1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 #![feature(bool_to_option)]
4 #![feature(box_patterns)]
5 #![feature(crate_visibility_modifier)]
6 #![feature(format_args_capture)]
7 #![feature(in_band_lifetimes)]
10 #![feature(min_specialization)]
11 #![feature(stmt_expr_attributes)]
12 #![feature(trusted_step)]
13 #![feature(try_blocks)]
14 #![recursion_limit = "256"]
17 extern crate rustc_middle;
21 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
22 use rustc_data_structures::graph::dominators::Dominators;
23 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorReported};
25 use rustc_hir::def_id::LocalDefId;
27 use rustc_index::bit_set::BitSet;
28 use rustc_index::vec::IndexVec;
29 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
30 use rustc_middle::mir::{
31 traversal, Body, ClearCrossCrate, Local, Location, Mutability, Operand, Place, PlaceElem,
32 PlaceRef, VarDebugInfoContents,
34 use rustc_middle::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
35 use rustc_middle::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
36 use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
37 use rustc_middle::ty::query::Providers;
38 use rustc_middle::ty::{self, CapturedPlace, ParamEnv, RegionVid, TyCtxt};
39 use rustc_session::lint::builtin::{MUTABLE_BORROW_RESERVATION_CONFLICT, UNUSED_MUT};
40 use rustc_span::{Span, Symbol, DUMMY_SP};
43 use smallvec::SmallVec;
44 use std::cell::RefCell;
45 use std::collections::BTreeMap;
50 use rustc_mir_dataflow::impls::{
51 EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
53 use rustc_mir_dataflow::move_paths::{InitIndex, MoveOutIndex, MovePathIndex};
54 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
55 use rustc_mir_dataflow::Analysis;
56 use rustc_mir_dataflow::MoveDataParamEnv;
58 use self::diagnostics::{AccessKind, RegionName};
59 use self::location::LocationTable;
60 use self::prefixes::PrefixSet;
61 use self::MutateMode::{JustWrite, WriteAndRead};
64 use self::path_utils::*;
68 mod constraint_generation;
76 mod member_constraints;
85 mod universal_regions;
88 // A public API provided for the Rust compiler consumers.
91 use borrow_set::{BorrowData, BorrowSet};
92 use dataflow::{BorrowIndex, BorrowckFlowState as Flows, BorrowckResults, Borrows};
93 use nll::{PoloniusOutput, ToRegionVid};
94 use place_ext::PlaceExt;
95 use places_conflict::{places_conflict, PlaceConflictBias};
96 use region_infer::RegionInferenceContext;
98 // FIXME(eddyb) perhaps move this somewhere more centrally.
101 place: CapturedPlace<'tcx>,
103 /// If true, the capture is behind a reference.
107 const DEREF_PROJECTION: &[PlaceElem<'_>; 1] = &[ProjectionElem::Deref];
109 pub fn provide(providers: &mut Providers) {
110 *providers = Providers {
111 mir_borrowck: |tcx, did| {
112 if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
113 tcx.mir_borrowck_const_arg(def)
115 mir_borrowck(tcx, ty::WithOptConstParam::unknown(did))
118 mir_borrowck_const_arg: |tcx, (did, param_did)| {
119 mir_borrowck(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
125 fn mir_borrowck<'tcx>(
127 def: ty::WithOptConstParam<LocalDefId>,
128 ) -> &'tcx BorrowCheckResult<'tcx> {
129 let (input_body, promoted) = tcx.mir_promoted(def);
130 debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
132 let opt_closure_req = tcx.infer_ctxt().with_opaque_type_inference(def.did).enter(|infcx| {
133 let input_body: &Body<'_> = &input_body.borrow();
134 let promoted: &IndexVec<_, _> = &promoted.borrow();
135 do_mir_borrowck(&infcx, input_body, promoted, false).0
137 debug!("mir_borrowck done");
139 tcx.arena.alloc(opt_closure_req)
142 /// Perform the actual borrow checking.
144 /// If `return_body_with_facts` is true, then return the body with non-erased
145 /// region ids on which the borrow checking was performed together with Polonius
147 #[instrument(skip(infcx, input_body, input_promoted), level = "debug")]
148 fn do_mir_borrowck<'a, 'tcx>(
149 infcx: &InferCtxt<'a, 'tcx>,
150 input_body: &Body<'tcx>,
151 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
152 return_body_with_facts: bool,
153 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
154 let def = input_body.source.with_opt_param().as_local().unwrap();
159 let param_env = tcx.param_env(def.did);
160 let id = tcx.hir().local_def_id_to_hir_id(def.did);
162 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
163 for var_debug_info in &input_body.var_debug_info {
164 if let VarDebugInfoContents::Place(place) = var_debug_info.value {
165 if let Some(local) = place.as_local() {
166 if let Some(prev_name) = local_names[local] {
167 if var_debug_info.name != prev_name {
169 var_debug_info.source_info.span,
170 "local {:?} has many names (`{}` vs `{}`)",
177 local_names[local] = Some(var_debug_info.name);
182 // Gather the upvars of a closure, if any.
