1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! This query borrow-checks the MIR to (further) ensure it is not broken.
13 use borrow_check::nll::region_infer::{RegionCausalInfo, RegionInferenceContext};
15 use rustc::hir::def_id::DefId;
16 use rustc::hir::map::definitions::DefPathData;
17 use rustc::infer::InferCtxt;
18 use rustc::ty::{self, ParamEnv, TyCtxt};
19 use rustc::ty::maps::Providers;
20 use rustc::mir::{AssertMessage, BasicBlock, BorrowKind, Location, Place};
21 use rustc::mir::{Mir, Mutability, Operand, Projection, ProjectionElem, Rvalue};
22 use rustc::mir::{Field, Statement, StatementKind, Terminator, TerminatorKind};
23 use rustc::mir::ClosureRegionRequirements;
25 use rustc_data_structures::fx::FxHashSet;
26 use rustc_data_structures::indexed_set::IdxSetBuf;
27 use rustc_data_structures::indexed_vec::Idx;
34 use dataflow::{do_dataflow, DebugFormatted};
35 use dataflow::FlowAtLocation;
36 use dataflow::MoveDataParamEnv;
37 use dataflow::{DataflowResultsConsumer};
38 use dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
39 use dataflow::{EverInitializedPlaces, MovingOutStatements};
40 use dataflow::{BorrowData, Borrows, ReserveOrActivateIndex};
41 use dataflow::indexes::BorrowIndex;
42 use dataflow::move_paths::{IllegalMoveOriginKind, MoveError};
43 use dataflow::move_paths::{HasMoveData, LookupResult, MoveData, MovePathIndex};
44 use util::borrowck_errors::{BorrowckErrors, Origin};
45 use util::collect_writes::FindAssignments;
49 use self::flows::Flows;
50 use self::prefixes::PrefixSet;
51 use self::MutateMode::{JustWrite, WriteAndRead};
59 pub fn provide(providers: &mut Providers) {
60 *providers = Providers {
66 fn mir_borrowck<'a, 'tcx>(
67 tcx: TyCtxt<'a, 'tcx, 'tcx>,
69 ) -> Option<ClosureRegionRequirements<'tcx>> {
70 let input_mir = tcx.mir_validated(def_id);
71 debug!("run query mir_borrowck: {}", tcx.item_path_str(def_id));
73 if !tcx.has_attr(def_id, "rustc_mir_borrowck") && !tcx.use_mir() {
77 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
78 let input_mir: &Mir = &input_mir.borrow();
79 do_mir_borrowck(&infcx, input_mir, def_id)
81 debug!("mir_borrowck done");
86 fn do_mir_borrowck<'a, 'gcx, 'tcx>(
87 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
88 input_mir: &Mir<'gcx>,
90 ) -> Option<ClosureRegionRequirements<'gcx>> {
92 let attributes = tcx.get_attrs(def_id);
93 let param_env = tcx.param_env(def_id);
95 .as_local_node_id(def_id)
96 .expect("do_mir_borrowck: non-local DefId");
98 // Make our own copy of the MIR. This copy will be modified (in place) to
99 // contain non-lexical lifetimes. It will have a lifetime tied
100 // to the inference context.
101 let mut mir: Mir<'tcx> = input_mir.clone();
102 let free_regions = if !tcx.nll() {
107 // Replace all regions with fresh inference variables.
108 Some(nll::replace_regions_in_mir(infcx, def_id, param_env, mir))
112 let move_data: MoveData<'tcx> = match MoveData::gather_moves(mir, tcx) {
113 Ok(move_data) => move_data,
114 Err((move_data, move_errors)) => {
115 for move_error in move_errors {
116 let (span, kind): (Span, IllegalMoveOriginKind) = match move_error {
117 MoveError::UnionMove { .. } => {
118 unimplemented!("don't know how to report union move errors yet.")
120 MoveError::IllegalMove {
121 cannot_move_out_of: o,
122 } => (o.span, o.kind),
124 let origin = Origin::Mir;
125 let mut err = match kind {
126 IllegalMoveOriginKind::Static => {
127 tcx.cannot_move_out_of(span, "static item", origin)
129 IllegalMoveOriginKind::BorrowedContent => {
130 tcx.cannot_move_out_of(span, "borrowed content", origin)
132 IllegalMoveOriginKind::InteriorOfTypeWithDestructor { container_ty: ty } => {
133 tcx.cannot_move_out_of_interior_of_drop(span, ty, origin)
135 IllegalMoveOriginKind::InteriorOfSliceOrArray { ty, is_index } => {
136 tcx.cannot_move_out_of_interior_noncopy(span, ty, is_index, origin)
145 let mdpe = MoveDataParamEnv {
146 move_data: move_data,
147 param_env: param_env,
149 let body_id = match tcx.def_key(def_id).disambiguated_data.data {
150 DefPathData::StructCtor | DefPathData::EnumVariant(_) => None,
151 _ => Some(tcx.hir.body_owned_by(id)),
154 let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len());
155 let mut flow_inits = FlowAtLocation::new(do_dataflow(
161 MaybeInitializedPlaces::new(tcx, mir, &mdpe),
162 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
164 let flow_uninits = FlowAtLocation::new(do_dataflow(
170 MaybeUninitializedPlaces::new(tcx, mir, &mdpe),
171 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
173 let flow_move_outs = FlowAtLocation::new(do_dataflow(
179 MovingOutStatements::new(tcx, mir, &mdpe),
180 |bd, i| DebugFormatted::new(&bd.move_data().moves[i]),
182 let flow_ever_inits = FlowAtLocation::new(do_dataflow(
188 EverInitializedPlaces::new(tcx, mir, &mdpe),
189 |bd, i| DebugFormatted::new(&bd.move_data().inits[i]),
192 // If we are in non-lexical mode, compute the non-lexical lifetimes.
193 let (opt_regioncx, opt_closure_req) = if let Some(free_regions) = free_regions {
194 let (regioncx, opt_closure_req) = nll::compute_regions(
203 (Some(Rc::new(regioncx)), opt_closure_req)
208 let flow_inits = flow_inits; // remove mut
210 let flow_borrows = FlowAtLocation::new(do_dataflow(
216 Borrows::new(tcx, mir, opt_regioncx.clone(), def_id, body_id),
218 DebugFormatted::new(&(i.kind(), rs.location(i.borrow_index())))
222 let movable_generator = !match tcx.hir.get(id) {
223 hir::map::Node::NodeExpr(&hir::Expr {
224 node: hir::ExprClosure(.., Some(hir::GeneratorMovability::Static)),
230 let mut mbcx = MirBorrowckCtxt {
234 move_data: &mdpe.move_data,
235 param_env: param_env,
237 locals_are_invalidated_at_exit: match tcx.hir.body_owner_kind(id) {
238 hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => false,
239 hir::BodyOwnerKind::Fn => true,
241 access_place_error_reported: FxHashSet(),
242 reservation_error_reported: FxHashSet(),
243 moved_error_reported: FxHashSet(),
244 nonlexical_regioncx: opt_regioncx,
245 nonlexical_cause_info: None,
248 let mut state = Flows::new(
256 mbcx.analyze_results(&mut state); // entry point for DataflowResultsConsumer
262 pub struct MirBorrowckCtxt<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
263 tcx: TyCtxt<'cx, 'gcx, 'tcx>,
265 node_id: ast::NodeId,
266 move_data: &'cx MoveData<'tcx>,
267 param_env: ParamEnv<'gcx>,
268 movable_generator: bool,
269 /// This keeps track of whether local variables are free-ed when the function
270 /// exits even without a `StorageDead`, which appears to be the case for
273 /// I'm not sure this is the right approach - @eddyb could you try and
275 locals_are_invalidated_at_exit: bool,
276 /// This field keeps track of when borrow errors are reported in the access_place function
277 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
278 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
279 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
281 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
282 /// This field keeps track of when borrow conflict errors are reported
283 /// for reservations, so that we don't report seemingly duplicate
284 /// errors for corresponding activations
286 /// FIXME: Ideally this would be a set of BorrowIndex, not Places,
287 /// but it is currently inconvenient to track down the BorrowIndex
288 /// at the time we detect and report a reservation error.
