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::RegionInferenceContext;
15 use rustc::hir::def_id::DefId;
16 use rustc::hir::map::definitions::DefPathData;
17 use rustc::infer::InferCtxt;
18 use rustc::lint::builtin::UNUSED_MUT;
19 use rustc::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
20 use rustc::mir::{ClearCrossCrate, Local, Location, Mir, Mutability, Operand, Place};
21 use rustc::mir::{Field, Projection, ProjectionElem, Rvalue, Statement, StatementKind};
22 use rustc::mir::{Terminator, TerminatorKind};
23 use rustc::ty::query::Providers;
24 use rustc::ty::{self, ParamEnv, TyCtxt};
26 use rustc_data_structures::graph::dominators::Dominators;
27 use rustc_data_structures::fx::FxHashSet;
28 use rustc_data_structures::indexed_set::IdxSetBuf;
29 use rustc_data_structures::indexed_vec::Idx;
30 use rustc_data_structures::small_vec::SmallVec;
36 use dataflow::indexes::BorrowIndex;
37 use dataflow::move_paths::{HasMoveData, LookupResult, MoveData, MoveError, MovePathIndex};
38 use dataflow::Borrows;
39 use dataflow::DataflowResultsConsumer;
40 use dataflow::FlowAtLocation;
41 use dataflow::MoveDataParamEnv;
42 use dataflow::{do_dataflow, DebugFormatted};
43 use dataflow::{EverInitializedPlaces, MovingOutStatements};
44 use dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
45 use util::borrowck_errors::{BorrowckErrors, Origin};
47 use self::borrow_set::{BorrowData, BorrowSet};
48 use self::flows::Flows;
49 use self::location::LocationTable;
50 use self::prefixes::PrefixSet;
51 use self::MutateMode::{JustWrite, WriteAndRead};
52 use self::mutability_errors::AccessKind;
54 use self::path_utils::*;
61 mod mutability_errors;
70 pub fn provide(providers: &mut Providers) {
71 *providers = Providers {
77 fn mir_borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> BorrowCheckResult<'tcx> {
78 let input_mir = tcx.mir_validated(def_id);
79 debug!("run query mir_borrowck: {}", tcx.item_path_str(def_id));
83 // Return early if we are not supposed to use MIR borrow checker for this function.
84 return_early = !tcx.has_attr(def_id, "rustc_mir") && !tcx.use_mir_borrowck();
86 if tcx.is_struct_constructor(def_id) {
87 // We are not borrow checking the automatically generated struct constructors
88 // because we want to accept structs such as this (taken from the `linked-hash-map`
91 // struct Qey<Q: ?Sized>(Q);
93 // MIR of this struct constructor looks something like this:
95 // fn Qey(_1: Q) -> Qey<Q>{
96 // let mut _0: Qey<Q>; // return place
99 // (_0.0: Q) = move _1; // bb0[0]: scope 0 at src/main.rs:1:1: 1:26
100 // return; // bb0[1]: scope 0 at src/main.rs:1:1: 1:26
104 // The problem here is that `(_0.0: Q) = move _1;` is valid only if `Q` is
105 // of statically known size, which is not known to be true because of the
106 // `Q: ?Sized` constraint. However, it is true because the constructor can be
107 // called only when `Q` is of statically known size.
112 return BorrowCheckResult {
113 closure_requirements: None,
114 used_mut_upvars: SmallVec::new(),
118 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
119 let input_mir: &Mir = &input_mir.borrow();
120 do_mir_borrowck(&infcx, input_mir, def_id)
122 debug!("mir_borrowck done");
127 fn do_mir_borrowck<'a, 'gcx, 'tcx>(
128 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
129 input_mir: &Mir<'gcx>,
131 ) -> BorrowCheckResult<'gcx> {
132 debug!("do_mir_borrowck(def_id = {:?})", def_id);
135 let attributes = tcx.get_attrs(def_id);
136 let param_env = tcx.param_env(def_id);
139 .as_local_node_id(def_id)
140 .expect("do_mir_borrowck: non-local DefId");
142 // Replace all regions with fresh inference variables. This
143 // requires first making our own copy of the MIR. This copy will
144 // be modified (in place) to contain non-lexical lifetimes. It
145 // will have a lifetime tied to the inference context.
146 let mut mir: Mir<'tcx> = input_mir.clone();
147 let free_regions = nll::replace_regions_in_mir(infcx, def_id, param_env, &mut mir);
148 let mir = &mir; // no further changes
149 let location_table = &LocationTable::new(mir);
151 let (move_data, move_errors): (MoveData<'tcx>, Option<Vec<MoveError<'tcx>>>) =
152 match MoveData::gather_moves(mir, tcx) {
153 Ok(move_data) => (move_data, None),
154 Err((move_data, move_errors)) => (move_data, Some(move_errors)),
157 let mdpe = MoveDataParamEnv {
158 move_data: move_data,
159 param_env: param_env,
161 let body_id = match tcx.def_key(def_id).disambiguated_data.data {
162 DefPathData::StructCtor | DefPathData::EnumVariant(_) => None,
163 _ => Some(tcx.hir.body_owned_by(id)),
166 let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len());
167 let mut flow_inits = FlowAtLocation::new(do_dataflow(
173 MaybeInitializedPlaces::new(tcx, mir, &mdpe),
174 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
176 let flow_uninits = FlowAtLocation::new(do_dataflow(
182 MaybeUninitializedPlaces::new(tcx, mir, &mdpe),
183 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
185 let flow_move_outs = FlowAtLocation::new(do_dataflow(
191 MovingOutStatements::new(tcx, mir, &mdpe),
192 |bd, i| DebugFormatted::new(&bd.move_data().moves[i]),
194 let flow_ever_inits = FlowAtLocation::new(do_dataflow(
200 EverInitializedPlaces::new(tcx, mir, &mdpe),
201 |bd, i| DebugFormatted::new(&bd.move_data().inits[i]),
204 let borrow_set = Rc::new(BorrowSet::build(tcx, mir));
206 // If we are in non-lexical mode, compute the non-lexical lifetimes.
