1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 use rustc::infer::InferCtxt;
4 use rustc::lint::builtin::MUTABLE_BORROW_RESERVATION_CONFLICT;
5 use rustc::lint::builtin::UNUSED_MUT;
7 read_only, traversal, Body, BodyAndCache, ClearCrossCrate, Local, Location, Mutability,
8 Operand, Place, PlaceElem, PlaceRef, ReadOnlyBodyAndCache,
10 use rustc::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
11 use rustc::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
12 use rustc::mir::{Terminator, TerminatorKind};
13 use rustc::ty::query::Providers;
14 use rustc::ty::{self, RegionVid, TyCtxt};
16 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
17 use rustc_data_structures::graph::dominators::Dominators;
18 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder};
20 use rustc_hir::{def_id::DefId, HirId, Node};
21 use rustc_index::bit_set::BitSet;
22 use rustc_index::vec::IndexVec;
25 use smallvec::SmallVec;
26 use std::cell::RefCell;
27 use std::collections::BTreeMap;
31 use rustc_span::{Span, DUMMY_SP};
32 use syntax::ast::Name;
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 pub fn provide(providers: &mut Providers<'_>) {
90 *providers = Providers { mir_borrowck, ..*providers };
93 fn mir_borrowck(tcx: TyCtxt<'_>, def_id: DefId) -> BorrowCheckResult<'_> {
94 let (input_body, promoted) = tcx.mir_validated(def_id);
95 debug!("run query mir_borrowck: {}", tcx.def_path_str(def_id));
97 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
98 let input_body: &Body<'_> = &input_body.borrow();
99 let promoted: &IndexVec<_, _> = &promoted.borrow();
100 do_mir_borrowck(&infcx, input_body, promoted, def_id)
102 debug!("mir_borrowck done");
107 fn do_mir_borrowck<'a, 'tcx>(
108 infcx: &InferCtxt<'a, 'tcx>,
109 input_body: &Body<'tcx>,
110 input_promoted: &IndexVec<Promoted, BodyAndCache<'tcx>>,
112 ) -> BorrowCheckResult<'tcx> {
113 debug!("do_mir_borrowck(def_id = {:?})", def_id);
116 let param_env = tcx.param_env(def_id);
117 let id = tcx.hir().as_local_hir_id(def_id).expect("do_mir_borrowck: non-local DefId");
119 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
120 for var_debug_info in &input_body.var_debug_info {
121 if let Some(local) = var_debug_info.place.as_local() {
122 if let Some(prev_name) = local_names[local] {
123 if var_debug_info.name != prev_name {
125 var_debug_info.source_info.span,
126 "local {:?} has many names (`{}` vs `{}`)",
133 local_names[local] = Some(var_debug_info.name);
137 // Gather the upvars of a closure, if any.
138 let tables = tcx.typeck_tables_of(def_id);
139 let upvars: Vec<_> = tables
143 .flat_map(|v| v.values())
145 let var_hir_id = upvar_id.var_path.hir_id;
146 let capture = tables.upvar_capture(*upvar_id);
147 let by_ref = match capture {
148 ty::UpvarCapture::ByValue => false,
149 ty::UpvarCapture::ByRef(..) => true,
151 let mut upvar = Upvar {
152 name: tcx.hir().name(var_hir_id),
155 mutability: Mutability::Not,
157 let bm = *tables.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
158 if bm == ty::BindByValue(hir::Mutability::Mut) {
159 upvar.mutability = Mutability::Mut;
165 // Replace all regions with fresh inference variables. This
166 // requires first making our own copy of the MIR. This copy will
167 // be modified (in place) to contain non-lexical lifetimes. It
168 // will have a lifetime tied to the inference context.
169 let body_clone: Body<'tcx> = input_body.clone();
170 let mut promoted = input_promoted.clone();
171 let mut body = BodyAndCache::new(body_clone);
173 nll::replace_regions_in_mir(infcx, def_id, param_env, &mut body, &mut promoted);
174 let body = read_only!(body); // no further changes
175 let promoted: IndexVec<_, _> = promoted.iter_mut().map(|body| read_only!(body)).collect();
177 let location_table = &LocationTable::new(&body);
179 let mut errors_buffer = Vec::new();
180 let (move_data, move_errors): (MoveData<'tcx>, Option<Vec<(Place<'tcx>, MoveError<'tcx>)>>) =
181 match MoveData::gather_moves(&body, tcx, param_env) {
182 Ok(move_data) => (move_data, None),
183 Err((move_data, move_errors)) => (move_data, Some(move_errors)),
186 let mdpe = MoveDataParamEnv { move_data, param_env };
188 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
189 .into_engine(tcx, &body, def_id)
190 .iterate_to_fixpoint()
191 .into_results_cursor(&body);
193 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
195 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
197 // Compute non-lexical lifetimes.
198 let nll::NllOutput { regioncx, polonius_output, opt_closure_req, nll_errors } =
199 nll::compute_regions(
212 // Dump MIR results into a file, if that is enabled. This let us
213 // write unit-tests, as well as helping with debugging.
214 nll::dump_mir_results(infcx, MirSource::item(def_id), &body, ®ioncx, &opt_closure_req);
216 // We also have a `#[rustc_nll]` annotation that causes us to dump
218 nll::dump_annotation(infcx, &body, def_id, ®ioncx, &opt_closure_req, &mut errors_buffer);
220 // The various `flow_*` structures can be large. We drop `flow_inits` here
221 // so it doesn't overlap with the others below. This reduces peak memory
222 // usage significantly on some benchmarks.
225 let regioncx = Rc::new(regioncx);
227 let flow_borrows = Borrows::new(tcx, &body, regioncx.clone(), &borrow_set)
228 .into_engine(tcx, &body, def_id)
229 .iterate_to_fixpoint();
230 let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
231 .into_engine(tcx, &body, def_id)
232 .iterate_to_fixpoint();
233 let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
234 .into_engine(tcx, &body, def_id)
235 .iterate_to_fixpoint();
237 let movable_generator = match tcx.hir().get(id) {
238 Node::Expr(&hir::Expr {
239 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
245 let dominators = body.dominators();
247 let mut mbcx = MirBorrowckCtxt {
251 move_data: &mdpe.move_data,
254 locals_are_invalidated_at_exit,
255 access_place_error_reported: Default::default(),
256 reservation_error_reported: Default::default(),
257 reservation_warnings: Default::default(),
258 move_error_reported: BTreeMap::new(),
259 uninitialized_error_reported: Default::default(),
262 used_mut: Default::default(),
263 used_mut_upvars: SmallVec::new(),
268 region_names: RefCell::default(),
269 next_region_name: RefCell::new(1),
273 // Compute and report region errors, if any.
274 mbcx.report_region_errors(nll_errors);
276 let results = BorrowckResults {
277 ever_inits: flow_ever_inits,
278 uninits: flow_uninits,
279 borrows: flow_borrows,
282 if let Some(errors) = move_errors {
283 mbcx.report_move_errors(errors);
286 dataflow::generic::visit_results(
288 traversal::reverse_postorder(&*body).map(|(bb, _)| bb),
293 // Convert any reservation warnings into lints.
