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");
104 tcx.arena.alloc(opt_closure_req)
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 if tables.tainted_by_errors {
140 infcx.set_tainted_by_errors();
142 let upvars: Vec<_> = tables
146 .flat_map(|v| v.values())
148 let var_hir_id = upvar_id.var_path.hir_id;
149 let capture = tables.upvar_capture(*upvar_id);
150 let by_ref = match capture {
151 ty::UpvarCapture::ByValue => false,
152 ty::UpvarCapture::ByRef(..) => true,
154 let mut upvar = Upvar {
155 name: tcx.hir().name(var_hir_id),
158 mutability: Mutability::Not,
160 let bm = *tables.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
161 if bm == ty::BindByValue(hir::Mutability::Mut) {
162 upvar.mutability = Mutability::Mut;
168 // Replace all regions with fresh inference variables. This
169 // requires first making our own copy of the MIR. This copy will
170 // be modified (in place) to contain non-lexical lifetimes. It
171 // will have a lifetime tied to the inference context.
172 let body_clone: Body<'tcx> = input_body.clone();
173 let mut promoted = input_promoted.clone();
174 let mut body = BodyAndCache::new(body_clone);
176 nll::replace_regions_in_mir(infcx, def_id, param_env, &mut body, &mut promoted);
177 let body = read_only!(body); // no further changes
178 let promoted: IndexVec<_, _> = promoted.iter_mut().map(|body| read_only!(body)).collect();
180 let location_table = &LocationTable::new(&body);
182 let mut errors_buffer = Vec::new();
183 let (move_data, move_errors): (MoveData<'tcx>, Option<Vec<(Place<'tcx>, MoveError<'tcx>)>>) =
184 match MoveData::gather_moves(&body, tcx, param_env) {
185 Ok(move_data) => (move_data, None),
186 Err((move_data, move_errors)) => (move_data, Some(move_errors)),
189 let mdpe = MoveDataParamEnv { move_data, param_env };
191 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
192 .into_engine(tcx, &body, def_id)
193 .iterate_to_fixpoint()
194 .into_results_cursor(&body);
196 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
198 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
200 // Compute non-lexical lifetimes.
207 } = nll::compute_regions(
220 // Dump MIR results into a file, if that is enabled. This let us
221 // write unit-tests, as well as helping with debugging.
222 nll::dump_mir_results(infcx, MirSource::item(def_id), &body, ®ioncx, &opt_closure_req);
224 // We also have a `#[rustc_nll]` annotation that causes us to dump
226 nll::dump_annotation(infcx, &body, def_id, ®ioncx, &opt_closure_req, &mut errors_buffer);
228 // The various `flow_*` structures can be large. We drop `flow_inits` here
229 // so it doesn't overlap with the others below. This reduces peak memory
230 // usage significantly on some benchmarks.
233 let regioncx = Rc::new(regioncx);
235 let flow_borrows = Borrows::new(tcx, &body, regioncx.clone(), &borrow_set)
236 .into_engine(tcx, &body, def_id)
237 .iterate_to_fixpoint();
238 let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
239 .into_engine(tcx, &body, def_id)
240 .iterate_to_fixpoint();
241 let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
242 .into_engine(tcx, &body, def_id)
243 .iterate_to_fixpoint();
245 let movable_generator = match tcx.hir().get(id) {
246 Node::Expr(&hir::Expr {
247 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
253 let dominators = body.dominators();
255 let mut mbcx = MirBorrowckCtxt {
259 move_data: &mdpe.move_data,
262 locals_are_invalidated_at_exit,
263 access_place_error_reported: Default::default(),
264 reservation_error_reported: Default::default(),
265 reservation_warnings: Default::default(),
266 move_error_reported: BTreeMap::new(),
267 uninitialized_error_reported: Default::default(),
270 used_mut: Default::default(),
271 used_mut_upvars: SmallVec::new(),
276 region_names: RefCell::default(),
277 next_region_name: RefCell::new(1),
281 // Compute and report region errors, if any.
282 mbcx.report_region_errors(nll_errors);
284 let results = BorrowckResults {
285 ever_inits: flow_ever_inits,
286 uninits: flow_uninits,
287 borrows: flow_borrows,
290 if let Some(errors) = move_errors {
291 mbcx.report_move_errors(errors);
294 dataflow::generic::visit_results(
296 traversal::reverse_postorder(&*body).map(|(bb, _)| bb),
301 // Convert any reservation warnings into lints.
302 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
303 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
304 let mut initial_diag =
305 mbcx.report_conflicting_borrow(location, (&place, span), bk, &borrow);
307 let scope = mbcx.body.source_info(location).scope;
308 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
309 ClearCrossCrate::Set(data) => data.lint_root,
313 // Span and message don't matter; we overwrite them below anyway
314 mbcx.infcx.tcx.struct_span_lint_hir(
315 MUTABLE_BORROW_RESERVATION_CONFLICT,
319 let mut diag = lint.build("");
321 diag.message = initial_diag.styled_message().clone();
322 diag.span = initial_diag.span.clone();
324 diag.buffer(&mut mbcx.errors_buffer);
327 initial_diag.cancel();
330 // For each non-user used mutable variable, check if it's been assigned from
331 // a user-declared local. If so, then put that local into the used_mut set.
332 // Note that this set is expected to be small - only upvars from closures
333 // would have a chance of erroneously adding non-user-defined mutable vars
335 let temporary_used_locals: FxHashSet<Local> = mbcx
338 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
341 // For the remaining unused locals that are marked as mutable, we avoid linting any that
342 // were never initialized. These locals may have been removed as unreachable code; or will be
343 // linted as unused variables.
344 let unused_mut_locals =
345 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
346 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
348 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
349 let used_mut = mbcx.used_mut;
350 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
351 let local_decl = &mbcx.body.local_decls[local];
352 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
353 ClearCrossCrate::Set(data) => data.lint_root,
357 // Skip over locals that begin with an underscore or have no name
358 match mbcx.local_names[local] {
360 if name.as_str().starts_with("_") {
367 let span = local_decl.source_info.span;
368 if span.desugaring_kind().is_some() {
369 // If the `mut` arises as part of a desugaring, we should ignore it.
373 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
374 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
375 lint.build("variable does not need to be mutable")
376 .span_suggestion_short(
380 Applicability::MachineApplicable,
386 // Buffer any move errors that we collected and de-duplicated.
