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use rustc::hir;
use rustc::hir::def_id::DefId;
use rustc::mir::{
self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, ConstraintCategory, Local,
LocalDecl, LocalKind, Location, Operand, Place, PlaceBase, Projection,
ProjectionElem, Rvalue, Statement, StatementKind, TerminatorKind, VarBindingForm,
};
use rustc::ty::{self, Ty};
use rustc_data_structures::fx::FxHashSet;
use rustc_data_structures::indexed_vec::Idx;
use rustc_errors::{Applicability, DiagnosticBuilder};
use syntax_pos::Span;
use syntax::source_map::DesugaringKind;
use super::nll::explain_borrow::BorrowExplanation;
use super::nll::region_infer::{RegionName, RegionNameSource};
use super::prefixes::IsPrefixOf;
use super::WriteKind;
use super::borrow_set::BorrowData;
use super::MirBorrowckCtxt;
use super::{InitializationRequiringAction, PrefixSet};
use super::error_reporting::{IncludingDowncast, UseSpans};
use crate::dataflow::drop_flag_effects;
use crate::dataflow::indexes::{MovePathIndex, MoveOutIndex};
use crate::util::borrowck_errors;
#[derive(Debug)]
struct MoveSite {
/// Index of the "move out" that we found. The `MoveData` can
/// then tell us where the move occurred.
moi: MoveOutIndex,
/// `true` if we traversed a back edge while walking from the point
/// of error to the move site.
traversed_back_edge: bool
}
/// Which case a StorageDeadOrDrop is for.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum StorageDeadOrDrop<'tcx> {
LocalStorageDead,
BoxedStorageDead,
Destructor(Ty<'tcx>),
}
impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
pub(super) fn report_use_of_moved_or_uninitialized(
&mut self,
location: Location,
desired_action: InitializationRequiringAction,
(moved_place, used_place, span): (&Place<'tcx>, &Place<'tcx>, Span),
mpi: MovePathIndex,
) {
debug!(
"report_use_of_moved_or_uninitialized: location={:?} desired_action={:?} \
moved_place={:?} used_place={:?} span={:?} mpi={:?}",
location, desired_action, moved_place, used_place, span, mpi
);
let use_spans = self.move_spans(moved_place, location)
.or_else(|| self.borrow_spans(span, location));
let span = use_spans.args_or_use();
let move_site_vec = self.get_moved_indexes(location, mpi);
debug!(
"report_use_of_moved_or_uninitialized: move_site_vec={:?}",
move_site_vec
);
let move_out_indices: Vec<_> = move_site_vec
.iter()
.map(|move_site| move_site.moi)
.collect();
if move_out_indices.is_empty() {
let root_place = self.prefixes(&used_place, PrefixSet::All).last().unwrap();
if self.uninitialized_error_reported.contains(root_place) {
debug!(
"report_use_of_moved_or_uninitialized place: error about {:?} suppressed",
root_place
);
return;
}
self.uninitialized_error_reported.insert(root_place.clone());
let item_msg = match self.describe_place_with_options(used_place,
IncludingDowncast(true)) {
Some(name) => format!("`{}`", name),
None => "value".to_owned(),
};
let mut err = self.cannot_act_on_uninitialized_variable(
span,
desired_action.as_noun(),
&self.describe_place_with_options(moved_place, IncludingDowncast(true))
.unwrap_or_else(|| "_".to_owned()),
);
err.span_label(span, format!("use of possibly uninitialized {}", item_msg));
use_spans.var_span_label(
&mut err,
format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
);
err.buffer(&mut self.errors_buffer);
} else {
if let Some((reported_place, _)) = self.move_error_reported.get(&move_out_indices) {
if self.prefixes(&reported_place, PrefixSet::All)
.any(|p| p == used_place)
{
debug!(
"report_use_of_moved_or_uninitialized place: error suppressed \
mois={:?}",
move_out_indices
);
return;
}
}
let msg = ""; //FIXME: add "partially " or "collaterally "
let mut err = self.cannot_act_on_moved_value(
span,
desired_action.as_noun(),
msg,
self.describe_place_with_options(&moved_place, IncludingDowncast(true)),
);
self.add_moved_or_invoked_closure_note(
location,
used_place,
&mut err,
);
let mut is_loop_move = false;
let is_partial_move = move_site_vec.iter().any(|move_site| {
let move_out = self.move_data.moves[(*move_site).moi];
let moved_place = &self.move_data.move_paths[move_out.path].place;
used_place != moved_place && used_place.is_prefix_of(moved_place)
});
for move_site in &move_site_vec {
let move_out = self.move_data.moves[(*move_site).moi];
let moved_place = &self.move_data.move_paths[move_out.path].place;
let move_spans = self.move_spans(moved_place, move_out.source);
let move_span = move_spans.args_or_use();
let move_msg = if move_spans.for_closure() {
" into closure"
} else {
""
};
if span == move_span {
err.span_label(
span,
format!("value moved{} here, in previous iteration of loop", move_msg),
);
is_loop_move = true;
} else if move_site.traversed_back_edge {
err.span_label(
move_span,
format!(
"value moved{} here, in previous iteration of loop",
move_msg
),
);
} else {
err.span_label(move_span, format!("value moved{} here", move_msg));
move_spans.var_span_label(
&mut err,
format!("variable moved due to use{}", move_spans.describe()),
);
}
if Some(DesugaringKind::ForLoop) == move_span.desugaring_kind() {
if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) {
err.span_suggestion(
move_span,
"consider borrowing to avoid moving into the for loop",
format!("&{}", snippet),
Applicability::MaybeIncorrect,
);
}
}
}
use_spans.var_span_label(
&mut err,
format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
);
if !is_loop_move {
err.span_label(
span,
format!(
"value {} here {}",
desired_action.as_verb_in_past_tense(),
if is_partial_move { "after partial move" } else { "after move" },
),
);
}
let ty = used_place.ty(self.body, self.infcx.tcx).ty;
let needs_note = match ty.sty {
ty::Closure(id, _) => {
let tables = self.infcx.tcx.typeck_tables_of(id);
let hir_id = self.infcx.tcx.hir().as_local_hir_id(id).unwrap();
tables.closure_kind_origins().get(hir_id).is_none()
}
_ => true,
};
if needs_note {
let mpi = self.move_data.moves[move_out_indices[0]].path;
let place = &self.move_data.move_paths[mpi].place;
let ty = place.ty(self.body, self.infcx.tcx).ty;
let opt_name = self.describe_place_with_options(place, IncludingDowncast(true));
let note_msg = match opt_name {
Some(ref name) => format!("`{}`", name),
None => "value".to_owned(),
};
if let ty::Param(param_ty) = ty.sty {
let tcx = self.infcx.tcx;
let generics = tcx.generics_of(self.mir_def_id);
let def_id = generics.type_param(&param_ty, tcx).def_id;
if let Some(sp) = tcx.hir().span_if_local(def_id) {
err.span_label(
sp,
"consider adding a `Copy` constraint to this type argument",
);
}
}
let span = if let Place::Base(PlaceBase::Local(local)) = place {
let decl = &self.body.local_decls[*local];
Some(decl.source_info.span)
} else {
None
};
self.note_type_does_not_implement_copy(
&mut err,
&note_msg,
ty,
span,
);
}
if let Some((_, mut old_err)) = self.move_error_reported
.insert(move_out_indices, (used_place.clone(), err))
{
// Cancel the old error so it doesn't ICE.
