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 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.
204 } = nll::compute_regions(
217 // Dump MIR results into a file, if that is enabled. This let us
218 // write unit-tests, as well as helping with debugging.
219 nll::dump_mir_results(infcx, MirSource::item(def_id), &body, ®ioncx, &opt_closure_req);
221 // We also have a `#[rustc_nll]` annotation that causes us to dump
223 nll::dump_annotation(infcx, &body, def_id, ®ioncx, &opt_closure_req, &mut errors_buffer);
225 // The various `flow_*` structures can be large. We drop `flow_inits` here
226 // so it doesn't overlap with the others below. This reduces peak memory
227 // usage significantly on some benchmarks.
230 let regioncx = Rc::new(regioncx);
232 let flow_borrows = Borrows::new(tcx, &body, regioncx.clone(), &borrow_set)
233 .into_engine(tcx, &body, def_id)
234 .iterate_to_fixpoint();
235 let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
236 .into_engine(tcx, &body, def_id)
237 .iterate_to_fixpoint();
238 let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
239 .into_engine(tcx, &body, def_id)
240 .iterate_to_fixpoint();
242 let movable_generator = match tcx.hir().get(id) {
243 Node::Expr(&hir::Expr {
244 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
250 let dominators = body.dominators();
252 let mut mbcx = MirBorrowckCtxt {
256 move_data: &mdpe.move_data,
259 locals_are_invalidated_at_exit,
260 access_place_error_reported: Default::default(),
261 reservation_error_reported: Default::default(),
262 reservation_warnings: Default::default(),
263 move_error_reported: BTreeMap::new(),
264 uninitialized_error_reported: Default::default(),
267 used_mut: Default::default(),
268 used_mut_upvars: SmallVec::new(),
273 region_names: RefCell::default(),
274 next_region_name: RefCell::new(1),
278 // Compute and report region errors, if any.
279 mbcx.report_region_errors(nll_errors);
281 let results = BorrowckResults {
282 ever_inits: flow_ever_inits,
283 uninits: flow_uninits,
284 borrows: flow_borrows,
287 if let Some(errors) = move_errors {
288 mbcx.report_move_errors(errors);
291 dataflow::generic::visit_results(
293 traversal::reverse_postorder(&*body).map(|(bb, _)| bb),
298 // Convert any reservation warnings into lints.
299 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
300 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
301 let mut initial_diag =
302 mbcx.report_conflicting_borrow(location, (&place, span), bk, &borrow);
304 let scope = mbcx.body.source_info(location).scope;
305 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
306 ClearCrossCrate::Set(data) => data.lint_root,
310 // Span and message don't matter; we overwrite them below anyway
311 mbcx.infcx.tcx.struct_span_lint_hir(
312 MUTABLE_BORROW_RESERVATION_CONFLICT,
316 let mut diag = lint.build("");
318 diag.message = initial_diag.styled_message().clone();
319 diag.span = initial_diag.span.clone();
321 diag.buffer(&mut mbcx.errors_buffer);
324 initial_diag.cancel();
327 // For each non-user used mutable variable, check if it's been assigned from
328 // a user-declared local. If so, then put that local into the used_mut set.
329 // Note that this set is expected to be small - only upvars from closures
330 // would have a chance of erroneously adding non-user-defined mutable vars
332 let temporary_used_locals: FxHashSet<Local> = mbcx
335 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
338 // For the remaining unused locals that are marked as mutable, we avoid linting any that
339 // were never initialized. These locals may have been removed as unreachable code; or will be
340 // linted as unused variables.
341 let unused_mut_locals =
342 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
343 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
345 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
346 let used_mut = mbcx.used_mut;
347 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
348 let local_decl = &mbcx.body.local_decls[local];
349 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
350 ClearCrossCrate::Set(data) => data.lint_root,
354 // Skip over locals that begin with an underscore or have no name
355 match mbcx.local_names[local] {
357 if name.as_str().starts_with("_") {
364 let span = local_decl.source_info.span;
365 if span.desugaring_kind().is_some() {
366 // If the `mut` arises as part of a desugaring, we should ignore it.
370 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
371 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
372 lint.build("variable does not need to be mutable")
373 .span_suggestion_short(
377 Applicability::MachineApplicable,
383 // Buffer any move errors that we collected and de-duplicated.
384 for (_, (_, diag)) in mbcx.move_error_reported {
385 diag.buffer(&mut mbcx.errors_buffer);
388 if !mbcx.errors_buffer.is_empty() {
389 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
391 for diag in mbcx.errors_buffer.drain(..) {
392 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
396 let result = BorrowCheckResult {
397 concrete_opaque_types: opaque_type_values,
398 closure_requirements: opt_closure_req,
399 used_mut_upvars: mbcx.used_mut_upvars,
402 debug!("do_mir_borrowck: result = {:#?}", result);
407 crate struct MirBorrowckCtxt<'cx, 'tcx> {
408 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
409 body: ReadOnlyBodyAndCache<'cx, 'tcx>,
411 move_data: &'cx MoveData<'tcx>,
413 /// Map from MIR `Location` to `LocationIndex`; created
414 /// when MIR borrowck begins.
415 location_table: &'cx LocationTable,
417 movable_generator: bool,
418 /// This keeps track of whether local variables are free-ed when the function
419 /// exits even without a `StorageDead`, which appears to be the case for
422 /// I'm not sure this is the right approach - @eddyb could you try and
424 locals_are_invalidated_at_exit: bool,
425 /// This field keeps track of when borrow errors are reported in the access_place function
426 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
427 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
428 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
430 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
431 /// This field keeps track of when borrow conflict errors are reported
432 /// for reservations, so that we don't report seemingly duplicate
433 /// errors for corresponding activations.
435 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
436 // but it is currently inconvenient to track down the `BorrowIndex`
437 // at the time we detect and report a reservation error.
438 reservation_error_reported: FxHashSet<Place<'tcx>>,
439 /// Migration warnings to be reported for #56254. We delay reporting these
440 /// so that we can suppress the warning if there's a corresponding error
441 /// for the activation of the borrow.
442 reservation_warnings:
443 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
444 /// This field keeps track of move errors that are to be reported for given move indicies.
446 /// There are situations where many errors can be reported for a single move out (see #53807)
447 /// and we want only the best of those errors.
449 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
450 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
451 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
452 /// all move errors have been reported, any diagnostics in this map are added to the buffer
455 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
456 /// when errors in the map are being re-added to the error buffer so that errors with the
457 /// same primary span come out in a consistent order.