387 for (_, (_, diag)) in mbcx.move_error_reported {
388 diag.buffer(&mut mbcx.errors_buffer);
391 if !mbcx.errors_buffer.is_empty() {
392 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
394 for diag in mbcx.errors_buffer.drain(..) {
395 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
399 let result = BorrowCheckResult {
400 concrete_opaque_types: opaque_type_values,
401 closure_requirements: opt_closure_req,
402 used_mut_upvars: mbcx.used_mut_upvars,
405 debug!("do_mir_borrowck: result = {:#?}", result);
410 crate struct MirBorrowckCtxt<'cx, 'tcx> {
411 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
412 body: ReadOnlyBodyAndCache<'cx, 'tcx>,
414 move_data: &'cx MoveData<'tcx>,
416 /// Map from MIR `Location` to `LocationIndex`; created
417 /// when MIR borrowck begins.
418 location_table: &'cx LocationTable,
420 movable_generator: bool,
421 /// This keeps track of whether local variables are free-ed when the function
422 /// exits even without a `StorageDead`, which appears to be the case for
425 /// I'm not sure this is the right approach - @eddyb could you try and
427 locals_are_invalidated_at_exit: bool,
428 /// This field keeps track of when borrow errors are reported in the access_place function
429 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
430 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
431 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
433 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
434 /// This field keeps track of when borrow conflict errors are reported
435 /// for reservations, so that we don't report seemingly duplicate
436 /// errors for corresponding activations.
438 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
439 // but it is currently inconvenient to track down the `BorrowIndex`
440 // at the time we detect and report a reservation error.
441 reservation_error_reported: FxHashSet<Place<'tcx>>,
442 /// Migration warnings to be reported for #56254. We delay reporting these
443 /// so that we can suppress the warning if there's a corresponding error
444 /// for the activation of the borrow.
445 reservation_warnings:
446 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
447 /// This field keeps track of move errors that are to be reported for given move indicies.
449 /// There are situations where many errors can be reported for a single move out (see #53807)
450 /// and we want only the best of those errors.
452 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
453 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
454 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
455 /// all move errors have been reported, any diagnostics in this map are added to the buffer
458 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
459 /// when errors in the map are being re-added to the error buffer so that errors with the
460 /// same primary span come out in a consistent order.
461 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'cx, 'tcx>, DiagnosticBuilder<'cx>)>,
462 /// This field keeps track of errors reported in the checking of uninitialized variables,
463 /// so that we don't report seemingly duplicate errors.
464 uninitialized_error_reported: FxHashSet<PlaceRef<'cx, 'tcx>>,
465 /// Errors to be reported buffer
466 errors_buffer: Vec<Diagnostic>,
467 /// This field keeps track of all the local variables that are declared mut and are mutated.
468 /// Used for the warning issued by an unused mutable local variable.
469 used_mut: FxHashSet<Local>,
470 /// If the function we're checking is a closure, then we'll need to report back the list of
471 /// mutable upvars that have been used. This field keeps track of them.
472 used_mut_upvars: SmallVec<[Field; 8]>,
473 /// Region inference context. This contains the results from region inference and lets us e.g.
474 /// find out which CFG points are contained in each borrow region.
475 regioncx: Rc<RegionInferenceContext<'tcx>>,
477 /// The set of borrows extracted from the MIR
478 borrow_set: Rc<BorrowSet<'tcx>>,
480 /// Dominators for MIR
481 dominators: Dominators<BasicBlock>,
483 /// Information about upvars not necessarily preserved in types or MIR
486 /// Names of local (user) variables (extracted from `var_debug_info`).
487 local_names: IndexVec<Local, Option<Name>>,
489 /// Record the region names generated for each region in the given
490 /// MIR def so that we can reuse them later in help/error messages.
491 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
493 /// The counter for generating new region names.
494 next_region_name: RefCell<usize>,
496 /// Results of Polonius analysis.
497 polonius_output: Option<Rc<PoloniusOutput>>,
501 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
502 // 2. loans made in overlapping scopes do not conflict
503 // 3. assignments do not affect things loaned out as immutable
504 // 4. moves do not affect things loaned out in any way
505 impl<'cx, 'tcx> dataflow::generic::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
506 type FlowState = Flows<'cx, 'tcx>;
510 flow_state: &Flows<'cx, 'tcx>,
511 stmt: &'cx Statement<'tcx>,
514 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
515 let span = stmt.source_info.span;
517 self.check_activations(location, span, flow_state);
520 StatementKind::Assign(box (ref lhs, ref rhs)) => {
521 self.consume_rvalue(location, (rhs, span), flow_state);
523 self.mutate_place(location, (lhs, span), Shallow(None), JustWrite, flow_state);
525 StatementKind::FakeRead(_, box ref place) => {
526 // Read for match doesn't access any memory and is used to
527 // assert that a place is safe and live. So we don't have to
528 // do any checks here.
530 // FIXME: Remove check that the place is initialized. This is
531 // needed for now because matches don't have never patterns yet.
532 // So this is the only place we prevent
536 self.check_if_path_or_subpath_is_moved(
538 InitializationRequiringAction::Use,
539 (place.as_ref(), span),
543 StatementKind::SetDiscriminant { ref place, variant_index: _ } => {
544 self.mutate_place(location, (place, span), Shallow(None), JustWrite, flow_state);
546 StatementKind::InlineAsm(ref asm) => {
547 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
549 // FIXME(eddyb) indirect inline asm outputs should
550 // be encoded through MIR place derefs instead.
554 (Deep, Read(ReadKind::Copy)),
555 LocalMutationIsAllowed::No,
558 self.check_if_path_or_subpath_is_moved(
560 InitializationRequiringAction::Use,
561 (output.as_ref(), o.span),
568 if o.is_rw { Deep } else { Shallow(None) },
569 if o.is_rw { WriteAndRead } else { JustWrite },
574 for (_, input) in asm.inputs.iter() {
575 self.consume_operand(location, (input, span), flow_state);
579 | StatementKind::AscribeUserType(..)
580 | StatementKind::Retag { .. }
581 | StatementKind::StorageLive(..) => {
582 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
585 StatementKind::StorageDead(local) => {
588 (&Place::from(local), span),
589 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
590 LocalMutationIsAllowed::Yes,
599 flow_state: &Flows<'cx, 'tcx>,
600 term: &'cx Terminator<'tcx>,
603 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
604 let span = term.source_info.span;
606 self.check_activations(loc, span, flow_state);
609 TerminatorKind::SwitchInt { ref discr, switch_ty: _, values: _, targets: _ } => {
610 self.consume_operand(loc, (discr, span), flow_state);
612 TerminatorKind::Drop { location: ref drop_place, target: _, unwind: _ } => {
613 let tcx = self.infcx.tcx;
615 // Compute the type with accurate region information.
616 let drop_place_ty = drop_place.ty(*self.body, self.infcx.tcx);
618 // Erase the regions.
619 let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
621 // "Lift" into the tcx -- once regions are erased, this type should be in the
622 // global arenas; this "lift" operation basically just asserts that is true, but
623 // that is useful later.
