1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 use rustc::lint::builtin::MUTABLE_BORROW_RESERVATION_CONFLICT;
4 use rustc::lint::builtin::UNUSED_MUT;
6 read_only, traversal, Body, BodyAndCache, ClearCrossCrate, Local, Location, Mutability,
7 Operand, Place, PlaceElem, PlaceRef, ReadOnlyBodyAndCache,
9 use rustc::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
10 use rustc::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
11 use rustc::mir::{Terminator, TerminatorKind};
12 use rustc::ty::query::Providers;
13 use rustc::ty::{self, RegionVid, TyCtxt};
15 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
16 use rustc_data_structures::graph::dominators::Dominators;
17 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder};
19 use rustc_hir::{def_id::DefId, HirId, Node};
20 use rustc_index::bit_set::BitSet;
21 use rustc_index::vec::IndexVec;
22 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
25 use smallvec::SmallVec;
26 use std::cell::RefCell;
27 use std::collections::BTreeMap;
31 use rustc_ast::ast::Name;
32 use rustc_span::{Span, DUMMY_SP};
35 use crate::dataflow::generic::{Analysis, BorrowckFlowState as Flows, BorrowckResults};
36 use crate::dataflow::indexes::{BorrowIndex, InitIndex, MoveOutIndex, MovePathIndex};
37 use crate::dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
38 use crate::dataflow::Borrows;
39 use crate::dataflow::EverInitializedPlaces;
40 use crate::dataflow::MoveDataParamEnv;
41 use crate::dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
42 use crate::transform::MirSource;
44 use self::diagnostics::{AccessKind, RegionName};
45 use self::location::LocationTable;
46 use self::prefixes::PrefixSet;
47 use self::MutateMode::{JustWrite, WriteAndRead};
49 use self::path_utils::*;
52 mod constraint_generation;
58 mod member_constraints;
67 mod universal_regions;
70 crate use borrow_set::{BorrowData, BorrowSet};
71 crate use nll::{PoloniusOutput, ToRegionVid};
72 crate use place_ext::PlaceExt;
73 crate use places_conflict::{places_conflict, PlaceConflictBias};
74 crate use region_infer::RegionInferenceContext;
76 // FIXME(eddyb) perhaps move this somewhere more centrally.
83 /// If true, the capture is behind a reference.
86 mutability: Mutability,
89 const DEREF_PROJECTION: &[PlaceElem<'_>; 1] = &[ProjectionElem::Deref];
91 pub fn provide(providers: &mut Providers<'_>) {
92 *providers = Providers { mir_borrowck, ..*providers };
95 fn mir_borrowck(tcx: TyCtxt<'_>, def_id: DefId) -> &BorrowCheckResult<'_> {
96 let (input_body, promoted) = tcx.mir_validated(def_id);
97 debug!("run query mir_borrowck: {}", tcx.def_path_str(def_id));
99 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
100 let input_body: &Body<'_> = &input_body.borrow();
101 let promoted: &IndexVec<_, _> = &promoted.borrow();
102 do_mir_borrowck(&infcx, input_body, promoted, def_id)
104 debug!("mir_borrowck done");
106 tcx.arena.alloc(opt_closure_req)
109 fn do_mir_borrowck<'a, 'tcx>(
110 infcx: &InferCtxt<'a, 'tcx>,
111 input_body: &Body<'tcx>,
112 input_promoted: &IndexVec<Promoted, BodyAndCache<'tcx>>,
114 ) -> BorrowCheckResult<'tcx> {
115 debug!("do_mir_borrowck(def_id = {:?})", def_id);
118 let param_env = tcx.param_env(def_id);
119 let id = tcx.hir().as_local_hir_id(def_id).expect("do_mir_borrowck: non-local DefId");
121 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
122 for var_debug_info in &input_body.var_debug_info {
123 if let Some(local) = var_debug_info.place.as_local() {
124 if let Some(prev_name) = local_names[local] {
125 if var_debug_info.name != prev_name {
127 var_debug_info.source_info.span,
128 "local {:?} has many names (`{}` vs `{}`)",
135 local_names[local] = Some(var_debug_info.name);
139 // Gather the upvars of a closure, if any.
140 let tables = tcx.typeck_tables_of(def_id);
141 if tables.tainted_by_errors {
142 infcx.set_tainted_by_errors();
144 let upvars: Vec<_> = tables
148 .flat_map(|v| v.values())
150 let var_hir_id = upvar_id.var_path.hir_id;
151 let capture = tables.upvar_capture(*upvar_id);
152 let by_ref = match capture {
153 ty::UpvarCapture::ByValue => false,
154 ty::UpvarCapture::ByRef(..) => true,
156 let mut upvar = Upvar {
157 name: tcx.hir().name(var_hir_id),
160 mutability: Mutability::Not,
162 let bm = *tables.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
163 if bm == ty::BindByValue(hir::Mutability::Mut) {
164 upvar.mutability = Mutability::Mut;
170 // Replace all regions with fresh inference variables. This
171 // requires first making our own copy of the MIR. This copy will
172 // be modified (in place) to contain non-lexical lifetimes. It
173 // will have a lifetime tied to the inference context.
174 let body_clone: Body<'tcx> = input_body.clone();
175 let mut promoted = input_promoted.clone();
176 let mut body = BodyAndCache::new(body_clone);
178 nll::replace_regions_in_mir(infcx, def_id, param_env, &mut body, &mut promoted);
179 let body = read_only!(body); // no further changes
180 let promoted: IndexVec<_, _> = promoted.iter_mut().map(|body| read_only!(body)).collect();
182 let location_table = &LocationTable::new(&body);
184 let mut errors_buffer = Vec::new();
185 let (move_data, move_errors): (MoveData<'tcx>, Option<Vec<(Place<'tcx>, MoveError<'tcx>)>>) =
186 match MoveData::gather_moves(&body, tcx, param_env) {
187 Ok(move_data) => (move_data, None),
188 Err((move_data, move_errors)) => (move_data, Some(move_errors)),
191 let mdpe = MoveDataParamEnv { move_data, param_env };
193 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
194 .into_engine(tcx, &body, def_id)
195 .iterate_to_fixpoint()
196 .into_results_cursor(&body);
198 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
200 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
202 // Compute non-lexical lifetimes.
209 } = nll::compute_regions(
222 // Dump MIR results into a file, if that is enabled. This let us
223 // write unit-tests, as well as helping with debugging.
224 nll::dump_mir_results(infcx, MirSource::item(def_id), &body, ®ioncx, &opt_closure_req);
226 // We also have a `#[rustc_regions]` annotation that causes us to dump
228 nll::dump_annotation(
238 // The various `flow_*` structures can be large. We drop `flow_inits` here
239 // so it doesn't overlap with the others below. This reduces peak memory
240 // usage significantly on some benchmarks.
