1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 use crate::borrow_check::nll::region_infer::RegionInferenceContext;
4 use rustc::hir::{self, HirId};
6 use rustc::hir::def_id::DefId;
7 use rustc::infer::InferCtxt;
8 use rustc::lint::builtin::UNUSED_MUT;
9 use rustc::lint::builtin::{MUTABLE_BORROW_RESERVATION_CONFLICT};
10 use rustc::middle::borrowck::SignalledError;
11 use rustc::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
13 ClearCrossCrate, Local, Location, Body, Mutability, Operand, Place, PlaceBase, Static,
17 use rustc::mir::{Field, Projection, ProjectionElem, Rvalue, Statement, StatementKind};
18 use rustc::mir::{Terminator, TerminatorKind};
19 use rustc::ty::query::Providers;
20 use rustc::ty::{self, TyCtxt};
22 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, Level};
23 use rustc_data_structures::bit_set::BitSet;
24 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
25 use rustc_data_structures::graph::dominators::Dominators;
26 use smallvec::SmallVec;
28 use std::collections::BTreeMap;
32 use syntax::ast::Name;
33 use syntax_pos::{Span, DUMMY_SP};
35 use crate::dataflow::indexes::{BorrowIndex, InitIndex, MoveOutIndex, MovePathIndex};
36 use crate::dataflow::move_paths::{HasMoveData, InitLocation, LookupResult, MoveData, MoveError};
37 use crate::dataflow::Borrows;
38 use crate::dataflow::DataflowResultsConsumer;
39 use crate::dataflow::FlowAtLocation;
40 use crate::dataflow::MoveDataParamEnv;
41 use crate::dataflow::{do_dataflow, DebugFormatted};
42 use crate::dataflow::EverInitializedPlaces;
43 use crate::dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
44 use crate::util::borrowck_errors::BorrowckErrors;
46 use self::borrow_set::{BorrowData, BorrowSet};
47 use self::flows::Flows;
48 use self::location::LocationTable;
49 use self::prefixes::PrefixSet;
50 use self::MutateMode::{JustWrite, WriteAndRead};
51 use self::mutability_errors::AccessKind;
53 use self::path_utils::*;
61 mod mutability_errors;
64 crate mod places_conflict;
70 // FIXME(eddyb) perhaps move this somewhere more centrally.
77 /// If true, the capture is behind a reference.
80 mutability: Mutability,
83 pub fn provide(providers: &mut Providers<'_>) {
84 *providers = Providers {
90 fn mir_borrowck(tcx: TyCtxt<'_>, def_id: DefId) -> BorrowCheckResult<'_> {
91 let input_body = tcx.mir_validated(def_id);
92 debug!("run query mir_borrowck: {}", tcx.def_path_str(def_id));
94 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
95 let input_body: &Body<'_> = &input_body.borrow();
96 do_mir_borrowck(&infcx, input_body, def_id)
98 debug!("mir_borrowck done");
103 fn do_mir_borrowck<'a, 'tcx>(
104 infcx: &InferCtxt<'a, 'tcx>,
105 input_body: &Body<'tcx>,
107 ) -> BorrowCheckResult<'tcx> {
108 debug!("do_mir_borrowck(def_id = {:?})", def_id);
111 let attributes = tcx.get_attrs(def_id);
112 let param_env = tcx.param_env(def_id);
115 .as_local_hir_id(def_id)
116 .expect("do_mir_borrowck: non-local DefId");
118 // Gather the upvars of a closure, if any.
119 let tables = tcx.typeck_tables_of(def_id);
120 let upvars: Vec<_> = tables
124 .flat_map(|v| v.values())
126 let var_hir_id = upvar_id.var_path.hir_id;
127 let capture = tables.upvar_capture(*upvar_id);
128 let by_ref = match capture {
129 ty::UpvarCapture::ByValue => false,
130 ty::UpvarCapture::ByRef(..) => true,
132 let mut upvar = Upvar {
133 name: tcx.hir().name(var_hir_id),
136 mutability: Mutability::Not,
138 let bm = *tables.pat_binding_modes().get(var_hir_id)
139 .expect("missing binding mode");
140 if bm == ty::BindByValue(hir::MutMutable) {
141 upvar.mutability = Mutability::Mut;
147 // Replace all regions with fresh inference variables. This
148 // requires first making our own copy of the MIR. This copy will
149 // be modified (in place) to contain non-lexical lifetimes. It
150 // will have a lifetime tied to the inference context.
151 let mut body: Body<'tcx> = input_body.clone();
152 let free_regions = nll::replace_regions_in_mir(infcx, def_id, param_env, &mut body);
153 let body = &body; // no further changes
154 let location_table = &LocationTable::new(body);
156 let mut errors_buffer = Vec::new();
157 let (move_data, move_errors): (MoveData<'tcx>, Option<Vec<(Place<'tcx>, MoveError<'tcx>)>>) =
158 match MoveData::gather_moves(body, tcx) {
159 Ok(move_data) => (move_data, None),
160 Err((move_data, move_errors)) => (move_data, Some(move_errors)),
163 let mdpe = MoveDataParamEnv {
164 move_data: move_data,
165 param_env: param_env,
168 let dead_unwinds = BitSet::new_empty(body.basic_blocks().len());
169 let mut flow_inits = FlowAtLocation::new(do_dataflow(
175 MaybeInitializedPlaces::new(tcx, body, &mdpe),
176 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
179 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
180 let borrow_set = Rc::new(BorrowSet::build(
181 tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
183 // If we are in non-lexical mode, compute the non-lexical lifetimes.
184 let (regioncx, polonius_output, opt_closure_req) = nll::compute_regions(
198 // The various `flow_*` structures can be large. We drop `flow_inits` here
199 // so it doesn't overlap with the others below. This reduces peak memory
200 // usage significantly on some benchmarks.
203 let regioncx = Rc::new(regioncx);
205 let flow_borrows = FlowAtLocation::new(do_dataflow(
211 Borrows::new(tcx, body, regioncx.clone(), &borrow_set),
212 |rs, i| DebugFormatted::new(&rs.location(i)),
214 let flow_uninits = FlowAtLocation::new(do_dataflow(
220 MaybeUninitializedPlaces::new(tcx, body, &mdpe),
221 |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
223 let flow_ever_inits = FlowAtLocation::new(do_dataflow(
229 EverInitializedPlaces::new(tcx, body, &mdpe),
230 |bd, i| DebugFormatted::new(&bd.move_data().inits[i]),
233 let movable_generator = match tcx.hir().get(id) {
234 Node::Expr(&hir::Expr {
235 node: hir::ExprKind::Closure(.., Some(hir::GeneratorMovability::Static)),
241 let dominators = body.dominators();
243 let mut mbcx = MirBorrowckCtxt {
247 move_data: &mdpe.move_data,
250 locals_are_invalidated_at_exit,
251 access_place_error_reported: Default::default(),
252 reservation_error_reported: Default::default(),
253 reservation_warnings: Default::default(),
254 move_error_reported: BTreeMap::new(),
255 uninitialized_error_reported: Default::default(),
257 nonlexical_regioncx: regioncx,
258 used_mut: Default::default(),
259 used_mut_upvars: SmallVec::new(),
265 let mut state = Flows::new(
272 if let Some(errors) = move_errors {
273 mbcx.report_move_errors(errors);
275 mbcx.analyze_results(&mut state); // entry point for DataflowResultsConsumer
277 // Convert any reservation warnings into lints.
