
{
1788 // If a closure captured our `target` and then assigned
1789 // into a place then we should annotate the closure in
1790 // case it ends up being assigned into the return place.
1792 self.annotate_fn_sig(*def_id
, substs
.as_closure().sig());
1794 "annotate_argument_and_return_for_borrow: \
1795 annotated_closure={:?} assigned_from_local={:?} \
1797 annotated_closure
, assigned_from_local
, assigned_to
1800 if assigned_to
== mir
::RETURN_PLACE
{
1801 // If it was assigned directly into the return place, then
1803 return annotated_closure
;
1805 // Otherwise, update the target.
1806 target
= assigned_to
;
1810 // If none of our closure's operands matched, then skip to the next
1815 // Otherwise, look at other types of assignment.
1816 let assigned_from
= match rvalue
{
1817 Rvalue
::Ref(_
, _
, assigned_from
) => assigned_from
,
1818 Rvalue
::Use(operand
) => match operand
{
1819 Operand
::Copy(assigned_from
) | Operand
::Move(assigned_from
) => {
1827 "annotate_argument_and_return_for_borrow: \
1828 assigned_from={:?}",
1832 // Find the local from the rvalue.
1833 let assigned_from_local
= match assigned_from
.local_or_deref_local() {
1834 Some(local
) => local
,
1838 "annotate_argument_and_return_for_borrow: \
1839 assigned_from_local={:?}",
1840 assigned_from_local
,
1843 // Check if our local matches the target - if so, we've assigned our
1844 // borrow to a new place.
1845 if assigned_from_local
!= target
{
1849 // If we assigned our `target` into a new place, then we should
1850 // check if it was the return place.
1852 "annotate_argument_and_return_for_borrow: \
1853 assigned_from_local={:?} assigned_to={:?}",
1854 assigned_from_local
, assigned_to
1856 if assigned_to
== mir
::RETURN_PLACE
{
1857 // If it was then return the annotated closure if there was one,
1858 // else, annotate this function.
1859 return annotated_closure
.or_else(fallback
);
1862 // If we didn't assign into the return place, then we just update
1864 target
= assigned_to
;
1869 // Check the terminator if we didn't find anything in the statements.
1870 let terminator
= &self.body
[location
.block
].terminator();
1872 "annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
1875 if let TerminatorKind
::Call { destination: Some((place, _)), args, .. }
=
1878 if let Some(assigned_to
) = place
.as_local() {
1880 "annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
1883 for operand
in args
{
1884 let assigned_from
= match operand
{
1885 Operand
::Copy(assigned_from
) | Operand
::Move(assigned_from
) => {
1891 "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1895 if let Some(assigned_from_local
) = assigned_from
.local_or_deref_local() {
1897 "annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
1898 assigned_from_local
,
1901 if assigned_to
== mir
::RETURN_PLACE
&& assigned_from_local
== target
{
1902 return annotated_closure
.or_else(fallback
);
1910 // If we haven't found an assignment into the return place, then we need not add
1912 debug
!("annotate_argument_and_return_for_borrow: none found");
1916 /// Annotate the first argument and return type of a function signature if they are
1921 sig
: ty
::PolyFnSig
<'tcx
>,
1922 ) -> Option
<AnnotatedBorrowFnSignature
<'tcx
>> {
1923 debug
!("annotate_fn_sig: did={:?} sig={:?}", did
, sig
);
1924 let is_closure
= self.infcx
.tcx
.is_closure(did
);
1925 let fn_hir_id
= self.infcx
.tcx
.hir().local_def_id_to_hir_id(did
.as_local()?
);
1926 let fn_decl
= self.infcx
.tcx
.hir().fn_decl_by_hir_id(fn_hir_id
)?
;
1928 // We need to work out which arguments to highlight. We do this by looking
1929 // at the return type, where there are three cases:
1931 // 1. If there are named arguments, then we should highlight the return type and
1932 // highlight any of the arguments that are also references with that lifetime.
1933 // If there are no arguments that have the same lifetime as the return type,
1934 // then don't highlight anything.
1935 // 2. The return type is a reference with an anonymous lifetime. If this is
1936 // the case, then we can take advantage of (and teach) the lifetime elision
1939 // We know that an error is being reported. So the arguments and return type
1940 // must satisfy the elision rules. Therefore, if there is a single argument
1941 // then that means the return type and first (and only) argument have the same
1942 // lifetime and the borrow isn't meeting that, we can highlight the argument
1945 // If there are multiple arguments then the first argument must be self (else
1946 // it would not satisfy the elision rules), so we can highlight self and the
1948 // 3. The return type is not a reference. In this case, we don't highlight
1950 let return_ty
= sig
.output();
1951 match return_ty
.skip_binder().kind() {
1952 ty
::Ref(return_region
, _
, _
) if return_region
.has_name() && !is_closure
=> {
1953 // This is case 1 from above, return type is a named reference so we need to
1954 // search for relevant arguments.