624 tcx.lift(&drop_place_ty).unwrap();
627 "visit_terminator_drop \
628 loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
629 loc, term, drop_place, drop_place_ty, span
635 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
636 LocalMutationIsAllowed::Yes,
640 TerminatorKind::DropAndReplace {
641 location: ref drop_place,
642 value: ref new_value,
646 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
647 self.consume_operand(loc, (new_value, span), flow_state);
649 TerminatorKind::Call {
656 self.consume_operand(loc, (func, span), flow_state);
658 self.consume_operand(loc, (arg, span), flow_state);
660 if let Some((ref dest, _ /*bb*/)) = *destination {
661 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
664 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
665 self.consume_operand(loc, (cond, span), flow_state);
666 use rustc::mir::AssertKind;
667 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
668 self.consume_operand(loc, (len, span), flow_state);
669 self.consume_operand(loc, (index, span), flow_state);
673 TerminatorKind::Yield { ref value, resume: _, ref resume_arg, drop: _ } => {
674 self.consume_operand(loc, (value, span), flow_state);
675 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
678 TerminatorKind::Goto { target: _ }
679 | TerminatorKind::Abort
680 | TerminatorKind::Unreachable
681 | TerminatorKind::Resume
682 | TerminatorKind::Return
683 | TerminatorKind::GeneratorDrop
684 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
685 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
686 // no data used, thus irrelevant to borrowck
691 fn visit_terminator_exit(
693 flow_state: &Flows<'cx, 'tcx>,
694 term: &'cx Terminator<'tcx>,
697 let span = term.source_info.span;
700 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
701 if self.movable_generator {
702 // Look for any active borrows to locals
703 let borrow_set = self.borrow_set.clone();
704 for i in flow_state.borrows.iter() {
705 let borrow = &borrow_set[i];
706 self.check_for_local_borrow(borrow, span);
711 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
712 // Returning from the function implicitly kills storage for all locals and statics.
713 // Often, the storage will already have been killed by an explicit
714 // StorageDead, but we don't always emit those (notably on unwind paths),
715 // so this "extra check" serves as a kind of backup.
716 let borrow_set = self.borrow_set.clone();
717 for i in flow_state.borrows.iter() {
718 let borrow = &borrow_set[i];
719 self.check_for_invalidation_at_exit(loc, borrow, span);
723 TerminatorKind::Abort
724 | TerminatorKind::Assert { .. }
725 | TerminatorKind::Call { .. }
726 | TerminatorKind::Drop { .. }
727 | TerminatorKind::DropAndReplace { .. }
728 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
729 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
730 | TerminatorKind::Goto { .. }
731 | TerminatorKind::SwitchInt { .. }
732 | TerminatorKind::Unreachable => {}
737 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
743 use self::AccessDepth::{Deep, Shallow};
744 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
746 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
747 enum ArtificialField {
752 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
754 /// From the RFC: "A *shallow* access means that the immediate
755 /// fields reached at P are accessed, but references or pointers
756 /// found within are not dereferenced. Right now, the only access
757 /// that is shallow is an assignment like `x = ...;`, which would
758 /// be a *shallow write* of `x`."
759 Shallow(Option<ArtificialField>),
761 /// From the RFC: "A *deep* access means that all data reachable
762 /// through the given place may be invalidated or accesses by
766 /// Access is Deep only when there is a Drop implementation that
767 /// can reach the data behind the reference.
771 /// Kind of access to a value: read or write
772 /// (For informational purposes only)
773 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
775 /// From the RFC: "A *read* means that the existing data may be
776 /// read, but will not be changed."
779 /// From the RFC: "A *write* means that the data may be mutated to
780 /// new values or otherwise invalidated (for example, it could be
781 /// de-initialized, as in a move operation).
784 /// For two-phase borrows, we distinguish a reservation (which is treated
785 /// like a Read) from an activation (which is treated like a write), and
786 /// each of those is furthermore distinguished from Reads/Writes above.
787 Reservation(WriteKind),
788 Activation(WriteKind, BorrowIndex),
791 /// Kind of read access to a value
792 /// (For informational purposes only)
793 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
799 /// Kind of write access to a value
800 /// (For informational purposes only)
801 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
804 MutableBorrow(BorrowKind),
809 /// When checking permissions for a place access, this flag is used to indicate that an immutable
810 /// local place can be mutated.
812 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
813 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
814 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
815 // `is_declared_mutable()`.
816 // - Take flow state into consideration in `is_assignable()` for local variables.
817 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
818 enum LocalMutationIsAllowed {
820 /// We want use of immutable upvars to cause a "write to immutable upvar"
821 /// error, not an "reassignment" error.
826 #[derive(Copy, Clone, Debug)]
827 enum InitializationRequiringAction {
836 struct RootPlace<'d, 'tcx> {
838 place_projection: &'d [PlaceElem<'tcx>],
839 is_local_mutation_allowed: LocalMutationIsAllowed,
842 impl InitializationRequiringAction {
843 fn as_noun(self) -> &'static str {
845 InitializationRequiringAction::Update => "update",
846 InitializationRequiringAction::Borrow => "borrow",
847 InitializationRequiringAction::MatchOn => "use", // no good noun
848 InitializationRequiringAction::Use => "use",
849 InitializationRequiringAction::Assignment => "assign",
850 InitializationRequiringAction::PartialAssignment => "assign to part",
854 fn as_verb_in_past_tense(self) -> &'static str {
856 InitializationRequiringAction::Update => "updated",
857 InitializationRequiringAction::Borrow => "borrowed",
858 InitializationRequiringAction::MatchOn => "matched on",
859 InitializationRequiringAction::Use => "used",
860 InitializationRequiringAction::Assignment => "assigned",
861 InitializationRequiringAction::PartialAssignment => "partially assigned",
866 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
867 fn body(&self) -> &'cx Body<'tcx> {
871 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
872 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
873 /// place is initialized and (b) it is not borrowed in some way that would prevent this
876 /// Returns `true` if an error is reported.
880 place_span: (&Place<'tcx>, Span),
881 kind: (AccessDepth, ReadOrWrite),
882 is_local_mutation_allowed: LocalMutationIsAllowed,
883 flow_state: &Flows<'cx, 'tcx>,
887 if let Activation(_, borrow_index) = rw {
888 if self.reservation_error_reported.contains(&place_span.0) {
890 "skipping access_place for activation of invalid reservation \
891 place: {:?} borrow_index: {:?}",
892 place_span.0, borrow_index
898 // Check is_empty() first because it's the common case, and doing that
899 // way we avoid the clone() call.