207 let (regioncx, polonius_output, opt_closure_req) = nll::compute_regions(
218 let regioncx = Rc::new(regioncx);
219 let flow_inits = flow_inits; // remove mut
221 let flow_borrows = FlowAtLocation::new(do_dataflow(
227 Borrows::new(tcx, mir, regioncx.clone(), def_id, body_id, &borrow_set),
228 |rs, i| DebugFormatted::new(&rs.location(i)),
231 let movable_generator = match tcx.hir.get(id) {
232 hir::map::Node::NodeExpr(&hir::Expr {
233 node: hir::ExprKind::Closure(.., Some(hir::GeneratorMovability::Static)),
239 let dominators = mir.dominators();
241 let mut mbcx = MirBorrowckCtxt {
245 move_data: &mdpe.move_data,
246 param_env: param_env,
249 locals_are_invalidated_at_exit: match tcx.hir.body_owner_kind(id) {
250 hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => false,
251 hir::BodyOwnerKind::Fn => true,
253 access_place_error_reported: FxHashSet(),
254 reservation_error_reported: FxHashSet(),
255 moved_error_reported: FxHashSet(),
256 nonlexical_regioncx: regioncx,
257 used_mut: FxHashSet(),
258 used_mut_upvars: SmallVec::new(),
263 let mut state = Flows::new(
272 if let Some(errors) = move_errors {
273 mbcx.report_move_errors(errors);
275 mbcx.analyze_results(&mut state); // entry point for DataflowResultsConsumer
277 // For each non-user used mutable variable, check if it's been assigned from
278 // a user-declared local. If so, then put that local into the used_mut set.
279 // Note that this set is expected to be small - only upvars from closures
280 // would have a chance of erroneously adding non-user-defined mutable vars
282 let temporary_used_locals: FxHashSet<Local> = mbcx
285 .filter(|&local| !mbcx.mir.local_decls[*local].is_user_variable.is_some())
288 mbcx.gather_used_muts(temporary_used_locals);
290 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
294 .mut_vars_and_args_iter()
295 .filter(|local| !mbcx.used_mut.contains(local))
297 if let ClearCrossCrate::Set(ref vsi) = mbcx.mir.source_scope_local_data {
298 let local_decl = &mbcx.mir.local_decls[local];
300 // Skip implicit `self` argument for closures
301 if local.index() == 1 && tcx.is_closure(mbcx.mir_def_id) {
305 // Skip over locals that begin with an underscore or have no name
306 match local_decl.name {
307 Some(name) => if name.as_str().starts_with("_") {
313 let span = local_decl.source_info.span;
314 let mut_span = tcx.sess.codemap().span_until_non_whitespace(span);
316 tcx.struct_span_lint_node(
318 vsi[local_decl.source_info.scope].lint_root,
320 "variable does not need to be mutable",
321 ).span_suggestion_short(mut_span, "remove this `mut`", "".to_owned())
326 let result = BorrowCheckResult {
327 closure_requirements: opt_closure_req,
328 used_mut_upvars: mbcx.used_mut_upvars,
331 debug!("do_mir_borrowck: result = {:#?}", result);
337 pub struct MirBorrowckCtxt<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
338 tcx: TyCtxt<'cx, 'gcx, 'tcx>,
341 move_data: &'cx MoveData<'tcx>,
343 /// Map from MIR `Location` to `LocationIndex`; created
344 /// when MIR borrowck begins.
345 location_table: &'cx LocationTable,
347 param_env: ParamEnv<'gcx>,
348 movable_generator: bool,
349 /// This keeps track of whether local variables are free-ed when the function
350 /// exits even without a `StorageDead`, which appears to be the case for
353 /// I'm not sure this is the right approach - @eddyb could you try and
355 locals_are_invalidated_at_exit: bool,
356 /// This field keeps track of when borrow errors are reported in the access_place function
357 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
358 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
359 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
361 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
362 /// This field keeps track of when borrow conflict errors are reported
363 /// for reservations, so that we don't report seemingly duplicate
364 /// errors for corresponding activations
366 /// FIXME: Ideally this would be a set of BorrowIndex, not Places,
367 /// but it is currently inconvenient to track down the BorrowIndex
368 /// at the time we detect and report a reservation error.
369 reservation_error_reported: FxHashSet<Place<'tcx>>,
370 /// This field keeps track of errors reported in the checking of moved variables,
371 /// so that we don't report report seemingly duplicate errors.
372 moved_error_reported: FxHashSet<Place<'tcx>>,
373 /// This field keeps track of all the local variables that are declared mut and are mutated.
374 /// Used for the warning issued by an unused mutable local variable.
375 used_mut: FxHashSet<Local>,
376 /// If the function we're checking is a closure, then we'll need to report back the list of
377 /// mutable upvars that have been used. This field keeps track of them.
378 used_mut_upvars: SmallVec<[Field; 8]>,
379 /// Non-lexical region inference context, if NLL is enabled. This
380 /// contains the results from region inference and lets us e.g.
381 /// find out which CFG points are contained in each borrow region.
382 nonlexical_regioncx: Rc<RegionInferenceContext<'tcx>>,
384 /// The set of borrows extracted from the MIR
385 borrow_set: Rc<BorrowSet<'tcx>>,
387 /// Dominators for MIR
388 dominators: Dominators<BasicBlock>,
392 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
393 // 2. loans made in overlapping scopes do not conflict
394 // 3. assignments do not affect things loaned out as immutable
395 // 4. moves do not affect things loaned out in any way
396 impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
397 type FlowState = Flows<'cx, 'gcx, 'tcx>;
399 fn mir(&self) -> &'cx Mir<'tcx> {
403 fn visit_block_entry(&mut self, bb: BasicBlock, flow_state: &Self::FlowState) {
404 debug!("MirBorrowckCtxt::process_block({:?}): {}", bb, flow_state);
407 fn visit_statement_entry(
410 stmt: &Statement<'tcx>,
411 flow_state: &Self::FlowState,
414 "MirBorrowckCtxt::process_statement({:?}, {:?}): {}",
415 location, stmt, flow_state
417 let span = stmt.source_info.span;
419 self.check_activations(location, span, flow_state);
422 StatementKind::Assign(ref lhs, ref rhs) => {
424 ContextKind::AssignRhs.new(location),
431 ContextKind::AssignLhs.new(location),
438 StatementKind::ReadForMatch(ref place) => {
440 ContextKind::ReadForMatch.new(location),
442 (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
443 LocalMutationIsAllowed::No,
447 StatementKind::SetDiscriminant {
452 ContextKind::SetDiscrim.new(location),
454 Shallow(Some(ArtificialField::Discriminant)),
459 StatementKind::InlineAsm {
464 let context = ContextKind::InlineAsm.new(location);
465 for (o, output) in asm.outputs.iter().zip(outputs) {
467 // FIXME(eddyb) indirect inline asm outputs should
468 // be encoeded through MIR place derefs instead.
