1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 use rustc::lint::builtin::MUTABLE_BORROW_RESERVATION_CONFLICT;
4 use rustc::lint::builtin::UNUSED_MUT;
6 read_only, traversal, Body, BodyAndCache, ClearCrossCrate, Local, Location, Mutability,
7 Operand, Place, PlaceElem, PlaceRef, ReadOnlyBodyAndCache,
9 use rustc::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
10 use rustc::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
11 use rustc::mir::{Terminator, TerminatorKind};
12 use rustc::ty::query::Providers;
13 use rustc::ty::{self, RegionVid, TyCtxt};
15 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
16 use rustc_data_structures::graph::dominators::Dominators;
17 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder};
19 use rustc_hir::{def_id::DefId, HirId, Node};
20 use rustc_index::bit_set::BitSet;
21 use rustc_index::vec::IndexVec;
22 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
25 use smallvec::SmallVec;
26 use std::cell::RefCell;
27 use std::collections::BTreeMap;
31 use rustc_ast::ast::Name;
32 use rustc_span::{Span, DUMMY_SP};
35 use crate::dataflow::generic::{Analysis, BorrowckFlowState as Flows, BorrowckResults};
36 use crate::dataflow::indexes::{BorrowIndex, InitIndex, MoveOutIndex, MovePathIndex};
37 use crate::dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
38 use crate::dataflow::Borrows;
39 use crate::dataflow::EverInitializedPlaces;
40 use crate::dataflow::MoveDataParamEnv;
41 use crate::dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
42 use crate::transform::MirSource;
44 use self::diagnostics::{AccessKind, RegionName};
45 use self::location::LocationTable;
46 use self::prefixes::PrefixSet;
47 use self::MutateMode::{JustWrite, WriteAndRead};
49 use self::path_utils::*;
52 mod constraint_generation;
58 mod member_constraints;
67 mod universal_regions;
70 crate use borrow_set::{BorrowData, BorrowSet};
71 crate use nll::{PoloniusOutput, ToRegionVid};
72 crate use place_ext::PlaceExt;
73 crate use places_conflict::{places_conflict, PlaceConflictBias};
74 crate use region_infer::RegionInferenceContext;
76 // FIXME(eddyb) perhaps move this somewhere more centrally.
83 /// If true, the capture is behind a reference.
86 mutability: Mutability,
89 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_regions]` annotation that causes us to dump
226 nll::dump_annotation(
236 // The various `flow_*` structures can be large. We drop `flow_inits` here
237 // so it doesn't overlap with the others below. This reduces peak memory
238 // usage significantly on some benchmarks.
241 let regioncx = Rc::new(regioncx);
243 let flow_borrows = Borrows::new(tcx, &body, regioncx.clone(), &borrow_set)
244 .into_engine(tcx, &body, def_id)
245 .iterate_to_fixpoint();
246 let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
247 .into_engine(tcx, &body, def_id)
248 .iterate_to_fixpoint();
249 let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
250 .into_engine(tcx, &body, def_id)
251 .iterate_to_fixpoint();
253 let movable_generator = match tcx.hir().get(id) {
254 Node::Expr(&hir::Expr {
255 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
261 let dominators = body.dominators();
263 let mut mbcx = MirBorrowckCtxt {
267 move_data: &mdpe.move_data,
270 locals_are_invalidated_at_exit,
271 access_place_error_reported: Default::default(),
272 reservation_error_reported: Default::default(),
273 reservation_warnings: Default::default(),
274 move_error_reported: BTreeMap::new(),
275 uninitialized_error_reported: Default::default(),
278 used_mut: Default::default(),
279 used_mut_upvars: SmallVec::new(),
284 region_names: RefCell::default(),
285 next_region_name: RefCell::new(1),
289 // Compute and report region errors, if any.
290 mbcx.report_region_errors(nll_errors);
292 let results = BorrowckResults {
293 ever_inits: flow_ever_inits,
294 uninits: flow_uninits,
295 borrows: flow_borrows,
298 if let Some(errors) = move_errors {
299 mbcx.report_move_errors(errors);
302 dataflow::generic::visit_results(
304 traversal::reverse_postorder(&*body).map(|(bb, _)| bb),
309 // Convert any reservation warnings into lints.
310 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
311 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
312 let mut initial_diag =
313 mbcx.report_conflicting_borrow(location, (&place, span), bk, &borrow);
315 let scope = mbcx.body.source_info(location).scope;
316 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
317 ClearCrossCrate::Set(data) => data.lint_root,
321 // Span and message don't matter; we overwrite them below anyway
322 mbcx.infcx.tcx.struct_span_lint_hir(
323 MUTABLE_BORROW_RESERVATION_CONFLICT,
327 let mut diag = lint.build("");
329 diag.message = initial_diag.styled_message().clone();
330 diag.span = initial_diag.span.clone();
332 diag.buffer(&mut mbcx.errors_buffer);
335 initial_diag.cancel();
338 // For each non-user used mutable variable, check if it's been assigned from
339 // a user-declared local. If so, then put that local into the used_mut set.
340 // Note that this set is expected to be small - only upvars from closures
341 // would have a chance of erroneously adding non-user-defined mutable vars
343 let temporary_used_locals: FxHashSet<Local> = mbcx
346 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
349 // For the remaining unused locals that are marked as mutable, we avoid linting any that
350 // were never initialized. These locals may have been removed as unreachable code; or will be
351 // linted as unused variables.
352 let unused_mut_locals =
353 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
354 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
356 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
357 let used_mut = mbcx.used_mut;
358 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
359 let local_decl = &mbcx.body.local_decls[local];
360 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
361 ClearCrossCrate::Set(data) => data.lint_root,
365 // Skip over locals that begin with an underscore or have no name
366 match mbcx.local_names[local] {
368 if name.as_str().starts_with('_') {
375 let span = local_decl.source_info.span;
376 if span.desugaring_kind().is_some() {
377 // If the `mut` arises as part of a desugaring, we should ignore it.
381 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
382 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
383 lint.build("variable does not need to be mutable")
384 .span_suggestion_short(
388 Applicability::MachineApplicable,
394 // Buffer any move errors that we collected and de-duplicated.
395 for (_, (_, diag)) in mbcx.move_error_reported {
396 diag.buffer(&mut mbcx.errors_buffer);
399 if !mbcx.errors_buffer.is_empty() {
400 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
402 for diag in mbcx.errors_buffer.drain(..) {
403 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
407 let result = BorrowCheckResult {
408 concrete_opaque_types: opaque_type_values,
409 closure_requirements: opt_closure_req,
410 used_mut_upvars: mbcx.used_mut_upvars,
413 debug!("do_mir_borrowck: result = {:#?}", result);
418 crate struct MirBorrowckCtxt<'cx, 'tcx> {
419 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
420 body: ReadOnlyBodyAndCache<'cx, 'tcx>,
422 move_data: &'cx MoveData<'tcx>,
424 /// Map from MIR `Location` to `LocationIndex`; created
425 /// when MIR borrowck begins.