243 let regioncx = Rc::new(regioncx);
245 let flow_borrows = Borrows::new(tcx, &body, regioncx.clone(), &borrow_set)
246 .into_engine(tcx, &body, def_id)
247 .iterate_to_fixpoint();
248 let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
249 .into_engine(tcx, &body, def_id)
250 .iterate_to_fixpoint();
251 let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
252 .into_engine(tcx, &body, def_id)
253 .iterate_to_fixpoint();
255 let movable_generator = match tcx.hir().get(id) {
256 Node::Expr(&hir::Expr {
257 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
263 let dominators = body.dominators();
265 let mut mbcx = MirBorrowckCtxt {
269 move_data: &mdpe.move_data,
272 locals_are_invalidated_at_exit,
273 access_place_error_reported: Default::default(),
274 reservation_error_reported: Default::default(),
275 reservation_warnings: Default::default(),
276 move_error_reported: BTreeMap::new(),
277 uninitialized_error_reported: Default::default(),
280 used_mut: Default::default(),
281 used_mut_upvars: SmallVec::new(),
286 region_names: RefCell::default(),
287 next_region_name: RefCell::new(1),
291 // Compute and report region errors, if any.
292 mbcx.report_region_errors(nll_errors);
294 let results = BorrowckResults {
295 ever_inits: flow_ever_inits,
296 uninits: flow_uninits,
297 borrows: flow_borrows,
300 if let Some(errors) = move_errors {
301 mbcx.report_move_errors(errors);
304 dataflow::generic::visit_results(
306 traversal::reverse_postorder(&*body).map(|(bb, _)| bb),
311 // Convert any reservation warnings into lints.
312 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
313 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
314 let mut initial_diag =
315 mbcx.report_conflicting_borrow(location, (&place, span), bk, &borrow);
317 let scope = mbcx.body.source_info(location).scope;
318 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
319 ClearCrossCrate::Set(data) => data.lint_root,
323 // Span and message don't matter; we overwrite them below anyway
324 mbcx.infcx.tcx.struct_span_lint_hir(
325 MUTABLE_BORROW_RESERVATION_CONFLICT,
329 let mut diag = lint.build("");
331 diag.message = initial_diag.styled_message().clone();
332 diag.span = initial_diag.span.clone();
334 diag.buffer(&mut mbcx.errors_buffer);
337 initial_diag.cancel();
340 // For each non-user used mutable variable, check if it's been assigned from
341 // a user-declared local. If so, then put that local into the used_mut set.
342 // Note that this set is expected to be small - only upvars from closures
343 // would have a chance of erroneously adding non-user-defined mutable vars
345 let temporary_used_locals: FxHashSet<Local> = mbcx
348 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
351 // For the remaining unused locals that are marked as mutable, we avoid linting any that
352 // were never initialized. These locals may have been removed as unreachable code; or will be
353 // linted as unused variables.
354 let unused_mut_locals =
355 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
356 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
358 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
359 let used_mut = mbcx.used_mut;
360 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
361 let local_decl = &mbcx.body.local_decls[local];
362 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
363 ClearCrossCrate::Set(data) => data.lint_root,
367 // Skip over locals that begin with an underscore or have no name
368 match mbcx.local_names[local] {
370 if name.as_str().starts_with('_') {
377 let span = local_decl.source_info.span;
378 if span.desugaring_kind().is_some() {
379 // If the `mut` arises as part of a desugaring, we should ignore it.
383 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
384 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
385 lint.build("variable does not need to be mutable")
386 .span_suggestion_short(
390 Applicability::MachineApplicable,
396 // Buffer any move errors that we collected and de-duplicated.
397 for (_, (_, diag)) in mbcx.move_error_reported {
398 diag.buffer(&mut mbcx.errors_buffer);
401 if !mbcx.errors_buffer.is_empty() {
402 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
404 for diag in mbcx.errors_buffer.drain(..) {
405 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
409 let result = BorrowCheckResult {
410 concrete_opaque_types: opaque_type_values,
411 closure_requirements: opt_closure_req,
412 used_mut_upvars: mbcx.used_mut_upvars,
415 debug!("do_mir_borrowck: result = {:#?}", result);
420 crate struct MirBorrowckCtxt<'cx, 'tcx> {
421 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
422 body: ReadOnlyBodyAndCache<'cx, 'tcx>,
424 move_data: &'cx MoveData<'tcx>,
426 /// Map from MIR `Location` to `LocationIndex`; created
427 /// when MIR borrowck begins.
428 location_table: &'cx LocationTable,
430 movable_generator: bool,
431 /// This keeps track of whether local variables are free-ed when the function
432 /// exits even without a `StorageDead`, which appears to be the case for
435 /// I'm not sure this is the right approach - @eddyb could you try and
437 locals_are_invalidated_at_exit: bool,
438 /// This field keeps track of when borrow errors are reported in the access_place function
439 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
440 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
441 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
443 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
444 /// This field keeps track of when borrow conflict errors are reported
445 /// for reservations, so that we don't report seemingly duplicate
446 /// errors for corresponding activations.
448 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
449 // but it is currently inconvenient to track down the `BorrowIndex`
450 // at the time we detect and report a reservation error.
451 reservation_error_reported: FxHashSet<Place<'tcx>>,
452 /// Migration warnings to be reported for #56254. We delay reporting these
453 /// so that we can suppress the warning if there's a corresponding error
454 /// for the activation of the borrow.
455 reservation_warnings:
456 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
457 /// This field keeps track of move errors that are to be reported for given move indices.
459 /// There are situations where many errors can be reported for a single move out (see #53807)
460 /// and we want only the best of those errors.
462 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
463 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
464 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
465 /// all move errors have been reported, any diagnostics in this map are added to the buffer
468 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
469 /// when errors in the map are being re-added to the error buffer so that errors with the
470 /// same primary span come out in a consistent order.
471 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'cx>)>,
472 /// This field keeps track of errors reported in the checking of uninitialized variables,
473 /// so that we don't report seemingly duplicate errors.
474 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
475 /// Errors to be reported buffer
476 errors_buffer: Vec<Diagnostic>,
477 /// This field keeps track of all the local variables that are declared mut and are mutated.
478 /// Used for the warning issued by an unused mutable local variable.
479 used_mut: FxHashSet<Local>,
480 /// If the function we're checking is a closure, then we'll need to report back the list of
481 /// mutable upvars that have been used. This field keeps track of them.
482 used_mut_upvars: SmallVec<[Field; 8]>,
483 /// Region inference context. This contains the results from region inference and lets us e.g.
484 /// find out which CFG points are contained in each borrow region.
485 regioncx: Rc<RegionInferenceContext<'tcx>>,
487 /// The set of borrows extracted from the MIR
488 borrow_set: Rc<BorrowSet<'tcx>>,
490 /// Dominators for MIR
491 dominators: Dominators<BasicBlock>,
493 /// Information about upvars not necessarily preserved in types or MIR
496 /// Names of local (user) variables (extracted from `var_debug_info`).
497 local_names: IndexVec<Local, Option<Name>>,
499 /// Record the region names generated for each region in the given
500 /// MIR def so that we can reuse them later in help/error messages.
501 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
503 /// The counter for generating new region names.
504 next_region_name: RefCell<usize>,
506 /// Results of Polonius analysis.