472 (Deep, Read(ReadKind::Copy)),
473 LocalMutationIsAllowed::No,
476 self.check_if_path_or_subpath_is_moved(
478 InitializationRequiringAction::Use,
486 if o.is_rw { Deep } else { Shallow(None) },
487 if o.is_rw { WriteAndRead } else { JustWrite },
492 for input in inputs {
493 self.consume_operand(context, (input, span), flow_state);
496 StatementKind::EndRegion(ref _rgn) => {
497 // ignored when consuming results (update to
498 // flow_state already handled).
501 | StatementKind::UserAssertTy(..)
502 | StatementKind::Validate(..)
503 | StatementKind::StorageLive(..) => {
504 // `Nop`, `UserAssertTy`, `Validate`, and `StorageLive` are irrelevant
507 StatementKind::StorageDead(local) => {
509 ContextKind::StorageDead.new(location),
510 (&Place::Local(local), span),
511 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
512 LocalMutationIsAllowed::Yes,
519 fn visit_terminator_entry(
522 term: &Terminator<'tcx>,
523 flow_state: &Self::FlowState,
527 "MirBorrowckCtxt::process_terminator({:?}, {:?}): {}",
528 location, term, flow_state
530 let span = term.source_info.span;
532 self.check_activations(location, span, flow_state);
535 TerminatorKind::SwitchInt {
541 self.consume_operand(ContextKind::SwitchInt.new(loc), (discr, span), flow_state);
543 TerminatorKind::Drop {
544 location: ref drop_place,
548 let gcx = self.tcx.global_tcx();
550 // Compute the type with accurate region information.
551 let drop_place_ty = drop_place.ty(self.mir, self.tcx);
553 // Erase the regions.
554 let drop_place_ty = self.tcx.erase_regions(&drop_place_ty).to_ty(self.tcx);
556 // "Lift" into the gcx -- once regions are erased, this type should be in the
557 // global arenas; this "lift" operation basically just asserts that is true, but
558 // that is useful later.
559 let drop_place_ty = gcx.lift(&drop_place_ty).unwrap();
561 self.visit_terminator_drop(loc, term, flow_state, drop_place, drop_place_ty, span);
563 TerminatorKind::DropAndReplace {
564 location: ref drop_place,
565 value: ref new_value,
570 ContextKind::DropAndReplace.new(loc),
576 self.consume_operand(
577 ContextKind::DropAndReplace.new(loc),
582 TerminatorKind::Call {
588 self.consume_operand(ContextKind::CallOperator.new(loc), (func, span), flow_state);
590 self.consume_operand(
591 ContextKind::CallOperand.new(loc),
596 if let Some((ref dest, _ /*bb*/)) = *destination {
598 ContextKind::CallDest.new(loc),
606 TerminatorKind::Assert {
613 self.consume_operand(ContextKind::Assert.new(loc), (cond, span), flow_state);
614 use rustc::mir::interpret::EvalErrorKind::BoundsCheck;
615 if let BoundsCheck { ref len, ref index } = *msg {
616 self.consume_operand(ContextKind::Assert.new(loc), (len, span), flow_state);
617 self.consume_operand(ContextKind::Assert.new(loc), (index, span), flow_state);
621 TerminatorKind::Yield {
626 self.consume_operand(ContextKind::Yield.new(loc), (value, span), flow_state);
628 if self.movable_generator {
629 // Look for any active borrows to locals
630 let borrow_set = self.borrow_set.clone();
631 flow_state.with_outgoing_borrows(|borrows| {
633 let borrow = &borrow_set[i];
634 self.check_for_local_borrow(borrow, span);
640 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
641 // Returning from the function implicitly kills storage for all locals and statics.
642 // Often, the storage will already have been killed by an explicit
643 // StorageDead, but we don't always emit those (notably on unwind paths),
644 // so this "extra check" serves as a kind of backup.
645 let borrow_set = self.borrow_set.clone();
646 flow_state.with_outgoing_borrows(|borrows| {
648 let borrow = &borrow_set[i];
649 let context = ContextKind::StorageDead.new(loc);
650 self.check_for_invalidation_at_exit(context, borrow, span);
654 TerminatorKind::Goto { target: _ }
655 | TerminatorKind::Abort
656 | TerminatorKind::Unreachable
657 | TerminatorKind::FalseEdges {
659 imaginary_targets: _,
661 | TerminatorKind::FalseUnwind {
665 // no data used, thus irrelevant to borrowck
671 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
677 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
678 use self::ShallowOrDeep::{Deep, Shallow};
680 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
681 enum ArtificialField {
686 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
688 /// From the RFC: "A *shallow* access means that the immediate
689 /// fields reached at P are accessed, but references or pointers
690 /// found within are not dereferenced. Right now, the only access
691 /// that is shallow is an assignment like `x = ...;`, which would
692 /// be a *shallow write* of `x`."
693 Shallow(Option<ArtificialField>),
695 /// From the RFC: "A *deep* access means that all data reachable
696 /// through the given place may be invalidated or accesses by
701 /// Kind of access to a value: read or write
702 /// (For informational purposes only)
703 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
705 /// From the RFC: "A *read* means that the existing data may be
706 /// read, but will not be changed."
709 /// From the RFC: "A *write* means that the data may be mutated to
710 /// new values or otherwise invalidated (for example, it could be
711 /// de-initialized, as in a move operation).
714 /// For two-phase borrows, we distinguish a reservation (which is treated
715 /// like a Read) from an activation (which is treated like a write), and
716 /// each of those is furthermore distinguished from Reads/Writes above.
717 Reservation(WriteKind),
718 Activation(WriteKind, BorrowIndex),
721 /// Kind of read access to a value
722 /// (For informational purposes only)
723 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
729 /// Kind of write access to a value
730 /// (For informational purposes only)
731 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
734 MutableBorrow(BorrowKind),
739 /// When checking permissions for a place access, this flag is used to indicate that an immutable
740 /// local place can be mutated.
742 /// FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
743 /// - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`
744 /// - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
745 /// `is_declared_mutable()`
746 /// - Take flow state into consideration in `is_assignable()` for local variables
747 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
748 enum LocalMutationIsAllowed {
750 /// We want use of immutable upvars to cause a "write to immutable upvar"
751 /// error, not an "reassignment" error.
