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::{self, 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::control_flow_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, MovePathIndex};
38 use dataflow::move_paths::{IllegalMoveOriginKind, MoveError};
39 use dataflow::Borrows;
40 use dataflow::DataflowResultsConsumer;
41 use dataflow::FlowAtLocation;
42 use dataflow::MoveDataParamEnv;
43 use dataflow::{do_dataflow, DebugFormatted};
44 use dataflow::{EverInitializedPlaces, MovingOutStatements};
45 use dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
46 use util::borrowck_errors::{BorrowckErrors, Origin};
47 use util::collect_writes::FindAssignments;
49 use self::borrow_set::{BorrowData, BorrowSet};
50 use self::flows::Flows;
51 use self::location::LocationTable;
52 use self::prefixes::PrefixSet;
53 use self::MutateMode::{JustWrite, WriteAndRead};
55 use self::path_utils::*;
68 pub fn provide(providers: &mut Providers) {
69 *providers = Providers {
75 fn mir_borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> BorrowCheckResult<'tcx> {
76 let input_mir = tcx.mir_validated(def_id);
77 debug!("run query mir_borrowck: {}", tcx.item_path_str(def_id));
81 // Return early if we are not supposed to use MIR borrow checker for this function.
82 return_early = !tcx.has_attr(def_id, "rustc_mir_borrowck") && !tcx.use_mir_borrowck();
84 if tcx.is_struct_constructor(def_id) {
85 // We are not borrow checking the automatically generated struct constructors
86 // because we want to accept structs such as this (taken from the `linked-hash-map`
89 // struct Qey<Q: ?Sized>(Q);
91 // MIR of this struct constructor looks something like this:
93 // fn Qey(_1: Q) -> Qey<Q>{
94 // let mut _0: Qey<Q>; // return place
97 // (_0.0: Q) = move _1; // bb0[0]: scope 0 at src/main.rs:1:1: 1:26
98 // return; // bb0[1]: scope 0 at src/main.rs:1:1: 1:26
102 // The problem here is that `(_0.0: Q) = move _1;` is valid only if `Q` is
103 // of statically known size, which is not known to be true because of the
104 // `Q: ?Sized` constraint. However, it is true because the constructor can be
105 // called only when `Q` is of statically known size.
110 return BorrowCheckResult {
111 closure_requirements: None,
112 used_mut_upvars: SmallVec::new(),
116 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
117 let input_mir: &Mir = &input_mir.borrow();
118 do_mir_borrowck(&infcx, input_mir, def_id)
120 debug!("mir_borrowck done");
125 fn do_mir_borrowck<'a, 'gcx, 'tcx>(
126 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
127 input_mir: &Mir<'gcx>,
129 ) -> BorrowCheckResult<'gcx> {
131 let attributes = tcx.get_attrs(def_id);
132 let param_env = tcx.param_env(def_id);
135 .as_local_node_id(def_id)
136 .expect("do_mir_borrowck: non-local DefId");
138 // Replace all regions with fresh inference variables. This
139 // requires first making our own copy of the MIR. This copy will
140 // be modified (in place) to contain non-lexical lifetimes. It
141 // will have a lifetime tied to the inference context.
142 let mut mir: Mir<'tcx> = input_mir.clone();
143 let free_regions = nll::replace_regions_in_mir(infcx, def_id, param_env, &mut mir);
144 let mir = &mir; // no further changes
145 let location_table = &LocationTable::new(mir);
147 let move_data: MoveData<'tcx> = match MoveData::gather_moves(mir, tcx) {
148 Ok(move_data) => move_data,
149 Err((move_data, move_errors)) => {
150 for move_error in move_errors {
151 let (span, kind): (Span, IllegalMoveOriginKind) = match move_error {
152 MoveError::UnionMove { .. } => {
153 unimplemented!("don't know how to report union move errors yet.")
155 MoveError::IllegalMove {
156 cannot_move_out_of: o,
157 } => (o.span, o.kind),
159 let origin = Origin::Mir;
160 let mut err = match kind {
161 IllegalMoveOriginKind::Static => {
162 tcx.cannot_move_out_of(span, "static item", origin)
164 IllegalMoveOriginKind::BorrowedContent { target_ty: ty } => {
165 // Inspect the type of the content behind the
166 // borrow to provide feedback about why this
167 // was a move rather than a copy.
169 ty::TyArray(..) | ty::TySlice(..) => {
170 tcx.cannot_move_out_of_interior_noncopy(span, ty, None, origin)
172 _ => tcx.cannot_move_out_of(span, "borrowed content", origin),
175 IllegalMoveOriginKind::InteriorOfTypeWithDestructor { container_ty: ty } => {
176 tcx.cannot_move_out_of_interior_of_drop(span, ty, origin)
178 IllegalMoveOriginKind::InteriorOfSliceOrArray { ty, is_index } => {
179 tcx.cannot_move_out_of_interior_noncopy(span, ty, Some(is_index), origin)
188 let mdpe = MoveDataParamEnv {
189 move_data: move_data,
190 param_env: param_env,
192 let body_id = match tcx.def_key(def_id).disambiguated_data.data {
193 DefPathData::StructCtor | DefPathData::EnumVariant(_) => None,
194 _ => Some(tcx.hir.body_owned_by(id)),
197 let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len());
198 let mut flow_inits = FlowAtLocation::new(do_dataflow(
204 MaybeInitializedPlaces::new(tcx, mir, &mdpe),
205 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
207 let flow_uninits = FlowAtLocation::new(do_dataflow(
213 MaybeUninitializedPlaces::new(tcx, mir, &mdpe),
214 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
216 let flow_move_outs = FlowAtLocation::new(do_dataflow(
222 MovingOutStatements::new(tcx, mir, &mdpe),
223 |bd, i| DebugFormatted::new(&bd.move_data().moves[i]),
225 let flow_ever_inits = FlowAtLocation::new(do_dataflow(
231 EverInitializedPlaces::new(tcx, mir, &mdpe),
232 |bd, i| DebugFormatted::new(&bd.move_data().inits[i]),
235 let borrow_set = Rc::new(BorrowSet::build(tcx, mir));
237 // If we are in non-lexical mode, compute the non-lexical lifetimes.
238 let (regioncx, polonius_output, opt_closure_req) = nll::compute_regions(
249 let regioncx = Rc::new(regioncx);
250 let flow_inits = flow_inits; // remove mut
252 let flow_borrows = FlowAtLocation::new(do_dataflow(
258 Borrows::new(tcx, mir, regioncx.clone(), def_id, body_id, &borrow_set),
259 |rs, i| DebugFormatted::new(&rs.location(i)),
262 let movable_generator = match tcx.hir.get(id) {
263 hir::map::Node::NodeExpr(&hir::Expr {
264 node: hir::ExprClosure(.., Some(hir::GeneratorMovability::Static)),
270 let dominators = mir.dominators();
272 let mut mbcx = MirBorrowckCtxt {
276 move_data: &mdpe.move_data,
277 param_env: param_env,
280 locals_are_invalidated_at_exit: match tcx.hir.body_owner_kind(id) {
281 hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => false,
282 hir::BodyOwnerKind::Fn => true,
284 access_place_error_reported: FxHashSet(),
285 reservation_error_reported: FxHashSet(),
286 moved_error_reported: FxHashSet(),
287 nonlexical_regioncx: regioncx,
288 used_mut: FxHashSet(),
289 used_mut_upvars: SmallVec::new(),
294 let mut state = Flows::new(
303 mbcx.analyze_results(&mut state); // entry point for DataflowResultsConsumer
305 // For each non-user used mutable variable, check if it's been assigned from
306 // a user-declared local. If so, then put that local into the used_mut set.