507 polonius_output: Option<Rc<PoloniusOutput>>,
511 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
512 // 2. loans made in overlapping scopes do not conflict
513 // 3. assignments do not affect things loaned out as immutable
514 // 4. moves do not affect things loaned out in any way
515 impl<'cx, 'tcx> dataflow::generic::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
516 type FlowState = Flows<'cx, 'tcx>;
520 flow_state: &Flows<'cx, 'tcx>,
521 stmt: &'cx Statement<'tcx>,
524 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
525 let span = stmt.source_info.span;
527 self.check_activations(location, span, flow_state);
530 StatementKind::Assign(box (ref lhs, ref rhs)) => {
531 self.consume_rvalue(location, (rhs, span), flow_state);
533 self.mutate_place(location, (lhs, span), Shallow(None), JustWrite, flow_state);
535 StatementKind::FakeRead(_, box ref place) => {
536 // Read for match doesn't access any memory and is used to
537 // assert that a place is safe and live. So we don't have to
538 // do any checks here.
540 // FIXME: Remove check that the place is initialized. This is
541 // needed for now because matches don't have never patterns yet.
542 // So this is the only place we prevent
546 self.check_if_path_or_subpath_is_moved(
548 InitializationRequiringAction::Use,
549 (place.as_ref(), span),
553 StatementKind::SetDiscriminant { ref place, variant_index: _ } => {
554 self.mutate_place(location, (place, span), Shallow(None), JustWrite, flow_state);
556 StatementKind::InlineAsm(ref asm) => {
557 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
559 // FIXME(eddyb) indirect inline asm outputs should
560 // be encoded through MIR place derefs instead.
564 (Deep, Read(ReadKind::Copy)),
565 LocalMutationIsAllowed::No,
568 self.check_if_path_or_subpath_is_moved(
570 InitializationRequiringAction::Use,
571 (output.as_ref(), o.span),
578 if o.is_rw { Deep } else { Shallow(None) },
579 if o.is_rw { WriteAndRead } else { JustWrite },
584 for (_, input) in asm.inputs.iter() {
585 self.consume_operand(location, (input, span), flow_state);
589 | StatementKind::AscribeUserType(..)
590 | StatementKind::Retag { .. }
591 | StatementKind::StorageLive(..) => {
592 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
595 StatementKind::StorageDead(local) => {
598 (&Place::from(local), span),
599 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
600 LocalMutationIsAllowed::Yes,
609 flow_state: &Flows<'cx, 'tcx>,
610 term: &'cx Terminator<'tcx>,
613 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
614 let span = term.source_info.span;
616 self.check_activations(loc, span, flow_state);
619 TerminatorKind::SwitchInt { ref discr, switch_ty: _, values: _, targets: _ } => {
620 self.consume_operand(loc, (discr, span), flow_state);
622 TerminatorKind::Drop { location: ref drop_place, target: _, unwind: _ } => {
623 let tcx = self.infcx.tcx;
625 // Compute the type with accurate region information.
626 let drop_place_ty = drop_place.ty(*self.body, self.infcx.tcx);
628 // Erase the regions.
629 let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
631 // "Lift" into the tcx -- once regions are erased, this type should be in the
632 // global arenas; this "lift" operation basically just asserts that is true, but
633 // that is useful later.
634 tcx.lift(&drop_place_ty).unwrap();
637 "visit_terminator_drop \
638 loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
639 loc, term, drop_place, drop_place_ty, span
645 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
646 LocalMutationIsAllowed::Yes,
650 TerminatorKind::DropAndReplace {
651 location: ref drop_place,
652 value: ref new_value,
656 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
657 self.consume_operand(loc, (new_value, span), flow_state);
659 TerminatorKind::Call {
666 self.consume_operand(loc, (func, span), flow_state);
668 self.consume_operand(loc, (arg, span), flow_state);
670 if let Some((ref dest, _ /*bb*/)) = *destination {
671 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
674 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
675 self.consume_operand(loc, (cond, span), flow_state);
676 use rustc::mir::AssertKind;
677 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
678 self.consume_operand(loc, (len, span), flow_state);
679 self.consume_operand(loc, (index, span), flow_state);
683 TerminatorKind::Yield { ref value, resume: _, ref resume_arg, drop: _ } => {
684 self.consume_operand(loc, (value, span), flow_state);
685 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
688 TerminatorKind::Goto { target: _ }
689 | TerminatorKind::Abort
690 | TerminatorKind::Unreachable
691 | TerminatorKind::Resume
692 | TerminatorKind::Return
693 | TerminatorKind::GeneratorDrop
694 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
695 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
696 // no data used, thus irrelevant to borrowck
701 fn visit_terminator_exit(
703 flow_state: &Flows<'cx, 'tcx>,
704 term: &'cx Terminator<'tcx>,
707 let span = term.source_info.span;
710 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
711 if self.movable_generator {
712 // Look for any active borrows to locals
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_local_borrow(borrow, span);
721 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
722 // Returning from the function implicitly kills storage for all locals and statics.
723 // Often, the storage will already have been killed by an explicit
724 // StorageDead, but we don't always emit those (notably on unwind paths),
725 // so this "extra check" serves as a kind of backup.
726 let borrow_set = self.borrow_set.clone();
727 for i in flow_state.borrows.iter() {
728 let borrow = &borrow_set[i];
729 self.check_for_invalidation_at_exit(loc, borrow, span);
733 TerminatorKind::Abort
734 | TerminatorKind::Assert { .. }
735 | TerminatorKind::Call { .. }
736 | TerminatorKind::Drop { .. }
737 | TerminatorKind::DropAndReplace { .. }
738 | TerminatorKind::FalseEdges { real_target: _, imaginary_target: _ }
739 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
740 | TerminatorKind::Goto { .. }
741 | TerminatorKind::SwitchInt { .. }
742 | TerminatorKind::Unreachable => {}
747 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
753 use self::AccessDepth::{Deep, Shallow};
754 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
756 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
757 enum ArtificialField {
762 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
764 /// From the RFC: "A *shallow* access means that the immediate
765 /// fields reached at P are accessed, but references or pointers
766 /// found within are not dereferenced. Right now, the only access
767 /// that is shallow is an assignment like `x = ...;`, which would
768 /// be a *shallow write* of `x`."
769 Shallow(Option<ArtificialField>),
771 /// From the RFC: "A *deep* access means that all data reachable
772 /// through the given place may be invalidated or accesses by
776 /// Access is Deep only when there is a Drop implementation that
777 /// can reach the data behind the reference.
781 /// Kind of access to a value: read or write
782 /// (For informational purposes only)
783 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
785 /// From the RFC: "A *read* means that the existing data may be
786 /// read, but will not be changed."
789 /// From the RFC: "A *write* means that the data may be mutated to
790 /// new values or otherwise invalidated (for example, it could be
791 /// de-initialized, as in a move operation).
794 /// For two-phase borrows, we distinguish a reservation (which is treated
795 /// like a Read) from an activation (which is treated like a write), and
796 /// each of those is furthermore distinguished from Reads/Writes above.