426 location_table: &'cx LocationTable,
428 movable_generator: bool,
429 /// This keeps track of whether local variables are free-ed when the function
430 /// exits even without a `StorageDead`, which appears to be the case for
433 /// I'm not sure this is the right approach - @eddyb could you try and
435 locals_are_invalidated_at_exit: bool,
436 /// This field keeps track of when borrow errors are reported in the access_place function
437 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
438 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
439 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
441 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
442 /// This field keeps track of when borrow conflict errors are reported
443 /// for reservations, so that we don't report seemingly duplicate
444 /// errors for corresponding activations.
446 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
447 // but it is currently inconvenient to track down the `BorrowIndex`
448 // at the time we detect and report a reservation error.
449 reservation_error_reported: FxHashSet<Place<'tcx>>,
450 /// Migration warnings to be reported for #56254. We delay reporting these
451 /// so that we can suppress the warning if there's a corresponding error
452 /// for the activation of the borrow.
453 reservation_warnings:
454 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
455 /// This field keeps track of move errors that are to be reported for given move indicies.
457 /// There are situations where many errors can be reported for a single move out (see #53807)
458 /// and we want only the best of those errors.
460 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
461 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
462 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
463 /// all move errors have been reported, any diagnostics in this map are added to the buffer
466 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
467 /// when errors in the map are being re-added to the error buffer so that errors with the
468 /// same primary span come out in a consistent order.
469 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'cx, 'tcx>, DiagnosticBuilder<'cx>)>,
470 /// This field keeps track of errors reported in the checking of uninitialized variables,
471 /// so that we don't report seemingly duplicate errors.
472 uninitialized_error_reported: FxHashSet<PlaceRef<'cx, 'tcx>>,
473 /// Errors to be reported buffer
474 errors_buffer: Vec<Diagnostic>,
475 /// This field keeps track of all the local variables that are declared mut and are mutated.
476 /// Used for the warning issued by an unused mutable local variable.
477 used_mut: FxHashSet<Local>,
478 /// If the function we're checking is a closure, then we'll need to report back the list of
479 /// mutable upvars that have been used. This field keeps track of them.
480 used_mut_upvars: SmallVec<[Field; 8]>,
481 /// Region inference context. This contains the results from region inference and lets us e.g.
482 /// find out which CFG points are contained in each borrow region.
483 regioncx: Rc<RegionInferenceContext<'tcx>>,
485 /// The set of borrows extracted from the MIR
486 borrow_set: Rc<BorrowSet<'tcx>>,
488 /// Dominators for MIR
489 dominators: Dominators<BasicBlock>,
491 /// Information about upvars not necessarily preserved in types or MIR
494 /// Names of local (user) variables (extracted from `var_debug_info`).
495 local_names: IndexVec<Local, Option<Name>>,
497 /// Record the region names generated for each region in the given
498 /// MIR def so that we can reuse them later in help/error messages.
499 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
501 /// The counter for generating new region names.
502 next_region_name: RefCell<usize>,
504 /// Results of Polonius analysis.
505 polonius_output: Option<Rc<PoloniusOutput>>,
509 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
510 // 2. loans made in overlapping scopes do not conflict
511 // 3. assignments do not affect things loaned out as immutable
512 // 4. moves do not affect things loaned out in any way
513 impl<'cx, 'tcx> dataflow::generic::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
514 type FlowState = Flows<'cx, 'tcx>;
518 flow_state: &Flows<'cx, 'tcx>,
519 stmt: &'cx Statement<'tcx>,
522 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
523 let span = stmt.source_info.span;
525 self.check_activations(location, span, flow_state);
528 StatementKind::Assign(box (ref lhs, ref rhs)) => {
529 self.consume_rvalue(location, (rhs, span), flow_state);
531 self.mutate_place(location, (lhs, span), Shallow(None), JustWrite, flow_state);
533 StatementKind::FakeRead(_, box ref place) => {
534 // Read for match doesn't access any memory and is used to
535 // assert that a place is safe and live. So we don't have to
536 // do any checks here.
538 // FIXME: Remove check that the place is initialized. This is
539 // needed for now because matches don't have never patterns yet.
540 // So this is the only place we prevent
544 self.check_if_path_or_subpath_is_moved(
546 InitializationRequiringAction::Use,
547 (place.as_ref(), span),
551 StatementKind::SetDiscriminant { ref place, variant_index: _ } => {
552 self.mutate_place(location, (place, span), Shallow(None), JustWrite, flow_state);
554 StatementKind::InlineAsm(ref asm) => {
555 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
557 // FIXME(eddyb) indirect inline asm outputs should
558 // be encoded through MIR place derefs instead.
562 (Deep, Read(ReadKind::Copy)),
563 LocalMutationIsAllowed::No,
566 self.check_if_path_or_subpath_is_moved(
568 InitializationRequiringAction::Use,
569 (output.as_ref(), o.span),
576 if o.is_rw { Deep } else { Shallow(None) },
577 if o.is_rw { WriteAndRead } else { JustWrite },
582 for (_, input) in asm.inputs.iter() {
583 self.consume_operand(location, (input, span), flow_state);
587 | StatementKind::AscribeUserType(..)
588 | StatementKind::Retag { .. }
589 | StatementKind::StorageLive(..) => {
590 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
593 StatementKind::StorageDead(local) => {
596 (&Place::from(local), span),
597 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
598 LocalMutationIsAllowed::Yes,
607 flow_state: &Flows<'cx, 'tcx>,
608 term: &'cx Terminator<'tcx>,
611 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
612 let span = term.source_info.span;
614 self.check_activations(loc, span, flow_state);
617 TerminatorKind::SwitchInt { ref discr, switch_ty: _, values: _, targets: _ } => {
618 self.consume_operand(loc, (discr, span), flow_state);
620 TerminatorKind::Drop { location: ref drop_place, target: _, unwind: _ } => {
621 let tcx = self.infcx.tcx;
623 // Compute the type with accurate region information.
624 let drop_place_ty = drop_place.ty(*self.body, self.infcx.tcx);
626 // Erase the regions.
627 let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
629 // "Lift" into the tcx -- once regions are erased, this type should be in the
630 // global arenas; this "lift" operation basically just asserts that is true, but
631 // that is useful later.
