1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
4 use rustc_data_structures::graph::dominators::Dominators;
5 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorReported};
7 use rustc_hir::def_id::LocalDefId;
8 use rustc_hir::{HirId, Node};
9 use rustc_index::bit_set::BitSet;
10 use rustc_index::vec::IndexVec;
11 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
12 use rustc_middle::mir::{
13 traversal, Body, ClearCrossCrate, Local, Location, Mutability, Operand, Place, PlaceElem,
16 use rustc_middle::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
17 use rustc_middle::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
18 use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
19 use rustc_middle::ty::query::Providers;
20 use rustc_middle::ty::{self, InstanceDef, RegionVid, TyCtxt};
21 use rustc_session::lint::builtin::{MUTABLE_BORROW_RESERVATION_CONFLICT, UNUSED_MUT};
22 use rustc_span::{Span, Symbol, DUMMY_SP};
25 use smallvec::SmallVec;
26 use std::cell::RefCell;
27 use std::collections::BTreeMap;
32 use crate::dataflow::impls::{
33 Borrows, EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
35 use crate::dataflow::indexes::{BorrowIndex, InitIndex, MoveOutIndex, MovePathIndex};
36 use crate::dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
37 use crate::dataflow::MoveDataParamEnv;
38 use crate::dataflow::{Analysis, BorrowckFlowState as Flows, BorrowckResults};
39 use crate::transform::MirSource;
41 use self::diagnostics::{AccessKind, RegionName};
42 use self::location::LocationTable;
43 use self::prefixes::PrefixSet;
44 use self::MutateMode::{JustWrite, WriteAndRead};
46 use self::path_utils::*;
49 mod constraint_generation;
56 mod member_constraints;
65 mod universal_regions;
68 crate use borrow_set::{BorrowData, BorrowSet};
69 crate use nll::{PoloniusOutput, ToRegionVid};
70 crate use place_ext::PlaceExt;
71 crate use places_conflict::{places_conflict, PlaceConflictBias};
72 crate use region_infer::RegionInferenceContext;
74 // FIXME(eddyb) perhaps move this somewhere more centrally.
81 /// If true, the capture is behind a reference.
84 mutability: Mutability,
87 const DEREF_PROJECTION: &[PlaceElem<'_>; 1] = &[ProjectionElem::Deref];
89 pub fn provide(providers: &mut Providers) {
90 *providers = Providers {
91 mir_borrowck: |tcx, did| {
92 if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
93 tcx.mir_borrowck_const_arg(def)
95 mir_borrowck(tcx, ty::WithOptConstParam::unknown(did))
98 mir_borrowck_const_arg: |tcx, (did, param_did)| {
99 mir_borrowck(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
105 fn mir_borrowck<'tcx>(
107 def: ty::WithOptConstParam<LocalDefId>,
108 ) -> &'tcx BorrowCheckResult<'tcx> {
109 let (input_body, promoted) = tcx.mir_validated(def);
110 debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
112 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
113 let input_body: &Body<'_> = &input_body.borrow();
114 let promoted: &IndexVec<_, _> = &promoted.borrow();
115 do_mir_borrowck(&infcx, input_body, promoted, def)
117 debug!("mir_borrowck done");
119 tcx.arena.alloc(opt_closure_req)
122 fn do_mir_borrowck<'a, 'tcx>(
123 infcx: &InferCtxt<'a, 'tcx>,
124 input_body: &Body<'tcx>,
125 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
126 def: ty::WithOptConstParam<LocalDefId>,
127 ) -> BorrowCheckResult<'tcx> {
128 debug!("do_mir_borrowck(def = {:?})", def);
131 let param_env = tcx.param_env(def.did);
132 let id = tcx.hir().as_local_hir_id(def.did);
134 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
135 for var_debug_info in &input_body.var_debug_info {
136 if let Some(local) = var_debug_info.place.as_local() {
137 if let Some(prev_name) = local_names[local] {
138 if var_debug_info.name != prev_name {
140 var_debug_info.source_info.span,
141 "local {:?} has many names (`{}` vs `{}`)",
148 local_names[local] = Some(var_debug_info.name);
152 // Gather the upvars of a closure, if any.
153 let tables = tcx.typeck_opt_const_arg(def);
154 if let Some(ErrorReported) = tables.tainted_by_errors {
155 infcx.set_tainted_by_errors();
157 let upvars: Vec<_> = tables
159 .get(&def.did.to_def_id())
161 .flat_map(|v| v.values())
163 let var_hir_id = upvar_id.var_path.hir_id;
164 let capture = tables.upvar_capture(*upvar_id);
165 let by_ref = match capture {
166 ty::UpvarCapture::ByValue => false,
167 ty::UpvarCapture::ByRef(..) => true,
169 let mut upvar = Upvar {
170 name: tcx.hir().name(var_hir_id),
173 mutability: Mutability::Not,
175 let bm = *tables.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
176 if bm == ty::BindByValue(hir::Mutability::Mut) {
177 upvar.mutability = Mutability::Mut;
183 // Replace all regions with fresh inference variables. This
184 // requires first making our own copy of the MIR. This copy will
185 // be modified (in place) to contain non-lexical lifetimes. It
186 // will have a lifetime tied to the inference context.
187 let mut body = input_body.clone();
188 let mut promoted = input_promoted.clone();
189 let free_regions = nll::replace_regions_in_mir(infcx, def, param_env, &mut body, &mut promoted);
190 let body = &body; // no further changes
192 let location_table = &LocationTable::new(&body);
194 let mut errors_buffer = Vec::new();
195 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
196 match MoveData::gather_moves(&body, tcx, param_env) {
197 Ok(move_data) => (move_data, Vec::new()),
198 Err((move_data, move_errors)) => (move_data, move_errors),
200 let promoted_errors = promoted
202 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
204 let mdpe = MoveDataParamEnv { move_data, param_env };
206 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
207 .into_engine(tcx, &body, def.did.to_def_id())
208 .iterate_to_fixpoint()
209 .into_results_cursor(&body);
211 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
213 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
215 // Compute non-lexical lifetimes.
222 } = nll::compute_regions(
236 // Dump MIR results into a file, if that is enabled. This let us
237 // write unit-tests, as well as helping with debugging.
238 nll::dump_mir_results(
240 MirSource { instance: InstanceDef::Item(def.to_global()), promoted: None },
246 // We also have a `#[rustc_regions]` annotation that causes us to dump
248 nll::dump_annotation(
258 // The various `flow_*` structures can be large. We drop `flow_inits` here
259 // so it doesn't overlap with the others below. This reduces peak memory
260 // usage significantly on some benchmarks.
