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::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::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};
46 use util::collect_writes::FindAssignments;
48 use self::borrow_set::{BorrowData, BorrowSet};
49 use self::flows::Flows;
50 use self::location::LocationTable;
51 use self::prefixes::PrefixSet;
52 use self::MutateMode::{JustWrite, WriteAndRead};
54 use self::path_utils::*;
69 pub fn provide(providers: &mut Providers) {
70 *providers = Providers {
76 fn mir_borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> BorrowCheckResult<'tcx> {
77 let input_mir = tcx.mir_validated(def_id);
78 debug!("run query mir_borrowck: {}", tcx.item_path_str(def_id));
82 // Return early if we are not supposed to use MIR borrow checker for this function.
83 return_early = !tcx.has_attr(def_id, "rustc_mir") && !tcx.use_mir_borrowck();
85 if tcx.is_struct_constructor(def_id) {
86 // We are not borrow checking the automatically generated struct constructors
87 // because we want to accept structs such as this (taken from the `linked-hash-map`
90 // struct Qey<Q: ?Sized>(Q);
92 // MIR of this struct constructor looks something like this:
94 // fn Qey(_1: Q) -> Qey<Q>{
95 // let mut _0: Qey<Q>; // return place
98 // (_0.0: Q) = move _1; // bb0[0]: scope 0 at src/main.rs:1:1: 1:26
99 // return; // bb0[1]: scope 0 at src/main.rs:1:1: 1:26
103 // The problem here is that `(_0.0: Q) = move _1;` is valid only if `Q` is
104 // of statically known size, which is not known to be true because of the
105 // `Q: ?Sized` constraint. However, it is true because the constructor can be
106 // called only when `Q` is of statically known size.
111 return BorrowCheckResult {
112 closure_requirements: None,
113 used_mut_upvars: SmallVec::new(),
117 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
118 let input_mir: &Mir = &input_mir.borrow();
119 do_mir_borrowck(&infcx, input_mir, def_id)
121 debug!("mir_borrowck done");
126 fn do_mir_borrowck<'a, 'gcx, 'tcx>(
127 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
128 input_mir: &Mir<'gcx>,
130 ) -> BorrowCheckResult<'gcx> {
131 debug!("do_mir_borrowck(def_id = {:?})", def_id);
134 let attributes = tcx.get_attrs(def_id);
135 let param_env = tcx.param_env(def_id);
138 .as_local_node_id(def_id)
139 .expect("do_mir_borrowck: non-local DefId");
141 // Replace all regions with fresh inference variables. This
142 // requires first making our own copy of the MIR. This copy will
143 // be modified (in place) to contain non-lexical lifetimes. It
144 // will have a lifetime tied to the inference context.
145 let mut mir: Mir<'tcx> = input_mir.clone();
146 let free_regions = nll::replace_regions_in_mir(infcx, def_id, param_env, &mut mir);
147 let mir = &mir; // no further changes
148 let location_table = &LocationTable::new(mir);
150 let move_data: MoveData<'tcx> = match MoveData::gather_moves(mir, tcx) {
151 Ok(move_data) => move_data,
152 Err((move_data, move_errors)) => {
153 move_errors::report_move_errors(&mir, tcx, move_errors, &move_data);
158 let mdpe = MoveDataParamEnv {
159 move_data: move_data,
160 param_env: param_env,
162 let body_id = match tcx.def_key(def_id).disambiguated_data.data {
163 DefPathData::StructCtor | DefPathData::EnumVariant(_) => None,
164 _ => Some(tcx.hir.body_owned_by(id)),
167 let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len());
168 let mut flow_inits = FlowAtLocation::new(do_dataflow(
174 MaybeInitializedPlaces::new(tcx, mir, &mdpe),
175 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
177 let flow_uninits = FlowAtLocation::new(do_dataflow(
183 MaybeUninitializedPlaces::new(tcx, mir, &mdpe),
184 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
186 let flow_move_outs = FlowAtLocation::new(do_dataflow(
192 MovingOutStatements::new(tcx, mir, &mdpe),
193 |bd, i| DebugFormatted::new(&bd.move_data().moves[i]),
195 let flow_ever_inits = FlowAtLocation::new(do_dataflow(
201 EverInitializedPlaces::new(tcx, mir, &mdpe),
202 |bd, i| DebugFormatted::new(&bd.move_data().inits[i]),
205 let borrow_set = Rc::new(BorrowSet::build(tcx, mir));
207 // If we are in non-lexical mode, compute the non-lexical lifetimes.
208 let (regioncx, polonius_output, opt_closure_req) = nll::compute_regions(
219 let regioncx = Rc::new(regioncx);
220 let flow_inits = flow_inits; // remove mut
222 let flow_borrows = FlowAtLocation::new(do_dataflow(
228 Borrows::new(tcx, mir, regioncx.clone(), def_id, body_id, &borrow_set),
229 |rs, i| DebugFormatted::new(&rs.location(i)),
232 let movable_generator = match tcx.hir.get(id) {
233 hir::map::Node::NodeExpr(&hir::Expr {
234 node: hir::ExprClosure(.., Some(hir::GeneratorMovability::Static)),
240 let dominators = mir.dominators();
242 let mut mbcx = MirBorrowckCtxt {
246 move_data: &mdpe.move_data,
247 param_env: param_env,
250 locals_are_invalidated_at_exit: match tcx.hir.body_owner_kind(id) {
251 hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => false,
252 hir::BodyOwnerKind::Fn => true,
254 access_place_error_reported: FxHashSet(),
255 reservation_error_reported: FxHashSet(),
256 moved_error_reported: FxHashSet(),
257 nonlexical_regioncx: regioncx,
258 used_mut: FxHashSet(),
259 used_mut_upvars: SmallVec::new(),
264 let mut state = Flows::new(
273 mbcx.analyze_results(&mut state); // entry point for DataflowResultsConsumer
275 // For each non-user used mutable variable, check if it's been assigned from
276 // a user-declared local. If so, then put that local into the used_mut set.
277 // Note that this set is expected to be small - only upvars from closures
278 // would have a chance of erroneously adding non-user-defined mutable vars
280 let temporary_used_locals: FxHashSet<Local> = mbcx
283 .filter(|&local| !mbcx.mir.local_decls[*local].is_user_variable.is_some())
286 mbcx.gather_used_muts(temporary_used_locals);
288 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
292 .mut_vars_and_args_iter()
293 .filter(|local| !mbcx.used_mut.contains(local))
295 if let ClearCrossCrate::Set(ref vsi) = mbcx.mir.source_scope_local_data {
296 let local_decl = &mbcx.mir.local_decls[local];
298 // Skip implicit `self` argument for closures
299 if local.index() == 1 && tcx.is_closure(mbcx.mir_def_id) {
303 // Skip over locals that begin with an underscore or have no name
304 match local_decl.name {
305 Some(name) => if name.as_str().starts_with("_") {
311 let span = local_decl.source_info.span;
312 let mut_span = tcx.sess.codemap().span_until_non_whitespace(span);
314 tcx.struct_span_lint_node(
316 vsi[local_decl.source_info.scope].lint_root,
318 "variable does not need to be mutable",
319 ).span_suggestion_short(mut_span, "remove this `mut`", "".to_owned())
324 let result = BorrowCheckResult {
325 closure_requirements: opt_closure_req,
326 used_mut_upvars: mbcx.used_mut_upvars,
329 debug!("do_mir_borrowck: result = {:#?}", result);
335 pub struct MirBorrowckCtxt<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
336 tcx: TyCtxt<'cx, 'gcx, 'tcx>,
339 move_data: &'cx MoveData<'tcx>,
341 /// Map from MIR `Location` to `LocationIndex`; created
342 /// when MIR borrowck begins.