307 // Note that this set is expected to be small - only upvars from closures
308 // would have a chance of erroneously adding non-user-defined mutable vars
310 let temporary_used_locals: FxHashSet<Local> = mbcx
313 .filter(|&local| !mbcx.mir.local_decls[*local].is_user_variable.is_some())
316 mbcx.gather_used_muts(temporary_used_locals);
318 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
322 .mut_vars_and_args_iter()
323 .filter(|local| !mbcx.used_mut.contains(local))
325 if let ClearCrossCrate::Set(ref vsi) = mbcx.mir.source_scope_local_data {
326 let local_decl = &mbcx.mir.local_decls[local];
328 // Skip implicit `self` argument for closures
329 if local.index() == 1 && tcx.is_closure(mbcx.mir_def_id) {
333 // Skip over locals that begin with an underscore or have no name
334 match local_decl.name {
335 Some(name) => if name.as_str().starts_with("_") {
341 let span = local_decl.source_info.span;
342 let mut_span = tcx.sess.codemap().span_until_non_whitespace(span);
344 tcx.struct_span_lint_node(
346 vsi[local_decl.source_info.scope].lint_root,
348 "variable does not need to be mutable",
349 ).span_suggestion_short(mut_span, "remove this `mut`", "".to_owned())
355 closure_requirements: opt_closure_req,
356 used_mut_upvars: mbcx.used_mut_upvars,
361 pub struct MirBorrowckCtxt<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
362 tcx: TyCtxt<'cx, 'gcx, 'tcx>,
365 move_data: &'cx MoveData<'tcx>,
367 /// Map from MIR `Location` to `LocationIndex`; created
368 /// when MIR borrowck begins.
369 location_table: &'cx LocationTable,
371 param_env: ParamEnv<'gcx>,
372 movable_generator: bool,
373 /// This keeps track of whether local variables are free-ed when the function
374 /// exits even without a `StorageDead`, which appears to be the case for
377 /// I'm not sure this is the right approach - @eddyb could you try and
379 locals_are_invalidated_at_exit: bool,
380 /// This field keeps track of when borrow errors are reported in the access_place function
381 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
382 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
383 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
385 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
386 /// This field keeps track of when borrow conflict errors are reported
387 /// for reservations, so that we don't report seemingly duplicate
388 /// errors for corresponding activations
390 /// FIXME: Ideally this would be a set of BorrowIndex, not Places,
391 /// but it is currently inconvenient to track down the BorrowIndex
392 /// at the time we detect and report a reservation error.
393 reservation_error_reported: FxHashSet<Place<'tcx>>,
394 /// This field keeps track of errors reported in the checking of moved variables,
395 /// so that we don't report report seemingly duplicate errors.
396 moved_error_reported: FxHashSet<Place<'tcx>>,
397 /// This field keeps track of all the local variables that are declared mut and are mutated.
398 /// Used for the warning issued by an unused mutable local variable.
399 used_mut: FxHashSet<Local>,
400 /// If the function we're checking is a closure, then we'll need to report back the list of
401 /// mutable upvars that have been used. This field keeps track of them.
402 used_mut_upvars: SmallVec<[Field; 8]>,
403 /// Non-lexical region inference context, if NLL is enabled. This
404 /// contains the results from region inference and lets us e.g.
405 /// find out which CFG points are contained in each borrow region.
406 nonlexical_regioncx: Rc<RegionInferenceContext<'tcx>>,
408 /// The set of borrows extracted from the MIR
409 borrow_set: Rc<BorrowSet<'tcx>>,
411 /// Dominators for MIR
412 dominators: Dominators<BasicBlock>,
416 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
417 // 2. loans made in overlapping scopes do not conflict
418 // 3. assignments do not affect things loaned out as immutable
419 // 4. moves do not affect things loaned out in any way
420 impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
421 type FlowState = Flows<'cx, 'gcx, 'tcx>;
423 fn mir(&self) -> &'cx Mir<'tcx> {
427 fn visit_block_entry(&mut self, bb: BasicBlock, flow_state: &Self::FlowState) {
428 debug!("MirBorrowckCtxt::process_block({:?}): {}", bb, flow_state);
431 fn visit_statement_entry(
434 stmt: &Statement<'tcx>,
435 flow_state: &Self::FlowState,
438 "MirBorrowckCtxt::process_statement({:?}, {:?}): {}",
439 location, stmt, flow_state
441 let span = stmt.source_info.span;
443 self.check_activations(location, span, flow_state);
446 StatementKind::Assign(ref lhs, ref rhs) => {
448 ContextKind::AssignRhs.new(location),
455 ContextKind::AssignLhs.new(location),
462 StatementKind::ReadForMatch(ref place) => {
464 ContextKind::ReadForMatch.new(location),
466 (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
467 LocalMutationIsAllowed::No,
471 StatementKind::SetDiscriminant {
476 ContextKind::SetDiscrim.new(location),
478 Shallow(Some(ArtificialField::Discriminant)),
483 StatementKind::InlineAsm {
488 let context = ContextKind::InlineAsm.new(location);
489 for (o, output) in asm.outputs.iter().zip(outputs) {
491 // FIXME(eddyb) indirect inline asm outputs should
492 // be encoeded through MIR place derefs instead.
496 (Deep, Read(ReadKind::Copy)),
497 LocalMutationIsAllowed::No,
500 self.check_if_path_or_subpath_is_moved(
502 InitializationRequiringAction::Use,
510 if o.is_rw { Deep } else { Shallow(None) },
511 if o.is_rw { WriteAndRead } else { JustWrite },
516 for input in inputs {
517 self.consume_operand(context, (input, span), flow_state);
520 StatementKind::EndRegion(ref _rgn) => {
521 // ignored when consuming results (update to
522 // flow_state already handled).
525 | StatementKind::UserAssertTy(..)
526 | StatementKind::Validate(..)
527 | StatementKind::StorageLive(..) => {
528 // `Nop`, `UserAssertTy`, `Validate`, and `StorageLive` are irrelevant
531 StatementKind::StorageDead(local) => {
533 ContextKind::StorageDead.new(location),
534 (&Place::Local(local), span),
535 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
536 LocalMutationIsAllowed::Yes,
543 fn visit_terminator_entry(
546 term: &Terminator<'tcx>,
547 flow_state: &Self::FlowState,
551 "MirBorrowckCtxt::process_terminator({:?}, {:?}): {}",
552 location, term, flow_state
554 let span = term.source_info.span;
556 self.check_activations(location, span, flow_state);
559 TerminatorKind::SwitchInt {
565 self.consume_operand(ContextKind::SwitchInt.new(loc), (discr, span), flow_state);
567 TerminatorKind::Drop {
568 location: ref drop_place,
572 let gcx = self.tcx.global_tcx();
574 // Compute the type with accurate region information.