797 Reservation(WriteKind),
798 Activation(WriteKind, BorrowIndex),
801 /// Kind of read access to a value
802 /// (For informational purposes only)
803 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
809 /// Kind of write access to a value
810 /// (For informational purposes only)
811 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
814 MutableBorrow(BorrowKind),
819 /// When checking permissions for a place access, this flag is used to indicate that an immutable
820 /// local place can be mutated.
822 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
823 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
824 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
825 // `is_declared_mutable()`.
826 // - Take flow state into consideration in `is_assignable()` for local variables.
827 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
828 enum LocalMutationIsAllowed {
830 /// We want use of immutable upvars to cause a "write to immutable upvar"
831 /// error, not an "reassignment" error.
836 #[derive(Copy, Clone, Debug)]
837 enum InitializationRequiringAction {
846 struct RootPlace<'tcx> {
848 place_projection: &'tcx [PlaceElem<'tcx>],
849 is_local_mutation_allowed: LocalMutationIsAllowed,
852 impl InitializationRequiringAction {
853 fn as_noun(self) -> &'static str {
855 InitializationRequiringAction::Update => "update",
856 InitializationRequiringAction::Borrow => "borrow",
857 InitializationRequiringAction::MatchOn => "use", // no good noun
858 InitializationRequiringAction::Use => "use",
859 InitializationRequiringAction::Assignment => "assign",
860 InitializationRequiringAction::PartialAssignment => "assign to part",
864 fn as_verb_in_past_tense(self) -> &'static str {
866 InitializationRequiringAction::Update => "updated",
867 InitializationRequiringAction::Borrow => "borrowed",
868 InitializationRequiringAction::MatchOn => "matched on",
869 InitializationRequiringAction::Use => "used",
870 InitializationRequiringAction::Assignment => "assigned",
871 InitializationRequiringAction::PartialAssignment => "partially assigned",
876 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
877 fn body(&self) -> &'cx Body<'tcx> {
881 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
882 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
883 /// place is initialized and (b) it is not borrowed in some way that would prevent this
886 /// Returns `true` if an error is reported.
890 place_span: (&Place<'tcx>, Span),
891 kind: (AccessDepth, ReadOrWrite),
892 is_local_mutation_allowed: LocalMutationIsAllowed,
893 flow_state: &Flows<'cx, 'tcx>,
897 if let Activation(_, borrow_index) = rw {
898 if self.reservation_error_reported.contains(&place_span.0) {
900 "skipping access_place for activation of invalid reservation \
901 place: {:?} borrow_index: {:?}",
902 place_span.0, borrow_index
908 // Check is_empty() first because it's the common case, and doing that
909 // way we avoid the clone() call.
910 if !self.access_place_error_reported.is_empty()
911 && self.access_place_error_reported.contains(&(*place_span.0, place_span.1))
914 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
920 let mutability_error = self.check_access_permissions(
923 is_local_mutation_allowed,
928 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
930 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
931 // Suppress this warning when there's an error being emitted for the
932 // same borrow: fixing the error is likely to fix the warning.
933 self.reservation_warnings.remove(&borrow_idx);
936 if conflict_error || mutability_error {
937 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
939 self.access_place_error_reported.insert((*place_span.0, place_span.1));
943 fn check_access_for_conflict(
946 place_span: (&Place<'tcx>, Span),
949 flow_state: &Flows<'cx, 'tcx>,
952 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
953 location, place_span, sd, rw,
956 let mut error_reported = false;
957 let tcx = self.infcx.tcx;
958 let body = self.body;
959 let body: &Body<'_> = &body;
960 let borrow_set = self.borrow_set.clone();
962 // Use polonius output if it has been enabled.
963 let polonius_output = self.polonius_output.clone();
964 let borrows_in_scope = if let Some(polonius) = &polonius_output {
965 let location = self.location_table.start_index(location);
966 Either::Left(polonius.errors_at(location).iter().copied())
968 Either::Right(flow_state.borrows.iter())
971 each_borrow_involving_path(
979 |this, borrow_index, borrow| match (rw, borrow.kind) {
980 // Obviously an activation is compatible with its own
981 // reservation (or even prior activating uses of same
982 // borrow); so don't check if they interfere.
984 // NOTE: *reservations* do conflict with themselves;
985 // thus aren't injecting unsoundenss w/ this check.)
986 (Activation(_, activating), _) if activating == borrow_index => {
988 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
989 skipping {:?} b/c activation of same borrow_index",
993 (borrow_index, borrow),
998 (Read(_), BorrowKind::Shared)
999 | (Read(_), BorrowKind::Shallow)
1000 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
1001 | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
1005 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1006 // Handled by initialization checks.
1010 (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
1011 // Reading from mere reservations of mutable-borrows is OK.
1012 if !is_active(&this.dominators, borrow, location) {
1013 assert!(allow_two_phase_borrow(borrow.kind));
1014 return Control::Continue;
1017 error_reported = true;
1020 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1021 .buffer(&mut this.errors_buffer);
1023 ReadKind::Borrow(bk) => {
1024 this.report_conflicting_borrow(location, place_span, bk, borrow)
1025 .buffer(&mut this.errors_buffer);
1031 (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shallow)
1032 | (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shared)
1034 tcx.migrate_borrowck()
1035 && this.borrow_set.location_map.contains_key(&location)
1038 let bi = this.borrow_set.location_map[&location];
1040 "recording invalid reservation of place: {:?} with \
1041 borrow index {:?} as warning",
1044 // rust-lang/rust#56254 - This was previously permitted on
1045 // the 2018 edition so we emit it as a warning. We buffer
1046 // these sepately so that we only emit a warning if borrow
1047 // checking was otherwise successful.
1048 this.reservation_warnings
1049 .insert(bi, (*place_span.0, place_span.1, location, bk, borrow.clone()));
1051 // Don't suppress actual errors.
1055 (Reservation(kind), _) | (Activation(kind, _), _) | (Write(kind), _) => {
1057 Reservation(..) => {
1059 "recording invalid reservation of \
1063 this.reservation_error_reported.insert(place_span.0.clone());
1065 Activation(_, activating) => {
1067 "observing check_place for activation of \
1068 borrow_index: {:?}",
1072 Read(..) | Write(..) => {}
1075 error_reported = true;
1077 WriteKind::MutableBorrow(bk) => {
1078 this.report_conflicting_borrow(location, place_span, bk, borrow)
1079 .buffer(&mut this.errors_buffer);
1081 WriteKind::StorageDeadOrDrop => this
1082 .report_borrowed_value_does_not_live_long_enough(
1088 WriteKind::Mutate => {
1089 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1091 WriteKind::Move => {
1092 this.report_move_out_while_borrowed(location, place_span, borrow)
1106 place_span: (&'cx Place<'tcx>, Span),
1109 flow_state: &Flows<'cx, 'tcx>,
1111 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1113 MutateMode::WriteAndRead => {
1114 self.check_if_path_or_subpath_is_moved(
1116 InitializationRequiringAction::Update,
1117 (place_span.0.as_ref(), place_span.1),
1121 MutateMode::JustWrite => {
1122 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1126 // Special case: you can assign a immutable local variable
1127 // (e.g., `x = ...`) so long as it has never been initialized
1128 // before (at this point in the flow).