294 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
295 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
296 let mut initial_diag =
297 mbcx.report_conflicting_borrow(location, (&place, span), bk, &borrow);
299 let scope = mbcx.body.source_info(location).scope;
300 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
301 ClearCrossCrate::Set(data) => data.lint_root,
305 // Span and message don't matter; we overwrite them below anyway
306 mbcx.infcx.tcx.struct_span_lint_hir(
307 MUTABLE_BORROW_RESERVATION_CONFLICT,
311 let mut diag = lint.build("");
313 diag.message = initial_diag.styled_message().clone();
314 diag.span = initial_diag.span.clone();
316 diag.buffer(&mut mbcx.errors_buffer);
319 initial_diag.cancel();
322 // For each non-user used mutable variable, check if it's been assigned from
323 // a user-declared local. If so, then put that local into the used_mut set.
324 // Note that this set is expected to be small - only upvars from closures
325 // would have a chance of erroneously adding non-user-defined mutable vars
327 let temporary_used_locals: FxHashSet<Local> = mbcx
330 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
333 // For the remaining unused locals that are marked as mutable, we avoid linting any that
334 // were never initialized. These locals may have been removed as unreachable code; or will be
335 // linted as unused variables.
336 let unused_mut_locals =
337 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
338 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
340 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
341 let used_mut = mbcx.used_mut;
342 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
343 let local_decl = &mbcx.body.local_decls[local];
344 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
345 ClearCrossCrate::Set(data) => data.lint_root,
349 // Skip over locals that begin with an underscore or have no name
350 match mbcx.local_names[local] {
352 if name.as_str().starts_with("_") {
359 let span = local_decl.source_info.span;
360 if span.desugaring_kind().is_some() {
361 // If the `mut` arises as part of a desugaring, we should ignore it.
365 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
366 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
367 lint.build("variable does not need to be mutable")
368 .span_suggestion_short(
372 Applicability::MachineApplicable,
378 // Buffer any move errors that we collected and de-duplicated.
379 for (_, (_, diag)) in mbcx.move_error_reported {
380 diag.buffer(&mut mbcx.errors_buffer);
383 if !mbcx.errors_buffer.is_empty() {
384 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
386 for diag in mbcx.errors_buffer.drain(..) {
387 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
391 let result = BorrowCheckResult {
392 closure_requirements: opt_closure_req,
393 used_mut_upvars: mbcx.used_mut_upvars,
396 debug!("do_mir_borrowck: result = {:#?}", result);
401 crate struct MirBorrowckCtxt<'cx, 'tcx> {
402 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
403 body: ReadOnlyBodyAndCache<'cx, 'tcx>,
405 move_data: &'cx MoveData<'tcx>,
407 /// Map from MIR `Location` to `LocationIndex`; created
408 /// when MIR borrowck begins.
409 location_table: &'cx LocationTable,
411 movable_generator: bool,
412 /// This keeps track of whether local variables are free-ed when the function
413 /// exits even without a `StorageDead`, which appears to be the case for
416 /// I'm not sure this is the right approach - @eddyb could you try and
418 locals_are_invalidated_at_exit: bool,
419 /// This field keeps track of when borrow errors are reported in the access_place function
420 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
421 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
422 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
424 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
425 /// This field keeps track of when borrow conflict errors are reported
426 /// for reservations, so that we don't report seemingly duplicate
427 /// errors for corresponding activations.
429 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
430 // but it is currently inconvenient to track down the `BorrowIndex`
431 // at the time we detect and report a reservation error.
432 reservation_error_reported: FxHashSet<Place<'tcx>>,
433 /// Migration warnings to be reported for #56254. We delay reporting these
434 /// so that we can suppress the warning if there's a corresponding error
435 /// for the activation of the borrow.
436 reservation_warnings:
437 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
438 /// This field keeps track of move errors that are to be reported for given move indicies.
440 /// There are situations where many errors can be reported for a single move out (see #53807)
441 /// and we want only the best of those errors.
443 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
444 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
445 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
446 /// all move errors have been reported, any diagnostics in this map are added to the buffer
449 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
450 /// when errors in the map are being re-added to the error buffer so that errors with the
451 /// same primary span come out in a consistent order.
452 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'cx, 'tcx>, DiagnosticBuilder<'cx>)>,
453 /// This field keeps track of errors reported in the checking of uninitialized variables,
454 /// so that we don't report seemingly duplicate errors.
455 uninitialized_error_reported: FxHashSet<PlaceRef<'cx, 'tcx>>,
456 /// Errors to be reported buffer
457 errors_buffer: Vec<Diagnostic>,
458 /// This field keeps track of all the local variables that are declared mut and are mutated.
459 /// Used for the warning issued by an unused mutable local variable.
460 used_mut: FxHashSet<Local>,
461 /// If the function we're checking is a closure, then we'll need to report back the list of
462 /// mutable upvars that have been used. This field keeps track of them.
463 used_mut_upvars: SmallVec<[Field; 8]>,
464 /// Region inference context. This contains the results from region inference and lets us e.g.
465 /// find out which CFG points are contained in each borrow region.
466 regioncx: Rc<RegionInferenceContext<'tcx>>,
468 /// The set of borrows extracted from the MIR
469 borrow_set: Rc<BorrowSet<'tcx>>,
471 /// Dominators for MIR
472 dominators: Dominators<BasicBlock>,
474 /// Information about upvars not necessarily preserved in types or MIR
477 /// Names of local (user) variables (extracted from `var_debug_info`).
478 local_names: IndexVec<Local, Option<Name>>,
480 /// Record the region names generated for each region in the given
481 /// MIR def so that we can reuse them later in help/error messages.
482 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
484 /// The counter for generating new region names.
485 next_region_name: RefCell<usize>,
487 /// Results of Polonius analysis.
488 polonius_output: Option<Rc<PoloniusOutput>>,
492 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
493 // 2. loans made in overlapping scopes do not conflict
494 // 3. assignments do not affect things loaned out as immutable
495 // 4. moves do not affect things loaned out in any way
496 impl<'cx, 'tcx> dataflow::generic::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
497 type FlowState = Flows<'cx, 'tcx>;
501 flow_state: &Flows<'cx, 'tcx>,
502 stmt: &'cx Statement<'tcx>,
505 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
506 let span = stmt.source_info.span;
508 self.check_activations(location, span, flow_state);
511 StatementKind::Assign(box (ref lhs, ref rhs)) => {
512 self.consume_rvalue(location, (rhs, span), flow_state);
514 self.mutate_place(location, (lhs, span), Shallow(None), JustWrite, flow_state);
516 StatementKind::FakeRead(_, box ref place) => {
517 // Read for match doesn't access any memory and is used to
518 // assert that a place is safe and live. So we don't have to
519 // do any checks here.
521 // FIXME: Remove check that the place is initialized. This is
522 // needed for now because matches don't have never patterns yet.