756 struct AccessErrorsReported {
757 mutability_error: bool,
759 conflict_error: bool,
762 #[derive(Copy, Clone)]
763 enum InitializationRequiringAction {
770 struct RootPlace<'d, 'tcx: 'd> {
771 place: &'d Place<'tcx>,
772 is_local_mutation_allowed: LocalMutationIsAllowed,
775 impl InitializationRequiringAction {
776 fn as_noun(self) -> &'static str {
778 InitializationRequiringAction::Update => "update",
779 InitializationRequiringAction::Borrow => "borrow",
780 InitializationRequiringAction::Use => "use",
781 InitializationRequiringAction::Assignment => "assign",
785 fn as_verb_in_past_tense(self) -> &'static str {
787 InitializationRequiringAction::Update => "updated",
788 InitializationRequiringAction::Borrow => "borrowed",
789 InitializationRequiringAction::Use => "used",
790 InitializationRequiringAction::Assignment => "assigned",
795 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
796 /// Invokes `access_place` as appropriate for dropping the value
797 /// at `drop_place`. Note that the *actual* `Drop` in the MIR is
798 /// always for a variable (e.g., `Drop(x)`) -- but we recursively
799 /// break this variable down into subpaths (e.g., `Drop(x.foo)`)
800 /// to indicate more precisely which fields might actually be
801 /// accessed by a destructor.
802 fn visit_terminator_drop(
805 term: &Terminator<'tcx>,
806 flow_state: &Flows<'cx, 'gcx, 'tcx>,
807 drop_place: &Place<'tcx>,
808 erased_drop_place_ty: ty::Ty<'gcx>,
811 let gcx = self.tcx.global_tcx();
812 let drop_field = |mir: &mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>,
813 (index, field): (usize, ty::Ty<'gcx>)| {
814 let field_ty = gcx.normalize_erasing_regions(mir.param_env, field);
815 let place = drop_place.clone().field(Field::new(index), field_ty);
817 mir.visit_terminator_drop(loc, term, flow_state, &place, field_ty, span);
820 match erased_drop_place_ty.sty {
821 // When a struct is being dropped, we need to check
822 // whether it has a destructor, if it does, then we can
823 // call it, if it does not then we need to check the
824 // individual fields instead. This way if `foo` has a
825 // destructor but `bar` does not, we will only check for
826 // borrows of `x.foo` and not `x.bar`. See #47703.
827 ty::TyAdt(def, substs) if def.is_struct() && !def.has_dtor(self.tcx) => {
829 .map(|field| field.ty(gcx, substs))
831 .for_each(|field| drop_field(self, field));
833 // Same as above, but for tuples.
834 ty::TyTuple(tys) => {
838 .for_each(|field| drop_field(self, field));
840 // Closures also have disjoint fields, but they are only
841 // directly accessed in the body of the closure.
842 ty::TyClosure(def, substs)
843 if *drop_place == Place::Local(Local::new(1))
844 && !self.mir.upvar_decls.is_empty() =>
847 .upvar_tys(def, self.tcx)
849 .for_each(|field| drop_field(self, field));
851 // Generators also have disjoint fields, but they are only
852 // directly accessed in the body of the generator.
853 ty::TyGenerator(def, substs, _)
854 if *drop_place == Place::Local(Local::new(1))
855 && !self.mir.upvar_decls.is_empty() =>
858 .upvar_tys(def, self.tcx)
860 .for_each(|field| drop_field(self, field));
863 // We have now refined the type of the value being
864 // dropped (potentially) to just the type of a
865 // subfield; so check whether that field's type still
866 // "needs drop". If so, we assume that the destructor
867 // may access any data it likes (i.e., a Deep Write).
868 if erased_drop_place_ty.needs_drop(gcx, self.param_env) {
870 ContextKind::Drop.new(loc),
872 (Deep, Write(WriteKind::StorageDeadOrDrop)),
873 LocalMutationIsAllowed::Yes,
881 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
882 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
883 /// place is initialized and (b) it is not borrowed in some way that would prevent this
886 /// Returns true if an error is reported, false otherwise.
890 place_span: (&Place<'tcx>, Span),
891 kind: (ShallowOrDeep, ReadOrWrite),
892 is_local_mutation_allowed: LocalMutationIsAllowed,
893 flow_state: &Flows<'cx, 'gcx, 'tcx>,
894 ) -> AccessErrorsReported {
897 if let Activation(_, borrow_index) = rw {
898 if self.reservation_error_reported.contains(&place_span.0) {
900 "skipping access_place for activation of invalid reservation \
901 place: {:?} borrow_index: {:?}",
902 place_span.0, borrow_index
904 return AccessErrorsReported {
905 mutability_error: false,
906 conflict_error: true,
912 .access_place_error_reported
913 .contains(&(place_span.0.clone(), place_span.1))
916 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
919 return AccessErrorsReported {
920 mutability_error: false,
921 conflict_error: true,
925 let mutability_error =
926 self.check_access_permissions(
929 is_local_mutation_allowed,
934 self.check_access_for_conflict(context, place_span, sd, rw, flow_state);
936 if conflict_error || mutability_error {
938 "access_place: logging error place_span=`{:?}` kind=`{:?}`",
941 self.access_place_error_reported
942 .insert((place_span.0.clone(), place_span.1));
945 AccessErrorsReported {
951 fn check_access_for_conflict(
954 place_span: (&Place<'tcx>, Span),
957 flow_state: &Flows<'cx, 'gcx, 'tcx>,
960 "check_access_for_conflict(context={:?}, place_span={:?}, sd={:?}, rw={:?})",
961 context, place_span, sd, rw,
964 let mut error_reported = false;
967 let location = self.location_table.start_index(context.loc);
968 let borrow_set = self.borrow_set.clone();
969 each_borrow_involving_path(
976 flow_state.borrows_in_scope(location),
977 |this, borrow_index, borrow| match (rw, borrow.kind) {
978 // Obviously an activation is compatible with its own
979 // reservation (or even prior activating uses of same
980 // borrow); so don't check if they interfere.
982 // NOTE: *reservations* do conflict with themselves;
983 // thus aren't injecting unsoundenss w/ this check.)
984 (Activation(_, activating), _) if activating == borrow_index => {
986 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
987 skipping {:?} b/c activation of same borrow_index",
991 (borrow_index, borrow),
996 (Read(_), BorrowKind::Shared) | (Reservation(..), BorrowKind::Shared) => {
1000 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
1001 // Reading from mere reservations of mutable-borrows is OK.