900 if !self.access_place_error_reported.is_empty()
901 && self.access_place_error_reported.contains(&(*place_span.0, place_span.1))
904 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
910 let mutability_error = self.check_access_permissions(
913 is_local_mutation_allowed,
918 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
920 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
921 // Suppress this warning when there's an error being emitted for the
922 // same borrow: fixing the error is likely to fix the warning.
923 self.reservation_warnings.remove(&borrow_idx);
926 if conflict_error || mutability_error {
927 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
929 self.access_place_error_reported.insert((*place_span.0, place_span.1));
933 fn check_access_for_conflict(
936 place_span: (&Place<'tcx>, Span),
939 flow_state: &Flows<'cx, 'tcx>,
942 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
943 location, place_span, sd, rw,
946 let mut error_reported = false;
947 let tcx = self.infcx.tcx;
948 let body = self.body;
949 let body: &Body<'_> = &body;
950 let borrow_set = self.borrow_set.clone();
952 // Use polonius output if it has been enabled.
953 let polonius_output = self.polonius_output.clone();
954 let borrows_in_scope = if let Some(polonius) = &polonius_output {
955 let location = self.location_table.start_index(location);
956 Either::Left(polonius.errors_at(location).iter().copied())
958 Either::Right(flow_state.borrows.iter())
961 each_borrow_involving_path(
969 |this, borrow_index, borrow| match (rw, borrow.kind) {
970 // Obviously an activation is compatible with its own
971 // reservation (or even prior activating uses of same
972 // borrow); so don't check if they interfere.
974 // NOTE: *reservations* do conflict with themselves;
975 // thus aren't injecting unsoundenss w/ this check.)
976 (Activation(_, activating), _) if activating == borrow_index => {
978 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
979 skipping {:?} b/c activation of same borrow_index",
983 (borrow_index, borrow),
988 (Read(_), BorrowKind::Shared)
989 | (Read(_), BorrowKind::Shallow)
990 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
991 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
995 (Write(WriteKind::Move), BorrowKind::Shallow) => {
996 // Handled by initialization checks.
1000 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
1001 // Reading from mere reservations of mutable-borrows is OK.
1002 if !is_active(&this.dominators, borrow, location) {
1003 assert!(allow_two_phase_borrow(borrow.kind));
1004 return Control::Continue;
1007 error_reported = true;
1010 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1011 .buffer(&mut this.errors_buffer);
1013 ReadKind::Borrow(bk) => {
1014 this.report_conflicting_borrow(location, place_span, bk, borrow)
1015 .buffer(&mut this.errors_buffer);
1021 (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shallow)
1022 | (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shared)
1024 tcx.migrate_borrowck()
1025 && this.borrow_set.location_map.contains_key(&location)
1028 let bi = this.borrow_set.location_map[&location];
1030 "recording invalid reservation of place: {:?} with \
1031 borrow index {:?} as warning",
1034 // rust-lang/rust#56254 - This was previously permitted on
1035 // the 2018 edition so we emit it as a warning. We buffer
1036 // these sepately so that we only emit a warning if borrow
1037 // checking was otherwise successful.
1038 this.reservation_warnings
1039 .insert(bi, (*place_span.0, place_span.1, location, bk, borrow.clone()));
1041 // Don't suppress actual errors.
1045 (Reservation(kind), _) | (Activation(kind, _), _) | (Write(kind), _) => {
1047 Reservation(..) => {
1049 "recording invalid reservation of \
1053 this.reservation_error_reported.insert(place_span.0.clone());
1055 Activation(_, activating) => {
1057 "observing check_place for activation of \
1058 borrow_index: {:?}",
1062 Read(..) | Write(..) => {}
1065 error_reported = true;
1067 WriteKind::MutableBorrow(bk) => {
1068 this.report_conflicting_borrow(location, place_span, bk, borrow)
1069 .buffer(&mut this.errors_buffer);
1071 WriteKind::StorageDeadOrDrop => this
1072 .report_borrowed_value_does_not_live_long_enough(
1078 WriteKind::Mutate => {
1079 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1081 WriteKind::Move => {
1082 this.report_move_out_while_borrowed(location, place_span, borrow)
1096 place_span: (&'cx Place<'tcx>, Span),
1099 flow_state: &Flows<'cx, 'tcx>,
1101 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1103 MutateMode::WriteAndRead => {
1104 self.check_if_path_or_subpath_is_moved(
1106 InitializationRequiringAction::Update,
1107 (place_span.0.as_ref(), place_span.1),
1111 MutateMode::JustWrite => {
1112 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1116 // Special case: you can assign a immutable local variable
1117 // (e.g., `x = ...`) so long as it has never been initialized
1118 // before (at this point in the flow).
1119 if let Some(local) = place_span.0.as_local() {
1120 if let Mutability::Not = self.body.local_decls[local].mutability {
1121 // check for reassignments to immutable local variables
1122 self.check_if_reassignment_to_immutable_state(
1123 location, local, place_span, flow_state,
1129 // Otherwise, use the normal access permission rules.
1133 (kind, Write(WriteKind::Mutate)),
1134 LocalMutationIsAllowed::No,
1142 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1143 flow_state: &Flows<'cx, 'tcx>,
1146 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1147 let access_kind = match bk {
1148 BorrowKind::Shallow => {
1149 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1151 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1152 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1153 let wk = WriteKind::MutableBorrow(bk);
1154 if allow_two_phase_borrow(bk) {
1155 (Deep, Reservation(wk))
1166 LocalMutationIsAllowed::No,
1170 let action = if bk == BorrowKind::Shallow {
1171 InitializationRequiringAction::MatchOn
1173 InitializationRequiringAction::Borrow
1176 self.check_if_path_or_subpath_is_moved(
1179 (place.as_ref(), span),
1184 Rvalue::AddressOf(mutability, ref place) => {
1185 let access_kind = match mutability {
1186 Mutability::Mut => (
1188 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1189 allow_two_phase_borrow: false,
1192 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1199 LocalMutationIsAllowed::No,
1203 self.check_if_path_or_subpath_is_moved(
1205 InitializationRequiringAction::Borrow,
1206 (place.as_ref(), span),
1211 Rvalue::Use(ref operand)
1212 | Rvalue::Repeat(ref operand, _)
1213 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1214 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1215 self.consume_operand(location, (operand, span), flow_state)
1218 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1219 let af = match *rvalue {
1220 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1221 Rvalue::Discriminant(..) => None,
1222 _ => unreachable!(),
1227 (Shallow(af), Read(ReadKind::Copy)),
1228 LocalMutationIsAllowed::No,
1231 self.check_if_path_or_subpath_is_moved(
1233 InitializationRequiringAction::Use,
1234 (place.as_ref(), span),
1239 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1240 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1241 self.consume_operand(location, (operand1, span), flow_state);
1242 self.consume_operand(location, (operand2, span), flow_state);
1245 Rvalue::NullaryOp(_op, _ty) => {
1246 // nullary ops take no dynamic input; no borrowck effect.