523 // So this is the only place we prevent
527 self.check_if_path_or_subpath_is_moved(
529 InitializationRequiringAction::Use,
530 (place.as_ref(), span),
534 StatementKind::SetDiscriminant { ref place, variant_index: _ } => {
535 self.mutate_place(location, (place, span), Shallow(None), JustWrite, flow_state);
537 StatementKind::InlineAsm(ref asm) => {
538 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
540 // FIXME(eddyb) indirect inline asm outputs should
541 // be encoded through MIR place derefs instead.
545 (Deep, Read(ReadKind::Copy)),
546 LocalMutationIsAllowed::No,
549 self.check_if_path_or_subpath_is_moved(
551 InitializationRequiringAction::Use,
552 (output.as_ref(), o.span),
559 if o.is_rw { Deep } else { Shallow(None) },
560 if o.is_rw { WriteAndRead } else { JustWrite },
565 for (_, input) in asm.inputs.iter() {
566 self.consume_operand(location, (input, span), flow_state);
570 | StatementKind::AscribeUserType(..)
571 | StatementKind::Retag { .. }
572 | StatementKind::StorageLive(..) => {
573 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
576 StatementKind::StorageDead(local) => {
579 (&Place::from(local), span),
580 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
581 LocalMutationIsAllowed::Yes,
590 flow_state: &Flows<'cx, 'tcx>,
591 term: &'cx Terminator<'tcx>,
594 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
595 let span = term.source_info.span;
597 self.check_activations(loc, span, flow_state);
600 TerminatorKind::SwitchInt { ref discr, switch_ty: _, values: _, targets: _ } => {
601 self.consume_operand(loc, (discr, span), flow_state);
603 TerminatorKind::Drop { location: ref drop_place, target: _, unwind: _ } => {
604 let tcx = self.infcx.tcx;
606 // Compute the type with accurate region information.
607 let drop_place_ty = drop_place.ty(*self.body, self.infcx.tcx);
609 // Erase the regions.
610 let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
612 // "Lift" into the tcx -- once regions are erased, this type should be in the
613 // global arenas; this "lift" operation basically just asserts that is true, but
614 // that is useful later.
615 tcx.lift(&drop_place_ty).unwrap();
618 "visit_terminator_drop \
619 loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
620 loc, term, drop_place, drop_place_ty, span
626 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
627 LocalMutationIsAllowed::Yes,
631 TerminatorKind::DropAndReplace {
632 location: ref drop_place,
633 value: ref new_value,
637 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
638 self.consume_operand(loc, (new_value, span), flow_state);
640 TerminatorKind::Call {
647 self.consume_operand(loc, (func, span), flow_state);
649 self.consume_operand(loc, (arg, span), flow_state);
651 if let Some((ref dest, _ /*bb*/)) = *destination {
652 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
655 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
656 self.consume_operand(loc, (cond, span), flow_state);
657 use rustc::mir::AssertKind;
658 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
659 self.consume_operand(loc, (len, span), flow_state);
660 self.consume_operand(loc, (index, span), flow_state);
664 TerminatorKind::Yield { ref value, resume: _, ref resume_arg, drop: _ } => {
665 self.consume_operand(loc, (value, span), flow_state);
666 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
669 TerminatorKind::Goto { target: _ }
670 | TerminatorKind::Abort
671 | TerminatorKind::Unreachable
672 | TerminatorKind::Resume
673 | TerminatorKind::Return
674 | TerminatorKind::GeneratorDrop
675 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
676 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
677 // no data used, thus irrelevant to borrowck
682 fn visit_terminator_exit(
684 flow_state: &Flows<'cx, 'tcx>,
685 term: &'cx Terminator<'tcx>,
688 let span = term.source_info.span;
691 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
692 if self.movable_generator {
693 // Look for any active borrows to locals
694 let borrow_set = self.borrow_set.clone();
695 for i in flow_state.borrows.iter() {
696 let borrow = &borrow_set[i];
697 self.check_for_local_borrow(borrow, span);
702 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
703 // Returning from the function implicitly kills storage for all locals and statics.
704 // Often, the storage will already have been killed by an explicit
705 // StorageDead, but we don't always emit those (notably on unwind paths),
706 // so this "extra check" serves as a kind of backup.
707 let borrow_set = self.borrow_set.clone();
708 for i in flow_state.borrows.iter() {
709 let borrow = &borrow_set[i];
710 self.check_for_invalidation_at_exit(loc, borrow, span);
714 TerminatorKind::Abort
715 | TerminatorKind::Assert { .. }
716 | TerminatorKind::Call { .. }
717 | TerminatorKind::Drop { .. }
718 | TerminatorKind::DropAndReplace { .. }
719 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
720 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
721 | TerminatorKind::Goto { .. }
722 | TerminatorKind::SwitchInt { .. }
723 | TerminatorKind::Unreachable => {}
728 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
734 use self::AccessDepth::{Deep, Shallow};
735 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
737 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
738 enum ArtificialField {
743 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
745 /// From the RFC: "A *shallow* access means that the immediate
746 /// fields reached at P are accessed, but references or pointers
747 /// found within are not dereferenced. Right now, the only access
748 /// that is shallow is an assignment like `x = ...;`, which would
749 /// be a *shallow write* of `x`."
750 Shallow(Option<ArtificialField>),
752 /// From the RFC: "A *deep* access means that all data reachable
753 /// through the given place may be invalidated or accesses by
757 /// Access is Deep only when there is a Drop implementation that
758 /// can reach the data behind the reference.
762 /// Kind of access to a value: read or write
763 /// (For informational purposes only)
764 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
766 /// From the RFC: "A *read* means that the existing data may be
767 /// read, but will not be changed."
770 /// From the RFC: "A *write* means that the data may be mutated to
771 /// new values or otherwise invalidated (for example, it could be
772 /// de-initialized, as in a move operation).
775 /// For two-phase borrows, we distinguish a reservation (which is treated
776 /// like a Read) from an activation (which is treated like a write), and
777 /// each of those is furthermore distinguished from Reads/Writes above.
778 Reservation(WriteKind),
779 Activation(WriteKind, BorrowIndex),
782 /// Kind of read access to a value
783 /// (For informational purposes only)
784 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
790 /// Kind of write access to a value
791 /// (For informational purposes only)
792 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
795 MutableBorrow(BorrowKind),
800 /// When checking permissions for a place access, this flag is used to indicate that an immutable
801 /// local place can be mutated.
803 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
804 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
805 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
806 // `is_declared_mutable()`.
807 // - Take flow state into consideration in `is_assignable()` for local variables.
808 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
809 enum LocalMutationIsAllowed {
811 /// We want use of immutable upvars to cause a "write to immutable upvar"
812 /// error, not an "reassignment" error.