183 let tables = tcx.typeck_opt_const_arg(def);
184 if let Some(ErrorReported) = tables.tainted_by_errors {
185 infcx.set_tainted_by_errors();
187 let upvars: Vec<_> = tables
188 .closure_min_captures_flattened(def.did.to_def_id())
189 .map(|captured_place| {
190 let capture = captured_place.info.capture_kind;
191 let by_ref = match capture {
192 ty::UpvarCapture::ByValue(_) => false,
193 ty::UpvarCapture::ByRef(..) => true,
195 Upvar { place: captured_place.clone(), by_ref }
199 // Replace all regions with fresh inference variables. This
200 // requires first making our own copy of the MIR. This copy will
201 // be modified (in place) to contain non-lexical lifetimes. It
202 // will have a lifetime tied to the inference context.
203 let mut body_owned = input_body.clone();
204 let mut promoted = input_promoted.clone();
206 nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
207 let body = &body_owned; // no further changes
209 let location_table_owned = LocationTable::new(body);
210 let location_table = &location_table_owned;
212 let mut errors_buffer = Vec::new();
213 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
214 match MoveData::gather_moves(&body, tcx, param_env) {
215 Ok(move_data) => (move_data, Vec::new()),
216 Err((move_data, move_errors)) => (move_data, move_errors),
218 let promoted_errors = promoted
220 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
222 let mdpe = MoveDataParamEnv { move_data, param_env };
224 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
225 .into_engine(tcx, &body)
226 .pass_name("borrowck")
227 .iterate_to_fixpoint()
228 .into_results_cursor(&body);
230 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
232 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
234 let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.debugging_opts.polonius;
236 // Compute non-lexical lifetimes.
244 } = nll::compute_regions(
258 // Dump MIR results into a file, if that is enabled. This let us
259 // write unit-tests, as well as helping with debugging.
260 nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
262 // We also have a `#[rustc_regions]` annotation that causes us to dump
264 nll::dump_annotation(
273 // The various `flow_*` structures can be large. We drop `flow_inits` here
274 // so it doesn't overlap with the others below. This reduces peak memory
275 // usage significantly on some benchmarks.
278 let regioncx = Rc::new(regioncx);
280 let flow_borrows = Borrows::new(tcx, body, ®ioncx, &borrow_set)
281 .into_engine(tcx, body)
282 .pass_name("borrowck")
283 .iterate_to_fixpoint();
284 let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &mdpe)
285 .into_engine(tcx, body)
286 .pass_name("borrowck")
287 .iterate_to_fixpoint();
288 let flow_ever_inits = EverInitializedPlaces::new(tcx, body, &mdpe)
289 .into_engine(tcx, body)
290 .pass_name("borrowck")
291 .iterate_to_fixpoint();
293 let movable_generator = !matches!(
295 Node::Expr(&hir::Expr {
296 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
301 for (idx, move_data_results) in promoted_errors {
302 let promoted_body = &promoted[idx];
304 if let Err((move_data, move_errors)) = move_data_results {
305 let mut promoted_mbcx = MirBorrowckCtxt {
309 move_data: &move_data,
310 location_table, // no need to create a real one for the promoted, it is not used
312 fn_self_span_reported: Default::default(),
313 locals_are_invalidated_at_exit,
314 access_place_error_reported: Default::default(),
315 reservation_error_reported: Default::default(),
316 reservation_warnings: Default::default(),
317 move_error_reported: BTreeMap::new(),
318 uninitialized_error_reported: Default::default(),
320 regioncx: regioncx.clone(),
321 used_mut: Default::default(),
322 used_mut_upvars: SmallVec::new(),
323 borrow_set: Rc::clone(&borrow_set),
324 dominators: Dominators::dummy(), // not used
326 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
327 region_names: RefCell::default(),
328 next_region_name: RefCell::new(1),
329 polonius_output: None,
331 promoted_mbcx.report_move_errors(move_errors);
332 errors_buffer = promoted_mbcx.errors_buffer;
336 let dominators = body.dominators();
338 let mut mbcx = MirBorrowckCtxt {
342 move_data: &mdpe.move_data,
345 locals_are_invalidated_at_exit,
346 fn_self_span_reported: Default::default(),
347 access_place_error_reported: Default::default(),
348 reservation_error_reported: Default::default(),
349 reservation_warnings: Default::default(),
350 move_error_reported: BTreeMap::new(),
351 uninitialized_error_reported: Default::default(),
353 regioncx: Rc::clone(®ioncx),
354 used_mut: Default::default(),
355 used_mut_upvars: SmallVec::new(),
356 borrow_set: Rc::clone(&borrow_set),
360 region_names: RefCell::default(),
361 next_region_name: RefCell::new(1),
365 // Compute and report region errors, if any.
