1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 use rustc::lint::builtin::MUTABLE_BORROW_RESERVATION_CONFLICT;
4 use rustc::lint::builtin::UNUSED_MUT;
6 read_only, traversal, Body, BodyAndCache, ClearCrossCrate, Local, Location, Mutability,
7 Operand, Place, PlaceElem, PlaceRef, ReadOnlyBodyAndCache,
9 use rustc::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
10 use rustc::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
11 use rustc::mir::{Terminator, TerminatorKind};
12 use rustc::ty::query::Providers;
13 use rustc::ty::{self, RegionVid, TyCtxt};
15 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
16 use rustc_data_structures::graph::dominators::Dominators;
17 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder};
19 use rustc_hir::{def_id::DefId, HirId, Node};
20 use rustc_index::bit_set::BitSet;
21 use rustc_index::vec::IndexVec;
22 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
25 use smallvec::SmallVec;
26 use std::cell::RefCell;
27 use std::collections::BTreeMap;
31 use rustc_ast::ast::Name;
32 use rustc_span::{Span, DUMMY_SP};
35 use crate::dataflow::generic::{Analysis, BorrowckFlowState as Flows, BorrowckResults};
36 use crate::dataflow::indexes::{BorrowIndex, InitIndex, MoveOutIndex, MovePathIndex};
37 use crate::dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
38 use crate::dataflow::Borrows;
39 use crate::dataflow::EverInitializedPlaces;
40 use crate::dataflow::MoveDataParamEnv;
41 use crate::dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
42 use crate::transform::MirSource;
44 use self::diagnostics::{AccessKind, RegionName};
45 use self::location::LocationTable;
46 use self::prefixes::PrefixSet;
47 use self::MutateMode::{JustWrite, WriteAndRead};
49 use self::path_utils::*;
52 mod constraint_generation;
58 mod member_constraints;
67 mod universal_regions;
70 crate use borrow_set::{BorrowData, BorrowSet};
71 crate use nll::{PoloniusOutput, ToRegionVid};
72 crate use place_ext::PlaceExt;
73 crate use places_conflict::{places_conflict, PlaceConflictBias};
74 crate use region_infer::RegionInferenceContext;
76 // FIXME(eddyb) perhaps move this somewhere more centrally.
83 /// If true, the capture is behind a reference.
86 mutability: Mutability,
89 const DEREF_PROJECTION: &[PlaceElem<'_>; 1] = &[ProjectionElem::Deref];
91 pub fn provide(providers: &mut Providers<'_>) {
92 *providers = Providers { mir_borrowck, ..*providers };
95 fn mir_borrowck(tcx: TyCtxt<'_>, def_id: DefId) -> &BorrowCheckResult<'_> {
96 let (input_body, promoted) = tcx.mir_validated(def_id);
97 debug!("run query mir_borrowck: {}", tcx.def_path_str(def_id));
99 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
100 let input_body: &Body<'_> = &input_body.borrow();
101 let promoted: &IndexVec<_, _> = &promoted.borrow();
102 do_mir_borrowck(&infcx, input_body, promoted, def_id)
104 debug!("mir_borrowck done");
106 tcx.arena.alloc(opt_closure_req)
109 fn do_mir_borrowck<'a, 'tcx>(
110 infcx: &InferCtxt<'a, 'tcx>,
111 input_body: &Body<'tcx>,
112 input_promoted: &IndexVec<Promoted, BodyAndCache<'tcx>>,
114 ) -> BorrowCheckResult<'tcx> {
115 debug!("do_mir_borrowck(def_id = {:?})", def_id);
118 let param_env = tcx.param_env(def_id);
119 let id = tcx.hir().as_local_hir_id(def_id).expect("do_mir_borrowck: non-local DefId");
121 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
122 for var_debug_info in &input_body.var_debug_info {
123 if let Some(local) = var_debug_info.place.as_local() {
124 if let Some(prev_name) = local_names[local] {
125 if var_debug_info.name != prev_name {
127 var_debug_info.source_info.span,
128 "local {:?} has many names (`{}` vs `{}`)",
135 local_names[local] = Some(var_debug_info.name);
139 // Gather the upvars of a closure, if any.
140 let tables = tcx.typeck_tables_of(def_id);
141 if tables.tainted_by_errors {
142 infcx.set_tainted_by_errors();
144 let upvars: Vec<_> = tables
148 .flat_map(|v| v.values())
150 let var_hir_id = upvar_id.var_path.hir_id;
151 let capture = tables.upvar_capture(*upvar_id);
152 let by_ref = match capture {
153 ty::UpvarCapture::ByValue => false,
154 ty::UpvarCapture::ByRef(..) => true,
156 let mut upvar = Upvar {
157 name: tcx.hir().name(var_hir_id),
160 mutability: Mutability::Not,
162 let bm = *tables.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
163 if bm == ty::BindByValue(hir::Mutability::Mut) {
164 upvar.mutability = Mutability::Mut;
170 // Replace all regions with fresh inference variables. This
171 // requires first making our own copy of the MIR. This copy will
172 // be modified (in place) to contain non-lexical lifetimes. It
173 // will have a lifetime tied to the inference context.
174 let body_clone: Body<'tcx> = input_body.clone();
175 let mut promoted = input_promoted.clone();
176 let mut body = BodyAndCache::new(body_clone);
178 nll::replace_regions_in_mir(infcx, def_id, param_env, &mut body, &mut promoted);
179 let body = read_only!(body); // no further changes
180 let promoted: IndexVec<_, _> = promoted.iter_mut().map(|body| read_only!(body)).collect();
182 let location_table = &LocationTable::new(&body);
184 let mut errors_buffer = Vec::new();
185 let (move_data, move_errors): (MoveData<'tcx>, Option<Vec<(Place<'tcx>, MoveError<'tcx>)>>) =
186 match MoveData::gather_moves(&body, tcx, param_env) {
187 Ok(move_data) => (move_data, None),
188 Err((move_data, move_errors)) => (move_data, Some(move_errors)),
191 let mdpe = MoveDataParamEnv { move_data, param_env };
193 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
194 .into_engine(tcx, &body, def_id)
195 .iterate_to_fixpoint()
196 .into_results_cursor(&body);
198 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
200 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
202 // Compute non-lexical lifetimes.
209 } = nll::compute_regions(
222 // Dump MIR results into a file, if that is enabled. This let us
223 // write unit-tests, as well as helping with debugging.
224 nll::dump_mir_results(infcx, MirSource::item(def_id), &body, ®ioncx, &opt_closure_req);
226 // We also have a `#[rustc_regions]` annotation that causes us to dump
228 nll::dump_annotation(
238 // The various `flow_*` structures can be large. We drop `flow_inits` here
239 // so it doesn't overlap with the others below. This reduces peak memory
240 // usage significantly on some benchmarks.