343 location_table: &'cx LocationTable,
345 param_env: ParamEnv<'gcx>,
346 movable_generator: bool,
347 /// This keeps track of whether local variables are free-ed when the function
348 /// exits even without a `StorageDead`, which appears to be the case for
351 /// I'm not sure this is the right approach - @eddyb could you try and
353 locals_are_invalidated_at_exit: bool,
354 /// This field keeps track of when borrow errors are reported in the access_place function
355 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
356 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
357 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
359 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
360 /// This field keeps track of when borrow conflict errors are reported
361 /// for reservations, so that we don't report seemingly duplicate
362 /// errors for corresponding activations
364 /// FIXME: Ideally this would be a set of BorrowIndex, not Places,
365 /// but it is currently inconvenient to track down the BorrowIndex
366 /// at the time we detect and report a reservation error.
367 reservation_error_reported: FxHashSet<Place<'tcx>>,
368 /// This field keeps track of errors reported in the checking of moved variables,
369 /// so that we don't report report seemingly duplicate errors.
370 moved_error_reported: FxHashSet<Place<'tcx>>,
371 /// This field keeps track of all the local variables that are declared mut and are mutated.
372 /// Used for the warning issued by an unused mutable local variable.
373 used_mut: FxHashSet<Local>,
374 /// If the function we're checking is a closure, then we'll need to report back the list of
375 /// mutable upvars that have been used. This field keeps track of them.
376 used_mut_upvars: SmallVec<[Field; 8]>,
377 /// Non-lexical region inference context, if NLL is enabled. This
378 /// contains the results from region inference and lets us e.g.
379 /// find out which CFG points are contained in each borrow region.
380 nonlexical_regioncx: Rc<RegionInferenceContext<'tcx>>,
382 /// The set of borrows extracted from the MIR
383 borrow_set: Rc<BorrowSet<'tcx>>,
385 /// Dominators for MIR
386 dominators: Dominators<BasicBlock>,
390 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
391 // 2. loans made in overlapping scopes do not conflict
392 // 3. assignments do not affect things loaned out as immutable
393 // 4. moves do not affect things loaned out in any way
394 impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
395 type FlowState = Flows<'cx, 'gcx, 'tcx>;
397 fn mir(&self) -> &'cx Mir<'tcx> {
401 fn visit_block_entry(&mut self, bb: BasicBlock, flow_state: &Self::FlowState) {
402 debug!("MirBorrowckCtxt::process_block({:?}): {}", bb, flow_state);
405 fn visit_statement_entry(
408 stmt: &Statement<'tcx>,
409 flow_state: &Self::FlowState,
412 "MirBorrowckCtxt::process_statement({:?}, {:?}): {}",
413 location, stmt, flow_state
415 let span = stmt.source_info.span;
417 self.check_activations(location, span, flow_state);
420 StatementKind::Assign(ref lhs, ref rhs) => {
422 ContextKind::AssignRhs.new(location),
429 ContextKind::AssignLhs.new(location),
436 StatementKind::ReadForMatch(ref place) => {
438 ContextKind::ReadForMatch.new(location),
440 (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
441 LocalMutationIsAllowed::No,
445 StatementKind::SetDiscriminant {
450 ContextKind::SetDiscrim.new(location),
452 Shallow(Some(ArtificialField::Discriminant)),
457 StatementKind::InlineAsm {
462 let context = ContextKind::InlineAsm.new(location);
463 for (o, output) in asm.outputs.iter().zip(outputs) {
465 // FIXME(eddyb) indirect inline asm outputs should
466 // be encoeded through MIR place derefs instead.
470 (Deep, Read(ReadKind::Copy)),
471 LocalMutationIsAllowed::No,
474 self.check_if_path_or_subpath_is_moved(
476 InitializationRequiringAction::Use,
484 if o.is_rw { Deep } else { Shallow(None) },
485 if o.is_rw { WriteAndRead } else { JustWrite },
490 for input in inputs {
491 self.consume_operand(context, (input, span), flow_state);
494 StatementKind::EndRegion(ref _rgn) => {
495 // ignored when consuming results (update to
496 // flow_state already handled).
499 | StatementKind::UserAssertTy(..)
500 | StatementKind::Validate(..)
501 | StatementKind::StorageLive(..) => {
502 // `Nop`, `UserAssertTy`, `Validate`, and `StorageLive` are irrelevant
505 StatementKind::StorageDead(local) => {
507 ContextKind::StorageDead.new(location),
508 (&Place::Local(local), span),
509 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
510 LocalMutationIsAllowed::Yes,
517 fn visit_terminator_entry(
520 term: &Terminator<'tcx>,
521 flow_state: &Self::FlowState,
525 "MirBorrowckCtxt::process_terminator({:?}, {:?}): {}",
526 location, term, flow_state
528 let span = term.source_info.span;
530 self.check_activations(location, span, flow_state);
533 TerminatorKind::SwitchInt {
539 self.consume_operand(ContextKind::SwitchInt.new(loc), (discr, span), flow_state);
541 TerminatorKind::Drop {
542 location: ref drop_place,
546 let gcx = self.tcx.global_tcx();
548 // Compute the type with accurate region information.
549 let drop_place_ty = drop_place.ty(self.mir, self.tcx);
551 // Erase the regions.
552 let drop_place_ty = self.tcx.erase_regions(&drop_place_ty).to_ty(self.tcx);
554 // "Lift" into the gcx -- once regions are erased, this type should be in the
555 // global arenas; this "lift" operation basically just asserts that is true, but
556 // that is useful later.