366 mbcx.report_region_errors(nll_errors);
368 let results = BorrowckResults {
369 ever_inits: flow_ever_inits,
370 uninits: flow_uninits,
371 borrows: flow_borrows,
374 mbcx.report_move_errors(move_errors);
376 rustc_mir_dataflow::visit_results(
378 traversal::reverse_postorder(body).map(|(bb, _)| bb),
383 // Convert any reservation warnings into lints.
384 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
385 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
386 let mut initial_diag = mbcx.report_conflicting_borrow(location, (place, span), bk, &borrow);
388 let scope = mbcx.body.source_info(location).scope;
389 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
390 ClearCrossCrate::Set(data) => data.lint_root,
394 // Span and message don't matter; we overwrite them below anyway
395 mbcx.infcx.tcx.struct_span_lint_hir(
396 MUTABLE_BORROW_RESERVATION_CONFLICT,
400 let mut diag = lint.build("");
402 diag.message = initial_diag.styled_message().clone();
403 diag.span = initial_diag.span.clone();
405 diag.buffer(&mut mbcx.errors_buffer);
408 initial_diag.cancel();
411 // For each non-user used mutable variable, check if it's been assigned from
412 // a user-declared local. If so, then put that local into the used_mut set.
413 // Note that this set is expected to be small - only upvars from closures
414 // would have a chance of erroneously adding non-user-defined mutable vars
416 let temporary_used_locals: FxHashSet<Local> = mbcx
419 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
422 // For the remaining unused locals that are marked as mutable, we avoid linting any that
423 // were never initialized. These locals may have been removed as unreachable code; or will be
424 // linted as unused variables.
425 let unused_mut_locals =
426 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
427 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
429 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
430 let used_mut = mbcx.used_mut;
431 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
432 let local_decl = &mbcx.body.local_decls[local];
433 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
434 ClearCrossCrate::Set(data) => data.lint_root,
438 // Skip over locals that begin with an underscore or have no name
439 match mbcx.local_names[local] {
441 if name.as_str().starts_with('_') {
448 let span = local_decl.source_info.span;
449 if span.desugaring_kind().is_some() {
450 // If the `mut` arises as part of a desugaring, we should ignore it.
454 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
455 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
456 lint.build("variable does not need to be mutable")
457 .span_suggestion_short(
461 Applicability::MachineApplicable,
467 // Buffer any move errors that we collected and de-duplicated.
468 for (_, (_, diag)) in mbcx.move_error_reported {
469 diag.buffer(&mut mbcx.errors_buffer);
472 if !mbcx.errors_buffer.is_empty() {
473 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
475 for diag in mbcx.errors_buffer.drain(..) {
476 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
480 let result = BorrowCheckResult {
481 concrete_opaque_types: opaque_type_values,
482 closure_requirements: opt_closure_req,
483 used_mut_upvars: mbcx.used_mut_upvars,
486 let body_with_facts = if return_body_with_facts {
487 let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
488 Some(Box::new(BodyWithBorrowckFacts {
490 input_facts: *polonius_input.expect("Polonius input facts were not generated"),
492 location_table: location_table_owned,
498 debug!("do_mir_borrowck: result = {:#?}", result);
500 (result, body_with_facts)
503 /// A `Body` with information computed by the borrow checker. This struct is
504 /// intended to be consumed by compiler consumers.
506 /// We need to include the MIR body here because the region identifiers must
507 /// match the ones in the Polonius facts.
508 pub struct BodyWithBorrowckFacts<'tcx> {
509 /// A mir body that contains region identifiers.
510 pub body: Body<'tcx>,
511 /// Polonius input facts.
512 pub input_facts: AllFacts,
513 /// Polonius output facts.
514 pub output_facts: Rc<self::nll::PoloniusOutput>,
515 /// The table that maps Polonius points to locations in the table.
516 pub location_table: LocationTable,
519 struct MirBorrowckCtxt<'cx, 'tcx> {
520 infcx: &'cx InferCtxt<'cx, 'tcx>,
521 param_env: ParamEnv<'tcx>,
522 body: &'cx Body<'tcx>,
523 move_data: &'cx MoveData<'tcx>,
525 /// Map from MIR `Location` to `LocationIndex`; created
526 /// when MIR borrowck begins.
527 location_table: &'cx LocationTable,
529 movable_generator: bool,
530 /// This keeps track of whether local variables are free-ed when the function
531 /// exits even without a `StorageDead`, which appears to be the case for
534 /// I'm not sure this is the right approach - @eddyb could you try and
536 locals_are_invalidated_at_exit: bool,
537 /// This field keeps track of when borrow errors are reported in the access_place function
538 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
539 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
540 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
542 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
543 /// This field keeps track of when borrow conflict errors are reported
544 /// for reservations, so that we don't report seemingly duplicate
545 /// errors for corresponding activations.