1955 let mut arguments
= Vec
::new();
1956 for (index
, argument
) in sig
.inputs().skip_binder().iter().enumerate() {
1957 if let ty
::Ref(argument_region
, _
, _
) = argument
.kind() {
1958 if argument_region
== return_region
{
1959 // Need to use the `rustc_middle::ty` types to compare against the
1960 // `return_region`. Then use the `rustc_hir` type to get only
1961 // the lifetime span.
1962 if let hir
::TyKind
::Rptr(lifetime
, _
) = &fn_decl
.inputs
[index
].kind
{
1963 // With access to the lifetime, we can get
1965 arguments
.push((*argument
, lifetime
.span
));
1967 bug
!("ty type is a ref but hir type is not");
1973 // We need to have arguments. This shouldn't happen, but it's worth checking.
1974 if arguments
.is_empty() {
1978 // We use a mix of the HIR and the Ty types to get information
1979 // as the HIR doesn't have full types for closure arguments.
1980 let return_ty
= sig
.output().skip_binder();
1981 let mut return_span
= fn_decl
.output
.span();
1982 if let hir
::FnRetTy
::Return(ty
) = &fn_decl
.output
{
1983 if let hir
::TyKind
::Rptr(lifetime
, _
) = ty
.kind
{
1984 return_span
= lifetime
.span
;
1988 Some(AnnotatedBorrowFnSignature
::NamedFunction
{
1994 ty
::Ref(_
, _
, _
) if is_closure
=> {
1995 // This is case 2 from above but only for closures, return type is anonymous
1996 // reference so we select
1997 // the first argument.
1998 let argument_span
= fn_decl
.inputs
.first()?
.span
;
1999 let argument_ty
= sig
.inputs().skip_binder().first()?
;
2001 // Closure arguments are wrapped in a tuple, so we need to get the first
2003 if let ty
::Tuple(elems
) = argument_ty
.kind() {
2004 let argument_ty
= elems
.first()?
.expect_ty();
2005 if let ty
::Ref(_
, _
, _
) = argument_ty
.kind() {
2006 return Some(AnnotatedBorrowFnSignature
::Closure
{
2015 ty
::Ref(_
, _
, _
) => {
2016 // This is also case 2 from above but for functions, return type is still an
2017 // anonymous reference so we select the first argument.
2018 let argument_span
= fn_decl
.inputs
.first()?
.span
;
2019 let argument_ty
= sig
.inputs().skip_binder().first()?
;
2021 let return_span
= fn_decl
.output
.span();
2022 let return_ty
= sig
.output().skip_binder();
2024 // We expect the first argument to be a reference.
2025 match argument_ty
.kind() {
2026 ty
::Ref(_
, _
, _
) => {}
2030 Some(AnnotatedBorrowFnSignature
::AnonymousFunction
{
2038 // This is case 3 from above, return type is not a reference so don't highlight
2047 enum AnnotatedBorrowFnSignature
<'tcx
> {
2049 arguments
: Vec
<(Ty
<'tcx
>, Span
)>,
2050 return_ty
: Ty
<'tcx
>,
2054 argument_ty
: Ty
<'tcx
>,
2055 argument_span
: Span
,
2056 return_ty
: Ty
<'tcx
>,
2060 argument_ty
: Ty
<'tcx
>,
2061 argument_span
: Span
,
2065 impl<'tcx
> AnnotatedBorrowFnSignature
<'tcx
> {
2066 /// Annotate the provided diagnostic with information about borrow from the fn signature that
2068 pub(in crate::borrow_check
) fn emit(
2070 cx
: &mut MirBorrowckCtxt
<'_
, 'tcx
>,
2071 diag
: &mut DiagnosticBuilder
<'_
>,
2074 AnnotatedBorrowFnSignature
::Closure { argument_ty, argument_span }
=> {
2077 format
!("has type `{}`", cx
.get_name_for_ty(argument_ty
, 0)),
2080 cx
.get_region_name_for_ty(argument_ty
, 0)
2082 AnnotatedBorrowFnSignature
::AnonymousFunction
{
2088 let argument_ty_name
= cx
.get_name_for_ty(argument_ty
, 0);
2089 diag
.span_label(*argument_span
, format
!("has type `{}`", argument_ty_name
));
2091 let return_ty_name
= cx
.get_name_for_ty(return_ty
, 0);
2092 let types_equal
= return_ty_name
== argument_ty_name
;
2097 if types_equal { "also " }
else { "" }
,
2103 "argument and return type have the same lifetime due to lifetime elision rules",
2106 "to learn more, visit <https://doc.rust-lang.org/book/ch10-03-\
2107 lifetime-syntax.html#lifetime-elision>",
2110 cx
.get_region_name_for_ty(return_ty
, 0)
2112 AnnotatedBorrowFnSignature
::NamedFunction { arguments, return_ty, return_span }
=> {
2113 // Region of return type and arguments checked to be the same earlier.
2114 let region_name
= cx
.get_region_name_for_ty(return_ty
, 0);
2115 for (_
, argument_span
) in arguments
{
2116 diag
.span_label(*argument_span
, format
!("has lifetime `{}`", region_name
));
2119 diag
.span_label(*return_span
, format
!("also has lifetime `{}`", region_name
,));
2122 "use data from the highlighted arguments which match the `{}` lifetime of \