278 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
279 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
280 let mut initial_diag =
281 mbcx.report_conflicting_borrow(location, (&place, span), bk, &borrow);
283 let lint_root = if let ClearCrossCrate::Set(ref vsi) = mbcx.body.source_scope_local_data {
284 let scope = mbcx.body.source_info(location).scope;
290 // Span and message don't matter; we overwrite them below anyway
291 let mut diag = mbcx.infcx.tcx.struct_span_lint_hir(
292 MUTABLE_BORROW_RESERVATION_CONFLICT, lint_root, DUMMY_SP, "");
294 diag.message = initial_diag.styled_message().clone();
295 diag.span = initial_diag.span.clone();
297 initial_diag.cancel();
298 diag.buffer(&mut mbcx.errors_buffer);
301 // For each non-user used mutable variable, check if it's been assigned from
302 // a user-declared local. If so, then put that local into the used_mut set.
303 // Note that this set is expected to be small - only upvars from closures
304 // would have a chance of erroneously adding non-user-defined mutable vars
306 let temporary_used_locals: FxHashSet<Local> = mbcx.used_mut.iter()
307 .filter(|&local| mbcx.body.local_decls[*local].is_user_variable.is_none())
310 // For the remaining unused locals that are marked as mutable, we avoid linting any that
311 // were never initialized. These locals may have been removed as unreachable code; or will be
312 // linted as unused variables.
313 let unused_mut_locals = mbcx.body.mut_vars_iter()
314 .filter(|local| !mbcx.used_mut.contains(local))
316 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
318 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
319 let used_mut = mbcx.used_mut;
320 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
321 if let ClearCrossCrate::Set(ref vsi) = mbcx.body.source_scope_local_data {
322 let local_decl = &mbcx.body.local_decls[local];
324 // Skip implicit `self` argument for closures
325 if local.index() == 1 && tcx.is_closure(mbcx.mir_def_id) {
329 // Skip over locals that begin with an underscore or have no name
330 match local_decl.name {
331 Some(name) => if name.as_str().starts_with("_") {
337 let span = local_decl.source_info.span;
338 if span.desugaring_kind().is_some() {
339 // If the `mut` arises as part of a desugaring, we should ignore it.
343 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
344 tcx.struct_span_lint_hir(
346 vsi[local_decl.source_info.scope].lint_root,
348 "variable does not need to be mutable",
350 .span_suggestion_short(
354 Applicability::MachineApplicable,
360 // Buffer any move errors that we collected and de-duplicated.
361 for (_, (_, diag)) in mbcx.move_error_reported {
362 diag.buffer(&mut mbcx.errors_buffer);
365 if !mbcx.errors_buffer.is_empty() {
366 mbcx.errors_buffer.sort_by_key(|diag| diag.span.primary_span());
368 if tcx.migrate_borrowck() {
369 // When borrowck=migrate, check if AST-borrowck would
370 // error on the given code.
372 // rust-lang/rust#55492, rust-lang/rust#58776 check the base def id
373 // for errors. AST borrowck is responsible for aggregating
374 // `signalled_any_error` from all of the nested closures here.
375 let base_def_id = tcx.closure_base_def_id(def_id);
377 match tcx.borrowck(base_def_id).signalled_any_error {
378 SignalledError::NoErrorsSeen => {
379 // if AST-borrowck signalled no errors, then
380 // downgrade all the buffered MIR-borrowck errors
383 for err in mbcx.errors_buffer.iter_mut() {
384 downgrade_if_error(err);
387 SignalledError::SawSomeError => {
388 // if AST-borrowck signalled a (cancelled) error,
389 // then we will just emit the buffered
390 // MIR-borrowck errors as normal.
395 for diag in mbcx.errors_buffer.drain(..) {
396 DiagnosticBuilder::new_diagnostic(mbcx.infcx.tcx.sess.diagnostic(), diag).emit();
400 let result = BorrowCheckResult {
401 closure_requirements: opt_closure_req,
402 used_mut_upvars: mbcx.used_mut_upvars,
405 debug!("do_mir_borrowck: result = {:#?}", result);
410 fn downgrade_if_error(diag: &mut Diagnostic) {
412 diag.level = Level::Warning;
414 "this error has been downgraded to a warning for backwards \
415 compatibility with previous releases",
417 "this represents potential undefined behavior in your code and \
418 this warning will become a hard error in the future",
420 "for more information, try `rustc --explain E0729`"
425 pub struct MirBorrowckCtxt<'cx, 'tcx> {
426 infcx: &'cx InferCtxt<'cx, 'tcx>,
427 body: &'cx Body<'tcx>,
429 move_data: &'cx MoveData<'tcx>,
431 /// Map from MIR `Location` to `LocationIndex`; created
432 /// when MIR borrowck begins.
433 location_table: &'cx LocationTable,
435 movable_generator: bool,
436 /// This keeps track of whether local variables are free-ed when the function
437 /// exits even without a `StorageDead`, which appears to be the case for
440 /// I'm not sure this is the right approach - @eddyb could you try and
442 locals_are_invalidated_at_exit: bool,
443 /// This field keeps track of when borrow errors are reported in the access_place function
444 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
445 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
446 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
448 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
449 /// This field keeps track of when borrow conflict errors are reported
450 /// for reservations, so that we don't report seemingly duplicate
451 /// errors for corresponding activations.
453 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
454 // but it is currently inconvenient to track down the `BorrowIndex`
455 // at the time we detect and report a reservation error.
456 reservation_error_reported: FxHashSet<Place<'tcx>>,
457 /// Migration warnings to be reported for #56254. We delay reporting these
458 /// so that we can suppress the warning if there's a corresponding error
459 /// for the activation of the borrow.
460 reservation_warnings: FxHashMap<
462 (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)
464 /// This field keeps track of move errors that are to be reported for given move indicies.
466 /// There are situations where many errors can be reported for a single move out (see #53807)
467 /// and we want only the best of those errors.
469 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
470 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
471 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
472 /// all move errors have been reported, any diagnostics in this map are added to the buffer
475 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
476 /// when errors in the map are being re-added to the error buffer so that errors with the
477 /// same primary span come out in a consistent order.
478 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (Place<'tcx>, DiagnosticBuilder<'cx>)>,
479 /// This field keeps track of errors reported in the checking of uninitialized variables,
480 /// so that we don't report seemingly duplicate errors.
481 uninitialized_error_reported: FxHashSet<Place<'tcx>>,
482 /// Errors to be reported buffer
483 errors_buffer: Vec<Diagnostic>,
484 /// This field keeps track of all the local variables that are declared mut and are mutated.
485 /// Used for the warning issued by an unused mutable local variable.
486 used_mut: FxHashSet<Local>,
487 /// If the function we're checking is a closure, then we'll need to report back the list of
488 /// mutable upvars that have been used. This field keeps track of them.
489 used_mut_upvars: SmallVec<[Field; 8]>,
490 /// Non-lexical region inference context, if NLL is enabled. This
491 /// contains the results from region inference and lets us e.g.
492 /// find out which CFG points are contained in each borrow region.