547 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
548 // but it is currently inconvenient to track down the `BorrowIndex`
549 // at the time we detect and report a reservation error.
550 reservation_error_reported: FxHashSet<Place<'tcx>>,
551 /// This fields keeps track of the `Span`s that we have
552 /// used to report extra information for `FnSelfUse`, to avoid
553 /// unnecessarily verbose errors.
554 fn_self_span_reported: FxHashSet<Span>,
555 /// Migration warnings to be reported for #56254. We delay reporting these
556 /// so that we can suppress the warning if there's a corresponding error
557 /// for the activation of the borrow.
558 reservation_warnings:
559 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
560 /// This field keeps track of move errors that are to be reported for given move indices.
562 /// There are situations where many errors can be reported for a single move out (see #53807)
563 /// and we want only the best of those errors.
565 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
566 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
567 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
568 /// all move errors have been reported, any diagnostics in this map are added to the buffer
571 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
572 /// when errors in the map are being re-added to the error buffer so that errors with the
573 /// same primary span come out in a consistent order.
574 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'cx>)>,
575 /// This field keeps track of errors reported in the checking of uninitialized variables,
576 /// so that we don't report seemingly duplicate errors.
577 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
578 /// Errors to be reported buffer
579 errors_buffer: Vec<Diagnostic>,
580 /// This field keeps track of all the local variables that are declared mut and are mutated.
581 /// Used for the warning issued by an unused mutable local variable.
582 used_mut: FxHashSet<Local>,
583 /// If the function we're checking is a closure, then we'll need to report back the list of
584 /// mutable upvars that have been used. This field keeps track of them.
585 used_mut_upvars: SmallVec<[Field; 8]>,
586 /// Region inference context. This contains the results from region inference and lets us e.g.
587 /// find out which CFG points are contained in each borrow region.
588 regioncx: Rc<RegionInferenceContext<'tcx>>,
590 /// The set of borrows extracted from the MIR
591 borrow_set: Rc<BorrowSet<'tcx>>,
593 /// Dominators for MIR
594 dominators: Dominators<BasicBlock>,
596 /// Information about upvars not necessarily preserved in types or MIR
597 upvars: Vec<Upvar<'tcx>>,
599 /// Names of local (user) variables (extracted from `var_debug_info`).
600 local_names: IndexVec<Local, Option<Symbol>>,
602 /// Record the region names generated for each region in the given
603 /// MIR def so that we can reuse them later in help/error messages.
604 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
606 /// The counter for generating new region names.
607 next_region_name: RefCell<usize>,
609 /// Results of Polonius analysis.
610 polonius_output: Option<Rc<PoloniusOutput>>,
614 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
615 // 2. loans made in overlapping scopes do not conflict
616 // 3. assignments do not affect things loaned out as immutable
617 // 4. moves do not affect things loaned out in any way
618 impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
619 type FlowState = Flows<'cx, 'tcx>;
621 fn visit_statement_before_primary_effect(
623 flow_state: &Flows<'cx, 'tcx>,
624 stmt: &'cx Statement<'tcx>,
627 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
628 let span = stmt.source_info.span;
630 self.check_activations(location, span, flow_state);
633 StatementKind::Assign(box (lhs, ref rhs)) => {
634 self.consume_rvalue(location, (rhs, span), flow_state);
636 self.mutate_place(location, (*lhs, span), Shallow(None), JustWrite, flow_state);
638 StatementKind::FakeRead(box (_, ref place)) => {
639 // Read for match doesn't access any memory and is used to
640 // assert that a place is safe and live. So we don't have to
641 // do any checks here.
643 // FIXME: Remove check that the place is initialized. This is
644 // needed for now because matches don't have never patterns yet.
645 // So this is the only place we prevent
649 self.check_if_path_or_subpath_is_moved(
651 InitializationRequiringAction::Use,
652 (place.as_ref(), span),
656 StatementKind::SetDiscriminant { place, variant_index: _ } => {
657 self.mutate_place(location, (**place, span), Shallow(None), JustWrite, flow_state);
659 StatementKind::LlvmInlineAsm(ref asm) => {
660 for (o, output) in iter::zip(&asm.asm.outputs, &*asm.outputs) {
662 // FIXME(eddyb) indirect inline asm outputs should
663 // be encoded through MIR place derefs instead.
667 (Deep, Read(ReadKind::Copy)),
668 LocalMutationIsAllowed::No,
671 self.check_if_path_or_subpath_is_moved(
673 InitializationRequiringAction::Use,
674 (output.as_ref(), o.span),
681 if o.is_rw { Deep } else { Shallow(None) },
682 if o.is_rw { WriteAndRead } else { JustWrite },
687 for (_, input) in asm.inputs.iter() {
688 self.consume_operand(location, (input, span), flow_state);
692 StatementKind::CopyNonOverlapping(box rustc_middle::mir::CopyNonOverlapping {
697 "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
701 | StatementKind::Coverage(..)