575 let drop_place_ty = drop_place.ty(self.mir, self.tcx);
577 // Erase the regions.
578 let drop_place_ty = self.tcx.erase_regions(&drop_place_ty).to_ty(self.tcx);
580 // "Lift" into the gcx -- once regions are erased, this type should be in the
581 // global arenas; this "lift" operation basically just asserts that is true, but
582 // that is useful later.
583 let drop_place_ty = gcx.lift(&drop_place_ty).unwrap();
585 self.visit_terminator_drop(loc, term, flow_state, drop_place, drop_place_ty, span);
587 TerminatorKind::DropAndReplace {
588 location: ref drop_place,
589 value: ref new_value,
594 ContextKind::DropAndReplace.new(loc),
600 self.consume_operand(
601 ContextKind::DropAndReplace.new(loc),
606 TerminatorKind::Call {
612 self.consume_operand(ContextKind::CallOperator.new(loc), (func, span), flow_state);
614 self.consume_operand(
615 ContextKind::CallOperand.new(loc),
620 if let Some((ref dest, _ /*bb*/)) = *destination {
622 ContextKind::CallDest.new(loc),
630 TerminatorKind::Assert {
637 self.consume_operand(ContextKind::Assert.new(loc), (cond, span), flow_state);
638 use rustc::mir::interpret::EvalErrorKind::BoundsCheck;
639 if let BoundsCheck { ref len, ref index } = *msg {
640 self.consume_operand(ContextKind::Assert.new(loc), (len, span), flow_state);
641 self.consume_operand(ContextKind::Assert.new(loc), (index, span), flow_state);
645 TerminatorKind::Yield {
650 self.consume_operand(ContextKind::Yield.new(loc), (value, span), flow_state);
652 if self.movable_generator {
653 // Look for any active borrows to locals
654 let borrow_set = self.borrow_set.clone();
655 flow_state.with_outgoing_borrows(|borrows| {
657 let borrow = &borrow_set[i];
658 self.check_for_local_borrow(borrow, span);
664 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
665 // Returning from the function implicitly kills storage for all locals and statics.
666 // Often, the storage will already have been killed by an explicit
667 // StorageDead, but we don't always emit those (notably on unwind paths),
668 // so this "extra check" serves as a kind of backup.
669 let borrow_set = self.borrow_set.clone();
670 flow_state.with_outgoing_borrows(|borrows| {
672 let borrow = &borrow_set[i];
673 let context = ContextKind::StorageDead.new(loc);
674 self.check_for_invalidation_at_exit(context, borrow, span);
678 TerminatorKind::Goto { target: _ }
679 | TerminatorKind::Abort
680 | TerminatorKind::Unreachable
681 | TerminatorKind::FalseEdges {
683 imaginary_targets: _,
685 | TerminatorKind::FalseUnwind {
689 // no data used, thus irrelevant to borrowck
695 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
701 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
702 use self::ShallowOrDeep::{Deep, Shallow};
704 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
705 enum ArtificialField {
710 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
712 /// From the RFC: "A *shallow* access means that the immediate
713 /// fields reached at P are accessed, but references or pointers
714 /// found within are not dereferenced. Right now, the only access
715 /// that is shallow is an assignment like `x = ...;`, which would
716 /// be a *shallow write* of `x`."
717 Shallow(Option<ArtificialField>),
719 /// From the RFC: "A *deep* access means that all data reachable
720 /// through the given place may be invalidated or accesses by
725 /// Kind of access to a value: read or write
726 /// (For informational purposes only)
727 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
729 /// From the RFC: "A *read* means that the existing data may be
730 /// read, but will not be changed."
733 /// From the RFC: "A *write* means that the data may be mutated to
734 /// new values or otherwise invalidated (for example, it could be
735 /// de-initialized, as in a move operation).
738 /// For two-phase borrows, we distinguish a reservation (which is treated
739 /// like a Read) from an activation (which is treated like a write), and
740 /// each of those is furthermore distinguished from Reads/Writes above.
741 Reservation(WriteKind),
742 Activation(WriteKind, BorrowIndex),
745 /// Kind of read access to a value
746 /// (For informational purposes only)
747 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
753 /// Kind of write access to a value
754 /// (For informational purposes only)
755 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
758 MutableBorrow(BorrowKind),
763 /// When checking permissions for a place access, this flag is used to indicate that an immutable
764 /// local place can be mutated.
766 /// FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
767 /// - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`
768 /// - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
769 /// `is_declared_mutable()`
770 /// - Take flow state into consideration in `is_assignable()` for local variables
771 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
772 enum LocalMutationIsAllowed {
774 /// We want use of immutable upvars to cause a "write to immutable upvar"
775 /// error, not an "reassignment" error.
780 struct AccessErrorsReported {
781 mutability_error: bool,
783 conflict_error: bool,
786 #[derive(Copy, Clone)]
787 enum InitializationRequiringAction {
794 struct RootPlace<'d, 'tcx: 'd> {
795 place: &'d Place<'tcx>,
796 is_local_mutation_allowed: LocalMutationIsAllowed,
799 impl InitializationRequiringAction {
800 fn as_noun(self) -> &'static str {
802 InitializationRequiringAction::Update => "update",
803 InitializationRequiringAction::Borrow => "borrow",
804 InitializationRequiringAction::Use => "use",
805 InitializationRequiringAction::Assignment => "assign",
809 fn as_verb_in_past_tense(self) -> &'static str {
811 InitializationRequiringAction::Update => "updated",
812 InitializationRequiringAction::Borrow => "borrowed",
813 InitializationRequiringAction::Use => "used",
814 InitializationRequiringAction::Assignment => "assigned",
819 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
820 /// Invokes `access_place` as appropriate for dropping the value
821 /// at `drop_place`. Note that the *actual* `Drop` in the MIR is
822 /// always for a variable (e.g., `Drop(x)`) -- but we recursively
823 /// break this variable down into subpaths (e.g., `Drop(x.foo)`)
824 /// to indicate more precisely which fields might actually be
825 /// accessed by a destructor.
826 fn visit_terminator_drop(
829 term: &Terminator<'tcx>,
830 flow_state: &Flows<'cx, 'gcx, 'tcx>,
831 drop_place: &Place<'tcx>,
832 erased_drop_place_ty: ty::Ty<'gcx>,
835 let gcx = self.tcx.global_tcx();
836 let drop_field = |mir: &mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>,
837 (index, field): (usize, ty::Ty<'gcx>)| {
838 let field_ty = gcx.normalize_erasing_regions(mir.param_env, field);
839 let place = drop_place.clone().field(Field::new(index), field_ty);
841 mir.visit_terminator_drop(loc, term, flow_state, &place, field_ty, span);
844 match erased_drop_place_ty.sty {
845 // When a struct is being dropped, we need to check
846 // whether it has a destructor, if it does, then we can
847 // call it, if it does not then we need to check the
848 // individual fields instead. This way if `foo` has a
849 // destructor but `bar` does not, we will only check for
850 // borrows of `x.foo` and not `x.bar`. See #47703.