1129 if let Some(local) = place_span.0.as_local() {
1130 if let Mutability::Not = self.body.local_decls[local].mutability {
1131 // check for reassignments to immutable local variables
1132 self.check_if_reassignment_to_immutable_state(
1133 location, local, place_span, flow_state,
1139 // Otherwise, use the normal access permission rules.
1143 (kind, Write(WriteKind::Mutate)),
1144 LocalMutationIsAllowed::No,
1152 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1153 flow_state: &Flows<'cx, 'tcx>,
1156 Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
1157 let access_kind = match bk {
1158 BorrowKind::Shallow => {
1159 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1161 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1162 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1163 let wk = WriteKind::MutableBorrow(bk);
1164 if allow_two_phase_borrow(bk) {
1165 (Deep, Reservation(wk))
1176 LocalMutationIsAllowed::No,
1180 let action = if bk == BorrowKind::Shallow {
1181 InitializationRequiringAction::MatchOn
1183 InitializationRequiringAction::Borrow
1186 self.check_if_path_or_subpath_is_moved(
1189 (place.as_ref(), span),
1194 Rvalue::AddressOf(mutability, ref place) => {
1195 let access_kind = match mutability {
1196 Mutability::Mut => (
1198 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1199 allow_two_phase_borrow: false,
1202 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1209 LocalMutationIsAllowed::No,
1213 self.check_if_path_or_subpath_is_moved(
1215 InitializationRequiringAction::Borrow,
1216 (place.as_ref(), span),
1221 Rvalue::Use(ref operand)
1222 | Rvalue::Repeat(ref operand, _)
1223 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1224 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1225 self.consume_operand(location, (operand, span), flow_state)
1228 Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => {
1229 let af = match *rvalue {
1230 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1231 Rvalue::Discriminant(..) => None,
1232 _ => unreachable!(),
1237 (Shallow(af), Read(ReadKind::Copy)),
1238 LocalMutationIsAllowed::No,
1241 self.check_if_path_or_subpath_is_moved(
1243 InitializationRequiringAction::Use,
1244 (place.as_ref(), span),
1249 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1250 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1251 self.consume_operand(location, (operand1, span), flow_state);
1252 self.consume_operand(location, (operand2, span), flow_state);
1255 Rvalue::NullaryOp(_op, _ty) => {
1256 // nullary ops take no dynamic input; no borrowck effect.
1258 // FIXME: is above actually true? Do we want to track
1259 // the fact that uninitialized data can be created via
1263 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1264 // We need to report back the list of mutable upvars that were
1265 // moved into the closure and subsequently used by the closure,
1266 // in order to populate our used_mut set.
1267 match **aggregate_kind {
1268 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1269 let BorrowCheckResult { used_mut_upvars, .. } =
1270 self.infcx.tcx.mir_borrowck(def_id);
1271 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1272 for field in used_mut_upvars {
1273 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1276 AggregateKind::Adt(..)
1277 | AggregateKind::Array(..)
1278 | AggregateKind::Tuple { .. } => (),
1281 for operand in operands {
1282 self.consume_operand(location, (operand, span), flow_state);
1288 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1289 let propagate_closure_used_mut_place = |this: &mut Self, place: &Place<'tcx>| {
1290 if !place.projection.is_empty() {
1291 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1292 this.used_mut_upvars.push(field);
1295 this.used_mut.insert(place.local);
1299 // This relies on the current way that by-value
1300 // captures of a closure are copied/moved directly
1301 // when generating MIR.
1303 Operand::Move(ref place) | Operand::Copy(ref place) => {
1304 match place.as_local() {
1305 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1306 if self.body.local_decls[local].ty.is_mutable_ptr() {
1307 // The variable will be marked as mutable by the borrow.
1310 // This is an edge case where we have a `move` closure
1311 // inside a non-move closure, and the inner closure
1312 // contains a mutation:
1315 // || { move || { i += 1; }; };
1317 // In this case our usual strategy of assuming that the
1318 // variable will be captured by mutable reference is
1319 // wrong, since `i` can be copied into the inner
1320 // closure from a shared reference.
1322 // As such we have to search for the local that this
1323 // capture comes from and mark it as being used as mut.
1325 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1326 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1327 &self.move_data.inits[init_index]
1329 bug!("temporary should be initialized exactly once")
1332 let loc = match init.location {
1333 InitLocation::Statement(stmt) => stmt,
1334 _ => bug!("temporary initialized in arguments"),
1337 let body = self.body;
1338 let bbd = &body[loc.block];
1339 let stmt = &bbd.statements[loc.statement_index];
1340 debug!("temporary assigned in: stmt={:?}", stmt);
1342 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, ref source))) =
1345 propagate_closure_used_mut_place(self, source);
1348 "closures should only capture user variables \
1349 or references to user variables"
1353 _ => propagate_closure_used_mut_place(self, place),
1356 Operand::Constant(..) => {}
1363 (operand, span): (&'cx Operand<'tcx>, Span),
1364 flow_state: &Flows<'cx, 'tcx>,
1367 Operand::Copy(ref place) => {
1368 // copy of place: check if this is "copy of frozen path"
1369 // (FIXME: see check_loans.rs)
1373 (Deep, Read(ReadKind::Copy)),
1374 LocalMutationIsAllowed::No,
1378 // Finally, check if path was already moved.
1379 self.check_if_path_or_subpath_is_moved(
1381 InitializationRequiringAction::Use,
1382 (place.as_ref(), span),
1386 Operand::Move(ref place) => {
1387 // move of place: check if this is move of already borrowed path
1391 (Deep, Write(WriteKind::Move)),
1392 LocalMutationIsAllowed::Yes,
1396 // Finally, check if path was already moved.
1397 self.check_if_path_or_subpath_is_moved(
1399 InitializationRequiringAction::Use,
1400 (place.as_ref(), span),
1404 Operand::Constant(_) => {}
1408 /// Checks whether a borrow of this place is invalidated when the function
1410 fn check_for_invalidation_at_exit(
1413 borrow: &BorrowData<'tcx>,
1416 debug!("check_for_invalidation_at_exit({:?})", borrow);
1417 let place = &borrow.borrowed_place;
1418 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1420 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1421 // we just know that all locals are dropped at function exit (otherwise
1422 // we'll have a memory leak) and assume that all statics have a destructor.
1424 // FIXME: allow thread-locals to borrow other thread locals?
1426 let (might_be_alive, will_be_dropped) =
1427 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1428 // Thread-locals might be dropped after the function exits
1429 // We have to dereference the outer reference because
1430 // borrows don't conflict behind shared references.
1431 root_place.projection = DEREF_PROJECTION;
1434 (false, self.locals_are_invalidated_at_exit)
1437 if !will_be_dropped {
1438 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1442 let sd = if might_be_alive { Deep } else { Shallow(None) };
1444 if places_conflict::borrow_conflicts_with_place(
1451 places_conflict::PlaceConflictBias::Overlap,
1453 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1454 // FIXME: should be talking about the region lifetime instead
1455 // of just a span here.