458 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'cx, 'tcx>, DiagnosticBuilder<'cx>)>,
459 /// This field keeps track of errors reported in the checking of uninitialized variables,
460 /// so that we don't report seemingly duplicate errors.
461 uninitialized_error_reported: FxHashSet<PlaceRef<'cx, 'tcx>>,
462 /// Errors to be reported buffer
463 errors_buffer: Vec<Diagnostic>,
464 /// This field keeps track of all the local variables that are declared mut and are mutated.
465 /// Used for the warning issued by an unused mutable local variable.
466 used_mut: FxHashSet<Local>,
467 /// If the function we're checking is a closure, then we'll need to report back the list of
468 /// mutable upvars that have been used. This field keeps track of them.
469 used_mut_upvars: SmallVec<[Field; 8]>,
470 /// Region inference context. This contains the results from region inference and lets us e.g.
471 /// find out which CFG points are contained in each borrow region.
472 regioncx: Rc<RegionInferenceContext<'tcx>>,
474 /// The set of borrows extracted from the MIR
475 borrow_set: Rc<BorrowSet<'tcx>>,
477 /// Dominators for MIR
478 dominators: Dominators<BasicBlock>,
480 /// Information about upvars not necessarily preserved in types or MIR
483 /// Names of local (user) variables (extracted from `var_debug_info`).
484 local_names: IndexVec<Local, Option<Name>>,
486 /// Record the region names generated for each region in the given
487 /// MIR def so that we can reuse them later in help/error messages.
488 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
490 /// The counter for generating new region names.
491 next_region_name: RefCell<usize>,
493 /// Results of Polonius analysis.
494 polonius_output: Option<Rc<PoloniusOutput>>,
498 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
499 // 2. loans made in overlapping scopes do not conflict
500 // 3. assignments do not affect things loaned out as immutable
501 // 4. moves do not affect things loaned out in any way
502 impl<'cx, 'tcx> dataflow::generic::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
503 type FlowState = Flows<'cx, 'tcx>;
507 flow_state: &Flows<'cx, 'tcx>,
508 stmt: &'cx Statement<'tcx>,
511 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
512 let span = stmt.source_info.span;
514 self.check_activations(location, span, flow_state);
517 StatementKind::Assign(box (ref lhs, ref rhs)) => {
518 self.consume_rvalue(location, (rhs, span), flow_state);
520 self.mutate_place(location, (lhs, span), Shallow(None), JustWrite, flow_state);
522 StatementKind::FakeRead(_, box ref place) => {
523 // Read for match doesn't access any memory and is used to
524 // assert that a place is safe and live. So we don't have to
525 // do any checks here.
527 // FIXME: Remove check that the place is initialized. This is
528 // needed for now because matches don't have never patterns yet.
529 // So this is the only place we prevent
533 self.check_if_path_or_subpath_is_moved(
535 InitializationRequiringAction::Use,
536 (place.as_ref(), span),
540 StatementKind::SetDiscriminant { ref place, variant_index: _ } => {
541 self.mutate_place(location, (place, span), Shallow(None), JustWrite, flow_state);
543 StatementKind::InlineAsm(ref asm) => {
544 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
546 // FIXME(eddyb) indirect inline asm outputs should
547 // be encoded through MIR place derefs instead.
551 (Deep, Read(ReadKind::Copy)),
552 LocalMutationIsAllowed::No,
555 self.check_if_path_or_subpath_is_moved(
557 InitializationRequiringAction::Use,
558 (output.as_ref(), o.span),
565 if o.is_rw { Deep } else { Shallow(None) },
566 if o.is_rw { WriteAndRead } else { JustWrite },
571 for (_, input) in asm.inputs.iter() {
572 self.consume_operand(location, (input, span), flow_state);
576 | StatementKind::AscribeUserType(..)
577 | StatementKind::Retag { .. }
578 | StatementKind::StorageLive(..) => {
579 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
582 StatementKind::StorageDead(local) => {
585 (&Place::from(local), span),
586 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
587 LocalMutationIsAllowed::Yes,
596 flow_state: &Flows<'cx, 'tcx>,
597 term: &'cx Terminator<'tcx>,
600 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
601 let span = term.source_info.span;
603 self.check_activations(loc, span, flow_state);
606 TerminatorKind::SwitchInt { ref discr, switch_ty: _, values: _, targets: _ } => {
607 self.consume_operand(loc, (discr, span), flow_state);
609 TerminatorKind::Drop { location: ref drop_place, target: _, unwind: _ } => {
610 let tcx = self.infcx.tcx;
612 // Compute the type with accurate region information.
613 let drop_place_ty = drop_place.ty(*self.body, self.infcx.tcx);
615 // Erase the regions.
616 let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
618 // "Lift" into the tcx -- once regions are erased, this type should be in the
619 // global arenas; this "lift" operation basically just asserts that is true, but
620 // that is useful later.
621 tcx.lift(&drop_place_ty).unwrap();
624 "visit_terminator_drop \
625 loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
626 loc, term, drop_place, drop_place_ty, span
632 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
633 LocalMutationIsAllowed::Yes,
637 TerminatorKind::DropAndReplace {
638 location: ref drop_place,
639 value: ref new_value,
643 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
644 self.consume_operand(loc, (new_value, span), flow_state);
646 TerminatorKind::Call {
653 self.consume_operand(loc, (func, span), flow_state);
655 self.consume_operand(loc, (arg, span), flow_state);
657 if let Some((ref dest, _ /*bb*/)) = *destination {
658 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
661 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
662 self.consume_operand(loc, (cond, span), flow_state);
663 use rustc::mir::AssertKind;
664 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
665 self.consume_operand(loc, (len, span), flow_state);
666 self.consume_operand(loc, (index, span), flow_state);
670 TerminatorKind::Yield { ref value, resume: _, ref resume_arg, drop: _ } => {
671 self.consume_operand(loc, (value, span), flow_state);
672 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
675 TerminatorKind::Goto { target: _ }
676 | TerminatorKind::Abort
677 | TerminatorKind::Unreachable
678 | TerminatorKind::Resume
679 | TerminatorKind::Return
680 | TerminatorKind::GeneratorDrop
681 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
682 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
683 // no data used, thus irrelevant to borrowck
688 fn visit_terminator_exit(
690 flow_state: &Flows<'cx, 'tcx>,
691 term: &'cx Terminator<'tcx>,
694 let span = term.source_info.span;
697 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
698 if self.movable_generator {
699 // Look for any active borrows to locals
700 let borrow_set = self.borrow_set.clone();
701 for i in flow_state.borrows.iter() {
702 let borrow = &borrow_set[i];
703 self.check_for_local_borrow(borrow, span);
708 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
709 // Returning from the function implicitly kills storage for all locals and statics.