1248 // FIXME: is above actually true? Do we want to track
1249 // the fact that uninitialized data can be created via
1253 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1254 // We need to report back the list of mutable upvars that were
1255 // moved into the closure and subsequently used by the closure,
1256 // in order to populate our used_mut set.
1257 match **aggregate_kind {
1258 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1259 let BorrowCheckResult { used_mut_upvars, .. } =
1260 self.infcx.tcx.mir_borrowck(def_id);
1261 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1262 for field in used_mut_upvars {
1263 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1266 AggregateKind::Adt(..)
1267 | AggregateKind::Array(..)
1268 | AggregateKind::Tuple { .. } => (),
1271 for operand in operands {
1272 self.consume_operand(location, (operand, span), flow_state);
1278 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1279 let propagate_closure_used_mut_place = |this: &mut Self, place: &Place<'tcx>| {
1280 if !place.projection.is_empty() {
1281 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1282 this.used_mut_upvars.push(field);
1285 this.used_mut.insert(place.local);
1289 // This relies on the current way that by-value
1290 // captures of a closure are copied/moved directly
1291 // when generating MIR.
1293 Operand::Move(ref place) | Operand::Copy(ref place) => {
1294 match place.as_local() {
1295 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1296 if self.body.local_decls[local].ty.is_mutable_ptr() {
1297 // The variable will be marked as mutable by the borrow.
1300 // This is an edge case where we have a `move` closure
1301 // inside a non-move closure, and the inner closure
1302 // contains a mutation:
1305 // || { move || { i += 1; }; };
1307 // In this case our usual strategy of assuming that the
1308 // variable will be captured by mutable reference is
1309 // wrong, since `i` can be copied into the inner
1310 // closure from a shared reference.
1312 // As such we have to search for the local that this
1313 // capture comes from and mark it as being used as mut.
1315 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1316 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1317 &self.move_data.inits[init_index]
1319 bug!("temporary should be initialized exactly once")
1322 let loc = match init.location {
1323 InitLocation::Statement(stmt) => stmt,
1324 _ => bug!("temporary initialized in arguments"),
1327 let body = self.body;
1328 let bbd = &body[loc.block];
1329 let stmt = &bbd.statements[loc.statement_index];
1330 debug!("temporary assigned in: stmt={:?}", stmt);
1332 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, ref source))) =
1335 propagate_closure_used_mut_place(self, source);
1338 "closures should only capture user variables \
1339 or references to user variables"
1343 _ => propagate_closure_used_mut_place(self, place),
1346 Operand::Constant(..) => {}
1353 (operand, span): (&'cx Operand<'tcx>, Span),
1354 flow_state: &Flows<'cx, 'tcx>,
1357 Operand::Copy(ref place) => {
1358 // copy of place: check if this is "copy of frozen path"
1359 // (FIXME: see check_loans.rs)
1363 (Deep, Read(ReadKind::Copy)),
1364 LocalMutationIsAllowed::No,
1368 // Finally, check if path was already moved.
1369 self.check_if_path_or_subpath_is_moved(
1371 InitializationRequiringAction::Use,
1372 (place.as_ref(), span),
1376 Operand::Move(ref place) => {
1377 // move of place: check if this is move of already borrowed path
1381 (Deep, Write(WriteKind::Move)),
1382 LocalMutationIsAllowed::Yes,
1386 // Finally, check if path was already moved.
1387 self.check_if_path_or_subpath_is_moved(
1389 InitializationRequiringAction::Use,
1390 (place.as_ref(), span),
1394 Operand::Constant(_) => {}
1398 /// Checks whether a borrow of this place is invalidated when the function
1400 fn check_for_invalidation_at_exit(
1403 borrow: &BorrowData<'tcx>,
1406 debug!("check_for_invalidation_at_exit({:?})", borrow);
1407 let place = &borrow.borrowed_place;
1408 let deref = [ProjectionElem::Deref];
1409 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1411 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1412 // we just know that all locals are dropped at function exit (otherwise
1413 // we'll have a memory leak) and assume that all statics have a destructor.
1415 // FIXME: allow thread-locals to borrow other thread locals?
1417 let (might_be_alive, will_be_dropped) =
1418 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1419 // Thread-locals might be dropped after the function exits
1420 // We have to dereference the outer reference because
1421 // borrows don't conflict behind shared references.
1422 root_place.projection = &deref;
1425 (false, self.locals_are_invalidated_at_exit)
1428 if !will_be_dropped {
1429 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1433 let sd = if might_be_alive { Deep } else { Shallow(None) };
1435 if places_conflict::borrow_conflicts_with_place(
1442 places_conflict::PlaceConflictBias::Overlap,
1444 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1445 // FIXME: should be talking about the region lifetime instead
1446 // of just a span here.
1447 let span = self.infcx.tcx.sess.source_map().end_point(span);
1448 self.report_borrowed_value_does_not_live_long_enough(
1457 /// Reports an error if this is a borrow of local data.
1458 /// This is called for all Yield expressions on movable generators
1459 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1460 debug!("check_for_local_borrow({:?})", borrow);
1462 if borrow_of_local_data(&borrow.borrowed_place) {
1463 let err = self.cannot_borrow_across_generator_yield(
1464 self.retrieve_borrow_spans(borrow).var_or_use(),
1468 err.buffer(&mut self.errors_buffer);
1472 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1473 // Two-phase borrow support: For each activation that is newly
1474 // generated at this statement, check if it interferes with
1476 let borrow_set = self.borrow_set.clone();
1477 for &borrow_index in borrow_set.activations_at_location(location) {
1478 let borrow = &borrow_set[borrow_index];
1480 // only mutable borrows should be 2-phase
1481 assert!(match borrow.kind {
1482 BorrowKind::Shared | BorrowKind::Shallow => false,
1483 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1488 (&borrow.borrowed_place, span),
1489 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1490 LocalMutationIsAllowed::No,
1493 // We do not need to call `check_if_path_or_subpath_is_moved`
1494 // again, as we already called it when we made the
1495 // initial reservation.
1499 fn check_if_reassignment_to_immutable_state(
1503 place_span: (&Place<'tcx>, Span),
1504 flow_state: &Flows<'cx, 'tcx>,
1506 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1508 // Check if any of the initializiations of `local` have happened yet:
1509 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1510 // And, if so, report an error.