817 #[derive(Copy, Clone, Debug)]
818 enum InitializationRequiringAction {
827 struct RootPlace<'d, 'tcx> {
829 place_projection: &'d [PlaceElem<'tcx>],
830 is_local_mutation_allowed: LocalMutationIsAllowed,
833 impl InitializationRequiringAction {
834 fn as_noun(self) -> &'static str {
836 InitializationRequiringAction::Update => "update",
837 InitializationRequiringAction::Borrow => "borrow",
838 InitializationRequiringAction::MatchOn => "use", // no good noun
839 InitializationRequiringAction::Use => "use",
840 InitializationRequiringAction::Assignment => "assign",
841 InitializationRequiringAction::PartialAssignment => "assign to part",
845 fn as_verb_in_past_tense(self) -> &'static str {
847 InitializationRequiringAction::Update => "updated",
848 InitializationRequiringAction::Borrow => "borrowed",
849 InitializationRequiringAction::MatchOn => "matched on",
850 InitializationRequiringAction::Use => "used",
851 InitializationRequiringAction::Assignment => "assigned",
852 InitializationRequiringAction::PartialAssignment => "partially assigned",
857 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
858 fn body(&self) -> &'cx Body<'tcx> {
862 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
863 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
864 /// place is initialized and (b) it is not borrowed in some way that would prevent this
867 /// Returns `true` if an error is reported.
871 place_span: (&Place<'tcx>, Span),
872 kind: (AccessDepth, ReadOrWrite),
873 is_local_mutation_allowed: LocalMutationIsAllowed,
874 flow_state: &Flows<'cx, 'tcx>,
878 if let Activation(_, borrow_index) = rw {
879 if self.reservation_error_reported.contains(&place_span.0) {
881 "skipping access_place for activation of invalid reservation \
882 place: {:?} borrow_index: {:?}",
883 place_span.0, borrow_index
889 // Check is_empty() first because it's the common case, and doing that
890 // way we avoid the clone() call.
891 if !self.access_place_error_reported.is_empty()
892 && self.access_place_error_reported.contains(&(*place_span.0, place_span.1))
895 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
901 let mutability_error = self.check_access_permissions(
904 is_local_mutation_allowed,
909 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
911 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
912 // Suppress this warning when there's an error being emitted for the
913 // same borrow: fixing the error is likely to fix the warning.
914 self.reservation_warnings.remove(&borrow_idx);
917 if conflict_error || mutability_error {
918 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
920 self.access_place_error_reported.insert((*place_span.0, place_span.1));
924 fn check_access_for_conflict(
927 place_span: (&Place<'tcx>, Span),
930 flow_state: &Flows<'cx, 'tcx>,
933 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
934 location, place_span, sd, rw,
937 let mut error_reported = false;
938 let tcx = self.infcx.tcx;
939 let body = self.body;
940 let body: &Body<'_> = &body;
941 let borrow_set = self.borrow_set.clone();
943 // Use polonius output if it has been enabled.
944 let polonius_output = self.polonius_output.clone();
945 let borrows_in_scope = if let Some(polonius) = &polonius_output {
946 let location = self.location_table.start_index(location);
947 Either::Left(polonius.errors_at(location).iter().copied())
949 Either::Right(flow_state.borrows.iter())
952 each_borrow_involving_path(
960 |this, borrow_index, borrow| match (rw, borrow.kind) {
961 // Obviously an activation is compatible with its own
962 // reservation (or even prior activating uses of same
963 // borrow); so don't check if they interfere.
965 // NOTE: *reservations* do conflict with themselves;
966 // thus aren't injecting unsoundenss w/ this check.)
967 (Activation(_, activating), _) if activating == borrow_index => {
969 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
970 skipping {:?} b/c activation of same borrow_index",
974 (borrow_index, borrow),
979 (Read(_), BorrowKind::Shared)
980 | (Read(_), BorrowKind::Shallow)
981 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
982 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
986 (Write(WriteKind::Move), BorrowKind::Shallow) => {
987 // Handled by initialization checks.
991 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
992 // Reading from mere reservations of mutable-borrows is OK.
993 if !is_active(&this.dominators, borrow, location) {
994 assert!(allow_two_phase_borrow(borrow.kind));
995 return Control::Continue;
998 error_reported = true;
1001 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1002 .buffer(&mut this.errors_buffer);
1004 ReadKind::Borrow(bk) => {
1005 this.report_conflicting_borrow(location, place_span, bk, borrow)
1006 .buffer(&mut this.errors_buffer);
1012 (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shallow)
1013 | (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shared)
1015 tcx.migrate_borrowck()
1016 && this.borrow_set.location_map.contains_key(&location)
1019 let bi = this.borrow_set.location_map[&location];
1021 "recording invalid reservation of place: {:?} with \
1022 borrow index {:?} as warning",
1025 // rust-lang/rust#56254 - This was previously permitted on
1026 // the 2018 edition so we emit it as a warning. We buffer
1027 // these sepately so that we only emit a warning if borrow
1028 // checking was otherwise successful.
1029 this.reservation_warnings
1030 .insert(bi, (*place_span.0, place_span.1, location, bk, borrow.clone()));
1032 // Don't suppress actual errors.
1036 (Reservation(kind), _) | (Activation(kind, _), _) | (Write(kind), _) => {
1038 Reservation(..) => {
1040 "recording invalid reservation of \
1044 this.reservation_error_reported.insert(place_span.0.clone());
1046 Activation(_, activating) => {
1048 "observing check_place for activation of \
1049 borrow_index: {:?}",
1053 Read(..) | Write(..) => {}
1056 error_reported = true;
1058 WriteKind::MutableBorrow(bk) => {
1059 this.report_conflicting_borrow(location, place_span, bk, borrow)
1060 .buffer(&mut this.errors_buffer);
1062 WriteKind::StorageDeadOrDrop => this
1063 .report_borrowed_value_does_not_live_long_enough(
1069 WriteKind::Mutate => {
1070 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1072 WriteKind::Move => {
1073 this.report_move_out_while_borrowed(location, place_span, borrow)
1087 place_span: (&'cx Place<'tcx>, Span),
1090 flow_state: &Flows<'cx, 'tcx>,
1092 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1094 MutateMode::WriteAndRead => {
1095 self.check_if_path_or_subpath_is_moved(
1097 InitializationRequiringAction::Update,
1098 (place_span.0.as_ref(), place_span.1),
1102 MutateMode::JustWrite => {
1103 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1107 // Special case: you can assign a immutable local variable
1108 // (e.g., `x = ...`) so long as it has never been initialized
1109 // before (at this point in the flow).
1110 if let Some(local) = place_span.0.as_local() {
1111 if let Mutability::Not = self.body.local_decls[local].mutability {
1112 // check for reassignments to immutable local variables
1113 self.check_if_reassignment_to_immutable_state(
1114 location, local, place_span, flow_state,
1120 // Otherwise, use the normal access permission rules.