710 // Often, the storage will already have been killed by an explicit
711 // StorageDead, but we don't always emit those (notably on unwind paths),
712 // so this "extra check" serves as a kind of backup.
713 let borrow_set = self.borrow_set.clone();
714 for i in flow_state.borrows.iter() {
715 let borrow = &borrow_set[i];
716 self.check_for_invalidation_at_exit(loc, borrow, span);
720 TerminatorKind::Abort
721 | TerminatorKind::Assert { .. }
722 | TerminatorKind::Call { .. }
723 | TerminatorKind::Drop { .. }
724 | TerminatorKind::DropAndReplace { .. }
725 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
726 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
727 | TerminatorKind::Goto { .. }
728 | TerminatorKind::SwitchInt { .. }
729 | TerminatorKind::Unreachable => {}
734 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
740 use self::AccessDepth::{Deep, Shallow};
741 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
743 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
744 enum ArtificialField {
749 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
751 /// From the RFC: "A *shallow* access means that the immediate
752 /// fields reached at P are accessed, but references or pointers
753 /// found within are not dereferenced. Right now, the only access
754 /// that is shallow is an assignment like `x = ...;`, which would
755 /// be a *shallow write* of `x`."
756 Shallow(Option<ArtificialField>),
758 /// From the RFC: "A *deep* access means that all data reachable
759 /// through the given place may be invalidated or accesses by
763 /// Access is Deep only when there is a Drop implementation that
764 /// can reach the data behind the reference.
768 /// Kind of access to a value: read or write
769 /// (For informational purposes only)
770 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
772 /// From the RFC: "A *read* means that the existing data may be
773 /// read, but will not be changed."
776 /// From the RFC: "A *write* means that the data may be mutated to
777 /// new values or otherwise invalidated (for example, it could be
778 /// de-initialized, as in a move operation).
781 /// For two-phase borrows, we distinguish a reservation (which is treated
782 /// like a Read) from an activation (which is treated like a write), and
783 /// each of those is furthermore distinguished from Reads/Writes above.
784 Reservation(WriteKind),
785 Activation(WriteKind, BorrowIndex),
788 /// Kind of read access to a value
789 /// (For informational purposes only)
790 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
796 /// Kind of write access to a value
797 /// (For informational purposes only)
798 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
801 MutableBorrow(BorrowKind),
806 /// When checking permissions for a place access, this flag is used to indicate that an immutable
807 /// local place can be mutated.
809 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
810 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
811 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
812 // `is_declared_mutable()`.
813 // - Take flow state into consideration in `is_assignable()` for local variables.
814 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
815 enum LocalMutationIsAllowed {
817 /// We want use of immutable upvars to cause a "write to immutable upvar"
818 /// error, not an "reassignment" error.
823 #[derive(Copy, Clone, Debug)]
824 enum InitializationRequiringAction {
833 struct RootPlace<'d, 'tcx> {
835 place_projection: &'d [PlaceElem<'tcx>],
836 is_local_mutation_allowed: LocalMutationIsAllowed,
839 impl InitializationRequiringAction {
840 fn as_noun(self) -> &'static str {
842 InitializationRequiringAction::Update => "update",
843 InitializationRequiringAction::Borrow => "borrow",
844 InitializationRequiringAction::MatchOn => "use", // no good noun
845 InitializationRequiringAction::Use => "use",
846 InitializationRequiringAction::Assignment => "assign",
847 InitializationRequiringAction::PartialAssignment => "assign to part",
851 fn as_verb_in_past_tense(self) -> &'static str {
853 InitializationRequiringAction::Update => "updated",
854 InitializationRequiringAction::Borrow => "borrowed",
855 InitializationRequiringAction::MatchOn => "matched on",
856 InitializationRequiringAction::Use => "used",
857 InitializationRequiringAction::Assignment => "assigned",
858 InitializationRequiringAction::PartialAssignment => "partially assigned",
863 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
864 fn body(&self) -> &'cx Body<'tcx> {
868 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
869 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
870 /// place is initialized and (b) it is not borrowed in some way that would prevent this
873 /// Returns `true` if an error is reported.
877 place_span: (&Place<'tcx>, Span),
878 kind: (AccessDepth, ReadOrWrite),
879 is_local_mutation_allowed: LocalMutationIsAllowed,
880 flow_state: &Flows<'cx, 'tcx>,
884 if let Activation(_, borrow_index) = rw {
885 if self.reservation_error_reported.contains(&place_span.0) {
887 "skipping access_place for activation of invalid reservation \
888 place: {:?} borrow_index: {:?}",
889 place_span.0, borrow_index
895 // Check is_empty() first because it's the common case, and doing that
896 // way we avoid the clone() call.
897 if !self.access_place_error_reported.is_empty()
898 && self.access_place_error_reported.contains(&(*place_span.0, place_span.1))
901 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
907 let mutability_error = self.check_access_permissions(
910 is_local_mutation_allowed,
915 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
917 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
918 // Suppress this warning when there's an error being emitted for the
919 // same borrow: fixing the error is likely to fix the warning.
920 self.reservation_warnings.remove(&borrow_idx);
923 if conflict_error || mutability_error {
924 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
926 self.access_place_error_reported.insert((*place_span.0, place_span.1));
930 fn check_access_for_conflict(
933 place_span: (&Place<'tcx>, Span),
936 flow_state: &Flows<'cx, 'tcx>,
939 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
940 location, place_span, sd, rw,
943 let mut error_reported = false;
944 let tcx = self.infcx.tcx;
945 let body = self.body;
946 let body: &Body<'_> = &body;
947 let borrow_set = self.borrow_set.clone();
949 // Use polonius output if it has been enabled.
950 let polonius_output = self.polonius_output.clone();
951 let borrows_in_scope = if let Some(polonius) = &polonius_output {
952 let location = self.location_table.start_index(location);
953 Either::Left(polonius.errors_at(location).iter().copied())
955 Either::Right(flow_state.borrows.iter())
958 each_borrow_involving_path(
966 |this, borrow_index, borrow| match (rw, borrow.kind) {
967 // Obviously an activation is compatible with its own
968 // reservation (or even prior activating uses of same
969 // borrow); so don't check if they interfere.