old_err.cancel();
}
}
}
pub(super) fn report_move_out_while_borrowed(
&mut self,
location: Location,
(place, span): (&Place<'tcx>, Span),
borrow: &BorrowData<'tcx>,
) {
debug!(
"report_move_out_while_borrowed: location={:?} place={:?} span={:?} borrow={:?}",
location, place, span, borrow
);
let value_msg = match self.describe_place(place) {
Some(name) => format!("`{}`", name),
None => "value".to_owned(),
};
let borrow_msg = match self.describe_place(&borrow.borrowed_place) {
Some(name) => format!("`{}`", name),
None => "value".to_owned(),
};
let borrow_spans = self.retrieve_borrow_spans(borrow);
let borrow_span = borrow_spans.args_or_use();
let move_spans = self.move_spans(place, location);
let span = move_spans.args_or_use();
let mut err = self.cannot_move_when_borrowed(
span,
&self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
);
err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
err.span_label(span, format!("move out of {} occurs here", value_msg));
borrow_spans.var_span_label(
&mut err,
format!("borrow occurs due to use{}", borrow_spans.describe())
);
move_spans.var_span_label(
&mut err,
format!("move occurs due to use{}", move_spans.describe())
);
self.explain_why_borrow_contains_point(
location,
borrow,
None,
).add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", Some(borrow_span));
err.buffer(&mut self.errors_buffer);
}
pub(super) fn report_use_while_mutably_borrowed(
&mut self,
location: Location,
(place, _span): (&Place<'tcx>, Span),
borrow: &BorrowData<'tcx>,
) -> DiagnosticBuilder<'cx> {
let borrow_spans = self.retrieve_borrow_spans(borrow);
let borrow_span = borrow_spans.args_or_use();
// Conflicting borrows are reported separately, so only check for move
// captures.
let use_spans = self.move_spans(place, location);
let span = use_spans.var_or_use();
let mut err = self.cannot_use_when_mutably_borrowed(
span,
&self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
borrow_span,
&self.describe_place(&borrow.borrowed_place)
.unwrap_or_else(|| "_".to_owned()),
);
borrow_spans.var_span_label(&mut err, {
let place = &borrow.borrowed_place;
let desc_place = self.describe_place(place).unwrap_or_else(|| "_".to_owned());
format!("borrow occurs due to use of `{}`{}", desc_place, borrow_spans.describe())
});
self.explain_why_borrow_contains_point(location, borrow, None)
.add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", None);
err
}
pub(super) fn report_conflicting_borrow(
&mut self,
location: Location,
(place, span): (&Place<'tcx>, Span),
gen_borrow_kind: BorrowKind,
issued_borrow: &BorrowData<'tcx>,
) -> DiagnosticBuilder<'cx> {
let issued_spans = self.retrieve_borrow_spans(issued_borrow);
let issued_span = issued_spans.args_or_use();
let borrow_spans = self.borrow_spans(span, location);
let span = borrow_spans.args_or_use();
let container_name = if issued_spans.for_generator() || borrow_spans.for_generator() {
"generator"
} else {
"closure"
};
let (desc_place, msg_place, msg_borrow, union_type_name) =
self.describe_place_for_conflicting_borrow(place, &issued_borrow.borrowed_place);
let explanation = self.explain_why_borrow_contains_point(location, issued_borrow, None);
let second_borrow_desc = if explanation.is_explained() {
"second "
} else {
""
};
// FIXME: supply non-"" `opt_via` when appropriate
let first_borrow_desc;
let mut err = match (
gen_borrow_kind,
"immutable",
"mutable",
issued_borrow.kind,
"immutable",
"mutable",
) {
(BorrowKind::Shared, lft, _, BorrowKind::Mut { .. }, _, rgt) => {
first_borrow_desc = "mutable ";
self.cannot_reborrow_already_borrowed(
span,
&desc_place,
&msg_place,
lft,
issued_span,
"it",
rgt,
&msg_borrow,
None,
)
}
(BorrowKind::Mut { .. }, _, lft, BorrowKind::Shared, rgt, _) => {
first_borrow_desc = "immutable ";
self.cannot_reborrow_already_borrowed(
span,
&desc_place,
&msg_place,
lft,
issued_span,
"it",
rgt,
&msg_borrow,
None,
)
}
(BorrowKind::Mut { .. }, _, _, BorrowKind::Mut { .. }, _, _) => {
first_borrow_desc = "first ";
self.cannot_mutably_borrow_multiply(
span,
&desc_place,
&msg_place,
issued_span,
&msg_borrow,
None,
)
}
(BorrowKind::Unique, _, _, BorrowKind::Unique, _, _) => {
first_borrow_desc = "first ";
self.cannot_uniquely_borrow_by_two_closures(
span,
&desc_place,
issued_span,
None,
)
}
(BorrowKind::Mut { .. }, _, _, BorrowKind::Shallow, _, _)
| (BorrowKind::Unique, _, _, BorrowKind::Shallow, _, _) => {
let mut err = self.cannot_mutate_in_match_guard(
span,
issued_span,
&desc_place,
"mutably borrow",
);
borrow_spans.var_span_label(
&mut err,
format!(
"borrow occurs due to use of `{}`{}", desc_place, borrow_spans.describe()
),
);
return err;
}
(BorrowKind::Unique, _, _, _, _, _) => {
first_borrow_desc = "first ";
self.cannot_uniquely_borrow_by_one_closure(
span,
container_name,
&desc_place,
"",
issued_span,
"it",
"",
None,
)
},
(BorrowKind::Shared, lft, _, BorrowKind::Unique, _, _) => {
first_borrow_desc = "first ";
self.cannot_reborrow_already_uniquely_borrowed(
span,
container_name,
&desc_place,
"",
lft,
issued_span,
"",
None,
second_borrow_desc,
)
}
(BorrowKind::Mut { .. }, _, lft, BorrowKind::Unique, _, _) => {
first_borrow_desc = "first ";
self.cannot_reborrow_already_uniquely_borrowed(
span,
container_name,
&desc_place,
"",
lft,
issued_span,
"",
None,
second_borrow_desc,
)
}
(BorrowKind::Shared, _, _, BorrowKind::Shared, _, _)
| (BorrowKind::Shared, _, _, BorrowKind::Shallow, _, _)
| (BorrowKind::Shallow, _, _, BorrowKind::Mut { .. }, _, _)
| (BorrowKind::Shallow, _, _, BorrowKind::Unique, _, _)
| (BorrowKind::Shallow, _, _, BorrowKind::Shared, _, _)
| (BorrowKind::Shallow, _, _, BorrowKind::Shallow, _, _) => unreachable!(),
};
if issued_spans == borrow_spans {
borrow_spans.var_span_label(
&mut err,
format!("borrows occur due to use of `{}`{}", desc_place, borrow_spans.describe()),