493 nonlexical_regioncx: Rc<RegionInferenceContext<'tcx>>,
495 /// The set of borrows extracted from the MIR
496 borrow_set: Rc<BorrowSet<'tcx>>,
498 /// Dominators for MIR
499 dominators: Dominators<BasicBlock>,
501 /// Information about upvars not necessarily preserved in types or MIR
506 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
507 // 2. loans made in overlapping scopes do not conflict
508 // 3. assignments do not affect things loaned out as immutable
509 // 4. moves do not affect things loaned out in any way
510 impl<'cx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
511 type FlowState = Flows<'cx, 'tcx>;
513 fn body(&self) -> &'cx Body<'tcx> {
517 fn visit_block_entry(&mut self, bb: BasicBlock, flow_state: &Self::FlowState) {
518 debug!("MirBorrowckCtxt::process_block({:?}): {}", bb, flow_state);
521 fn visit_statement_entry(
524 stmt: &Statement<'tcx>,
525 flow_state: &Self::FlowState,
528 "MirBorrowckCtxt::process_statement({:?}, {:?}): {}",
529 location, stmt, flow_state
531 let span = stmt.source_info.span;
533 self.check_activations(location, span, flow_state);
536 StatementKind::Assign(ref lhs, ref rhs) => {
551 StatementKind::FakeRead(_, ref place) => {
552 // Read for match doesn't access any memory and is used to
553 // assert that a place is safe and live. So we don't have to
554 // do any checks here.
556 // FIXME: Remove check that the place is initialized. This is
557 // needed for now because matches don't have never patterns yet.
558 // So this is the only place we prevent
562 self.check_if_path_or_subpath_is_moved(
564 InitializationRequiringAction::Use,
569 StatementKind::SetDiscriminant {
581 StatementKind::InlineAsm(ref asm) => {
582 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
584 // FIXME(eddyb) indirect inline asm outputs should
585 // be encoded through MIR place derefs instead.
589 (Deep, Read(ReadKind::Copy)),
590 LocalMutationIsAllowed::No,
593 self.check_if_path_or_subpath_is_moved(
595 InitializationRequiringAction::Use,
603 if o.is_rw { Deep } else { Shallow(None) },
604 if o.is_rw { WriteAndRead } else { JustWrite },
609 for (_, input) in asm.inputs.iter() {
610 self.consume_operand(location, (input, span), flow_state);
614 | StatementKind::AscribeUserType(..)
615 | StatementKind::Retag { .. }
616 | StatementKind::StorageLive(..) => {
617 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
620 StatementKind::StorageDead(local) => {
623 (&Place::from(local), span),
624 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
625 LocalMutationIsAllowed::Yes,
632 fn visit_terminator_entry(
635 term: &Terminator<'tcx>,
636 flow_state: &Self::FlowState,
640 "MirBorrowckCtxt::process_terminator({:?}, {:?}): {}",
641 location, term, flow_state
643 let span = term.source_info.span;
645 self.check_activations(location, span, flow_state);
648 TerminatorKind::SwitchInt {
654 self.consume_operand(loc, (discr, span), flow_state);
656 TerminatorKind::Drop {
657 location: ref drop_place,
661 let gcx = self.infcx.tcx.global_tcx();
663 // Compute the type with accurate region information.
664 let drop_place_ty = drop_place.ty(self.body, self.infcx.tcx);
666 // Erase the regions.
667 let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
669 // "Lift" into the gcx -- once regions are erased, this type should be in the
670 // global arenas; this "lift" operation basically just asserts that is true, but
671 // that is useful later.
672 gcx.lift_to_global(&drop_place_ty).unwrap();
674 debug!("visit_terminator_drop \
675 loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
676 loc, term, drop_place, drop_place_ty, span);
681 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
682 LocalMutationIsAllowed::Yes,
686 TerminatorKind::DropAndReplace {
687 location: ref drop_place,
688 value: ref new_value,
699 self.consume_operand(
705 TerminatorKind::Call {
712 self.consume_operand(loc, (func, span), flow_state);
714 self.consume_operand(
720 if let Some((ref dest, _ /*bb*/)) = *destination {
730 TerminatorKind::Assert {
737 self.consume_operand(loc, (cond, span), flow_state);
738 use rustc::mir::interpret::InterpError::BoundsCheck;
739 if let BoundsCheck { ref len, ref index } = *msg {
740 self.consume_operand(loc, (len, span), flow_state);
741 self.consume_operand(loc, (index, span), flow_state);
745 TerminatorKind::Yield {
750 self.consume_operand(loc, (value, span), flow_state);
752 if self.movable_generator {
753 // Look for any active borrows to locals
754 let borrow_set = self.borrow_set.clone();
755 flow_state.with_outgoing_borrows(|borrows| {
757 let borrow = &borrow_set[i];
758 self.check_for_local_borrow(borrow, span);
764 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
765 // Returning from the function implicitly kills storage for all locals and statics.
766 // Often, the storage will already have been killed by an explicit
767 // StorageDead, but we don't always emit those (notably on unwind paths),
768 // so this "extra check" serves as a kind of backup.
769 let borrow_set = self.borrow_set.clone();
770 flow_state.with_outgoing_borrows(|borrows| {
772 let borrow = &borrow_set[i];
773 self.check_for_invalidation_at_exit(loc, borrow, span);
777 TerminatorKind::Goto { target: _ }
778 | TerminatorKind::Abort
779 | TerminatorKind::Unreachable
780 | TerminatorKind::FalseEdges {
784 | TerminatorKind::FalseUnwind {
788 // no data used, thus irrelevant to borrowck
794 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
800 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
801 use self::AccessDepth::{Deep, Shallow};
803 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
804 enum ArtificialField {
809 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
811 /// From the RFC: "A *shallow* access means that the immediate
812 /// fields reached at P are accessed, but references or pointers
813 /// found within are not dereferenced. Right now, the only access
814 /// that is shallow is an assignment like `x = ...;`, which would
815 /// be a *shallow write* of `x`."
816 Shallow(Option<ArtificialField>),
818 /// From the RFC: "A *deep* access means that all data reachable
819 /// through the given place may be invalidated or accesses by
823 /// Access is Deep only when there is a Drop implementation that
824 /// can reach the data behind the reference.
828 /// Kind of access to a value: read or write
829 /// (For informational purposes only)
830 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
832 /// From the RFC: "A *read* means that the existing data may be
833 /// read, but will not be changed."
836 /// From the RFC: "A *write* means that the data may be mutated to
837 /// new values or otherwise invalidated (for example, it could be
838 /// de-initialized, as in a move operation).
841 /// For two-phase borrows, we distinguish a reservation (which is treated
842 /// like a Read) from an activation (which is treated like a write), and
843 /// each of those is furthermore distinguished from Reads/Writes above.
844 Reservation(WriteKind),
845 Activation(WriteKind, BorrowIndex),
848 /// Kind of read access to a value
849 /// (For informational purposes only)
850 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
856 /// Kind of write access to a value
857 /// (For informational purposes only)
858 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
861 MutableBorrow(BorrowKind),
866 /// When checking permissions for a place access, this flag is used to indicate that an immutable
867 /// local place can be mutated.
869 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
870 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
871 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
872 // `is_declared_mutable()`.
873 // - Take flow state into consideration in `is_assignable()` for local variables.