1511 let init = &self.move_data.inits[init_index];
1512 let span = init.span(&self.body);
1513 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1517 fn check_if_full_path_is_moved(
1520 desired_action: InitializationRequiringAction,
1521 place_span: (PlaceRef<'cx, 'tcx>, Span),
1522 flow_state: &Flows<'cx, 'tcx>,
1524 let maybe_uninits = &flow_state.uninits;
1528 // 1. Move of `a.b.c`, use of `a.b.c`
1529 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1530 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1531 // partial initialization support, one might have `a.x`
1532 // initialized but not `a.b`.
1536 // 4. Move of `a.b.c`, use of `a.b.d`
1537 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1538 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1539 // must have been initialized for the use to be sound.
1540 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1542 // The dataflow tracks shallow prefixes distinctly (that is,
1543 // field-accesses on P distinctly from P itself), in order to
1544 // track substructure initialization separately from the whole
1547 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1548 // which we have a MovePath is `a.b`, then that means that the
1549 // initialization state of `a.b` is all we need to inspect to
1550 // know if `a.b.c` is valid (and from that we infer that the
1551 // dereference and `.d` access is also valid, since we assume
1552 // `a.b.c` is assigned a reference to a initialized and
1553 // well-formed record structure.)
1555 // Therefore, if we seek out the *closest* prefix for which we
1556 // have a MovePath, that should capture the initialization
1557 // state for the place scenario.
1559 // This code covers scenarios 1, 2, and 3.
1561 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1562 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1563 if maybe_uninits.contains(mpi) {
1564 self.report_use_of_moved_or_uninitialized(
1567 (prefix, place_span.0, place_span.1),
1570 } // Only query longest prefix with a MovePath, not further
1571 // ancestors; dataflow recurs on children when parents
1572 // move (to support partial (re)inits).
1574 // (I.e., querying parents breaks scenario 7; but may want
1575 // to do such a query based on partial-init feature-gate.)
1578 /// Subslices correspond to multiple move paths, so we iterate through the
1579 /// elements of the base array. For each element we check
1581 /// * Does this element overlap with our slice.
1582 /// * Is any part of it uninitialized.
1583 fn check_if_subslice_element_is_moved(
1586 desired_action: InitializationRequiringAction,
1587 place_span: (PlaceRef<'cx, 'tcx>, Span),
1588 maybe_uninits: &BitSet<MovePathIndex>,
1592 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1593 let move_paths = &self.move_data.move_paths;
1594 let mut child = move_paths[mpi].first_child;
1595 while let Some(child_mpi) = child {
1596 let child_move_path = &move_paths[child_mpi];
1597 let last_proj = child_move_path.place.projection.last().unwrap();
1598 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1599 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1601 if (from..to).contains(offset) {
1603 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1604 maybe_uninits.contains(mpi)
1607 if let Some(uninit_child) = uninit_child {
1608 self.report_use_of_moved_or_uninitialized(
1611 (place_span.0, place_span.0, place_span.1),
1614 return; // don't bother finding other problems.
1618 child = child_move_path.next_sibling;
1623 fn check_if_path_or_subpath_is_moved(
1626 desired_action: InitializationRequiringAction,
1627 place_span: (PlaceRef<'cx, 'tcx>, Span),
1628 flow_state: &Flows<'cx, 'tcx>,
1630 let maybe_uninits = &flow_state.uninits;
1634 // 1. Move of `a.b.c`, use of `a` or `a.b`
1635 // partial initialization support, one might have `a.x`
1636 // initialized but not `a.b`.
1637 // 2. All bad scenarios from `check_if_full_path_is_moved`
1641 // 3. Move of `a.b.c`, use of `a.b.d`
1642 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1643 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1644 // must have been initialized for the use to be sound.
1645 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1647 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1649 if let [base_proj @ .., ProjectionElem::Subslice { from, to, from_end: false }] =
1650 place_span.0.projection
1653 Place::ty_from(place_span.0.local, base_proj, self.body(), self.infcx.tcx);
1654 if let ty::Array(..) = place_ty.ty.kind {
1655 let array_place = PlaceRef { local: place_span.0.local, projection: base_proj };
1656 self.check_if_subslice_element_is_moved(
1659 (array_place, place_span.1),
1668 // A move of any shallow suffix of `place` also interferes
1669 // with an attempt to use `place`. This is scenario 3 above.
1671 // (Distinct from handling of scenarios 1+2+4 above because
1672 // `place` does not interfere with suffixes of its prefixes,
1673 // e.g., `a.b.c` does not interfere with `a.b.d`)
1675 // This code covers scenario 1.
1677 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1678 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1679 let uninit_mpi = self
1681 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1683 if let Some(uninit_mpi) = uninit_mpi {
1684 self.report_use_of_moved_or_uninitialized(
1687 (place_span.0, place_span.0, place_span.1),
1690 return; // don't bother finding other problems.
1695 /// Currently MoveData does not store entries for all places in
1696 /// the input MIR. For example it will currently filter out
1697 /// places that are Copy; thus we do not track places of shared
1698 /// reference type. This routine will walk up a place along its
1699 /// prefixes, searching for a foundational place that *is*
1700 /// tracked in the MoveData.
1702 /// An Err result includes a tag indicated why the search failed.
1703 /// Currently this can only occur if the place is built off of a
1704 /// static variable, as we do not track those in the MoveData.
1705 fn move_path_closest_to(
1707 place: PlaceRef<'_, 'tcx>,
1708 ) -> (PlaceRef<'cx, 'tcx>, MovePathIndex) {
1709 match self.move_data.rev_lookup.find(place) {
1710 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1711 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1713 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1717 fn move_path_for_place(&mut self, place: PlaceRef<'_, 'tcx>) -> Option<MovePathIndex> {
1718 // If returns None, then there is no move path corresponding
1719 // to a direct owner of `place` (which means there is nothing
1720 // that borrowck tracks for its analysis).
1722 match self.move_data.rev_lookup.find(place) {
1723 LookupResult::Parent(_) => None,
1724 LookupResult::Exact(mpi) => Some(mpi),
1728 fn check_if_assigned_path_is_moved(
1731 (place, span): (&'cx Place<'tcx>, Span),
1732 flow_state: &Flows<'cx, 'tcx>,
1734 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1736 // None case => assigning to `x` does not require `x` be initialized.
1737 let mut cursor = &*place.projection.as_ref();
1738 while let [proj_base @ .., elem] = cursor {
1742 ProjectionElem::Index(_/*operand*/) |
1743 ProjectionElem::ConstantIndex { .. } |
1744 // assigning to P[i] requires P to be valid.
1745 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1746 // assigning to (P->variant) is okay if assigning to `P` is okay
1748 // FIXME: is this true even if P is a adt with a dtor?