263 let regioncx = Rc::new(regioncx);
265 let flow_borrows = Borrows::new(tcx, &body, regioncx.clone(), &borrow_set)
266 .into_engine(tcx, &body, def.did.to_def_id())
267 .iterate_to_fixpoint();
268 let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
269 .into_engine(tcx, &body, def.did.to_def_id())
270 .iterate_to_fixpoint();
271 let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
272 .into_engine(tcx, &body, def.did.to_def_id())
273 .iterate_to_fixpoint();
275 let movable_generator = match tcx.hir().get(id) {
276 Node::Expr(&hir::Expr {
277 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
283 for (idx, move_data_results) in promoted_errors {
284 let promoted_body = &promoted[idx];
285 let dominators = promoted_body.dominators();
287 if let Err((move_data, move_errors)) = move_data_results {
288 let mut promoted_mbcx = MirBorrowckCtxt {
292 move_data: &move_data,
293 location_table: &LocationTable::new(promoted_body),
295 fn_self_span_reported: Default::default(),
296 locals_are_invalidated_at_exit,
297 access_place_error_reported: Default::default(),
298 reservation_error_reported: Default::default(),
299 reservation_warnings: Default::default(),
300 move_error_reported: BTreeMap::new(),
301 uninitialized_error_reported: Default::default(),
303 regioncx: regioncx.clone(),
304 used_mut: Default::default(),
305 used_mut_upvars: SmallVec::new(),
306 borrow_set: borrow_set.clone(),
309 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
310 region_names: RefCell::default(),
311 next_region_name: RefCell::new(1),
312 polonius_output: None,
314 promoted_mbcx.report_move_errors(move_errors);
315 errors_buffer = promoted_mbcx.errors_buffer;
319 let dominators = body.dominators();
321 let mut mbcx = MirBorrowckCtxt {
325 move_data: &mdpe.move_data,
328 locals_are_invalidated_at_exit,
329 fn_self_span_reported: Default::default(),
330 access_place_error_reported: Default::default(),
331 reservation_error_reported: Default::default(),
332 reservation_warnings: Default::default(),
333 move_error_reported: BTreeMap::new(),
334 uninitialized_error_reported: Default::default(),
337 used_mut: Default::default(),
338 used_mut_upvars: SmallVec::new(),
343 region_names: RefCell::default(),
344 next_region_name: RefCell::new(1),
348 // Compute and report region errors, if any.
349 mbcx.report_region_errors(nll_errors);
351 let results = BorrowckResults {
352 ever_inits: flow_ever_inits,
353 uninits: flow_uninits,
354 borrows: flow_borrows,
357 mbcx.report_move_errors(move_errors);
359 dataflow::visit_results(
361 traversal::reverse_postorder(&body).map(|(bb, _)| bb),
366 // Convert any reservation warnings into lints.
367 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
368 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
369 let mut initial_diag = mbcx.report_conflicting_borrow(location, (place, span), bk, &borrow);
371 let scope = mbcx.body.source_info(location).scope;
372 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
373 ClearCrossCrate::Set(data) => data.lint_root,
377 // Span and message don't matter; we overwrite them below anyway
378 mbcx.infcx.tcx.struct_span_lint_hir(
379 MUTABLE_BORROW_RESERVATION_CONFLICT,
383 let mut diag = lint.build("");
385 diag.message = initial_diag.styled_message().clone();
386 diag.span = initial_diag.span.clone();
388 diag.buffer(&mut mbcx.errors_buffer);
391 initial_diag.cancel();
394 // For each non-user used mutable variable, check if it's been assigned from
395 // a user-declared local. If so, then put that local into the used_mut set.
396 // Note that this set is expected to be small - only upvars from closures
397 // would have a chance of erroneously adding non-user-defined mutable vars
399 let temporary_used_locals: FxHashSet<Local> = mbcx
402 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
405 // For the remaining unused locals that are marked as mutable, we avoid linting any that
406 // were never initialized. These locals may have been removed as unreachable code; or will be
407 // linted as unused variables.
408 let unused_mut_locals =
409 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
410 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
412 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
413 let used_mut = mbcx.used_mut;
414 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
415 let local_decl = &mbcx.body.local_decls[local];
416 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
417 ClearCrossCrate::Set(data) => data.lint_root,
421 // Skip over locals that begin with an underscore or have no name
422 match mbcx.local_names[local] {
424 if name.as_str().starts_with('_') {
431 let span = local_decl.source_info.span;
432 if span.desugaring_kind().is_some() {
433 // If the `mut` arises as part of a desugaring, we should ignore it.
437 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
438 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
439 lint.build("variable does not need to be mutable")
440 .span_suggestion_short(
444 Applicability::MachineApplicable,
450 // Buffer any move errors that we collected and de-duplicated.
451 for (_, (_, diag)) in mbcx.move_error_reported {
452 diag.buffer(&mut mbcx.errors_buffer);
455 if !mbcx.errors_buffer.is_empty() {
456 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
458 for diag in mbcx.errors_buffer.drain(..) {
459 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
463 let result = BorrowCheckResult {
464 concrete_opaque_types: opaque_type_values,
465 closure_requirements: opt_closure_req,
466 used_mut_upvars: mbcx.used_mut_upvars,
469 debug!("do_mir_borrowck: result = {:#?}", result);
474 crate struct MirBorrowckCtxt<'cx, 'tcx> {
475 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
476 body: &'cx Body<'tcx>,
477 mir_def_id: LocalDefId,
478 move_data: &'cx MoveData<'tcx>,
480 /// Map from MIR `Location` to `LocationIndex`; created
481 /// when MIR borrowck begins.
482 location_table: &'cx LocationTable,
484 movable_generator: bool,
485 /// This keeps track of whether local variables are free-ed when the function
486 /// exits even without a `StorageDead`, which appears to be the case for
489 /// I'm not sure this is the right approach - @eddyb could you try and
491 locals_are_invalidated_at_exit: bool,
492 /// This field keeps track of when borrow errors are reported in the access_place function
493 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
494 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
495 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
497 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
498 /// This field keeps track of when borrow conflict errors are reported
499 /// for reservations, so that we don't report seemingly duplicate
500 /// errors for corresponding activations.
502 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
503 // but it is currently inconvenient to track down the `BorrowIndex`
504 // at the time we detect and report a reservation error.
505 reservation_error_reported: FxHashSet<Place<'tcx>>,
506 /// This fields keeps track of the `Span`s that we have
507 /// used to report extra information for `FnSelfUse`, to avoid
508 /// unnecessarily verbose errors.
509 fn_self_span_reported: FxHashSet<Span>,
510 /// Migration warnings to be reported for #56254. We delay reporting these
511 /// so that we can suppress the warning if there's a corresponding error
512 /// for the activation of the borrow.
513 reservation_warnings:
514 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
515 /// This field keeps track of move errors that are to be reported for given move indices.
517 /// There are situations where many errors can be reported for a single move out (see #53807)
518 /// and we want only the best of those errors.
520 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
521 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
522 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
523 /// all move errors have been reported, any diagnostics in this map are added to the buffer
526 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
527 /// when errors in the map are being re-added to the error buffer so that errors with the
528 /// same primary span come out in a consistent order.
529 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'cx>)>,
530 /// This field keeps track of errors reported in the checking of uninitialized variables,
531 /// so that we don't report seemingly duplicate errors.
532 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
533 /// Errors to be reported buffer
534 errors_buffer: Vec<Diagnostic>,
535 /// This field keeps track of all the local variables that are declared mut and are mutated.
536 /// Used for the warning issued by an unused mutable local variable.
537 used_mut: FxHashSet<Local>,
538 /// If the function we're checking is a closure, then we'll need to report back the list of
539 /// mutable upvars that have been used. This field keeps track of them.