874 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
875 enum LocalMutationIsAllowed {
877 /// We want use of immutable upvars to cause a "write to immutable upvar"
878 /// error, not an "reassignment" error.
883 #[derive(Copy, Clone, Debug)]
884 enum InitializationRequiringAction {
893 struct RootPlace<'d, 'tcx> {
894 place: &'d Place<'tcx>,
895 is_local_mutation_allowed: LocalMutationIsAllowed,
898 impl InitializationRequiringAction {
899 fn as_noun(self) -> &'static str {
901 InitializationRequiringAction::Update => "update",
902 InitializationRequiringAction::Borrow => "borrow",
903 InitializationRequiringAction::MatchOn => "use", // no good noun
904 InitializationRequiringAction::Use => "use",
905 InitializationRequiringAction::Assignment => "assign",
906 InitializationRequiringAction::PartialAssignment => "assign to part",
910 fn as_verb_in_past_tense(self) -> &'static str {
912 InitializationRequiringAction::Update => "updated",
913 InitializationRequiringAction::Borrow => "borrowed",
914 InitializationRequiringAction::MatchOn => "matched on",
915 InitializationRequiringAction::Use => "used",
916 InitializationRequiringAction::Assignment => "assigned",
917 InitializationRequiringAction::PartialAssignment => "partially assigned",
922 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
923 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
924 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
925 /// place is initialized and (b) it is not borrowed in some way that would prevent this
928 /// Returns `true` if an error is reported.
932 place_span: (&Place<'tcx>, Span),
933 kind: (AccessDepth, ReadOrWrite),
934 is_local_mutation_allowed: LocalMutationIsAllowed,
935 flow_state: &Flows<'cx, 'tcx>,
939 if let Activation(_, borrow_index) = rw {
940 if self.reservation_error_reported.contains(&place_span.0) {
942 "skipping access_place for activation of invalid reservation \
943 place: {:?} borrow_index: {:?}",
944 place_span.0, borrow_index
950 // Check is_empty() first because it's the common case, and doing that
951 // way we avoid the clone() call.
952 if !self.access_place_error_reported.is_empty() &&
954 .access_place_error_reported
955 .contains(&(place_span.0.clone(), place_span.1))
958 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
964 let mutability_error =
965 self.check_access_permissions(
968 is_local_mutation_allowed,
973 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
975 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
976 // Suppress this warning when there's an error being emited for the
977 // same borrow: fixing the error is likely to fix the warning.
978 self.reservation_warnings.remove(&borrow_idx);
981 if conflict_error || mutability_error {
983 "access_place: logging error place_span=`{:?}` kind=`{:?}`",
987 self.access_place_error_reported
988 .insert((place_span.0.clone(), place_span.1));
992 fn check_access_for_conflict(
995 place_span: (&Place<'tcx>, Span),
998 flow_state: &Flows<'cx, 'tcx>,
1001 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
1002 location, place_span, sd, rw,
1005 let mut error_reported = false;
1006 let tcx = self.infcx.tcx;
1007 let body = self.body;
1008 let location_table = self.location_table.start_index(location);
1009 let borrow_set = self.borrow_set.clone();
1010 each_borrow_involving_path(
1017 flow_state.borrows_in_scope(location_table),
1018 |this, borrow_index, borrow| match (rw, borrow.kind) {
1019 // Obviously an activation is compatible with its own
1020 // reservation (or even prior activating uses of same
1021 // borrow); so don't check if they interfere.
1023 // NOTE: *reservations* do conflict with themselves;
1024 // thus aren't injecting unsoundenss w/ this check.)
1025 (Activation(_, activating), _) if activating == borrow_index => {
1027 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1028 skipping {:?} b/c activation of same borrow_index",
1032 (borrow_index, borrow),
1037 (Read(_), BorrowKind::Shared)
1038 | (Read(_), BorrowKind::Shallow)
1039 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
1040 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
1044 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1045 // Handled by initialization checks.
1049 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
1050 // Reading from mere reservations of mutable-borrows is OK.
1051 if !is_active(&this.dominators, borrow, location) {
1052 assert!(allow_two_phase_borrow(borrow.kind));
1053 return Control::Continue;
1056 error_reported = true;
1059 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1060 .buffer(&mut this.errors_buffer);
1062 ReadKind::Borrow(bk) => {
1063 this.report_conflicting_borrow(location, place_span, bk, borrow)
1064 .buffer(&mut this.errors_buffer);
1070 (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shallow)
1071 | (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shared) if {
1072 tcx.migrate_borrowck() && this.borrow_set.location_map.contains_key(&location)
1074 let bi = this.borrow_set.location_map[&location];
1076 "recording invalid reservation of place: {:?} with \
1077 borrow index {:?} as warning",
1081 // rust-lang/rust#56254 - This was previously permitted on
1082 // the 2018 edition so we emit it as a warning. We buffer
1083 // these sepately so that we only emit a warning if borrow
1084 // checking was otherwise successful.
1085 this.reservation_warnings.insert(
1087 (place_span.0.clone(), place_span.1, location, bk, borrow.clone()),
1090 // Don't suppress actual errors.
1094 (Reservation(kind), _)
1095 | (Activation(kind, _), _)
1096 | (Write(kind), _) => {
1098 Reservation(..) => {
1100 "recording invalid reservation of \
1104 this.reservation_error_reported.insert(place_span.0.clone());
1106 Activation(_, activating) => {
1108 "observing check_place for activation of \
1109 borrow_index: {:?}",
1113 Read(..) | Write(..) => {}
1116 error_reported = true;
1118 WriteKind::MutableBorrow(bk) => {
1119 this.report_conflicting_borrow(location, place_span, bk, borrow)
1120 .buffer(&mut this.errors_buffer);
1122 WriteKind::StorageDeadOrDrop => {
1123 this.report_borrowed_value_does_not_live_long_enough(
1129 WriteKind::Mutate => {
1130 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1132 WriteKind::Move => {
1133 this.report_move_out_while_borrowed(location, place_span, borrow)
1147 place_span: (&Place<'tcx>, Span),
1150 flow_state: &Flows<'cx, 'tcx>,
1152 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1154 MutateMode::WriteAndRead => {
1155 self.check_if_path_or_subpath_is_moved(
1157 InitializationRequiringAction::Update,
1162 MutateMode::JustWrite => {
1163 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1167 // Special case: you can assign a immutable local variable
1168 // (e.g., `x = ...`) so long as it has never been initialized
1169 // before (at this point in the flow).
1170 if let &Place::Base(PlaceBase::Local(local)) = place_span.0 {
1171 if let Mutability::Not = self.body.local_decls[local].mutability {
1172 // check for reassignments to immutable local variables
1173 self.check_if_reassignment_to_immutable_state(
1183 // Otherwise, use the normal access permission rules.