1124 (kind, Write(WriteKind::Mutate)),
1125 LocalMutationIsAllowed::No,
1133 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1134 flow_state: &Flows<'cx, 'tcx>,
1137 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1138 let access_kind = match bk {
1139 BorrowKind::Shallow => {
1140 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1142 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1143 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1144 let wk = WriteKind::MutableBorrow(bk);
1145 if allow_two_phase_borrow(bk) {
1146 (Deep, Reservation(wk))
1157 LocalMutationIsAllowed::No,
1161 let action = if bk == BorrowKind::Shallow {
1162 InitializationRequiringAction::MatchOn
1164 InitializationRequiringAction::Borrow
1167 self.check_if_path_or_subpath_is_moved(
1170 (place.as_ref(), span),
1175 Rvalue::AddressOf(mutability, ref place) => {
1176 let access_kind = match mutability {
1177 Mutability::Mut => (
1179 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1180 allow_two_phase_borrow: false,
1183 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1190 LocalMutationIsAllowed::No,
1194 self.check_if_path_or_subpath_is_moved(
1196 InitializationRequiringAction::Borrow,
1197 (place.as_ref(), span),
1202 Rvalue::Use(ref operand)
1203 | Rvalue::Repeat(ref operand, _)
1204 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1205 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1206 self.consume_operand(location, (operand, span), flow_state)
1209 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1210 let af = match *rvalue {
1211 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1212 Rvalue::Discriminant(..) => None,
1213 _ => unreachable!(),
1218 (Shallow(af), Read(ReadKind::Copy)),
1219 LocalMutationIsAllowed::No,
1222 self.check_if_path_or_subpath_is_moved(
1224 InitializationRequiringAction::Use,
1225 (place.as_ref(), span),
1230 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1231 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1232 self.consume_operand(location, (operand1, span), flow_state);
1233 self.consume_operand(location, (operand2, span), flow_state);
1236 Rvalue::NullaryOp(_op, _ty) => {
1237 // nullary ops take no dynamic input; no borrowck effect.
1239 // FIXME: is above actually true? Do we want to track
1240 // the fact that uninitialized data can be created via
1244 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1245 // We need to report back the list of mutable upvars that were
1246 // moved into the closure and subsequently used by the closure,
1247 // in order to populate our used_mut set.
1248 match **aggregate_kind {
1249 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1250 let BorrowCheckResult { used_mut_upvars, .. } =
1251 self.infcx.tcx.mir_borrowck(def_id);
1252 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1253 for field in used_mut_upvars {
1254 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1257 AggregateKind::Adt(..)
1258 | AggregateKind::Array(..)
1259 | AggregateKind::Tuple { .. } => (),
1262 for operand in operands {
1263 self.consume_operand(location, (operand, span), flow_state);
1269 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1270 let propagate_closure_used_mut_place = |this: &mut Self, place: &Place<'tcx>| {
1271 if !place.projection.is_empty() {
1272 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1273 this.used_mut_upvars.push(field);
1276 this.used_mut.insert(place.local);
1280 // This relies on the current way that by-value
1281 // captures of a closure are copied/moved directly
1282 // when generating MIR.
1284 Operand::Move(ref place) | Operand::Copy(ref place) => {
1285 match place.as_local() {
1286 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1287 if self.body.local_decls[local].ty.is_mutable_ptr() {
1288 // The variable will be marked as mutable by the borrow.
1291 // This is an edge case where we have a `move` closure
1292 // inside a non-move closure, and the inner closure
1293 // contains a mutation:
1296 // || { move || { i += 1; }; };
1298 // In this case our usual strategy of assuming that the
1299 // variable will be captured by mutable reference is
1300 // wrong, since `i` can be copied into the inner
1301 // closure from a shared reference.
1303 // As such we have to search for the local that this
1304 // capture comes from and mark it as being used as mut.
1306 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1307 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1308 &self.move_data.inits[init_index]
1310 bug!("temporary should be initialized exactly once")
1313 let loc = match init.location {
1314 InitLocation::Statement(stmt) => stmt,
1315 _ => bug!("temporary initialized in arguments"),
1318 let body = self.body;
1319 let bbd = &body[loc.block];
1320 let stmt = &bbd.statements[loc.statement_index];
1321 debug!("temporary assigned in: stmt={:?}", stmt);
1323 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, ref source))) =
1326 propagate_closure_used_mut_place(self, source);
1329 "closures should only capture user variables \
1330 or references to user variables"
1334 _ => propagate_closure_used_mut_place(self, place),
1337 Operand::Constant(..) => {}
1344 (operand, span): (&'cx Operand<'tcx>, Span),
1345 flow_state: &Flows<'cx, 'tcx>,
1348 Operand::Copy(ref place) => {
1349 // copy of place: check if this is "copy of frozen path"
1350 // (FIXME: see check_loans.rs)
1354 (Deep, Read(ReadKind::Copy)),
1355 LocalMutationIsAllowed::No,
1359 // Finally, check if path was already moved.
1360 self.check_if_path_or_subpath_is_moved(
1362 InitializationRequiringAction::Use,
1363 (place.as_ref(), span),
1367 Operand::Move(ref place) => {
1368 // move of place: check if this is move of already borrowed path
1372 (Deep, Write(WriteKind::Move)),
1373 LocalMutationIsAllowed::Yes,
1377 // Finally, check if path was already moved.
1378 self.check_if_path_or_subpath_is_moved(
1380 InitializationRequiringAction::Use,
1381 (place.as_ref(), span),
1385 Operand::Constant(_) => {}
1389 /// Checks whether a borrow of this place is invalidated when the function
1391 fn check_for_invalidation_at_exit(
1394 borrow: &BorrowData<'tcx>,
1397 debug!("check_for_invalidation_at_exit({:?})", borrow);
1398 let place = &borrow.borrowed_place;
1399 let deref = [ProjectionElem::Deref];
1400 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1402 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1403 // we just know that all locals are dropped at function exit (otherwise
1404 // we'll have a memory leak) and assume that all statics have a destructor.
1406 // FIXME: allow thread-locals to borrow other thread locals?
1408 let (might_be_alive, will_be_dropped) =
1409 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1410 // Thread-locals might be dropped after the function exits
1411 // We have to dereference the outer reference because
1412 // borrows don't conflict behind shared references.
1413 root_place.projection = &deref;
1416 (false, self.locals_are_invalidated_at_exit)
1419 if !will_be_dropped {
1420 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1424 let sd = if might_be_alive { Deep } else { Shallow(None) };
1426 if places_conflict::borrow_conflicts_with_place(
1433 places_conflict::PlaceConflictBias::Overlap,
1435 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1436 // FIXME: should be talking about the region lifetime instead
1437 // of just a span here.
1438 let span = self.infcx.tcx.sess.source_map().end_point(span);
1439 self.report_borrowed_value_does_not_live_long_enough(
1448 /// Reports an error if this is a borrow of local data.
1449 /// This is called for all Yield expressions on movable generators
1450 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1451 debug!("check_for_local_borrow({:?})", borrow);
1453 if borrow_of_local_data(&borrow.borrowed_place) {
1454 let err = self.cannot_borrow_across_generator_yield(
1455 self.retrieve_borrow_spans(borrow).var_or_use(),
1459 err.buffer(&mut self.errors_buffer);
1463 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1464 // Two-phase borrow support: For each activation that is newly
1465 // generated at this statement, check if it interferes with
1467 let borrow_set = self.borrow_set.clone();
1468 for &borrow_index in borrow_set.activations_at_location(location) {
1469 let borrow = &borrow_set[borrow_index];
1471 // only mutable borrows should be 2-phase
1472 assert!(match borrow.kind {
1473 BorrowKind::Shared | BorrowKind::Shallow => false,
1474 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1479 (&borrow.borrowed_place, span),
1480 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1481 LocalMutationIsAllowed::No,
1484 // We do not need to call `check_if_path_or_subpath_is_moved`
1485 // again, as we already called it when we made the
1486 // initial reservation.