540 used_mut_upvars: SmallVec<[Field; 8]>,
541 /// Region inference context. This contains the results from region inference and lets us e.g.
542 /// find out which CFG points are contained in each borrow region.
543 regioncx: Rc<RegionInferenceContext<'tcx>>,
545 /// The set of borrows extracted from the MIR
546 borrow_set: Rc<BorrowSet<'tcx>>,
548 /// Dominators for MIR
549 dominators: Dominators<BasicBlock>,
551 /// Information about upvars not necessarily preserved in types or MIR
554 /// Names of local (user) variables (extracted from `var_debug_info`).
555 local_names: IndexVec<Local, Option<Symbol>>,
557 /// Record the region names generated for each region in the given
558 /// MIR def so that we can reuse them later in help/error messages.
559 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
561 /// The counter for generating new region names.
562 next_region_name: RefCell<usize>,
564 /// Results of Polonius analysis.
565 polonius_output: Option<Rc<PoloniusOutput>>,
569 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
570 // 2. loans made in overlapping scopes do not conflict
571 // 3. assignments do not affect things loaned out as immutable
572 // 4. moves do not affect things loaned out in any way
573 impl<'cx, 'tcx> dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
574 type FlowState = Flows<'cx, 'tcx>;
576 fn visit_statement_before_primary_effect(
578 flow_state: &Flows<'cx, 'tcx>,
579 stmt: &'cx Statement<'tcx>,
582 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
583 let span = stmt.source_info.span;
585 self.check_activations(location, span, flow_state);
588 StatementKind::Assign(box (lhs, ref rhs)) => {
589 self.consume_rvalue(location, (rhs, span), flow_state);
591 self.mutate_place(location, (*lhs, span), Shallow(None), JustWrite, flow_state);
593 StatementKind::FakeRead(_, box ref place) => {
594 // Read for match doesn't access any memory and is used to
595 // assert that a place is safe and live. So we don't have to
596 // do any checks here.
598 // FIXME: Remove check that the place is initialized. This is
599 // needed for now because matches don't have never patterns yet.
600 // So this is the only place we prevent
604 self.check_if_path_or_subpath_is_moved(
606 InitializationRequiringAction::Use,
607 (place.as_ref(), span),
611 StatementKind::SetDiscriminant { place, variant_index: _ } => {
612 self.mutate_place(location, (**place, span), Shallow(None), JustWrite, flow_state);
614 StatementKind::LlvmInlineAsm(ref asm) => {
615 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
617 // FIXME(eddyb) indirect inline asm outputs should
618 // be encoded through MIR place derefs instead.
622 (Deep, Read(ReadKind::Copy)),
623 LocalMutationIsAllowed::No,
626 self.check_if_path_or_subpath_is_moved(
628 InitializationRequiringAction::Use,
629 (output.as_ref(), o.span),
636 if o.is_rw { Deep } else { Shallow(None) },
637 if o.is_rw { WriteAndRead } else { JustWrite },
642 for (_, input) in asm.inputs.iter() {
643 self.consume_operand(location, (input, span), flow_state);
647 | StatementKind::AscribeUserType(..)
648 | StatementKind::Retag { .. }
649 | StatementKind::StorageLive(..) => {
650 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
653 StatementKind::StorageDead(local) => {
656 (Place::from(*local), span),
657 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
658 LocalMutationIsAllowed::Yes,
665 fn visit_terminator_before_primary_effect(
667 flow_state: &Flows<'cx, 'tcx>,
668 term: &'cx Terminator<'tcx>,
671 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
672 let span = term.source_info.span;
674 self.check_activations(loc, span, flow_state);
677 TerminatorKind::SwitchInt { ref discr, switch_ty: _, values: _, targets: _ } => {
678 self.consume_operand(loc, (discr, span), flow_state);
680 TerminatorKind::Drop { place: ref drop_place, target: _, unwind: _ } => {
681 let tcx = self.infcx.tcx;
683 // Compute the type with accurate region information.
684 let drop_place_ty = drop_place.ty(self.body, self.infcx.tcx);
686 // Erase the regions.
687 let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
689 // "Lift" into the tcx -- once regions are erased, this type should be in the
690 // global arenas; this "lift" operation basically just asserts that is true, but
691 // that is useful later.
692 tcx.lift(&drop_place_ty).unwrap();
695 "visit_terminator_drop \
696 loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
697 loc, term, drop_place, drop_place_ty, span
703 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
704 LocalMutationIsAllowed::Yes,
708 TerminatorKind::DropAndReplace {
710 value: ref new_value,
714 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
715 self.consume_operand(loc, (new_value, span), flow_state);
717 TerminatorKind::Call {
725 self.consume_operand(loc, (func, span), flow_state);
727 self.consume_operand(loc, (arg, span), flow_state);
729 if let Some((dest, _ /*bb*/)) = *destination {
730 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
733 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
734 self.consume_operand(loc, (cond, span), flow_state);
735 use rustc_middle::mir::AssertKind;
736 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
737 self.consume_operand(loc, (len, span), flow_state);
738 self.consume_operand(loc, (index, span), flow_state);
742 TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
743 self.consume_operand(loc, (value, span), flow_state);
744 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
747 TerminatorKind::InlineAsm {
756 InlineAsmOperand::In { reg: _, ref value }
757 | InlineAsmOperand::Const { ref value } => {
758 self.consume_operand(loc, (value, span), flow_state);
760 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
761 if let Some(place) = place {
771 InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
772 self.consume_operand(loc, (in_value, span), flow_state);
773 if let Some(out_place) = out_place {
783 InlineAsmOperand::SymFn { value: _ }
784 | InlineAsmOperand::SymStatic { def_id: _ } => {}
789 TerminatorKind::Goto { target: _ }
790 | TerminatorKind::Abort
791 | TerminatorKind::Unreachable
792 | TerminatorKind::Resume
793 | TerminatorKind::Return
794 | TerminatorKind::GeneratorDrop
795 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
796 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
797 // no data used, thus irrelevant to borrowck
802 fn visit_terminator_after_primary_effect(
804 flow_state: &Flows<'cx, 'tcx>,
805 term: &'cx Terminator<'tcx>,
808 let span = term.source_info.span;
811 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
812 if self.movable_generator {
813 // Look for any active borrows to locals
814 let borrow_set = self.borrow_set.clone();
815 for i in flow_state.borrows.iter() {
816 let borrow = &borrow_set[i];
817 self.check_for_local_borrow(borrow, span);
822 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
823 // Returning from the function implicitly kills storage for all locals and statics.
824 // Often, the storage will already have been killed by an explicit
825 // StorageDead, but we don't always emit those (notably on unwind paths),
826 // so this "extra check" serves as a kind of backup.
827 let borrow_set = self.borrow_set.clone();
828 for i in flow_state.borrows.iter() {
829 let borrow = &borrow_set[i];
830 self.check_for_invalidation_at_exit(loc, borrow, span);
834 TerminatorKind::Abort
835 | TerminatorKind::Assert { .. }
836 | TerminatorKind::Call { .. }
837 | TerminatorKind::Drop { .. }
838 | TerminatorKind::DropAndReplace { .. }
839 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
840 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
841 | TerminatorKind::Goto { .. }
842 | TerminatorKind::SwitchInt { .. }
843 | TerminatorKind::Unreachable
844 | TerminatorKind::InlineAsm { .. } => {}
849 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
855 use self::AccessDepth::{Deep, Shallow};
856 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
858 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
859 enum ArtificialField {
864 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
866 /// From the RFC: "A *shallow* access means that the immediate
867 /// fields reached at P are accessed, but references or pointers
868 /// found within are not dereferenced. Right now, the only access
869 /// that is shallow is an assignment like `x = ...;`, which would
870 /// be a *shallow write* of `x`."