557 let drop_place_ty = gcx.lift(&drop_place_ty).unwrap();
559 self.visit_terminator_drop(loc, term, flow_state, drop_place, drop_place_ty, span);
561 TerminatorKind::DropAndReplace {
562 location: ref drop_place,
563 value: ref new_value,
568 ContextKind::DropAndReplace.new(loc),
574 self.consume_operand(
575 ContextKind::DropAndReplace.new(loc),
580 TerminatorKind::Call {
586 self.consume_operand(ContextKind::CallOperator.new(loc), (func, span), flow_state);
588 self.consume_operand(
589 ContextKind::CallOperand.new(loc),
594 if let Some((ref dest, _ /*bb*/)) = *destination {
596 ContextKind::CallDest.new(loc),
604 TerminatorKind::Assert {
611 self.consume_operand(ContextKind::Assert.new(loc), (cond, span), flow_state);
612 use rustc::mir::interpret::EvalErrorKind::BoundsCheck;
613 if let BoundsCheck { ref len, ref index } = *msg {
614 self.consume_operand(ContextKind::Assert.new(loc), (len, span), flow_state);
615 self.consume_operand(ContextKind::Assert.new(loc), (index, span), flow_state);
619 TerminatorKind::Yield {
624 self.consume_operand(ContextKind::Yield.new(loc), (value, span), flow_state);
626 if self.movable_generator {
627 // Look for any active borrows to locals
628 let borrow_set = self.borrow_set.clone();
629 flow_state.with_outgoing_borrows(|borrows| {
631 let borrow = &borrow_set[i];
632 self.check_for_local_borrow(borrow, span);
638 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
639 // Returning from the function implicitly kills storage for all locals and statics.
640 // Often, the storage will already have been killed by an explicit
641 // StorageDead, but we don't always emit those (notably on unwind paths),
642 // so this "extra check" serves as a kind of backup.
643 let borrow_set = self.borrow_set.clone();
644 flow_state.with_outgoing_borrows(|borrows| {
646 let borrow = &borrow_set[i];
647 let context = ContextKind::StorageDead.new(loc);
648 self.check_for_invalidation_at_exit(context, borrow, span);
652 TerminatorKind::Goto { target: _ }
653 | TerminatorKind::Abort
654 | TerminatorKind::Unreachable
655 | TerminatorKind::FalseEdges {
657 imaginary_targets: _,
659 | TerminatorKind::FalseUnwind {
663 // no data used, thus irrelevant to borrowck
669 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
675 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
676 use self::ShallowOrDeep::{Deep, Shallow};
678 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
679 enum ArtificialField {
684 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
686 /// From the RFC: "A *shallow* access means that the immediate
687 /// fields reached at P are accessed, but references or pointers
688 /// found within are not dereferenced. Right now, the only access
689 /// that is shallow is an assignment like `x = ...;`, which would
690 /// be a *shallow write* of `x`."
691 Shallow(Option<ArtificialField>),
693 /// From the RFC: "A *deep* access means that all data reachable
694 /// through the given place may be invalidated or accesses by
699 /// Kind of access to a value: read or write
700 /// (For informational purposes only)
701 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
703 /// From the RFC: "A *read* means that the existing data may be
704 /// read, but will not be changed."
707 /// From the RFC: "A *write* means that the data may be mutated to
708 /// new values or otherwise invalidated (for example, it could be
709 /// de-initialized, as in a move operation).
712 /// For two-phase borrows, we distinguish a reservation (which is treated
713 /// like a Read) from an activation (which is treated like a write), and
714 /// each of those is furthermore distinguished from Reads/Writes above.
715 Reservation(WriteKind),
716 Activation(WriteKind, BorrowIndex),
719 /// Kind of read access to a value
720 /// (For informational purposes only)
721 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
727 /// Kind of write access to a value
728 /// (For informational purposes only)
729 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
732 MutableBorrow(BorrowKind),
737 /// When checking permissions for a place access, this flag is used to indicate that an immutable
738 /// local place can be mutated.
740 /// FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
741 /// - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`
742 /// - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
743 /// `is_declared_mutable()`
744 /// - Take flow state into consideration in `is_assignable()` for local variables
745 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
746 enum LocalMutationIsAllowed {
748 /// We want use of immutable upvars to cause a "write to immutable upvar"
749 /// error, not an "reassignment" error.
754 struct AccessErrorsReported {
755 mutability_error: bool,
757 conflict_error: bool,
760 #[derive(Copy, Clone)]
761 enum InitializationRequiringAction {
768 struct RootPlace<'d, 'tcx: 'd> {
769 place: &'d Place<'tcx>,
770 is_local_mutation_allowed: LocalMutationIsAllowed,
773 impl InitializationRequiringAction {
774 fn as_noun(self) -> &'static str {
776 InitializationRequiringAction::Update => "update",
777 InitializationRequiringAction::Borrow => "borrow",
778 InitializationRequiringAction::Use => "use",
779 InitializationRequiringAction::Assignment => "assign",
783 fn as_verb_in_past_tense(self) -> &'static str {
785 InitializationRequiringAction::Update => "updated",
786 InitializationRequiringAction::Borrow => "borrowed",
787 InitializationRequiringAction::Use => "used",
788 InitializationRequiringAction::Assignment => "assigned",
793 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
794 /// Invokes `access_place` as appropriate for dropping the value
795 /// at `drop_place`. Note that the *actual* `Drop` in the MIR is
796 /// always for a variable (e.g., `Drop(x)`) -- but we recursively
797 /// break this variable down into subpaths (e.g., `Drop(x.foo)`)
798 /// to indicate more precisely which fields might actually be
799 /// accessed by a destructor.
800 fn visit_terminator_drop(
803 term: &Terminator<'tcx>,
804 flow_state: &Flows<'cx, 'gcx, 'tcx>,
805 drop_place: &Place<'tcx>,
806 erased_drop_place_ty: ty::Ty<'gcx>,
809 let gcx = self.tcx.global_tcx();
810 let drop_field = |mir: &mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>,
811 (index, field): (usize, ty::Ty<'gcx>)| {
812 let field_ty = gcx.normalize_erasing_regions(mir.param_env, field);
813 let place = drop_place.clone().field(Field::new(index), field_ty);
815 mir.visit_terminator_drop(loc, term, flow_state, &place, field_ty, span);
818 match erased_drop_place_ty.sty {
819 // When a struct is being dropped, we need to check
820 // whether it has a destructor, if it does, then we can
821 // call it, if it does not then we need to check the
822 // individual fields instead. This way if `foo` has a
823 // destructor but `bar` does not, we will only check for
824 // borrows of `x.foo` and not `x.bar`. See #47703.
825 ty::TyAdt(def, substs) if def.is_struct() && !def.has_dtor(self.tcx) => {
827 .map(|field| field.ty(gcx, substs))
829 .for_each(|field| drop_field(self, field));
831 // Same as above, but for tuples.
832 ty::TyTuple(tys) => {
836 .for_each(|field| drop_field(self, field));
838 // Closures also have disjoint fields, but they are only
839 // directly accessed in the body of the closure.
840 ty::TyClosure(def, substs)
841 if *drop_place == Place::Local(Local::new(1))
842 && !self.mir.upvar_decls.is_empty() =>
845 .upvar_tys(def, self.tcx)
847 .for_each(|field| drop_field(self, field));
849 // Generators also have disjoint fields, but they are only
850 // directly accessed in the body of the generator.
851 ty::TyGenerator(def, substs, _)
852 if *drop_place == Place::Local(Local::new(1))
853 && !self.mir.upvar_decls.is_empty() =>
856 .upvar_tys(def, self.tcx)
858 .for_each(|field| drop_field(self, field));
861 // We have now refined the type of the value being
862 // dropped (potentially) to just the type of a
863 // subfield; so check whether that field's type still
864 // "needs drop". If so, we assume that the destructor
865 // may access any data it likes (i.e., a Deep Write).