1187 (kind, Write(WriteKind::Mutate)),
1188 LocalMutationIsAllowed::No,
1196 (rvalue, span): (&Rvalue<'tcx>, Span),
1197 flow_state: &Flows<'cx, 'tcx>,
1200 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1201 let access_kind = match bk {
1202 BorrowKind::Shallow => {
1203 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1205 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1206 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1207 let wk = WriteKind::MutableBorrow(bk);
1208 if allow_two_phase_borrow(bk) {
1209 (Deep, Reservation(wk))
1220 LocalMutationIsAllowed::No,
1224 let action = if bk == BorrowKind::Shallow {
1225 InitializationRequiringAction::MatchOn
1227 InitializationRequiringAction::Borrow
1230 self.check_if_path_or_subpath_is_moved(
1238 Rvalue::Use(ref operand)
1239 | Rvalue::Repeat(ref operand, _)
1240 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1241 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1242 self.consume_operand(location, (operand, span), flow_state)
1245 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1246 let af = match *rvalue {
1247 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1248 Rvalue::Discriminant(..) => None,
1249 _ => unreachable!(),
1254 (Shallow(af), Read(ReadKind::Copy)),
1255 LocalMutationIsAllowed::No,
1258 self.check_if_path_or_subpath_is_moved(
1260 InitializationRequiringAction::Use,
1266 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1267 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1268 self.consume_operand(location, (operand1, span), flow_state);
1269 self.consume_operand(location, (operand2, span), flow_state);
1272 Rvalue::NullaryOp(_op, _ty) => {
1273 // nullary ops take no dynamic input; no borrowck effect.
1275 // FIXME: is above actually true? Do we want to track
1276 // the fact that uninitialized data can be created via
1280 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1281 // We need to report back the list of mutable upvars that were
1282 // moved into the closure and subsequently used by the closure,
1283 // in order to populate our used_mut set.
1284 match **aggregate_kind {
1285 AggregateKind::Closure(def_id, _)
1286 | AggregateKind::Generator(def_id, _, _) => {
1287 let BorrowCheckResult {
1289 } = self.infcx.tcx.mir_borrowck(def_id);
1290 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1291 for field in used_mut_upvars {
1292 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1295 AggregateKind::Adt(..)
1296 | AggregateKind::Array(..)
1297 | AggregateKind::Tuple { .. } => (),
1300 for operand in operands {
1301 self.consume_operand(location, (operand, span), flow_state);
1307 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1308 let propagate_closure_used_mut_place = |this: &mut Self, place: &Place<'tcx>| {
1310 Place::Projection { .. } => {
1311 if let Some(field) = this.is_upvar_field_projection(place) {
1312 this.used_mut_upvars.push(field);
1315 Place::Base(PlaceBase::Local(local)) => {
1316 this.used_mut.insert(local);
1318 Place::Base(PlaceBase::Static(_)) => {}
1322 // This relies on the current way that by-value
1323 // captures of a closure are copied/moved directly
1324 // when generating MIR.
1326 Operand::Move(Place::Base(PlaceBase::Local(local)))
1327 | Operand::Copy(Place::Base(PlaceBase::Local(local)))
1328 if self.body.local_decls[local].is_user_variable.is_none() =>
1330 if self.body.local_decls[local].ty.is_mutable_pointer() {
1331 // The variable will be marked as mutable by the borrow.
1334 // This is an edge case where we have a `move` closure
1335 // inside a non-move closure, and the inner closure
1336 // contains a mutation:
1339 // || { move || { i += 1; }; };
1341 // In this case our usual strategy of assuming that the
1342 // variable will be captured by mutable reference is
1343 // wrong, since `i` can be copied into the inner
1344 // closure from a shared reference.
1346 // As such we have to search for the local that this
1347 // capture comes from and mark it as being used as mut.
1349 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1350 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1351 &self.move_data.inits[init_index]
1353 bug!("temporary should be initialized exactly once")
1356 let loc = match init.location {
1357 InitLocation::Statement(stmt) => stmt,
1358 _ => bug!("temporary initialized in arguments"),
1361 let bbd = &self.body[loc.block];
1362 let stmt = &bbd.statements[loc.statement_index];
1363 debug!("temporary assigned in: stmt={:?}", stmt);
1365 if let StatementKind::Assign(_, box Rvalue::Ref(_, _, ref source)) = stmt.kind {
1366 propagate_closure_used_mut_place(self, source);
1368 bug!("closures should only capture user variables \
1369 or references to user variables");
1372 Operand::Move(ref place)
1373 | Operand::Copy(ref place) => {
1374 propagate_closure_used_mut_place(self, place);
1376 Operand::Constant(..) => {}
1383 (operand, span): (&Operand<'tcx>, Span),
1384 flow_state: &Flows<'cx, 'tcx>,
1387 Operand::Copy(ref place) => {
1388 // copy of place: check if this is "copy of frozen path"
1389 // (FIXME: see check_loans.rs)
1393 (Deep, Read(ReadKind::Copy)),
1394 LocalMutationIsAllowed::No,
1398 // Finally, check if path was already moved.
1399 self.check_if_path_or_subpath_is_moved(
1401 InitializationRequiringAction::Use,
1406 Operand::Move(ref place) => {
1407 // move of place: check if this is move of already borrowed path
1411 (Deep, Write(WriteKind::Move)),
1412 LocalMutationIsAllowed::Yes,
1416 // Finally, check if path was already moved.
1417 self.check_if_path_or_subpath_is_moved(
1419 InitializationRequiringAction::Use,
1424 Operand::Constant(_) => {}
1428 /// Checks whether a borrow of this place is invalidated when the function
1430 fn check_for_invalidation_at_exit(
1433 borrow: &BorrowData<'tcx>,
1436 debug!("check_for_invalidation_at_exit({:?})", borrow);
1437 let place = &borrow.borrowed_place;
1438 let root_place = self.prefixes(place, PrefixSet::All).last().unwrap();
1440 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1441 // we just know that all locals are dropped at function exit (otherwise
1442 // we'll have a memory leak) and assume that all statics have a destructor.
1444 // FIXME: allow thread-locals to borrow other thread locals?
1445 let (might_be_alive, will_be_dropped) = match root_place {
1446 Place::Base(PlaceBase::Static(box Static{ kind: StaticKind::Promoted(_), .. })) => {
1449 Place::Base(PlaceBase::Static(box Static{ kind: StaticKind::Static(_), .. })) => {
1450 // Thread-locals might be dropped after the function exits, but
1451 // "true" statics will never be.
1452 (true, self.is_place_thread_local(&root_place))
1454 Place::Base(PlaceBase::Local(_)) => {
1455 // Locals are always dropped at function exit, and if they
1456 // have a destructor it would've been called already.
1457 (false, self.locals_are_invalidated_at_exit)
1459 Place::Projection(..) => {
1460 bug!("root of {:?} is a projection ({:?})?", place, root_place)
1464 if !will_be_dropped {
1466 "place_is_invalidated_at_exit({:?}) - won't be dropped",
1472 let sd = if might_be_alive { Deep } else { Shallow(None) };
1474 if places_conflict::borrow_conflicts_with_place(
1481 places_conflict::PlaceConflictBias::Overlap,
1483 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1484 // FIXME: should be talking about the region lifetime instead
1485 // of just a span here.
1486 let span = self.infcx.tcx.sess.source_map().end_point(span);
1487 self.report_borrowed_value_does_not_live_long_enough(
1496 /// Reports an error if this is a borrow of local data.