243 let regioncx = Rc::new(regioncx);
245 let flow_borrows = Borrows::new(tcx, &body, regioncx.clone(), &borrow_set)
246 .into_engine(tcx, &body, def_id)
247 .iterate_to_fixpoint();
248 let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
249 .into_engine(tcx, &body, def_id)
250 .iterate_to_fixpoint();
251 let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
252 .into_engine(tcx, &body, def_id)
253 .iterate_to_fixpoint();
255 let movable_generator = match tcx.hir().get(id) {
256 Node::Expr(&hir::Expr {
257 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
263 let dominators = body.dominators();
265 let mut mbcx = MirBorrowckCtxt {
269 move_data: &mdpe.move_data,
272 locals_are_invalidated_at_exit,
273 access_place_error_reported: Default::default(),
274 reservation_error_reported: Default::default(),
275 reservation_warnings: Default::default(),
276 move_error_reported: BTreeMap::new(),
277 uninitialized_error_reported: Default::default(),
280 used_mut: Default::default(),
281 used_mut_upvars: SmallVec::new(),
286 region_names: RefCell::default(),
287 next_region_name: RefCell::new(1),
291 // Compute and report region errors, if any.
292 mbcx.report_region_errors(nll_errors);
294 let results = BorrowckResults {
295 ever_inits: flow_ever_inits,
296 uninits: flow_uninits,
297 borrows: flow_borrows,
300 if let Some(errors) = move_errors {
301 mbcx.report_move_errors(errors);
304 dataflow::generic::visit_results(
306 traversal::reverse_postorder(&*body).map(|(bb, _)| bb),
311 // Convert any reservation warnings into lints.
312 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
313 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
314 let mut initial_diag =
315 mbcx.report_conflicting_borrow(location, (&place, span), bk, &borrow);
317 let scope = mbcx.body.source_info(location).scope;
318 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
319 ClearCrossCrate::Set(data) => data.lint_root,
323 // Span and message don't matter; we overwrite them below anyway
324 mbcx.infcx.tcx.struct_span_lint_hir(
325 MUTABLE_BORROW_RESERVATION_CONFLICT,
329 let mut diag = lint.build("");
331 diag.message = initial_diag.styled_message().clone();
332 diag.span = initial_diag.span.clone();
334 diag.buffer(&mut mbcx.errors_buffer);
337 initial_diag.cancel();
340 // For each non-user used mutable variable, check if it's been assigned from
341 // a user-declared local. If so, then put that local into the used_mut set.
342 // Note that this set is expected to be small - only upvars from closures
343 // would have a chance of erroneously adding non-user-defined mutable vars
345 let temporary_used_locals: FxHashSet<Local> = mbcx
348 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
351 // For the remaining unused locals that are marked as mutable, we avoid linting any that
352 // were never initialized. These locals may have been removed as unreachable code; or will be
353 // linted as unused variables.
354 let unused_mut_locals =
355 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
356 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
358 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
359 let used_mut = mbcx.used_mut;
360 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
361 let local_decl = &mbcx.body.local_decls[local];
362 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
363 ClearCrossCrate::Set(data) => data.lint_root,
367 // Skip over locals that begin with an underscore or have no name
368 match mbcx.local_names[local] {
370 if name.as_str().starts_with('_') {
377 let span = local_decl.source_info.span;
378 if span.desugaring_kind().is_some() {
379 // If the `mut` arises as part of a desugaring, we should ignore it.
383 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
384 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
385 lint.build("variable does not need to be mutable")
386 .span_suggestion_short(
390 Applicability::MachineApplicable,
396 // Buffer any move errors that we collected and de-duplicated.
397 for (_, (_, diag)) in mbcx.move_error_reported {
398 diag.buffer(&mut mbcx.errors_buffer);
401 if !mbcx.errors_buffer.is_empty() {
402 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
404 for diag in mbcx.errors_buffer.drain(..) {
405 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
409 let result = BorrowCheckResult {
410 concrete_opaque_types: opaque_type_values,
411 closure_requirements: opt_closure_req,
412 used_mut_upvars: mbcx.used_mut_upvars,
415 debug!("do_mir_borrowck: result = {:#?}", result);
420 crate struct MirBorrowckCtxt<'cx, 'tcx> {
421 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
422 body: ReadOnlyBodyAndCache<'cx, 'tcx>,
424 move_data: &'cx MoveData<'tcx>,
426 /// Map from MIR `Location` to `LocationIndex`; created
427 /// when MIR borrowck begins.
428 location_table: &'cx LocationTable,
430 movable_generator: bool,
431 /// This keeps track of whether local variables are free-ed when the function
432 /// exits even without a `StorageDead`, which appears to be the case for
435 /// I'm not sure this is the right approach - @eddyb could you try and
437 locals_are_invalidated_at_exit: bool,
438 /// This field keeps track of when borrow errors are reported in the access_place function
439 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
440 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
441 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
443 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
444 /// This field keeps track of when borrow conflict errors are reported
445 /// for reservations, so that we don't report seemingly duplicate
446 /// errors for corresponding activations.
448 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
449 // but it is currently inconvenient to track down the `BorrowIndex`
450 // at the time we detect and report a reservation error.
451 reservation_error_reported: FxHashSet<Place<'tcx>>,
452 /// Migration warnings to be reported for #56254. We delay reporting these
453 /// so that we can suppress the warning if there's a corresponding error
454 /// for the activation of the borrow.
455 reservation_warnings:
456 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
457 /// This field keeps track of move errors that are to be reported for given move indicies.
459 /// There are situations where many errors can be reported for a single move out (see #53807)
460 /// and we want only the best of those errors.
462 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
463 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
464 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
465 /// all move errors have been reported, any diagnostics in this map are added to the buffer
468 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
469 /// when errors in the map are being re-added to the error buffer so that errors with the
470 /// same primary span come out in a consistent order.
472 BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx, 'tcx>, DiagnosticBuilder<'cx>)>,
473 /// This field keeps track of errors reported in the checking of uninitialized variables,
474 /// so that we don't report seemingly duplicate errors.
475 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx, 'tcx>>,
476 /// Errors to be reported buffer
477 errors_buffer: Vec<Diagnostic>,
478 /// This field keeps track of all the local variables that are declared mut and are mutated.
479 /// Used for the warning issued by an unused mutable local variable.
480 used_mut: FxHashSet<Local>,
481 /// If the function we're checking is a closure, then we'll need to report back the list of
482 /// mutable upvars that have been used. This field keeps track of them.
483 used_mut_upvars: SmallVec<[Field; 8]>,
484 /// Region inference context. This contains the results from region inference and lets us e.g.
485 /// find out which CFG points are contained in each borrow region.
486 regioncx: Rc<RegionInferenceContext<'tcx>>,
488 /// The set of borrows extracted from the MIR
489 borrow_set: Rc<BorrowSet<'tcx>>,
491 /// Dominators for MIR
492 dominators: Dominators<BasicBlock>,
494 /// Information about upvars not necessarily preserved in types or MIR
497 /// Names of local (user) variables (extracted from `var_debug_info`).
498 local_names: IndexVec<Local, Option<Name>>,
500 /// Record the region names generated for each region in the given
501 /// MIR def so that we can reuse them later in help/error messages.
502 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
504 /// The counter for generating new region names.
505 next_region_name: RefCell<usize>,
507 /// Results of Polonius analysis.