871 Shallow(Option<ArtificialField>),
873 /// From the RFC: "A *deep* access means that all data reachable
874 /// through the given place may be invalidated or accesses by
878 /// Access is Deep only when there is a Drop implementation that
879 /// can reach the data behind the reference.
883 /// Kind of access to a value: read or write
884 /// (For informational purposes only)
885 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
887 /// From the RFC: "A *read* means that the existing data may be
888 /// read, but will not be changed."
891 /// From the RFC: "A *write* means that the data may be mutated to
892 /// new values or otherwise invalidated (for example, it could be
893 /// de-initialized, as in a move operation).
896 /// For two-phase borrows, we distinguish a reservation (which is treated
897 /// like a Read) from an activation (which is treated like a write), and
898 /// each of those is furthermore distinguished from Reads/Writes above.
899 Reservation(WriteKind),
900 Activation(WriteKind, BorrowIndex),
903 /// Kind of read access to a value
904 /// (For informational purposes only)
905 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
911 /// Kind of write access to a value
912 /// (For informational purposes only)
913 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
916 MutableBorrow(BorrowKind),
921 /// When checking permissions for a place access, this flag is used to indicate that an immutable
922 /// local place can be mutated.
924 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
925 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
926 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
927 // `is_declared_mutable()`.
928 // - Take flow state into consideration in `is_assignable()` for local variables.
929 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
930 enum LocalMutationIsAllowed {
932 /// We want use of immutable upvars to cause a "write to immutable upvar"
933 /// error, not an "reassignment" error.
938 #[derive(Copy, Clone, Debug)]
939 enum InitializationRequiringAction {
948 struct RootPlace<'tcx> {
950 place_projection: &'tcx [PlaceElem<'tcx>],
951 is_local_mutation_allowed: LocalMutationIsAllowed,
954 impl InitializationRequiringAction {
955 fn as_noun(self) -> &'static str {
957 InitializationRequiringAction::Update => "update",
958 InitializationRequiringAction::Borrow => "borrow",
959 InitializationRequiringAction::MatchOn => "use", // no good noun
960 InitializationRequiringAction::Use => "use",
961 InitializationRequiringAction::Assignment => "assign",
962 InitializationRequiringAction::PartialAssignment => "assign to part",
966 fn as_verb_in_past_tense(self) -> &'static str {
968 InitializationRequiringAction::Update => "updated",
969 InitializationRequiringAction::Borrow => "borrowed",
970 InitializationRequiringAction::MatchOn => "matched on",
971 InitializationRequiringAction::Use => "used",
972 InitializationRequiringAction::Assignment => "assigned",
973 InitializationRequiringAction::PartialAssignment => "partially assigned",
978 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
979 fn body(&self) -> &'cx Body<'tcx> {
983 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
984 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
985 /// place is initialized and (b) it is not borrowed in some way that would prevent this
988 /// Returns `true` if an error is reported.
992 place_span: (Place<'tcx>, Span),
993 kind: (AccessDepth, ReadOrWrite),
994 is_local_mutation_allowed: LocalMutationIsAllowed,
995 flow_state: &Flows<'cx, 'tcx>,
999 if let Activation(_, borrow_index) = rw {
1000 if self.reservation_error_reported.contains(&place_span.0) {
1002 "skipping access_place for activation of invalid reservation \
1003 place: {:?} borrow_index: {:?}",
1004 place_span.0, borrow_index
1010 // Check is_empty() first because it's the common case, and doing that
1011 // way we avoid the clone() call.
1012 if !self.access_place_error_reported.is_empty()
1013 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
1016 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
1022 let mutability_error = self.check_access_permissions(
1025 is_local_mutation_allowed,
1029 let conflict_error =
1030 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
1032 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
1033 // Suppress this warning when there's an error being emitted for the
1034 // same borrow: fixing the error is likely to fix the warning.
1035 self.reservation_warnings.remove(&borrow_idx);
1038 if conflict_error || mutability_error {
1039 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
1041 self.access_place_error_reported.insert((place_span.0, place_span.1));
1045 fn check_access_for_conflict(
1048 place_span: (Place<'tcx>, Span),
1051 flow_state: &Flows<'cx, 'tcx>,
1054 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
1055 location, place_span, sd, rw,
1058 let mut error_reported = false;
1059 let tcx = self.infcx.tcx;
1060 let body = self.body;
1061 let borrow_set = self.borrow_set.clone();
1063 // Use polonius output if it has been enabled.
1064 let polonius_output = self.polonius_output.clone();
1065 let borrows_in_scope = if let Some(polonius) = &polonius_output {
1066 let location = self.location_table.start_index(location);
1067 Either::Left(polonius.errors_at(location).iter().copied())
1069 Either::Right(flow_state.borrows.iter())
1072 each_borrow_involving_path(
1080 |this, borrow_index, borrow| match (rw, borrow.kind) {
1081 // Obviously an activation is compatible with its own
1082 // reservation (or even prior activating uses of same
1083 // borrow); so don't check if they interfere.
1085 // NOTE: *reservations* do conflict with themselves;
1086 // thus aren't injecting unsoundenss w/ this check.)
1087 (Activation(_, activating), _) if activating == borrow_index => {
1089 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1090 skipping {:?} b/c activation of same borrow_index",
1094 (borrow_index, borrow),
1099 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1101 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1102 BorrowKind::Unique | BorrowKind::Mut { .. },
1103 ) => Control::Continue,
1105 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1106 // Handled by initialization checks.
1110 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1111 // Reading from mere reservations of mutable-borrows is OK.
1112 if !is_active(&this.dominators, borrow, location) {
1113 assert!(allow_two_phase_borrow(borrow.kind));
1114 return Control::Continue;
1117 error_reported = true;
1120 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1121 .buffer(&mut this.errors_buffer);
1123 ReadKind::Borrow(bk) => {
1124 this.report_conflicting_borrow(location, place_span, bk, borrow)
1125 .buffer(&mut this.errors_buffer);
1132 Reservation(WriteKind::MutableBorrow(bk)),
1133 BorrowKind::Shallow | BorrowKind::Shared,
1134 ) if { tcx.migrate_borrowck() && this.borrow_set.contains(&location) } => {
1135 let bi = this.borrow_set.get_index_of(&location).unwrap();
1137 "recording invalid reservation of place: {:?} with \
1138 borrow index {:?} as warning",
1141 // rust-lang/rust#56254 - This was previously permitted on
1142 // the 2018 edition so we emit it as a warning. We buffer
1143 // these sepately so that we only emit a warning if borrow
1144 // checking was otherwise successful.
1145 this.reservation_warnings
1146 .insert(bi, (place_span.0, place_span.1, location, bk, borrow.clone()));
1148 // Don't suppress actual errors.