632 tcx.lift(&drop_place_ty).unwrap();
635 "visit_terminator_drop \
636 loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
637 loc, term, drop_place, drop_place_ty, span
643 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
644 LocalMutationIsAllowed::Yes,
648 TerminatorKind::DropAndReplace {
649 location: ref drop_place,
650 value: ref new_value,
654 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
655 self.consume_operand(loc, (new_value, span), flow_state);
657 TerminatorKind::Call {
664 self.consume_operand(loc, (func, span), flow_state);
666 self.consume_operand(loc, (arg, span), flow_state);
668 if let Some((ref dest, _ /*bb*/)) = *destination {
669 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
672 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
673 self.consume_operand(loc, (cond, span), flow_state);
674 use rustc::mir::AssertKind;
675 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
676 self.consume_operand(loc, (len, span), flow_state);
677 self.consume_operand(loc, (index, span), flow_state);
681 TerminatorKind::Yield { ref value, resume: _, ref resume_arg, drop: _ } => {
682 self.consume_operand(loc, (value, span), flow_state);
683 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
686 TerminatorKind::Goto { target: _ }
687 | TerminatorKind::Abort
688 | TerminatorKind::Unreachable
689 | TerminatorKind::Resume
690 | TerminatorKind::Return
691 | TerminatorKind::GeneratorDrop
692 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
693 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
694 // no data used, thus irrelevant to borrowck
699 fn visit_terminator_exit(
701 flow_state: &Flows<'cx, 'tcx>,
702 term: &'cx Terminator<'tcx>,
705 let span = term.source_info.span;
708 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
709 if self.movable_generator {
710 // Look for any active borrows to locals
711 let borrow_set = self.borrow_set.clone();
712 for i in flow_state.borrows.iter() {
713 let borrow = &borrow_set[i];
714 self.check_for_local_borrow(borrow, span);
719 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
720 // Returning from the function implicitly kills storage for all locals and statics.
721 // Often, the storage will already have been killed by an explicit
722 // StorageDead, but we don't always emit those (notably on unwind paths),
723 // so this "extra check" serves as a kind of backup.
724 let borrow_set = self.borrow_set.clone();
725 for i in flow_state.borrows.iter() {
726 let borrow = &borrow_set[i];
727 self.check_for_invalidation_at_exit(loc, borrow, span);
731 TerminatorKind::Abort
732 | TerminatorKind::Assert { .. }
733 | TerminatorKind::Call { .. }
734 | TerminatorKind::Drop { .. }
735 | TerminatorKind::DropAndReplace { .. }
736 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
737 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
738 | TerminatorKind::Goto { .. }
739 | TerminatorKind::SwitchInt { .. }
740 | TerminatorKind::Unreachable => {}
745 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
751 use self::AccessDepth::{Deep, Shallow};
752 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
754 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
755 enum ArtificialField {
760 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
762 /// From the RFC: "A *shallow* access means that the immediate
763 /// fields reached at P are accessed, but references or pointers
764 /// found within are not dereferenced. Right now, the only access
765 /// that is shallow is an assignment like `x = ...;`, which would
766 /// be a *shallow write* of `x`."
767 Shallow(Option<ArtificialField>),
769 /// From the RFC: "A *deep* access means that all data reachable
770 /// through the given place may be invalidated or accesses by
774 /// Access is Deep only when there is a Drop implementation that
775 /// can reach the data behind the reference.
779 /// Kind of access to a value: read or write
780 /// (For informational purposes only)
781 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
783 /// From the RFC: "A *read* means that the existing data may be
784 /// read, but will not be changed."
787 /// From the RFC: "A *write* means that the data may be mutated to
788 /// new values or otherwise invalidated (for example, it could be
789 /// de-initialized, as in a move operation).
792 /// For two-phase borrows, we distinguish a reservation (which is treated
793 /// like a Read) from an activation (which is treated like a write), and
794 /// each of those is furthermore distinguished from Reads/Writes above.
795 Reservation(WriteKind),
796 Activation(WriteKind, BorrowIndex),
799 /// Kind of read access to a value
800 /// (For informational purposes only)
801 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
807 /// Kind of write access to a value
808 /// (For informational purposes only)
809 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
812 MutableBorrow(BorrowKind),
817 /// When checking permissions for a place access, this flag is used to indicate that an immutable
818 /// local place can be mutated.
820 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
821 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
822 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
823 // `is_declared_mutable()`.
824 // - Take flow state into consideration in `is_assignable()` for local variables.
825 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
826 enum LocalMutationIsAllowed {
828 /// We want use of immutable upvars to cause a "write to immutable upvar"
829 /// error, not an "reassignment" error.
834 #[derive(Copy, Clone, Debug)]
835 enum InitializationRequiringAction {
844 struct RootPlace<'d, 'tcx> {
846 place_projection: &'d [PlaceElem<'tcx>],
847 is_local_mutation_allowed: LocalMutationIsAllowed,
850 impl InitializationRequiringAction {
851 fn as_noun(self) -> &'static str {
853 InitializationRequiringAction::Update => "update",
854 InitializationRequiringAction::Borrow => "borrow",
855 InitializationRequiringAction::MatchOn => "use", // no good noun
856 InitializationRequiringAction::Use => "use",
857 InitializationRequiringAction::Assignment => "assign",
858 InitializationRequiringAction::PartialAssignment => "assign to part",
862 fn as_verb_in_past_tense(self) -> &'static str {
864 InitializationRequiringAction::Update => "updated",
865 InitializationRequiringAction::Borrow => "borrowed",
866 InitializationRequiringAction::MatchOn => "matched on",
867 InitializationRequiringAction::Use => "used",
868 InitializationRequiringAction::Assignment => "assigned",
869 InitializationRequiringAction::PartialAssignment => "partially assigned",
874 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
875 fn body(&self) -> &'cx Body<'tcx> {
879 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
880 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
881 /// place is initialized and (b) it is not borrowed in some way that would prevent this
884 /// Returns `true` if an error is reported.
888 place_span: (&Place<'tcx>, Span),
889 kind: (AccessDepth, ReadOrWrite),
890 is_local_mutation_allowed: LocalMutationIsAllowed,
891 flow_state: &Flows<'cx, 'tcx>,
895 if let Activation(_, borrow_index) = rw {
896 if self.reservation_error_reported.contains(&place_span.0) {
898 "skipping access_place for activation of invalid reservation \
899 place: {:?} borrow_index: {:?}",
900 place_span.0, borrow_index
906 // Check is_empty() first because it's the common case, and doing that
907 // way we avoid the clone() call.