508 polonius_output: Option<Rc<PoloniusOutput>>,
512 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
513 // 2. loans made in overlapping scopes do not conflict
514 // 3. assignments do not affect things loaned out as immutable
515 // 4. moves do not affect things loaned out in any way
516 impl<'cx, 'tcx> dataflow::generic::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
517 type FlowState = Flows<'cx, 'tcx>;
521 flow_state: &Flows<'cx, 'tcx>,
522 stmt: &'cx Statement<'tcx>,
525 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
526 let span = stmt.source_info.span;
528 self.check_activations(location, span, flow_state);
531 StatementKind::Assign(box (ref lhs, ref rhs)) => {
532 self.consume_rvalue(location, (rhs, span), flow_state);
534 self.mutate_place(location, (lhs, span), Shallow(None), JustWrite, flow_state);
536 StatementKind::FakeRead(_, box ref place) => {
537 // Read for match doesn't access any memory and is used to
538 // assert that a place is safe and live. So we don't have to
539 // do any checks here.
541 // FIXME: Remove check that the place is initialized. This is
542 // needed for now because matches don't have never patterns yet.
543 // So this is the only place we prevent
547 self.check_if_path_or_subpath_is_moved(
549 InitializationRequiringAction::Use,
550 (place.as_ref(), span),
554 StatementKind::SetDiscriminant { ref place, variant_index: _ } => {
555 self.mutate_place(location, (place, span), Shallow(None), JustWrite, flow_state);
557 StatementKind::InlineAsm(ref asm) => {
558 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
560 // FIXME(eddyb) indirect inline asm outputs should
561 // be encoded through MIR place derefs instead.
565 (Deep, Read(ReadKind::Copy)),
566 LocalMutationIsAllowed::No,
569 self.check_if_path_or_subpath_is_moved(
571 InitializationRequiringAction::Use,
572 (output.as_ref(), o.span),
579 if o.is_rw { Deep } else { Shallow(None) },
580 if o.is_rw { WriteAndRead } else { JustWrite },
585 for (_, input) in asm.inputs.iter() {
586 self.consume_operand(location, (input, span), flow_state);
590 | StatementKind::AscribeUserType(..)
591 | StatementKind::Retag { .. }
592 | StatementKind::StorageLive(..) => {
593 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
596 StatementKind::StorageDead(local) => {
599 (&Place::from(local), span),
600 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
601 LocalMutationIsAllowed::Yes,
610 flow_state: &Flows<'cx, 'tcx>,
611 term: &'cx Terminator<'tcx>,
614 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
615 let span = term.source_info.span;
617 self.check_activations(loc, span, flow_state);
620 TerminatorKind::SwitchInt { ref discr, switch_ty: _, values: _, targets: _ } => {
621 self.consume_operand(loc, (discr, span), flow_state);
623 TerminatorKind::Drop { location: ref drop_place, target: _, unwind: _ } => {
624 let tcx = self.infcx.tcx;
626 // Compute the type with accurate region information.
627 let drop_place_ty = drop_place.ty(*self.body, self.infcx.tcx);
629 // Erase the regions.
630 let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
632 // "Lift" into the tcx -- once regions are erased, this type should be in the
633 // global arenas; this "lift" operation basically just asserts that is true, but
634 // that is useful later.
635 tcx.lift(&drop_place_ty).unwrap();
638 "visit_terminator_drop \
639 loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
640 loc, term, drop_place, drop_place_ty, span
646 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
647 LocalMutationIsAllowed::Yes,
651 TerminatorKind::DropAndReplace {
652 location: ref drop_place,
653 value: ref new_value,
657 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
658 self.consume_operand(loc, (new_value, span), flow_state);
660 TerminatorKind::Call {
667 self.consume_operand(loc, (func, span), flow_state);
669 self.consume_operand(loc, (arg, span), flow_state);
671 if let Some((ref dest, _ /*bb*/)) = *destination {
672 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
675 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
676 self.consume_operand(loc, (cond, span), flow_state);
677 use rustc::mir::AssertKind;
678 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
679 self.consume_operand(loc, (len, span), flow_state);
680 self.consume_operand(loc, (index, span), flow_state);
684 TerminatorKind::Yield { ref value, resume: _, ref resume_arg, drop: _ } => {
685 self.consume_operand(loc, (value, span), flow_state);
686 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
689 TerminatorKind::Goto { target: _ }
690 | TerminatorKind::Abort
691 | TerminatorKind::Unreachable
692 | TerminatorKind::Resume
693 | TerminatorKind::Return
694 | TerminatorKind::GeneratorDrop
695 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
696 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
697 // no data used, thus irrelevant to borrowck
702 fn visit_terminator_exit(
704 flow_state: &Flows<'cx, 'tcx>,
705 term: &'cx Terminator<'tcx>,
708 let span = term.source_info.span;
711 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
712 if self.movable_generator {
713 // Look for any active borrows to locals
714 let borrow_set = self.borrow_set.clone();
715 for i in flow_state.borrows.iter() {
716 let borrow = &borrow_set[i];
717 self.check_for_local_borrow(borrow, span);
722 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
723 // Returning from the function implicitly kills storage for all locals and statics.
724 // Often, the storage will already have been killed by an explicit
725 // StorageDead, but we don't always emit those (notably on unwind paths),
726 // so this "extra check" serves as a kind of backup.
727 let borrow_set = self.borrow_set.clone();
728 for i in flow_state.borrows.iter() {
729 let borrow = &borrow_set[i];
730 self.check_for_invalidation_at_exit(loc, borrow, span);
734 TerminatorKind::Abort
735 | TerminatorKind::Assert { .. }
736 | TerminatorKind::Call { .. }
737 | TerminatorKind::Drop { .. }
738 | TerminatorKind::DropAndReplace { .. }
739 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
740 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
741 | TerminatorKind::Goto { .. }
742 | TerminatorKind::SwitchInt { .. }
743 | TerminatorKind::Unreachable => {}
748 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
754 use self::AccessDepth::{Deep, Shallow};
755 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
757 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
758 enum ArtificialField {
763 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
765 /// From the RFC: "A *shallow* access means that the immediate
766 /// fields reached at P are accessed, but references or pointers
767 /// found within are not dereferenced. Right now, the only access
768 /// that is shallow is an assignment like `x = ...;`, which would
769 /// be a *shallow write* of `x`."
770 Shallow(Option<ArtificialField>),
772 /// From the RFC: "A *deep* access means that all data reachable
773 /// through the given place may be invalidated or accesses by
777 /// Access is Deep only when there is a Drop implementation that
778 /// can reach the data behind the reference.
782 /// Kind of access to a value: read or write
783 /// (For informational purposes only)
784 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
786 /// From the RFC: "A *read* means that the existing data may be
787 /// read, but will not be changed."
790 /// From the RFC: "A *write* means that the data may be mutated to
791 /// new values or otherwise invalidated (for example, it could be
792 /// de-initialized, as in a move operation).
795 /// For two-phase borrows, we distinguish a reservation (which is treated
796 /// like a Read) from an activation (which is treated like a write), and
797 /// each of those is furthermore distinguished from Reads/Writes above.