);
} else {
let borrow_place = &issued_borrow.borrowed_place;
let borrow_place_desc = self.describe_place(borrow_place)
.unwrap_or_else(|| "_".to_owned());
issued_spans.var_span_label(
&mut err,
format!(
"first borrow occurs due to use of `{}`{}",
borrow_place_desc,
issued_spans.describe(),
),
);
borrow_spans.var_span_label(
&mut err,
format!(
"second borrow occurs due to use of `{}`{}",
desc_place,
borrow_spans.describe(),
),
);
}
if union_type_name != "" {
err.note(&format!(
"`{}` is a field of the union `{}`, so it overlaps the field `{}`",
msg_place, union_type_name, msg_borrow,
));
}
explanation.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&mut err,
first_borrow_desc,
None,
);
err
}
/// Returns the description of the root place for a conflicting borrow and the full
/// descriptions of the places that caused the conflict.
///
/// In the simplest case, where there are no unions involved, if a mutable borrow of `x` is
/// attempted while a shared borrow is live, then this function will return:
///
/// ("x", "", "")
///
/// In the simple union case, if a mutable borrow of a union field `x.z` is attempted while
/// a shared borrow of another field `x.y`, then this function will return:
///
/// ("x", "x.z", "x.y")
///
/// In the more complex union case, where the union is a field of a struct, then if a mutable
/// borrow of a union field in a struct `x.u.z` is attempted while a shared borrow of
/// another field `x.u.y`, then this function will return:
///
/// ("x.u", "x.u.z", "x.u.y")
///
/// This is used when creating error messages like below:
///
/// > cannot borrow `a.u` (via `a.u.z.c`) as immutable because it is also borrowed as
/// > mutable (via `a.u.s.b`) [E0502]
pub(super) fn describe_place_for_conflicting_borrow(
&self,
first_borrowed_place: &Place<'tcx>,
second_borrowed_place: &Place<'tcx>,
) -> (String, String, String, String) {
// Define a small closure that we can use to check if the type of a place
// is a union.
let union_ty = |place: &Place<'tcx>| -> Option<Ty<'tcx>> {
let ty = place.ty(self.body, self.infcx.tcx).ty;
ty.ty_adt_def().filter(|adt| adt.is_union()).map(|_| ty)
};
let describe_place = |place| self.describe_place(place).unwrap_or_else(|| "_".to_owned());
// Start with an empty tuple, so we can use the functions on `Option` to reduce some
// code duplication (particularly around returning an empty description in the failure
// case).
Some(())
.filter(|_| {
// If we have a conflicting borrow of the same place, then we don't want to add
// an extraneous "via x.y" to our diagnostics, so filter out this case.
first_borrowed_place != second_borrowed_place
})
.and_then(|_| {
// We're going to want to traverse the first borrowed place to see if we can find
// field access to a union. If we find that, then we will keep the place of the
// union being accessed and the field that was being accessed so we can check the
// second borrowed place for the same union and a access to a different field.
let mut current = first_borrowed_place;
while let Place::Projection(box Projection { base, elem }) = current {
match elem {
ProjectionElem::Field(field, _) if union_ty(base).is_some() => {
return Some((base, field));
},
_ => current = base,
}
}
None
})
.and_then(|(target_base, target_field)| {
// With the place of a union and a field access into it, we traverse the second
// borrowed place and look for a access to a different field of the same union.
let mut current = second_borrowed_place;
while let Place::Projection(box Projection { base, elem }) = current {
if let ProjectionElem::Field(field, _) = elem {
if let Some(union_ty) = union_ty(base) {
if field != target_field && base == target_base {
return Some((
describe_place(base),
describe_place(first_borrowed_place),
describe_place(second_borrowed_place),
union_ty.to_string(),
));
}
}
}
current = base;
}
None
})
.unwrap_or_else(|| {
// If we didn't find a field access into a union, or both places match, then
// only return the description of the first place.
(
describe_place(first_borrowed_place),
"".to_string(),
"".to_string(),
"".to_string(),
)
})
}
/// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
///
/// This means that some data referenced by `borrow` needs to live
/// past the point where the StorageDeadOrDrop of `place` occurs.
/// This is usually interpreted as meaning that `place` has too
/// short a lifetime. (But sometimes it is more useful to report
/// it as a more direct conflict between the execution of a
/// `Drop::drop` with an aliasing borrow.)
pub(super) fn report_borrowed_value_does_not_live_long_enough(
&mut self,
location: Location,
borrow: &BorrowData<'tcx>,
place_span: (&Place<'tcx>, Span),
kind: Option<WriteKind>,
) {
debug!(
"report_borrowed_value_does_not_live_long_enough(\
{:?}, {:?}, {:?}, {:?}\
)",
location, borrow, place_span, kind
);
let drop_span = place_span.1;
let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
.last()
.unwrap();
let borrow_spans = self.retrieve_borrow_spans(borrow);
let borrow_span = borrow_spans.var_or_use();
let proper_span = match *root_place {
Place::Base(PlaceBase::Local(local)) => self.body.local_decls[local].source_info.span,
_ => drop_span,
};
if self.access_place_error_reported
.contains(&(root_place.clone(), borrow_span))
{
debug!(
"suppressing access_place error when borrow doesn't live long enough for {:?}",
borrow_span
);
return;
}
self.access_place_error_reported
.insert((root_place.clone(), borrow_span));
if let StorageDeadOrDrop::Destructor(dropped_ty) =
self.classify_drop_access_kind(&borrow.borrowed_place)
{
// If a borrow of path `B` conflicts with drop of `D` (and
// we're not in the uninteresting case where `B` is a
// prefix of `D`), then report this as a more interesting
// destructor conflict.