866 if erased_drop_place_ty.needs_drop(gcx, self.param_env) {
868 ContextKind::Drop.new(loc),
870 (Deep, Write(WriteKind::StorageDeadOrDrop)),
871 LocalMutationIsAllowed::Yes,
879 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
880 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
881 /// place is initialized and (b) it is not borrowed in some way that would prevent this
884 /// Returns true if an error is reported, false otherwise.
888 place_span: (&Place<'tcx>, Span),
889 kind: (ShallowOrDeep, ReadOrWrite),
890 is_local_mutation_allowed: LocalMutationIsAllowed,
891 flow_state: &Flows<'cx, 'gcx, 'tcx>,
892 ) -> AccessErrorsReported {
895 if let Activation(_, borrow_index) = rw {
896 if self.reservation_error_reported.contains(&place_span.0) {
898 "skipping access_place for activation of invalid reservation \
899 place: {:?} borrow_index: {:?}",
900 place_span.0, borrow_index
902 return AccessErrorsReported {
903 mutability_error: false,
904 conflict_error: true,
910 .access_place_error_reported
911 .contains(&(place_span.0.clone(), place_span.1))
914 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
917 return AccessErrorsReported {
918 mutability_error: false,
919 conflict_error: true,
923 let mutability_error =
924 self.check_access_permissions(place_span, rw, is_local_mutation_allowed, flow_state);
926 self.check_access_for_conflict(context, place_span, sd, rw, flow_state);
928 if conflict_error || mutability_error {
930 "access_place: logging error place_span=`{:?}` kind=`{:?}`",
933 self.access_place_error_reported
934 .insert((place_span.0.clone(), place_span.1));
937 AccessErrorsReported {
943 fn check_access_for_conflict(
946 place_span: (&Place<'tcx>, Span),
949 flow_state: &Flows<'cx, 'gcx, 'tcx>,
952 "check_access_for_conflict(context={:?}, place_span={:?}, sd={:?}, rw={:?})",
953 context, place_span, sd, rw,
956 let mut error_reported = false;
959 let location = self.location_table.start_index(context.loc);
960 let borrow_set = self.borrow_set.clone();
961 each_borrow_involving_path(
968 flow_state.borrows_in_scope(location),
969 |this, borrow_index, borrow| match (rw, borrow.kind) {
970 // Obviously an activation is compatible with its own
971 // reservation (or even prior activating uses of same
972 // borrow); so don't check if they interfere.
974 // NOTE: *reservations* do conflict with themselves;
975 // thus aren't injecting unsoundenss w/ this check.)
976 (Activation(_, activating), _) if activating == borrow_index => {
978 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
979 skipping {:?} b/c activation of same borrow_index",
983 (borrow_index, borrow),
988 (Read(_), BorrowKind::Shared) | (Reservation(..), BorrowKind::Shared) => {
992 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
993 // Reading from mere reservations of mutable-borrows is OK.
994 if !is_active(&this.dominators, borrow, context.loc) {
995 assert!(allow_two_phase_borrow(&this.tcx, borrow.kind));
996 return Control::Continue;
1001 error_reported = true;
1002 this.report_use_while_mutably_borrowed(context, place_span, borrow)
1004 ReadKind::Borrow(bk) => {
1005 error_reported = true;
1006 this.report_conflicting_borrow(context, place_span, bk, &borrow)
1012 (Reservation(kind), BorrowKind::Unique)
1013 | (Reservation(kind), BorrowKind::Mut { .. })
1014 | (Activation(kind, _), _)
1015 | (Write(kind), _) => {
1019 "recording invalid reservation of \
1023 this.reservation_error_reported.insert(place_span.0.clone());
1025 Activation(_, activating) => {
1027 "observing check_place for activation of \
1028 borrow_index: {:?}",
1032 Read(..) | Write(..) => {}
1036 WriteKind::MutableBorrow(bk) => {
1037 error_reported = true;
1038 this.report_conflicting_borrow(context, place_span, bk, &borrow)
1040 WriteKind::StorageDeadOrDrop => {
1041 error_reported = true;
1042 this.report_borrowed_value_does_not_live_long_enough(
1049 WriteKind::Mutate => {
1050 error_reported = true;
1051 this.report_illegal_mutation_of_borrowed(context, place_span, borrow)
1053 WriteKind::Move => {
1054 error_reported = true;
1055 this.report_move_out_while_borrowed(context, place_span, &borrow)
1069 place_span: (&Place<'tcx>, Span),
1070 kind: ShallowOrDeep,
1072 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1074 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1076 MutateMode::WriteAndRead => {
1077 self.check_if_path_or_subpath_is_moved(
1079 InitializationRequiringAction::Update,
1084 MutateMode::JustWrite => {
1085 self.check_if_assigned_path_is_moved(context, place_span, flow_state);
1089 let errors_reported = self.access_place(
1092 (kind, Write(WriteKind::Mutate)),
1093 // We want immutable upvars to cause an "assignment to immutable var"
1094 // error, not an "reassignment of immutable var" error, because the
1095 // latter can't find a good previous assignment span.
1097 // There's probably a better way to do this.
1098 LocalMutationIsAllowed::ExceptUpvars,
1102 if !errors_reported.mutability_error {
1103 // check for reassignments to immutable local variables
1104 self.check_if_reassignment_to_immutable_state(context, place_span, flow_state);
1111 (rvalue, span): (&Rvalue<'tcx>, Span),
1112 _location: Location,
1113 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1116 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1117 let access_kind = match bk {
1118 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1119 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1120 let wk = WriteKind::MutableBorrow(bk);
1121 if allow_two_phase_borrow(&self.tcx, bk) {
1122 (Deep, Reservation(wk))
1133 LocalMutationIsAllowed::No,
1137 self.check_if_path_or_subpath_is_moved(
1139 InitializationRequiringAction::Borrow,
1145 Rvalue::Use(ref operand)
1146 | Rvalue::Repeat(ref operand, _)
1147 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1148 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1149 self.consume_operand(context, (operand, span), flow_state)
1152 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1153 let af = match *rvalue {
1154 Rvalue::Len(..) => ArtificialField::ArrayLength,
1155 Rvalue::Discriminant(..) => ArtificialField::Discriminant,
1156 _ => unreachable!(),
1161 (Shallow(Some(af)), Read(ReadKind::Copy)),
1162 LocalMutationIsAllowed::No,
1165 self.check_if_path_or_subpath_is_moved(
1167 InitializationRequiringAction::Use,
1173 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1174 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1175 self.consume_operand(context, (operand1, span), flow_state);
1176 self.consume_operand(context, (operand2, span), flow_state);
1179 Rvalue::NullaryOp(_op, _ty) => {
1180 // nullary ops take no dynamic input; no borrowck effect.
1182 // FIXME: is above actually true? Do we want to track
1183 // the fact that uninitialized data can be created via
1187 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1188 // We need to report back the list of mutable upvars that were
1189 // moved into the closure and subsequently used by the closure,
1190 // in order to populate our used_mut set.