798 Reservation(WriteKind),
799 Activation(WriteKind, BorrowIndex),
802 /// Kind of read access to a value
803 /// (For informational purposes only)
804 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
810 /// Kind of write access to a value
811 /// (For informational purposes only)
812 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
815 MutableBorrow(BorrowKind),
820 /// When checking permissions for a place access, this flag is used to indicate that an immutable
821 /// local place can be mutated.
823 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
824 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
825 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
826 // `is_declared_mutable()`.
827 // - Take flow state into consideration in `is_assignable()` for local variables.
828 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
829 enum LocalMutationIsAllowed {
831 /// We want use of immutable upvars to cause a "write to immutable upvar"
832 /// error, not an "reassignment" error.
837 #[derive(Copy, Clone, Debug)]
838 enum InitializationRequiringAction {
847 struct RootPlace<'tcx> {
849 place_projection: &'tcx [PlaceElem<'tcx>],
850 is_local_mutation_allowed: LocalMutationIsAllowed,
853 impl InitializationRequiringAction {
854 fn as_noun(self) -> &'static str {
856 InitializationRequiringAction::Update => "update",
857 InitializationRequiringAction::Borrow => "borrow",
858 InitializationRequiringAction::MatchOn => "use", // no good noun
859 InitializationRequiringAction::Use => "use",
860 InitializationRequiringAction::Assignment => "assign",
861 InitializationRequiringAction::PartialAssignment => "assign to part",
865 fn as_verb_in_past_tense(self) -> &'static str {
867 InitializationRequiringAction::Update => "updated",
868 InitializationRequiringAction::Borrow => "borrowed",
869 InitializationRequiringAction::MatchOn => "matched on",
870 InitializationRequiringAction::Use => "used",
871 InitializationRequiringAction::Assignment => "assigned",
872 InitializationRequiringAction::PartialAssignment => "partially assigned",
877 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
878 fn body(&self) -> &'cx Body<'tcx> {
882 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
883 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
884 /// place is initialized and (b) it is not borrowed in some way that would prevent this
887 /// Returns `true` if an error is reported.
891 place_span: (&Place<'tcx>, Span),
892 kind: (AccessDepth, ReadOrWrite),
893 is_local_mutation_allowed: LocalMutationIsAllowed,
894 flow_state: &Flows<'cx, 'tcx>,
898 if let Activation(_, borrow_index) = rw {
899 if self.reservation_error_reported.contains(&place_span.0) {
901 "skipping access_place for activation of invalid reservation \
902 place: {:?} borrow_index: {:?}",
903 place_span.0, borrow_index
909 // Check is_empty() first because it's the common case, and doing that
910 // way we avoid the clone() call.
911 if !self.access_place_error_reported.is_empty()
912 && self.access_place_error_reported.contains(&(*place_span.0, place_span.1))
915 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
921 let mutability_error = self.check_access_permissions(
924 is_local_mutation_allowed,
929 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
931 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
932 // Suppress this warning when there's an error being emitted for the
933 // same borrow: fixing the error is likely to fix the warning.
934 self.reservation_warnings.remove(&borrow_idx);
937 if conflict_error || mutability_error {
938 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
940 self.access_place_error_reported.insert((*place_span.0, place_span.1));
944 fn check_access_for_conflict(
947 place_span: (&Place<'tcx>, Span),
950 flow_state: &Flows<'cx, 'tcx>,
953 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
954 location, place_span, sd, rw,
957 let mut error_reported = false;
958 let tcx = self.infcx.tcx;
959 let body = self.body;
960 let body: &Body<'_> = &body;
961 let borrow_set = self.borrow_set.clone();
963 // Use polonius output if it has been enabled.
964 let polonius_output = self.polonius_output.clone();
965 let borrows_in_scope = if let Some(polonius) = &polonius_output {
966 let location = self.location_table.start_index(location);
967 Either::Left(polonius.errors_at(location).iter().copied())
969 Either::Right(flow_state.borrows.iter())
972 each_borrow_involving_path(
980 |this, borrow_index, borrow| match (rw, borrow.kind) {
981 // Obviously an activation is compatible with its own
982 // reservation (or even prior activating uses of same
983 // borrow); so don't check if they interfere.
985 // NOTE: *reservations* do conflict with themselves;
986 // thus aren't injecting unsoundenss w/ this check.)
987 (Activation(_, activating), _) if activating == borrow_index => {
989 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
990 skipping {:?} b/c activation of same borrow_index",
994 (borrow_index, borrow),
999 (Read(_), BorrowKind::Shared)
1000 | (Read(_), BorrowKind::Shallow)
1001 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
1002 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
1006 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1007 // Handled by initialization checks.
1011 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
1012 // Reading from mere reservations of mutable-borrows is OK.
1013 if !is_active(&this.dominators, borrow, location) {
1014 assert!(allow_two_phase_borrow(borrow.kind));
1015 return Control::Continue;
1018 error_reported = true;
1021 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1022 .buffer(&mut this.errors_buffer);
1024 ReadKind::Borrow(bk) => {
1025 this.report_conflicting_borrow(location, place_span, bk, borrow)
1026 .buffer(&mut this.errors_buffer);
1032 (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shallow)
1033 | (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shared)
1035 tcx.migrate_borrowck()
1036 && this.borrow_set.location_map.contains_key(&location)
1039 let bi = this.borrow_set.location_map[&location];
1041 "recording invalid reservation of place: {:?} with \
1042 borrow index {:?} as warning",
1045 // rust-lang/rust#56254 - This was previously permitted on
1046 // the 2018 edition so we emit it as a warning. We buffer
1047 // these sepately so that we only emit a warning if borrow
1048 // checking was otherwise successful.
1049 this.reservation_warnings
1050 .insert(bi, (*place_span.0, place_span.1, location, bk, borrow.clone()));
1052 // Don't suppress actual errors.
1056 (Reservation(kind), _) | (Activation(kind, _), _) | (Write(kind), _) => {
1058 Reservation(..) => {
1060 "recording invalid reservation of \
1064 this.reservation_error_reported.insert(place_span.0.clone());
1066 Activation(_, activating) => {
1068 "observing check_place for activation of \
1069 borrow_index: {:?}",
1073 Read(..) | Write(..) => {}
1076 error_reported = true;
1078 WriteKind::MutableBorrow(bk) => {
1079 this.report_conflicting_borrow(location, place_span, bk, borrow)
1080 .buffer(&mut this.errors_buffer);
1082 WriteKind::StorageDeadOrDrop => this
1083 .report_borrowed_value_does_not_live_long_enough(
1089 WriteKind::Mutate => {
1090 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1092 WriteKind::Move => {
1093 this.report_move_out_while_borrowed(location, place_span, borrow)
1107 place_span: (&'cx Place<'tcx>, Span),
1110 flow_state: &Flows<'cx, 'tcx>,
1112 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1114 MutateMode::WriteAndRead => {
1115 self.check_if_path_or_subpath_is_moved(
1117 InitializationRequiringAction::Update,
1118 (place_span.0.as_ref(), place_span.1),
1122 MutateMode::JustWrite => {
1123 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1127 // Special case: you can assign a immutable local variable
1128 // (e.g., `x = ...`) so long as it has never been initialized
1129 // before (at this point in the flow).