1152 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1154 Reservation(..) => {
1156 "recording invalid reservation of \
1160 this.reservation_error_reported.insert(place_span.0);
1162 Activation(_, activating) => {
1164 "observing check_place for activation of \
1165 borrow_index: {:?}",
1169 Read(..) | Write(..) => {}
1172 error_reported = true;
1174 WriteKind::MutableBorrow(bk) => {
1175 this.report_conflicting_borrow(location, place_span, bk, borrow)
1176 .buffer(&mut this.errors_buffer);
1178 WriteKind::StorageDeadOrDrop => this
1179 .report_borrowed_value_does_not_live_long_enough(
1185 WriteKind::Mutate => {
1186 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1188 WriteKind::Move => {
1189 this.report_move_out_while_borrowed(location, place_span, borrow)
1203 place_span: (Place<'tcx>, Span),
1206 flow_state: &Flows<'cx, 'tcx>,
1208 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1210 MutateMode::WriteAndRead => {
1211 self.check_if_path_or_subpath_is_moved(
1213 InitializationRequiringAction::Update,
1214 (place_span.0.as_ref(), place_span.1),
1218 MutateMode::JustWrite => {
1219 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1223 // Special case: you can assign a immutable local variable
1224 // (e.g., `x = ...`) so long as it has never been initialized
1225 // before (at this point in the flow).
1226 if let Some(local) = place_span.0.as_local() {
1227 if let Mutability::Not = self.body.local_decls[local].mutability {
1228 // check for reassignments to immutable local variables
1229 self.check_if_reassignment_to_immutable_state(
1230 location, local, place_span, flow_state,
1236 // Otherwise, use the normal access permission rules.
1240 (kind, Write(WriteKind::Mutate)),
1241 LocalMutationIsAllowed::No,
1249 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1250 flow_state: &Flows<'cx, 'tcx>,
1253 Rvalue::Ref(_ /*rgn*/, bk, place) => {
1254 let access_kind = match bk {
1255 BorrowKind::Shallow => {
1256 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1258 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1259 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1260 let wk = WriteKind::MutableBorrow(bk);
1261 if allow_two_phase_borrow(bk) {
1262 (Deep, Reservation(wk))
1273 LocalMutationIsAllowed::No,
1277 let action = if bk == BorrowKind::Shallow {
1278 InitializationRequiringAction::MatchOn
1280 InitializationRequiringAction::Borrow
1283 self.check_if_path_or_subpath_is_moved(
1286 (place.as_ref(), span),
1291 Rvalue::AddressOf(mutability, place) => {
1292 let access_kind = match mutability {
1293 Mutability::Mut => (
1295 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1296 allow_two_phase_borrow: false,
1299 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1306 LocalMutationIsAllowed::No,
1310 self.check_if_path_or_subpath_is_moved(
1312 InitializationRequiringAction::Borrow,
1313 (place.as_ref(), span),
1318 Rvalue::ThreadLocalRef(_) => {}
1320 Rvalue::Use(ref operand)
1321 | Rvalue::Repeat(ref operand, _)
1322 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1323 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1324 self.consume_operand(location, (operand, span), flow_state)
1327 Rvalue::Len(place) | Rvalue::Discriminant(place) => {
1328 let af = match *rvalue {
1329 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1330 Rvalue::Discriminant(..) => None,
1331 _ => unreachable!(),
1336 (Shallow(af), Read(ReadKind::Copy)),
1337 LocalMutationIsAllowed::No,
1340 self.check_if_path_or_subpath_is_moved(
1342 InitializationRequiringAction::Use,
1343 (place.as_ref(), span),
1348 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1349 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1350 self.consume_operand(location, (operand1, span), flow_state);
1351 self.consume_operand(location, (operand2, span), flow_state);
1354 Rvalue::NullaryOp(_op, _ty) => {
1355 // nullary ops take no dynamic input; no borrowck effect.
1357 // FIXME: is above actually true? Do we want to track
1358 // the fact that uninitialized data can be created via
1362 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1363 // We need to report back the list of mutable upvars that were
1364 // moved into the closure and subsequently used by the closure,
1365 // in order to populate our used_mut set.
1366 match **aggregate_kind {
1367 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1368 let BorrowCheckResult { used_mut_upvars, .. } =
1369 self.infcx.tcx.mir_borrowck(def_id.expect_local());
1370 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1371 for field in used_mut_upvars {
1372 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1375 AggregateKind::Adt(..)
1376 | AggregateKind::Array(..)
1377 | AggregateKind::Tuple { .. } => (),
1380 for operand in operands {
1381 self.consume_operand(location, (operand, span), flow_state);
1387 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1388 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1389 if !place.projection.is_empty() {
1390 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1391 this.used_mut_upvars.push(field);
1394 this.used_mut.insert(place.local);
1398 // This relies on the current way that by-value
1399 // captures of a closure are copied/moved directly
1400 // when generating MIR.
1402 Operand::Move(place) | Operand::Copy(place) => {
1403 match place.as_local() {
1404 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1405 if self.body.local_decls[local].ty.is_mutable_ptr() {
1406 // The variable will be marked as mutable by the borrow.
1409 // This is an edge case where we have a `move` closure
1410 // inside a non-move closure, and the inner closure
1411 // contains a mutation:
1414 // || { move || { i += 1; }; };
1416 // In this case our usual strategy of assuming that the
1417 // variable will be captured by mutable reference is
1418 // wrong, since `i` can be copied into the inner
1419 // closure from a shared reference.
1421 // As such we have to search for the local that this
1422 // capture comes from and mark it as being used as mut.
1424 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1425 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1426 &self.move_data.inits[init_index]
1428 bug!("temporary should be initialized exactly once")
1431 let loc = match init.location {
1432 InitLocation::Statement(stmt) => stmt,
1433 _ => bug!("temporary initialized in arguments"),
1436 let body = self.body;
1437 let bbd = &body[loc.block];
1438 let stmt = &bbd.statements[loc.statement_index];
1439 debug!("temporary assigned in: stmt={:?}", stmt);
1441 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1443 propagate_closure_used_mut_place(self, source);
1446 "closures should only capture user variables \
1447 or references to user variables"
1451 _ => propagate_closure_used_mut_place(self, place),
1454 Operand::Constant(..) => {}
1461 (operand, span): (&'cx Operand<'tcx>, Span),
1462 flow_state: &Flows<'cx, 'tcx>,
1465 Operand::Copy(place) => {
1466 // copy of place: check if this is "copy of frozen path"
1467 // (FIXME: see check_loans.rs)
1471 (Deep, Read(ReadKind::Copy)),
1472 LocalMutationIsAllowed::No,
1476 // Finally, check if path was already moved.
1477 self.check_if_path_or_subpath_is_moved(
1479 InitializationRequiringAction::Use,
1480 (place.as_ref(), span),
1484 Operand::Move(place) => {
1485 // move of place: check if this is move of already borrowed path
1489 (Deep, Write(WriteKind::Move)),
1490 LocalMutationIsAllowed::Yes,
1494 // Finally, check if path was already moved.