1191 match **aggregate_kind {
1192 AggregateKind::Closure(def_id, _)
1193 | AggregateKind::Generator(def_id, _, _) => {
1194 let BorrowCheckResult {
1196 } = self.tcx.mir_borrowck(def_id);
1197 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1198 for field in used_mut_upvars {
1199 // This relies on the current way that by-value
1200 // captures of a closure are copied/moved directly
1201 // when generating MIR.
1202 match operands[field.index()] {
1203 Operand::Move(Place::Local(local))
1204 | Operand::Copy(Place::Local(local)) => {
1205 self.used_mut.insert(local);
1207 Operand::Move(ref place @ Place::Projection(_))
1208 | Operand::Copy(ref place @ Place::Projection(_)) => {
1209 if let Some(field) = self.is_upvar_field_projection(place) {
1210 self.used_mut_upvars.push(field);
1213 Operand::Move(Place::Static(..))
1214 | Operand::Copy(Place::Static(..))
1215 | Operand::Constant(..) => {}
1219 AggregateKind::Adt(..)
1220 | AggregateKind::Array(..)
1221 | AggregateKind::Tuple { .. } => (),
1224 for operand in operands {
1225 self.consume_operand(context, (operand, span), flow_state);
1234 (operand, span): (&Operand<'tcx>, Span),
1235 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1238 Operand::Copy(ref place) => {
1239 // copy of place: check if this is "copy of frozen path"
1240 // (FIXME: see check_loans.rs)
1244 (Deep, Read(ReadKind::Copy)),
1245 LocalMutationIsAllowed::No,
1249 // Finally, check if path was already moved.
1250 self.check_if_path_or_subpath_is_moved(
1252 InitializationRequiringAction::Use,
1257 Operand::Move(ref place) => {
1258 // move of place: check if this is move of already borrowed path
1262 (Deep, Write(WriteKind::Move)),
1263 LocalMutationIsAllowed::Yes,
1267 // Finally, check if path was already moved.
1268 self.check_if_path_or_subpath_is_moved(
1270 InitializationRequiringAction::Use,
1275 Operand::Constant(_) => {}
1279 /// Returns whether a borrow of this place is invalidated when the function
1281 fn check_for_invalidation_at_exit(
1284 borrow: &BorrowData<'tcx>,
1287 debug!("check_for_invalidation_at_exit({:?})", borrow);
1288 let place = &borrow.borrowed_place;
1289 let root_place = self.prefixes(place, PrefixSet::All).last().unwrap();
1291 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1292 // we just know that all locals are dropped at function exit (otherwise
1293 // we'll have a memory leak) and assume that all statics have a destructor.
1295 // FIXME: allow thread-locals to borrow other thread locals?
1296 let (might_be_alive, will_be_dropped) = match root_place {
1297 Place::Static(statik) => {
1298 // Thread-locals might be dropped after the function exits, but
1299 // "true" statics will never be.
1300 let is_thread_local = self
1302 .get_attrs(statik.def_id)
1304 .any(|attr| attr.check_name("thread_local"));
1306 (true, is_thread_local)
1308 Place::Local(_) => {
1309 // Locals are always dropped at function exit, and if they
1310 // have a destructor it would've been called already.
1311 (false, self.locals_are_invalidated_at_exit)
1313 Place::Projection(..) => {
1314 bug!("root of {:?} is a projection ({:?})?", place, root_place)
1318 if !will_be_dropped {
1320 "place_is_invalidated_at_exit({:?}) - won't be dropped",
1326 // FIXME: replace this with a proper borrow_conflicts_with_place when
1328 let sd = if might_be_alive { Deep } else { Shallow(None) };
1330 if places_conflict::places_conflict(self.tcx, self.mir, place, root_place, sd) {
1331 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1332 // FIXME: should be talking about the region lifetime instead
1333 // of just a span here.
1334 let span = self.tcx.sess.codemap().end_point(span);
1335 self.report_borrowed_value_does_not_live_long_enough(
1344 /// Reports an error if this is a borrow of local data.
1345 /// This is called for all Yield statements on movable generators
1346 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1347 debug!("check_for_local_borrow({:?})", borrow);
1349 if borrow_of_local_data(&borrow.borrowed_place) {
1351 .cannot_borrow_across_generator_yield(
1352 self.retrieve_borrow_span(borrow),
1360 fn check_activations(
1364 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1366 if !self.tcx.two_phase_borrows() {
1370 // Two-phase borrow support: For each activation that is newly
1371 // generated at this statement, check if it interferes with
1373 let borrow_set = self.borrow_set.clone();
1374 for &borrow_index in borrow_set.activations_at_location(location) {
1375 let borrow = &borrow_set[borrow_index];
1377 // only mutable borrows should be 2-phase
1378 assert!(match borrow.kind {
1379 BorrowKind::Shared => false,
1380 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1384 ContextKind::Activation.new(location),
1385 (&borrow.borrowed_place, span),
1388 Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index),
1390 LocalMutationIsAllowed::No,
1393 // We do not need to call `check_if_path_or_subpath_is_moved`
1394 // again, as we already called it when we made the
1395 // initial reservation.
1400 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1401 fn check_if_reassignment_to_immutable_state(
1404 (place, span): (&Place<'tcx>, Span),
1405 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1407 debug!("check_if_reassignment_to_immutable_state({:?})", place);
1408 // determine if this path has a non-mut owner (and thus needs checking).
1409 let err_place = match self.is_mutable(place, LocalMutationIsAllowed::No) {
1411 Err(place) => place,
1414 "check_if_reassignment_to_immutable_state({:?}) - is an imm local",
1418 for i in flow_state.ever_inits.iter_incoming() {
1419 let init = self.move_data.inits[i];
1420 let init_place = &self.move_data.move_paths[init.path].place;
1421 if places_conflict::places_conflict(self.tcx, self.mir, &init_place, place, Deep) {
1422 self.report_illegal_reassignment(context, (place, span), init.span, err_place);
1428 fn check_if_full_path_is_moved(
1431 desired_action: InitializationRequiringAction,
1432 place_span: (&Place<'tcx>, Span),
1433 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1435 // FIXME: analogous code in check_loans first maps `place` to
1436 // its base_path ... but is that what we want here?
1437 let place = self.base_path(place_span.0);
1439 let maybe_uninits = &flow_state.uninits;
1440 let curr_move_outs = &flow_state.move_outs;
1444 // 1. Move of `a.b.c`, use of `a.b.c`
1445 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1446 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1447 // partial initialization support, one might have `a.x`
1448 // initialized but not `a.b`.
1452 // 4. Move of `a.b.c`, use of `a.b.d`
1453 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1454 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1455 // must have been initialized for the use to be sound.