1130 if let Some(local) = place_span.0.as_local() {
1131 if let Mutability::Not = self.body.local_decls[local].mutability {
1132 // check for reassignments to immutable local variables
1133 self.check_if_reassignment_to_immutable_state(
1134 location, local, place_span, flow_state,
1140 // Otherwise, use the normal access permission rules.
1144 (kind, Write(WriteKind::Mutate)),
1145 LocalMutationIsAllowed::No,
1153 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1154 flow_state: &Flows<'cx, 'tcx>,
1157 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1158 let access_kind = match bk {
1159 BorrowKind::Shallow => {
1160 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1162 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1163 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1164 let wk = WriteKind::MutableBorrow(bk);
1165 if allow_two_phase_borrow(bk) {
1166 (Deep, Reservation(wk))
1177 LocalMutationIsAllowed::No,
1181 let action = if bk == BorrowKind::Shallow {
1182 InitializationRequiringAction::MatchOn
1184 InitializationRequiringAction::Borrow
1187 self.check_if_path_or_subpath_is_moved(
1190 (place.as_ref(), span),
1195 Rvalue::AddressOf(mutability, ref place) => {
1196 let access_kind = match mutability {
1197 Mutability::Mut => (
1199 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1200 allow_two_phase_borrow: false,
1203 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1210 LocalMutationIsAllowed::No,
1214 self.check_if_path_or_subpath_is_moved(
1216 InitializationRequiringAction::Borrow,
1217 (place.as_ref(), span),
1222 Rvalue::Use(ref operand)
1223 | Rvalue::Repeat(ref operand, _)
1224 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1225 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1226 self.consume_operand(location, (operand, span), flow_state)
1229 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1230 let af = match *rvalue {
1231 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1232 Rvalue::Discriminant(..) => None,
1233 _ => unreachable!(),
1238 (Shallow(af), Read(ReadKind::Copy)),
1239 LocalMutationIsAllowed::No,
1242 self.check_if_path_or_subpath_is_moved(
1244 InitializationRequiringAction::Use,
1245 (place.as_ref(), span),
1250 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1251 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1252 self.consume_operand(location, (operand1, span), flow_state);
1253 self.consume_operand(location, (operand2, span), flow_state);
1256 Rvalue::NullaryOp(_op, _ty) => {
1257 // nullary ops take no dynamic input; no borrowck effect.
1259 // FIXME: is above actually true? Do we want to track
1260 // the fact that uninitialized data can be created via
1264 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1265 // We need to report back the list of mutable upvars that were
1266 // moved into the closure and subsequently used by the closure,
1267 // in order to populate our used_mut set.
1268 match **aggregate_kind {
1269 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1270 let BorrowCheckResult { used_mut_upvars, .. } =
1271 self.infcx.tcx.mir_borrowck(def_id);
1272 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1273 for field in used_mut_upvars {
1274 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1277 AggregateKind::Adt(..)
1278 | AggregateKind::Array(..)
1279 | AggregateKind::Tuple { .. } => (),
1282 for operand in operands {
1283 self.consume_operand(location, (operand, span), flow_state);
1289 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1290 let propagate_closure_used_mut_place = |this: &mut Self, place: &Place<'tcx>| {
1291 if !place.projection.is_empty() {
1292 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1293 this.used_mut_upvars.push(field);
1296 this.used_mut.insert(place.local);
1300 // This relies on the current way that by-value
1301 // captures of a closure are copied/moved directly
1302 // when generating MIR.
1304 Operand::Move(ref place) | Operand::Copy(ref place) => {
1305 match place.as_local() {
1306 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1307 if self.body.local_decls[local].ty.is_mutable_ptr() {
1308 // The variable will be marked as mutable by the borrow.
1311 // This is an edge case where we have a `move` closure
1312 // inside a non-move closure, and the inner closure
1313 // contains a mutation:
1316 // || { move || { i += 1; }; };
1318 // In this case our usual strategy of assuming that the
1319 // variable will be captured by mutable reference is
1320 // wrong, since `i` can be copied into the inner
1321 // closure from a shared reference.
1323 // As such we have to search for the local that this
1324 // capture comes from and mark it as being used as mut.
1326 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1327 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1328 &self.move_data.inits[init_index]
1330 bug!("temporary should be initialized exactly once")
1333 let loc = match init.location {
1334 InitLocation::Statement(stmt) => stmt,
1335 _ => bug!("temporary initialized in arguments"),
1338 let body = self.body;
1339 let bbd = &body[loc.block];
1340 let stmt = &bbd.statements[loc.statement_index];
1341 debug!("temporary assigned in: stmt={:?}", stmt);
1343 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, ref source))) =
1346 propagate_closure_used_mut_place(self, source);
1349 "closures should only capture user variables \
1350 or references to user variables"
1354 _ => propagate_closure_used_mut_place(self, place),
1357 Operand::Constant(..) => {}
1364 (operand, span): (&'cx Operand<'tcx>, Span),
1365 flow_state: &Flows<'cx, 'tcx>,
1368 Operand::Copy(ref place) => {
1369 // copy of place: check if this is "copy of frozen path"
1370 // (FIXME: see check_loans.rs)
1374 (Deep, Read(ReadKind::Copy)),
1375 LocalMutationIsAllowed::No,
1379 // Finally, check if path was already moved.
1380 self.check_if_path_or_subpath_is_moved(
1382 InitializationRequiringAction::Use,
1383 (place.as_ref(), span),
1387 Operand::Move(ref place) => {
1388 // move of place: check if this is move of already borrowed path
1392 (Deep, Write(WriteKind::Move)),
1393 LocalMutationIsAllowed::Yes,
1397 // Finally, check if path was already moved.
1398 self.check_if_path_or_subpath_is_moved(
1400 InitializationRequiringAction::Use,
1401 (place.as_ref(), span),
1405 Operand::Constant(_) => {}
1409 /// Checks whether a borrow of this place is invalidated when the function
1411 fn check_for_invalidation_at_exit(
1414 borrow: &BorrowData<'tcx>,
1417 debug!("check_for_invalidation_at_exit({:?})", borrow);
1418 let place = &borrow.borrowed_place;
1419 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1421 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1422 // we just know that all locals are dropped at function exit (otherwise
1423 // we'll have a memory leak) and assume that all statics have a destructor.
1425 // FIXME: allow thread-locals to borrow other thread locals?
1427 let (might_be_alive, will_be_dropped) =
1428 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1429 // Thread-locals might be dropped after the function exits
1430 // We have to dereference the outer reference because
1431 // borrows don't conflict behind shared references.
1432 root_place.projection = DEREF_PROJECTION;
1435 (false, self.locals_are_invalidated_at_exit)
1438 if !will_be_dropped {
1439 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1443 let sd = if might_be_alive { Deep } else { Shallow(None) };
1445 if places_conflict::borrow_conflicts_with_place(
1452 places_conflict::PlaceConflictBias::Overlap,
1454 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1455 // FIXME: should be talking about the region lifetime instead
1456 // of just a span here.