289 reservation_error_reported: FxHashSet<Place<'tcx>>,
290 /// This field keeps track of errors reported in the checking of moved variables,
291 /// so that we don't report report seemingly duplicate errors.
292 moved_error_reported: FxHashSet<Place<'tcx>>,
293 /// Non-lexical region inference context, if NLL is enabled. This
294 /// contains the results from region inference and lets us e.g.
295 /// find out which CFG points are contained in each borrow region.
296 nonlexical_regioncx: Option<Rc<RegionInferenceContext<'tcx>>>,
297 nonlexical_cause_info: Option<RegionCausalInfo>,
301 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
302 // 2. loans made in overlapping scopes do not conflict
303 // 3. assignments do not affect things loaned out as immutable
304 // 4. moves do not affect things loaned out in any way
305 impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
306 type FlowState = Flows<'cx, 'gcx, 'tcx>;
308 fn mir(&self) -> &'cx Mir<'tcx> {
312 fn visit_block_entry(&mut self, bb: BasicBlock, flow_state: &Self::FlowState) {
313 debug!("MirBorrowckCtxt::process_block({:?}): {}", bb, flow_state);
316 fn visit_statement_entry(
319 stmt: &Statement<'tcx>,
320 flow_state: &Self::FlowState,
323 "MirBorrowckCtxt::process_statement({:?}, {:?}): {}",
324 location, stmt, flow_state
326 let span = stmt.source_info.span;
328 self.check_activations(location, span, flow_state);
331 StatementKind::Assign(ref lhs, ref rhs) => {
333 ContextKind::AssignRhs.new(location),
340 ContextKind::AssignLhs.new(location),
347 StatementKind::SetDiscriminant {
352 ContextKind::SetDiscrim.new(location),
354 Shallow(Some(ArtificialField::Discriminant)),
359 StatementKind::InlineAsm {
364 let context = ContextKind::InlineAsm.new(location);
365 for (o, output) in asm.outputs.iter().zip(outputs) {
367 // FIXME(eddyb) indirect inline asm outputs should
368 // be encoeded through MIR place derefs instead.
372 (Deep, Read(ReadKind::Copy)),
373 LocalMutationIsAllowed::No,
376 self.check_if_path_or_subpath_is_moved(
378 InitializationRequiringAction::Use,
386 if o.is_rw { Deep } else { Shallow(None) },
387 if o.is_rw { WriteAndRead } else { JustWrite },
392 for input in inputs {
393 self.consume_operand(context, (input, span), flow_state);
396 StatementKind::EndRegion(ref _rgn) => {
397 // ignored when consuming results (update to
398 // flow_state already handled).
401 StatementKind::UserAssertTy(..) |
402 StatementKind::Validate(..) |
403 StatementKind::StorageLive(..) => {
404 // `Nop`, `UserAssertTy`, `Validate`, and `StorageLive` are irrelevant
407 StatementKind::StorageDead(local) => {
409 ContextKind::StorageDead.new(location),
410 (&Place::Local(local), span),
411 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
412 LocalMutationIsAllowed::Yes,
419 fn visit_terminator_entry(
422 term: &Terminator<'tcx>,
423 flow_state: &Self::FlowState,
427 "MirBorrowckCtxt::process_terminator({:?}, {:?}): {}",
428 location, term, flow_state
430 let span = term.source_info.span;
432 self.check_activations(location, span, flow_state);
435 TerminatorKind::SwitchInt {
441 self.consume_operand(ContextKind::SwitchInt.new(loc), (discr, span), flow_state);
443 TerminatorKind::Drop {
444 location: ref drop_place,
448 let gcx = self.tcx.global_tcx();
450 // Compute the type with accurate region information.
451 let drop_place_ty = drop_place.ty(self.mir, self.tcx);
453 // Erase the regions.
454 let drop_place_ty = self.tcx.erase_regions(&drop_place_ty).to_ty(self.tcx);
456 // "Lift" into the gcx -- once regions are erased, this type should be in the
457 // global arenas; this "lift" operation basically just asserts that is true, but
458 // that is useful later.
459 let drop_place_ty = gcx.lift(&drop_place_ty).unwrap();
461 self.visit_terminator_drop(loc, term, flow_state, drop_place, drop_place_ty, span);
463 TerminatorKind::DropAndReplace {
464 location: ref drop_place,
465 value: ref new_value,
470 ContextKind::DropAndReplace.new(loc),
476 self.consume_operand(
477 ContextKind::DropAndReplace.new(loc),
482 TerminatorKind::Call {
488 self.consume_operand(ContextKind::CallOperator.new(loc), (func, span), flow_state);
490 self.consume_operand(
491 ContextKind::CallOperand.new(loc),
496 if let Some((ref dest, _ /*bb*/)) = *destination {
498 ContextKind::CallDest.new(loc),
506 TerminatorKind::Assert {
513 self.consume_operand(ContextKind::Assert.new(loc), (cond, span), flow_state);
515 AssertMessage::BoundsCheck { ref len, ref index } => {
516 self.consume_operand(ContextKind::Assert.new(loc), (len, span), flow_state);
517 self.consume_operand(
518 ContextKind::Assert.new(loc),
523 AssertMessage::Math(_ /*const_math_err*/) => {}
524 AssertMessage::GeneratorResumedAfterReturn => {}
525 AssertMessage::GeneratorResumedAfterPanic => {}
529 TerminatorKind::Yield {
534 self.consume_operand(ContextKind::Yield.new(loc), (value, span), flow_state);
536 if self.movable_generator {
537 // Look for any active borrows to locals
538 let domain = flow_state.borrows.operator();
539 let data = domain.borrows();
540 flow_state.borrows.with_iter_outgoing(|borrows| {
542 let borrow = &data[i.borrow_index()];
543 self.check_for_local_borrow(borrow, span);
549 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
550 // Returning from the function implicitly kills storage for all locals and statics.
551 // Often, the storage will already have been killed by an explicit
552 // StorageDead, but we don't always emit those (notably on unwind paths),
553 // so this "extra check" serves as a kind of backup.
554 let domain = flow_state.borrows.operator();
555 let data = domain.borrows();
556 flow_state.borrows.with_iter_outgoing(|borrows| {
558 let borrow = &data[i.borrow_index()];
559 let context = ContextKind::StorageDead.new(loc);
560 self.check_for_invalidation_at_exit(context, borrow, span, flow_state);
564 TerminatorKind::Goto { target: _ }
565 | TerminatorKind::Abort
566 | TerminatorKind::Unreachable
567 | TerminatorKind::FalseEdges {
569 imaginary_targets: _,
571 | TerminatorKind::FalseUnwind {
575 // no data used, thus irrelevant to borrowck
581 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
587 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
593 use self::ShallowOrDeep::{Deep, Shallow};
594 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
596 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
597 enum ArtificialField {
602 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
604 /// From the RFC: "A *shallow* access means that the immediate
605 /// fields reached at P are accessed, but references or pointers
606 /// found within are not dereferenced. Right now, the only access
607 /// that is shallow is an assignment like `x = ...;`, which would
608 /// be a *shallow write* of `x`."
609 Shallow(Option<ArtificialField>),
611 /// From the RFC: "A *deep* access means that all data reachable
612 /// through the given place may be invalidated or accesses by
617 /// Kind of access to a value: read or write
618 /// (For informational purposes only)
619 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
621 /// From the RFC: "A *read* means that the existing data may be
622 /// read, but will not be changed."
625 /// From the RFC: "A *write* means that the data may be mutated to
626 /// new values or otherwise invalidated (for example, it could be
627 /// de-initialized, as in a move operation).
630 /// For two-phase borrows, we distinguish a reservation (which is treated
631 /// like a Read) from an activation (which is treated like a write), and
632 /// each of those is furthermore distinguished from Reads/Writes above.