if !borrow.borrowed_place.is_prefix_of(place_span.0) {
self.report_borrow_conflicts_with_destructor(
location, borrow, place_span, kind, dropped_ty,
);
return;
}
}
let place_desc = self.describe_place(&borrow.borrowed_place);
let kind_place = kind.filter(|_| place_desc.is_some()).map(|k| (k, place_span.0));
let explanation = self.explain_why_borrow_contains_point(location, &borrow, kind_place);
let err = match (place_desc, explanation) {
(Some(_), _) if self.is_place_thread_local(root_place) => {
self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span)
}
// If the outlives constraint comes from inside the closure,
// for example:
//
// let x = 0;
// let y = &x;
// Box::new(|| y) as Box<Fn() -> &'static i32>
//
// then just use the normal error. The closure isn't escaping
// and `move` will not help here.
(
Some(ref name),
BorrowExplanation::MustBeValidFor {
category: category @ ConstraintCategory::Return,
from_closure: false,
ref region_name,
span,
..
},
)
| (
Some(ref name),
BorrowExplanation::MustBeValidFor {
category: category @ ConstraintCategory::CallArgument,
from_closure: false,
ref region_name,
span,
..
},
) if borrow_spans.for_closure() => self.report_escaping_closure_capture(
borrow_spans.args_or_use(),
borrow_span,
region_name,
category,
span,
&format!("`{}`", name),
),
(
ref name,
BorrowExplanation::MustBeValidFor {
category: ConstraintCategory::Assignment,
from_closure: false,
region_name: RegionName {
source: RegionNameSource::AnonRegionFromUpvar(upvar_span, ref upvar_name),
..
},
span,
..
},
) => self.report_escaping_data(borrow_span, name, upvar_span, upvar_name, span),
(Some(name), explanation) => self.report_local_value_does_not_live_long_enough(
location,
&name,
&borrow,
drop_span,
borrow_spans,
explanation,
),
(None, explanation) => self.report_temporary_value_does_not_live_long_enough(
location,
&borrow,
drop_span,
borrow_spans,
proper_span,
explanation,
),
};
err.buffer(&mut self.errors_buffer);
}
fn report_local_value_does_not_live_long_enough(
&mut self,
location: Location,
name: &str,
borrow: &BorrowData<'tcx>,
drop_span: Span,
borrow_spans: UseSpans,
explanation: BorrowExplanation,
) -> DiagnosticBuilder<'cx> {
debug!(
"report_local_value_does_not_live_long_enough(\
{:?}, {:?}, {:?}, {:?}, {:?}\
)",
location, name, borrow, drop_span, borrow_spans
);
let borrow_span = borrow_spans.var_or_use();
if let BorrowExplanation::MustBeValidFor {
category,
span,
ref opt_place_desc,
from_closure: false,
..
} = explanation {
if let Some(diag) = self.try_report_cannot_return_reference_to_local(
borrow,
borrow_span,
span,
category,
opt_place_desc.as_ref(),
) {
return diag;
}
}
let mut err = self.path_does_not_live_long_enough(
borrow_span,
&format!("`{}`", name),
);
if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
let region_name = annotation.emit(self, &mut err);
err.span_label(
borrow_span,
format!("`{}` would have to be valid for `{}`...", name, region_name),
);
if let Some(fn_hir_id) = self.infcx.tcx.hir().as_local_hir_id(self.mir_def_id) {
err.span_label(
drop_span,
format!(
"...but `{}` will be dropped here, when the function `{}` returns",
name,
self.infcx.tcx.hir().name(fn_hir_id),
),
);
err.note(
"functions cannot return a borrow to data owned within the function's scope, \
functions can only return borrows to data passed as arguments",
);
err.note(
"to learn more, visit <https://doc.rust-lang.org/book/ch04-02-\
references-and-borrowing.html#dangling-references>",
);
} else {
err.span_label(
drop_span,
format!("...but `{}` dropped here while still borrowed", name),
);
}
if let BorrowExplanation::MustBeValidFor { .. } = explanation {
} else {
explanation.add_explanation_to_diagnostic(
self.infcx.tcx,
self.body,
&mut err,
"",
None,
);
}
} else {
err.span_label(borrow_span, "borrowed value does not live long enough");
err.span_label(
drop_span,
format!("`{}` dropped here while still borrowed", name),
);
let within = if borrow_spans.for_generator() {
" by generator"
} else {
""
};
borrow_spans.args_span_label(
&mut err,
format!("value captured here{}", within),
);
explanation.add_explanation_to_diagnostic(
self.infcx.tcx, self.body, &mut err, "", None);
}
err
}
fn report_borrow_conflicts_with_destructor(
&mut self,
location: Location,
borrow: &BorrowData<'tcx>,
(place, drop_span): (&Place<'tcx>, Span),
kind: Option<WriteKind>,
dropped_ty: Ty<'tcx>,
) {
debug!(
"report_borrow_conflicts_with_destructor(\
{:?}, {:?}, ({:?}, {:?}), {:?}\
)",
location, borrow, place, drop_span, kind,
);
let borrow_spans = self.retrieve_borrow_spans(borrow);
let borrow_span = borrow_spans.var_or_use();
let mut err = self.cannot_borrow_across_destructor(borrow_span);
let what_was_dropped = match self.describe_place(place) {
Some(name) => format!("`{}`", name.as_str()),
None => String::from("temporary value"),
};
let label = match self.describe_place(&borrow.borrowed_place) {
Some(borrowed) => format!(
"here, drop of {D} needs exclusive access to `{B}`, \
because the type `{T}` implements the `Drop` trait",
D = what_was_dropped,
T = dropped_ty,
B = borrowed
),
None => format!(
"here is drop of {D}; whose type `{T}` implements the `Drop` trait",
D = what_was_dropped,
T = dropped_ty
),
};
err.span_label(drop_span, label);
// Only give this note and suggestion if they could be relevant.