1457 let span = self.infcx.tcx.sess.source_map().end_point(span);
1458 self.report_borrowed_value_does_not_live_long_enough(
1467 /// Reports an error if this is a borrow of local data.
1468 /// This is called for all Yield expressions on movable generators
1469 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1470 debug!("check_for_local_borrow({:?})", borrow);
1472 if borrow_of_local_data(&borrow.borrowed_place) {
1473 let err = self.cannot_borrow_across_generator_yield(
1474 self.retrieve_borrow_spans(borrow).var_or_use(),
1478 err.buffer(&mut self.errors_buffer);
1482 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1483 // Two-phase borrow support: For each activation that is newly
1484 // generated at this statement, check if it interferes with
1486 let borrow_set = self.borrow_set.clone();
1487 for &borrow_index in borrow_set.activations_at_location(location) {
1488 let borrow = &borrow_set[borrow_index];
1490 // only mutable borrows should be 2-phase
1491 assert!(match borrow.kind {
1492 BorrowKind::Shared | BorrowKind::Shallow => false,
1493 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1498 (&borrow.borrowed_place, span),
1499 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1500 LocalMutationIsAllowed::No,
1503 // We do not need to call `check_if_path_or_subpath_is_moved`
1504 // again, as we already called it when we made the
1505 // initial reservation.
1509 fn check_if_reassignment_to_immutable_state(
1513 place_span: (&Place<'tcx>, Span),
1514 flow_state: &Flows<'cx, 'tcx>,
1516 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1518 // Check if any of the initializiations of `local` have happened yet:
1519 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1520 // And, if so, report an error.
1521 let init = &self.move_data.inits[init_index];
1522 let span = init.span(&self.body);
1523 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1527 fn check_if_full_path_is_moved(
1530 desired_action: InitializationRequiringAction,
1531 place_span: (PlaceRef<'tcx, 'tcx>, Span),
1532 flow_state: &Flows<'cx, 'tcx>,
1534 let maybe_uninits = &flow_state.uninits;
1538 // 1. Move of `a.b.c`, use of `a.b.c`
1539 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1540 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1541 // partial initialization support, one might have `a.x`
1542 // initialized but not `a.b`.
1546 // 4. Move of `a.b.c`, use of `a.b.d`
1547 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1548 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1549 // must have been initialized for the use to be sound.
1550 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1552 // The dataflow tracks shallow prefixes distinctly (that is,
1553 // field-accesses on P distinctly from P itself), in order to
1554 // track substructure initialization separately from the whole
1557 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1558 // which we have a MovePath is `a.b`, then that means that the
1559 // initialization state of `a.b` is all we need to inspect to
1560 // know if `a.b.c` is valid (and from that we infer that the
1561 // dereference and `.d` access is also valid, since we assume
1562 // `a.b.c` is assigned a reference to a initialized and
1563 // well-formed record structure.)
1565 // Therefore, if we seek out the *closest* prefix for which we
1566 // have a MovePath, that should capture the initialization
1567 // state for the place scenario.
1569 // This code covers scenarios 1, 2, and 3.
1571 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1572 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1573 if maybe_uninits.contains(mpi) {
1574 self.report_use_of_moved_or_uninitialized(
1577 (prefix, place_span.0, place_span.1),
1580 } // Only query longest prefix with a MovePath, not further
1581 // ancestors; dataflow recurs on children when parents
1582 // move (to support partial (re)inits).
1584 // (I.e., querying parents breaks scenario 7; but may want
1585 // to do such a query based on partial-init feature-gate.)
1588 /// Subslices correspond to multiple move paths, so we iterate through the
1589 /// elements of the base array. For each element we check
1591 /// * Does this element overlap with our slice.
1592 /// * Is any part of it uninitialized.
1593 fn check_if_subslice_element_is_moved(
1596 desired_action: InitializationRequiringAction,
1597 place_span: (PlaceRef<'tcx, 'tcx>, Span),
1598 maybe_uninits: &BitSet<MovePathIndex>,
1602 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1603 let move_paths = &self.move_data.move_paths;
1605 let root_path = &move_paths[mpi];
1606 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1607 let last_proj = child_move_path.place.projection.last().unwrap();
1608 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1609 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1611 if (from..to).contains(offset) {
1613 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1614 maybe_uninits.contains(mpi)
1617 if let Some(uninit_child) = uninit_child {
1618 self.report_use_of_moved_or_uninitialized(
1621 (place_span.0, place_span.0, place_span.1),
1624 return; // don't bother finding other problems.
1632 fn check_if_path_or_subpath_is_moved(
1635 desired_action: InitializationRequiringAction,
1636 place_span: (PlaceRef<'tcx, '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 if let [base_proj @ .., ProjectionElem::Subslice { from, to, from_end: false }] =
1659 place_span.0.projection
1662 Place::ty_from(place_span.0.local, base_proj, self.body(), self.infcx.tcx);
1663 if let ty::Array(..) = place_ty.ty.kind {
1664 let array_place = PlaceRef { local: place_span.0.local, projection: base_proj };
1665 self.check_if_subslice_element_is_moved(
1668 (array_place, place_span.1),
1677 // A move of any shallow suffix of `place` also interferes
1678 // with an attempt to use `place`. This is scenario 3 above.
1680 // (Distinct from handling of scenarios 1+2+4 above because
1681 // `place` does not interfere with suffixes of its prefixes,
1682 // e.g., `a.b.c` does not interfere with `a.b.d`)
1684 // This code covers scenario 1.
1686 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1687 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1688 let uninit_mpi = self
1690 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1692 if let Some(uninit_mpi) = uninit_mpi {
1693 self.report_use_of_moved_or_uninitialized(
1696 (place_span.0, place_span.0, place_span.1),
1699 return; // don't bother finding other problems.
1704 /// Currently MoveData does not store entries for all places in
1705 /// the input MIR. For example it will currently filter out
1706 /// places that are Copy; thus we do not track places of shared
1707 /// reference type. This routine will walk up a place along its
1708 /// prefixes, searching for a foundational place that *is*
1709 /// tracked in the MoveData.
1711 /// An Err result includes a tag indicated why the search failed.
1712 /// Currently this can only occur if the place is built off of a
1713 /// static variable, as we do not track those in the MoveData.
1714 fn move_path_closest_to(
1716 place: PlaceRef<'_, 'tcx>,
1717 ) -> (PlaceRef<'cx, 'tcx>, MovePathIndex) {
1718 match self.move_data.rev_lookup.find(place) {
1719 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1720 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1722 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1726 fn move_path_for_place(&mut self, place: PlaceRef<'_, 'tcx>) -> Option<MovePathIndex> {
1727 // If returns None, then there is no move path corresponding
1728 // to a direct owner of `place` (which means there is nothing
1729 // that borrowck tracks for its analysis).