971 // NOTE: *reservations* do conflict with themselves;
972 // thus aren't injecting unsoundenss w/ this check.)
973 (Activation(_, activating), _) if activating == borrow_index => {
975 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
976 skipping {:?} b/c activation of same borrow_index",
980 (borrow_index, borrow),
985 (Read(_), BorrowKind::Shared)
986 | (Read(_), BorrowKind::Shallow)
987 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
988 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
992 (Write(WriteKind::Move), BorrowKind::Shallow) => {
993 // Handled by initialization checks.
997 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
998 // Reading from mere reservations of mutable-borrows is OK.
999 if !is_active(&this.dominators, borrow, location) {
1000 assert!(allow_two_phase_borrow(borrow.kind));
1001 return Control::Continue;
1004 error_reported = true;
1007 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1008 .buffer(&mut this.errors_buffer);
1010 ReadKind::Borrow(bk) => {
1011 this.report_conflicting_borrow(location, place_span, bk, borrow)
1012 .buffer(&mut this.errors_buffer);
1018 (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shallow)
1019 | (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shared)
1021 tcx.migrate_borrowck()
1022 && this.borrow_set.location_map.contains_key(&location)
1025 let bi = this.borrow_set.location_map[&location];
1027 "recording invalid reservation of place: {:?} with \
1028 borrow index {:?} as warning",
1031 // rust-lang/rust#56254 - This was previously permitted on
1032 // the 2018 edition so we emit it as a warning. We buffer
1033 // these sepately so that we only emit a warning if borrow
1034 // checking was otherwise successful.
1035 this.reservation_warnings
1036 .insert(bi, (*place_span.0, place_span.1, location, bk, borrow.clone()));
1038 // Don't suppress actual errors.
1042 (Reservation(kind), _) | (Activation(kind, _), _) | (Write(kind), _) => {
1044 Reservation(..) => {
1046 "recording invalid reservation of \
1050 this.reservation_error_reported.insert(place_span.0.clone());
1052 Activation(_, activating) => {
1054 "observing check_place for activation of \
1055 borrow_index: {:?}",
1059 Read(..) | Write(..) => {}
1062 error_reported = true;
1064 WriteKind::MutableBorrow(bk) => {
1065 this.report_conflicting_borrow(location, place_span, bk, borrow)
1066 .buffer(&mut this.errors_buffer);
1068 WriteKind::StorageDeadOrDrop => this
1069 .report_borrowed_value_does_not_live_long_enough(
1075 WriteKind::Mutate => {
1076 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1078 WriteKind::Move => {
1079 this.report_move_out_while_borrowed(location, place_span, borrow)
1093 place_span: (&'cx Place<'tcx>, Span),
1096 flow_state: &Flows<'cx, 'tcx>,
1098 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1100 MutateMode::WriteAndRead => {
1101 self.check_if_path_or_subpath_is_moved(
1103 InitializationRequiringAction::Update,
1104 (place_span.0.as_ref(), place_span.1),
1108 MutateMode::JustWrite => {
1109 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1113 // Special case: you can assign a immutable local variable
1114 // (e.g., `x = ...`) so long as it has never been initialized
1115 // before (at this point in the flow).
1116 if let Some(local) = place_span.0.as_local() {
1117 if let Mutability::Not = self.body.local_decls[local].mutability {
1118 // check for reassignments to immutable local variables
1119 self.check_if_reassignment_to_immutable_state(
1120 location, local, place_span, flow_state,
1126 // Otherwise, use the normal access permission rules.
1130 (kind, Write(WriteKind::Mutate)),
1131 LocalMutationIsAllowed::No,
1139 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1140 flow_state: &Flows<'cx, 'tcx>,
1143 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1144 let access_kind = match bk {
1145 BorrowKind::Shallow => {
1146 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1148 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1149 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1150 let wk = WriteKind::MutableBorrow(bk);
1151 if allow_two_phase_borrow(bk) {
1152 (Deep, Reservation(wk))
1163 LocalMutationIsAllowed::No,
1167 let action = if bk == BorrowKind::Shallow {
1168 InitializationRequiringAction::MatchOn
1170 InitializationRequiringAction::Borrow
1173 self.check_if_path_or_subpath_is_moved(
1176 (place.as_ref(), span),
1181 Rvalue::AddressOf(mutability, ref place) => {
1182 let access_kind = match mutability {
1183 Mutability::Mut => (
1185 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1186 allow_two_phase_borrow: false,
1189 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1196 LocalMutationIsAllowed::No,
1200 self.check_if_path_or_subpath_is_moved(
1202 InitializationRequiringAction::Borrow,
1203 (place.as_ref(), span),
1208 Rvalue::Use(ref operand)
1209 | Rvalue::Repeat(ref operand, _)
1210 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1211 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1212 self.consume_operand(location, (operand, span), flow_state)
1215 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1216 let af = match *rvalue {
1217 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1218 Rvalue::Discriminant(..) => None,
1219 _ => unreachable!(),
1224 (Shallow(af), Read(ReadKind::Copy)),
1225 LocalMutationIsAllowed::No,
1228 self.check_if_path_or_subpath_is_moved(
1230 InitializationRequiringAction::Use,
1231 (place.as_ref(), span),
1236 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1237 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1238 self.consume_operand(location, (operand1, span), flow_state);
1239 self.consume_operand(location, (operand2, span), flow_state);
1242 Rvalue::NullaryOp(_op, _ty) => {
1243 // nullary ops take no dynamic input; no borrowck effect.
1245 // FIXME: is above actually true? Do we want to track
1246 // the fact that uninitialized data can be created via
1250 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1251 // We need to report back the list of mutable upvars that were
1252 // moved into the closure and subsequently used by the closure,
1253 // in order to populate our used_mut set.
1254 match **aggregate_kind {
1255 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1256 let BorrowCheckResult { used_mut_upvars, .. } =
1257 self.infcx.tcx.mir_borrowck(def_id);
1258 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1259 for field in used_mut_upvars {
1260 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1263 AggregateKind::Adt(..)
1264 | AggregateKind::Array(..)