633 Reservation(WriteKind),
634 Activation(WriteKind, BorrowIndex),
637 /// Kind of read access to a value
638 /// (For informational purposes only)
639 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
645 /// Kind of write access to a value
646 /// (For informational purposes only)
647 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
650 MutableBorrow(BorrowKind),
655 /// When checking permissions for a place access, this flag is used to indicate that an immutable
656 /// local place can be mutated.
658 /// FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
659 /// - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`
660 /// - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
661 /// `is_declared_mutable()`
662 /// - Take flow state into consideration in `is_assignable()` for local variables
663 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
664 enum LocalMutationIsAllowed {
666 /// We want use of immutable upvars to cause a "write to immutable upvar"
667 /// error, not an "reassignment" error.
672 struct AccessErrorsReported {
673 mutability_error: bool,
675 conflict_error: bool,
678 #[derive(Copy, Clone)]
679 enum InitializationRequiringAction {
686 impl InitializationRequiringAction {
687 fn as_noun(self) -> &'static str {
689 InitializationRequiringAction::Update => "update",
690 InitializationRequiringAction::Borrow => "borrow",
691 InitializationRequiringAction::Use => "use",
692 InitializationRequiringAction::Assignment => "assign",
696 fn as_verb_in_past_tense(self) -> &'static str {
698 InitializationRequiringAction::Update => "updated",
699 InitializationRequiringAction::Borrow => "borrowed",
700 InitializationRequiringAction::Use => "used",
701 InitializationRequiringAction::Assignment => "assigned",
706 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
707 /// Returns true if the borrow represented by `kind` is
708 /// allowed to be split into separate Reservation and
709 /// Activation phases.
710 fn allow_two_phase_borrow(&self, kind: BorrowKind) -> bool {
711 self.tcx.two_phase_borrows()
712 && (kind.allows_two_phase_borrow()
713 || self.tcx.sess.opts.debugging_opts.two_phase_beyond_autoref)
716 /// Invokes `access_place` as appropriate for dropping the value
717 /// at `drop_place`. Note that the *actual* `Drop` in the MIR is
718 /// always for a variable (e.g., `Drop(x)`) -- but we recursively
719 /// break this variable down into subpaths (e.g., `Drop(x.foo)`)
720 /// to indicate more precisely which fields might actually be
721 /// accessed by a destructor.
722 fn visit_terminator_drop(
725 term: &Terminator<'tcx>,
726 flow_state: &Flows<'cx, 'gcx, 'tcx>,
727 drop_place: &Place<'tcx>,
728 erased_drop_place_ty: ty::Ty<'gcx>,
731 match erased_drop_place_ty.sty {
732 // When a struct is being dropped, we need to check
733 // whether it has a destructor, if it does, then we can
734 // call it, if it does not then we need to check the
735 // individual fields instead. This way if `foo` has a
736 // destructor but `bar` does not, we will only check for
737 // borrows of `x.foo` and not `x.bar`. See #47703.
738 ty::TyAdt(def, substs) if def.is_struct() && !def.has_dtor(self.tcx) => {
739 for (index, field) in def.all_fields().enumerate() {
740 let gcx = self.tcx.global_tcx();
741 let field_ty = field.ty(gcx, substs);
742 let field_ty = gcx.normalize_erasing_regions(self.param_env, field_ty);
743 let place = drop_place.clone().field(Field::new(index), field_ty);
745 self.visit_terminator_drop(loc, term, flow_state, &place, field_ty, span);
749 // We have now refined the type of the value being
750 // dropped (potentially) to just the type of a
751 // subfield; so check whether that field's type still
752 // "needs drop". If so, we assume that the destructor
753 // may access any data it likes (i.e., a Deep Write).
754 let gcx = self.tcx.global_tcx();
755 if erased_drop_place_ty.needs_drop(gcx, self.param_env) {
757 ContextKind::Drop.new(loc),
759 (Deep, Write(WriteKind::StorageDeadOrDrop)),
760 LocalMutationIsAllowed::Yes,
768 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
769 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
770 /// place is initialized and (b) it is not borrowed in some way that would prevent this
773 /// Returns true if an error is reported, false otherwise.
777 place_span: (&Place<'tcx>, Span),
778 kind: (ShallowOrDeep, ReadOrWrite),
779 is_local_mutation_allowed: LocalMutationIsAllowed,
780 flow_state: &Flows<'cx, 'gcx, 'tcx>,
781 ) -> AccessErrorsReported {
784 if let Activation(_, borrow_index) = rw {
785 if self.reservation_error_reported.contains(&place_span.0) {
787 "skipping access_place for activation of invalid reservation \
788 place: {:?} borrow_index: {:?}",
789 place_span.0, borrow_index
791 return AccessErrorsReported {
792 mutability_error: false,
793 conflict_error: true,
798 if self.access_place_error_reported
799 .contains(&(place_span.0.clone(), place_span.1))
802 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
805 return AccessErrorsReported {
806 mutability_error: false,
807 conflict_error: true,
811 let mutability_error =
812 self.check_access_permissions(place_span, rw, is_local_mutation_allowed);
814 self.check_access_for_conflict(context, place_span, sd, rw, flow_state);
816 if conflict_error || mutability_error {
818 "access_place: logging error place_span=`{:?}` kind=`{:?}`",
821 self.access_place_error_reported
822 .insert((place_span.0.clone(), place_span.1));
825 AccessErrorsReported {
831 fn check_access_for_conflict(
834 place_span: (&Place<'tcx>, Span),
837 flow_state: &Flows<'cx, 'gcx, 'tcx>,
839 let mut error_reported = false;
840 self.each_borrow_involving_path(
844 |this, index, borrow| match (rw, borrow.kind) {
845 // Obviously an activation is compatible with its own
846 // reservation (or even prior activating uses of same
847 // borrow); so don't check if they interfere.
849 // NOTE: *reservations* do conflict with themselves;
850 // thus aren't injecting unsoundenss w/ this check.)
851 (Activation(_, activating), _) if activating == index.borrow_index() => {
853 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
854 skipping {:?} b/c activation of same borrow_index: {:?}",
864 (Read(_), BorrowKind::Shared) | (Reservation(..), BorrowKind::Shared) => {
868 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
869 // Reading from mere reservations of mutable-borrows is OK.
870 if this.allow_two_phase_borrow(borrow.kind) && index.is_reservation() {
871 return Control::Continue;
876 error_reported = true;
877 this.report_use_while_mutably_borrowed(context, place_span, borrow)
879 ReadKind::Borrow(bk) => {
880 let end_issued_loan_span = flow_state
883 .opt_region_end_span(&borrow.region);
884 error_reported = true;
885 this.report_conflicting_borrow(
890 end_issued_loan_span,
897 (Reservation(kind), BorrowKind::Unique)
898 | (Reservation(kind), BorrowKind::Mut { .. })
899 | (Activation(kind, _), _)
900 | (Write(kind), _) => {
904 "recording invalid reservation of \
908 this.reservation_error_reported.insert(place_span.0.clone());
910 Activation(_, activating) => {
912 "observing check_place for activation of \
917 Read(..) | Write(..) => {}
921 WriteKind::MutableBorrow(bk) => {
922 let end_issued_loan_span = flow_state
925 .opt_region_end_span(&borrow.region);
927 error_reported = true;
928 this.report_conflicting_borrow(
933 end_issued_loan_span,
936 WriteKind::StorageDeadOrDrop => {
937 error_reported = true;
938 this.report_borrowed_value_does_not_live_long_enough(
942 flow_state.borrows.operator(),
945 WriteKind::Mutate => {
946 error_reported = true;
947 this.report_illegal_mutation_of_borrowed(context, place_span, borrow)
950 error_reported = true;
951 this.report_move_out_while_borrowed(context, place_span, &borrow)
965 place_span: (&Place<'tcx>, Span),
968 flow_state: &Flows<'cx, 'gcx, 'tcx>,
970 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
972 MutateMode::WriteAndRead => {
973 self.check_if_path_or_subpath_is_moved(
975 InitializationRequiringAction::Update,
980 MutateMode::JustWrite => {
981 self.check_if_assigned_path_is_moved(context, place_span, flow_state);
985 let errors_reported = self.access_place(
988 (kind, Write(WriteKind::Mutate)),
989 // We want immutable upvars to cause an "assignment to immutable var"
990 // error, not an "reassignment of immutable var" error, because the
991 // latter can't find a good previous assignment span.