1731 match self.move_data.rev_lookup.find(place) {
1732 LookupResult::Parent(_) => None,
1733 LookupResult::Exact(mpi) => Some(mpi),
1737 fn check_if_assigned_path_is_moved(
1740 (place, span): (&'cx Place<'tcx>, Span),
1741 flow_state: &Flows<'cx, 'tcx>,
1743 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1745 // None case => assigning to `x` does not require `x` be initialized.
1746 let mut cursor = &*place.projection.as_ref();
1747 while let [proj_base @ .., elem] = cursor {
1751 ProjectionElem::Index(_/*operand*/) |
1752 ProjectionElem::ConstantIndex { .. } |
1753 // assigning to P[i] requires P to be valid.
1754 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1755 // assigning to (P->variant) is okay if assigning to `P` is okay
1757 // FIXME: is this true even if P is a adt with a dtor?
1760 // assigning to (*P) requires P to be initialized
1761 ProjectionElem::Deref => {
1762 self.check_if_full_path_is_moved(
1763 location, InitializationRequiringAction::Use,
1766 projection: proj_base,
1767 }, span), flow_state);
1768 // (base initialized; no need to
1773 ProjectionElem::Subslice { .. } => {
1774 panic!("we don't allow assignments to subslices, location: {:?}",
1778 ProjectionElem::Field(..) => {
1779 // if type of `P` has a dtor, then
1780 // assigning to `P.f` requires `P` itself
1781 // be already initialized
1782 let tcx = self.infcx.tcx;
1783 let base_ty = Place::ty_from(place.local, proj_base, self.body(), tcx).ty;
1784 match base_ty.kind {
1785 ty::Adt(def, _) if def.has_dtor(tcx) => {
1786 self.check_if_path_or_subpath_is_moved(
1787 location, InitializationRequiringAction::Assignment,
1790 projection: proj_base,
1791 }, span), flow_state);
1793 // (base initialized; no need to
1798 // Once `let s; s.x = V; read(s.x);`,
1799 // is allowed, remove this match arm.
1800 ty::Adt(..) | ty::Tuple(..) => {
1801 check_parent_of_field(self, location, PlaceRef {
1803 projection: proj_base,
1804 }, span, flow_state);
1806 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1807 // partial initialization, do not complain about unnecessary `mut` on
1808 // an attempt to do a partial initialization.
1809 self.used_mut.insert(place.local);
1818 fn check_parent_of_field<'cx, 'tcx>(
1819 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1821 base: PlaceRef<'tcx, 'tcx>,
1823 flow_state: &Flows<'cx, 'tcx>,
1825 // rust-lang/rust#21232: Until Rust allows reads from the
1826 // initialized parts of partially initialized structs, we
1827 // will, starting with the 2018 edition, reject attempts
1828 // to write to structs that are not fully initialized.
1830 // In other words, *until* we allow this:
1832 // 1. `let mut s; s.x = Val; read(s.x);`
1834 // we will for now disallow this:
1836 // 2. `let mut s; s.x = Val;`
1840 // 3. `let mut s = ...; drop(s); s.x=Val;`
1842 // This does not use check_if_path_or_subpath_is_moved,
1843 // because we want to *allow* reinitializations of fields:
1844 // e.g., want to allow
1846 // `let mut s = ...; drop(s.x); s.x=Val;`
1848 // This does not use check_if_full_path_is_moved on
1849 // `base`, because that would report an error about the
1850 // `base` as a whole, but in this scenario we *really*
1851 // want to report an error about the actual thing that was
1852 // moved, which may be some prefix of `base`.
1854 // Shallow so that we'll stop at any dereference; we'll
1855 // report errors about issues with such bases elsewhere.
1856 let maybe_uninits = &flow_state.uninits;
1858 // Find the shortest uninitialized prefix you can reach
1859 // without going over a Deref.
1860 let mut shortest_uninit_seen = None;
1861 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1862 let mpi = match this.move_path_for_place(prefix) {
1867 if maybe_uninits.contains(mpi) {
1869 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1870 shortest_uninit_seen,
1873 shortest_uninit_seen = Some((prefix, mpi));
1875 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1879 if let Some((prefix, mpi)) = shortest_uninit_seen {
1880 // Check for a reassignment into a uninitialized field of a union (for example,
1881 // after a move out). In this case, do not report a error here. There is an
1882 // exception, if this is the first assignment into the union (that is, there is
1883 // no move out from an earlier location) then this is an attempt at initialization
1884 // of the union - we should error in that case.
1885 let tcx = this.infcx.tcx;
1886 if let ty::Adt(def, _) =
1887 Place::ty_from(base.local, base.projection, this.body(), tcx).ty.kind
1890 if this.move_data.path_map[mpi].iter().any(|moi| {
1891 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1898 this.report_use_of_moved_or_uninitialized(
1900 InitializationRequiringAction::PartialAssignment,
1901 (prefix, base, span),
1908 /// Checks the permissions for the given place and read or write kind
1910 /// Returns `true` if an error is reported.
1911 fn check_access_permissions(
1913 (place, span): (&Place<'tcx>, Span),
1915 is_local_mutation_allowed: LocalMutationIsAllowed,
1916 flow_state: &Flows<'cx, 'tcx>,
1920 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1921 place, kind, is_local_mutation_allowed
1928 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1929 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1930 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1931 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1932 let is_local_mutation_allowed = match borrow_kind {
1933 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1934 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1935 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1937 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1939 self.add_used_mut(root_place, flow_state);
1943 error_access = AccessKind::MutableBorrow;
1944 the_place_err = place_err;
1948 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1949 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1951 self.add_used_mut(root_place, flow_state);
1955 error_access = AccessKind::Mutate;
1956 the_place_err = place_err;
1961 Reservation(WriteKind::Move)
1962 | Write(WriteKind::Move)
1963 | Reservation(WriteKind::StorageDeadOrDrop)
1964 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1965 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shallow))
1966 | Write(WriteKind::StorageDeadOrDrop)
1967 | Write(WriteKind::MutableBorrow(BorrowKind::Shared))
1968 | Write(WriteKind::MutableBorrow(BorrowKind::Shallow)) => {
1969 if let (Err(_), true) = (
1970 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
1971 self.errors_buffer.is_empty(),
1973 // rust-lang/rust#46908: In pure NLL mode this code path should be
1974 // unreachable, but we use `delay_span_bug` because we can hit this when
1975 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1976 // enabled. We don't want to ICE for that case, as other errors will have
1977 // been emitted (#52262).
1978 self.infcx.tcx.sess.delay_span_bug(
1981 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1989 // permission checks are done at Reservation point.
1992 Read(ReadKind::Borrow(BorrowKind::Unique))
1993 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1994 | Read(ReadKind::Borrow(BorrowKind::Shared))
1995 | Read(ReadKind::Borrow(BorrowKind::Shallow))
1996 | Read(ReadKind::Copy) => {
1997 // Access authorized
2002 // rust-lang/rust#21232, #54986: during period where we reject
2003 // partial initialization, do not complain about mutability
2004 // errors except for actual mutation (as opposed to an attempt
2005 // to do a partial initialization).