1456 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1458 // The dataflow tracks shallow prefixes distinctly (that is,
1459 // field-accesses on P distinctly from P itself), in order to
1460 // track substructure initialization separately from the whole
1463 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1464 // which we have a MovePath is `a.b`, then that means that the
1465 // initialization state of `a.b` is all we need to inspect to
1466 // know if `a.b.c` is valid (and from that we infer that the
1467 // dereference and `.d` access is also valid, since we assume
1468 // `a.b.c` is assigned a reference to a initialized and
1469 // well-formed record structure.)
1471 // Therefore, if we seek out the *closest* prefix for which we
1472 // have a MovePath, that should capture the initialization
1473 // state for the place scenario.
1475 // This code covers scenarios 1, 2, and 3.
1477 debug!("check_if_full_path_is_moved place: {:?}", place);
1478 match self.move_path_closest_to(place) {
1480 if maybe_uninits.contains(&mpi) {
1481 self.report_use_of_moved_or_uninitialized(
1488 return; // don't bother finding other problems.
1491 Err(NoMovePathFound::ReachedStatic) => {
1492 // Okay: we do not build MoveData for static variables
1493 } // Only query longest prefix with a MovePath, not further
1494 // ancestors; dataflow recurs on children when parents
1495 // move (to support partial (re)inits).
1497 // (I.e. querying parents breaks scenario 7; but may want
1498 // to do such a query based on partial-init feature-gate.)
1502 fn check_if_path_or_subpath_is_moved(
1505 desired_action: InitializationRequiringAction,
1506 place_span: (&Place<'tcx>, Span),
1507 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1509 // FIXME: analogous code in check_loans first maps `place` to
1510 // its base_path ... but is that what we want here?
1511 let place = self.base_path(place_span.0);
1513 let maybe_uninits = &flow_state.uninits;
1514 let curr_move_outs = &flow_state.move_outs;
1518 // 1. Move of `a.b.c`, use of `a` or `a.b`
1519 // partial initialization support, one might have `a.x`
1520 // initialized but not `a.b`.
1521 // 2. All bad scenarios from `check_if_full_path_is_moved`
1525 // 3. Move of `a.b.c`, use of `a.b.d`
1526 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1527 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1528 // must have been initialized for the use to be sound.
1529 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1531 self.check_if_full_path_is_moved(context, desired_action, place_span, flow_state);
1533 // A move of any shallow suffix of `place` also interferes
1534 // with an attempt to use `place`. This is scenario 3 above.
1536 // (Distinct from handling of scenarios 1+2+4 above because
1537 // `place` does not interfere with suffixes of its prefixes,
1538 // e.g. `a.b.c` does not interfere with `a.b.d`)
1540 // This code covers scenario 1.
1542 debug!("check_if_path_or_subpath_is_moved place: {:?}", place);
1543 if let Some(mpi) = self.move_path_for_place(place) {
1544 if let Some(child_mpi) = maybe_uninits.has_any_child_of(mpi) {
1545 self.report_use_of_moved_or_uninitialized(
1552 return; // don't bother finding other problems.
1557 /// Currently MoveData does not store entries for all places in
1558 /// the input MIR. For example it will currently filter out
1559 /// places that are Copy; thus we do not track places of shared
1560 /// reference type. This routine will walk up a place along its
1561 /// prefixes, searching for a foundational place that *is*
1562 /// tracked in the MoveData.
1564 /// An Err result includes a tag indicated why the search failed.
1565 /// Currently this can only occur if the place is built off of a
1566 /// static variable, as we do not track those in the MoveData.
1567 fn move_path_closest_to(
1569 place: &Place<'tcx>,
1570 ) -> Result<MovePathIndex, NoMovePathFound> {
1571 let mut last_prefix = place;
1572 for prefix in self.prefixes(place, PrefixSet::All) {
1573 if let Some(mpi) = self.move_path_for_place(prefix) {
1576 last_prefix = prefix;
1578 match *last_prefix {
1579 Place::Local(_) => panic!("should have move path for every Local"),
1580 Place::Projection(_) => panic!("PrefixSet::All meant don't stop for Projection"),
1581 Place::Static(_) => return Err(NoMovePathFound::ReachedStatic),
1585 fn move_path_for_place(&mut self, place: &Place<'tcx>) -> Option<MovePathIndex> {
1586 // If returns None, then there is no move path corresponding
1587 // to a direct owner of `place` (which means there is nothing
1588 // that borrowck tracks for its analysis).
1590 match self.move_data.rev_lookup.find(place) {
1591 LookupResult::Parent(_) => None,
1592 LookupResult::Exact(mpi) => Some(mpi),
1596 fn check_if_assigned_path_is_moved(
1599 (place, span): (&Place<'tcx>, Span),
1600 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1602 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1603 // recur down place; dispatch to external checks when necessary
1604 let mut place = place;
1607 Place::Local(_) | Place::Static(_) => {
1608 // assigning to `x` does not require `x` be initialized.
1611 Place::Projection(ref proj) => {
1612 let Projection { ref base, ref elem } = **proj;
1614 ProjectionElem::Index(_/*operand*/) |
1615 ProjectionElem::ConstantIndex { .. } |
1616 // assigning to P[i] requires P to be valid.
1617 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1618 // assigning to (P->variant) is okay if assigning to `P` is okay
1620 // FIXME: is this true even if P is a adt with a dtor?
1623 // assigning to (*P) requires P to be initialized
1624 ProjectionElem::Deref => {
1625 self.check_if_full_path_is_moved(
1626 context, InitializationRequiringAction::Use,
1627 (base, span), flow_state);
1628 // (base initialized; no need to
1633 ProjectionElem::Subslice { .. } => {
1634 panic!("we don't allow assignments to subslices, context: {:?}",
1638 ProjectionElem::Field(..) => {
1639 // if type of `P` has a dtor, then
1640 // assigning to `P.f` requires `P` itself
1641 // be already initialized
1643 match base.ty(self.mir, tcx).to_ty(tcx).sty {
1644 ty::TyAdt(def, _) if def.has_dtor(tcx) => {
1646 // FIXME: analogous code in
1647 // check_loans.rs first maps
1648 // `base` to its base_path.
1650 self.check_if_path_or_subpath_is_moved(
1651 context, InitializationRequiringAction::Assignment,
1652 (base, span), flow_state);
1654 // (base initialized; no need to
1670 /// Check the permissions for the given place and read or write kind
1672 /// Returns true if an error is reported, false otherwise.
1673 fn check_access_permissions(
1675 (place, span): (&Place<'tcx>, Span),
1677 is_local_mutation_allowed: LocalMutationIsAllowed,
1678 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1681 "check_access_permissions({:?}, {:?}, {:?})",
1682 place, kind, is_local_mutation_allowed
1685 #[derive(Copy, Clone, Debug)]
1694 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1695 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1696 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1697 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1698 let is_local_mutation_allowed = match borrow_kind {
1699 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1700 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1701 BorrowKind::Shared => unreachable!(),
1703 match self.is_mutable(place, is_local_mutation_allowed) {
1705 self.add_used_mut(root_place, flow_state);
1709 error_access = AccessKind::MutableBorrow;
1710 the_place_err = place_err;
1714 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1715 match self.is_mutable(place, is_local_mutation_allowed) {
1717 self.add_used_mut(root_place, flow_state);
1721 error_access = AccessKind::Mutate;
1722 the_place_err = place_err;
1727 Reservation(WriteKind::Move)
1728 | Write(WriteKind::Move)
1729 | Reservation(WriteKind::StorageDeadOrDrop)
1730 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1731 | Write(WriteKind::StorageDeadOrDrop)
1732 | Write(WriteKind::MutableBorrow(BorrowKind::Shared)) => {
1733 if let Err(_place_err) = self.is_mutable(place, is_local_mutation_allowed) {
1734 self.tcx.sess.delay_span_bug(
1737 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1745 // permission checks are done at Reservation point.