1495 self.check_if_path_or_subpath_is_moved(
1497 InitializationRequiringAction::Use,
1498 (place.as_ref(), span),
1502 Operand::Constant(_) => {}
1506 /// Checks whether a borrow of this place is invalidated when the function
1508 fn check_for_invalidation_at_exit(
1511 borrow: &BorrowData<'tcx>,
1514 debug!("check_for_invalidation_at_exit({:?})", borrow);
1515 let place = borrow.borrowed_place;
1516 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1518 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1519 // we just know that all locals are dropped at function exit (otherwise
1520 // we'll have a memory leak) and assume that all statics have a destructor.
1522 // FIXME: allow thread-locals to borrow other thread locals?
1524 let (might_be_alive, will_be_dropped) =
1525 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1526 // Thread-locals might be dropped after the function exits
1527 // We have to dereference the outer reference because
1528 // borrows don't conflict behind shared references.
1529 root_place.projection = DEREF_PROJECTION;
1532 (false, self.locals_are_invalidated_at_exit)
1535 if !will_be_dropped {
1536 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1540 let sd = if might_be_alive { Deep } else { Shallow(None) };
1542 if places_conflict::borrow_conflicts_with_place(
1549 places_conflict::PlaceConflictBias::Overlap,
1551 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1552 // FIXME: should be talking about the region lifetime instead
1553 // of just a span here.
1554 let span = self.infcx.tcx.sess.source_map().end_point(span);
1555 self.report_borrowed_value_does_not_live_long_enough(
1564 /// Reports an error if this is a borrow of local data.
1565 /// This is called for all Yield expressions on movable generators
1566 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1567 debug!("check_for_local_borrow({:?})", borrow);
1569 if borrow_of_local_data(borrow.borrowed_place) {
1570 let err = self.cannot_borrow_across_generator_yield(
1571 self.retrieve_borrow_spans(borrow).var_or_use(),
1575 err.buffer(&mut self.errors_buffer);
1579 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1580 // Two-phase borrow support: For each activation that is newly
1581 // generated at this statement, check if it interferes with
1583 let borrow_set = self.borrow_set.clone();
1584 for &borrow_index in borrow_set.activations_at_location(location) {
1585 let borrow = &borrow_set[borrow_index];
1587 // only mutable borrows should be 2-phase
1588 assert!(match borrow.kind {
1589 BorrowKind::Shared | BorrowKind::Shallow => false,
1590 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1595 (borrow.borrowed_place, span),
1596 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1597 LocalMutationIsAllowed::No,
1600 // We do not need to call `check_if_path_or_subpath_is_moved`
1601 // again, as we already called it when we made the
1602 // initial reservation.
1606 fn check_if_reassignment_to_immutable_state(
1610 place_span: (Place<'tcx>, Span),
1611 flow_state: &Flows<'cx, 'tcx>,
1613 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1615 // Check if any of the initializiations of `local` have happened yet:
1616 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1617 // And, if so, report an error.
1618 let init = &self.move_data.inits[init_index];
1619 let span = init.span(&self.body);
1620 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1624 fn check_if_full_path_is_moved(
1627 desired_action: InitializationRequiringAction,
1628 place_span: (PlaceRef<'tcx>, Span),
1629 flow_state: &Flows<'cx, 'tcx>,
1631 let maybe_uninits = &flow_state.uninits;
1635 // 1. Move of `a.b.c`, use of `a.b.c`
1636 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1637 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1638 // partial initialization support, one might have `a.x`
1639 // initialized but not `a.b`.
1643 // 4. Move of `a.b.c`, use of `a.b.d`
1644 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1645 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1646 // must have been initialized for the use to be sound.
1647 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1649 // The dataflow tracks shallow prefixes distinctly (that is,
1650 // field-accesses on P distinctly from P itself), in order to
1651 // track substructure initialization separately from the whole
1654 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1655 // which we have a MovePath is `a.b`, then that means that the
1656 // initialization state of `a.b` is all we need to inspect to
1657 // know if `a.b.c` is valid (and from that we infer that the
1658 // dereference and `.d` access is also valid, since we assume
1659 // `a.b.c` is assigned a reference to a initialized and
1660 // well-formed record structure.)
1662 // Therefore, if we seek out the *closest* prefix for which we
1663 // have a MovePath, that should capture the initialization
1664 // state for the place scenario.
1666 // This code covers scenarios 1, 2, and 3.
1668 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1669 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1670 if maybe_uninits.contains(mpi) {
1671 self.report_use_of_moved_or_uninitialized(
1674 (prefix, place_span.0, place_span.1),
1677 } // Only query longest prefix with a MovePath, not further
1678 // ancestors; dataflow recurs on children when parents
1679 // move (to support partial (re)inits).
1681 // (I.e., querying parents breaks scenario 7; but may want
1682 // to do such a query based on partial-init feature-gate.)
1685 /// Subslices correspond to multiple move paths, so we iterate through the
1686 /// elements of the base array. For each element we check
1688 /// * Does this element overlap with our slice.
1689 /// * Is any part of it uninitialized.
1690 fn check_if_subslice_element_is_moved(
1693 desired_action: InitializationRequiringAction,
1694 place_span: (PlaceRef<'tcx>, Span),
1695 maybe_uninits: &BitSet<MovePathIndex>,
1699 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1700 let move_paths = &self.move_data.move_paths;
1702 let root_path = &move_paths[mpi];
1703 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1704 let last_proj = child_move_path.place.projection.last().unwrap();
1705 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1706 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1708 if (from..to).contains(offset) {
1710 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1711 maybe_uninits.contains(mpi)
1714 if let Some(uninit_child) = uninit_child {
1715 self.report_use_of_moved_or_uninitialized(
1718 (place_span.0, place_span.0, place_span.1),
1721 return; // don't bother finding other problems.
1729 fn check_if_path_or_subpath_is_moved(
1732 desired_action: InitializationRequiringAction,
1733 place_span: (PlaceRef<'tcx>, Span),
1734 flow_state: &Flows<'cx, 'tcx>,
1736 let maybe_uninits = &flow_state.uninits;
1740 // 1. Move of `a.b.c`, use of `a` or `a.b`
1741 // partial initialization support, one might have `a.x`
1742 // initialized but not `a.b`.
1743 // 2. All bad scenarios from `check_if_full_path_is_moved`
1747 // 3. Move of `a.b.c`, use of `a.b.d`
1748 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1749 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1750 // must have been initialized for the use to be sound.
1751 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1753 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1755 if let [base_proj @ .., ProjectionElem::Subslice { from, to, from_end: false }] =
1756 place_span.0.projection
1759 Place::ty_from(place_span.0.local, base_proj, self.body(), self.infcx.tcx);
1760 if let ty::Array(..) = place_ty.ty.kind {
1761 let array_place = PlaceRef { local: place_span.0.local, projection: base_proj };
1762 self.check_if_subslice_element_is_moved(
1765 (array_place, place_span.1),
1774 // A move of any shallow suffix of `place` also interferes
1775 // with an attempt to use `place`. This is scenario 3 above.
1777 // (Distinct from handling of scenarios 1+2+4 above because
1778 // `place` does not interfere with suffixes of its prefixes,
1779 // e.g., `a.b.c` does not interfere with `a.b.d`)
1781 // This code covers scenario 1.