702 | StatementKind::AscribeUserType(..)
703 | StatementKind::Retag { .. }
704 | StatementKind::StorageLive(..) => {
705 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
708 StatementKind::StorageDead(local) => {
711 (Place::from(*local), span),
712 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
713 LocalMutationIsAllowed::Yes,
720 fn visit_terminator_before_primary_effect(
722 flow_state: &Flows<'cx, 'tcx>,
723 term: &'cx Terminator<'tcx>,
726 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
727 let span = term.source_info.span;
729 self.check_activations(loc, span, flow_state);
732 TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
733 self.consume_operand(loc, (discr, span), flow_state);
735 TerminatorKind::Drop { place, target: _, unwind: _ } => {
737 "visit_terminator_drop \
738 loc: {:?} term: {:?} place: {:?} span: {:?}",
739 loc, term, place, span
745 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
746 LocalMutationIsAllowed::Yes,
750 TerminatorKind::DropAndReplace {
752 value: ref new_value,
756 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
757 self.consume_operand(loc, (new_value, span), flow_state);
759 TerminatorKind::Call {
767 self.consume_operand(loc, (func, span), flow_state);
769 self.consume_operand(loc, (arg, span), flow_state);
771 if let Some((dest, _ /*bb*/)) = *destination {
772 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
775 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
776 self.consume_operand(loc, (cond, span), flow_state);
777 use rustc_middle::mir::AssertKind;
778 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
779 self.consume_operand(loc, (len, span), flow_state);
780 self.consume_operand(loc, (index, span), flow_state);
784 TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
785 self.consume_operand(loc, (value, span), flow_state);
786 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
789 TerminatorKind::InlineAsm {
798 InlineAsmOperand::In { reg: _, ref value } => {
799 self.consume_operand(loc, (value, span), flow_state);
801 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
802 if let Some(place) = place {
812 InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
813 self.consume_operand(loc, (in_value, span), flow_state);
814 if let Some(out_place) = out_place {
824 InlineAsmOperand::Const { value: _ }
825 | InlineAsmOperand::SymFn { value: _ }
826 | InlineAsmOperand::SymStatic { def_id: _ } => {}
831 TerminatorKind::Goto { target: _ }
832 | TerminatorKind::Abort
833 | TerminatorKind::Unreachable
834 | TerminatorKind::Resume
835 | TerminatorKind::Return
836 | TerminatorKind::GeneratorDrop
837 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
838 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
839 // no data used, thus irrelevant to borrowck
844 fn visit_terminator_after_primary_effect(
846 flow_state: &Flows<'cx, 'tcx>,
847 term: &'cx Terminator<'tcx>,
850 let span = term.source_info.span;
853 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
854 if self.movable_generator {
855 // Look for any active borrows to locals
856 let borrow_set = self.borrow_set.clone();
857 for i in flow_state.borrows.iter() {
858 let borrow = &borrow_set[i];
859 self.check_for_local_borrow(borrow, span);
864 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
865 // Returning from the function implicitly kills storage for all locals and statics.
866 // Often, the storage will already have been killed by an explicit
867 // StorageDead, but we don't always emit those (notably on unwind paths),
868 // so this "extra check" serves as a kind of backup.
869 let borrow_set = self.borrow_set.clone();
870 for i in flow_state.borrows.iter() {
871 let borrow = &borrow_set[i];
872 self.check_for_invalidation_at_exit(loc, borrow, span);
876 TerminatorKind::Abort
877 | TerminatorKind::Assert { .. }
878 | TerminatorKind::Call { .. }
879 | TerminatorKind::Drop { .. }
880 | TerminatorKind::DropAndReplace { .. }
881 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
882 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
883 | TerminatorKind::Goto { .. }
884 | TerminatorKind::SwitchInt { .. }
885 | TerminatorKind::Unreachable
886 | TerminatorKind::InlineAsm { .. } => {}
891 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
897 use self::AccessDepth::{Deep, Shallow};
898 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
900 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
901 enum ArtificialField {
906 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
908 /// From the RFC: "A *shallow* access means that the immediate
909 /// fields reached at P are accessed, but references or pointers
910 /// found within are not dereferenced. Right now, the only access
911 /// that is shallow is an assignment like `x = ...;`, which would
912 /// be a *shallow write* of `x`."
913 Shallow(Option<ArtificialField>),
915 /// From the RFC: "A *deep* access means that all data reachable
916 /// through the given place may be invalidated or accesses by
920 /// Access is Deep only when there is a Drop implementation that
921 /// can reach the data behind the reference.