993 // There's probably a better way to do this.
994 LocalMutationIsAllowed::ExceptUpvars,
998 if !errors_reported.mutability_error {
999 // check for reassignments to immutable local variables
1000 self.check_if_reassignment_to_immutable_state(context, place_span, flow_state);
1007 (rvalue, span): (&Rvalue<'tcx>, Span),
1008 _location: Location,
1009 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1012 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1013 let access_kind = match bk {
1014 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1015 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1016 let wk = WriteKind::MutableBorrow(bk);
1017 if self.allow_two_phase_borrow(bk) {
1018 (Deep, Reservation(wk))
1029 LocalMutationIsAllowed::No,
1033 self.check_if_path_or_subpath_is_moved(
1035 InitializationRequiringAction::Borrow,
1041 Rvalue::Use(ref operand)
1042 | Rvalue::Repeat(ref operand, _)
1043 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1044 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1045 self.consume_operand(context, (operand, span), flow_state)
1048 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1049 let af = match *rvalue {
1050 Rvalue::Len(..) => ArtificialField::ArrayLength,
1051 Rvalue::Discriminant(..) => ArtificialField::Discriminant,
1052 _ => unreachable!(),
1057 (Shallow(Some(af)), Read(ReadKind::Copy)),
1058 LocalMutationIsAllowed::No,
1061 self.check_if_path_or_subpath_is_moved(
1063 InitializationRequiringAction::Use,
1069 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1070 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1071 self.consume_operand(context, (operand1, span), flow_state);
1072 self.consume_operand(context, (operand2, span), flow_state);
1075 Rvalue::NullaryOp(_op, _ty) => {
1076 // nullary ops take no dynamic input; no borrowck effect.
1078 // FIXME: is above actually true? Do we want to track
1079 // the fact that uninitialized data can be created via
1083 Rvalue::Aggregate(ref _aggregate_kind, ref operands) => for operand in operands {
1084 self.consume_operand(context, (operand, span), flow_state);
1092 (operand, span): (&Operand<'tcx>, Span),
1093 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1096 Operand::Copy(ref place) => {
1097 // copy of place: check if this is "copy of frozen path"
1098 // (FIXME: see check_loans.rs)
1102 (Deep, Read(ReadKind::Copy)),
1103 LocalMutationIsAllowed::No,
1107 // Finally, check if path was already moved.
1108 self.check_if_path_or_subpath_is_moved(
1110 InitializationRequiringAction::Use,
1115 Operand::Move(ref place) => {
1116 // move of place: check if this is move of already borrowed path
1120 (Deep, Write(WriteKind::Move)),
1121 LocalMutationIsAllowed::Yes,
1125 // Finally, check if path was already moved.
1126 self.check_if_path_or_subpath_is_moved(
1128 InitializationRequiringAction::Use,
1133 Operand::Constant(_) => {}
1137 /// Returns whether a borrow of this place is invalidated when the function
1139 fn check_for_invalidation_at_exit(
1142 borrow: &BorrowData<'tcx>,
1144 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1146 debug!("check_for_invalidation_at_exit({:?})", borrow);
1147 let place = &borrow.borrowed_place;
1148 let root_place = self.prefixes(place, PrefixSet::All).last().unwrap();
1150 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1151 // we just know that all locals are dropped at function exit (otherwise
1152 // we'll have a memory leak) and assume that all statics have a destructor.
1154 // FIXME: allow thread-locals to borrow other thread locals?
1155 let (might_be_alive, will_be_dropped) = match root_place {
1156 Place::Static(statik) => {
1157 // Thread-locals might be dropped after the function exits, but
1158 // "true" statics will never be.
1159 let is_thread_local = self.tcx
1160 .get_attrs(statik.def_id)
1162 .any(|attr| attr.check_name("thread_local"));
1164 (true, is_thread_local)
1166 Place::Local(_) => {
1167 // Locals are always dropped at function exit, and if they
1168 // have a destructor it would've been called already.
1169 (false, self.locals_are_invalidated_at_exit)
1171 Place::Projection(..) => {
1172 bug!("root of {:?} is a projection ({:?})?", place, root_place)
1176 if !will_be_dropped {
1178 "place_is_invalidated_at_exit({:?}) - won't be dropped",
1184 // FIXME: replace this with a proper borrow_conflicts_with_place when
1186 let sd = if might_be_alive { Deep } else { Shallow(None) };
1188 if self.places_conflict(place, root_place, sd) {
1189 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1190 // FIXME: should be talking about the region lifetime instead
1191 // of just a span here.
1192 let span = self.tcx.sess.codemap().end_point(span);
1193 self.report_borrowed_value_does_not_live_long_enough(
1197 flow_state.borrows.operator(),
1202 /// Reports an error if this is a borrow of local data.
1203 /// This is called for all Yield statements on movable generators
1204 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1205 fn borrow_of_local_data<'tcx>(place: &Place<'tcx>) -> bool {
1207 Place::Static(..) => false,
1208 Place::Local(..) => true,
1209 Place::Projection(box proj) => {
1211 // Reborrow of already borrowed data is ignored
1212 // Any errors will be caught on the initial borrow
1213 ProjectionElem::Deref => false,
1215 // For interior references and downcasts, find out if the base is local
1216 ProjectionElem::Field(..)
1217 | ProjectionElem::Index(..)
1218 | ProjectionElem::ConstantIndex { .. }
1219 | ProjectionElem::Subslice { .. }
1220 | ProjectionElem::Downcast(..) => borrow_of_local_data(&proj.base),
1226 debug!("check_for_local_borrow({:?})", borrow);
1228 if borrow_of_local_data(&borrow.borrowed_place) {
1230 .cannot_borrow_across_generator_yield(
1231 self.retrieve_borrow_span(borrow),
1239 fn check_activations(
1243 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1245 if !self.tcx.two_phase_borrows() {
1249 // Two-phase borrow support: For each activation that is newly
1250 // generated at this statement, check if it interferes with
1252 let domain = flow_state.borrows.operator();
1253 let data = domain.borrows();
1254 flow_state.borrows.each_gen_bit(|gen| {
1255 if gen.is_activation() {
1256 let borrow_index = gen.borrow_index();
1257 let borrow = &data[borrow_index];
1258 // currently the flow analysis registers
1259 // activations for both mutable and immutable
1260 // borrows. So make sure we are talking about a
1261 // mutable borrow before we check it.
1263 BorrowKind::Shared => return,
1264 BorrowKind::Unique | BorrowKind::Mut { .. } => {}
1268 ContextKind::Activation.new(location),
1269 (&borrow.borrowed_place, span),
1272 Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index),
1274 LocalMutationIsAllowed::No,
1277 // We do not need to call `check_if_path_or_subpath_is_moved`
1278 // again, as we already called it when we made the
1279 // initial reservation.
1285 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1286 fn check_if_reassignment_to_immutable_state(
1289 (place, span): (&Place<'tcx>, Span),
1290 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1292 debug!("check_if_reassignment_to_immutable_state({:?})", place);
1293 // determine if this path has a non-mut owner (and thus needs checking).
1294 if let Ok(()) = self.is_mutable(place, LocalMutationIsAllowed::No) {
1298 "check_if_reassignment_to_immutable_state({:?}) - is an imm local",
1302 for i in flow_state.ever_inits.iter_incoming() {
1303 let init = self.move_data.inits[i];
1304 let init_place = &self.move_data.move_paths[init.path].place;
1305 if self.places_conflict(&init_place, place, Deep) {
1306 self.report_illegal_reassignment(context, (place, span), init.span);
1312 fn check_if_full_path_is_moved(
1315 desired_action: InitializationRequiringAction,
1316 place_span: (&Place<'tcx>, Span),
1317 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1319 // FIXME: analogous code in check_loans first maps `place` to
1320 // its base_path ... but is that what we want here?