1783 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1784 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1785 let uninit_mpi = self
1787 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1789 if let Some(uninit_mpi) = uninit_mpi {
1790 self.report_use_of_moved_or_uninitialized(
1793 (place_span.0, place_span.0, place_span.1),
1796 return; // don't bother finding other problems.
1801 /// Currently MoveData does not store entries for all places in
1802 /// the input MIR. For example it will currently filter out
1803 /// places that are Copy; thus we do not track places of shared
1804 /// reference type. This routine will walk up a place along its
1805 /// prefixes, searching for a foundational place that *is*
1806 /// tracked in the MoveData.
1808 /// An Err result includes a tag indicated why the search failed.
1809 /// Currently this can only occur if the place is built off of a
1810 /// static variable, as we do not track those in the MoveData.
1811 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1812 match self.move_data.rev_lookup.find(place) {
1813 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1814 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1816 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1820 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1821 // If returns None, then there is no move path corresponding
1822 // to a direct owner of `place` (which means there is nothing
1823 // that borrowck tracks for its analysis).
1825 match self.move_data.rev_lookup.find(place) {
1826 LookupResult::Parent(_) => None,
1827 LookupResult::Exact(mpi) => Some(mpi),
1831 fn check_if_assigned_path_is_moved(
1834 (place, span): (Place<'tcx>, Span),
1835 flow_state: &Flows<'cx, 'tcx>,
1837 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1839 // None case => assigning to `x` does not require `x` be initialized.
1840 let mut cursor = &*place.projection.as_ref();
1841 while let [proj_base @ .., elem] = cursor {
1845 ProjectionElem::Index(_/*operand*/) |
1846 ProjectionElem::ConstantIndex { .. } |
1847 // assigning to P[i] requires P to be valid.
1848 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1849 // assigning to (P->variant) is okay if assigning to `P` is okay
1851 // FIXME: is this true even if P is a adt with a dtor?
1854 // assigning to (*P) requires P to be initialized
1855 ProjectionElem::Deref => {
1856 self.check_if_full_path_is_moved(
1857 location, InitializationRequiringAction::Use,
1860 projection: proj_base,
1861 }, span), flow_state);
1862 // (base initialized; no need to
1867 ProjectionElem::Subslice { .. } => {
1868 panic!("we don't allow assignments to subslices, location: {:?}",
1872 ProjectionElem::Field(..) => {
1873 // if type of `P` has a dtor, then
1874 // assigning to `P.f` requires `P` itself
1875 // be already initialized
1876 let tcx = self.infcx.tcx;
1877 let base_ty = Place::ty_from(place.local, proj_base, self.body(), tcx).ty;
1878 match base_ty.kind {
1879 ty::Adt(def, _) if def.has_dtor(tcx) => {
1880 self.check_if_path_or_subpath_is_moved(
1881 location, InitializationRequiringAction::Assignment,
1884 projection: proj_base,
1885 }, span), flow_state);
1887 // (base initialized; no need to
1892 // Once `let s; s.x = V; read(s.x);`,
1893 // is allowed, remove this match arm.
1894 ty::Adt(..) | ty::Tuple(..) => {
1895 check_parent_of_field(self, location, PlaceRef {
1897 projection: proj_base,
1898 }, span, flow_state);
1900 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1901 // partial initialization, do not complain about unnecessary `mut` on
1902 // an attempt to do a partial initialization.
1903 self.used_mut.insert(place.local);
1912 fn check_parent_of_field<'cx, 'tcx>(
1913 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1915 base: PlaceRef<'tcx>,
1917 flow_state: &Flows<'cx, 'tcx>,
1919 // rust-lang/rust#21232: Until Rust allows reads from the
1920 // initialized parts of partially initialized structs, we
1921 // will, starting with the 2018 edition, reject attempts
1922 // to write to structs that are not fully initialized.
1924 // In other words, *until* we allow this:
1926 // 1. `let mut s; s.x = Val; read(s.x);`
1928 // we will for now disallow this:
1930 // 2. `let mut s; s.x = Val;`
1934 // 3. `let mut s = ...; drop(s); s.x=Val;`
1936 // This does not use check_if_path_or_subpath_is_moved,
1937 // because we want to *allow* reinitializations of fields:
1938 // e.g., want to allow
1940 // `let mut s = ...; drop(s.x); s.x=Val;`
1942 // This does not use check_if_full_path_is_moved on
1943 // `base`, because that would report an error about the
1944 // `base` as a whole, but in this scenario we *really*
1945 // want to report an error about the actual thing that was
1946 // moved, which may be some prefix of `base`.
1948 // Shallow so that we'll stop at any dereference; we'll
1949 // report errors about issues with such bases elsewhere.
1950 let maybe_uninits = &flow_state.uninits;
1952 // Find the shortest uninitialized prefix you can reach
1953 // without going over a Deref.
1954 let mut shortest_uninit_seen = None;
1955 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1956 let mpi = match this.move_path_for_place(prefix) {
1961 if maybe_uninits.contains(mpi) {
1963 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1964 shortest_uninit_seen,
1967 shortest_uninit_seen = Some((prefix, mpi));
1969 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1973 if let Some((prefix, mpi)) = shortest_uninit_seen {
1974 // Check for a reassignment into a uninitialized field of a union (for example,
1975 // after a move out). In this case, do not report a error here. There is an
1976 // exception, if this is the first assignment into the union (that is, there is
1977 // no move out from an earlier location) then this is an attempt at initialization
1978 // of the union - we should error in that case.
1979 let tcx = this.infcx.tcx;
1980 if let ty::Adt(def, _) =
1981 Place::ty_from(base.local, base.projection, this.body(), tcx).ty.kind
1984 if this.move_data.path_map[mpi].iter().any(|moi| {
1985 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1992 this.report_use_of_moved_or_uninitialized(
1994 InitializationRequiringAction::PartialAssignment,
1995 (prefix, base, span),
2002 /// Checks the permissions for the given place and read or write kind
2004 /// Returns `true` if an error is reported.
2005 fn check_access_permissions(
2007 (place, span): (Place<'tcx>, Span),
2009 is_local_mutation_allowed: LocalMutationIsAllowed,
2010 flow_state: &Flows<'cx, 'tcx>,
2014 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
2015 place, kind, is_local_mutation_allowed
2022 Reservation(WriteKind::MutableBorrow(
2023 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
2025 | Write(WriteKind::MutableBorrow(
2026 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
2028 let is_local_mutation_allowed = match borrow_kind {
2029 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
2030 BorrowKind::Mut { .. } => is_local_mutation_allowed,
2031 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
2033 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
2035 self.add_used_mut(root_place, flow_state);
2039 error_access = AccessKind::MutableBorrow;
2040 the_place_err = place_err;
2044 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
2045 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
2047 self.add_used_mut(root_place, flow_state);
2051 error_access = AccessKind::Mutate;
2052 the_place_err = place_err;
2059 | WriteKind::StorageDeadOrDrop
2060 | WriteKind::MutableBorrow(BorrowKind::Shared)
2061 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2065 | WriteKind::StorageDeadOrDrop
2066 | WriteKind::MutableBorrow(BorrowKind::Shared)
2067 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2069 if let (Err(_), true) = (
2070 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
2071 self.errors_buffer.is_empty(),
2073 // rust-lang/rust#46908: In pure NLL mode this code path should be
2074 // unreachable, but we use `delay_span_bug` because we can hit this when
2075 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
2076 // enabled. We don't want to ICE for that case, as other errors will have
2077 // been emitted (#52262).