925 /// Kind of access to a value: read or write
926 /// (For informational purposes only)
927 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
929 /// From the RFC: "A *read* means that the existing data may be
930 /// read, but will not be changed."
933 /// From the RFC: "A *write* means that the data may be mutated to
934 /// new values or otherwise invalidated (for example, it could be
935 /// de-initialized, as in a move operation).
938 /// For two-phase borrows, we distinguish a reservation (which is treated
939 /// like a Read) from an activation (which is treated like a write), and
940 /// each of those is furthermore distinguished from Reads/Writes above.
941 Reservation(WriteKind),
942 Activation(WriteKind, BorrowIndex),
945 /// Kind of read access to a value
946 /// (For informational purposes only)
947 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
953 /// Kind of write access to a value
954 /// (For informational purposes only)
955 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
958 MutableBorrow(BorrowKind),
963 /// When checking permissions for a place access, this flag is used to indicate that an immutable
964 /// local place can be mutated.
966 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
967 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
968 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
969 // `is_declared_mutable()`.
970 // - Take flow state into consideration in `is_assignable()` for local variables.
971 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
972 enum LocalMutationIsAllowed {
974 /// We want use of immutable upvars to cause a "write to immutable upvar"
975 /// error, not an "reassignment" error.
980 #[derive(Copy, Clone, Debug)]
981 enum InitializationRequiringAction {
990 struct RootPlace<'tcx> {
992 place_projection: &'tcx [PlaceElem<'tcx>],
993 is_local_mutation_allowed: LocalMutationIsAllowed,
996 impl InitializationRequiringAction {
997 fn as_noun(self) -> &'static str {
999 InitializationRequiringAction::Update => "update",
1000 InitializationRequiringAction::Borrow => "borrow",
1001 InitializationRequiringAction::MatchOn => "use", // no good noun
1002 InitializationRequiringAction::Use => "use",
1003 InitializationRequiringAction::Assignment => "assign",
1004 InitializationRequiringAction::PartialAssignment => "assign to part",
1008 fn as_verb_in_past_tense(self) -> &'static str {
1010 InitializationRequiringAction::Update => "updated",
1011 InitializationRequiringAction::Borrow => "borrowed",
1012 InitializationRequiringAction::MatchOn => "matched on",
1013 InitializationRequiringAction::Use => "used",
1014 InitializationRequiringAction::Assignment => "assigned",
1015 InitializationRequiringAction::PartialAssignment => "partially assigned",
1020 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
1021 fn body(&self) -> &'cx Body<'tcx> {
1025 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
1026 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
1027 /// place is initialized and (b) it is not borrowed in some way that would prevent this
1030 /// Returns `true` if an error is reported.
1034 place_span: (Place<'tcx>, Span),
1035 kind: (AccessDepth, ReadOrWrite),
1036 is_local_mutation_allowed: LocalMutationIsAllowed,
1037 flow_state: &Flows<'cx, 'tcx>,
1039 let (sd, rw) = kind;
1041 if let Activation(_, borrow_index) = rw {
1042 if self.reservation_error_reported.contains(&place_span.0) {
1044 "skipping access_place for activation of invalid reservation \
1045 place: {:?} borrow_index: {:?}",
1046 place_span.0, borrow_index
1052 // Check is_empty() first because it's the common case, and doing that
1053 // way we avoid the clone() call.
1054 if !self.access_place_error_reported.is_empty()
1055 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
1058 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
1064 let mutability_error = self.check_access_permissions(
1067 is_local_mutation_allowed,
1071 let conflict_error =
1072 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
1074 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
1075 // Suppress this warning when there's an error being emitted for the
1076 // same borrow: fixing the error is likely to fix the warning.
1077 self.reservation_warnings.remove(&borrow_idx);
1080 if conflict_error || mutability_error {
1081 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
1083 self.access_place_error_reported.insert((place_span.0, place_span.1));
1087 fn check_access_for_conflict(
1090 place_span: (Place<'tcx>, Span),
1093 flow_state: &Flows<'cx, 'tcx>,
1096 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
1097 location, place_span, sd, rw,
1100 let mut error_reported = false;
1101 let tcx = self.infcx.tcx;
1102 let body = self.body;
1103 let borrow_set = self.borrow_set.clone();
1105 // Use polonius output if it has been enabled.
1106 let polonius_output = self.polonius_output.clone();
1107 let borrows_in_scope = if let Some(polonius) = &polonius_output {
1108 let location = self.location_table.start_index(location);
1109 Either::Left(polonius.errors_at(location).iter().copied())
1111 Either::Right(flow_state.borrows.iter())
1114 each_borrow_involving_path(
1122 |this, borrow_index, borrow| match (rw, borrow.kind) {
1123 // Obviously an activation is compatible with its own
1124 // reservation (or even prior activating uses of same
1125 // borrow); so don't check if they interfere.
1127 // NOTE: *reservations* do conflict with themselves;
1128 // thus aren't injecting unsoundenss w/ this check.)