1265 | AggregateKind::Tuple { .. } => (),
1268 for operand in operands {
1269 self.consume_operand(location, (operand, span), flow_state);
1275 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1276 let propagate_closure_used_mut_place = |this: &mut Self, place: &Place<'tcx>| {
1277 if !place.projection.is_empty() {
1278 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1279 this.used_mut_upvars.push(field);
1282 this.used_mut.insert(place.local);
1286 // This relies on the current way that by-value
1287 // captures of a closure are copied/moved directly
1288 // when generating MIR.
1290 Operand::Move(ref place) | Operand::Copy(ref place) => {
1291 match place.as_local() {
1292 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1293 if self.body.local_decls[local].ty.is_mutable_ptr() {
1294 // The variable will be marked as mutable by the borrow.
1297 // This is an edge case where we have a `move` closure
1298 // inside a non-move closure, and the inner closure
1299 // contains a mutation:
1302 // || { move || { i += 1; }; };
1304 // In this case our usual strategy of assuming that the
1305 // variable will be captured by mutable reference is
1306 // wrong, since `i` can be copied into the inner
1307 // closure from a shared reference.
1309 // As such we have to search for the local that this
1310 // capture comes from and mark it as being used as mut.
1312 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1313 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1314 &self.move_data.inits[init_index]
1316 bug!("temporary should be initialized exactly once")
1319 let loc = match init.location {
1320 InitLocation::Statement(stmt) => stmt,
1321 _ => bug!("temporary initialized in arguments"),
1324 let body = self.body;
1325 let bbd = &body[loc.block];
1326 let stmt = &bbd.statements[loc.statement_index];
1327 debug!("temporary assigned in: stmt={:?}", stmt);
1329 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, ref source))) =
1332 propagate_closure_used_mut_place(self, source);
1335 "closures should only capture user variables \
1336 or references to user variables"
1340 _ => propagate_closure_used_mut_place(self, place),
1343 Operand::Constant(..) => {}
1350 (operand, span): (&'cx Operand<'tcx>, Span),
1351 flow_state: &Flows<'cx, 'tcx>,
1354 Operand::Copy(ref place) => {
1355 // copy of place: check if this is "copy of frozen path"
1356 // (FIXME: see check_loans.rs)
1360 (Deep, Read(ReadKind::Copy)),
1361 LocalMutationIsAllowed::No,
1365 // Finally, check if path was already moved.
1366 self.check_if_path_or_subpath_is_moved(
1368 InitializationRequiringAction::Use,
1369 (place.as_ref(), span),
1373 Operand::Move(ref place) => {
1374 // move of place: check if this is move of already borrowed path
1378 (Deep, Write(WriteKind::Move)),
1379 LocalMutationIsAllowed::Yes,
1383 // Finally, check if path was already moved.
1384 self.check_if_path_or_subpath_is_moved(
1386 InitializationRequiringAction::Use,
1387 (place.as_ref(), span),
1391 Operand::Constant(_) => {}
1395 /// Checks whether a borrow of this place is invalidated when the function
1397 fn check_for_invalidation_at_exit(
1400 borrow: &BorrowData<'tcx>,
1403 debug!("check_for_invalidation_at_exit({:?})", borrow);
1404 let place = &borrow.borrowed_place;
1405 let deref = [ProjectionElem::Deref];
1406 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1408 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1409 // we just know that all locals are dropped at function exit (otherwise
1410 // we'll have a memory leak) and assume that all statics have a destructor.
1412 // FIXME: allow thread-locals to borrow other thread locals?
1414 let (might_be_alive, will_be_dropped) =
1415 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1416 // Thread-locals might be dropped after the function exits
1417 // We have to dereference the outer reference because
1418 // borrows don't conflict behind shared references.
1419 root_place.projection = &deref;
1422 (false, self.locals_are_invalidated_at_exit)
1425 if !will_be_dropped {
1426 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1430 let sd = if might_be_alive { Deep } else { Shallow(None) };
1432 if places_conflict::borrow_conflicts_with_place(
1439 places_conflict::PlaceConflictBias::Overlap,
1441 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1442 // FIXME: should be talking about the region lifetime instead
1443 // of just a span here.
1444 let span = self.infcx.tcx.sess.source_map().end_point(span);
1445 self.report_borrowed_value_does_not_live_long_enough(
1454 /// Reports an error if this is a borrow of local data.
1455 /// This is called for all Yield expressions on movable generators
1456 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1457 debug!("check_for_local_borrow({:?})", borrow);
1459 if borrow_of_local_data(&borrow.borrowed_place) {
1460 let err = self.cannot_borrow_across_generator_yield(
1461 self.retrieve_borrow_spans(borrow).var_or_use(),
1465 err.buffer(&mut self.errors_buffer);
1469 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1470 // Two-phase borrow support: For each activation that is newly
1471 // generated at this statement, check if it interferes with
1473 let borrow_set = self.borrow_set.clone();
1474 for &borrow_index in borrow_set.activations_at_location(location) {
1475 let borrow = &borrow_set[borrow_index];
1477 // only mutable borrows should be 2-phase
1478 assert!(match borrow.kind {
1479 BorrowKind::Shared | BorrowKind::Shallow => false,
1480 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1485 (&borrow.borrowed_place, span),
1486 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1487 LocalMutationIsAllowed::No,
1490 // We do not need to call `check_if_path_or_subpath_is_moved`
1491 // again, as we already called it when we made the
1492 // initial reservation.
1496 fn check_if_reassignment_to_immutable_state(
1500 place_span: (&Place<'tcx>, Span),
1501 flow_state: &Flows<'cx, 'tcx>,
1503 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1505 // Check if any of the initializiations of `local` have happened yet:
1506 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1507 // And, if so, report an error.
1508 let init = &self.move_data.inits[init_index];
1509 let span = init.span(&self.body);
1510 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1514 fn check_if_full_path_is_moved(
1517 desired_action: InitializationRequiringAction,
1518 place_span: (PlaceRef<'cx, 'tcx>, Span),
1519 flow_state: &Flows<'cx, 'tcx>,
1521 let maybe_uninits = &flow_state.uninits;
1525 // 1. Move of `a.b.c`, use of `a.b.c`
1526 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1527 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1528 // partial initialization support, one might have `a.x`
1529 // initialized but not `a.b`.
1533 // 4. Move of `a.b.c`, use of `a.b.d`
1534 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1535 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1536 // must have been initialized for the use to be sound.