1497 /// This is called for all Yield statements on movable generators
1498 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1499 debug!("check_for_local_borrow({:?})", borrow);
1501 if borrow_of_local_data(&borrow.borrowed_place) {
1502 let err = self.infcx.tcx
1503 .cannot_borrow_across_generator_yield(
1504 self.retrieve_borrow_spans(borrow).var_or_use(),
1508 err.buffer(&mut self.errors_buffer);
1512 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1513 // Two-phase borrow support: For each activation that is newly
1514 // generated at this statement, check if it interferes with
1516 let borrow_set = self.borrow_set.clone();
1517 for &borrow_index in borrow_set.activations_at_location(location) {
1518 let borrow = &borrow_set[borrow_index];
1520 // only mutable borrows should be 2-phase
1521 assert!(match borrow.kind {
1522 BorrowKind::Shared | BorrowKind::Shallow => false,
1523 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1528 (&borrow.borrowed_place, span),
1531 Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index),
1533 LocalMutationIsAllowed::No,
1536 // We do not need to call `check_if_path_or_subpath_is_moved`
1537 // again, as we already called it when we made the
1538 // initial reservation.
1543 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
1544 fn check_if_reassignment_to_immutable_state(
1548 place_span: (&Place<'tcx>, Span),
1549 flow_state: &Flows<'cx, 'tcx>,
1551 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1553 // Check if any of the initializiations of `local` have happened yet:
1554 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1555 // And, if so, report an error.
1556 let init = &self.move_data.inits[init_index];
1557 let span = init.span(&self.body);
1558 self.report_illegal_reassignment(
1559 location, place_span, span, place_span.0
1564 fn check_if_full_path_is_moved(
1567 desired_action: InitializationRequiringAction,
1568 place_span: (&Place<'tcx>, Span),
1569 flow_state: &Flows<'cx, 'tcx>,
1571 let maybe_uninits = &flow_state.uninits;
1575 // 1. Move of `a.b.c`, use of `a.b.c`
1576 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1577 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1578 // partial initialization support, one might have `a.x`
1579 // initialized but not `a.b`.
1583 // 4. Move of `a.b.c`, use of `a.b.d`
1584 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1585 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1586 // must have been initialized for the use to be sound.
1587 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1589 // The dataflow tracks shallow prefixes distinctly (that is,
1590 // field-accesses on P distinctly from P itself), in order to
1591 // track substructure initialization separately from the whole
1594 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1595 // which we have a MovePath is `a.b`, then that means that the
1596 // initialization state of `a.b` is all we need to inspect to
1597 // know if `a.b.c` is valid (and from that we infer that the
1598 // dereference and `.d` access is also valid, since we assume
1599 // `a.b.c` is assigned a reference to a initialized and
1600 // well-formed record structure.)
1602 // Therefore, if we seek out the *closest* prefix for which we
1603 // have a MovePath, that should capture the initialization
1604 // state for the place scenario.
1606 // This code covers scenarios 1, 2, and 3.
1608 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1609 match self.move_path_closest_to(place_span.0) {
1610 Ok((prefix, mpi)) => {
1611 if maybe_uninits.contains(mpi) {
1612 self.report_use_of_moved_or_uninitialized(
1615 (prefix, place_span.0, place_span.1),
1618 return; // don't bother finding other problems.
1621 Err(NoMovePathFound::ReachedStatic) => {
1622 // Okay: we do not build MoveData for static variables
1623 } // Only query longest prefix with a MovePath, not further
1624 // ancestors; dataflow recurs on children when parents
1625 // move (to support partial (re)inits).
1627 // (I.e., querying parents breaks scenario 7; but may want
1628 // to do such a query based on partial-init feature-gate.)
1632 fn check_if_path_or_subpath_is_moved(
1635 desired_action: InitializationRequiringAction,
1636 place_span: (&Place<'tcx>, Span),
1637 flow_state: &Flows<'cx, 'tcx>,
1639 let maybe_uninits = &flow_state.uninits;
1643 // 1. Move of `a.b.c`, use of `a` or `a.b`
1644 // partial initialization support, one might have `a.x`
1645 // initialized but not `a.b`.
1646 // 2. All bad scenarios from `check_if_full_path_is_moved`
1650 // 3. Move of `a.b.c`, use of `a.b.d`
1651 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1652 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1653 // must have been initialized for the use to be sound.
1654 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1656 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1658 // A move of any shallow suffix of `place` also interferes
1659 // with an attempt to use `place`. This is scenario 3 above.
1661 // (Distinct from handling of scenarios 1+2+4 above because
1662 // `place` does not interfere with suffixes of its prefixes,
1663 // e.g., `a.b.c` does not interfere with `a.b.d`)
1665 // This code covers scenario 1.
1667 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1668 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1669 if let Some(child_mpi) = maybe_uninits.has_any_child_of(mpi) {
1670 self.report_use_of_moved_or_uninitialized(
1673 (place_span.0, place_span.0, place_span.1),
1676 return; // don't bother finding other problems.
1681 /// Currently MoveData does not store entries for all places in
1682 /// the input MIR. For example it will currently filter out
1683 /// places that are Copy; thus we do not track places of shared
1684 /// reference type. This routine will walk up a place along its
1685 /// prefixes, searching for a foundational place that *is*
1686 /// tracked in the MoveData.
1688 /// An Err result includes a tag indicated why the search failed.
1689 /// Currently this can only occur if the place is built off of a
1690 /// static variable, as we do not track those in the MoveData.
1691 fn move_path_closest_to<'a>(
1693 place: &'a Place<'tcx>,
1694 ) -> Result<(&'a Place<'tcx>, MovePathIndex), NoMovePathFound> where 'cx: 'a {
1695 let mut last_prefix = place;
1696 for prefix in self.prefixes(place, PrefixSet::All) {
1697 if let Some(mpi) = self.move_path_for_place(prefix) {
1698 return Ok((prefix, mpi));
1700 last_prefix = prefix;
1702 match *last_prefix {
1703 Place::Base(PlaceBase::Local(_)) => panic!("should have move path for every Local"),
1704 Place::Projection(_) => panic!("PrefixSet::All meant don't stop for Projection"),
1705 Place::Base(PlaceBase::Static(_)) => Err(NoMovePathFound::ReachedStatic),
1709 fn move_path_for_place(&mut self, place: &Place<'tcx>) -> Option<MovePathIndex> {
1710 // If returns None, then there is no move path corresponding
1711 // to a direct owner of `place` (which means there is nothing
1712 // that borrowck tracks for its analysis).
1714 match self.move_data.rev_lookup.find(place) {
1715 LookupResult::Parent(_) => None,
1716 LookupResult::Exact(mpi) => Some(mpi),
1720 fn check_if_assigned_path_is_moved(
1723 (place, span): (&Place<'tcx>, Span),
1724 flow_state: &Flows<'cx, 'tcx>,
1726 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1727 // recur down place; dispatch to external checks when necessary
1728 let mut place = place;
1731 Place::Base(PlaceBase::Local(_)) | Place::Base(PlaceBase::Static(_)) => {
1732 // assigning to `x` does not require `x` be initialized.
1735 Place::Projection(ref proj) => {
1736 let Projection { ref base, ref elem } = **proj;
1738 ProjectionElem::Index(_/*operand*/) |
1739 ProjectionElem::ConstantIndex { .. } |
1740 // assigning to P[i] requires P to be valid.
1741 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1742 // assigning to (P->variant) is okay if assigning to `P` is okay
1744 // FIXME: is this true even if P is a adt with a dtor?