1002 if !is_active(&this.dominators, borrow, context.loc) {
1003 assert!(allow_two_phase_borrow(&this.tcx, borrow.kind));
1004 return Control::Continue;
1009 error_reported = true;
1010 this.report_use_while_mutably_borrowed(context, place_span, borrow)
1012 ReadKind::Borrow(bk) => {
1013 error_reported = true;
1014 this.report_conflicting_borrow(context, place_span, bk, &borrow)
1020 (Reservation(kind), BorrowKind::Unique)
1021 | (Reservation(kind), BorrowKind::Mut { .. })
1022 | (Activation(kind, _), _)
1023 | (Write(kind), _) => {
1027 "recording invalid reservation of \
1031 this.reservation_error_reported.insert(place_span.0.clone());
1033 Activation(_, activating) => {
1035 "observing check_place for activation of \
1036 borrow_index: {:?}",
1040 Read(..) | Write(..) => {}
1044 WriteKind::MutableBorrow(bk) => {
1045 error_reported = true;
1046 this.report_conflicting_borrow(context, place_span, bk, &borrow)
1048 WriteKind::StorageDeadOrDrop => {
1049 error_reported = true;
1050 this.report_borrowed_value_does_not_live_long_enough(
1057 WriteKind::Mutate => {
1058 error_reported = true;
1059 this.report_illegal_mutation_of_borrowed(context, place_span, borrow)
1061 WriteKind::Move => {
1062 error_reported = true;
1063 this.report_move_out_while_borrowed(context, place_span, &borrow)
1077 place_span: (&Place<'tcx>, Span),
1078 kind: ShallowOrDeep,
1080 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1082 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1084 MutateMode::WriteAndRead => {
1085 self.check_if_path_or_subpath_is_moved(
1087 InitializationRequiringAction::Update,
1092 MutateMode::JustWrite => {
1093 self.check_if_assigned_path_is_moved(context, place_span, flow_state);
1097 let errors_reported = self.access_place(
1100 (kind, Write(WriteKind::Mutate)),
1101 // We want immutable upvars to cause an "assignment to immutable var"
1102 // error, not an "reassignment of immutable var" error, because the
1103 // latter can't find a good previous assignment span.
1105 // There's probably a better way to do this.
1106 LocalMutationIsAllowed::ExceptUpvars,
1110 if !errors_reported.mutability_error {
1111 // check for reassignments to immutable local variables
1112 self.check_if_reassignment_to_immutable_state(context, place_span, flow_state);
1119 (rvalue, span): (&Rvalue<'tcx>, Span),
1120 _location: Location,
1121 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1124 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1125 let access_kind = match bk {
1126 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1127 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1128 let wk = WriteKind::MutableBorrow(bk);
1129 if allow_two_phase_borrow(&self.tcx, bk) {
1130 (Deep, Reservation(wk))
1141 LocalMutationIsAllowed::No,
1145 self.check_if_path_or_subpath_is_moved(
1147 InitializationRequiringAction::Borrow,
1153 Rvalue::Use(ref operand)
1154 | Rvalue::Repeat(ref operand, _)
1155 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1156 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1157 self.consume_operand(context, (operand, span), flow_state)
1160 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1161 let af = match *rvalue {
1162 Rvalue::Len(..) => ArtificialField::ArrayLength,
1163 Rvalue::Discriminant(..) => ArtificialField::Discriminant,
1164 _ => unreachable!(),
1169 (Shallow(Some(af)), Read(ReadKind::Copy)),
1170 LocalMutationIsAllowed::No,
1173 self.check_if_path_or_subpath_is_moved(
1175 InitializationRequiringAction::Use,
1181 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1182 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1183 self.consume_operand(context, (operand1, span), flow_state);
1184 self.consume_operand(context, (operand2, span), flow_state);
1187 Rvalue::NullaryOp(_op, _ty) => {
1188 // nullary ops take no dynamic input; no borrowck effect.
1190 // FIXME: is above actually true? Do we want to track
1191 // the fact that uninitialized data can be created via
1195 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1196 // We need to report back the list of mutable upvars that were
1197 // moved into the closure and subsequently used by the closure,
1198 // in order to populate our used_mut set.
1199 match **aggregate_kind {
1200 AggregateKind::Closure(def_id, _)
1201 | AggregateKind::Generator(def_id, _, _) => {
1202 let BorrowCheckResult {
1204 } = self.tcx.mir_borrowck(def_id);
1205 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1206 for field in used_mut_upvars {
1207 // This relies on the current way that by-value
1208 // captures of a closure are copied/moved directly
1209 // when generating MIR.
1210 match operands[field.index()] {
1211 Operand::Move(Place::Local(local))
1212 | Operand::Copy(Place::Local(local)) => {
1213 self.used_mut.insert(local);
1215 Operand::Move(ref place @ Place::Projection(_))
1216 | Operand::Copy(ref place @ Place::Projection(_)) => {
1217 if let Some(field) = self.is_upvar_field_projection(place) {
1218 self.used_mut_upvars.push(field);
1221 Operand::Move(Place::Static(..))
1222 | Operand::Copy(Place::Static(..))
1223 | Operand::Constant(..) => {}
1227 AggregateKind::Adt(..)
1228 | AggregateKind::Array(..)
1229 | AggregateKind::Tuple { .. } => (),
1232 for operand in operands {
1233 self.consume_operand(context, (operand, span), flow_state);
1242 (operand, span): (&Operand<'tcx>, Span),
1243 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1246 Operand::Copy(ref place) => {
1247 // copy of place: check if this is "copy of frozen path"
1248 // (FIXME: see check_loans.rs)
1252 (Deep, Read(ReadKind::Copy)),
1253 LocalMutationIsAllowed::No,
1257 // Finally, check if path was already moved.
1258 self.check_if_path_or_subpath_is_moved(
1260 InitializationRequiringAction::Use,
1265 Operand::Move(ref place) => {
1266 // move of place: check if this is move of already borrowed path
1270 (Deep, Write(WriteKind::Move)),
1271 LocalMutationIsAllowed::Yes,
1275 // Finally, check if path was already moved.
1276 self.check_if_path_or_subpath_is_moved(
1278 InitializationRequiringAction::Use,
1283 Operand::Constant(_) => {}
1287 /// Returns whether a borrow of this place is invalidated when the function
1289 fn check_for_invalidation_at_exit(
1292 borrow: &BorrowData<'tcx>,
1295 debug!("check_for_invalidation_at_exit({:?})", borrow);
1296 let place = &borrow.borrowed_place;
1297 let root_place = self.prefixes(place, PrefixSet::All).last().unwrap();
1299 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1300 // we just know that all locals are dropped at function exit (otherwise
1301 // we'll have a memory leak) and assume that all statics have a destructor.
1303 // FIXME: allow thread-locals to borrow other thread locals?
1304 let (might_be_alive, will_be_dropped) = match root_place {
1305 Place::Static(statik) => {
1306 // Thread-locals might be dropped after the function exits, but
1307 // "true" statics will never be.