1321 let place = self.base_path(place_span.0);
1323 let maybe_uninits = &flow_state.uninits;
1324 let curr_move_outs = &flow_state.move_outs;
1328 // 1. Move of `a.b.c`, use of `a.b.c`
1329 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1330 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1331 // partial initialization support, one might have `a.x`
1332 // initialized but not `a.b`.
1336 // 4. Move of `a.b.c`, use of `a.b.d`
1337 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1338 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1339 // must have been initialized for the use to be sound.
1340 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1342 // The dataflow tracks shallow prefixes distinctly (that is,
1343 // field-accesses on P distinctly from P itself), in order to
1344 // track substructure initialization separately from the whole
1347 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1348 // which we have a MovePath is `a.b`, then that means that the
1349 // initialization state of `a.b` is all we need to inspect to
1350 // know if `a.b.c` is valid (and from that we infer that the
1351 // dereference and `.d` access is also valid, since we assume
1352 // `a.b.c` is assigned a reference to a initialized and
1353 // well-formed record structure.)
1355 // Therefore, if we seek out the *closest* prefix for which we
1356 // have a MovePath, that should capture the initialization
1357 // state for the place scenario.
1359 // This code covers scenarios 1, 2, and 3.
1361 debug!("check_if_full_path_is_moved place: {:?}", place);
1362 match self.move_path_closest_to(place) {
1364 if maybe_uninits.contains(&mpi) {
1365 self.report_use_of_moved_or_uninitialized(
1372 return; // don't bother finding other problems.
1375 Err(NoMovePathFound::ReachedStatic) => {
1376 // Okay: we do not build MoveData for static variables
1377 } // Only query longest prefix with a MovePath, not further
1378 // ancestors; dataflow recurs on children when parents
1379 // move (to support partial (re)inits).
1381 // (I.e. querying parents breaks scenario 7; but may want
1382 // to do such a query based on partial-init feature-gate.)
1386 fn check_if_path_or_subpath_is_moved(
1389 desired_action: InitializationRequiringAction,
1390 place_span: (&Place<'tcx>, Span),
1391 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1393 // FIXME: analogous code in check_loans first maps `place` to
1394 // its base_path ... but is that what we want here?
1395 let place = self.base_path(place_span.0);
1397 let maybe_uninits = &flow_state.uninits;
1398 let curr_move_outs = &flow_state.move_outs;
1402 // 1. Move of `a.b.c`, use of `a` or `a.b`
1403 // partial initialization support, one might have `a.x`
1404 // initialized but not `a.b`.
1405 // 2. All bad scenarios from `check_if_full_path_is_moved`
1409 // 3. Move of `a.b.c`, use of `a.b.d`
1410 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1411 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1412 // must have been initialized for the use to be sound.
1413 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1415 self.check_if_full_path_is_moved(context, desired_action, place_span, flow_state);
1417 // A move of any shallow suffix of `place` also interferes
1418 // with an attempt to use `place`. This is scenario 3 above.
1420 // (Distinct from handling of scenarios 1+2+4 above because
1421 // `place` does not interfere with suffixes of its prefixes,
1422 // e.g. `a.b.c` does not interfere with `a.b.d`)
1424 // This code covers scenario 1.
1426 debug!("check_if_path_or_subpath_is_moved place: {:?}", place);
1427 if let Some(mpi) = self.move_path_for_place(place) {
1428 if let Some(child_mpi) = maybe_uninits.has_any_child_of(mpi) {
1429 self.report_use_of_moved_or_uninitialized(
1436 return; // don't bother finding other problems.
1441 /// Currently MoveData does not store entries for all places in
1442 /// the input MIR. For example it will currently filter out
1443 /// places that are Copy; thus we do not track places of shared
1444 /// reference type. This routine will walk up a place along its
1445 /// prefixes, searching for a foundational place that *is*
1446 /// tracked in the MoveData.
1448 /// An Err result includes a tag indicated why the search failed.
1449 /// Currently this can only occur if the place is built off of a
1450 /// static variable, as we do not track those in the MoveData.
1451 fn move_path_closest_to(
1453 place: &Place<'tcx>,
1454 ) -> Result<MovePathIndex, NoMovePathFound> {
1455 let mut last_prefix = place;
1456 for prefix in self.prefixes(place, PrefixSet::All) {
1457 if let Some(mpi) = self.move_path_for_place(prefix) {
1460 last_prefix = prefix;
1462 match *last_prefix {
1463 Place::Local(_) => panic!("should have move path for every Local"),
1464 Place::Projection(_) => panic!("PrefixSet::All meant don't stop for Projection"),
1465 Place::Static(_) => return Err(NoMovePathFound::ReachedStatic),
1469 fn move_path_for_place(&mut self, place: &Place<'tcx>) -> Option<MovePathIndex> {
1470 // If returns None, then there is no move path corresponding
1471 // to a direct owner of `place` (which means there is nothing
1472 // that borrowck tracks for its analysis).
1474 match self.move_data.rev_lookup.find(place) {
1475 LookupResult::Parent(_) => None,
1476 LookupResult::Exact(mpi) => Some(mpi),
1480 fn check_if_assigned_path_is_moved(
1483 (place, span): (&Place<'tcx>, Span),
1484 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1486 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1487 // recur down place; dispatch to external checks when necessary
1488 let mut place = place;
1491 Place::Local(_) | Place::Static(_) => {
1492 // assigning to `x` does not require `x` be initialized.
1495 Place::Projection(ref proj) => {
1496 let Projection { ref base, ref elem } = **proj;
1498 ProjectionElem::Index(_/*operand*/) |
1499 ProjectionElem::ConstantIndex { .. } |
1500 // assigning to P[i] requires P to be valid.
1501 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1502 // assigning to (P->variant) is okay if assigning to `P` is okay
1504 // FIXME: is this true even if P is a adt with a dtor?
1507 // assigning to (*P) requires P to be initialized
1508 ProjectionElem::Deref => {
1509 self.check_if_full_path_is_moved(
1510 context, InitializationRequiringAction::Use,
1511 (base, span), flow_state);
1512 // (base initialized; no need to
1517 ProjectionElem::Subslice { .. } => {
1518 panic!("we don't allow assignments to subslices, context: {:?}",
1522 ProjectionElem::Field(..) => {
1523 // if type of `P` has a dtor, then
1524 // assigning to `P.f` requires `P` itself
1525 // be already initialized
1527 match base.ty(self.mir, tcx).to_ty(tcx).sty {
1528 ty::TyAdt(def, _) if def.has_dtor(tcx) => {
1530 // FIXME: analogous code in
1531 // check_loans.rs first maps
1532 // `base` to its base_path.
1534 self.check_if_path_or_subpath_is_moved(
1535 context, InitializationRequiringAction::Assignment,
1536 (base, span), flow_state);
1538 // (base initialized; no need to
1554 fn specialized_description(&self, place:&Place<'tcx>) -> Option<String>{
1555 if let Some(_name) = self.describe_place(place) {
1556 Some(format!("data in a `&` reference"))
1562 fn get_default_err_msg(&self, place:&Place<'tcx>) -> String{
1563 match self.describe_place(place) {
1564 Some(name) => format!("immutable item `{}`", name),
1565 None => "immutable item".to_owned(),
1569 fn get_secondary_err_msg(&self, place:&Place<'tcx>) -> String{
1570 match self.specialized_description(place) {
1571 Some(_) => format!("data in a `&` reference"),
1572 None => self.get_default_err_msg(place)
1576 fn get_primary_err_msg(&self, place:&Place<'tcx>) -> String{
1577 if let Some(name) = self.describe_place(place) {
1578 format!("`{}` is a `&` reference, so the data it refers to cannot be written", name)
1580 format!("cannot assign through `&`-reference")
1584 /// Check the permissions for the given place and read or write kind
1586 /// Returns true if an error is reported, false otherwise.