908 if !self.access_place_error_reported.is_empty()
909 && self.access_place_error_reported.contains(&(*place_span.0, place_span.1))
912 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
918 let mutability_error = self.check_access_permissions(
921 is_local_mutation_allowed,
926 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
928 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
929 // Suppress this warning when there's an error being emitted for the
930 // same borrow: fixing the error is likely to fix the warning.
931 self.reservation_warnings.remove(&borrow_idx);
934 if conflict_error || mutability_error {
935 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
937 self.access_place_error_reported.insert((*place_span.0, place_span.1));
941 fn check_access_for_conflict(
944 place_span: (&Place<'tcx>, Span),
947 flow_state: &Flows<'cx, 'tcx>,
950 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
951 location, place_span, sd, rw,
954 let mut error_reported = false;
955 let tcx = self.infcx.tcx;
956 let body = self.body;
957 let body: &Body<'_> = &body;
958 let borrow_set = self.borrow_set.clone();
960 // Use polonius output if it has been enabled.
961 let polonius_output = self.polonius_output.clone();
962 let borrows_in_scope = if let Some(polonius) = &polonius_output {
963 let location = self.location_table.start_index(location);
964 Either::Left(polonius.errors_at(location).iter().copied())
966 Either::Right(flow_state.borrows.iter())
969 each_borrow_involving_path(
977 |this, borrow_index, borrow| match (rw, borrow.kind) {
978 // Obviously an activation is compatible with its own
979 // reservation (or even prior activating uses of same
980 // borrow); so don't check if they interfere.
982 // NOTE: *reservations* do conflict with themselves;
983 // thus aren't injecting unsoundenss w/ this check.)
984 (Activation(_, activating), _) if activating == borrow_index => {
986 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
987 skipping {:?} b/c activation of same borrow_index",
991 (borrow_index, borrow),
996 (Read(_), BorrowKind::Shared)
997 | (Read(_), BorrowKind::Shallow)
998 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
999 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
1003 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1004 // Handled by initialization checks.
1008 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
1009 // Reading from mere reservations of mutable-borrows is OK.
1010 if !is_active(&this.dominators, borrow, location) {
1011 assert!(allow_two_phase_borrow(borrow.kind));
1012 return Control::Continue;
1015 error_reported = true;
1018 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1019 .buffer(&mut this.errors_buffer);
1021 ReadKind::Borrow(bk) => {
1022 this.report_conflicting_borrow(location, place_span, bk, borrow)
1023 .buffer(&mut this.errors_buffer);
1029 (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shallow)
1030 | (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shared)
1032 tcx.migrate_borrowck()
1033 && this.borrow_set.location_map.contains_key(&location)
1036 let bi = this.borrow_set.location_map[&location];
1038 "recording invalid reservation of place: {:?} with \
1039 borrow index {:?} as warning",
1042 // rust-lang/rust#56254 - This was previously permitted on
1043 // the 2018 edition so we emit it as a warning. We buffer
1044 // these sepately so that we only emit a warning if borrow
1045 // checking was otherwise successful.
1046 this.reservation_warnings
1047 .insert(bi, (*place_span.0, place_span.1, location, bk, borrow.clone()));
1049 // Don't suppress actual errors.
1053 (Reservation(kind), _) | (Activation(kind, _), _) | (Write(kind), _) => {
1055 Reservation(..) => {
1057 "recording invalid reservation of \
1061 this.reservation_error_reported.insert(place_span.0.clone());
1063 Activation(_, activating) => {
1065 "observing check_place for activation of \
1066 borrow_index: {:?}",
1070 Read(..) | Write(..) => {}
1073 error_reported = true;
1075 WriteKind::MutableBorrow(bk) => {
1076 this.report_conflicting_borrow(location, place_span, bk, borrow)
1077 .buffer(&mut this.errors_buffer);
1079 WriteKind::StorageDeadOrDrop => this
1080 .report_borrowed_value_does_not_live_long_enough(
1086 WriteKind::Mutate => {
1087 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1089 WriteKind::Move => {
1090 this.report_move_out_while_borrowed(location, place_span, borrow)
1104 place_span: (&'cx Place<'tcx>, Span),
1107 flow_state: &Flows<'cx, 'tcx>,
1109 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1111 MutateMode::WriteAndRead => {
1112 self.check_if_path_or_subpath_is_moved(
1114 InitializationRequiringAction::Update,
1115 (place_span.0.as_ref(), place_span.1),
1119 MutateMode::JustWrite => {
1120 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1124 // Special case: you can assign a immutable local variable
1125 // (e.g., `x = ...`) so long as it has never been initialized
1126 // before (at this point in the flow).
1127 if let Some(local) = place_span.0.as_local() {
1128 if let Mutability::Not = self.body.local_decls[local].mutability {
1129 // check for reassignments to immutable local variables
1130 self.check_if_reassignment_to_immutable_state(
1131 location, local, place_span, flow_state,
1137 // Otherwise, use the normal access permission rules.
1141 (kind, Write(WriteKind::Mutate)),
1142 LocalMutationIsAllowed::No,
1150 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1151 flow_state: &Flows<'cx, 'tcx>,
1154 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1155 let access_kind = match bk {
1156 BorrowKind::Shallow => {
1157 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1159 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1160 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1161 let wk = WriteKind::MutableBorrow(bk);
1162 if allow_two_phase_borrow(bk) {
1163 (Deep, Reservation(wk))
1174 LocalMutationIsAllowed::No,
1178 let action = if bk == BorrowKind::Shallow {
1179 InitializationRequiringAction::MatchOn
1181 InitializationRequiringAction::Borrow
1184 self.check_if_path_or_subpath_is_moved(
1187 (place.as_ref(), span),
1192 Rvalue::AddressOf(mutability, ref place) => {
1193 let access_kind = match mutability {
1194 Mutability::Mut => (
1196 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1197 allow_two_phase_borrow: false,
1200 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1207 LocalMutationIsAllowed::No,
1211 self.check_if_path_or_subpath_is_moved(
1213 InitializationRequiringAction::Borrow,
1214 (place.as_ref(), span),
1219 Rvalue::Use(ref operand)
1220 | Rvalue::Repeat(ref operand, _)
1221 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1222 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1223 self.consume_operand(location, (operand, span), flow_state)
1226 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1227 let af = match *rvalue {
1228 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1229 Rvalue::Discriminant(..) => None,
1230 _ => unreachable!(),
1235 (Shallow(af), Read(ReadKind::Copy)),
1236 LocalMutationIsAllowed::No,
1239 self.check_if_path_or_subpath_is_moved(
1241 InitializationRequiringAction::Use,
1242 (place.as_ref(), span),
1247 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1248 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1249 self.consume_operand(location, (operand1, span), flow_state);
1250 self.consume_operand(location, (operand2, span), flow_state);
1253 Rvalue::NullaryOp(_op, _ty) => {
1254 // nullary ops take no dynamic input; no borrowck effect.
