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Remove mutable_borrow_reservation_conflict lint and allow the code pattern #96268

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May 6, 2022
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Remove mutable_borrow_reservation_conflict lint and allow the code pattern #96268

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4 changes: 0 additions & 4 deletions compiler/rustc_borrowck/src/borrow_set.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -167,10 +167,6 @@ impl<'tcx> BorrowSet<'tcx> {
crate fn get_index_of(&self, location: &Location) -> Option<BorrowIndex> {
self.location_map.get_index_of(location).map(BorrowIndex::from)
}

crate fn contains(&self, location: &Location) -> bool {
self.location_map.contains_key(location)
}
}

struct GatherBorrows<'a, 'tcx> {
Expand Down
73 changes: 8 additions & 65 deletions compiler/rustc_borrowck/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,14 +35,13 @@ use rustc_middle::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, Stat
use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::{self, CapturedPlace, ParamEnv, RegionVid, TyCtxt};
use rustc_session::lint::builtin::{MUTABLE_BORROW_RESERVATION_CONFLICT, UNUSED_MUT};
use rustc_span::{Span, Symbol, DUMMY_SP};
use rustc_session::lint::builtin::UNUSED_MUT;
use rustc_span::{Span, Symbol};

use either::Either;
use smallvec::SmallVec;
use std::cell::RefCell;
use std::collections::BTreeMap;
use std::mem;
use std::rc::Rc;

use rustc_mir_dataflow::impls::{
Expand Down Expand Up @@ -313,7 +312,6 @@ fn do_mir_borrowck<'a, 'tcx>(
locals_are_invalidated_at_exit,
access_place_error_reported: Default::default(),
reservation_error_reported: Default::default(),
reservation_warnings: Default::default(),
uninitialized_error_reported: Default::default(),
regioncx: regioncx.clone(),
used_mut: Default::default(),
Expand Down Expand Up @@ -345,7 +343,6 @@ fn do_mir_borrowck<'a, 'tcx>(
fn_self_span_reported: Default::default(),
access_place_error_reported: Default::default(),
reservation_error_reported: Default::default(),
reservation_warnings: Default::default(),
uninitialized_error_reported: Default::default(),
regioncx: Rc::clone(&regioncx),
used_mut: Default::default(),
Expand Down Expand Up @@ -378,34 +375,6 @@ fn do_mir_borrowck<'a, 'tcx>(
&mut mbcx,
);

// Convert any reservation warnings into lints.
let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
for (_, (place, span, location, bk, borrow)) in reservation_warnings {
let initial_diag = mbcx.report_conflicting_borrow(location, (place, span), bk, &borrow);

let scope = mbcx.body.source_info(location).scope;
let lint_root = match &mbcx.body.source_scopes[scope].local_data {
ClearCrossCrate::Set(data) => data.lint_root,
_ => tcx.hir().local_def_id_to_hir_id(def.did),
};

// Span and message don't matter; we overwrite them below anyway
mbcx.infcx.tcx.struct_span_lint_hir(
MUTABLE_BORROW_RESERVATION_CONFLICT,
lint_root,
DUMMY_SP,
|lint| {
let mut diag = lint.build("");

diag.message = initial_diag.styled_message().clone();
diag.span = initial_diag.span.clone();

mbcx.buffer_non_error_diag(diag);
},
);
initial_diag.cancel();
}

// For each non-user used mutable variable, check if it's been assigned from
// a user-declared local. If so, then put that local into the used_mut set.
// Note that this set is expected to be small - only upvars from closures
Expand Down Expand Up @@ -540,11 +509,6 @@ struct MirBorrowckCtxt<'cx, 'tcx> {
/// used to report extra information for `FnSelfUse`, to avoid
/// unnecessarily verbose errors.
fn_self_span_reported: FxHashSet<Span>,
/// Migration warnings to be reported for #56254. We delay reporting these
/// so that we can suppress the warning if there's a corresponding error
/// for the activation of the borrow.
reservation_warnings:
FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
/// This field keeps track of errors reported in the checking of uninitialized variables,
/// so that we don't report seemingly duplicate errors.
uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
Expand Down Expand Up @@ -996,12 +960,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
let conflict_error =
self.check_access_for_conflict(location, place_span, sd, rw, flow_state);

if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
// Suppress this warning when there's an error being emitted for the
// same borrow: fixing the error is likely to fix the warning.
self.reservation_warnings.remove(&borrow_idx);
}

if conflict_error || mutability_error {
debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
self.access_place_error_reported.insert((place_span.0, place_span.1));
Expand Down Expand Up @@ -1068,6 +1026,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
BorrowKind::Unique | BorrowKind::Mut { .. },
) => Control::Continue,

(Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
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// This used to be a future compatibility warning (to be
// disallowed on NLL). See rust-lang/rust#56254
Control::Continue
}