1751 // assigning to (*P) requires P to be initialized
1752 ProjectionElem::Deref => {
1753 self.check_if_full_path_is_moved(
1754 location, InitializationRequiringAction::Use,
1757 projection: proj_base,
1758 }, span), flow_state);
1759 // (base initialized; no need to
1764 ProjectionElem::Subslice { .. } => {
1765 panic!("we don't allow assignments to subslices, location: {:?}",
1769 ProjectionElem::Field(..) => {
1770 // if type of `P` has a dtor, then
1771 // assigning to `P.f` requires `P` itself
1772 // be already initialized
1773 let tcx = self.infcx.tcx;
1774 let base_ty = Place::ty_from(place.local, proj_base, self.body(), tcx).ty;
1775 match base_ty.kind {
1776 ty::Adt(def, _) if def.has_dtor(tcx) => {
1777 self.check_if_path_or_subpath_is_moved(
1778 location, InitializationRequiringAction::Assignment,
1781 projection: proj_base,
1782 }, span), flow_state);
1784 // (base initialized; no need to
1789 // Once `let s; s.x = V; read(s.x);`,
1790 // is allowed, remove this match arm.
1791 ty::Adt(..) | ty::Tuple(..) => {
1792 check_parent_of_field(self, location, PlaceRef {
1794 projection: proj_base,
1795 }, span, flow_state);
1797 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1798 // partial initialization, do not complain about unnecessary `mut` on
1799 // an attempt to do a partial initialization.
1800 self.used_mut.insert(place.local);
1809 fn check_parent_of_field<'cx, 'tcx>(
1810 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1812 base: PlaceRef<'cx, 'tcx>,
1814 flow_state: &Flows<'cx, 'tcx>,
1816 // rust-lang/rust#21232: Until Rust allows reads from the
1817 // initialized parts of partially initialized structs, we
1818 // will, starting with the 2018 edition, reject attempts
1819 // to write to structs that are not fully initialized.
1821 // In other words, *until* we allow this:
1823 // 1. `let mut s; s.x = Val; read(s.x);`
1825 // we will for now disallow this:
1827 // 2. `let mut s; s.x = Val;`
1831 // 3. `let mut s = ...; drop(s); s.x=Val;`
1833 // This does not use check_if_path_or_subpath_is_moved,
1834 // because we want to *allow* reinitializations of fields:
1835 // e.g., want to allow
1837 // `let mut s = ...; drop(s.x); s.x=Val;`
1839 // This does not use check_if_full_path_is_moved on
1840 // `base`, because that would report an error about the
1841 // `base` as a whole, but in this scenario we *really*
1842 // want to report an error about the actual thing that was
1843 // moved, which may be some prefix of `base`.
1845 // Shallow so that we'll stop at any dereference; we'll
1846 // report errors about issues with such bases elsewhere.
1847 let maybe_uninits = &flow_state.uninits;
1849 // Find the shortest uninitialized prefix you can reach
1850 // without going over a Deref.
1851 let mut shortest_uninit_seen = None;
1852 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1853 let mpi = match this.move_path_for_place(prefix) {
1858 if maybe_uninits.contains(mpi) {
1860 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1861 shortest_uninit_seen,
1864 shortest_uninit_seen = Some((prefix, mpi));
1866 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1870 if let Some((prefix, mpi)) = shortest_uninit_seen {
1871 // Check for a reassignment into a uninitialized field of a union (for example,
1872 // after a move out). In this case, do not report a error here. There is an
1873 // exception, if this is the first assignment into the union (that is, there is
1874 // no move out from an earlier location) then this is an attempt at initialization
1875 // of the union - we should error in that case.
1876 let tcx = this.infcx.tcx;
1877 if let ty::Adt(def, _) =
1878 Place::ty_from(base.local, base.projection, this.body(), tcx).ty.kind
1881 if this.move_data.path_map[mpi].iter().any(|moi| {
1882 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1889 this.report_use_of_moved_or_uninitialized(
1891 InitializationRequiringAction::PartialAssignment,
1892 (prefix, base, span),
1899 /// Checks the permissions for the given place and read or write kind
1901 /// Returns `true` if an error is reported.
1902 fn check_access_permissions(
1904 (place, span): (&Place<'tcx>, Span),
1906 is_local_mutation_allowed: LocalMutationIsAllowed,
1907 flow_state: &Flows<'cx, 'tcx>,
1911 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1912 place, kind, is_local_mutation_allowed
1919 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1920 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1921 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1922 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1923 let is_local_mutation_allowed = match borrow_kind {
1924 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1925 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1926 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1928 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1930 self.add_used_mut(root_place, flow_state);
1934 error_access = AccessKind::MutableBorrow;
1935 the_place_err = place_err;
1939 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1940 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1942 self.add_used_mut(root_place, flow_state);
1946 error_access = AccessKind::Mutate;
1947 the_place_err = place_err;
1952 Reservation(WriteKind::Move)
1953 | Write(WriteKind::Move)
1954 | Reservation(WriteKind::StorageDeadOrDrop)
1955 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1956 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shallow))
1957 | Write(WriteKind::StorageDeadOrDrop)
1958 | Write(WriteKind::MutableBorrow(BorrowKind::Shared))
1959 | Write(WriteKind::MutableBorrow(BorrowKind::Shallow)) => {
1960 if let (Err(_), true) = (
1961 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
1962 self.errors_buffer.is_empty(),
1964 // rust-lang/rust#46908: In pure NLL mode this code path should be
1965 // unreachable, but we use `delay_span_bug` because we can hit this when
1966 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1967 // enabled. We don't want to ICE for that case, as other errors will have
1968 // been emitted (#52262).
1969 self.infcx.tcx.sess.delay_span_bug(
1972 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1980 // permission checks are done at Reservation point.
1983 Read(ReadKind::Borrow(BorrowKind::Unique))
1984 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1985 | Read(ReadKind::Borrow(BorrowKind::Shared))
1986 | Read(ReadKind::Borrow(BorrowKind::Shallow))
1987 | Read(ReadKind::Copy) => {
1988 // Access authorized
1993 // rust-lang/rust#21232, #54986: during period where we reject
1994 // partial initialization, do not complain about mutability
1995 // errors except for actual mutation (as opposed to an attempt
1996 // to do a partial initialization).
1997 let previously_initialized =
1998 self.is_local_ever_initialized(place.local, flow_state).is_some();
2000 // at this point, we have set up the error reporting state.
2001 if previously_initialized {
2002 self.report_mutability_error(place, span, the_place_err, error_access, location);
2009 fn is_local_ever_initialized(
2012 flow_state: &Flows<'cx, 'tcx>,
2013 ) -> Option<InitIndex> {
2014 let mpi = self.move_data.rev_lookup.find_local(local);
2015 let ii = &self.move_data.init_path_map[mpi];
2017 if flow_state.ever_inits.contains(index) {
2024 /// Adds the place into the used mutable variables set
2025 fn add_used_mut<'d>(&mut self, root_place: RootPlace<'d, 'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2027 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2028 // If the local may have been initialized, and it is now currently being
2029 // mutated, then it is justified to be annotated with the `mut`
2030 // keyword, since the mutation may be a possible reassignment.