851 ty::TyAdt(def, substs) if def.is_struct() && !def.has_dtor(self.tcx) => {
853 .map(|field| field.ty(gcx, substs))
855 .for_each(|field| drop_field(self, field));
857 // Same as above, but for tuples.
858 ty::TyTuple(tys) => {
862 .for_each(|field| drop_field(self, field));
864 // Closures also have disjoint fields, but they are only
865 // directly accessed in the body of the closure.
866 ty::TyClosure(def, substs)
867 if *drop_place == Place::Local(Local::new(1))
868 && !self.mir.upvar_decls.is_empty() =>
871 .upvar_tys(def, self.tcx)
873 .for_each(|field| drop_field(self, field));
875 // Generators also have disjoint fields, but they are only
876 // directly accessed in the body of the generator.
877 ty::TyGenerator(def, substs, _)
878 if *drop_place == Place::Local(Local::new(1))
879 && !self.mir.upvar_decls.is_empty() =>
882 .upvar_tys(def, self.tcx)
884 .for_each(|field| drop_field(self, field));
887 // We have now refined the type of the value being
888 // dropped (potentially) to just the type of a
889 // subfield; so check whether that field's type still
890 // "needs drop". If so, we assume that the destructor
891 // may access any data it likes (i.e., a Deep Write).
892 if erased_drop_place_ty.needs_drop(gcx, self.param_env) {
894 ContextKind::Drop.new(loc),
896 (Deep, Write(WriteKind::StorageDeadOrDrop)),
897 LocalMutationIsAllowed::Yes,
905 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
906 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
907 /// place is initialized and (b) it is not borrowed in some way that would prevent this
910 /// Returns true if an error is reported, false otherwise.
914 place_span: (&Place<'tcx>, Span),
915 kind: (ShallowOrDeep, ReadOrWrite),
916 is_local_mutation_allowed: LocalMutationIsAllowed,
917 flow_state: &Flows<'cx, 'gcx, 'tcx>,
918 ) -> AccessErrorsReported {
921 if let Activation(_, borrow_index) = rw {
922 if self.reservation_error_reported.contains(&place_span.0) {
924 "skipping access_place for activation of invalid reservation \
925 place: {:?} borrow_index: {:?}",
926 place_span.0, borrow_index
928 return AccessErrorsReported {
929 mutability_error: false,
930 conflict_error: true,
936 .access_place_error_reported
937 .contains(&(place_span.0.clone(), place_span.1))
940 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
943 return AccessErrorsReported {
944 mutability_error: false,
945 conflict_error: true,
949 let mutability_error =
950 self.check_access_permissions(place_span, rw, is_local_mutation_allowed, flow_state);
952 self.check_access_for_conflict(context, place_span, sd, rw, flow_state);
954 if conflict_error || mutability_error {
956 "access_place: logging error place_span=`{:?}` kind=`{:?}`",
959 self.access_place_error_reported
960 .insert((place_span.0.clone(), place_span.1));
963 AccessErrorsReported {
969 fn check_access_for_conflict(
972 place_span: (&Place<'tcx>, Span),
975 flow_state: &Flows<'cx, 'gcx, 'tcx>,
978 "check_access_for_conflict(context={:?}, place_span={:?}, sd={:?}, rw={:?})",
979 context, place_span, sd, rw,
982 let mut error_reported = false;
985 let location = self.location_table.start_index(context.loc);
986 let borrow_set = self.borrow_set.clone();
987 each_borrow_involving_path(
994 flow_state.borrows_in_scope(location),
995 |this, borrow_index, borrow| match (rw, borrow.kind) {
996 // Obviously an activation is compatible with its own
997 // reservation (or even prior activating uses of same
998 // borrow); so don't check if they interfere.
1000 // NOTE: *reservations* do conflict with themselves;
1001 // thus aren't injecting unsoundenss w/ this check.)
1002 (Activation(_, activating), _) if activating == borrow_index => {
1004 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1005 skipping {:?} b/c activation of same borrow_index",
1009 (borrow_index, borrow),
1014 (Read(_), BorrowKind::Shared) | (Reservation(..), BorrowKind::Shared) => {
1018 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
1019 // Reading from mere reservations of mutable-borrows is OK.
1020 if !is_active(&this.dominators, borrow, context.loc) {
1021 assert!(allow_two_phase_borrow(&this.tcx, borrow.kind));
1022 return Control::Continue;
1027 error_reported = true;
1028 this.report_use_while_mutably_borrowed(context, place_span, borrow)
1030 ReadKind::Borrow(bk) => {
1031 error_reported = true;
1032 this.report_conflicting_borrow(context, place_span, bk, &borrow)
1038 (Reservation(kind), BorrowKind::Unique)
1039 | (Reservation(kind), BorrowKind::Mut { .. })
1040 | (Activation(kind, _), _)
1041 | (Write(kind), _) => {
1045 "recording invalid reservation of \
1049 this.reservation_error_reported.insert(place_span.0.clone());
1051 Activation(_, activating) => {
1053 "observing check_place for activation of \
1054 borrow_index: {:?}",
1058 Read(..) | Write(..) => {}
1062 WriteKind::MutableBorrow(bk) => {
1063 error_reported = true;
1064 this.report_conflicting_borrow(context, place_span, bk, &borrow)
1066 WriteKind::StorageDeadOrDrop => {
1067 error_reported = true;
1068 this.report_borrowed_value_does_not_live_long_enough(
1075 WriteKind::Mutate => {
1076 error_reported = true;
1077 this.report_illegal_mutation_of_borrowed(context, place_span, borrow)
1079 WriteKind::Move => {
1080 error_reported = true;
1081 this.report_move_out_while_borrowed(context, place_span, &borrow)
1095 place_span: (&Place<'tcx>, Span),
1096 kind: ShallowOrDeep,
1098 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1100 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1102 MutateMode::WriteAndRead => {
1103 self.check_if_path_or_subpath_is_moved(
1105 InitializationRequiringAction::Update,
1110 MutateMode::JustWrite => {
1111 self.check_if_assigned_path_is_moved(context, place_span, flow_state);
1115 let errors_reported = self.access_place(
1118 (kind, Write(WriteKind::Mutate)),
1119 // We want immutable upvars to cause an "assignment to immutable var"
1120 // error, not an "reassignment of immutable var" error, because the
1121 // latter can't find a good previous assignment span.
1123 // There's probably a better way to do this.