1456 let span = self.infcx.tcx.sess.source_map().end_point(span);
1457 self.report_borrowed_value_does_not_live_long_enough(
1466 /// Reports an error if this is a borrow of local data.
1467 /// This is called for all Yield expressions on movable generators
1468 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1469 debug!("check_for_local_borrow({:?})", borrow);
1471 if borrow_of_local_data(&borrow.borrowed_place) {
1472 let err = self.cannot_borrow_across_generator_yield(
1473 self.retrieve_borrow_spans(borrow).var_or_use(),
1477 err.buffer(&mut self.errors_buffer);
1481 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1482 // Two-phase borrow support: For each activation that is newly
1483 // generated at this statement, check if it interferes with
1485 let borrow_set = self.borrow_set.clone();
1486 for &borrow_index in borrow_set.activations_at_location(location) {
1487 let borrow = &borrow_set[borrow_index];
1489 // only mutable borrows should be 2-phase
1490 assert!(match borrow.kind {
1491 BorrowKind::Shared | BorrowKind::Shallow => false,
1492 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1497 (&borrow.borrowed_place, span),
1498 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1499 LocalMutationIsAllowed::No,
1502 // We do not need to call `check_if_path_or_subpath_is_moved`
1503 // again, as we already called it when we made the
1504 // initial reservation.
1508 fn check_if_reassignment_to_immutable_state(
1512 place_span: (&Place<'tcx>, Span),
1513 flow_state: &Flows<'cx, 'tcx>,
1515 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1517 // Check if any of the initializiations of `local` have happened yet:
1518 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1519 // And, if so, report an error.
1520 let init = &self.move_data.inits[init_index];
1521 let span = init.span(&self.body);
1522 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1526 fn check_if_full_path_is_moved(
1529 desired_action: InitializationRequiringAction,
1530 place_span: (PlaceRef<'tcx>, Span),
1531 flow_state: &Flows<'cx, 'tcx>,
1533 let maybe_uninits = &flow_state.uninits;
1537 // 1. Move of `a.b.c`, use of `a.b.c`
1538 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1539 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1540 // partial initialization support, one might have `a.x`
1541 // initialized but not `a.b`.
1545 // 4. Move of `a.b.c`, use of `a.b.d`
1546 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1547 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1548 // must have been initialized for the use to be sound.
1549 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1551 // The dataflow tracks shallow prefixes distinctly (that is,
1552 // field-accesses on P distinctly from P itself), in order to
1553 // track substructure initialization separately from the whole
1556 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1557 // which we have a MovePath is `a.b`, then that means that the
1558 // initialization state of `a.b` is all we need to inspect to
1559 // know if `a.b.c` is valid (and from that we infer that the
1560 // dereference and `.d` access is also valid, since we assume
1561 // `a.b.c` is assigned a reference to a initialized and
1562 // well-formed record structure.)
1564 // Therefore, if we seek out the *closest* prefix for which we
1565 // have a MovePath, that should capture the initialization
1566 // state for the place scenario.
1568 // This code covers scenarios 1, 2, and 3.
1570 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1571 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1572 if maybe_uninits.contains(mpi) {
1573 self.report_use_of_moved_or_uninitialized(
1576 (prefix, place_span.0, place_span.1),
1579 } // Only query longest prefix with a MovePath, not further
1580 // ancestors; dataflow recurs on children when parents
1581 // move (to support partial (re)inits).
1583 // (I.e., querying parents breaks scenario 7; but may want
1584 // to do such a query based on partial-init feature-gate.)
1587 /// Subslices correspond to multiple move paths, so we iterate through the
1588 /// elements of the base array. For each element we check
1590 /// * Does this element overlap with our slice.
1591 /// * Is any part of it uninitialized.
1592 fn check_if_subslice_element_is_moved(
1595 desired_action: InitializationRequiringAction,
1596 place_span: (PlaceRef<'tcx>, Span),
1597 maybe_uninits: &BitSet<MovePathIndex>,
1601 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1602 let move_paths = &self.move_data.move_paths;
1604 let root_path = &move_paths[mpi];
1605 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1606 let last_proj = child_move_path.place.projection.last().unwrap();
1607 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1608 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1610 if (from..to).contains(offset) {
1612 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1613 maybe_uninits.contains(mpi)
1616 if let Some(uninit_child) = uninit_child {
1617 self.report_use_of_moved_or_uninitialized(
1620 (place_span.0, place_span.0, place_span.1),
1623 return; // don't bother finding other problems.
1631 fn check_if_path_or_subpath_is_moved(
1634 desired_action: InitializationRequiringAction,
1635 place_span: (PlaceRef<'tcx>, Span),
1636 flow_state: &Flows<'cx, 'tcx>,
1638 let maybe_uninits = &flow_state.uninits;
1642 // 1. Move of `a.b.c`, use of `a` or `a.b`
1643 // partial initialization support, one might have `a.x`
1644 // initialized but not `a.b`.
1645 // 2. All bad scenarios from `check_if_full_path_is_moved`
1649 // 3. Move of `a.b.c`, use of `a.b.d`
1650 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1651 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1652 // must have been initialized for the use to be sound.
1653 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1655 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1657 if let [base_proj @ .., ProjectionElem::Subslice { from, to, from_end: false }] =
1658 place_span.0.projection
1661 Place::ty_from(place_span.0.local, base_proj, self.body(), self.infcx.tcx);
1662 if let ty::Array(..) = place_ty.ty.kind {
1663 let array_place = PlaceRef { local: place_span.0.local, projection: base_proj };
1664 self.check_if_subslice_element_is_moved(
1667 (array_place, place_span.1),
1676 // A move of any shallow suffix of `place` also interferes
1677 // with an attempt to use `place`. This is scenario 3 above.
1679 // (Distinct from handling of scenarios 1+2+4 above because
1680 // `place` does not interfere with suffixes of its prefixes,
1681 // e.g., `a.b.c` does not interfere with `a.b.d`)
1683 // This code covers scenario 1.
1685 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1686 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1687 let uninit_mpi = self
1689 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1691 if let Some(uninit_mpi) = uninit_mpi {
1692 self.report_use_of_moved_or_uninitialized(
1695 (place_span.0, place_span.0, place_span.1),
1698 return; // don't bother finding other problems.
1703 /// Currently MoveData does not store entries for all places in
1704 /// the input MIR. For example it will currently filter out
1705 /// places that are Copy; thus we do not track places of shared
1706 /// reference type. This routine will walk up a place along its
1707 /// prefixes, searching for a foundational place that *is*
1708 /// tracked in the MoveData.
1710 /// An Err result includes a tag indicated why the search failed.
1711 /// Currently this can only occur if the place is built off of a
1712 /// static variable, as we do not track those in the MoveData.
1713 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1714 match self.move_data.rev_lookup.find(place) {
1715 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1716 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1718 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1722 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1723 // If returns None, then there is no move path corresponding
1724 // to a direct owner of `place` (which means there is nothing
1725 // that borrowck tracks for its analysis).