(Write(WriteKind::Move), BorrowKind::Shallow) => {
// Handled by initialization checks.
Control::Continue
Expand Down Expand Up @@ -1096,27 +1060,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
Control::Break
}

(
Reservation(WriteKind::MutableBorrow(bk)),
BorrowKind::Shallow | BorrowKind::Shared,
) if { tcx.migrate_borrowck() && this.borrow_set.contains(&location) } => {
let bi = this.borrow_set.get_index_of(&location).unwrap();
debug!(
"recording invalid reservation of place: {:?} with \
borrow index {:?} as warning",
place_span.0, bi,
);
// rust-lang/rust#56254 - This was previously permitted on
// the 2018 edition so we emit it as a warning. We buffer
// these separately so that we only emit a warning if borrow
// checking was otherwise successful.
this.reservation_warnings
.insert(bi, (place_span.0, place_span.1, location, bk, borrow.clone()));

// Don't suppress actual errors.
Control::Continue
}

(Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
match rw {
Reservation(..) => {
Expand Down
5 changes: 5 additions & 0 deletions compiler/rustc_lint/src/lib.rs
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Expand Up @@ -491,6 +491,11 @@ fn register_builtins(store: &mut LintStore, no_interleave_lints: bool) {
"converted into hard error, see RFC 2972 \
<https://github.com/rust-lang/rfcs/blob/master/text/2972-constrained-naked.md> for more information",
);
store.register_removed(
"mutable_borrow_reservation_conflict",
"now allowed, see issue #59159 \
<https://github.com/rust-lang/rust/issues/59159> for more information",
);
}

fn register_internals(store: &mut LintStore) {
Expand Down
35 changes: 0 additions & 35 deletions compiler/rustc_lint_defs/src/builtin.rs
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Expand Up @@ -2345,40 +2345,6 @@ declare_lint! {
};
}

declare_lint! {
/// The `mutable_borrow_reservation_conflict` lint detects the reservation
/// of a two-phased borrow that conflicts with other shared borrows.
///
/// ### Example
///
/// ```rust
/// let mut v = vec![0, 1, 2];
/// let shared = &v;
/// v.push(shared.len());
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This is a [future-incompatible] lint to transition this to a hard error
/// in the future. See [issue #59159] for a complete description of the
/// problem, and some possible solutions.
///
/// [issue #59159]: https://github.com/rust-lang/rust/issues/59159
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub MUTABLE_BORROW_RESERVATION_CONFLICT,
Warn,
"reservation of a two-phased borrow conflicts with other shared borrows",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::Custom(
"this borrowing pattern was not meant to be accepted, \
and may become a hard error in the future"
),
reference: "issue #59159 <https://github.com/rust-lang/rust/issues/59159>",
};
}

declare_lint! {
/// The `soft_unstable` lint detects unstable features that were
/// unintentionally allowed on stable.
Expand Down Expand Up @@ -3179,7 +3145,6 @@ declare_lint_pass! {
META_VARIABLE_MISUSE,
DEPRECATED_IN_FUTURE,
AMBIGUOUS_ASSOCIATED_ITEMS,
MUTABLE_BORROW_RESERVATION_CONFLICT,
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I think we don't normally remove these altogether but rather move them to some list of deprecated lints ...

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It gets registered as removed here: https://github.com/rust-lang/rust/pull/96268/files#diff-cfb1d20a5949dd50b9769edb62eaf10a0de66734637fe71d35bdcf8fb06d767bR494

INDIRECT_STRUCTURAL_MATCH,
POINTER_STRUCTURAL_MATCH,
NONTRIVIAL_STRUCTURAL_MATCH,
Expand Down
15 changes: 2 additions & 13 deletions src/test/ui/borrowck/suggest-local-var-imm-and-mut.nll.stderr
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Expand Up @@ -7,23 +7,12 @@ LL | self.foo(self.bar());
| | | mutable borrow occurs here
| | immutable borrow later used by call
| immutable borrow occurs here
|
help: try adding a local storing this argument...
--> $DIR/suggest-local-var-imm-and-mut.rs:12:22
|
LL | self.foo(self.bar());
| ^^^^^^^^^^
help: ...and then using that local as the argument to this call
--> $DIR/suggest-local-var-imm-and-mut.rs:12:13
|
LL | self.foo(self.bar());
| ^^^^^^^^^^^^^^^^^^^^