let explanation =
self.explain_why_borrow_contains_point(location, borrow, kind.map(|k| (k, place)));
match explanation {
BorrowExplanation::UsedLater { .. }
| BorrowExplanation::UsedLaterWhenDropped { .. } => {
err.note("consider using a `let` binding to create a longer lived value");
}
_ => {}
}
explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", None);
err.buffer(&mut self.errors_buffer);
}
fn report_thread_local_value_does_not_live_long_enough(
&mut self,
drop_span: Span,
borrow_span: Span,
) -> DiagnosticBuilder<'cx> {
debug!(
"report_thread_local_value_does_not_live_long_enough(\
{:?}, {:?}\
)",
drop_span, borrow_span
);
let mut err = self.thread_local_value_does_not_live_long_enough(borrow_span);
err.span_label(
borrow_span,
"thread-local variables cannot be borrowed beyond the end of the function",
);
err.span_label(drop_span, "end of enclosing function is here");
err
}
fn report_temporary_value_does_not_live_long_enough(
&mut self,
location: Location,
borrow: &BorrowData<'tcx>,
drop_span: Span,
borrow_spans: UseSpans,
proper_span: Span,
explanation: BorrowExplanation,
) -> DiagnosticBuilder<'cx> {
debug!(
"report_temporary_value_does_not_live_long_enough(\
{:?}, {:?}, {:?}, {:?}\
)",
location, borrow, drop_span, proper_span
);
if let BorrowExplanation::MustBeValidFor {
category,
span,
from_closure: false,
..
} = explanation {
if let Some(diag) = self.try_report_cannot_return_reference_to_local(
borrow,
proper_span,
span,
category,
None,
) {
return diag;
}
}
let mut err = self.temporary_value_borrowed_for_too_long(proper_span);
err.span_label(
proper_span,
"creates a temporary which is freed while still in use",
);
err.span_label(
drop_span,
"temporary value is freed at the end of this statement",
);
match explanation {
BorrowExplanation::UsedLater(..)
| BorrowExplanation::UsedLaterInLoop(..)
| BorrowExplanation::UsedLaterWhenDropped { .. } => {
// Only give this note and suggestion if it could be relevant.
err.note("consider using a `let` binding to create a longer lived value");
}
_ => {}
}
explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", None);
let within = if borrow_spans.for_generator() {
" by generator"
} else {
""
};
borrow_spans.args_span_label(
&mut err,
format!("value captured here{}", within),
);
err
}
fn try_report_cannot_return_reference_to_local(
&self,
borrow: &BorrowData<'tcx>,
borrow_span: Span,
return_span: Span,
category: ConstraintCategory,
opt_place_desc: Option<&String>,
) -> Option<DiagnosticBuilder<'cx>> {
let return_kind = match category {
ConstraintCategory::Return => "return",
ConstraintCategory::Yield => "yield",
_ => return None,
};
// FIXME use a better heuristic than Spans
let reference_desc = if return_span == self.body.source_info(borrow.reserve_location).span {
"reference to"
} else {
"value referencing"
};
let (place_desc, note) = if let Some(place_desc) = opt_place_desc {
let local_kind = match borrow.borrowed_place {
Place::Base(PlaceBase::Local(local)) => {
match self.body.local_kind(local) {
LocalKind::ReturnPointer
| LocalKind::Temp => bug!("temporary or return pointer with a name"),
LocalKind::Var => "local variable ",
LocalKind::Arg
if !self.upvars.is_empty()
&& local == Local::new(1) => {
"variable captured by `move` "
}
LocalKind::Arg => {
"function parameter "
}
}
}
_ => "local data ",
};
(
format!("{}`{}`", local_kind, place_desc),
format!("`{}` is borrowed here", place_desc),
)
} else {
let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
.last()
.unwrap();
let local = if let Place::Base(PlaceBase::Local(local)) = *root_place {
local
} else {
bug!("try_report_cannot_return_reference_to_local: not a local")
};
match self.body.local_kind(local) {
LocalKind::ReturnPointer | LocalKind::Temp => {
(
"temporary value".to_string(),
"temporary value created here".to_string(),
)
}
LocalKind::Arg => {
(
"function parameter".to_string(),
"function parameter borrowed here".to_string(),
)
},
LocalKind::Var => bug!("local variable without a name"),
}
};
let mut err = self.cannot_return_reference_to_local(
return_span,
return_kind,
reference_desc,
&place_desc,
);
if return_span != borrow_span {
err.span_label(borrow_span, note);
}
Some(err)
}
fn report_escaping_closure_capture(
&mut self,
args_span: Span,
var_span: Span,
fr_name: &RegionName,
category: ConstraintCategory,
constraint_span: Span,
captured_var: &str,
) -> DiagnosticBuilder<'cx> {
let tcx = self.infcx.tcx;
let mut err = self.cannot_capture_in_long_lived_closure(
args_span,
captured_var,
var_span,
);
let suggestion = match tcx.sess.source_map().span_to_snippet(args_span) {
Ok(string) => format!("move {}", string),
Err(_) => "move |<args>| <body>".to_string()
};
err.span_suggestion(
args_span,
&format!("to force the closure to take ownership of {} (and any \
other referenced variables), use the `move` keyword",
captured_var),
suggestion,
Applicability::MachineApplicable,
);
match category {
ConstraintCategory::Return => {
err.span_note(constraint_span, "closure is returned here");
}
ConstraintCategory::CallArgument => {
fr_name.highlight_region_name(&mut err);
err.span_note(
constraint_span,
&format!("function requires argument type to outlive `{}`", fr_name),
);
}
_ => bug!("report_escaping_closure_capture called with unexpected constraint \
category: `{:?}`", category),
}
err
}
fn report_escaping_data(
&mut self,
borrow_span: Span,
name: &Option<String>,
upvar_span: Span,
upvar_name: &str,
escape_span: Span,
) -> DiagnosticBuilder<'cx> {
let tcx = self.infcx.tcx;
let escapes_from = if tcx.is_closure(self.mir_def_id) {
let tables = tcx.typeck_tables_of(self.mir_def_id);
let mir_hir_id = tcx.hir().def_index_to_hir_id(self.mir_def_id.index);
match tables.node_type(mir_hir_id).sty {
ty::Closure(..) => "closure",
ty::Generator(..) => "generator",
_ => bug!("Closure body doesn't have a closure or generator type"),
}
} else {
"function"
};
let mut err = borrowck_errors::borrowed_data_escapes_closure(
tcx,
escape_span,
escapes_from,
);
err.span_label(
upvar_span,
format!(
"`{}` is declared here, outside of the {} body",
upvar_name, escapes_from
),
);
err.span_label(
borrow_span,
format!(
"borrow is only valid in the {} body",
escapes_from
),
);
if let Some(name) = name {
err.span_label(
escape_span,
format!("reference to `{}` escapes the {} body here", name, escapes_from),
);
} else {
err.span_label(
escape_span,
format!("reference escapes the {} body here", escapes_from),
);
}
err
}
fn get_moved_indexes(&mut self, location: Location, mpi: MovePathIndex) -> Vec<MoveSite> {
let body = self.body;
let mut stack = Vec::new();
stack.extend(body.predecessor_locations(location).map(|predecessor| {
let is_back_edge = location.dominates(predecessor, &self.dominators);
(predecessor, is_back_edge)
}));
let mut visited = FxHashSet::default();
let mut result = vec![];
'dfs: while let Some((location, is_back_edge)) = stack.pop() {
debug!(
"report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
location, is_back_edge
);
if !visited.insert(location) {
continue;
}
// check for moves
let stmt_kind = body[location.block]
.statements
.get(location.statement_index)
.map(|s| &s.kind);
if let Some(StatementKind::StorageDead(..)) = stmt_kind {
// this analysis only tries to find moves explicitly
// written by the user, so we ignore the move-outs
// created by `StorageDead` and at the beginning
// of a function.