1727 match self.move_data.rev_lookup.find(place) {
1728 LookupResult::Parent(_) => None,
1729 LookupResult::Exact(mpi) => Some(mpi),
1733 fn check_if_assigned_path_is_moved(
1736 (place, span): (&'cx Place<'tcx>, Span),
1737 flow_state: &Flows<'cx, 'tcx>,
1739 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1741 // None case => assigning to `x` does not require `x` be initialized.
1742 let mut cursor = &*place.projection.as_ref();
1743 while let [proj_base @ .., elem] = cursor {
1747 ProjectionElem::Index(_/*operand*/) |
1748 ProjectionElem::ConstantIndex { .. } |
1749 // assigning to P[i] requires P to be valid.
1750 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1751 // assigning to (P->variant) is okay if assigning to `P` is okay
1753 // FIXME: is this true even if P is a adt with a dtor?
1756 // assigning to (*P) requires P to be initialized
1757 ProjectionElem::Deref => {
1758 self.check_if_full_path_is_moved(
1759 location, InitializationRequiringAction::Use,
1762 projection: proj_base,
1763 }, span), flow_state);
1764 // (base initialized; no need to
1769 ProjectionElem::Subslice { .. } => {
1770 panic!("we don't allow assignments to subslices, location: {:?}",
1774 ProjectionElem::Field(..) => {
1775 // if type of `P` has a dtor, then
1776 // assigning to `P.f` requires `P` itself
1777 // be already initialized
1778 let tcx = self.infcx.tcx;
1779 let base_ty = Place::ty_from(place.local, proj_base, self.body(), tcx).ty;
1780 match base_ty.kind {
1781 ty::Adt(def, _) if def.has_dtor(tcx) => {
1782 self.check_if_path_or_subpath_is_moved(
1783 location, InitializationRequiringAction::Assignment,
1786 projection: proj_base,
1787 }, span), flow_state);
1789 // (base initialized; no need to
1794 // Once `let s; s.x = V; read(s.x);`,
1795 // is allowed, remove this match arm.
1796 ty::Adt(..) | ty::Tuple(..) => {
1797 check_parent_of_field(self, location, PlaceRef {
1799 projection: proj_base,
1800 }, span, flow_state);
1802 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1803 // partial initialization, do not complain about unnecessary `mut` on
1804 // an attempt to do a partial initialization.
1805 self.used_mut.insert(place.local);
1814 fn check_parent_of_field<'cx, 'tcx>(
1815 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1817 base: PlaceRef<'tcx>,
1819 flow_state: &Flows<'cx, 'tcx>,
1821 // rust-lang/rust#21232: Until Rust allows reads from the
1822 // initialized parts of partially initialized structs, we
1823 // will, starting with the 2018 edition, reject attempts
1824 // to write to structs that are not fully initialized.
1826 // In other words, *until* we allow this:
1828 // 1. `let mut s; s.x = Val; read(s.x);`
1830 // we will for now disallow this:
1832 // 2. `let mut s; s.x = Val;`
1836 // 3. `let mut s = ...; drop(s); s.x=Val;`
1838 // This does not use check_if_path_or_subpath_is_moved,
1839 // because we want to *allow* reinitializations of fields:
1840 // e.g., want to allow
1842 // `let mut s = ...; drop(s.x); s.x=Val;`
1844 // This does not use check_if_full_path_is_moved on
1845 // `base`, because that would report an error about the
1846 // `base` as a whole, but in this scenario we *really*
1847 // want to report an error about the actual thing that was
1848 // moved, which may be some prefix of `base`.
1850 // Shallow so that we'll stop at any dereference; we'll
1851 // report errors about issues with such bases elsewhere.
1852 let maybe_uninits = &flow_state.uninits;
1854 // Find the shortest uninitialized prefix you can reach
1855 // without going over a Deref.
1856 let mut shortest_uninit_seen = None;
1857 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1858 let mpi = match this.move_path_for_place(prefix) {
1863 if maybe_uninits.contains(mpi) {
1865 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1866 shortest_uninit_seen,
1869 shortest_uninit_seen = Some((prefix, mpi));
1871 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1875 if let Some((prefix, mpi)) = shortest_uninit_seen {
1876 // Check for a reassignment into a uninitialized field of a union (for example,
1877 // after a move out). In this case, do not report a error here. There is an
1878 // exception, if this is the first assignment into the union (that is, there is
1879 // no move out from an earlier location) then this is an attempt at initialization
1880 // of the union - we should error in that case.
1881 let tcx = this.infcx.tcx;
1882 if let ty::Adt(def, _) =
1883 Place::ty_from(base.local, base.projection, this.body(), tcx).ty.kind
1886 if this.move_data.path_map[mpi].iter().any(|moi| {
1887 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1894 this.report_use_of_moved_or_uninitialized(
1896 InitializationRequiringAction::PartialAssignment,
1897 (prefix, base, span),
1904 /// Checks the permissions for the given place and read or write kind
1906 /// Returns `true` if an error is reported.
1907 fn check_access_permissions(
1909 (place, span): (&Place<'tcx>, Span),
1911 is_local_mutation_allowed: LocalMutationIsAllowed,
1912 flow_state: &Flows<'cx, 'tcx>,
1916 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1917 place, kind, is_local_mutation_allowed
1924 Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1925 | Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
1926 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
1927 | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
1928 let is_local_mutation_allowed = match borrow_kind {
1929 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1930 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1931 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1933 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1935 self.add_used_mut(root_place, flow_state);
1939 error_access = AccessKind::MutableBorrow;
1940 the_place_err = place_err;
1944 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1945 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1947 self.add_used_mut(root_place, flow_state);
1951 error_access = AccessKind::Mutate;
1952 the_place_err = place_err;
1957 Reservation(WriteKind::Move)
1958 | Write(WriteKind::Move)
1959 | Reservation(WriteKind::StorageDeadOrDrop)
1960 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
1961 | Reservation(WriteKind::MutableBorrow(BorrowKind::Shallow))
1962 | Write(WriteKind::StorageDeadOrDrop)
1963 | Write(WriteKind::MutableBorrow(BorrowKind::Shared))
1964 | Write(WriteKind::MutableBorrow(BorrowKind::Shallow)) => {
1965 if let (Err(_), true) = (
1966 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
1967 self.errors_buffer.is_empty(),
1969 // rust-lang/rust#46908: In pure NLL mode this code path should be
1970 // unreachable, but we use `delay_span_bug` because we can hit this when
1971 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1972 // enabled. We don't want to ICE for that case, as other errors will have
1973 // been emitted (#52262).
1974 self.infcx.tcx.sess.delay_span_bug(
1977 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1985 // permission checks are done at Reservation point.
1988 Read(ReadKind::Borrow(BorrowKind::Unique))
1989 | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
1990 | Read(ReadKind::Borrow(BorrowKind::Shared))
1991 | Read(ReadKind::Borrow(BorrowKind::Shallow))
1992 | Read(ReadKind::Copy) => {
1993 // Access authorized
1998 // rust-lang/rust#21232, #54986: during period where we reject
1999 // partial initialization, do not complain about mutability
2000 // errors except for actual mutation (as opposed to an attempt
2001 // to do a partial initialization).