error[E0502]: cannot borrow `*self` as mutable because it is also borrowed as immutable
--> $DIR/suggest-local-var-imm-and-mut.rs:24:39
--> $DIR/suggest-local-var-imm-and-mut.rs:24:29
|
LL | Self::foo(self, Self::bar(self));
| --------- ---- ^^^^ mutable borrow occurs here
| --------- ---- ^^^^^^^^^^^^^^^ mutable borrow occurs here
| | |
| | immutable borrow occurs here
| immutable borrow later used by call
Expand Down
17 changes: 0 additions & 17 deletions src/test/ui/borrowck/two-phase-cannot-nest-mut-self-calls.stderr
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Expand Up @@ -13,23 +13,6 @@ LL | |
LL | | 0
LL | | });
| |______- immutable borrow occurs here
|
help: try adding a local storing this argument...
--> $DIR/two-phase-cannot-nest-mut-self-calls.rs:16:9
|
LL | vec.push(2);
| ^^^^^^^^^^^
help: ...and then using that local as the argument to this call
--> $DIR/two-phase-cannot-nest-mut-self-calls.rs:14:5
|
LL | / vec.get({
LL | |
LL | | vec.push(2);
LL | |
LL | |
LL | | 0
LL | | });
| |______^

error: aborting due to previous error

Expand Down
25 changes: 25 additions & 0 deletions src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.base.stderr
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@@ -0,0 +1,25 @@
error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
--> $DIR/two-phase-reservation-sharing-interference-2.rs:19:5
|
LL | let shared = &v;
| -- immutable borrow occurs here
LL |
LL | v.extend(shared);
| ^^------^^^^^^^^
| | |
| | immutable borrow later used by call
| mutable borrow occurs here

error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
--> $DIR/two-phase-reservation-sharing-interference-2.rs:27:5
|
LL | v.extend(&v);
| ^^------^--^
| | | |
| | | immutable borrow occurs here
| | immutable borrow later used by call
| mutable borrow occurs here

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0502`.
18 changes: 1 addition & 17 deletions src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2015.stderr
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Expand Up @@ -20,22 +20,6 @@ LL | v.extend(&v);
| | immutable borrow later used by call
| mutable borrow occurs here

warning: cannot borrow `v` as mutable because it is also borrowed as immutable
--> $DIR/two-phase-reservation-sharing-interference-2.rs:40:5
|
LL | let shared = &v;
| -- immutable borrow occurs here
LL |
LL | v.push(shared.len());
| ^^^^^^^------------^
| | |
| | immutable borrow later used here
| mutable borrow occurs here
|
= note: `#[warn(mutable_borrow_reservation_conflict)]` on by default
= warning: this borrowing pattern was not meant to be accepted, and may become a hard error in the future
= note: for more information, see issue #59159 <https://github.com/rust-lang/rust/issues/59159>

error: aborting due to 2 previous errors; 1 warning emitted
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0502`.
18 changes: 1 addition & 17 deletions src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2018.stderr
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Expand Up @@ -20,22 +20,6 @@ LL | v.extend(&v);
| | immutable borrow later used by call
| mutable borrow occurs here

warning: cannot borrow `v` as mutable because it is also borrowed as immutable
--> $DIR/two-phase-reservation-sharing-interference-2.rs:40:5
|
LL | let shared = &v;
| -- immutable borrow occurs here
LL |
LL | v.push(shared.len());
| ^^^^^^^------------^
| | |
| | immutable borrow later used here
| mutable borrow occurs here
|
= note: `#[warn(mutable_borrow_reservation_conflict)]` on by default
= warning: this borrowing pattern was not meant to be accepted, and may become a hard error in the future
= note: for more information, see issue #59159 <https://github.com/rust-lang/rust/issues/59159>

error: aborting due to 2 previous errors; 1 warning emitted
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0502`.
25 changes: 25 additions & 0 deletions src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll.stderr
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@@ -0,0 +1,25 @@
error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
--> $DIR/two-phase-reservation-sharing-interference-2.rs:19:5
|
LL | let shared = &v;
| -- immutable borrow occurs here
LL |
LL | v.extend(shared);
| ^^------^^^^^^^^
| | |
| | immutable borrow later used by call
| mutable borrow occurs here

error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
--> $DIR/two-phase-reservation-sharing-interference-2.rs:27:5
|
LL | v.extend(&v);
| ^^------^--^
| | | |
| | | immutable borrow occurs here
| | immutable borrow later used by call
| mutable borrow occurs here

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0502`.
20 changes: 4 additions & 16 deletions src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2015.stderr
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Expand Up @@ -5,9 +5,9 @@ LL | let shared = &v;
| -- immutable borrow occurs here
LL |
LL | v.extend(shared);
| ^^^^^^^^^------^
| | |
| | immutable borrow later used here
| ^^------^^^^^^^^
| | |
| | immutable borrow later used by call
| mutable borrow occurs here

error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
Expand All @@ -20,18 +20,6 @@ LL | v.extend(&v);
| | immutable borrow later used by call
| mutable borrow occurs here

error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
--> $DIR/two-phase-reservation-sharing-interference-2.rs:40:5
|
LL | let shared = &v;
| -- immutable borrow occurs here
LL |
LL | v.push(shared.len());
| ^^^^^^^------------^
| | |
| | immutable borrow later used here
| mutable borrow occurs here

error: aborting due to 3 previous errors
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0502`.
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