2078 self.infcx.tcx.sess.delay_span_bug(
2081 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2089 // permission checks are done at Reservation point.
2095 | BorrowKind::Mut { .. }
2096 | BorrowKind::Shared
2097 | BorrowKind::Shallow,
2101 // Access authorized
2106 // rust-lang/rust#21232, #54986: during period where we reject
2107 // partial initialization, do not complain about mutability
2108 // errors except for actual mutation (as opposed to an attempt
2109 // to do a partial initialization).
2110 let previously_initialized =
2111 self.is_local_ever_initialized(place.local, flow_state).is_some();
2113 // at this point, we have set up the error reporting state.
2114 if previously_initialized {
2115 self.report_mutability_error(place, span, the_place_err, error_access, location);
2122 fn is_local_ever_initialized(
2125 flow_state: &Flows<'cx, 'tcx>,
2126 ) -> Option<InitIndex> {
2127 let mpi = self.move_data.rev_lookup.find_local(local);
2128 let ii = &self.move_data.init_path_map[mpi];
2130 if flow_state.ever_inits.contains(index) {
2137 /// Adds the place into the used mutable variables set
2138 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2140 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2141 // If the local may have been initialized, and it is now currently being
2142 // mutated, then it is justified to be annotated with the `mut`
2143 // keyword, since the mutation may be a possible reassignment.
2144 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2145 && self.is_local_ever_initialized(local, flow_state).is_some()
2147 self.used_mut.insert(local);
2152 place_projection: _,
2153 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2157 place_projection: place_projection @ [.., _],
2158 is_local_mutation_allowed: _,
2160 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2162 projection: place_projection,
2164 self.used_mut_upvars.push(field);
2170 /// Whether this value can be written or borrowed mutably.
2171 /// Returns the root place if the place passed in is a projection.
2174 place: PlaceRef<'tcx>,
2175 is_local_mutation_allowed: LocalMutationIsAllowed,
2176 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2178 PlaceRef { local, projection: [] } => {
2179 let local = &self.body.local_decls[local];
2180 match local.mutability {
2181 Mutability::Not => match is_local_mutation_allowed {
2182 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2183 place_local: place.local,
2184 place_projection: place.projection,
2185 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2187 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2188 place_local: place.local,
2189 place_projection: place.projection,
2190 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2192 LocalMutationIsAllowed::No => Err(place),
2194 Mutability::Mut => Ok(RootPlace {
2195 place_local: place.local,
2196 place_projection: place.projection,
2197 is_local_mutation_allowed,
2201 PlaceRef { local: _, projection: [proj_base @ .., elem] } => {
2203 ProjectionElem::Deref => {
2205 Place::ty_from(place.local, proj_base, self.body(), self.infcx.tcx).ty;
2207 // Check the kind of deref to decide
2208 match base_ty.kind {
2209 ty::Ref(_, _, mutbl) => {
2211 // Shared borrowed data is never mutable
2212 hir::Mutability::Not => Err(place),
2213 // Mutably borrowed data is mutable, but only if we have a
2214 // unique path to the `&mut`
2215 hir::Mutability::Mut => {
2216 let mode = match self.is_upvar_field_projection(place) {
2217 Some(field) if self.upvars[field.index()].by_ref => {
2218 is_local_mutation_allowed
2220 _ => LocalMutationIsAllowed::Yes,
2224 PlaceRef { local: place.local, projection: proj_base },
2230 ty::RawPtr(tnm) => {
2232 // `*const` raw pointers are not mutable
2233 hir::Mutability::Not => Err(place),
2234 // `*mut` raw pointers are always mutable, regardless of
2235 // context. The users have to check by themselves.
2236 hir::Mutability::Mut => Ok(RootPlace {
2237 place_local: place.local,
2238 place_projection: place.projection,
2239 is_local_mutation_allowed,
2243 // `Box<T>` owns its content, so mutable if its location is mutable
2244 _ if base_ty.is_box() => self.is_mutable(
2245 PlaceRef { local: place.local, projection: proj_base },
2246 is_local_mutation_allowed,
2248 // Deref should only be for reference, pointers or boxes
2249 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2252 // All other projections are owned by their base path, so mutable if
2253 // base path is mutable
2254 ProjectionElem::Field(..)
2255 | ProjectionElem::Index(..)
2256 | ProjectionElem::ConstantIndex { .. }
2257 | ProjectionElem::Subslice { .. }
2258 | ProjectionElem::Downcast(..) => {
2259 let upvar_field_projection = self.is_upvar_field_projection(place);
2260 if let Some(field) = upvar_field_projection {
2261 let upvar = &self.upvars[field.index()];
2263 "upvar.mutability={:?} local_mutation_is_allowed={:?} \
2265 upvar, is_local_mutation_allowed, place
2267 match (upvar.mutability, is_local_mutation_allowed) {
2270 LocalMutationIsAllowed::No
2271 | LocalMutationIsAllowed::ExceptUpvars,
2273 (Mutability::Not, LocalMutationIsAllowed::Yes)
2274 | (Mutability::Mut, _) => {
2275 // Subtle: this is an upvar
2276 // reference, so it looks like
2277 // `self.foo` -- we want to double
2278 // check that the location `*self`
2279 // is mutable (i.e., this is not a
2280 // `Fn` closure). But if that
2281 // check succeeds, we want to
2282 // *blame* the mutability on
2283 // `place` (that is,
2284 // `self.foo`). This is used to
2285 // propagate the info about
2286 // whether mutability declarations
2287 // are used outwards, so that we register
2288 // the outer variable as mutable. Otherwise a
2289 // test like this fails to record the `mut`
2293 // fn foo<F: FnOnce()>(_f: F) { }
2295 // let var = Vec::new();
2301 let _ = self.is_mutable(
2302 PlaceRef { local: place.local, projection: proj_base },
2303 is_local_mutation_allowed,
2306 place_local: place.local,
2307 place_projection: place.projection,
2308 is_local_mutation_allowed,
2314 PlaceRef { local: place.local, projection: proj_base },
2315 is_local_mutation_allowed,
2324 /// If `place` is a field projection, and the field is being projected from a closure type,
2325 /// then returns the index of the field being projected. Note that this closure will always
2326 /// be `self` in the current MIR, because that is the only time we directly access the fields
2327 /// of a closure type.
2328 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2329 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2333 /// The degree of overlap between 2 places for borrow-checking.
2335 /// The places might partially overlap - in this case, we give
2336 /// up and say that they might conflict. This occurs when
2337 /// different fields of a union are borrowed. For example,
2338 /// if `u` is a union, we have no way of telling how disjoint
2339 /// `u.a.x` and `a.b.y` are.
2341 /// The places have the same type, and are either completely disjoint
2342 /// or equal - i.e., they can't "partially" overlap as can occur with
2343 /// unions. This is the "base case" on which we recur for extensions
2346 /// The places are disjoint, so we know all extensions of them
2347 /// will also be disjoint.