1490 fn check_if_reassignment_to_immutable_state(
1494 place_span: (&Place<'tcx>, Span),
1495 flow_state: &Flows<'cx, 'tcx>,
1497 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1499 // Check if any of the initializiations of `local` have happened yet:
1500 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1501 // And, if so, report an error.
1502 let init = &self.move_data.inits[init_index];
1503 let span = init.span(&self.body);
1504 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1508 fn check_if_full_path_is_moved(
1511 desired_action: InitializationRequiringAction,
1512 place_span: (PlaceRef<'cx, 'tcx>, Span),
1513 flow_state: &Flows<'cx, 'tcx>,
1515 let maybe_uninits = &flow_state.uninits;
1519 // 1. Move of `a.b.c`, use of `a.b.c`
1520 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1521 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1522 // partial initialization support, one might have `a.x`
1523 // initialized but not `a.b`.
1527 // 4. Move of `a.b.c`, use of `a.b.d`
1528 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1529 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1530 // must have been initialized for the use to be sound.
1531 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1533 // The dataflow tracks shallow prefixes distinctly (that is,
1534 // field-accesses on P distinctly from P itself), in order to
1535 // track substructure initialization separately from the whole
1538 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1539 // which we have a MovePath is `a.b`, then that means that the
1540 // initialization state of `a.b` is all we need to inspect to
1541 // know if `a.b.c` is valid (and from that we infer that the
1542 // dereference and `.d` access is also valid, since we assume
1543 // `a.b.c` is assigned a reference to a initialized and
1544 // well-formed record structure.)
1546 // Therefore, if we seek out the *closest* prefix for which we
1547 // have a MovePath, that should capture the initialization
1548 // state for the place scenario.
1550 // This code covers scenarios 1, 2, and 3.
1552 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1553 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1554 if maybe_uninits.contains(mpi) {
1555 self.report_use_of_moved_or_uninitialized(
1558 (prefix, place_span.0, place_span.1),
1561 } // Only query longest prefix with a MovePath, not further
1562 // ancestors; dataflow recurs on children when parents
1563 // move (to support partial (re)inits).
1565 // (I.e., querying parents breaks scenario 7; but may want
1566 // to do such a query based on partial-init feature-gate.)
1569 /// Subslices correspond to multiple move paths, so we iterate through the
1570 /// elements of the base array. For each element we check
1572 /// * Does this element overlap with our slice.
1573 /// * Is any part of it uninitialized.
1574 fn check_if_subslice_element_is_moved(
1577 desired_action: InitializationRequiringAction,
1578 place_span: (PlaceRef<'cx, 'tcx>, Span),
1579 maybe_uninits: &BitSet<MovePathIndex>,
1583 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1584 let move_paths = &self.move_data.move_paths;
1585 let mut child = move_paths[mpi].first_child;
1586 while let Some(child_mpi) = child {
1587 let child_move_path = &move_paths[child_mpi];
1588 let last_proj = child_move_path.place.projection.last().unwrap();
1589 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1590 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1592 if (from..to).contains(offset) {
1594 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1595 maybe_uninits.contains(mpi)
1598 if let Some(uninit_child) = uninit_child {
1599 self.report_use_of_moved_or_uninitialized(
1602 (place_span.0, place_span.0, place_span.1),
1605 return; // don't bother finding other problems.
1609 child = child_move_path.next_sibling;
1614 fn check_if_path_or_subpath_is_moved(
1617 desired_action: InitializationRequiringAction,
1618 place_span: (PlaceRef<'cx, 'tcx>, Span),
1619 flow_state: &Flows<'cx, 'tcx>,
1621 let maybe_uninits = &flow_state.uninits;
1625 // 1. Move of `a.b.c`, use of `a` or `a.b`
1626 // partial initialization support, one might have `a.x`
1627 // initialized but not `a.b`.
1628 // 2. All bad scenarios from `check_if_full_path_is_moved`
1632 // 3. Move of `a.b.c`, use of `a.b.d`
1633 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1634 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1635 // must have been initialized for the use to be sound.
1636 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1638 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1640 if let [base_proj @ .., ProjectionElem::Subslice { from, to, from_end: false }] =
1641 place_span.0.projection
1644 Place::ty_from(place_span.0.local, base_proj, self.body(), self.infcx.tcx);
1645 if let ty::Array(..) = place_ty.ty.kind {
1646 let array_place = PlaceRef { local: place_span.0.local, projection: base_proj };
1647 self.check_if_subslice_element_is_moved(
1650 (array_place, place_span.1),
1659 // A move of any shallow suffix of `place` also interferes
1660 // with an attempt to use `place`. This is scenario 3 above.
1662 // (Distinct from handling of scenarios 1+2+4 above because
1663 // `place` does not interfere with suffixes of its prefixes,
1664 // e.g., `a.b.c` does not interfere with `a.b.d`)
1666 // This code covers scenario 1.
1668 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1669 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1670 let uninit_mpi = self
1672 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1674 if let Some(uninit_mpi) = uninit_mpi {
1675 self.report_use_of_moved_or_uninitialized(
1678 (place_span.0, place_span.0, place_span.1),
1681 return; // don't bother finding other problems.
1686 /// Currently MoveData does not store entries for all places in
1687 /// the input MIR. For example it will currently filter out
1688 /// places that are Copy; thus we do not track places of shared
1689 /// reference type. This routine will walk up a place along its
1690 /// prefixes, searching for a foundational place that *is*
1691 /// tracked in the MoveData.
1693 /// An Err result includes a tag indicated why the search failed.
1694 /// Currently this can only occur if the place is built off of a
1695 /// static variable, as we do not track those in the MoveData.
1696 fn move_path_closest_to(
1698 place: PlaceRef<'_, 'tcx>,
1699 ) -> (PlaceRef<'cx, 'tcx>, MovePathIndex) {
1700 match self.move_data.rev_lookup.find(place) {
1701 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1702 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1704 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1708 fn move_path_for_place(&mut self, place: PlaceRef<'_, 'tcx>) -> Option<MovePathIndex> {
1709 // If returns None, then there is no move path corresponding
1710 // to a direct owner of `place` (which means there is nothing
1711 // that borrowck tracks for its analysis).
1713 match self.move_data.rev_lookup.find(place) {
1714 LookupResult::Parent(_) => None,
1715 LookupResult::Exact(mpi) => Some(mpi),
1719 fn check_if_assigned_path_is_moved(
1722 (place, span): (&'cx Place<'tcx>, Span),
1723 flow_state: &Flows<'cx, 'tcx>,
1725 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1727 // None case => assigning to `x` does not require `x` be initialized.