1256 // FIXME: is above actually true? Do we want to track
1257 // the fact that uninitialized data can be created via
1261 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1262 // We need to report back the list of mutable upvars that were
1263 // moved into the closure and subsequently used by the closure,
1264 // in order to populate our used_mut set.
1265 match **aggregate_kind {
1266 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1267 let BorrowCheckResult { used_mut_upvars, .. } =
1268 self.infcx.tcx.mir_borrowck(def_id);
1269 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1270 for field in used_mut_upvars {
1271 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1274 AggregateKind::Adt(..)
1275 | AggregateKind::Array(..)
1276 | AggregateKind::Tuple { .. } => (),
1279 for operand in operands {
1280 self.consume_operand(location, (operand, span), flow_state);
1286 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1287 let propagate_closure_used_mut_place = |this: &mut Self, place: &Place<'tcx>| {
1288 if !place.projection.is_empty() {
1289 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1290 this.used_mut_upvars.push(field);
1293 this.used_mut.insert(place.local);
1297 // This relies on the current way that by-value
1298 // captures of a closure are copied/moved directly
1299 // when generating MIR.
1301 Operand::Move(ref place) | Operand::Copy(ref place) => {
1302 match place.as_local() {
1303 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1304 if self.body.local_decls[local].ty.is_mutable_ptr() {
1305 // The variable will be marked as mutable by the borrow.
1308 // This is an edge case where we have a `move` closure
1309 // inside a non-move closure, and the inner closure
1310 // contains a mutation:
1313 // || { move || { i += 1; }; };
1315 // In this case our usual strategy of assuming that the
1316 // variable will be captured by mutable reference is
1317 // wrong, since `i` can be copied into the inner
1318 // closure from a shared reference.
1320 // As such we have to search for the local that this
1321 // capture comes from and mark it as being used as mut.
1323 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1324 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1325 &self.move_data.inits[init_index]
1327 bug!("temporary should be initialized exactly once")
1330 let loc = match init.location {
1331 InitLocation::Statement(stmt) => stmt,
1332 _ => bug!("temporary initialized in arguments"),
1335 let body = self.body;
1336 let bbd = &body[loc.block];
1337 let stmt = &bbd.statements[loc.statement_index];
1338 debug!("temporary assigned in: stmt={:?}", stmt);
1340 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, ref source))) =
1343 propagate_closure_used_mut_place(self, source);
1346 "closures should only capture user variables \
1347 or references to user variables"
1351 _ => propagate_closure_used_mut_place(self, place),
1354 Operand::Constant(..) => {}
1361 (operand, span): (&'cx Operand<'tcx>, Span),
1362 flow_state: &Flows<'cx, 'tcx>,
1365 Operand::Copy(ref place) => {
1366 // copy of place: check if this is "copy of frozen path"
1367 // (FIXME: see check_loans.rs)
1371 (Deep, Read(ReadKind::Copy)),
1372 LocalMutationIsAllowed::No,
1376 // Finally, check if path was already moved.
1377 self.check_if_path_or_subpath_is_moved(
1379 InitializationRequiringAction::Use,
1380 (place.as_ref(), span),
1384 Operand::Move(ref place) => {
1385 // move of place: check if this is move of already borrowed path
1389 (Deep, Write(WriteKind::Move)),
1390 LocalMutationIsAllowed::Yes,
1394 // Finally, check if path was already moved.
1395 self.check_if_path_or_subpath_is_moved(
1397 InitializationRequiringAction::Use,
1398 (place.as_ref(), span),
1402 Operand::Constant(_) => {}
1406 /// Checks whether a borrow of this place is invalidated when the function
1408 fn check_for_invalidation_at_exit(
1411 borrow: &BorrowData<'tcx>,
1414 debug!("check_for_invalidation_at_exit({:?})", borrow);
1415 let place = &borrow.borrowed_place;
1416 let deref = [ProjectionElem::Deref];
1417 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1419 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1420 // we just know that all locals are dropped at function exit (otherwise
1421 // we'll have a memory leak) and assume that all statics have a destructor.
1423 // FIXME: allow thread-locals to borrow other thread locals?
1425 let (might_be_alive, will_be_dropped) =
1426 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1427 // Thread-locals might be dropped after the function exits
1428 // We have to dereference the outer reference because
1429 // borrows don't conflict behind shared references.
1430 root_place.projection = &deref;
1433 (false, self.locals_are_invalidated_at_exit)
1436 if !will_be_dropped {
1437 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1441 let sd = if might_be_alive { Deep } else { Shallow(None) };
1443 if places_conflict::borrow_conflicts_with_place(
1450 places_conflict::PlaceConflictBias::Overlap,
1452 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1453 // FIXME: should be talking about the region lifetime instead
1454 // of just a span here.
1455 let span = self.infcx.tcx.sess.source_map().end_point(span);
1456 self.report_borrowed_value_does_not_live_long_enough(
1465 /// Reports an error if this is a borrow of local data.
1466 /// This is called for all Yield expressions on movable generators
1467 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1468 debug!("check_for_local_borrow({:?})", borrow);
1470 if borrow_of_local_data(&borrow.borrowed_place) {
1471 let err = self.cannot_borrow_across_generator_yield(
1472 self.retrieve_borrow_spans(borrow).var_or_use(),
1476 err.buffer(&mut self.errors_buffer);
1480 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1481 // Two-phase borrow support: For each activation that is newly
1482 // generated at this statement, check if it interferes with
1484 let borrow_set = self.borrow_set.clone();
1485 for &borrow_index in borrow_set.activations_at_location(location) {
1486 let borrow = &borrow_set[borrow_index];
1488 // only mutable borrows should be 2-phase
1489 assert!(match borrow.kind {
1490 BorrowKind::Shared | BorrowKind::Shallow => false,
1491 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1496 (&borrow.borrowed_place, span),
1497 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1498 LocalMutationIsAllowed::No,
1501 // We do not need to call `check_if_path_or_subpath_is_moved`
1502 // again, as we already called it when we made the
1503 // initial reservation.
1507 fn check_if_reassignment_to_immutable_state(
1511 place_span: (&Place<'tcx>, Span),
1512 flow_state: &Flows<'cx, 'tcx>,
1514 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1516 // Check if any of the initializiations of `local` have happened yet:
1517 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1518 // And, if so, report an error.