} else {
// If we are found a use of a.b.c which was in error, then we want to look for
// moves not only of a.b.c but also a.b and a.
//
// Note that the moves data already includes "parent" paths, so we don't have to
// worry about the other case: that is, if there is a move of a.b.c, it is already
// marked as a move of a.b and a as well, so we will generate the correct errors
// there.
let mut mpis = vec![mpi];
let move_paths = &self.move_data.move_paths;
mpis.extend(move_paths[mpi].parents(move_paths));
for moi in &self.move_data.loc_map[location] {
debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
if mpis.contains(&self.move_data.moves[*moi].path) {
debug!("report_use_of_moved_or_uninitialized: found");
result.push(MoveSite {
moi: *moi,
traversed_back_edge: is_back_edge,
});
// Strictly speaking, we could continue our DFS here. There may be
// other moves that can reach the point of error. But it is kind of
// confusing to highlight them.
//
// Example:
//
// ```
// let a = vec![];
// let b = a;
// let c = a;
// drop(a); // <-- current point of error
// ```
//
// Because we stop the DFS here, we only highlight `let c = a`,
// and not `let b = a`. We will of course also report an error at
// `let c = a` which highlights `let b = a` as the move.
continue 'dfs;
}
}
}
// check for inits
let mut any_match = false;
drop_flag_effects::for_location_inits(
self.infcx.tcx,
self.body,
self.move_data,
location,
|m| {
if m == mpi {
any_match = true;
}
},
);
if any_match {
continue 'dfs;
}
stack.extend(body.predecessor_locations(location).map(|predecessor| {
let back_edge = location.dominates(predecessor, &self.dominators);
(predecessor, is_back_edge || back_edge)
}));
}
result
}
pub(super) fn report_illegal_mutation_of_borrowed(
&mut self,
location: Location,
(place, span): (&Place<'tcx>, Span),
loan: &BorrowData<'tcx>,
) {
let loan_spans = self.retrieve_borrow_spans(loan);
let loan_span = loan_spans.args_or_use();
if loan.kind == BorrowKind::Shallow {
let mut err = self.cannot_mutate_in_match_guard(
span,
loan_span,
&self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
"assign",
);
loan_spans.var_span_label(
&mut err,
format!("borrow occurs due to use{}", loan_spans.describe()),
);
err.buffer(&mut self.errors_buffer);
return;
}
let mut err = self.cannot_assign_to_borrowed(
span,
loan_span,
&self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
);
loan_spans.var_span_label(
&mut err,
format!("borrow occurs due to use{}", loan_spans.describe()),
);
self.explain_why_borrow_contains_point(location, loan, None)
.add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", None);
err.buffer(&mut self.errors_buffer);
}
/// Reports an illegal reassignment; for example, an assignment to
/// (part of) a non-`mut` local that occurs potentially after that
/// local has already been initialized. `place` is the path being
/// assigned; `err_place` is a place providing a reason why
/// `place` is not mutable (e.g., the non-`mut` local `x` in an
/// assignment to `x.f`).
pub(super) fn report_illegal_reassignment(
&mut self,
_location: Location,
(place, span): (&Place<'tcx>, Span),
assigned_span: Span,
err_place: &Place<'tcx>,
) {
let (from_arg, local_decl) = if let Place::Base(PlaceBase::Local(local)) = *err_place {
if let LocalKind::Arg = self.body.local_kind(local) {
(true, Some(&self.body.local_decls[local]))
} else {
(false, Some(&self.body.local_decls[local]))
}
} else {
(false, None)
};
// If root local is initialized immediately (everything apart from let
// PATTERN;) then make the error refer to that local, rather than the
// place being assigned later.
let (place_description, assigned_span) = match local_decl {
Some(LocalDecl {
is_user_variable: Some(ClearCrossCrate::Clear),
..
})
| Some(LocalDecl {
is_user_variable:
Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
opt_match_place: None,
..
}))),
..
})
| Some(LocalDecl {
is_user_variable: None,
..
})
| None => (self.describe_place(place), assigned_span),
Some(decl) => (self.describe_place(err_place), decl.source_info.span),
};
let mut err = self.cannot_reassign_immutable(
span,
place_description.as_ref().map(AsRef::as_ref).unwrap_or("_"),
from_arg,
);
let msg = if from_arg {
"cannot assign to immutable argument"
} else {
"cannot assign twice to immutable variable"
};
if span != assigned_span {
if !from_arg {
let value_msg = match place_description {
Some(name) => format!("`{}`", name),
None => "value".to_owned(),
};
err.span_label(assigned_span, format!("first assignment to {}", value_msg));
}
}
if let Some(decl) = local_decl {
if let Some(name) = decl.name {
if decl.can_be_made_mutable() {
err.span_suggestion(
decl.source_info.span,
"make this binding mutable",
format!("mut {}", name),
Applicability::MachineApplicable,
);
}
}
}
err.span_label(span, msg);
err.buffer(&mut self.errors_buffer);
}
fn classify_drop_access_kind(&self, place: &Place<'tcx>) -> StorageDeadOrDrop<'tcx> {
let tcx = self.infcx.tcx;
match place {
Place::Base(PlaceBase::Local(_)) |
Place::Base(PlaceBase::Static(_)) => {
StorageDeadOrDrop::LocalStorageDead
}
Place::Projection(box Projection { base, elem }) => {
let base_access = self.classify_drop_access_kind(base);
match elem {
ProjectionElem::Deref => match base_access {
StorageDeadOrDrop::LocalStorageDead
| StorageDeadOrDrop::BoxedStorageDead => {
assert!(
base.ty(self.body, tcx).ty.is_box(),
"Drop of value behind a reference or raw pointer"
);
StorageDeadOrDrop::BoxedStorageDead
}
StorageDeadOrDrop::Destructor(_) => base_access,
},
ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
let base_ty = base.ty(self.body, tcx).ty;
match base_ty.sty {
ty::Adt(def, _) if def.has_dtor(tcx) => {
// Report the outermost adt with a destructor
match base_access {
StorageDeadOrDrop::Destructor(_) => base_access,
StorageDeadOrDrop::LocalStorageDead
| StorageDeadOrDrop::BoxedStorageDead => {
StorageDeadOrDrop::Destructor(base_ty)
}
}
}
_ => base_access,
}
}
ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Subslice { .. }
| ProjectionElem::Index(_) => base_access,
}
}
}
}
/// Annotate argument and return type of function and closure with (synthesized) lifetime for
/// borrow of local value that does not live long enough.