1748 Read(ReadKind::Borrow(BorrowKind::Unique))
1749 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1750 | Read(ReadKind::Borrow(BorrowKind::Shared))
1751 | Read(ReadKind::Copy) => {
1752 // Access authorized
1757 // at this point, we have set up the error reporting state.
1760 let item_msg = match self.describe_place(place) {
1761 Some(name) => format!("immutable item `{}`", name),
1762 None => "immutable item".to_owned(),
1765 // `act` and `acted_on` are strings that let us abstract over
1766 // the verbs used in some diagnostic messages.
1770 match error_access {
1771 AccessKind::Mutate => {
1772 let item_msg = match the_place_err {
1773 Place::Projection(box Projection {
1775 elem: ProjectionElem::Deref,
1776 }) => match self.describe_place(place) {
1777 Some(description) => {
1778 format!("`{}` which is behind a `&` reference", description)
1780 None => format!("data in a `&` reference"),
1784 err = self.tcx.cannot_assign(span, &item_msg, Origin::Mir);
1786 acted_on = "written";
1788 AccessKind::MutableBorrow => {
1791 .cannot_borrow_path_as_mutable(span, &item_msg, Origin::Mir);
1792 act = "borrow as mutable";
1793 acted_on = "borrowed as mutable";
1797 match the_place_err {
1798 // We want to suggest users use `let mut` for local (user
1799 // variable) mutations...
1800 Place::Local(local) if self.mir.local_decls[*local].can_be_made_mutable() => {
1801 // ... but it doesn't make sense to suggest it on
1802 // variables that are `ref x`, `ref mut x`, `&self`,
1803 // or `&mut self` (such variables are simply not
1805 let local_decl = &self.mir.local_decls[*local];
1806 assert_eq!(local_decl.mutability, Mutability::Not);
1808 err.span_label(span, format!("cannot {ACT}", ACT = act));
1809 err.span_suggestion(
1810 local_decl.source_info.span,
1811 "consider changing this to be mutable",
1812 format!("mut {}", local_decl.name.unwrap()),
1816 // complete hack to approximate old AST-borrowck
1817 // diagnostic: if the span starts with a mutable borrow of
1818 // a local variable, then just suggest the user remove it.
1821 if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1822 snippet.starts_with("&mut ")
1828 err.span_label(span, format!("cannot {ACT}", ACT = act));
1829 err.span_label(span, "try removing `&mut` here");
1832 // We want to point out when a `&` can be readily replaced
1835 // FIXME: can this case be generalized to work for an
1836 // arbitrary base for the projection?
1837 Place::Projection(box Projection {
1838 base: Place::Local(local),
1839 elem: ProjectionElem::Deref,
1840 }) if self.mir.local_decls[*local].is_nonref_binding() =>
1842 let (err_help_span, suggested_code) =
1843 find_place_to_suggest_ampmut(self.tcx, self.mir, *local);
1844 err.span_suggestion(
1846 "consider changing this to be a mutable reference",
1850 let local_decl = &self.mir.local_decls[*local];
1851 if let Some(name) = local_decl.name {
1855 "`{NAME}` is a `&` reference, \
1856 so the data it refers to cannot be {ACTED_ON}",
1864 format!("cannot {ACT} through `&`-reference", ACT = act),
1870 err.span_label(span, format!("cannot {ACT}", ACT = act));
1877 // Returns the span to highlight and the associated text to
1878 // present when suggesting that the user use an `&mut`.
1880 // When we want to suggest a user change a local variable to be a `&mut`, there
1881 // are three potential "obvious" things to highlight:
1883 // let ident [: Type] [= RightHandSideExresssion];
1884 // ^^^^^ ^^^^ ^^^^^^^^^^^^^^^^^^^^^^^
1887 // We can always fallback on highlighting the first. But chances are good that
1888 // the user experience will be better if we highlight one of the others if possible;
1889 // for example, if the RHS is present and the Type is not, then the type is going to
1890 // be inferred *from* the RHS, which means we should highlight that (and suggest
1891 // that they borrow the RHS mutably).
1892 fn find_place_to_suggest_ampmut<'cx, 'gcx, 'tcx>(
1893 tcx: TyCtxt<'cx, 'gcx, 'tcx>,
1896 ) -> (Span, String) {
1897 // This implementation attempts to emulate AST-borrowck prioritization
1898 // by trying (3.), then (2.) and finally falling back on (1.).
1899 let locations = mir.find_assignments(local);
1900 if locations.len() > 0 {
1901 let assignment_rhs_span = mir.source_info(locations[0]).span;
1902 let snippet = tcx.sess.codemap().span_to_snippet(assignment_rhs_span);
1903 if let Ok(src) = snippet {
1904 // pnkfelix inherited code; believes intention is
1905 // highlighted text will always be `&<expr>` and
1906 // thus can transform to `&mut` by slicing off
1907 // first ASCII character and prepending "&mut ".
1908 if src.starts_with('&') {
1909 let borrowed_expr = src[1..].to_string();
1910 return (assignment_rhs_span, format!("&mut {}", borrowed_expr));
1915 let local_decl = &mir.local_decls[local];
1916 let highlight_span = match local_decl.is_user_variable {
1917 // if this is a variable binding with an explicit type,
1918 // try to highlight that for the suggestion.
1919 Some(ClearCrossCrate::Set(mir::BindingForm::Var(mir::VarBindingForm {
1920 opt_ty_info: Some(ty_span),
1924 Some(ClearCrossCrate::Clear) => bug!("saw cleared local state"),
1926 // otherwise, just highlight the span associated with
1927 // the (MIR) LocalDecl.
1928 _ => local_decl.source_info.span,
1931 let ty_mut = local_decl.ty.builtin_deref(true).unwrap();
1932 assert_eq!(ty_mut.mutbl, hir::MutImmutable);
1933 return (highlight_span, format!("&mut {}", ty_mut.ty));
1937 /// Adds the place into the used mutable variables set
1938 fn add_used_mut<'d>(
1940 root_place: RootPlace<'d, 'tcx>,
1941 flow_state: &Flows<'cx, 'gcx, 'tcx>,
1945 place: Place::Local(local),
1946 is_local_mutation_allowed,
1948 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes {
1949 // If the local may be initialized, and it is now currently being
1950 // mutated, then it is justified to be annotated with the `mut`
1951 // keyword, since the mutation may be a possible reassignment.