1124 LocalMutationIsAllowed::ExceptUpvars,
1128 if !errors_reported.mutability_error {
1129 // check for reassignments to immutable local variables
1130 self.check_if_reassignment_to_immutable_state(context, place_span, flow_state);
1137 (rvalue, span): (&Rvalue<'tcx>, Span),
1138 _location: Location,
1139 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1142 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1143 let access_kind = match bk {
1144 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1145 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1146 let wk = WriteKind::MutableBorrow(bk);
1147 if allow_two_phase_borrow(&self.tcx, bk) {
1148 (Deep, Reservation(wk))
1159 LocalMutationIsAllowed::No,
1163 self.check_if_path_or_subpath_is_moved(
1165 InitializationRequiringAction::Borrow,
1171 Rvalue::Use(ref operand)
1172 | Rvalue::Repeat(ref operand, _)
1173 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1174 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1175 self.consume_operand(context, (operand, span), flow_state)
1178 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1179 let af = match *rvalue {
1180 Rvalue::Len(..) => ArtificialField::ArrayLength,
1181 Rvalue::Discriminant(..) => ArtificialField::Discriminant,
1182 _ => unreachable!(),
1187 (Shallow(Some(af)), Read(ReadKind::Copy)),
1188 LocalMutationIsAllowed::No,
1191 self.check_if_path_or_subpath_is_moved(
1193 InitializationRequiringAction::Use,
1199 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1200 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1201 self.consume_operand(context, (operand1, span), flow_state);
1202 self.consume_operand(context, (operand2, span), flow_state);
1205 Rvalue::NullaryOp(_op, _ty) => {
1206 // nullary ops take no dynamic input; no borrowck effect.
1208 // FIXME: is above actually true? Do we want to track
1209 // the fact that uninitialized data can be created via
1213 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1214 // We need to report back the list of mutable upvars that were
1215 // moved into the closure and subsequently used by the closure,
1216 // in order to populate our used_mut set.
1217 if let AggregateKind::Closure(def_id, _) = &**aggregate_kind {
1218 let BorrowCheckResult {
1220 } = self.tcx.mir_borrowck(*def_id);
1221 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1222 for field in used_mut_upvars {
1223 match operands[field.index()] {
1224 Operand::Move(Place::Local(local)) => {
1225 self.used_mut.insert(local);
1227 Operand::Move(ref place @ Place::Projection(_)) => {
1228 if let Some(field) = self.is_upvar_field_projection(place) {
1229 self.used_mut_upvars.push(field);
1232 Operand::Move(Place::Static(..))
1234 | Operand::Constant(..) => {}
1239 for operand in operands {
1240 self.consume_operand(context, (operand, span), flow_state);
1249 (operand, span): (&Operand<'tcx>, Span),
1250 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1253 Operand::Copy(ref place) => {
1254 // copy of place: check if this is "copy of frozen path"
1255 // (FIXME: see check_loans.rs)
1259 (Deep, Read(ReadKind::Copy)),
1260 LocalMutationIsAllowed::No,
1264 // Finally, check if path was already moved.
1265 self.check_if_path_or_subpath_is_moved(
1267 InitializationRequiringAction::Use,
1272 Operand::Move(ref place) => {
1273 // move of place: check if this is move of already borrowed path
1277 (Deep, Write(WriteKind::Move)),
1278 LocalMutationIsAllowed::Yes,
1282 // Finally, check if path was already moved.
1283 self.check_if_path_or_subpath_is_moved(
1285 InitializationRequiringAction::Use,
1290 Operand::Constant(_) => {}
1294 /// Returns whether a borrow of this place is invalidated when the function
1296 fn check_for_invalidation_at_exit(
1299 borrow: &BorrowData<'tcx>,
1302 debug!("check_for_invalidation_at_exit({:?})", borrow);
1303 let place = &borrow.borrowed_place;
1304 let root_place = self.prefixes(place, PrefixSet::All).last().unwrap();
1306 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1307 // we just know that all locals are dropped at function exit (otherwise
1308 // we'll have a memory leak) and assume that all statics have a destructor.
1310 // FIXME: allow thread-locals to borrow other thread locals?
1311 let (might_be_alive, will_be_dropped) = match root_place {
1312 Place::Static(statik) => {
1313 // Thread-locals might be dropped after the function exits, but
1314 // "true" statics will never be.
1315 let is_thread_local = self
1317 .get_attrs(statik.def_id)
1319 .any(|attr| attr.check_name("thread_local"));
1321 (true, is_thread_local)
1323 Place::Local(_) => {
1324 // Locals are always dropped at function exit, and if they
1325 // have a destructor it would've been called already.
1326 (false, self.locals_are_invalidated_at_exit)
1328 Place::Projection(..) => {
1329 bug!("root of {:?} is a projection ({:?})?", place, root_place)
1333 if !will_be_dropped {
1335 "place_is_invalidated_at_exit({:?}) - won't be dropped",
1341 // FIXME: replace this with a proper borrow_conflicts_with_place when
1343 let sd = if might_be_alive { Deep } else { Shallow(None) };
1345 if places_conflict(self.tcx, self.mir, place, root_place, sd) {
1346 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1347 // FIXME: should be talking about the region lifetime instead
1348 // of just a span here.
1349 let span = self.tcx.sess.codemap().end_point(span);
1350 self.report_borrowed_value_does_not_live_long_enough(
1359 /// Reports an error if this is a borrow of local data.
1360 /// This is called for all Yield statements on movable generators
1361 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1362 debug!("check_for_local_borrow({:?})", borrow);
1364 if borrow_of_local_data(&borrow.borrowed_place) {
1366 .cannot_borrow_across_generator_yield(
1367 self.retrieve_borrow_span(borrow),
1375 fn check_activations(
1379 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1381 if !self.tcx.two_phase_borrows() {
1385 // Two-phase borrow support: For each activation that is newly
1386 // generated at this statement, check if it interferes with
1388 let borrow_set = self.borrow_set.clone();
1389 for &borrow_index in borrow_set.activations_at_location(location) {
1390 let borrow = &borrow_set[borrow_index];
1392 // only mutable borrows should be 2-phase
1393 assert!(match borrow.kind {
1394 BorrowKind::Shared => false,
1395 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1399 ContextKind::Activation.new(location),
1400 (&borrow.borrowed_place, span),
1403 Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index),
1405 LocalMutationIsAllowed::No,
1408 // We do not need to call `check_if_path_or_subpath_is_moved`
1409 // again, as we already called it when we made the
1410 // initial reservation.
1415 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1416 fn check_if_reassignment_to_immutable_state(
1419 (place, span): (&Place<'tcx>, Span),
1420 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1422 debug!("check_if_reassignment_to_immutable_state({:?})", place);
1423 // determine if this path has a non-mut owner (and thus needs checking).
1424 let err_place = match self.is_mutable(place, LocalMutationIsAllowed::No) {
1426 Err(place) => place,
1429 "check_if_reassignment_to_immutable_state({:?}) - is an imm local",
1433 for i in flow_state.ever_inits.iter_incoming() {
1434 let init = self.move_data.inits[i];
1435 let init_place = &self.move_data.move_paths[init.path].place;
1436 if places_conflict(self.tcx, self.mir, &init_place, place, Deep) {
1437 self.report_illegal_reassignment(context, (place, span), init.span, err_place);
1443 fn check_if_full_path_is_moved(
1446 desired_action: InitializationRequiringAction,
1447 place_span: (&Place<'tcx>, Span),
1448 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1450 // FIXME: analogous code in check_loans first maps `place` to
1451 // its base_path ... but is that what we want here?