fn annotate_argument_and_return_for_borrow(
&self,
borrow: &BorrowData<'tcx>,
) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
// Define a fallback for when we can't match a closure.
let fallback = || {
let is_closure = self.infcx.tcx.is_closure(self.mir_def_id);
if is_closure {
None
} else {
let ty = self.infcx.tcx.type_of(self.mir_def_id);
match ty.sty {
ty::FnDef(_, _) | ty::FnPtr(_) => self.annotate_fn_sig(
self.mir_def_id,
self.infcx.tcx.fn_sig(self.mir_def_id),
),
_ => None,
}
}
};
// In order to determine whether we need to annotate, we need to check whether the reserve
// place was an assignment into a temporary.
//
// If it was, we check whether or not that temporary is eventually assigned into the return
// place. If it was, we can add annotations about the function's return type and arguments
// and it'll make sense.
let location = borrow.reserve_location;
debug!(
"annotate_argument_and_return_for_borrow: location={:?}",
location
);
if let Some(&Statement { kind: StatementKind::Assign(ref reservation, _), ..})
= &self.body[location.block].statements.get(location.statement_index)
{
debug!(
"annotate_argument_and_return_for_borrow: reservation={:?}",
reservation
);
// Check that the initial assignment of the reserve location is into a temporary.
let mut target = *match reservation {
Place::Base(PlaceBase::Local(local))
if self.body.local_kind(*local) == LocalKind::Temp => local,
_ => return None,
};
// Next, look through the rest of the block, checking if we are assigning the
// `target` (that is, the place that contains our borrow) to anything.
let mut annotated_closure = None;
for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
debug!(
"annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
target, stmt
);
if let StatementKind::Assign(
Place::Base(PlaceBase::Local(assigned_to)),
box rvalue
) = &stmt.kind {
debug!(
"annotate_argument_and_return_for_borrow: assigned_to={:?} \
rvalue={:?}",
assigned_to, rvalue
);
// Check if our `target` was captured by a closure.
if let Rvalue::Aggregate(
box AggregateKind::Closure(def_id, substs),
operands,
) = rvalue
{
for operand in operands {
let assigned_from = match operand {
Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
assigned_from
}
_ => continue,
};
debug!(
"annotate_argument_and_return_for_borrow: assigned_from={:?}",
assigned_from
);
// Find the local from the operand.
let assigned_from_local = match assigned_from.local_or_deref_local() {
Some(local) => local,
None => continue,
};
if assigned_from_local != target {
continue;
}
// If a closure captured our `target` and then assigned
// into a place then we should annotate the closure in
// case it ends up being assigned into the return place.
annotated_closure = self.annotate_fn_sig(
*def_id,
self.infcx.closure_sig(*def_id, *substs),
);
debug!(
"annotate_argument_and_return_for_borrow: \
annotated_closure={:?} assigned_from_local={:?} \
assigned_to={:?}",
annotated_closure, assigned_from_local, assigned_to
);
if *assigned_to == mir::RETURN_PLACE {
// If it was assigned directly into the return place, then
// return now.
return annotated_closure;
} else {
// Otherwise, update the target.
target = *assigned_to;
}
}
// If none of our closure's operands matched, then skip to the next
// statement.
continue;
}
// Otherwise, look at other types of assignment.
let assigned_from = match rvalue {
Rvalue::Ref(_, _, assigned_from) => assigned_from,
Rvalue::Use(operand) => match operand {
Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
assigned_from
}
_ => continue,
},
_ => continue,
};
debug!(
"annotate_argument_and_return_for_borrow: \
assigned_from={:?}",
assigned_from,
);
// Find the local from the rvalue.
let assigned_from_local = match assigned_from.local_or_deref_local() {
Some(local) => local,
None => continue,
};
debug!(
"annotate_argument_and_return_for_borrow: \
assigned_from_local={:?}",
assigned_from_local,
);
// Check if our local matches the target - if so, we've assigned our
// borrow to a new place.
if assigned_from_local != target {
continue;
}
// If we assigned our `target` into a new place, then we should
// check if it was the return place.
debug!(
"annotate_argument_and_return_for_borrow: \
assigned_from_local={:?} assigned_to={:?}",
assigned_from_local, assigned_to
);
if *assigned_to == mir::RETURN_PLACE {
// If it was then return the annotated closure if there was one,
// else, annotate this function.
return annotated_closure.or_else(fallback);
}
// If we didn't assign into the return place, then we just update
// the target.
target = *assigned_to;
}
}
// Check the terminator if we didn't find anything in the statements.
let terminator = &self.body[location.block].terminator();
debug!(
"annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
target, terminator
);
if let TerminatorKind::Call {
destination: Some((Place::Base(PlaceBase::Local(assigned_to)), _)),
args,
..