1952 let mpi = self.move_data.rev_lookup.find_local(*local);
1953 let ii = &self.move_data.init_path_map[mpi];
1955 if flow_state.ever_inits.contains(index) {
1956 self.used_mut.insert(*local);
1964 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
1967 place: place @ Place::Projection(_),
1968 is_local_mutation_allowed: _,
1970 if let Some(field) = self.is_upvar_field_projection(&place) {
1971 self.used_mut_upvars.push(field);
1975 place: Place::Static(..),
1976 is_local_mutation_allowed: _,
1981 /// Whether this value be written or borrowed mutably.
1982 /// Returns the root place if the place passed in is a projection.
1985 place: &'d Place<'tcx>,
1986 is_local_mutation_allowed: LocalMutationIsAllowed,
1987 ) -> Result<RootPlace<'d, 'tcx>, &'d Place<'tcx>> {
1989 Place::Local(local) => {
1990 let local = &self.mir.local_decls[local];
1991 match local.mutability {
1992 Mutability::Not => match is_local_mutation_allowed {
1993 LocalMutationIsAllowed::Yes => Ok(RootPlace {
1995 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
1997 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
1999 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2001 LocalMutationIsAllowed::No => Err(place),
2003 Mutability::Mut => Ok(RootPlace {
2005 is_local_mutation_allowed,
2009 Place::Static(ref static_) => {
2010 if self.tcx.is_static(static_.def_id) != Some(hir::Mutability::MutMutable) {
2015 is_local_mutation_allowed,
2019 Place::Projection(ref proj) => {
2021 ProjectionElem::Deref => {
2022 let base_ty = proj.base.ty(self.mir, self.tcx).to_ty(self.tcx);
2024 // Check the kind of deref to decide
2026 ty::TyRef(_, _, mutbl) => {
2028 // Shared borrowed data is never mutable
2029 hir::MutImmutable => Err(place),
2030 // Mutably borrowed data is mutable, but only if we have a
2031 // unique path to the `&mut`
2032 hir::MutMutable => {
2033 let mode = match self.is_upvar_field_projection(&proj.base)
2037 self.mir.upvar_decls[field.index()].by_ref
2040 is_local_mutation_allowed
2042 _ => LocalMutationIsAllowed::Yes,
2045 self.is_mutable(&proj.base, mode)
2049 ty::TyRawPtr(tnm) => {
2051 // `*const` raw pointers are not mutable
2052 hir::MutImmutable => return Err(place),
2053 // `*mut` raw pointers are always mutable, regardless of
2054 // context. The users have to check by themselves.
2055 hir::MutMutable => {
2056 return Ok(RootPlace {
2058 is_local_mutation_allowed,
2063 // `Box<T>` owns its content, so mutable if its location is mutable
2064 _ if base_ty.is_box() => {
2065 self.is_mutable(&proj.base, is_local_mutation_allowed)
2067 // Deref should only be for reference, pointers or boxes
2068 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2071 // All other projections are owned by their base path, so mutable if
2072 // base path is mutable
2073 ProjectionElem::Field(..)
2074 | ProjectionElem::Index(..)
2075 | ProjectionElem::ConstantIndex { .. }
2076 | ProjectionElem::Subslice { .. }
2077 | ProjectionElem::Downcast(..) => {
2078 if let Some(field) = self.is_upvar_field_projection(place) {
2079 let decl = &self.mir.upvar_decls[field.index()];
2081 "decl.mutability={:?} local_mutation_is_allowed={:?} place={:?}",
2082 decl, is_local_mutation_allowed, place
2084 match (decl.mutability, is_local_mutation_allowed) {
2085 (Mutability::Not, LocalMutationIsAllowed::No)
2086 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2089 (Mutability::Not, LocalMutationIsAllowed::Yes)
2090 | (Mutability::Mut, _) => {
2091 // Subtle: this is an upvar
2092 // reference, so it looks like
2093 // `self.foo` -- we want to double
2094 // check that the context `*self`
2095 // is mutable (i.e., this is not a
2096 // `Fn` closure). But if that
2097 // check succeeds, we want to
2098 // *blame* the mutability on
2099 // `place` (that is,
2100 // `self.foo`). This is used to
2101 // propagate the info about
2102 // whether mutability declarations
2103 // are used outwards, so that we register
2104 // the outer variable as mutable. Otherwise a
2105 // test like this fails to record the `mut`
2109 // fn foo<F: FnOnce()>(_f: F) { }
2111 // let var = Vec::new();
2117 let _ = self.is_mutable(&proj.base, is_local_mutation_allowed)?;
2120 is_local_mutation_allowed,
2125 self.is_mutable(&proj.base, is_local_mutation_allowed)
2133 /// If this is a field projection, and the field is being projected from a closure type,
2134 /// then returns the index of the field being projected. Note that this closure will always
2135 /// be `self` in the current MIR, because that is the only time we directly access the fields
2136 /// of a closure type.
2137 fn is_upvar_field_projection(&self, place: &Place<'tcx>) -> Option<Field> {
2139 Place::Projection(ref proj) => match proj.elem {
2140 ProjectionElem::Field(field, _ty) => {
2141 let base_ty = proj.base.ty(self.mir, self.tcx).to_ty(self.tcx);
2143 if base_ty.is_closure() || base_ty.is_generator() {
2156 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2157 enum NoMovePathFound {
2161 /// The degree of overlap between 2 places for borrow-checking.
2163 /// The places might partially overlap - in this case, we give
2164 /// up and say that they might conflict. This occurs when
2165 /// different fields of a union are borrowed. For example,
2166 /// if `u` is a union, we have no way of telling how disjoint
2167 /// `u.a.x` and `a.b.y` are.
2169 /// The places have the same type, and are either completely disjoint
2170 /// or equal - i.e. they can't "partially" overlap as can occur with
2171 /// unions. This is the "base case" on which we recur for extensions
2174 /// The places are disjoint, so we know all extensions of them
2175 /// will also be disjoint.
2179 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
2180 // FIXME (#16118): function intended to allow the borrow checker
2181 // to be less precise in its handling of Box while still allowing
2182 // moves out of a Box. They should be removed when/if we stop
2183 // treating Box specially (e.g. when/if DerefMove is added...)
2185 fn base_path<'d>(&self, place: &'d Place<'tcx>) -> &'d Place<'tcx> {
2186 //! Returns the base of the leftmost (deepest) dereference of an
2187 //! Box in `place`. If there is no dereference of an Box
2188 //! in `place`, then it just returns `place` itself.
2190 let mut cursor = place;
2191 let mut deepest = place;
2193 let proj = match *cursor {
2194 Place::Local(..) | Place::Static(..) => return deepest,
2195 Place::Projection(ref proj) => proj,
2197 if proj.elem == ProjectionElem::Deref
2198 && place.ty(self.mir, self.tcx).to_ty(self.tcx).is_box()
2200 deepest = &proj.base;
2202 cursor = &proj.base;
2207 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2213 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2233 fn new(self, loc: Location) -> Context {