1129 (Activation(_, activating), _) if activating == borrow_index => {
1131 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1132 skipping {:?} b/c activation of same borrow_index",
1136 (borrow_index, borrow),
1141 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1143 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1144 BorrowKind::Unique | BorrowKind::Mut { .. },
1145 ) => Control::Continue,
1147 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1148 // Handled by initialization checks.
1152 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1153 // Reading from mere reservations of mutable-borrows is OK.
1154 if !is_active(&this.dominators, borrow, location) {
1155 assert!(allow_two_phase_borrow(borrow.kind));
1156 return Control::Continue;
1159 error_reported = true;
1162 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1163 .buffer(&mut this.errors_buffer);
1165 ReadKind::Borrow(bk) => {
1166 this.report_conflicting_borrow(location, place_span, bk, borrow)
1167 .buffer(&mut this.errors_buffer);
1174 Reservation(WriteKind::MutableBorrow(bk)),
1175 BorrowKind::Shallow | BorrowKind::Shared,
1176 ) if { tcx.migrate_borrowck() && this.borrow_set.contains(&location) } => {
1177 let bi = this.borrow_set.get_index_of(&location).unwrap();
1179 "recording invalid reservation of place: {:?} with \
1180 borrow index {:?} as warning",
1183 // rust-lang/rust#56254 - This was previously permitted on
1184 // the 2018 edition so we emit it as a warning. We buffer
1185 // these sepately so that we only emit a warning if borrow
1186 // checking was otherwise successful.
1187 this.reservation_warnings
1188 .insert(bi, (place_span.0, place_span.1, location, bk, borrow.clone()));
1190 // Don't suppress actual errors.
1194 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1196 Reservation(..) => {
1198 "recording invalid reservation of \
1202 this.reservation_error_reported.insert(place_span.0);
1204 Activation(_, activating) => {
1206 "observing check_place for activation of \
1207 borrow_index: {:?}",
1211 Read(..) | Write(..) => {}
1214 error_reported = true;
1216 WriteKind::MutableBorrow(bk) => {
1217 this.report_conflicting_borrow(location, place_span, bk, borrow)
1218 .buffer(&mut this.errors_buffer);
1220 WriteKind::StorageDeadOrDrop => this
1221 .report_borrowed_value_does_not_live_long_enough(
1227 WriteKind::Mutate => {
1228 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1230 WriteKind::Move => {
1231 this.report_move_out_while_borrowed(location, place_span, borrow)
1245 place_span: (Place<'tcx>, Span),
1248 flow_state: &Flows<'cx, 'tcx>,
1250 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1252 MutateMode::WriteAndRead => {
1253 self.check_if_path_or_subpath_is_moved(
1255 InitializationRequiringAction::Update,
1256 (place_span.0.as_ref(), place_span.1),
1260 MutateMode::JustWrite => {
1261 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1265 // Special case: you can assign an immutable local variable
1266 // (e.g., `x = ...`) so long as it has never been initialized
1267 // before (at this point in the flow).
1268 if let Some(local) = place_span.0.as_local() {
1269 if let Mutability::Not = self.body.local_decls[local].mutability {
1270 // check for reassignments to immutable local variables
1271 self.check_if_reassignment_to_immutable_state(
1272 location, local, place_span, flow_state,
1278 // Otherwise, use the normal access permission rules.
1282 (kind, Write(WriteKind::Mutate)),
1283 LocalMutationIsAllowed::No,
1291 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1292 flow_state: &Flows<'cx, 'tcx>,
1295 Rvalue::Ref(_ /*rgn*/, bk, place) => {
1296 let access_kind = match bk {
1297 BorrowKind::Shallow => {
1298 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1300 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1301 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1302 let wk = WriteKind::MutableBorrow(bk);
1303 if allow_two_phase_borrow(bk) {
1304 (Deep, Reservation(wk))
1315 LocalMutationIsAllowed::No,
1319 let action = if bk == BorrowKind::Shallow {
1320 InitializationRequiringAction::MatchOn
1322 InitializationRequiringAction::Borrow
1325 self.check_if_path_or_subpath_is_moved(
1328 (place.as_ref(), span),
1333 Rvalue::AddressOf(mutability, place) => {
1334 let access_kind = match mutability {
1335 Mutability::Mut => (
1337 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1338 allow_two_phase_borrow: false,
1341 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1348 LocalMutationIsAllowed::No,
1352 self.check_if_path_or_subpath_is_moved(
1354 InitializationRequiringAction::Borrow,
1355 (place.as_ref(), span),
1360 Rvalue::ThreadLocalRef(_) => {}
1362 Rvalue::Use(ref operand)
1363 | Rvalue::Repeat(ref operand, _)
1364 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1365 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/)
1366 | Rvalue::ShallowInitBox(ref operand, _ /*ty*/) => {
1367 self.consume_operand(location, (operand, span), flow_state)
1370 Rvalue::Len(place) | Rvalue::Discriminant(place) => {
1371 let af = match *rvalue {
1372 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1373 Rvalue::Discriminant(..) => None,
1374 _ => unreachable!(),
1379 (Shallow(af), Read(ReadKind::Copy)),
1380 LocalMutationIsAllowed::No,
1383 self.check_if_path_or_subpath_is_moved(
1385 InitializationRequiringAction::Use,
1386 (place.as_ref(), span),
1391 Rvalue::BinaryOp(_bin_op, box (ref operand1, ref operand2))
1392 | Rvalue::CheckedBinaryOp(_bin_op, box (ref operand1, ref operand2)) => {
1393 self.consume_operand(location, (operand1, span), flow_state);
1394 self.consume_operand(location, (operand2, span), flow_state);
1397 Rvalue::NullaryOp(_op, _ty) => {
1398 // nullary ops take no dynamic input; no borrowck effect.