1452 let place = self.base_path(place_span.0);
1454 let maybe_uninits = &flow_state.uninits;
1455 let curr_move_outs = &flow_state.move_outs;
1459 // 1. Move of `a.b.c`, use of `a.b.c`
1460 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1461 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1462 // partial initialization support, one might have `a.x`
1463 // initialized but not `a.b`.
1467 // 4. Move of `a.b.c`, use of `a.b.d`
1468 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1469 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1470 // must have been initialized for the use to be sound.
1471 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1473 // The dataflow tracks shallow prefixes distinctly (that is,
1474 // field-accesses on P distinctly from P itself), in order to
1475 // track substructure initialization separately from the whole
1478 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1479 // which we have a MovePath is `a.b`, then that means that the
1480 // initialization state of `a.b` is all we need to inspect to
1481 // know if `a.b.c` is valid (and from that we infer that the
1482 // dereference and `.d` access is also valid, since we assume
1483 // `a.b.c` is assigned a reference to a initialized and
1484 // well-formed record structure.)
1486 // Therefore, if we seek out the *closest* prefix for which we
1487 // have a MovePath, that should capture the initialization
1488 // state for the place scenario.
1490 // This code covers scenarios 1, 2, and 3.
1492 debug!("check_if_full_path_is_moved place: {:?}", place);
1493 match self.move_path_closest_to(place) {
1495 if maybe_uninits.contains(&mpi) {
1496 self.report_use_of_moved_or_uninitialized(
1503 return; // don't bother finding other problems.
1506 Err(NoMovePathFound::ReachedStatic) => {
1507 // Okay: we do not build MoveData for static variables
1508 } // Only query longest prefix with a MovePath, not further
1509 // ancestors; dataflow recurs on children when parents
1510 // move (to support partial (re)inits).
1512 // (I.e. querying parents breaks scenario 7; but may want
1513 // to do such a query based on partial-init feature-gate.)
1517 fn check_if_path_or_subpath_is_moved(
1520 desired_action: InitializationRequiringAction,
1521 place_span: (&Place<'tcx>, Span),
1522 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1524 // FIXME: analogous code in check_loans first maps `place` to
1525 // its base_path ... but is that what we want here?
1526 let place = self.base_path(place_span.0);
1528 let maybe_uninits = &flow_state.uninits;
1529 let curr_move_outs = &flow_state.move_outs;
1533 // 1. Move of `a.b.c`, use of `a` or `a.b`
1534 // partial initialization support, one might have `a.x`
1535 // initialized but not `a.b`.
1536 // 2. All bad scenarios from `check_if_full_path_is_moved`
1540 // 3. Move of `a.b.c`, use of `a.b.d`
1541 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1542 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1543 // must have been initialized for the use to be sound.
1544 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1546 self.check_if_full_path_is_moved(context, desired_action, place_span, flow_state);
1548 // A move of any shallow suffix of `place` also interferes
1549 // with an attempt to use `place`. This is scenario 3 above.
1551 // (Distinct from handling of scenarios 1+2+4 above because
1552 // `place` does not interfere with suffixes of its prefixes,
1553 // e.g. `a.b.c` does not interfere with `a.b.d`)
1555 // This code covers scenario 1.
1557 debug!("check_if_path_or_subpath_is_moved place: {:?}", place);
1558 if let Some(mpi) = self.move_path_for_place(place) {
1559 if let Some(child_mpi) = maybe_uninits.has_any_child_of(mpi) {
1560 self.report_use_of_moved_or_uninitialized(
1567 return; // don't bother finding other problems.
1572 /// Currently MoveData does not store entries for all places in
1573 /// the input MIR. For example it will currently filter out
1574 /// places that are Copy; thus we do not track places of shared
1575 /// reference type. This routine will walk up a place along its
1576 /// prefixes, searching for a foundational place that *is*
1577 /// tracked in the MoveData.
1579 /// An Err result includes a tag indicated why the search failed.
1580 /// Currently this can only occur if the place is built off of a
1581 /// static variable, as we do not track those in the MoveData.
1582 fn move_path_closest_to(
1584 place: &Place<'tcx>,
1585 ) -> Result<MovePathIndex, NoMovePathFound> {
1586 let mut last_prefix = place;
1587 for prefix in self.prefixes(place, PrefixSet::All) {
1588 if let Some(mpi) = self.move_path_for_place(prefix) {
1591 last_prefix = prefix;
1593 match *last_prefix {
1594 Place::Local(_) => panic!("should have move path for every Local"),
1595 Place::Projection(_) => panic!("PrefixSet::All meant don't stop for Projection"),
1596 Place::Static(_) => return Err(NoMovePathFound::ReachedStatic),
1600 fn move_path_for_place(&mut self, place: &Place<'tcx>) -> Option<MovePathIndex> {
1601 // If returns None, then there is no move path corresponding
1602 // to a direct owner of `place` (which means there is nothing
1603 // that borrowck tracks for its analysis).
1605 match self.move_data.rev_lookup.find(place) {
1606 LookupResult::Parent(_) => None,
1607 LookupResult::Exact(mpi) => Some(mpi),
1611 fn check_if_assigned_path_is_moved(
1614 (place, span): (&Place<'tcx>, Span),
1615 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1617 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1618 // recur down place; dispatch to external checks when necessary
1619 let mut place = place;
1622 Place::Local(_) | Place::Static(_) => {
1623 // assigning to `x` does not require `x` be initialized.
1626 Place::Projection(ref proj) => {
1627 let Projection { ref base, ref elem } = **proj;
1629 ProjectionElem::Index(_/*operand*/) |
1630 ProjectionElem::ConstantIndex { .. } |
1631 // assigning to P[i] requires P to be valid.
1632 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1633 // assigning to (P->variant) is okay if assigning to `P` is okay
1635 // FIXME: is this true even if P is a adt with a dtor?
1638 // assigning to (*P) requires P to be initialized
1639 ProjectionElem::Deref => {
1640 self.check_if_full_path_is_moved(
1641 context, InitializationRequiringAction::Use,
1642 (base, span), flow_state);
1643 // (base initialized; no need to
1648 ProjectionElem::Subslice { .. } => {
1649 panic!("we don't allow assignments to subslices, context: {:?}",
1653 ProjectionElem::Field(..) => {
1654 // if type of `P` has a dtor, then
1655 // assigning to `P.f` requires `P` itself
1656 // be already initialized
1658 match base.ty(self.mir, tcx).to_ty(tcx).sty {
1659 ty::TyAdt(def, _) if def.has_dtor(tcx) => {
1661 // FIXME: analogous code in
1662 // check_loans.rs first maps
1663 // `base` to its base_path.
1665 self.check_if_path_or_subpath_is_moved(
1666 context, InitializationRequiringAction::Assignment,
1667 (base, span), flow_state);
1669 // (base initialized; no need to
1685 /// Check the permissions for the given place and read or write kind
1687 /// Returns true if an error is reported, false otherwise.