1587 fn check_access_permissions(
1589 (place, span): (&Place<'tcx>, Span),
1591 is_local_mutation_allowed: LocalMutationIsAllowed,
1594 "check_access_permissions({:?}, {:?}, {:?})",
1595 place, kind, is_local_mutation_allowed
1597 let mut error_reported = false;
1599 Reservation(WriteKind::MutableBorrow(BorrowKind::Unique))
1600 | Write(WriteKind::MutableBorrow(BorrowKind::Unique)) => {
1601 if let Err(_place_err) = self.is_mutable(place, LocalMutationIsAllowed::Yes) {
1602 span_bug!(span, "&unique borrow for {:?} should not fail", place);
1605 Reservation(WriteKind::MutableBorrow(BorrowKind::Mut { .. }))
1606 | Write(WriteKind::MutableBorrow(BorrowKind::Mut { .. })) => if let Err(place_err) =
1607 self.is_mutable(place, is_local_mutation_allowed)
1609 error_reported = true;
1610 let item_msg = self.get_default_err_msg(place);
1611 let mut err = self.tcx
1612 .cannot_borrow_path_as_mutable(span, &item_msg, Origin::Mir);
1613 err.span_label(span, "cannot borrow as mutable");
1615 if place != place_err {
1616 if let Some(name) = self.describe_place(place_err) {
1617 err.note(&format!("the value which is causing this path not to be mutable \
1618 is...: `{}`", name));
1624 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1626 if let Err(place_err) = self.is_mutable(place, is_local_mutation_allowed) {
1627 error_reported = true;
1628 let mut err_info = None;
1631 Place::Projection(box Projection {
1632 ref base, elem:ProjectionElem::Deref}) => {
1634 Place::Local(local) => {
1635 let locations = self.mir.find_assignments(local);
1636 if locations.len() > 0 {
1637 let item_msg = if error_reported {
1638 self.get_secondary_err_msg(base)
1640 self.get_default_err_msg(place)
1642 let sp = self.mir.source_info(locations[0]).span;
1643 let mut to_suggest_span = String::new();
1645 self.tcx.sess.codemap().span_to_snippet(sp) {
1646 to_suggest_span = src[1..].to_string();
1650 "consider changing this to be a \
1654 self.get_primary_err_msg(base)));
1663 if let Some((err_help_span,
1667 sec_span)) = err_info {
1668 let mut err = self.tcx.cannot_assign(span, &item_msg, Origin::Mir);
1669 err.span_suggestion(err_help_span,
1671 format!("&mut {}", to_suggest_span));
1672 if place != place_err {
1673 err.span_label(span, sec_span);
1677 let item_msg_ = self.get_default_err_msg(place);
1678 let mut err = self.tcx.cannot_assign(span, &item_msg_, Origin::Mir);
1679 err.span_label(span, "cannot mutate");
1680 if place != place_err {
1681 if let Some(name) = self.describe_place(place_err) {
1682 err.note(&format!("the value which is causing this path not to be \
1683 mutable is...: `{}`", name));
1690 Reservation(WriteKind::Move)
1691 | Reservation(WriteKind::StorageDeadOrDrop)
1692 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1693 | Write(WriteKind::Move)
1694 | Write(WriteKind::StorageDeadOrDrop)
1695 | Write(WriteKind::MutableBorrow(BorrowKind::Shared)) => {
1696 if let Err(_place_err) = self.is_mutable(place, is_local_mutation_allowed) {
1697 self.tcx.sess.delay_span_bug(
1700 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1706 Activation(..) => {} // permission checks are done at Reservation point.
1707 Read(ReadKind::Borrow(BorrowKind::Unique))
1708 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1709 | Read(ReadKind::Borrow(BorrowKind::Shared))
1710 | Read(ReadKind::Copy) => {} // Access authorized
1716 /// Can this value be written or borrowed mutably
1719 place: &'d Place<'tcx>,
1720 is_local_mutation_allowed: LocalMutationIsAllowed,
1721 ) -> Result<(), &'d Place<'tcx>> {
1723 Place::Local(local) => {
1724 let local = &self.mir.local_decls[local];
1725 match local.mutability {
1726 Mutability::Not => match is_local_mutation_allowed {
1727 LocalMutationIsAllowed::Yes | LocalMutationIsAllowed::ExceptUpvars => {
1730 LocalMutationIsAllowed::No => Err(place),
1732 Mutability::Mut => Ok(()),
1735 Place::Static(ref static_) =>
1736 if self.tcx.is_static(static_.def_id) != Some(hir::Mutability::MutMutable) {
1741 Place::Projection(ref proj) => {
1743 ProjectionElem::Deref => {
1744 let base_ty = proj.base.ty(self.mir, self.tcx).to_ty(self.tcx);
1746 // Check the kind of deref to decide
1748 ty::TyRef(_, tnm) => {
1750 // Shared borrowed data is never mutable
1751 hir::MutImmutable => Err(place),
1752 // Mutably borrowed data is mutable, but only if we have a
1753 // unique path to the `&mut`
1754 hir::MutMutable => {
1755 let mode = match self.is_upvar_field_projection(&proj.base)
1759 self.mir.upvar_decls[field.index()].by_ref
1762 is_local_mutation_allowed
1764 _ => LocalMutationIsAllowed::Yes,
1767 self.is_mutable(&proj.base, mode)
1771 ty::TyRawPtr(tnm) => {
1773 // `*const` raw pointers are not mutable
1774 hir::MutImmutable => return Err(place),
1775 // `*mut` raw pointers are always mutable, regardless of context
1776 // The users have to check by themselve.
1777 hir::MutMutable => return Ok(()),
1780 // `Box<T>` owns its content, so mutable if its location is mutable
1781 _ if base_ty.is_box() => {
1782 self.is_mutable(&proj.base, is_local_mutation_allowed)
1784 // Deref should only be for reference, pointers or boxes
1785 _ => bug!("Deref of unexpected type: {:?}", base_ty),
1788 // All other projections are owned by their base path, so mutable if
1789 // base path is mutable
1790 ProjectionElem::Field(..)
1791 | ProjectionElem::Index(..)
1792 | ProjectionElem::ConstantIndex { .. }
1793 | ProjectionElem::Subslice { .. }
1794 | ProjectionElem::Downcast(..) => {
1795 if let Some(field) = self.is_upvar_field_projection(place) {
1796 let decl = &self.mir.upvar_decls[field.index()];
1798 "decl.mutability={:?} local_mutation_is_allowed={:?} place={:?}",
1799 decl, is_local_mutation_allowed, place
1801 match (decl.mutability, is_local_mutation_allowed) {
1802 (Mutability::Not, LocalMutationIsAllowed::No)
1803 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
1806 (Mutability::Not, LocalMutationIsAllowed::Yes)
1807 | (Mutability::Mut, _) => {
1808 self.is_mutable(&proj.base, is_local_mutation_allowed)
1812 self.is_mutable(&proj.base, is_local_mutation_allowed)
1820 /// If this is a field projection, and the field is being projected from a closure type,
1821 /// then returns the index of the field being projected. Note that this closure will always
1822 /// be `self` in the current MIR, because that is the only time we directly access the fields
1823 /// of a closure type.
1824 fn is_upvar_field_projection(&self, place: &Place<'tcx>) -> Option<Field> {
1826 Place::Projection(ref proj) => match proj.elem {
1827 ProjectionElem::Field(field, _ty) => {
1828 let is_projection_from_ty_closure = proj.base
1829 .ty(self.mir, self.tcx)
1833 if is_projection_from_ty_closure {
1846 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
1847 enum NoMovePathFound {
1851 /// The degree of overlap between 2 places for borrow-checking.
1853 /// The places might partially overlap - in this case, we give
1854 /// up and say that they might conflict. This occurs when
1855 /// different fields of a union are borrowed. For example,
1856 /// if `u` is a union, we have no way of telling how disjoint
1857 /// `u.a.x` and `a.b.y` are.