1537 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1539 // The dataflow tracks shallow prefixes distinctly (that is,
1540 // field-accesses on P distinctly from P itself), in order to
1541 // track substructure initialization separately from the whole
1544 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1545 // which we have a MovePath is `a.b`, then that means that the
1546 // initialization state of `a.b` is all we need to inspect to
1547 // know if `a.b.c` is valid (and from that we infer that the
1548 // dereference and `.d` access is also valid, since we assume
1549 // `a.b.c` is assigned a reference to a initialized and
1550 // well-formed record structure.)
1552 // Therefore, if we seek out the *closest* prefix for which we
1553 // have a MovePath, that should capture the initialization
1554 // state for the place scenario.
1556 // This code covers scenarios 1, 2, and 3.
1558 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1559 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1560 if maybe_uninits.contains(mpi) {
1561 self.report_use_of_moved_or_uninitialized(
1564 (prefix, place_span.0, place_span.1),
1567 } // Only query longest prefix with a MovePath, not further
1568 // ancestors; dataflow recurs on children when parents
1569 // move (to support partial (re)inits).
1571 // (I.e., querying parents breaks scenario 7; but may want
1572 // to do such a query based on partial-init feature-gate.)
1575 /// Subslices correspond to multiple move paths, so we iterate through the
1576 /// elements of the base array. For each element we check
1578 /// * Does this element overlap with our slice.
1579 /// * Is any part of it uninitialized.
1580 fn check_if_subslice_element_is_moved(
1583 desired_action: InitializationRequiringAction,
1584 place_span: (PlaceRef<'cx, 'tcx>, Span),
1585 maybe_uninits: &BitSet<MovePathIndex>,
1589 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1590 let move_paths = &self.move_data.move_paths;
1591 let mut child = move_paths[mpi].first_child;
1592 while let Some(child_mpi) = child {
1593 let child_move_path = &move_paths[child_mpi];
1594 let last_proj = child_move_path.place.projection.last().unwrap();
1595 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1596 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1598 if (from..to).contains(offset) {
1600 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1601 maybe_uninits.contains(mpi)
1604 if let Some(uninit_child) = uninit_child {
1605 self.report_use_of_moved_or_uninitialized(
1608 (place_span.0, place_span.0, place_span.1),
1611 return; // don't bother finding other problems.
1615 child = child_move_path.next_sibling;
1620 fn check_if_path_or_subpath_is_moved(
1623 desired_action: InitializationRequiringAction,
1624 place_span: (PlaceRef<'cx, 'tcx>, Span),
1625 flow_state: &Flows<'cx, 'tcx>,
1627 let maybe_uninits = &flow_state.uninits;
1631 // 1. Move of `a.b.c`, use of `a` or `a.b`
1632 // partial initialization support, one might have `a.x`
1633 // initialized but not `a.b`.
1634 // 2. All bad scenarios from `check_if_full_path_is_moved`
1638 // 3. Move of `a.b.c`, use of `a.b.d`
1639 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1640 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1641 // must have been initialized for the use to be sound.
1642 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1644 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1646 if let [base_proj @ .., ProjectionElem::Subslice { from, to, from_end: false }] =
1647 place_span.0.projection
1650 Place::ty_from(place_span.0.local, base_proj, self.body(), self.infcx.tcx);
1651 if let ty::Array(..) = place_ty.ty.kind {
1652 let array_place = PlaceRef { local: place_span.0.local, projection: base_proj };
1653 self.check_if_subslice_element_is_moved(
1656 (array_place, place_span.1),
1665 // A move of any shallow suffix of `place` also interferes
1666 // with an attempt to use `place`. This is scenario 3 above.
1668 // (Distinct from handling of scenarios 1+2+4 above because
1669 // `place` does not interfere with suffixes of its prefixes,
1670 // e.g., `a.b.c` does not interfere with `a.b.d`)
1672 // This code covers scenario 1.
1674 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1675 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1676 let uninit_mpi = self
1678 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1680 if let Some(uninit_mpi) = uninit_mpi {
1681 self.report_use_of_moved_or_uninitialized(
1684 (place_span.0, place_span.0, place_span.1),
1687 return; // don't bother finding other problems.
1692 /// Currently MoveData does not store entries for all places in
1693 /// the input MIR. For example it will currently filter out
1694 /// places that are Copy; thus we do not track places of shared
1695 /// reference type. This routine will walk up a place along its
1696 /// prefixes, searching for a foundational place that *is*
1697 /// tracked in the MoveData.
1699 /// An Err result includes a tag indicated why the search failed.
1700 /// Currently this can only occur if the place is built off of a
1701 /// static variable, as we do not track those in the MoveData.
1702 fn move_path_closest_to(
1704 place: PlaceRef<'_, 'tcx>,
1705 ) -> (PlaceRef<'cx, 'tcx>, MovePathIndex) {
1706 match self.move_data.rev_lookup.find(place) {
1707 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1708 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1710 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1714 fn move_path_for_place(&mut self, place: PlaceRef<'_, 'tcx>) -> Option<MovePathIndex> {
1715 // If returns None, then there is no move path corresponding
1716 // to a direct owner of `place` (which means there is nothing
1717 // that borrowck tracks for its analysis).
1719 match self.move_data.rev_lookup.find(place) {
1720 LookupResult::Parent(_) => None,
1721 LookupResult::Exact(mpi) => Some(mpi),
1725 fn check_if_assigned_path_is_moved(
1728 (place, span): (&'cx Place<'tcx>, Span),
1729 flow_state: &Flows<'cx, 'tcx>,
1731 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1733 // None case => assigning to `x` does not require `x` be initialized.
1734 let mut cursor = &*place.projection.as_ref();
1735 while let [proj_base @ .., elem] = cursor {
1739 ProjectionElem::Index(_/*operand*/) |
1740 ProjectionElem::ConstantIndex { .. } |
1741 // assigning to P[i] requires P to be valid.
1742 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1743 // assigning to (P->variant) is okay if assigning to `P` is okay
1745 // FIXME: is this true even if P is a adt with a dtor?
1748 // assigning to (*P) requires P to be initialized
1749 ProjectionElem::Deref => {
1750 self.check_if_full_path_is_moved(
1751 location, InitializationRequiringAction::Use,
1754 projection: proj_base,
1755 }, span), flow_state);
1756 // (base initialized; no need to
1761 ProjectionElem::Subslice { .. } => {
1762 panic!("we don't allow assignments to subslices, location: {:?}",
1766 ProjectionElem::Field(..) => {
1767 // if type of `P` has a dtor, then
1768 // assigning to `P.f` requires `P` itself
1769 // be already initialized
1770 let tcx = self.infcx.tcx;
1771 let base_ty = Place::ty_from(place.local, proj_base, self.body(), tcx).ty;
1772 match base_ty.kind {
1773 ty::Adt(def, _) if def.has_dtor(tcx) => {
1774 self.check_if_path_or_subpath_is_moved(
1775 location, InitializationRequiringAction::Assignment,
1778 projection: proj_base,
1779 }, span), flow_state);
1781 // (base initialized; no need to
1786 // Once `let s; s.x = V; read(s.x);`,
1787 // is allowed, remove this match arm.