1688 fn check_access_permissions(
1690 (place, span): (&Place<'tcx>, Span),
1692 is_local_mutation_allowed: LocalMutationIsAllowed,
1693 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1696 "check_access_permissions({:?}, {:?}, {:?})",
1697 place, kind, is_local_mutation_allowed
1700 #[derive(Copy, Clone, Debug)]
1709 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1710 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1711 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1712 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1713 let is_local_mutation_allowed = match borrow_kind {
1714 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1715 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1716 BorrowKind::Shared => unreachable!(),
1718 match self.is_mutable(place, is_local_mutation_allowed) {
1720 self.add_used_mut(root_place, flow_state);
1724 error_access = AccessKind::MutableBorrow;
1725 the_place_err = place_err;
1729 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1730 match self.is_mutable(place, is_local_mutation_allowed) {
1732 self.add_used_mut(root_place, flow_state);
1736 error_access = AccessKind::Mutate;
1737 the_place_err = place_err;
1742 Reservation(WriteKind::Move)
1743 | Write(WriteKind::Move)
1744 | Reservation(WriteKind::StorageDeadOrDrop)
1745 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1746 | Write(WriteKind::StorageDeadOrDrop)
1747 | Write(WriteKind::MutableBorrow(BorrowKind::Shared)) => {
1748 if let Err(_place_err) = self.is_mutable(place, is_local_mutation_allowed) {
1749 self.tcx.sess.delay_span_bug(
1752 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1760 // permission checks are done at Reservation point.
1763 Read(ReadKind::Borrow(BorrowKind::Unique))
1764 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1765 | Read(ReadKind::Borrow(BorrowKind::Shared))
1766 | Read(ReadKind::Copy) => {
1767 // Access authorized
1772 // at this point, we have set up the error reporting state.
1775 let item_msg = match self.describe_place(place) {
1776 Some(name) => format!("immutable item `{}`", name),
1777 None => "immutable item".to_owned(),
1780 // `act` and `acted_on` are strings that let us abstract over
1781 // the verbs used in some diagnostic messages.
1785 match error_access {
1786 AccessKind::Mutate => {
1787 let item_msg = match the_place_err {
1788 Place::Projection(box Projection {
1790 elem: ProjectionElem::Deref,
1791 }) => match self.describe_place(place) {
1792 Some(description) => {
1793 format!("`{}` which is behind a `&` reference", description)
1795 None => format!("data in a `&` reference"),
1799 err = self.tcx.cannot_assign(span, &item_msg, Origin::Mir);
1801 acted_on = "written";
1803 AccessKind::MutableBorrow => {
1806 .cannot_borrow_path_as_mutable(span, &item_msg, Origin::Mir);
1807 act = "borrow as mutable";
1808 acted_on = "borrowed as mutable";
1812 match the_place_err {
1813 // We want to suggest users use `let mut` for local (user
1814 // variable) mutations...
1815 Place::Local(local) if self.mir.local_decls[*local].can_be_made_mutable() => {
1816 // ... but it doesn't make sense to suggest it on
1817 // variables that are `ref x`, `ref mut x`, `&self`,
1818 // or `&mut self` (such variables are simply not
1820 let local_decl = &self.mir.local_decls[*local];
1821 assert_eq!(local_decl.mutability, Mutability::Not);
1823 err.span_label(span, format!("cannot {ACT}", ACT = act));
1824 err.span_suggestion(
1825 local_decl.source_info.span,
1826 "consider changing this to be mutable",
1827 format!("mut {}", local_decl.name.unwrap()),
1831 // complete hack to approximate old AST-borrowck
1832 // diagnostic: if the span starts with a mutable borrow of
1833 // a local variable, then just suggest the user remove it.
1836 if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1837 snippet.starts_with("&mut ")
1843 err.span_label(span, format!("cannot {ACT}", ACT = act));
1844 err.span_label(span, "try removing `&mut` here");
1847 // We want to point out when a `&` can be readily replaced
1850 // FIXME: can this case be generalized to work for an
1851 // arbitrary base for the projection?
1852 Place::Projection(box Projection {
1853 base: Place::Local(local),
1854 elem: ProjectionElem::Deref,
1855 }) if self.mir.local_decls[*local].is_nonref_binding() =>
1857 let (err_help_span, suggested_code) =
1858 find_place_to_suggest_ampmut(self.tcx, self.mir, *local);
1859 err.span_suggestion(
1861 "consider changing this to be a mutable reference",
1865 let local_decl = &self.mir.local_decls[*local];
1866 if let Some(name) = local_decl.name {
1870 "`{NAME}` is a `&` reference, \
1871 so the data it refers to cannot be {ACTED_ON}",
1879 format!("cannot {ACT} through `&`-reference", ACT = act),
1885 err.span_label(span, format!("cannot {ACT}", ACT = act));
1892 // Returns the span to highlight and the associated text to
1893 // present when suggesting that the user use an `&mut`.
1895 // When we want to suggest a user change a local variable to be a `&mut`, there
1896 // are three potential "obvious" things to highlight:
1898 // let ident [: Type] [= RightHandSideExresssion];
1899 // ^^^^^ ^^^^ ^^^^^^^^^^^^^^^^^^^^^^^
1902 // We can always fallback on highlighting the first. But chances are good that
1903 // the user experience will be better if we highlight one of the others if possible;
1904 // for example, if the RHS is present and the Type is not, then the type is going to
1905 // be inferred *from* the RHS, which means we should highlight that (and suggest
1906 // that they borrow the RHS mutably).
1907 fn find_place_to_suggest_ampmut<'cx, 'gcx, 'tcx>(
1908 tcx: TyCtxt<'cx, 'gcx, 'tcx>,
1911 ) -> (Span, String) {
1912 // This implementation attempts to emulate AST-borrowck prioritization
1913 // by trying (3.), then (2.) and finally falling back on (1.).
1914 let locations = mir.find_assignments(local);
1915 if locations.len() > 0 {
1916 let assignment_rhs_span = mir.source_info(locations[0]).span;
1917 let snippet = tcx.sess.codemap().span_to_snippet(assignment_rhs_span);
1918 if let Ok(src) = snippet {
1919 // pnkfelix inherited code; believes intention is
1920 // highlighted text will always be `&<expr>` and
1921 // thus can transform to `&mut` by slicing off
1922 // first ASCII character and prepending "&mut ".
1923 let borrowed_expr = src[1..].to_string();
1924 return (assignment_rhs_span, format!("&mut {}", borrowed_expr));
1928 let local_decl = &mir.local_decls[local];
1929 let highlight_span = match local_decl.is_user_variable {
1930 // if this is a variable binding with an explicit type,
1931 // try to highlight that for the suggestion.
1932 Some(ClearCrossCrate::Set(mir::BindingForm::Var(mir::VarBindingForm {
1933 opt_ty_info: Some(ty_span),
1937 Some(ClearCrossCrate::Clear) => bug!("saw cleared local state"),
1939 // otherwise, just highlight the span associated with
1940 // the (MIR) LocalDecl.
1941 _ => local_decl.source_info.span,
1944 let ty_mut = local_decl.ty.builtin_deref(true).unwrap();
1945 assert_eq!(ty_mut.mutbl, hir::MutImmutable);
1946 return (highlight_span, format!("&mut {}", ty_mut.ty));
1950 /// Adds the place into the used mutable variables set
1951 fn add_used_mut<'d>(
1953 root_place: RootPlace<'d, 'tcx>,
1954 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1958 place: Place::Local(local),
1959 is_local_mutation_allowed,
1961 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes {
1962 // If the local may be initialized, and it is now currently being
1963 // mutated, then it is justified to be annotated with the `mut`
1964 // keyword, since the mutation may be a possible reassignment.