1859 /// The places have the same type, and are either completely disjoint
1860 /// or equal - i.e. they can't "partially" overlap as can occur with
1861 /// unions. This is the "base case" on which we recur for extensions
1864 /// The places are disjoint, so we know all extensions of them
1865 /// will also be disjoint.
1869 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1870 // Given that the bases of `elem1` and `elem2` are always either equal
1871 // or disjoint (and have the same type!), return the overlap situation
1872 // between `elem1` and `elem2`.
1873 fn place_element_conflict(&self, elem1: &Place<'tcx>, elem2: &Place<'tcx>) -> Overlap {
1874 match (elem1, elem2) {
1875 (Place::Local(l1), Place::Local(l2)) => {
1877 // the same local - base case, equal
1878 debug!("place_element_conflict: DISJOINT-OR-EQ-LOCAL");
1879 Overlap::EqualOrDisjoint
1881 // different locals - base case, disjoint
1882 debug!("place_element_conflict: DISJOINT-LOCAL");
1886 (Place::Static(static1), Place::Static(static2)) => {
1887 if static1.def_id != static2.def_id {
1888 debug!("place_element_conflict: DISJOINT-STATIC");
1890 } else if self.tcx.is_static(static1.def_id) == Some(hir::Mutability::MutMutable) {
1891 // We ignore mutable statics - they can only be unsafe code.
1892 debug!("place_element_conflict: IGNORE-STATIC-MUT");
1895 debug!("place_element_conflict: DISJOINT-OR-EQ-STATIC");
1896 Overlap::EqualOrDisjoint
1899 (Place::Local(_), Place::Static(_)) | (Place::Static(_), Place::Local(_)) => {
1900 debug!("place_element_conflict: DISJOINT-STATIC-LOCAL");
1903 (Place::Projection(pi1), Place::Projection(pi2)) => {
1904 match (&pi1.elem, &pi2.elem) {
1905 (ProjectionElem::Deref, ProjectionElem::Deref) => {
1906 // derefs (e.g. `*x` vs. `*x`) - recur.
1907 debug!("place_element_conflict: DISJOINT-OR-EQ-DEREF");
1908 Overlap::EqualOrDisjoint
1910 (ProjectionElem::Field(f1, _), ProjectionElem::Field(f2, _)) => {
1912 // same field (e.g. `a.y` vs. `a.y`) - recur.
1913 debug!("place_element_conflict: DISJOINT-OR-EQ-FIELD");
1914 Overlap::EqualOrDisjoint
1916 let ty = pi1.base.ty(self.mir, self.tcx).to_ty(self.tcx);
1918 ty::TyAdt(def, _) if def.is_union() => {
1919 // Different fields of a union, we are basically stuck.
1920 debug!("place_element_conflict: STUCK-UNION");
1924 // Different fields of a struct (`a.x` vs. `a.y`). Disjoint!
1925 debug!("place_element_conflict: DISJOINT-FIELD");
1931 (ProjectionElem::Downcast(_, v1), ProjectionElem::Downcast(_, v2)) => {
1932 // different variants are treated as having disjoint fields,
1933 // even if they occupy the same "space", because it's
1934 // impossible for 2 variants of the same enum to exist
1935 // (and therefore, to be borrowed) at the same time.
1937 // Note that this is different from unions - we *do* allow
1938 // this code to compile:
1941 // fn foo(x: &mut Result<i32, i32>) {
1942 // let mut v = None;
1943 // if let Ok(ref mut a) = *x {
1946 // // here, you would *think* that the
1947 // // *entirety* of `x` would be borrowed,
1948 // // but in fact only the `Ok` variant is,
1949 // // so the `Err` variant is *entirely free*:
1950 // if let Err(ref mut a) = *x {
1957 debug!("place_element_conflict: DISJOINT-OR-EQ-FIELD");
1958 Overlap::EqualOrDisjoint
1960 debug!("place_element_conflict: DISJOINT-FIELD");
1964 (ProjectionElem::Index(..), ProjectionElem::Index(..))
1965 | (ProjectionElem::Index(..), ProjectionElem::ConstantIndex { .. })
1966 | (ProjectionElem::Index(..), ProjectionElem::Subslice { .. })
1967 | (ProjectionElem::ConstantIndex { .. }, ProjectionElem::Index(..))
1969 ProjectionElem::ConstantIndex { .. },
1970 ProjectionElem::ConstantIndex { .. },
1972 | (ProjectionElem::ConstantIndex { .. }, ProjectionElem::Subslice { .. })
1973 | (ProjectionElem::Subslice { .. }, ProjectionElem::Index(..))
1974 | (ProjectionElem::Subslice { .. }, ProjectionElem::ConstantIndex { .. })
1975 | (ProjectionElem::Subslice { .. }, ProjectionElem::Subslice { .. }) => {
1976 // Array indexes (`a[0]` vs. `a[i]`). These can either be disjoint
1977 // (if the indexes differ) or equal (if they are the same), so this
1978 // is the recursive case that gives "equal *or* disjoint" its meaning.
1980 // Note that by construction, MIR at borrowck can't subdivide
1981 // `Subslice` accesses (e.g. `a[2..3][i]` will never be present) - they
1982 // are only present in slice patterns, and we "merge together" nested
1983 // slice patterns. That means we don't have to think about these. It's
1984 // probably a good idea to assert this somewhere, but I'm too lazy.
1986 // FIXME(#8636) we might want to return Disjoint if
1987 // both projections are constant and disjoint.
1988 debug!("place_element_conflict: DISJOINT-OR-EQ-ARRAY");
1989 Overlap::EqualOrDisjoint
1992 (ProjectionElem::Deref, _)
1993 | (ProjectionElem::Field(..), _)
1994 | (ProjectionElem::Index(..), _)
1995 | (ProjectionElem::ConstantIndex { .. }, _)
1996 | (ProjectionElem::Subslice { .. }, _)
1997 | (ProjectionElem::Downcast(..), _) => bug!(
1998 "mismatched projections in place_element_conflict: {:?} and {:?}",
2004 (Place::Projection(_), _) | (_, Place::Projection(_)) => bug!(
2005 "unexpected elements in place_element_conflict: {:?} and {:?}",
2012 /// Returns whether an access of kind `access` to `access_place` conflicts with
2013 /// a borrow/full access to `borrow_place` (for deep accesses to mutable
2014 /// locations, this function is symmetric between `borrow_place` & `access_place`).
2017 borrow_place: &Place<'tcx>,
2018 access_place: &Place<'tcx>,
2019 access: ShallowOrDeep,
2022 "places_conflict({:?},{:?},{:?})",
2023 borrow_place, access_place, access
2026 // Return all the prefixes of `place` in reverse order, including
2028 fn place_elements<'a, 'tcx>(place: &'a Place<'tcx>) -> Vec<&'a Place<'tcx>> {
2029 let mut result = vec![];
2030 let mut place = place;
2034 Place::Projection(interior) => {
2035 place = &interior.base;
2037 Place::Local(_) | Place::Static(_) => {
2045 let borrow_components = place_elements(borrow_place);
2046 let access_components = place_elements(access_place);
2048 "places_conflict: components {:?} / {:?}",
2049 borrow_components, access_components
2052 let borrow_components = borrow_components
2055 .chain(iter::repeat(None));
2056 let access_components = access_components
2059 .chain(iter::repeat(None));
2060 // The borrowck rules for proving disjointness are applied from the "root" of the
2061 // borrow forwards, iterating over "similar" projections in lockstep until
2062 // we can prove overlap one way or another. Essentially, we treat `Overlap` as
2063 // a monoid and report a conflict if the product ends up not being `Disjoint`.
2065 // At each step, if we didn't run out of borrow or place, we know that our elements
2066 // have the same type, and that they only overlap if they are the identical.
2068 // For example, if we are comparing these:
2069 // BORROW: (*x1[2].y).z.a
2070 // ACCESS: (*x1[i].y).w.b
2072 // Then our steps are:
2073 // x1 | x1 -- places are the same
2074 // x1[2] | x1[i] -- equal or disjoint (disjoint if indexes differ)
2075 // x1[2].y | x1[i].y -- equal or disjoint
2076 // *x1[2].y | *x1[i].y -- equal or disjoint
2077 // (*x1[2].y).z | (*x1[i].y).w -- we are disjoint and don't need to check more!