2031 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2032 && self.is_local_ever_initialized(local, flow_state).is_some()
2034 self.used_mut.insert(local);
2039 place_projection: _,
2040 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2044 place_projection: place_projection @ [.., _],
2045 is_local_mutation_allowed: _,
2047 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2049 projection: place_projection,
2051 self.used_mut_upvars.push(field);
2057 /// Whether this value can be written or borrowed mutably.
2058 /// Returns the root place if the place passed in is a projection.
2061 place: PlaceRef<'d, 'tcx>,
2062 is_local_mutation_allowed: LocalMutationIsAllowed,
2063 ) -> Result<RootPlace<'d, 'tcx>, PlaceRef<'d, 'tcx>> {
2065 PlaceRef { local, projection: [] } => {
2066 let local = &self.body.local_decls[local];
2067 match local.mutability {
2068 Mutability::Not => match is_local_mutation_allowed {
2069 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2070 place_local: place.local,
2071 place_projection: place.projection,
2072 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2074 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2075 place_local: place.local,
2076 place_projection: place.projection,
2077 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2079 LocalMutationIsAllowed::No => Err(place),
2081 Mutability::Mut => Ok(RootPlace {
2082 place_local: place.local,
2083 place_projection: place.projection,
2084 is_local_mutation_allowed,
2088 PlaceRef { local: _, projection: [proj_base @ .., elem] } => {
2090 ProjectionElem::Deref => {
2092 Place::ty_from(place.local, proj_base, self.body(), self.infcx.tcx).ty;
2094 // Check the kind of deref to decide
2095 match base_ty.kind {
2096 ty::Ref(_, _, mutbl) => {
2098 // Shared borrowed data is never mutable
2099 hir::Mutability::Not => Err(place),
2100 // Mutably borrowed data is mutable, but only if we have a
2101 // unique path to the `&mut`
2102 hir::Mutability::Mut => {
2103 let mode = match self.is_upvar_field_projection(place) {
2104 Some(field) if self.upvars[field.index()].by_ref => {
2105 is_local_mutation_allowed
2107 _ => LocalMutationIsAllowed::Yes,
2111 PlaceRef { local: place.local, projection: proj_base },
2117 ty::RawPtr(tnm) => {
2119 // `*const` raw pointers are not mutable
2120 hir::Mutability::Not => Err(place),
2121 // `*mut` raw pointers are always mutable, regardless of
2122 // context. The users have to check by themselves.
2123 hir::Mutability::Mut => Ok(RootPlace {
2124 place_local: place.local,
2125 place_projection: place.projection,
2126 is_local_mutation_allowed,
2130 // `Box<T>` owns its content, so mutable if its location is mutable
2131 _ if base_ty.is_box() => self.is_mutable(
2132 PlaceRef { local: place.local, projection: proj_base },
2133 is_local_mutation_allowed,
2135 // Deref should only be for reference, pointers or boxes
2136 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2139 // All other projections are owned by their base path, so mutable if
2140 // base path is mutable
2141 ProjectionElem::Field(..)
2142 | ProjectionElem::Index(..)
2143 | ProjectionElem::ConstantIndex { .. }
2144 | ProjectionElem::Subslice { .. }
2145 | ProjectionElem::Downcast(..) => {
2146 let upvar_field_projection = self.is_upvar_field_projection(place);
2147 if let Some(field) = upvar_field_projection {
2148 let upvar = &self.upvars[field.index()];
2150 "upvar.mutability={:?} local_mutation_is_allowed={:?} \
2152 upvar, is_local_mutation_allowed, place
2154 match (upvar.mutability, is_local_mutation_allowed) {
2155 (Mutability::Not, LocalMutationIsAllowed::No)
2156 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2159 (Mutability::Not, LocalMutationIsAllowed::Yes)
2160 | (Mutability::Mut, _) => {
2161 // Subtle: this is an upvar
2162 // reference, so it looks like
2163 // `self.foo` -- we want to double
2164 // check that the location `*self`
2165 // is mutable (i.e., this is not a
2166 // `Fn` closure). But if that
2167 // check succeeds, we want to
2168 // *blame* the mutability on
2169 // `place` (that is,
2170 // `self.foo`). This is used to
2171 // propagate the info about
2172 // whether mutability declarations
2173 // are used outwards, so that we register
2174 // the outer variable as mutable. Otherwise a
2175 // test like this fails to record the `mut`
2179 // fn foo<F: FnOnce()>(_f: F) { }
2181 // let var = Vec::new();
2187 let _ = self.is_mutable(
2188 PlaceRef { local: place.local, projection: proj_base },
2189 is_local_mutation_allowed,
2192 place_local: place.local,
2193 place_projection: place.projection,
2194 is_local_mutation_allowed,
2200 PlaceRef { local: place.local, projection: proj_base },
2201 is_local_mutation_allowed,
2210 /// If `place` is a field projection, and the field is being projected from a closure type,
2211 /// then returns the index of the field being projected. Note that this closure will always
2212 /// be `self` in the current MIR, because that is the only time we directly access the fields
2213 /// of a closure type.
2214 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'cx, 'tcx>) -> Option<Field> {
2215 let mut place_projection = place_ref.projection;
2216 let mut by_ref = false;
2218 if let [proj_base @ .., ProjectionElem::Deref] = place_projection {
2219 place_projection = proj_base;
2223 match place_projection {
2224 [base @ .., ProjectionElem::Field(field, _ty)] => {
2225 let tcx = self.infcx.tcx;
2226 let base_ty = Place::ty_from(place_ref.local, base, self.body(), tcx).ty;
2228 if (base_ty.is_closure() || base_ty.is_generator())
2229 && (!by_ref || self.upvars[field.index()].by_ref)
2242 /// The degree of overlap between 2 places for borrow-checking.
2244 /// The places might partially overlap - in this case, we give
2245 /// up and say that they might conflict. This occurs when
2246 /// different fields of a union are borrowed. For example,
2247 /// if `u` is a union, we have no way of telling how disjoint
2248 /// `u.a.x` and `a.b.y` are.
2250 /// The places have the same type, and are either completely disjoint
2251 /// or equal - i.e., they can't "partially" overlap as can occur with
2252 /// unions. This is the "base case" on which we recur for extensions
2255 /// The places are disjoint, so we know all extensions of them
2256 /// will also be disjoint.