1728 let mut cursor = &*place.projection.as_ref();
1729 while let [proj_base @ .., elem] = cursor {
1733 ProjectionElem::Index(_/*operand*/) |
1734 ProjectionElem::ConstantIndex { .. } |
1735 // assigning to P[i] requires P to be valid.
1736 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1737 // assigning to (P->variant) is okay if assigning to `P` is okay
1739 // FIXME: is this true even if P is a adt with a dtor?
1742 // assigning to (*P) requires P to be initialized
1743 ProjectionElem::Deref => {
1744 self.check_if_full_path_is_moved(
1745 location, InitializationRequiringAction::Use,
1748 projection: proj_base,
1749 }, span), flow_state);
1750 // (base initialized; no need to
1755 ProjectionElem::Subslice { .. } => {
1756 panic!("we don't allow assignments to subslices, location: {:?}",
1760 ProjectionElem::Field(..) => {
1761 // if type of `P` has a dtor, then
1762 // assigning to `P.f` requires `P` itself
1763 // be already initialized
1764 let tcx = self.infcx.tcx;
1765 let base_ty = Place::ty_from(place.local, proj_base, self.body(), tcx).ty;
1766 match base_ty.kind {
1767 ty::Adt(def, _) if def.has_dtor(tcx) => {
1768 self.check_if_path_or_subpath_is_moved(
1769 location, InitializationRequiringAction::Assignment,
1772 projection: proj_base,
1773 }, span), flow_state);
1775 // (base initialized; no need to
1780 // Once `let s; s.x = V; read(s.x);`,
1781 // is allowed, remove this match arm.
1782 ty::Adt(..) | ty::Tuple(..) => {
1783 check_parent_of_field(self, location, PlaceRef {
1785 projection: proj_base,
1786 }, span, flow_state);
1788 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1789 // partial initialization, do not complain about unnecessary `mut` on
1790 // an attempt to do a partial initialization.
1791 self.used_mut.insert(place.local);
1800 fn check_parent_of_field<'cx, 'tcx>(
1801 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1803 base: PlaceRef<'cx, 'tcx>,
1805 flow_state: &Flows<'cx, 'tcx>,
1807 // rust-lang/rust#21232: Until Rust allows reads from the
1808 // initialized parts of partially initialized structs, we
1809 // will, starting with the 2018 edition, reject attempts
1810 // to write to structs that are not fully initialized.
1812 // In other words, *until* we allow this:
1814 // 1. `let mut s; s.x = Val; read(s.x);`
1816 // we will for now disallow this:
1818 // 2. `let mut s; s.x = Val;`
1822 // 3. `let mut s = ...; drop(s); s.x=Val;`
1824 // This does not use check_if_path_or_subpath_is_moved,
1825 // because we want to *allow* reinitializations of fields:
1826 // e.g., want to allow
1828 // `let mut s = ...; drop(s.x); s.x=Val;`
1830 // This does not use check_if_full_path_is_moved on
1831 // `base`, because that would report an error about the
1832 // `base` as a whole, but in this scenario we *really*
1833 // want to report an error about the actual thing that was
1834 // moved, which may be some prefix of `base`.
1836 // Shallow so that we'll stop at any dereference; we'll
1837 // report errors about issues with such bases elsewhere.
1838 let maybe_uninits = &flow_state.uninits;
1840 // Find the shortest uninitialized prefix you can reach
1841 // without going over a Deref.
1842 let mut shortest_uninit_seen = None;
1843 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1844 let mpi = match this.move_path_for_place(prefix) {
1849 if maybe_uninits.contains(mpi) {
1851 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1852 shortest_uninit_seen,
1855 shortest_uninit_seen = Some((prefix, mpi));
1857 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1861 if let Some((prefix, mpi)) = shortest_uninit_seen {
1862 // Check for a reassignment into a uninitialized field of a union (for example,
1863 // after a move out). In this case, do not report a error here. There is an
1864 // exception, if this is the first assignment into the union (that is, there is
1865 // no move out from an earlier location) then this is an attempt at initialization
1866 // of the union - we should error in that case.
1867 let tcx = this.infcx.tcx;
1868 if let ty::Adt(def, _) =
1869 Place::ty_from(base.local, base.projection, this.body(), tcx).ty.kind
1872 if this.move_data.path_map[mpi].iter().any(|moi| {
1873 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1880 this.report_use_of_moved_or_uninitialized(
1882 InitializationRequiringAction::PartialAssignment,
1883 (prefix, base, span),
1890 /// Checks the permissions for the given place and read or write kind
1892 /// Returns `true` if an error is reported.
1893 fn check_access_permissions(
1895 (place, span): (&Place<'tcx>, Span),
1897 is_local_mutation_allowed: LocalMutationIsAllowed,
1898 flow_state: &Flows<'cx, 'tcx>,
1902 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1903 place, kind, is_local_mutation_allowed
1910 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1911 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1912 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1913 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1914 let is_local_mutation_allowed = match borrow_kind {
1915 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1916 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1917 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1919 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1921 self.add_used_mut(root_place, flow_state);
1925 error_access = AccessKind::MutableBorrow;
1926 the_place_err = place_err;
1930 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1931 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1933 self.add_used_mut(root_place, flow_state);
1937 error_access = AccessKind::Mutate;
1938 the_place_err = place_err;
1943 Reservation(WriteKind::Move)
1944 | Write(WriteKind::Move)
1945 | Reservation(WriteKind::StorageDeadOrDrop)
1946 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1947 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shallow))
1948 | Write(WriteKind::StorageDeadOrDrop)
1949 | Write(WriteKind::MutableBorrow(BorrowKind::Shared))
1950 | Write(WriteKind::MutableBorrow(BorrowKind::Shallow)) => {
1951 if let (Err(_), true) = (
1952 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
1953 self.errors_buffer.is_empty(),
1955 // rust-lang/rust#46908: In pure NLL mode this code path should be
1956 // unreachable, but we use `delay_span_bug` because we can hit this when
1957 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1958 // enabled. We don't want to ICE for that case, as other errors will have
1959 // been emitted (#52262).
1960 self.infcx.tcx.sess.delay_span_bug(
1963 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1971 // permission checks are done at Reservation point.
1974 Read(ReadKind::Borrow(BorrowKind::Unique))
1975 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1976 | Read(ReadKind::Borrow(BorrowKind::Shared))
1977 | Read(ReadKind::Borrow(BorrowKind::Shallow))
1978 | Read(ReadKind::Copy) => {
1979 // Access authorized
1984 // rust-lang/rust#21232, #54986: during period where we reject
1985 // partial initialization, do not complain about mutability
1986 // errors except for actual mutation (as opposed to an attempt
1987 // to do a partial initialization).
1988 let previously_initialized =
1989 self.is_local_ever_initialized(place.local, flow_state).is_some();
1991 // at this point, we have set up the error reporting state.