1519 let init = &self.move_data.inits[init_index];
1520 let span = init.span(&self.body);
1521 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1525 fn check_if_full_path_is_moved(
1528 desired_action: InitializationRequiringAction,
1529 place_span: (PlaceRef<'cx, 'tcx>, Span),
1530 flow_state: &Flows<'cx, 'tcx>,
1532 let maybe_uninits = &flow_state.uninits;
1536 // 1. Move of `a.b.c`, use of `a.b.c`
1537 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1538 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1539 // partial initialization support, one might have `a.x`
1540 // initialized but not `a.b`.
1544 // 4. Move of `a.b.c`, use of `a.b.d`
1545 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1546 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1547 // must have been initialized for the use to be sound.
1548 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1550 // The dataflow tracks shallow prefixes distinctly (that is,
1551 // field-accesses on P distinctly from P itself), in order to
1552 // track substructure initialization separately from the whole
1555 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1556 // which we have a MovePath is `a.b`, then that means that the
1557 // initialization state of `a.b` is all we need to inspect to
1558 // know if `a.b.c` is valid (and from that we infer that the
1559 // dereference and `.d` access is also valid, since we assume
1560 // `a.b.c` is assigned a reference to a initialized and
1561 // well-formed record structure.)
1563 // Therefore, if we seek out the *closest* prefix for which we
1564 // have a MovePath, that should capture the initialization
1565 // state for the place scenario.
1567 // This code covers scenarios 1, 2, and 3.
1569 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1570 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1571 if maybe_uninits.contains(mpi) {
1572 self.report_use_of_moved_or_uninitialized(
1575 (prefix, place_span.0, place_span.1),
1578 } // Only query longest prefix with a MovePath, not further
1579 // ancestors; dataflow recurs on children when parents
1580 // move (to support partial (re)inits).
1582 // (I.e., querying parents breaks scenario 7; but may want
1583 // to do such a query based on partial-init feature-gate.)
1586 /// Subslices correspond to multiple move paths, so we iterate through the
1587 /// elements of the base array. For each element we check
1589 /// * Does this element overlap with our slice.
1590 /// * Is any part of it uninitialized.
1591 fn check_if_subslice_element_is_moved(
1594 desired_action: InitializationRequiringAction,
1595 place_span: (PlaceRef<'cx, 'tcx>, Span),
1596 maybe_uninits: &BitSet<MovePathIndex>,
1600 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1601 let move_paths = &self.move_data.move_paths;
1603 let root_path = &move_paths[mpi];
1604 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1605 let last_proj = child_move_path.place.projection.last().unwrap();
1606 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1607 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1609 if (from..to).contains(offset) {
1611 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1612 maybe_uninits.contains(mpi)
1615 if let Some(uninit_child) = uninit_child {
1616 self.report_use_of_moved_or_uninitialized(
1619 (place_span.0, place_span.0, place_span.1),
1622 return; // don't bother finding other problems.
1630 fn check_if_path_or_subpath_is_moved(
1633 desired_action: InitializationRequiringAction,
1634 place_span: (PlaceRef<'cx, 'tcx>, Span),
1635 flow_state: &Flows<'cx, 'tcx>,
1637 let maybe_uninits = &flow_state.uninits;
1641 // 1. Move of `a.b.c`, use of `a` or `a.b`
1642 // partial initialization support, one might have `a.x`
1643 // initialized but not `a.b`.
1644 // 2. All bad scenarios from `check_if_full_path_is_moved`
1648 // 3. Move of `a.b.c`, use of `a.b.d`
1649 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1650 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1651 // must have been initialized for the use to be sound.
1652 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1654 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1656 if let [base_proj @ .., ProjectionElem::Subslice { from, to, from_end: false }] =
1657 place_span.0.projection
1660 Place::ty_from(place_span.0.local, base_proj, self.body(), self.infcx.tcx);
1661 if let ty::Array(..) = place_ty.ty.kind {
1662 let array_place = PlaceRef { local: place_span.0.local, projection: base_proj };
1663 self.check_if_subslice_element_is_moved(
1666 (array_place, place_span.1),
1675 // A move of any shallow suffix of `place` also interferes
1676 // with an attempt to use `place`. This is scenario 3 above.
1678 // (Distinct from handling of scenarios 1+2+4 above because
1679 // `place` does not interfere with suffixes of its prefixes,
1680 // e.g., `a.b.c` does not interfere with `a.b.d`)
1682 // This code covers scenario 1.
1684 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1685 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1686 let uninit_mpi = self
1688 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1690 if let Some(uninit_mpi) = uninit_mpi {
1691 self.report_use_of_moved_or_uninitialized(
1694 (place_span.0, place_span.0, place_span.1),
1697 return; // don't bother finding other problems.
1702 /// Currently MoveData does not store entries for all places in
1703 /// the input MIR. For example it will currently filter out
1704 /// places that are Copy; thus we do not track places of shared
1705 /// reference type. This routine will walk up a place along its
1706 /// prefixes, searching for a foundational place that *is*
1707 /// tracked in the MoveData.
1709 /// An Err result includes a tag indicated why the search failed.
1710 /// Currently this can only occur if the place is built off of a
1711 /// static variable, as we do not track those in the MoveData.
1712 fn move_path_closest_to(
1714 place: PlaceRef<'_, 'tcx>,
1715 ) -> (PlaceRef<'cx, 'tcx>, MovePathIndex) {
1716 match self.move_data.rev_lookup.find(place) {
1717 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1718 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1720 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1724 fn move_path_for_place(&mut self, place: PlaceRef<'_, 'tcx>) -> Option<MovePathIndex> {
1725 // If returns None, then there is no move path corresponding
1726 // to a direct owner of `place` (which means there is nothing
1727 // that borrowck tracks for its analysis).
1729 match self.move_data.rev_lookup.find(place) {
1730 LookupResult::Parent(_) => None,
1731 LookupResult::Exact(mpi) => Some(mpi),
1735 fn check_if_assigned_path_is_moved(
1738 (place, span): (&'cx Place<'tcx>, Span),
1739 flow_state: &Flows<'cx, 'tcx>,
1741 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1743 // None case => assigning to `x` does not require `x` be initialized.
1744 let mut cursor = &*place.projection.as_ref();
1745 while let [proj_base @ .., elem] = cursor {
1749 ProjectionElem::Index(_/*operand*/) |
1750 ProjectionElem::ConstantIndex { .. } |
1751 // assigning to P[i] requires P to be valid.
1752 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1753 // assigning to (P->variant) is okay if assigning to `P` is okay
1755 // FIXME: is this true even if P is a adt with a dtor?