1788 ty::Adt(..) | ty::Tuple(..) => {
1789 check_parent_of_field(self, location, PlaceRef {
1791 projection: proj_base,
1792 }, span, flow_state);
1794 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1795 // partial initialization, do not complain about unnecessary `mut` on
1796 // an attempt to do a partial initialization.
1797 self.used_mut.insert(place.local);
1806 fn check_parent_of_field<'cx, 'tcx>(
1807 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1809 base: PlaceRef<'cx, 'tcx>,
1811 flow_state: &Flows<'cx, 'tcx>,
1813 // rust-lang/rust#21232: Until Rust allows reads from the
1814 // initialized parts of partially initialized structs, we
1815 // will, starting with the 2018 edition, reject attempts
1816 // to write to structs that are not fully initialized.
1818 // In other words, *until* we allow this:
1820 // 1. `let mut s; s.x = Val; read(s.x);`
1822 // we will for now disallow this:
1824 // 2. `let mut s; s.x = Val;`
1828 // 3. `let mut s = ...; drop(s); s.x=Val;`
1830 // This does not use check_if_path_or_subpath_is_moved,
1831 // because we want to *allow* reinitializations of fields:
1832 // e.g., want to allow
1834 // `let mut s = ...; drop(s.x); s.x=Val;`
1836 // This does not use check_if_full_path_is_moved on
1837 // `base`, because that would report an error about the
1838 // `base` as a whole, but in this scenario we *really*
1839 // want to report an error about the actual thing that was
1840 // moved, which may be some prefix of `base`.
1842 // Shallow so that we'll stop at any dereference; we'll
1843 // report errors about issues with such bases elsewhere.
1844 let maybe_uninits = &flow_state.uninits;
1846 // Find the shortest uninitialized prefix you can reach
1847 // without going over a Deref.
1848 let mut shortest_uninit_seen = None;
1849 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1850 let mpi = match this.move_path_for_place(prefix) {
1855 if maybe_uninits.contains(mpi) {
1857 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1858 shortest_uninit_seen,
1861 shortest_uninit_seen = Some((prefix, mpi));
1863 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1867 if let Some((prefix, mpi)) = shortest_uninit_seen {
1868 // Check for a reassignment into a uninitialized field of a union (for example,
1869 // after a move out). In this case, do not report a error here. There is an
1870 // exception, if this is the first assignment into the union (that is, there is
1871 // no move out from an earlier location) then this is an attempt at initialization
1872 // of the union - we should error in that case.
1873 let tcx = this.infcx.tcx;
1874 if let ty::Adt(def, _) =
1875 Place::ty_from(base.local, base.projection, this.body(), tcx).ty.kind
1878 if this.move_data.path_map[mpi].iter().any(|moi| {
1879 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1886 this.report_use_of_moved_or_uninitialized(
1888 InitializationRequiringAction::PartialAssignment,
1889 (prefix, base, span),
1896 /// Checks the permissions for the given place and read or write kind
1898 /// Returns `true` if an error is reported.
1899 fn check_access_permissions(
1901 (place, span): (&Place<'tcx>, Span),
1903 is_local_mutation_allowed: LocalMutationIsAllowed,
1904 flow_state: &Flows<'cx, 'tcx>,
1908 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1909 place, kind, is_local_mutation_allowed
1916 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1917 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1918 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1919 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1920 let is_local_mutation_allowed = match borrow_kind {
1921 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1922 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1923 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1925 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1927 self.add_used_mut(root_place, flow_state);
1931 error_access = AccessKind::MutableBorrow;
1932 the_place_err = place_err;
1936 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1937 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1939 self.add_used_mut(root_place, flow_state);
1943 error_access = AccessKind::Mutate;
1944 the_place_err = place_err;
1949 Reservation(WriteKind::Move)
1950 | Write(WriteKind::Move)
1951 | Reservation(WriteKind::StorageDeadOrDrop)
1952 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1953 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shallow))
1954 | Write(WriteKind::StorageDeadOrDrop)
1955 | Write(WriteKind::MutableBorrow(BorrowKind::Shared))
1956 | Write(WriteKind::MutableBorrow(BorrowKind::Shallow)) => {
1957 if let (Err(_), true) = (
1958 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
1959 self.errors_buffer.is_empty(),
1961 // rust-lang/rust#46908: In pure NLL mode this code path should be
1962 // unreachable, but we use `delay_span_bug` because we can hit this when
1963 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1964 // enabled. We don't want to ICE for that case, as other errors will have
1965 // been emitted (#52262).
1966 self.infcx.tcx.sess.delay_span_bug(
1969 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1977 // permission checks are done at Reservation point.
1980 Read(ReadKind::Borrow(BorrowKind::Unique))
1981 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1982 | Read(ReadKind::Borrow(BorrowKind::Shared))
1983 | Read(ReadKind::Borrow(BorrowKind::Shallow))
1984 | Read(ReadKind::Copy) => {
1985 // Access authorized
1990 // rust-lang/rust#21232, #54986: during period where we reject
1991 // partial initialization, do not complain about mutability
1992 // errors except for actual mutation (as opposed to an attempt
1993 // to do a partial initialization).
1994 let previously_initialized =
1995 self.is_local_ever_initialized(place.local, flow_state).is_some();
1997 // at this point, we have set up the error reporting state.
1998 if previously_initialized {
1999 self.report_mutability_error(place, span, the_place_err, error_access, location);
2006 fn is_local_ever_initialized(
2009 flow_state: &Flows<'cx, 'tcx>,
2010 ) -> Option<InitIndex> {
2011 let mpi = self.move_data.rev_lookup.find_local(local);
2012 let ii = &self.move_data.init_path_map[mpi];
2014 if flow_state.ever_inits.contains(index) {
2021 /// Adds the place into the used mutable variables set
2022 fn add_used_mut<'d>(&mut self, root_place: RootPlace<'d, 'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2024 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2025 // If the local may have been initialized, and it is now currently being
2026 // mutated, then it is justified to be annotated with the `mut`
2027 // keyword, since the mutation may be a possible reassignment.