1747 // assigning to (*P) requires P to be initialized
1748 ProjectionElem::Deref => {
1749 self.check_if_full_path_is_moved(
1750 location, InitializationRequiringAction::Use,
1751 (base, span), flow_state);
1752 // (base initialized; no need to
1757 ProjectionElem::Subslice { .. } => {
1758 panic!("we don't allow assignments to subslices, location: {:?}",
1762 ProjectionElem::Field(..) => {
1763 // if type of `P` has a dtor, then
1764 // assigning to `P.f` requires `P` itself
1765 // be already initialized
1766 let tcx = self.infcx.tcx;
1767 match base.ty(self.body, tcx).ty.sty {
1768 ty::Adt(def, _) if def.has_dtor(tcx) => {
1769 self.check_if_path_or_subpath_is_moved(
1770 location, InitializationRequiringAction::Assignment,
1771 (base, span), flow_state);
1773 // (base initialized; no need to
1779 // Once `let s; s.x = V; read(s.x);`,
1780 // is allowed, remove this match arm.
1781 ty::Adt(..) | ty::Tuple(..) => {
1782 check_parent_of_field(self, location, base, span, flow_state);
1784 if let Some(local) = place.base_local() {
1785 // rust-lang/rust#21232,
1786 // #54499, #54986: during
1787 // period where we reject
1788 // partial initialization, do
1789 // not complain about
1790 // unnecessary `mut` on an
1791 // attempt to do a partial
1793 self.used_mut.insert(local);
1807 fn check_parent_of_field<'cx, 'tcx>(
1808 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1812 flow_state: &Flows<'cx, 'tcx>,
1814 // rust-lang/rust#21232: Until Rust allows reads from the
1815 // initialized parts of partially initialized structs, we
1816 // will, starting with the 2018 edition, reject attempts
1817 // to write to structs that are not fully initialized.
1819 // In other words, *until* we allow this:
1821 // 1. `let mut s; s.x = Val; read(s.x);`
1823 // we will for now disallow this:
1825 // 2. `let mut s; s.x = Val;`
1829 // 3. `let mut s = ...; drop(s); s.x=Val;`
1831 // This does not use check_if_path_or_subpath_is_moved,
1832 // because we want to *allow* reinitializations of fields:
1833 // e.g., want to allow
1835 // `let mut s = ...; drop(s.x); s.x=Val;`
1837 // This does not use check_if_full_path_is_moved on
1838 // `base`, because that would report an error about the
1839 // `base` as a whole, but in this scenario we *really*
1840 // want to report an error about the actual thing that was
1841 // moved, which may be some prefix of `base`.
1843 // Shallow so that we'll stop at any dereference; we'll
1844 // report errors about issues with such bases elsewhere.
1845 let maybe_uninits = &flow_state.uninits;
1847 // Find the shortest uninitialized prefix you can reach
1848 // without going over a Deref.
1849 let mut shortest_uninit_seen = None;
1850 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1851 let mpi = match this.move_path_for_place(prefix) {
1852 Some(mpi) => mpi, None => continue,
1855 if maybe_uninits.contains(mpi) {
1856 debug!("check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1857 shortest_uninit_seen, Some((prefix, mpi)));
1858 shortest_uninit_seen = Some((prefix, mpi));
1860 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1864 if let Some((prefix, mpi)) = shortest_uninit_seen {
1865 // Check for a reassignment into a uninitialized field of a union (for example,
1866 // after a move out). In this case, do not report a error here. There is an
1867 // exception, if this is the first assignment into the union (that is, there is
1868 // no move out from an earlier location) then this is an attempt at initialization
1869 // of the union - we should error in that case.
1870 let tcx = this.infcx.tcx;
1871 if let ty::Adt(def, _) = base.ty(this.body, tcx).ty.sty {
1873 if this.move_data.path_map[mpi].iter().any(|moi| {
1874 this.move_data.moves[*moi].source.is_predecessor_of(
1875 location, this.body,
1883 this.report_use_of_moved_or_uninitialized(
1885 InitializationRequiringAction::PartialAssignment,
1886 (prefix, base, span),
1893 /// Checks the permissions for the given place and read or write kind
1895 /// Returns `true` if an error is reported.
1896 fn check_access_permissions(
1898 (place, span): (&Place<'tcx>, Span),
1900 is_local_mutation_allowed: LocalMutationIsAllowed,
1901 flow_state: &Flows<'cx, 'tcx>,
1905 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1906 place, kind, is_local_mutation_allowed
1912 // rust-lang/rust#21232, #54986: during period where we reject
1913 // partial initialization, do not complain about mutability
1914 // errors except for actual mutation (as opposed to an attempt
1915 // to do a partial initialization).
1916 let previously_initialized = if let Some(local) = place.base_local() {
1917 self.is_local_ever_initialized(local, flow_state).is_some()
1923 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1924 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1925 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1926 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1927 let is_local_mutation_allowed = match borrow_kind {
1928 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1929 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1930 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1932 match self.is_mutable(place, is_local_mutation_allowed) {
1934 self.add_used_mut(root_place, flow_state);
1938 error_access = AccessKind::MutableBorrow;
1939 the_place_err = place_err;
1943 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1944 match self.is_mutable(place, is_local_mutation_allowed) {
1946 self.add_used_mut(root_place, flow_state);
1950 error_access = AccessKind::Mutate;
1951 the_place_err = place_err;
1956 Reservation(wk @ WriteKind::Move)
1957 | Write(wk @ WriteKind::Move)
1958 | Reservation(wk @ WriteKind::StorageDeadOrDrop)
1959 | Reservation(wk @ WriteKind::MutableBorrow(BorrowKind::Shared))
1960 | Reservation(wk @ WriteKind::MutableBorrow(BorrowKind::Shallow))
1961 | Write(wk @ WriteKind::StorageDeadOrDrop)
1962 | Write(wk @ WriteKind::MutableBorrow(BorrowKind::Shared))
1963 | Write(wk @ WriteKind::MutableBorrow(BorrowKind::Shallow)) => {
1964 if let (Err(_place_err), true) = (
1965 self.is_mutable(place, is_local_mutation_allowed),
1966 self.errors_buffer.is_empty()
1968 if self.infcx.tcx.migrate_borrowck() {
1969 // rust-lang/rust#46908: In pure NLL mode this
1970 // code path should be unreachable (and thus
1971 // we signal an ICE in the else branch
1972 // here). But we can legitimately get here
1973 // under borrowck=migrate mode, so instead of
1974 // ICE'ing we instead report a legitimate
1975 // error (which will then be downgraded to a
1976 // warning by the migrate machinery).
1977 error_access = match wk {
1978 WriteKind::MutableBorrow(_) => AccessKind::MutableBorrow,
1979 WriteKind::Move => AccessKind::Move,
1980 WriteKind::StorageDeadOrDrop |
1981 WriteKind::Mutate => AccessKind::Mutate,
1983 self.report_mutability_error(
1993 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2002 // permission checks are done at Reservation point.
2005 Read(ReadKind::Borrow(BorrowKind::Unique))
2006 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
2007 | Read(ReadKind::Borrow(BorrowKind::Shared))
2008 | Read(ReadKind::Borrow(BorrowKind::Shallow))
2009 | Read(ReadKind::Copy) => {
2010 // Access authorized
2015 // at this point, we have set up the error reporting state.