1308 let is_thread_local = self
1310 .get_attrs(statik.def_id)
1312 .any(|attr| attr.check_name("thread_local"));
1314 (true, is_thread_local)
1316 Place::Local(_) => {
1317 // Locals are always dropped at function exit, and if they
1318 // have a destructor it would've been called already.
1319 (false, self.locals_are_invalidated_at_exit)
1321 Place::Projection(..) => {
1322 bug!("root of {:?} is a projection ({:?})?", place, root_place)
1326 if !will_be_dropped {
1328 "place_is_invalidated_at_exit({:?}) - won't be dropped",
1334 // FIXME: replace this with a proper borrow_conflicts_with_place when
1336 let sd = if might_be_alive { Deep } else { Shallow(None) };
1338 if places_conflict::places_conflict(self.tcx, self.mir, place, root_place, sd) {
1339 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1340 // FIXME: should be talking about the region lifetime instead
1341 // of just a span here.
1342 let span = self.tcx.sess.codemap().end_point(span);
1343 self.report_borrowed_value_does_not_live_long_enough(
1352 /// Reports an error if this is a borrow of local data.
1353 /// This is called for all Yield statements on movable generators
1354 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1355 debug!("check_for_local_borrow({:?})", borrow);
1357 if borrow_of_local_data(&borrow.borrowed_place) {
1359 .cannot_borrow_across_generator_yield(
1360 self.retrieve_borrow_span(borrow),
1368 fn check_activations(
1372 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1374 if !self.tcx.two_phase_borrows() {
1378 // Two-phase borrow support: For each activation that is newly
1379 // generated at this statement, check if it interferes with
1381 let borrow_set = self.borrow_set.clone();
1382 for &borrow_index in borrow_set.activations_at_location(location) {
1383 let borrow = &borrow_set[borrow_index];
1385 // only mutable borrows should be 2-phase
1386 assert!(match borrow.kind {
1387 BorrowKind::Shared => false,
1388 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1392 ContextKind::Activation.new(location),
1393 (&borrow.borrowed_place, span),
1396 Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index),
1398 LocalMutationIsAllowed::No,
1401 // We do not need to call `check_if_path_or_subpath_is_moved`
1402 // again, as we already called it when we made the
1403 // initial reservation.
1408 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1409 fn check_if_reassignment_to_immutable_state(
1412 (place, span): (&Place<'tcx>, Span),
1413 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1415 debug!("check_if_reassignment_to_immutable_state({:?})", place);
1416 // determine if this path has a non-mut owner (and thus needs checking).
1417 let err_place = match self.is_mutable(place, LocalMutationIsAllowed::No) {
1419 Err(place) => place,
1422 "check_if_reassignment_to_immutable_state({:?}) - is an imm local",
1426 for i in flow_state.ever_inits.iter_incoming() {
1427 let init = self.move_data.inits[i];
1428 let init_place = &self.move_data.move_paths[init.path].place;
1429 if places_conflict::places_conflict(self.tcx, self.mir, &init_place, place, Deep) {
1430 self.report_illegal_reassignment(context, (place, span), init.span, err_place);
1436 fn check_if_full_path_is_moved(
1439 desired_action: InitializationRequiringAction,
1440 place_span: (&Place<'tcx>, Span),
1441 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1443 // FIXME: analogous code in check_loans first maps `place` to
1444 // its base_path ... but is that what we want here?
1445 let place = self.base_path(place_span.0);
1447 let maybe_uninits = &flow_state.uninits;
1448 let curr_move_outs = &flow_state.move_outs;
1452 // 1. Move of `a.b.c`, use of `a.b.c`
1453 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1454 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1455 // partial initialization support, one might have `a.x`
1456 // initialized but not `a.b`.
1460 // 4. Move of `a.b.c`, use of `a.b.d`
1461 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1462 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1463 // must have been initialized for the use to be sound.
1464 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1466 // The dataflow tracks shallow prefixes distinctly (that is,
1467 // field-accesses on P distinctly from P itself), in order to
1468 // track substructure initialization separately from the whole
1471 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1472 // which we have a MovePath is `a.b`, then that means that the
1473 // initialization state of `a.b` is all we need to inspect to
1474 // know if `a.b.c` is valid (and from that we infer that the
1475 // dereference and `.d` access is also valid, since we assume
1476 // `a.b.c` is assigned a reference to a initialized and
1477 // well-formed record structure.)
1479 // Therefore, if we seek out the *closest* prefix for which we
1480 // have a MovePath, that should capture the initialization
1481 // state for the place scenario.
1483 // This code covers scenarios 1, 2, and 3.
1485 debug!("check_if_full_path_is_moved place: {:?}", place);
1486 match self.move_path_closest_to(place) {
1488 if maybe_uninits.contains(&mpi) {
1489 self.report_use_of_moved_or_uninitialized(
1496 return; // don't bother finding other problems.
1499 Err(NoMovePathFound::ReachedStatic) => {
1500 // Okay: we do not build MoveData for static variables
1501 } // Only query longest prefix with a MovePath, not further
1502 // ancestors; dataflow recurs on children when parents
1503 // move (to support partial (re)inits).
1505 // (I.e. querying parents breaks scenario 7; but may want
1506 // to do such a query based on partial-init feature-gate.)
1510 fn check_if_path_or_subpath_is_moved(
1513 desired_action: InitializationRequiringAction,
1514 place_span: (&Place<'tcx>, Span),
1515 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1517 // FIXME: analogous code in check_loans first maps `place` to
1518 // its base_path ... but is that what we want here?
1519 let place = self.base_path(place_span.0);
1521 let maybe_uninits = &flow_state.uninits;
1522 let curr_move_outs = &flow_state.move_outs;
1526 // 1. Move of `a.b.c`, use of `a` or `a.b`
1527 // partial initialization support, one might have `a.x`
1528 // initialized but not `a.b`.
1529 // 2. All bad scenarios from `check_if_full_path_is_moved`
1533 // 3. Move of `a.b.c`, use of `a.b.d`
1534 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1535 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1536 // must have been initialized for the use to be sound.
1537 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1539 self.check_if_full_path_is_moved(context, desired_action, place_span, flow_state);
1541 // A move of any shallow suffix of `place` also interferes
1542 // with an attempt to use `place`. This is scenario 3 above.
1544 // (Distinct from handling of scenarios 1+2+4 above because
1545 // `place` does not interfere with suffixes of its prefixes,
1546 // e.g. `a.b.c` does not interfere with `a.b.d`)
1548 // This code covers scenario 1.