2079 // Because `zip` does potentially bad things to the iterator inside, this loop
2080 // also handles the case where the access might be a *prefix* of the borrow, e.g.
2082 // BORROW: (*x1[2].y).z.a
2085 // Then our steps are:
2086 // x1 | x1 -- places are the same
2087 // x1[2] | x1[i] -- equal or disjoint (disjoint if indexes differ)
2088 // x1[2].y | x1[i].y -- equal or disjoint
2090 // -- here we run out of access - the borrow can access a part of it. If this
2091 // is a full deep access, then we *know* the borrow conflicts with it. However,
2092 // if the access is shallow, then we can proceed:
2094 // x1[2].y | (*x1[i].y) -- a deref! the access can't get past this, so we
2097 // Our invariant is, that at each step of the iteration:
2098 // - If we didn't run out of access to match, our borrow and access are comparable
2099 // and either equal or disjoint.
2100 // - If we did run out of accesss, the borrow can access a part of it.
2101 for (borrow_c, access_c) in borrow_components.zip(access_components) {
2102 // loop invariant: borrow_c is always either equal to access_c or disjoint from it.
2103 debug!("places_conflict: {:?} vs. {:?}", borrow_c, access_c);
2104 match (borrow_c, access_c) {
2106 // If we didn't run out of access, the borrow can access all of our
2107 // place (e.g. a borrow of `a.b` with an access to `a.b.c`),
2108 // so we have a conflict.
2110 // If we did, then we still know that the borrow can access a *part*
2111 // of our place that our access cares about (a borrow of `a.b.c`
2112 // with an access to `a.b`), so we still have a conflict.
2114 // FIXME: Differs from AST-borrowck; includes drive-by fix
2115 // to #38899. Will probably need back-compat mode flag.
2116 debug!("places_conflict: full borrow, CONFLICT");
2119 (Some(borrow_c), None) => {
2120 // We know that the borrow can access a part of our place. This
2121 // is a conflict if that is a part our access cares about.
2123 let (base, elem) = match borrow_c {
2124 Place::Projection(box Projection { base, elem }) => (base, elem),
2125 _ => bug!("place has no base?"),
2127 let base_ty = base.ty(self.mir, self.tcx).to_ty(self.tcx);
2129 match (elem, &base_ty.sty, access) {
2130 (_, _, Shallow(Some(ArtificialField::Discriminant)))
2131 | (_, _, Shallow(Some(ArtificialField::ArrayLength))) => {
2132 // The discriminant and array length are like
2133 // additional fields on the type; they do not
2134 // overlap any existing data there. Furthermore,
2135 // they cannot actually be a prefix of any
2136 // borrowed place (at least in MIR as it is
2139 // e.g. a (mutable) borrow of `a[5]` while we read the
2140 // array length of `a`.
2141 debug!("places_conflict: implicit field");
2145 (ProjectionElem::Deref, _, Shallow(None)) => {
2146 // e.g. a borrow of `*x.y` while we shallowly access `x.y` or some
2147 // prefix thereof - the shallow access can't touch anything behind
2149 debug!("places_conflict: shallow access behind ptr");
2153 ProjectionElem::Deref,
2158 mutbl: hir::MutImmutable,
2163 // the borrow goes through a dereference of a shared reference.
2165 // I'm not sure why we are tracking these borrows - shared
2166 // references can *always* be aliased, which means the
2167 // permission check already account for this borrow.
2168 debug!("places_conflict: behind a shared ref");
2172 (ProjectionElem::Deref, _, Deep)
2173 | (ProjectionElem::Field { .. }, _, _)
2174 | (ProjectionElem::Index { .. }, _, _)
2175 | (ProjectionElem::ConstantIndex { .. }, _, _)
2176 | (ProjectionElem::Subslice { .. }, _, _)
2177 | (ProjectionElem::Downcast { .. }, _, _) => {
2178 // Recursive case. This can still be disjoint on a
2179 // further iteration if this a shallow access and
2180 // there's a deref later on, e.g. a borrow
2181 // of `*x.y` while accessing `x`.
2185 (Some(borrow_c), Some(access_c)) => {
2186 match self.place_element_conflict(&borrow_c, access_c) {
2187 Overlap::Arbitrary => {
2188 // We have encountered different fields of potentially
2189 // the same union - the borrow now partially overlaps.
2191 // There is no *easy* way of comparing the fields
2192 // further on, because they might have different types
2193 // (e.g. borrows of `u.a.0` and `u.b.y` where `.0` and
2194 // `.y` come from different structs).
2196 // We could try to do some things here - e.g. count
2197 // dereferences - but that's probably not a good
2198 // idea, at least for now, so just give up and
2199 // report a conflict. This is unsafe code anyway so
2200 // the user could always use raw pointers.
2201 debug!("places_conflict: arbitrary -> conflict");
2204 Overlap::EqualOrDisjoint => {
2205 // This is the recursive case - proceed to the next element.
2207 Overlap::Disjoint => {
2208 // We have proven the borrow disjoint - further
2209 // projections will remain disjoint.
2210 debug!("places_conflict: disjoint");
2217 unreachable!("iter::repeat returned None")
2220 /// This function iterates over all of the current borrows
2221 /// (represented by 1-bits in `flow_state.borrows`) that conflict
2222 /// with an access to a place, invoking the `op` callback for each
2225 /// "Current borrow" here means a borrow that reaches the point in
2226 /// the control-flow where the access occurs.
2228 /// The borrow's phase is represented by the ReserveOrActivateIndex
2229 /// passed to the callback: one can call `is_reservation()` and
2230 /// `is_activation()` to determine what phase the borrow is
2231 /// currently in, when such distinction matters.
2232 fn each_borrow_involving_path<F>(
2235 access_place: (ShallowOrDeep, &Place<'tcx>),
2236 flow_state: &Flows<'cx, 'gcx, 'tcx>,
2239 F: FnMut(&mut Self, ReserveOrActivateIndex, &BorrowData<'tcx>) -> Control,
2241 let (access, place) = access_place;
2243 // FIXME: analogous code in check_loans first maps `place` to
2246 let data = flow_state.borrows.operator().borrows();
2248 // check for loan restricting path P being used. Accounts for
2249 // borrows of P, P.a.b, etc.
2250 let mut iter_incoming = flow_state.borrows.iter_incoming();
2251 while let Some(i) = iter_incoming.next() {
2252 let borrowed = &data[i.borrow_index()];
2254 if self.places_conflict(&borrowed.borrowed_place, place, access) {
2256 "each_borrow_involving_path: {:?} @ {:?} vs. {:?}/{:?}",
2257 i, borrowed, place, access
2259 let ctrl = op(self, i, borrowed);
2260 if ctrl == Control::Break {
2268 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
2269 // FIXME (#16118): function intended to allow the borrow checker
2270 // to be less precise in its handling of Box while still allowing
2271 // moves out of a Box. They should be removed when/if we stop
2272 // treating Box specially (e.g. when/if DerefMove is added...)
2274 fn base_path<'d>(&self, place: &'d Place<'tcx>) -> &'d Place<'tcx> {
2275 //! Returns the base of the leftmost (deepest) dereference of an
2276 //! Box in `place`. If there is no dereference of an Box
2277 //! in `place`, then it just returns `place` itself.
2279 let mut cursor = place;
2280 let mut deepest = place;
2282 let proj = match *cursor {
2283 Place::Local(..) | Place::Static(..) => return deepest,
2284 Place::Projection(ref proj) => proj,
2286 if proj.elem == ProjectionElem::Deref
2287 && place.ty(self.mir, self.tcx).to_ty(self.tcx).is_box()
2289 deepest = &proj.base;
2291 cursor = &proj.base;
2296 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2302 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2321 fn new(self, loc: Location) -> Context {