1965 let mpi = self.move_data.rev_lookup.find_local(*local);
1966 let ii = &self.move_data.init_path_map[mpi];
1968 if flow_state.ever_inits.contains(index) {
1969 self.used_mut.insert(*local);
1976 place: place @ Place::Projection(_),
1977 is_local_mutation_allowed: _,
1979 if let Some(field) = self.is_upvar_field_projection(&place) {
1980 self.used_mut_upvars.push(field);
1984 place: Place::Static(..),
1985 is_local_mutation_allowed: _,
1990 /// Whether this value be written or borrowed mutably.
1991 /// Returns the root place if the place passed in is a projection.
1994 place: &'d Place<'tcx>,
1995 is_local_mutation_allowed: LocalMutationIsAllowed,
1996 ) -> Result<RootPlace<'d, 'tcx>, &'d Place<'tcx>> {
1998 Place::Local(local) => {
1999 let local = &self.mir.local_decls[local];
2000 match local.mutability {
2001 Mutability::Not => match is_local_mutation_allowed {
2002 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2004 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2006 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2008 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2010 LocalMutationIsAllowed::No => Err(place),
2012 Mutability::Mut => Ok(RootPlace {
2014 is_local_mutation_allowed,
2018 Place::Static(ref static_) => {
2019 if self.tcx.is_static(static_.def_id) != Some(hir::Mutability::MutMutable) {
2024 is_local_mutation_allowed,
2028 Place::Projection(ref proj) => {
2030 ProjectionElem::Deref => {
2031 let base_ty = proj.base.ty(self.mir, self.tcx).to_ty(self.tcx);
2033 // Check the kind of deref to decide
2035 ty::TyRef(_, _, mutbl) => {
2037 // Shared borrowed data is never mutable
2038 hir::MutImmutable => Err(place),
2039 // Mutably borrowed data is mutable, but only if we have a
2040 // unique path to the `&mut`
2041 hir::MutMutable => {
2042 let mode = match self.is_upvar_field_projection(&proj.base)
2046 self.mir.upvar_decls[field.index()].by_ref
2049 is_local_mutation_allowed
2051 _ => LocalMutationIsAllowed::Yes,
2054 self.is_mutable(&proj.base, mode)
2058 ty::TyRawPtr(tnm) => {
2060 // `*const` raw pointers are not mutable
2061 hir::MutImmutable => return Err(place),
2062 // `*mut` raw pointers are always mutable, regardless of
2063 // context. The users have to check by themselves.
2064 hir::MutMutable => {
2065 return Ok(RootPlace {
2067 is_local_mutation_allowed,
2072 // `Box<T>` owns its content, so mutable if its location is mutable
2073 _ if base_ty.is_box() => {
2074 self.is_mutable(&proj.base, is_local_mutation_allowed)
2076 // Deref should only be for reference, pointers or boxes
2077 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2080 // All other projections are owned by their base path, so mutable if
2081 // base path is mutable
2082 ProjectionElem::Field(..)
2083 | ProjectionElem::Index(..)
2084 | ProjectionElem::ConstantIndex { .. }
2085 | ProjectionElem::Subslice { .. }
2086 | ProjectionElem::Downcast(..) => {
2087 if let Some(field) = self.is_upvar_field_projection(place) {
2088 let decl = &self.mir.upvar_decls[field.index()];
2090 "decl.mutability={:?} local_mutation_is_allowed={:?} place={:?}",
2091 decl, is_local_mutation_allowed, place
2093 match (decl.mutability, is_local_mutation_allowed) {
2094 (Mutability::Not, LocalMutationIsAllowed::No)
2095 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2098 (Mutability::Not, LocalMutationIsAllowed::Yes)
2099 | (Mutability::Mut, _) => {
2100 // Subtle: this is an upvar
2101 // reference, so it looks like
2102 // `self.foo` -- we want to double
2103 // check that the context `*self`
2104 // is mutable (i.e., this is not a
2105 // `Fn` closure). But if that
2106 // check succeeds, we want to
2107 // *blame* the mutability on
2108 // `place` (that is,
2109 // `self.foo`). This is used to
2110 // propagate the info about
2111 // whether mutability declarations
2112 // are used outwards, so that we register
2113 // the outer variable as mutable. Otherwise a
2114 // test like this fails to record the `mut`
2118 // fn foo<F: FnOnce()>(_f: F) { }
2120 // let var = Vec::new();
2126 let _ = self.is_mutable(&proj.base, is_local_mutation_allowed)?;
2129 is_local_mutation_allowed,
2134 self.is_mutable(&proj.base, is_local_mutation_allowed)
2142 /// If this is a field projection, and the field is being projected from a closure type,
2143 /// then returns the index of the field being projected. Note that this closure will always
2144 /// be `self` in the current MIR, because that is the only time we directly access the fields
2145 /// of a closure type.
2146 fn is_upvar_field_projection(&self, place: &Place<'tcx>) -> Option<Field> {
2148 Place::Projection(ref proj) => match proj.elem {
2149 ProjectionElem::Field(field, _ty) => {
2150 let is_projection_from_ty_closure = proj
2152 .ty(self.mir, self.tcx)
2156 if is_projection_from_ty_closure {
2169 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2170 enum NoMovePathFound {
2174 /// The degree of overlap between 2 places for borrow-checking.
2176 /// The places might partially overlap - in this case, we give
2177 /// up and say that they might conflict. This occurs when
2178 /// different fields of a union are borrowed. For example,
2179 /// if `u` is a union, we have no way of telling how disjoint
2180 /// `u.a.x` and `a.b.y` are.
2182 /// The places have the same type, and are either completely disjoint
2183 /// or equal - i.e. they can't "partially" overlap as can occur with
2184 /// unions. This is the "base case" on which we recur for extensions
2187 /// The places are disjoint, so we know all extensions of them
2188 /// will also be disjoint.
2192 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
2193 // FIXME (#16118): function intended to allow the borrow checker
2194 // to be less precise in its handling of Box while still allowing
2195 // moves out of a Box. They should be removed when/if we stop
2196 // treating Box specially (e.g. when/if DerefMove is added...)
2198 fn base_path<'d>(&self, place: &'d Place<'tcx>) -> &'d Place<'tcx> {
2199 //! Returns the base of the leftmost (deepest) dereference of an
2200 //! Box in `place`. If there is no dereference of an Box
2201 //! in `place`, then it just returns `place` itself.
2203 let mut cursor = place;
2204 let mut deepest = place;
2206 let proj = match *cursor {
2207 Place::Local(..) | Place::Static(..) => return deepest,
2208 Place::Projection(ref proj) => proj,
2210 if proj.elem == ProjectionElem::Deref
2211 && place.ty(self.mir, self.tcx).to_ty(self.tcx).is_box()
2213 deepest = &proj.base;
2215 cursor = &proj.base;
2220 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2226 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2246 fn new(self, loc: Location) -> Context {