} = &terminator.kind
{
debug!(
"annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
assigned_to, args
);
for operand in args {
let assigned_from = match operand {
Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
assigned_from
}
_ => continue,
};
debug!(
"annotate_argument_and_return_for_borrow: assigned_from={:?}",
assigned_from,
);
if let Some(assigned_from_local) = assigned_from.local_or_deref_local() {
debug!(
"annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
assigned_from_local,
);
if *assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
return annotated_closure.or_else(fallback);
}
}
}
}
}
// If we haven't found an assignment into the return place, then we need not add
// any annotations.
debug!("annotate_argument_and_return_for_borrow: none found");
None
}
/// Annotate the first argument and return type of a function signature if they are
/// references.
fn annotate_fn_sig(
&self,
did: DefId,
sig: ty::PolyFnSig<'tcx>,
) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
let is_closure = self.infcx.tcx.is_closure(did);
let fn_hir_id = self.infcx.tcx.hir().as_local_hir_id(did)?;
let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(fn_hir_id)?;
// We need to work out which arguments to highlight. We do this by looking
// at the return type, where there are three cases:
//
// 1. If there are named arguments, then we should highlight the return type and
// highlight any of the arguments that are also references with that lifetime.
// If there are no arguments that have the same lifetime as the return type,
// then don't highlight anything.
// 2. The return type is a reference with an anonymous lifetime. If this is
// the case, then we can take advantage of (and teach) the lifetime elision
// rules.
//
// We know that an error is being reported. So the arguments and return type
// must satisfy the elision rules. Therefore, if there is a single argument
// then that means the return type and first (and only) argument have the same
// lifetime and the borrow isn't meeting that, we can highlight the argument
// and return type.
//
// If there are multiple arguments then the first argument must be self (else
// it would not satisfy the elision rules), so we can highlight self and the
// return type.
// 3. The return type is not a reference. In this case, we don't highlight
// anything.
let return_ty = sig.output();
match return_ty.skip_binder().sty {
ty::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
// This is case 1 from above, return type is a named reference so we need to
// search for relevant arguments.
let mut arguments = Vec::new();
for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
if let ty::Ref(argument_region, _, _) = argument.sty {
if argument_region == return_region {
// Need to use the `rustc::ty` types to compare against the
// `return_region`. Then use the `rustc::hir` type to get only
// the lifetime span.
if let hir::TyKind::Rptr(lifetime, _) = &fn_decl.inputs[index].node {
// With access to the lifetime, we can get
// the span of it.
arguments.push((*argument, lifetime.span));
} else {
bug!("ty type is a ref but hir type is not");
}
}
}
}
// We need to have arguments. This shouldn't happen, but it's worth checking.
if arguments.is_empty() {
return None;
}
// We use a mix of the HIR and the Ty types to get information
// as the HIR doesn't have full types for closure arguments.
let return_ty = *sig.output().skip_binder();
let mut return_span = fn_decl.output.span();
if let hir::FunctionRetTy::Return(ty) = &fn_decl.output {
if let hir::TyKind::Rptr(lifetime, _) = ty.node {
return_span = lifetime.span;
}
}
Some(AnnotatedBorrowFnSignature::NamedFunction {
arguments,
return_ty,
return_span,
})
}
ty::Ref(_, _, _) if is_closure => {
// This is case 2 from above but only for closures, return type is anonymous
// reference so we select
// the first argument.
let argument_span = fn_decl.inputs.first()?.span;
let argument_ty = sig.inputs().skip_binder().first()?;
// Closure arguments are wrapped in a tuple, so we need to get the first
// from that.
if let ty::Tuple(elems) = argument_ty.sty {
let argument_ty = elems.first()?.expect_ty();
if let ty::Ref(_, _, _) = argument_ty.sty {
return Some(AnnotatedBorrowFnSignature::Closure {
argument_ty,
argument_span,
});
}
}
None
}
ty::Ref(_, _, _) => {
// This is also case 2 from above but for functions, return type is still an
// anonymous reference so we select the first argument.
let argument_span = fn_decl.inputs.first()?.span;
let argument_ty = sig.inputs().skip_binder().first()?;
let return_span = fn_decl.output.span();
let return_ty = *sig.output().skip_binder();
// We expect the first argument to be a reference.
match argument_ty.sty {
ty::Ref(_, _, _) => {}
_ => return None,
}
Some(AnnotatedBorrowFnSignature::AnonymousFunction {
argument_ty,
argument_span,
return_ty,
return_span,
})
}
_ => {
// This is case 3 from above, return type is not a reference so don't highlight
// anything.
None
}
}
}
}
#[derive(Debug)]
enum AnnotatedBorrowFnSignature<'tcx> {
NamedFunction {
arguments: Vec<(Ty<'tcx>, Span)>,
return_ty: Ty<'tcx>,
return_span: Span,
},
AnonymousFunction {
argument_ty: Ty<'tcx>,
argument_span: Span,
return_ty: Ty<'tcx>,
return_span: Span,
},
Closure {
argument_ty: Ty<'tcx>,
argument_span: Span,
},
}
impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
/// Annotate the provided diagnostic with information about borrow from the fn signature that
/// helps explain.
pub(super) fn emit(
&self,
cx: &mut MirBorrowckCtxt<'_, 'tcx>,
diag: &mut DiagnosticBuilder<'_>,
) -> String {
match self {
AnnotatedBorrowFnSignature::Closure {
argument_ty,
argument_span,
} => {
diag.span_label(
*argument_span,
format!("has type `{}`", cx.get_name_for_ty(argument_ty, 0)),
);
cx.get_region_name_for_ty(argument_ty, 0)
}
AnnotatedBorrowFnSignature::AnonymousFunction {
argument_ty,
argument_span,
return_ty,
return_span,
} => {
let argument_ty_name = cx.get_name_for_ty(argument_ty, 0);
diag.span_label(*argument_span, format!("has type `{}`", argument_ty_name));
let return_ty_name = cx.get_name_for_ty(return_ty, 0);
let types_equal = return_ty_name == argument_ty_name;
diag.span_label(
*return_span,
format!(
"{}has type `{}`",
if types_equal { "also " } else { "" },
return_ty_name,
),
);
diag.note(
"argument and return type have the same lifetime due to lifetime elision rules",
);
diag.note(
"to learn more, visit <https://doc.rust-lang.org/book/ch10-03-\
lifetime-syntax.html#lifetime-elision>",
);
cx.get_region_name_for_ty(return_ty, 0)
}
AnnotatedBorrowFnSignature::NamedFunction {
arguments,
return_ty,
return_span,
} => {
// Region of return type and arguments checked to be the same earlier.
let region_name = cx.get_region_name_for_ty(return_ty, 0);
for (_, argument_span) in arguments {
diag.span_label(*argument_span, format!("has lifetime `{}`", region_name));
}
diag.span_label(
*return_span,
format!("also has lifetime `{}`", region_name,),
);
diag.help(&format!(
"use data from the highlighted arguments which match the `{}` lifetime of \
the return type",
region_name,
));
region_name
}
}
}
}
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