1550 debug!("check_if_path_or_subpath_is_moved place: {:?}", place);
1551 if let Some(mpi) = self.move_path_for_place(place) {
1552 if let Some(child_mpi) = maybe_uninits.has_any_child_of(mpi) {
1553 self.report_use_of_moved_or_uninitialized(
1560 return; // don't bother finding other problems.
1565 /// Currently MoveData does not store entries for all places in
1566 /// the input MIR. For example it will currently filter out
1567 /// places that are Copy; thus we do not track places of shared
1568 /// reference type. This routine will walk up a place along its
1569 /// prefixes, searching for a foundational place that *is*
1570 /// tracked in the MoveData.
1572 /// An Err result includes a tag indicated why the search failed.
1573 /// Currently this can only occur if the place is built off of a
1574 /// static variable, as we do not track those in the MoveData.
1575 fn move_path_closest_to(
1577 place: &Place<'tcx>,
1578 ) -> Result<MovePathIndex, NoMovePathFound> {
1579 let mut last_prefix = place;
1580 for prefix in self.prefixes(place, PrefixSet::All) {
1581 if let Some(mpi) = self.move_path_for_place(prefix) {
1584 last_prefix = prefix;
1586 match *last_prefix {
1587 Place::Local(_) => panic!("should have move path for every Local"),
1588 Place::Projection(_) => panic!("PrefixSet::All meant don't stop for Projection"),
1589 Place::Static(_) => return Err(NoMovePathFound::ReachedStatic),
1593 fn move_path_for_place(&mut self, place: &Place<'tcx>) -> Option<MovePathIndex> {
1594 // If returns None, then there is no move path corresponding
1595 // to a direct owner of `place` (which means there is nothing
1596 // that borrowck tracks for its analysis).
1598 match self.move_data.rev_lookup.find(place) {
1599 LookupResult::Parent(_) => None,
1600 LookupResult::Exact(mpi) => Some(mpi),
1604 fn check_if_assigned_path_is_moved(
1607 (place, span): (&Place<'tcx>, Span),
1608 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1610 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1611 // recur down place; dispatch to external checks when necessary
1612 let mut place = place;
1615 Place::Local(_) | Place::Static(_) => {
1616 // assigning to `x` does not require `x` be initialized.
1619 Place::Projection(ref proj) => {
1620 let Projection { ref base, ref elem } = **proj;
1622 ProjectionElem::Index(_/*operand*/) |
1623 ProjectionElem::ConstantIndex { .. } |
1624 // assigning to P[i] requires P to be valid.
1625 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1626 // assigning to (P->variant) is okay if assigning to `P` is okay
1628 // FIXME: is this true even if P is a adt with a dtor?
1631 // assigning to (*P) requires P to be initialized
1632 ProjectionElem::Deref => {
1633 self.check_if_full_path_is_moved(
1634 context, InitializationRequiringAction::Use,
1635 (base, span), flow_state);
1636 // (base initialized; no need to
1641 ProjectionElem::Subslice { .. } => {
1642 panic!("we don't allow assignments to subslices, context: {:?}",
1646 ProjectionElem::Field(..) => {
1647 // if type of `P` has a dtor, then
1648 // assigning to `P.f` requires `P` itself
1649 // be already initialized
1651 match base.ty(self.mir, tcx).to_ty(tcx).sty {
1652 ty::TyAdt(def, _) if def.has_dtor(tcx) => {
1654 // FIXME: analogous code in
1655 // check_loans.rs first maps
1656 // `base` to its base_path.
1658 self.check_if_path_or_subpath_is_moved(
1659 context, InitializationRequiringAction::Assignment,
1660 (base, span), flow_state);
1662 // (base initialized; no need to
1679 /// Check the permissions for the given place and read or write kind
1681 /// Returns true if an error is reported, false otherwise.
1682 fn check_access_permissions(
1684 (place, span): (&Place<'tcx>, Span),
1686 is_local_mutation_allowed: LocalMutationIsAllowed,
1687 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1691 "check_access_permissions({:?}, {:?}, {:?})",
1692 place, kind, is_local_mutation_allowed
1699 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1700 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1701 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1702 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1703 let is_local_mutation_allowed = match borrow_kind {
1704 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1705 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1706 BorrowKind::Shared => unreachable!(),
1708 match self.is_mutable(place, is_local_mutation_allowed) {
1710 self.add_used_mut(root_place, flow_state);
1714 error_access = AccessKind::MutableBorrow;
1715 the_place_err = place_err;
1719 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1720 match self.is_mutable(place, is_local_mutation_allowed) {
1722 self.add_used_mut(root_place, flow_state);
1726 error_access = AccessKind::Mutate;
1727 the_place_err = place_err;
1732 Reservation(WriteKind::Move)
1733 | Write(WriteKind::Move)
1734 | Reservation(WriteKind::StorageDeadOrDrop)
1735 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1736 | Write(WriteKind::StorageDeadOrDrop)
1737 | Write(WriteKind::MutableBorrow(BorrowKind::Shared)) => {
1738 if let Err(_place_err) = self.is_mutable(place, is_local_mutation_allowed) {
1739 self.tcx.sess.delay_span_bug(
1742 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1750 // permission checks are done at Reservation point.
1753 Read(ReadKind::Borrow(BorrowKind::Unique))
1754 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1755 | Read(ReadKind::Borrow(BorrowKind::Shared))
1756 | Read(ReadKind::Copy) => {
1757 // Access authorized
1762 // at this point, we have set up the error reporting state.
1763 self.report_mutability_error(
1773 /// Adds the place into the used mutable variables set
1774 fn add_used_mut<'d>(
1776 root_place: RootPlace<'d, 'tcx>,
1777 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1781 place: Place::Local(local),
1782 is_local_mutation_allowed,
1784 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes {
1785 // If the local may be initialized, and it is now currently being
1786 // mutated, then it is justified to be annotated with the `mut`
1787 // keyword, since the mutation may be a possible reassignment.
1788 let mpi = self.move_data.rev_lookup.find_local(*local);
1789 let ii = &self.move_data.init_path_map[mpi];
1791 if flow_state.ever_inits.contains(index) {
1792 self.used_mut.insert(*local);
1800 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
1803 place: place @ Place::Projection(_),
1804 is_local_mutation_allowed: _,
1806 if let Some(field) = self.is_upvar_field_projection(&place) {
1807 self.used_mut_upvars.push(field);
1811 place: Place::Static(..),
1812 is_local_mutation_allowed: _,
1817 /// Whether this value be written or borrowed mutably.