2002 let previously_initialized =
2003 self.is_local_ever_initialized(place.local, flow_state).is_some();
2005 // at this point, we have set up the error reporting state.
2006 if previously_initialized {
2007 self.report_mutability_error(place, span, the_place_err, error_access, location);
2014 fn is_local_ever_initialized(
2017 flow_state: &Flows<'cx, 'tcx>,
2018 ) -> Option<InitIndex> {
2019 let mpi = self.move_data.rev_lookup.find_local(local);
2020 let ii = &self.move_data.init_path_map[mpi];
2022 if flow_state.ever_inits.contains(index) {
2029 /// Adds the place into the used mutable variables set
2030 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2032 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2033 // If the local may have been initialized, and it is now currently being
2034 // mutated, then it is justified to be annotated with the `mut`
2035 // keyword, since the mutation may be a possible reassignment.
2036 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2037 && self.is_local_ever_initialized(local, flow_state).is_some()
2039 self.used_mut.insert(local);
2044 place_projection: _,
2045 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2049 place_projection: place_projection @ [.., _],
2050 is_local_mutation_allowed: _,
2052 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2054 projection: place_projection,
2056 self.used_mut_upvars.push(field);
2062 /// Whether this value can be written or borrowed mutably.
2063 /// Returns the root place if the place passed in is a projection.
2066 place: PlaceRef<'tcx>,
2067 is_local_mutation_allowed: LocalMutationIsAllowed,
2068 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2070 PlaceRef { local, projection: [] } => {
2071 let local = &self.body.local_decls[local];
2072 match local.mutability {
2073 Mutability::Not => match is_local_mutation_allowed {
2074 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2075 place_local: place.local,
2076 place_projection: place.projection,
2077 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2079 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2080 place_local: place.local,
2081 place_projection: place.projection,
2082 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2084 LocalMutationIsAllowed::No => Err(place),
2086 Mutability::Mut => Ok(RootPlace {
2087 place_local: place.local,
2088 place_projection: place.projection,
2089 is_local_mutation_allowed,
2093 PlaceRef { local: _, projection: [proj_base @ .., elem] } => {
2095 ProjectionElem::Deref => {
2097 Place::ty_from(place.local, proj_base, self.body(), self.infcx.tcx).ty;
2099 // Check the kind of deref to decide
2100 match base_ty.kind {
2101 ty::Ref(_, _, mutbl) => {
2103 // Shared borrowed data is never mutable
2104 hir::Mutability::Not => Err(place),
2105 // Mutably borrowed data is mutable, but only if we have a
2106 // unique path to the `&mut`
2107 hir::Mutability::Mut => {
2108 let mode = match self.is_upvar_field_projection(place) {
2109 Some(field) if self.upvars[field.index()].by_ref => {
2110 is_local_mutation_allowed
2112 _ => LocalMutationIsAllowed::Yes,
2116 PlaceRef { local: place.local, projection: proj_base },
2122 ty::RawPtr(tnm) => {
2124 // `*const` raw pointers are not mutable
2125 hir::Mutability::Not => Err(place),
2126 // `*mut` raw pointers are always mutable, regardless of
2127 // context. The users have to check by themselves.
2128 hir::Mutability::Mut => Ok(RootPlace {
2129 place_local: place.local,
2130 place_projection: place.projection,
2131 is_local_mutation_allowed,
2135 // `Box<T>` owns its content, so mutable if its location is mutable
2136 _ if base_ty.is_box() => self.is_mutable(
2137 PlaceRef { local: place.local, projection: proj_base },
2138 is_local_mutation_allowed,
2140 // Deref should only be for reference, pointers or boxes
2141 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2144 // All other projections are owned by their base path, so mutable if
2145 // base path is mutable
2146 ProjectionElem::Field(..)
2147 | ProjectionElem::Index(..)
2148 | ProjectionElem::ConstantIndex { .. }
2149 | ProjectionElem::Subslice { .. }
2150 | ProjectionElem::Downcast(..) => {
2151 let upvar_field_projection = self.is_upvar_field_projection(place);
2152 if let Some(field) = upvar_field_projection {
2153 let upvar = &self.upvars[field.index()];
2155 "upvar.mutability={:?} local_mutation_is_allowed={:?} \
2157 upvar, is_local_mutation_allowed, place
2159 match (upvar.mutability, is_local_mutation_allowed) {
2160 (Mutability::Not, LocalMutationIsAllowed::No)
2161 | (Mutability::Not, LocalMutationIsAllowed::ExceptUpvars) => {
2164 (Mutability::Not, LocalMutationIsAllowed::Yes)
2165 | (Mutability::Mut, _) => {
2166 // Subtle: this is an upvar
2167 // reference, so it looks like
2168 // `self.foo` -- we want to double
2169 // check that the location `*self`
2170 // is mutable (i.e., this is not a
2171 // `Fn` closure). But if that
2172 // check succeeds, we want to
2173 // *blame* the mutability on
2174 // `place` (that is,
2175 // `self.foo`). This is used to
2176 // propagate the info about
2177 // whether mutability declarations
2178 // are used outwards, so that we register
2179 // the outer variable as mutable. Otherwise a
2180 // test like this fails to record the `mut`
2184 // fn foo<F: FnOnce()>(_f: F) { }
2186 // let var = Vec::new();
2192 let _ = self.is_mutable(
2193 PlaceRef { local: place.local, projection: proj_base },
2194 is_local_mutation_allowed,
2197 place_local: place.local,
2198 place_projection: place.projection,
2199 is_local_mutation_allowed,
2205 PlaceRef { local: place.local, projection: proj_base },
2206 is_local_mutation_allowed,
2215 /// If `place` is a field projection, and the field is being projected from a closure type,
2216 /// then returns the index of the field being projected. Note that this closure will always
2217 /// be `self` in the current MIR, because that is the only time we directly access the fields
2218 /// of a closure type.
2219 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2220 let mut place_projection = place_ref.projection;
2221 let mut by_ref = false;
2223 if let [proj_base @ .., ProjectionElem::Deref] = place_projection {
2224 place_projection = proj_base;
2228 match place_projection {
2229 [base @ .., ProjectionElem::Field(field, _ty)] => {
2230 let tcx = self.infcx.tcx;
2231 let base_ty = Place::ty_from(place_ref.local, base, self.body(), tcx).ty;
2233 if (base_ty.is_closure() || base_ty.is_generator())
2234 && (!by_ref || self.upvars[field.index()].by_ref)
2247 /// The degree of overlap between 2 places for borrow-checking.
2249 /// The places might partially overlap - in this case, we give
2250 /// up and say that they might conflict. This occurs when
2251 /// different fields of a union are borrowed. For example,
2252 /// if `u` is a union, we have no way of telling how disjoint
2253 /// `u.a.x` and `a.b.y` are.
2255 /// The places have the same type, and are either completely disjoint
2256 /// or equal - i.e., they can't "partially" overlap as can occur with
2257 /// unions. This is the "base case" on which we recur for extensions
2260 /// The places are disjoint, so we know all extensions of them
2261 /// will also be disjoint.