2006 let previously_initialized =
2007 self.is_local_ever_initialized(place.local, flow_state).is_some();
2009 // at this point, we have set up the error reporting state.
2010 if previously_initialized {
2011 self.report_mutability_error(place, span, the_place_err, error_access, location);
2018 fn is_local_ever_initialized(
2021 flow_state: &Flows<'cx, 'tcx>,
2022 ) -> Option<InitIndex> {
2023 let mpi = self.move_data.rev_lookup.find_local(local);
2024 let ii = &self.move_data.init_path_map[mpi];
2026 if flow_state.ever_inits.contains(index) {
2033 /// Adds the place into the used mutable variables set
2034 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2036 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2037 // If the local may have been initialized, and it is now currently being
2038 // mutated, then it is justified to be annotated with the `mut`
2039 // keyword, since the mutation may be a possible reassignment.
2040 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2041 && self.is_local_ever_initialized(local, flow_state).is_some()
2043 self.used_mut.insert(local);
2048 place_projection: _,
2049 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2053 place_projection: place_projection @ [.., _],
2054 is_local_mutation_allowed: _,
2056 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2058 projection: place_projection,
2060 self.used_mut_upvars.push(field);
2066 /// Whether this value can be written or borrowed mutably.
2067 /// Returns the root place if the place passed in is a projection.
2070 place: PlaceRef<'tcx, 'tcx>,
2071 is_local_mutation_allowed: LocalMutationIsAllowed,
2072 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx, 'tcx>> {
2074 PlaceRef { local, projection: [] } => {
2075 let local = &self.body.local_decls[local];
2076 match local.mutability {
2077 Mutability::Not => match is_local_mutation_allowed {
2078 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2079 place_local: place.local,
2080 place_projection: place.projection,
2081 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2083 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2084 place_local: place.local,
2085 place_projection: place.projection,
2086 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2088 LocalMutationIsAllowed::No => Err(place),
2090 Mutability::Mut => Ok(RootPlace {
2091 place_local: place.local,
2092 place_projection: place.projection,
2093 is_local_mutation_allowed,
2097 PlaceRef { local: _, projection: [proj_base @ .., elem] } => {
2099 ProjectionElem::Deref => {
2101 Place::ty_from(place.local, proj_base, self.body(), self.infcx.tcx).ty;
2103 // Check the kind of deref to decide
2104 match base_ty.kind {
2105 ty::Ref(_, _, mutbl) => {
2107 // Shared borrowed data is never mutable
2108 hir::Mutability::Not => Err(place),
2109 // Mutably borrowed data is mutable, but only if we have a
2110 // unique path to the `&mut`
2111 hir::Mutability::Mut => {
2112 let mode = match self.is_upvar_field_projection(place) {
2113 Some(field) if self.upvars[field.index()].by_ref => {
2114 is_local_mutation_allowed
2116 _ => LocalMutationIsAllowed::Yes,
2120 PlaceRef { local: place.local, projection: proj_base },
2126 ty::RawPtr(tnm) => {
2128 // `*const` raw pointers are not mutable
2129 hir::Mutability::Not => Err(place),
2130 // `*mut` raw pointers are always mutable, regardless of
2131 // context. The users have to check by themselves.
2132 hir::Mutability::Mut => Ok(RootPlace {
2133 place_local: place.local,
2134 place_projection: place.projection,
2135 is_local_mutation_allowed,
2139 // `Box<T>` owns its content, so mutable if its location is mutable
2140 _ if base_ty.is_box() => self.is_mutable(
2141 PlaceRef { local: place.local, projection: proj_base },
2142 is_local_mutation_allowed,
2144 // Deref should only be for reference, pointers or boxes
2145 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2148 // All other projections are owned by their base path, so mutable if
2149 // base path is mutable
2150 ProjectionElem::Field(..)
2151 | ProjectionElem::Index(..)
2152 | ProjectionElem::ConstantIndex { .. }
2153 | ProjectionElem::Subslice { .. }
2154 | ProjectionElem::Downcast(..) => {
2155 let upvar_field_projection = self.is_upvar_field_projection(place);
2156 if let Some(field) = upvar_field_projection {
2157 let upvar = &self.upvars[field.index()];
2159 "upvar.mutability={:?} local_mutation_is_allowed={:?} \
2161 upvar, is_local_mutation_allowed, place
2163 match (upvar.mutability, is_local_mutation_allowed) {
2164 (Mutability::Not, LocalMutationIsAllowed::No)
2165 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2168 (Mutability::Not, LocalMutationIsAllowed::Yes)
2169 | (Mutability::Mut, _) => {
2170 // Subtle: this is an upvar
2171 // reference, so it looks like
2172 // `self.foo` -- we want to double
2173 // check that the location `*self`
2174 // is mutable (i.e., this is not a
2175 // `Fn` closure). But if that
2176 // check succeeds, we want to
2177 // *blame* the mutability on
2178 // `place` (that is,
2179 // `self.foo`). This is used to
2180 // propagate the info about
2181 // whether mutability declarations
2182 // are used outwards, so that we register
2183 // the outer variable as mutable. Otherwise a
2184 // test like this fails to record the `mut`
2188 // fn foo<F: FnOnce()>(_f: F) { }
2190 // let var = Vec::new();
2196 let _ = self.is_mutable(
2197 PlaceRef { local: place.local, projection: proj_base },
2198 is_local_mutation_allowed,
2201 place_local: place.local,
2202 place_projection: place.projection,
2203 is_local_mutation_allowed,
2209 PlaceRef { local: place.local, projection: proj_base },
2210 is_local_mutation_allowed,
2219 /// If `place` is a field projection, and the field is being projected from a closure type,
2220 /// then returns the index of the field being projected. Note that this closure will always
2221 /// be `self` in the current MIR, because that is the only time we directly access the fields
2222 /// of a closure type.
2223 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'cx, 'tcx>) -> Option<Field> {
2224 let mut place_projection = place_ref.projection;
2225 let mut by_ref = false;
2227 if let [proj_base @ .., ProjectionElem::Deref] = place_projection {
2228 place_projection = proj_base;
2232 match place_projection {
2233 [base @ .., ProjectionElem::Field(field, _ty)] => {
2234 let tcx = self.infcx.tcx;
2235 let base_ty = Place::ty_from(place_ref.local, base, self.body(), tcx).ty;
2237 if (base_ty.is_closure() || base_ty.is_generator())
2238 && (!by_ref || self.upvars[field.index()].by_ref)
2251 /// The degree of overlap between 2 places for borrow-checking.
2253 /// The places might partially overlap - in this case, we give
2254 /// up and say that they might conflict. This occurs when
2255 /// different fields of a union are borrowed. For example,
2256 /// if `u` is a union, we have no way of telling how disjoint
2257 /// `u.a.x` and `a.b.y` are.
2259 /// The places have the same type, and are either completely disjoint
2260 /// or equal - i.e., they can't "partially" overlap as can occur with
2261 /// unions. This is the "base case" on which we recur for extensions
2264 /// The places are disjoint, so we know all extensions of them
2265 /// will also be disjoint.