1818 /// Returns the root place if the place passed in is a projection.
1821 place: &'d Place<'tcx>,
1822 is_local_mutation_allowed: LocalMutationIsAllowed,
1823 ) -> Result<RootPlace<'d, 'tcx>, &'d Place<'tcx>> {
1825 Place::Local(local) => {
1826 let local = &self.mir.local_decls[local];
1827 match local.mutability {
1828 Mutability::Not => match is_local_mutation_allowed {
1829 LocalMutationIsAllowed::Yes => Ok(RootPlace {
1831 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
1833 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
1835 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
1837 LocalMutationIsAllowed::No => Err(place),
1839 Mutability::Mut => Ok(RootPlace {
1841 is_local_mutation_allowed,
1845 Place::Static(ref static_) => {
1846 if self.tcx.is_static(static_.def_id) != Some(hir::Mutability::MutMutable) {
1851 is_local_mutation_allowed,
1855 Place::Projection(ref proj) => {
1857 ProjectionElem::Deref => {
1858 let base_ty = proj.base.ty(self.mir, self.tcx).to_ty(self.tcx);
1860 // Check the kind of deref to decide
1862 ty::TyRef(_, _, mutbl) => {
1864 // Shared borrowed data is never mutable
1865 hir::MutImmutable => Err(place),
1866 // Mutably borrowed data is mutable, but only if we have a
1867 // unique path to the `&mut`
1868 hir::MutMutable => {
1869 let mode = match self.is_upvar_field_projection(&proj.base)
1873 self.mir.upvar_decls[field.index()].by_ref
1876 is_local_mutation_allowed
1878 _ => LocalMutationIsAllowed::Yes,
1881 self.is_mutable(&proj.base, mode)
1885 ty::TyRawPtr(tnm) => {
1887 // `*const` raw pointers are not mutable
1888 hir::MutImmutable => return Err(place),
1889 // `*mut` raw pointers are always mutable, regardless of
1890 // context. The users have to check by themselves.
1891 hir::MutMutable => {
1892 return Ok(RootPlace {
1894 is_local_mutation_allowed,
1899 // `Box<T>` owns its content, so mutable if its location is mutable
1900 _ if base_ty.is_box() => {
1901 self.is_mutable(&proj.base, is_local_mutation_allowed)
1903 // Deref should only be for reference, pointers or boxes
1904 _ => bug!("Deref of unexpected type: {:?}", base_ty),
1907 // All other projections are owned by their base path, so mutable if
1908 // base path is mutable
1909 ProjectionElem::Field(..)
1910 | ProjectionElem::Index(..)
1911 | ProjectionElem::ConstantIndex { .. }
1912 | ProjectionElem::Subslice { .. }
1913 | ProjectionElem::Downcast(..) => {
1914 if let Some(field) = self.is_upvar_field_projection(place) {
1915 let decl = &self.mir.upvar_decls[field.index()];
1917 "decl.mutability={:?} local_mutation_is_allowed={:?} place={:?}",
1918 decl, is_local_mutation_allowed, place
1920 match (decl.mutability, is_local_mutation_allowed) {
1921 (Mutability::Not, LocalMutationIsAllowed::No)
1922 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
1925 (Mutability::Not, LocalMutationIsAllowed::Yes)
1926 | (Mutability::Mut, _) => {
1927 // Subtle: this is an upvar
1928 // reference, so it looks like
1929 // `self.foo` -- we want to double
1930 // check that the context `*self`
1931 // is mutable (i.e., this is not a
1932 // `Fn` closure). But if that
1933 // check succeeds, we want to
1934 // *blame* the mutability on
1935 // `place` (that is,
1936 // `self.foo`). This is used to
1937 // propagate the info about
1938 // whether mutability declarations
1939 // are used outwards, so that we register
1940 // the outer variable as mutable. Otherwise a
1941 // test like this fails to record the `mut`
1945 // fn foo<F: FnOnce()>(_f: F) { }
1947 // let var = Vec::new();
1953 let _ = self.is_mutable(&proj.base, is_local_mutation_allowed)?;
1956 is_local_mutation_allowed,
1961 self.is_mutable(&proj.base, is_local_mutation_allowed)
1969 /// If this is a field projection, and the field is being projected from a closure type,
1970 /// then returns the index of the field being projected. Note that this closure will always
1971 /// be `self` in the current MIR, because that is the only time we directly access the fields
1972 /// of a closure type.
1973 fn is_upvar_field_projection(&self, place: &Place<'tcx>) -> Option<Field> {
1975 Place::Projection(ref proj) => match proj.elem {
1976 ProjectionElem::Field(field, _ty) => {
1977 let base_ty = proj.base.ty(self.mir, self.tcx).to_ty(self.tcx);
1979 if base_ty.is_closure() || base_ty.is_generator() {
1992 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
1993 enum NoMovePathFound {
1997 /// The degree of overlap between 2 places for borrow-checking.
1999 /// The places might partially overlap - in this case, we give
2000 /// up and say that they might conflict. This occurs when
2001 /// different fields of a union are borrowed. For example,
2002 /// if `u` is a union, we have no way of telling how disjoint
2003 /// `u.a.x` and `a.b.y` are.
2005 /// The places have the same type, and are either completely disjoint
2006 /// or equal - i.e. they can't "partially" overlap as can occur with
2007 /// unions. This is the "base case" on which we recur for extensions
2010 /// The places are disjoint, so we know all extensions of them
2011 /// will also be disjoint.
2015 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
2016 // FIXME (#16118): function intended to allow the borrow checker
2017 // to be less precise in its handling of Box while still allowing
2018 // moves out of a Box. They should be removed when/if we stop
2019 // treating Box specially (e.g. when/if DerefMove is added...)
2021 fn base_path<'d>(&self, place: &'d Place<'tcx>) -> &'d Place<'tcx> {
2022 //! Returns the base of the leftmost (deepest) dereference of an
2023 //! Box in `place`. If there is no dereference of an Box
2024 //! in `place`, then it just returns `place` itself.
2026 let mut cursor = place;
2027 let mut deepest = place;
2029 let proj = match *cursor {
2030 Place::Local(..) | Place::Static(..) => return deepest,
2031 Place::Projection(ref proj) => proj,
2033 if proj.elem == ProjectionElem::Deref
2034 && place.ty(self.mir, self.tcx).to_ty(self.tcx).is_box()
2036 deepest = &proj.base;
2038 cursor = &proj.base;
2043 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2049 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2069 fn new(self, loc: Location) -> Context {