2028 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2029 && self.is_local_ever_initialized(local, flow_state).is_some()
2031 self.used_mut.insert(local);
2036 place_projection: _,
2037 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2041 place_projection: place_projection @ [.., _],
2042 is_local_mutation_allowed: _,
2044 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2046 projection: place_projection,
2048 self.used_mut_upvars.push(field);
2054 /// Whether this value can be written or borrowed mutably.
2055 /// Returns the root place if the place passed in is a projection.
2058 place: PlaceRef<'d, 'tcx>,
2059 is_local_mutation_allowed: LocalMutationIsAllowed,
2060 ) -> Result<RootPlace<'d, 'tcx>, PlaceRef<'d, 'tcx>> {
2062 PlaceRef { local, projection: [] } => {
2063 let local = &self.body.local_decls[local];
2064 match local.mutability {
2065 Mutability::Not => match is_local_mutation_allowed {
2066 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2067 place_local: place.local,
2068 place_projection: place.projection,
2069 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2071 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2072 place_local: place.local,
2073 place_projection: place.projection,
2074 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2076 LocalMutationIsAllowed::No => Err(place),
2078 Mutability::Mut => Ok(RootPlace {
2079 place_local: place.local,
2080 place_projection: place.projection,
2081 is_local_mutation_allowed,
2085 PlaceRef { local: _, projection: [proj_base @ .., elem] } => {
2087 ProjectionElem::Deref => {
2089 Place::ty_from(place.local, proj_base, self.body(), self.infcx.tcx).ty;
2091 // Check the kind of deref to decide
2092 match base_ty.kind {
2093 ty::Ref(_, _, mutbl) => {
2095 // Shared borrowed data is never mutable
2096 hir::Mutability::Not => Err(place),
2097 // Mutably borrowed data is mutable, but only if we have a
2098 // unique path to the `&mut`
2099 hir::Mutability::Mut => {
2100 let mode = match self.is_upvar_field_projection(place) {
2101 Some(field) if self.upvars[field.index()].by_ref => {
2102 is_local_mutation_allowed
2104 _ => LocalMutationIsAllowed::Yes,
2108 PlaceRef { local: place.local, projection: proj_base },
2114 ty::RawPtr(tnm) => {
2116 // `*const` raw pointers are not mutable
2117 hir::Mutability::Not => Err(place),
2118 // `*mut` raw pointers are always mutable, regardless of
2119 // context. The users have to check by themselves.
2120 hir::Mutability::Mut => Ok(RootPlace {
2121 place_local: place.local,
2122 place_projection: place.projection,
2123 is_local_mutation_allowed,
2127 // `Box<T>` owns its content, so mutable if its location is mutable
2128 _ if base_ty.is_box() => self.is_mutable(
2129 PlaceRef { local: place.local, projection: proj_base },
2130 is_local_mutation_allowed,
2132 // Deref should only be for reference, pointers or boxes
2133 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2136 // All other projections are owned by their base path, so mutable if
2137 // base path is mutable
2138 ProjectionElem::Field(..)
2139 | ProjectionElem::Index(..)
2140 | ProjectionElem::ConstantIndex { .. }
2141 | ProjectionElem::Subslice { .. }
2142 | ProjectionElem::Downcast(..) => {
2143 let upvar_field_projection = self.is_upvar_field_projection(place);
2144 if let Some(field) = upvar_field_projection {
2145 let upvar = &self.upvars[field.index()];
2147 "upvar.mutability={:?} local_mutation_is_allowed={:?} \
2149 upvar, is_local_mutation_allowed, place
2151 match (upvar.mutability, is_local_mutation_allowed) {
2152 (Mutability::Not, LocalMutationIsAllowed::No)
2153 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2156 (Mutability::Not, LocalMutationIsAllowed::Yes)
2157 | (Mutability::Mut, _) => {
2158 // Subtle: this is an upvar
2159 // reference, so it looks like
2160 // `self.foo` -- we want to double
2161 // check that the location `*self`
2162 // is mutable (i.e., this is not a
2163 // `Fn` closure). But if that
2164 // check succeeds, we want to
2165 // *blame* the mutability on
2166 // `place` (that is,
2167 // `self.foo`). This is used to
2168 // propagate the info about
2169 // whether mutability declarations
2170 // are used outwards, so that we register
2171 // the outer variable as mutable. Otherwise a
2172 // test like this fails to record the `mut`
2176 // fn foo<F: FnOnce()>(_f: F) { }
2178 // let var = Vec::new();
2184 let _ = self.is_mutable(
2185 PlaceRef { local: place.local, projection: proj_base },
2186 is_local_mutation_allowed,
2189 place_local: place.local,
2190 place_projection: place.projection,
2191 is_local_mutation_allowed,
2197 PlaceRef { local: place.local, projection: proj_base },
2198 is_local_mutation_allowed,
2207 /// If `place` is a field projection, and the field is being projected from a closure type,
2208 /// then returns the index of the field being projected. Note that this closure will always
2209 /// be `self` in the current MIR, because that is the only time we directly access the fields
2210 /// of a closure type.
2211 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'cx, 'tcx>) -> Option<Field> {
2212 let mut place_projection = place_ref.projection;
2213 let mut by_ref = false;
2215 if let [proj_base @ .., ProjectionElem::Deref] = place_projection {
2216 place_projection = proj_base;
2220 match place_projection {
2221 [base @ .., ProjectionElem::Field(field, _ty)] => {
2222 let tcx = self.infcx.tcx;
2223 let base_ty = Place::ty_from(place_ref.local, base, self.body(), tcx).ty;
2225 if (base_ty.is_closure() || base_ty.is_generator())
2226 && (!by_ref || self.upvars[field.index()].by_ref)
2239 /// The degree of overlap between 2 places for borrow-checking.
2241 /// The places might partially overlap - in this case, we give
2242 /// up and say that they might conflict. This occurs when
2243 /// different fields of a union are borrowed. For example,
2244 /// if `u` is a union, we have no way of telling how disjoint
2245 /// `u.a.x` and `a.b.y` are.
2247 /// The places have the same type, and are either completely disjoint
2248 /// or equal - i.e., they can't "partially" overlap as can occur with
2249 /// unions. This is the "base case" on which we recur for extensions
2252 /// The places are disjoint, so we know all extensions of them
2253 /// will also be disjoint.