1758 // assigning to (*P) requires P to be initialized
1759 ProjectionElem::Deref => {
1760 self.check_if_full_path_is_moved(
1761 location, InitializationRequiringAction::Use,
1764 projection: proj_base,
1765 }, span), flow_state);
1766 // (base initialized; no need to
1771 ProjectionElem::Subslice { .. } => {
1772 panic!("we don't allow assignments to subslices, location: {:?}",
1776 ProjectionElem::Field(..) => {
1777 // if type of `P` has a dtor, then
1778 // assigning to `P.f` requires `P` itself
1779 // be already initialized
1780 let tcx = self.infcx.tcx;
1781 let base_ty = Place::ty_from(place.local, proj_base, self.body(), tcx).ty;
1782 match base_ty.kind {
1783 ty::Adt(def, _) if def.has_dtor(tcx) => {
1784 self.check_if_path_or_subpath_is_moved(
1785 location, InitializationRequiringAction::Assignment,
1788 projection: proj_base,
1789 }, span), flow_state);
1791 // (base initialized; no need to
1796 // Once `let s; s.x = V; read(s.x);`,
1797 // is allowed, remove this match arm.
1798 ty::Adt(..) | ty::Tuple(..) => {
1799 check_parent_of_field(self, location, PlaceRef {
1801 projection: proj_base,
1802 }, span, flow_state);
1804 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1805 // partial initialization, do not complain about unnecessary `mut` on
1806 // an attempt to do a partial initialization.
1807 self.used_mut.insert(place.local);
1816 fn check_parent_of_field<'cx, 'tcx>(
1817 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1819 base: PlaceRef<'cx, 'tcx>,
1821 flow_state: &Flows<'cx, 'tcx>,
1823 // rust-lang/rust#21232: Until Rust allows reads from the
1824 // initialized parts of partially initialized structs, we
1825 // will, starting with the 2018 edition, reject attempts
1826 // to write to structs that are not fully initialized.
1828 // In other words, *until* we allow this:
1830 // 1. `let mut s; s.x = Val; read(s.x);`
1832 // we will for now disallow this:
1834 // 2. `let mut s; s.x = Val;`
1838 // 3. `let mut s = ...; drop(s); s.x=Val;`
1840 // This does not use check_if_path_or_subpath_is_moved,
1841 // because we want to *allow* reinitializations of fields:
1842 // e.g., want to allow
1844 // `let mut s = ...; drop(s.x); s.x=Val;`
1846 // This does not use check_if_full_path_is_moved on
1847 // `base`, because that would report an error about the
1848 // `base` as a whole, but in this scenario we *really*
1849 // want to report an error about the actual thing that was
1850 // moved, which may be some prefix of `base`.
1852 // Shallow so that we'll stop at any dereference; we'll
1853 // report errors about issues with such bases elsewhere.
1854 let maybe_uninits = &flow_state.uninits;
1856 // Find the shortest uninitialized prefix you can reach
1857 // without going over a Deref.
1858 let mut shortest_uninit_seen = None;
1859 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1860 let mpi = match this.move_path_for_place(prefix) {
1865 if maybe_uninits.contains(mpi) {
1867 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1868 shortest_uninit_seen,
1871 shortest_uninit_seen = Some((prefix, mpi));
1873 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1877 if let Some((prefix, mpi)) = shortest_uninit_seen {
1878 // Check for a reassignment into a uninitialized field of a union (for example,
1879 // after a move out). In this case, do not report a error here. There is an
1880 // exception, if this is the first assignment into the union (that is, there is
1881 // no move out from an earlier location) then this is an attempt at initialization
1882 // of the union - we should error in that case.
1883 let tcx = this.infcx.tcx;
1884 if let ty::Adt(def, _) =
1885 Place::ty_from(base.local, base.projection, this.body(), tcx).ty.kind
1888 if this.move_data.path_map[mpi].iter().any(|moi| {
1889 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1896 this.report_use_of_moved_or_uninitialized(
1898 InitializationRequiringAction::PartialAssignment,
1899 (prefix, base, span),
1906 /// Checks the permissions for the given place and read or write kind
1908 /// Returns `true` if an error is reported.
1909 fn check_access_permissions(
1911 (place, span): (&Place<'tcx>, Span),
1913 is_local_mutation_allowed: LocalMutationIsAllowed,
1914 flow_state: &Flows<'cx, 'tcx>,
1918 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1919 place, kind, is_local_mutation_allowed
1926 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1927 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1928 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1929 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1930 let is_local_mutation_allowed = match borrow_kind {
1931 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1932 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1933 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1935 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1937 self.add_used_mut(root_place, flow_state);
1941 error_access = AccessKind::MutableBorrow;
1942 the_place_err = place_err;
1946 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1947 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1949 self.add_used_mut(root_place, flow_state);
1953 error_access = AccessKind::Mutate;
1954 the_place_err = place_err;
1959 Reservation(WriteKind::Move)
1960 | Write(WriteKind::Move)
1961 | Reservation(WriteKind::StorageDeadOrDrop)
1962 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1963 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shallow))
1964 | Write(WriteKind::StorageDeadOrDrop)
1965 | Write(WriteKind::MutableBorrow(BorrowKind::Shared))
1966 | Write(WriteKind::MutableBorrow(BorrowKind::Shallow)) => {
1967 if let (Err(_), true) = (
1968 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
1969 self.errors_buffer.is_empty(),
1971 // rust-lang/rust#46908: In pure NLL mode this code path should be
1972 // unreachable, but we use `delay_span_bug` because we can hit this when
1973 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1974 // enabled. We don't want to ICE for that case, as other errors will have
1975 // been emitted (#52262).
1976 self.infcx.tcx.sess.delay_span_bug(
1979 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1987 // permission checks are done at Reservation point.
1990 Read(ReadKind::Borrow(BorrowKind::Unique))
1991 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1992 | Read(ReadKind::Borrow(BorrowKind::Shared))
1993 | Read(ReadKind::Borrow(BorrowKind::Shallow))
1994 | Read(ReadKind::Copy) => {
1995 // Access authorized
2000 // rust-lang/rust#21232, #54986: during period where we reject
2001 // partial initialization, do not complain about mutability
2002 // errors except for actual mutation (as opposed to an attempt
2003 // to do a partial initialization).
2004 let previously_initialized =
2005 self.is_local_ever_initialized(place.local, flow_state).is_some();
2007 // at this point, we have set up the error reporting state.
2008 if previously_initialized {
2009 self.report_mutability_error(place, span, the_place_err, error_access, location);
2016 fn is_local_ever_initialized(
2019 flow_state: &Flows<'cx, 'tcx>,
2020 ) -> Option<InitIndex> {
2021 let mpi = self.move_data.rev_lookup.find_local(local);
2022 let ii = &self.move_data.init_path_map[mpi];
2024 if flow_state.ever_inits.contains(index) {
2031 /// Adds the place into the used mutable variables set
2032 fn add_used_mut<'d>(&mut self, root_place: RootPlace<'d, 'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2034 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2035 // If the local may have been initialized, and it is now currently being
2036 // mutated, then it is justified to be annotated with the `mut`
2037 // keyword, since the mutation may be a possible reassignment.