2016 return if previously_initialized {
2017 self.report_mutability_error(
2030 fn is_local_ever_initialized(
2033 flow_state: &Flows<'cx, 'tcx>,
2034 ) -> Option<InitIndex> {
2035 let mpi = self.move_data.rev_lookup.find_local(local);
2036 let ii = &self.move_data.init_path_map[mpi];
2038 if flow_state.ever_inits.contains(index) {
2045 /// Adds the place into the used mutable variables set
2046 fn add_used_mut<'d>(&mut self, root_place: RootPlace<'d, 'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2049 place: Place::Base(PlaceBase::Local(local)),
2050 is_local_mutation_allowed,
2052 // If the local may have been initialized, and it is now currently being
2053 // mutated, then it is justified to be annotated with the `mut`
2054 // keyword, since the mutation may be a possible reassignment.
2055 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes &&
2056 self.is_local_ever_initialized(*local, flow_state).is_some()
2058 self.used_mut.insert(*local);
2063 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2066 place: place @ Place::Projection(_),
2067 is_local_mutation_allowed: _,
2069 if let Some(field) = self.is_upvar_field_projection(place) {
2070 self.used_mut_upvars.push(field);
2074 place: Place::Base(PlaceBase::Static(..)),
2075 is_local_mutation_allowed: _,
2080 /// Whether this value can be written or borrowed mutably.
2081 /// Returns the root place if the place passed in is a projection.
2084 place: &'d Place<'tcx>,
2085 is_local_mutation_allowed: LocalMutationIsAllowed,
2086 ) -> Result<RootPlace<'d, 'tcx>, &'d Place<'tcx>> {
2088 Place::Base(PlaceBase::Local(local)) => {
2089 let local = &self.body.local_decls[local];
2090 match local.mutability {
2091 Mutability::Not => match is_local_mutation_allowed {
2092 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2094 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2096 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2098 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2100 LocalMutationIsAllowed::No => Err(place),
2102 Mutability::Mut => Ok(RootPlace {
2104 is_local_mutation_allowed,
2108 // The rules for promotion are made by `qualify_consts`, there wouldn't even be a
2109 // `Place::Promoted` if the promotion weren't 100% legal. So we just forward this
2110 Place::Base(PlaceBase::Static(box Static{kind: StaticKind::Promoted(_), ..})) =>
2113 is_local_mutation_allowed,
2115 Place::Base(PlaceBase::Static(box Static{ kind: StaticKind::Static(def_id), .. })) => {
2116 if !self.infcx.tcx.is_mutable_static(def_id) {
2121 is_local_mutation_allowed,
2125 Place::Projection(ref proj) => {
2127 ProjectionElem::Deref => {
2128 let base_ty = proj.base.ty(self.body, self.infcx.tcx).ty;
2130 // Check the kind of deref to decide
2132 ty::Ref(_, _, mutbl) => {
2134 // Shared borrowed data is never mutable
2135 hir::MutImmutable => Err(place),
2136 // Mutably borrowed data is mutable, but only if we have a
2137 // unique path to the `&mut`
2138 hir::MutMutable => {
2139 let mode = match self.is_upvar_field_projection(place) {
2141 if self.upvars[field.index()].by_ref =>
2143 is_local_mutation_allowed
2145 _ => LocalMutationIsAllowed::Yes,
2148 self.is_mutable(&proj.base, mode)
2152 ty::RawPtr(tnm) => {
2154 // `*const` raw pointers are not mutable
2155 hir::MutImmutable => Err(place),
2156 // `*mut` raw pointers are always mutable, regardless of
2157 // context. The users have to check by themselves.
2158 hir::MutMutable => {
2161 is_local_mutation_allowed,
2166 // `Box<T>` owns its content, so mutable if its location is mutable
2167 _ if base_ty.is_box() => {
2168 self.is_mutable(&proj.base, is_local_mutation_allowed)
2170 // Deref should only be for reference, pointers or boxes
2171 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2174 // All other projections are owned by their base path, so mutable if
2175 // base path is mutable
2176 ProjectionElem::Field(..)
2177 | ProjectionElem::Index(..)
2178 | ProjectionElem::ConstantIndex { .. }
2179 | ProjectionElem::Subslice { .. }
2180 | ProjectionElem::Downcast(..) => {
2181 let upvar_field_projection = self.is_upvar_field_projection(place);
2182 if let Some(field) = upvar_field_projection {
2183 let upvar = &self.upvars[field.index()];
2185 "upvar.mutability={:?} local_mutation_is_allowed={:?} place={:?}",
2186 upvar, is_local_mutation_allowed, place
2188 match (upvar.mutability, is_local_mutation_allowed) {
2189 (Mutability::Not, LocalMutationIsAllowed::No)
2190 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2193 (Mutability::Not, LocalMutationIsAllowed::Yes)
2194 | (Mutability::Mut, _) => {
2195 // Subtle: this is an upvar
2196 // reference, so it looks like
2197 // `self.foo` -- we want to double
2198 // check that the location `*self`
2199 // is mutable (i.e., this is not a
2200 // `Fn` closure). But if that
2201 // check succeeds, we want to
2202 // *blame* the mutability on
2203 // `place` (that is,
2204 // `self.foo`). This is used to
2205 // propagate the info about
2206 // whether mutability declarations
2207 // are used outwards, so that we register
2208 // the outer variable as mutable. Otherwise a
2209 // test like this fails to record the `mut`
2213 // fn foo<F: FnOnce()>(_f: F) { }
2215 // let var = Vec::new();
2221 let _ = self.is_mutable(&proj.base, is_local_mutation_allowed)?;
2224 is_local_mutation_allowed,
2229 self.is_mutable(&proj.base, is_local_mutation_allowed)
2237 /// If `place` is a field projection, and the field is being projected from a closure type,
2238 /// then returns the index of the field being projected. Note that this closure will always
2239 /// be `self` in the current MIR, because that is the only time we directly access the fields
2240 /// of a closure type.
2241 pub fn is_upvar_field_projection(&self, place: &Place<'tcx>) -> Option<Field> {
2242 let (place, by_ref) = if let Place::Projection(ref proj) = place {
2243 if let ProjectionElem::Deref = proj.elem {
2253 Place::Projection(ref proj) => match proj.elem {
2254 ProjectionElem::Field(field, _ty) => {
2255 let tcx = self.infcx.tcx;
2256 let base_ty = proj.base.ty(self.body, tcx).ty;
2258 if (base_ty.is_closure() || base_ty.is_generator()) &&
2259 (!by_ref || self.upvars[field.index()].by_ref)
2273 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2274 enum NoMovePathFound {
2278 /// The degree of overlap between 2 places for borrow-checking.
2280 /// The places might partially overlap - in this case, we give
2281 /// up and say that they might conflict. This occurs when
2282 /// different fields of a union are borrowed. For example,
2283 /// if `u` is a union, we have no way of telling how disjoint
2284 /// `u.a.x` and `a.b.y` are.
2286 /// The places have the same type, and are either completely disjoint
2287 /// or equal - i.e., they can't "partially" overlap as can occur with
2288 /// unions. This is the "base case" on which we recur for extensions
2291 /// The places are disjoint, so we know all extensions of them
2292 /// will also be disjoint.