1992 if previously_initialized {
1993 self.report_mutability_error(place, span, the_place_err, error_access, location);
2000 fn is_local_ever_initialized(
2003 flow_state: &Flows<'cx, 'tcx>,
2004 ) -> Option<InitIndex> {
2005 let mpi = self.move_data.rev_lookup.find_local(local);
2006 let ii = &self.move_data.init_path_map[mpi];
2008 if flow_state.ever_inits.contains(index) {
2015 /// Adds the place into the used mutable variables set
2016 fn add_used_mut<'d>(&mut self, root_place: RootPlace<'d, 'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2018 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2019 // If the local may have been initialized, and it is now currently being
2020 // mutated, then it is justified to be annotated with the `mut`
2021 // keyword, since the mutation may be a possible reassignment.
2022 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2023 && self.is_local_ever_initialized(local, flow_state).is_some()
2025 self.used_mut.insert(local);
2030 place_projection: _,
2031 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2035 place_projection: place_projection @ [.., _],
2036 is_local_mutation_allowed: _,
2038 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2040 projection: place_projection,
2042 self.used_mut_upvars.push(field);
2048 /// Whether this value can be written or borrowed mutably.
2049 /// Returns the root place if the place passed in is a projection.
2052 place: PlaceRef<'d, 'tcx>,
2053 is_local_mutation_allowed: LocalMutationIsAllowed,
2054 ) -> Result<RootPlace<'d, 'tcx>, PlaceRef<'d, 'tcx>> {
2056 PlaceRef { local, projection: [] } => {
2057 let local = &self.body.local_decls[local];
2058 match local.mutability {
2059 Mutability::Not => match is_local_mutation_allowed {
2060 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2061 place_local: place.local,
2062 place_projection: place.projection,
2063 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2065 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2066 place_local: place.local,
2067 place_projection: place.projection,
2068 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2070 LocalMutationIsAllowed::No => Err(place),
2072 Mutability::Mut => Ok(RootPlace {
2073 place_local: place.local,
2074 place_projection: place.projection,
2075 is_local_mutation_allowed,
2079 PlaceRef { local: _, projection: [proj_base @ .., elem] } => {
2081 ProjectionElem::Deref => {
2083 Place::ty_from(place.local, proj_base, self.body(), self.infcx.tcx).ty;
2085 // Check the kind of deref to decide
2086 match base_ty.kind {
2087 ty::Ref(_, _, mutbl) => {
2089 // Shared borrowed data is never mutable
2090 hir::Mutability::Not => Err(place),
2091 // Mutably borrowed data is mutable, but only if we have a
2092 // unique path to the `&mut`
2093 hir::Mutability::Mut => {
2094 let mode = match self.is_upvar_field_projection(place) {
2095 Some(field) if self.upvars[field.index()].by_ref => {
2096 is_local_mutation_allowed
2098 _ => LocalMutationIsAllowed::Yes,
2102 PlaceRef { local: place.local, projection: proj_base },
2108 ty::RawPtr(tnm) => {
2110 // `*const` raw pointers are not mutable
2111 hir::Mutability::Not => Err(place),
2112 // `*mut` raw pointers are always mutable, regardless of
2113 // context. The users have to check by themselves.
2114 hir::Mutability::Mut => Ok(RootPlace {
2115 place_local: place.local,
2116 place_projection: place.projection,
2117 is_local_mutation_allowed,
2121 // `Box<T>` owns its content, so mutable if its location is mutable
2122 _ if base_ty.is_box() => self.is_mutable(
2123 PlaceRef { local: place.local, projection: proj_base },
2124 is_local_mutation_allowed,
2126 // Deref should only be for reference, pointers or boxes
2127 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2130 // All other projections are owned by their base path, so mutable if
2131 // base path is mutable
2132 ProjectionElem::Field(..)
2133 | ProjectionElem::Index(..)
2134 | ProjectionElem::ConstantIndex { .. }
2135 | ProjectionElem::Subslice { .. }
2136 | ProjectionElem::Downcast(..) => {
2137 let upvar_field_projection = self.is_upvar_field_projection(place);
2138 if let Some(field) = upvar_field_projection {
2139 let upvar = &self.upvars[field.index()];
2141 "upvar.mutability={:?} local_mutation_is_allowed={:?} \
2143 upvar, is_local_mutation_allowed, place
2145 match (upvar.mutability, is_local_mutation_allowed) {
2146 (Mutability::Not, LocalMutationIsAllowed::No)
2147 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2150 (Mutability::Not, LocalMutationIsAllowed::Yes)
2151 | (Mutability::Mut, _) => {
2152 // Subtle: this is an upvar
2153 // reference, so it looks like
2154 // `self.foo` -- we want to double
2155 // check that the location `*self`
2156 // is mutable (i.e., this is not a
2157 // `Fn` closure). But if that
2158 // check succeeds, we want to
2159 // *blame* the mutability on
2160 // `place` (that is,
2161 // `self.foo`). This is used to
2162 // propagate the info about
2163 // whether mutability declarations
2164 // are used outwards, so that we register
2165 // the outer variable as mutable. Otherwise a
2166 // test like this fails to record the `mut`
2170 // fn foo<F: FnOnce()>(_f: F) { }
2172 // let var = Vec::new();
2178 let _ = self.is_mutable(
2179 PlaceRef { local: place.local, projection: proj_base },
2180 is_local_mutation_allowed,
2183 place_local: place.local,
2184 place_projection: place.projection,
2185 is_local_mutation_allowed,
2191 PlaceRef { local: place.local, projection: proj_base },
2192 is_local_mutation_allowed,
2201 /// If `place` is a field projection, and the field is being projected from a closure type,
2202 /// then returns the index of the field being projected. Note that this closure will always
2203 /// be `self` in the current MIR, because that is the only time we directly access the fields
2204 /// of a closure type.
2205 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'cx, 'tcx>) -> Option<Field> {
2206 let mut place_projection = place_ref.projection;
2207 let mut by_ref = false;
2209 if let [proj_base @ .., ProjectionElem::Deref] = place_projection {
2210 place_projection = proj_base;
2214 match place_projection {
2215 [base @ .., ProjectionElem::Field(field, _ty)] => {
2216 let tcx = self.infcx.tcx;
2217 let base_ty = Place::ty_from(place_ref.local, base, self.body(), tcx).ty;
2219 if (base_ty.is_closure() || base_ty.is_generator())
2220 && (!by_ref || self.upvars[field.index()].by_ref)
2233 /// The degree of overlap between 2 places for borrow-checking.
2235 /// The places might partially overlap - in this case, we give
2236 /// up and say that they might conflict. This occurs when
2237 /// different fields of a union are borrowed. For example,
2238 /// if `u` is a union, we have no way of telling how disjoint
2239 /// `u.a.x` and `a.b.y` are.
2241 /// The places have the same type, and are either completely disjoint
2242 /// or equal - i.e., they can't "partially" overlap as can occur with
2243 /// unions. This is the "base case" on which we recur for extensions
2246 /// The places are disjoint, so we know all extensions of them
2247 /// will also be disjoint.