2038 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2039 && self.is_local_ever_initialized(local, flow_state).is_some()
2041 self.used_mut.insert(local);
2046 place_projection: _,
2047 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2051 place_projection: place_projection @ [.., _],
2052 is_local_mutation_allowed: _,
2054 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2056 projection: place_projection,
2058 self.used_mut_upvars.push(field);
2064 /// Whether this value can be written or borrowed mutably.
2065 /// Returns the root place if the place passed in is a projection.
2068 place: PlaceRef<'d, 'tcx>,
2069 is_local_mutation_allowed: LocalMutationIsAllowed,
2070 ) -> Result<RootPlace<'d, 'tcx>, PlaceRef<'d, 'tcx>> {
2072 PlaceRef { local, projection: [] } => {
2073 let local = &self.body.local_decls[local];
2074 match local.mutability {
2075 Mutability::Not => match is_local_mutation_allowed {
2076 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2077 place_local: place.local,
2078 place_projection: place.projection,
2079 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2081 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2082 place_local: place.local,
2083 place_projection: place.projection,
2084 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2086 LocalMutationIsAllowed::No => Err(place),
2088 Mutability::Mut => Ok(RootPlace {
2089 place_local: place.local,
2090 place_projection: place.projection,
2091 is_local_mutation_allowed,
2095 PlaceRef { local: _, projection: [proj_base @ .., elem] } => {
2097 ProjectionElem::Deref => {
2099 Place::ty_from(place.local, proj_base, self.body(), self.infcx.tcx).ty;
2101 // Check the kind of deref to decide
2102 match base_ty.kind {
2103 ty::Ref(_, _, mutbl) => {
2105 // Shared borrowed data is never mutable
2106 hir::Mutability::Not => Err(place),
2107 // Mutably borrowed data is mutable, but only if we have a
2108 // unique path to the `&mut`
2109 hir::Mutability::Mut => {
2110 let mode = match self.is_upvar_field_projection(place) {
2111 Some(field) if self.upvars[field.index()].by_ref => {
2112 is_local_mutation_allowed
2114 _ => LocalMutationIsAllowed::Yes,
2118 PlaceRef { local: place.local, projection: proj_base },
2124 ty::RawPtr(tnm) => {
2126 // `*const` raw pointers are not mutable
2127 hir::Mutability::Not => Err(place),
2128 // `*mut` raw pointers are always mutable, regardless of
2129 // context. The users have to check by themselves.
2130 hir::Mutability::Mut => Ok(RootPlace {
2131 place_local: place.local,
2132 place_projection: place.projection,
2133 is_local_mutation_allowed,
2137 // `Box<T>` owns its content, so mutable if its location is mutable
2138 _ if base_ty.is_box() => self.is_mutable(
2139 PlaceRef { local: place.local, projection: proj_base },
2140 is_local_mutation_allowed,
2142 // Deref should only be for reference, pointers or boxes
2143 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2146 // All other projections are owned by their base path, so mutable if
2147 // base path is mutable
2148 ProjectionElem::Field(..)
2149 | ProjectionElem::Index(..)
2150 | ProjectionElem::ConstantIndex { .. }
2151 | ProjectionElem::Subslice { .. }
2152 | ProjectionElem::Downcast(..) => {
2153 let upvar_field_projection = self.is_upvar_field_projection(place);
2154 if let Some(field) = upvar_field_projection {
2155 let upvar = &self.upvars[field.index()];
2157 "upvar.mutability={:?} local_mutation_is_allowed={:?} \
2159 upvar, is_local_mutation_allowed, place
2161 match (upvar.mutability, is_local_mutation_allowed) {
2162 (Mutability::Not, LocalMutationIsAllowed::No)
2163 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2166 (Mutability::Not, LocalMutationIsAllowed::Yes)
2167 | (Mutability::Mut, _) => {
2168 // Subtle: this is an upvar
2169 // reference, so it looks like
2170 // `self.foo` -- we want to double
2171 // check that the location `*self`
2172 // is mutable (i.e., this is not a
2173 // `Fn` closure). But if that
2174 // check succeeds, we want to
2175 // *blame* the mutability on
2176 // `place` (that is,
2177 // `self.foo`). This is used to
2178 // propagate the info about
2179 // whether mutability declarations
2180 // are used outwards, so that we register
2181 // the outer variable as mutable. Otherwise a
2182 // test like this fails to record the `mut`
2186 // fn foo<F: FnOnce()>(_f: F) { }
2188 // let var = Vec::new();
2194 let _ = self.is_mutable(
2195 PlaceRef { local: place.local, projection: proj_base },
2196 is_local_mutation_allowed,
2199 place_local: place.local,
2200 place_projection: place.projection,
2201 is_local_mutation_allowed,
2207 PlaceRef { local: place.local, projection: proj_base },
2208 is_local_mutation_allowed,
2217 /// If `place` is a field projection, and the field is being projected from a closure type,
2218 /// then returns the index of the field being projected. Note that this closure will always
2219 /// be `self` in the current MIR, because that is the only time we directly access the fields
2220 /// of a closure type.
2221 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'cx, 'tcx>) -> Option<Field> {
2222 let mut place_projection = place_ref.projection;
2223 let mut by_ref = false;
2225 if let [proj_base @ .., ProjectionElem::Deref] = place_projection {
2226 place_projection = proj_base;
2230 match place_projection {
2231 [base @ .., ProjectionElem::Field(field, _ty)] => {
2232 let tcx = self.infcx.tcx;
2233 let base_ty = Place::ty_from(place_ref.local, base, self.body(), tcx).ty;
2235 if (base_ty.is_closure() || base_ty.is_generator())
2236 && (!by_ref || self.upvars[field.index()].by_ref)
2249 /// The degree of overlap between 2 places for borrow-checking.
2251 /// The places might partially overlap - in this case, we give
2252 /// up and say that they might conflict. This occurs when
2253 /// different fields of a union are borrowed. For example,
2254 /// if `u` is a union, we have no way of telling how disjoint
2255 /// `u.a.x` and `a.b.y` are.
2257 /// The places have the same type, and are either completely disjoint
2258 /// or equal - i.e., they can't "partially" overlap as can occur with
2259 /// unions. This is the "base case" on which we recur for extensions
2262 /// The places are disjoint, so we know all extensions of them
2263 /// will also be disjoint.