1400 // FIXME: is above actually true? Do we want to track
1401 // the fact that uninitialized data can be created via
1405 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1406 // We need to report back the list of mutable upvars that were
1407 // moved into the closure and subsequently used by the closure,
1408 // in order to populate our used_mut set.
1409 match **aggregate_kind {
1410 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1411 let BorrowCheckResult { used_mut_upvars, .. } =
1412 self.infcx.tcx.mir_borrowck(def_id.expect_local());
1413 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1414 for field in used_mut_upvars {
1415 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1418 AggregateKind::Adt(..)
1419 | AggregateKind::Array(..)
1420 | AggregateKind::Tuple { .. } => (),
1423 for operand in operands {
1424 self.consume_operand(location, (operand, span), flow_state);
1430 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1431 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1432 // We have three possibilities here:
1433 // a. We are modifying something through a mut-ref
1434 // b. We are modifying something that is local to our parent
1435 // c. Current body is a nested closure, and we are modifying path starting from
1436 // a Place captured by our parent closure.
1438 // Handle (c), the path being modified is exactly the path captured by our parent
1439 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1440 this.used_mut_upvars.push(field);
1444 for (place_ref, proj) in place.iter_projections().rev() {
1446 if proj == ProjectionElem::Deref {
1447 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1448 // We aren't modifying a variable directly
1449 ty::Ref(_, _, hir::Mutability::Mut) => return,
1456 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1457 this.used_mut_upvars.push(field);
1463 this.used_mut.insert(place.local);
1466 // This relies on the current way that by-value
1467 // captures of a closure are copied/moved directly
1468 // when generating MIR.
1470 Operand::Move(place) | Operand::Copy(place) => {
1471 match place.as_local() {
1472 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1473 if self.body.local_decls[local].ty.is_mutable_ptr() {
1474 // The variable will be marked as mutable by the borrow.
1477 // This is an edge case where we have a `move` closure
1478 // inside a non-move closure, and the inner closure
1479 // contains a mutation:
1482 // || { move || { i += 1; }; };
1484 // In this case our usual strategy of assuming that the
1485 // variable will be captured by mutable reference is
1486 // wrong, since `i` can be copied into the inner
1487 // closure from a shared reference.
1489 // As such we have to search for the local that this
1490 // capture comes from and mark it as being used as mut.
1492 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1493 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1494 &self.move_data.inits[init_index]
1496 bug!("temporary should be initialized exactly once")
1499 let loc = match init.location {
1500 InitLocation::Statement(stmt) => stmt,
1501 _ => bug!("temporary initialized in arguments"),
1504 let body = self.body;
1505 let bbd = &body[loc.block];
1506 let stmt = &bbd.statements[loc.statement_index];
1507 debug!("temporary assigned in: stmt={:?}", stmt);
1509 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1511 propagate_closure_used_mut_place(self, source);
1514 "closures should only capture user variables \
1515 or references to user variables"
1519 _ => propagate_closure_used_mut_place(self, place),
1522 Operand::Constant(..) => {}
1529 (operand, span): (&'cx Operand<'tcx>, Span),
1530 flow_state: &Flows<'cx, 'tcx>,
1533 Operand::Copy(place) => {
1534 // copy of place: check if this is "copy of frozen path"
1535 // (FIXME: see check_loans.rs)
1539 (Deep, Read(ReadKind::Copy)),
1540 LocalMutationIsAllowed::No,
1544 // Finally, check if path was already moved.
1545 self.check_if_path_or_subpath_is_moved(
1547 InitializationRequiringAction::Use,
1548 (place.as_ref(), span),
1552 Operand::Move(place) => {
1553 // move of place: check if this is move of already borrowed path
1557 (Deep, Write(WriteKind::Move)),
1558 LocalMutationIsAllowed::Yes,
1562 // Finally, check if path was already moved.
1563 self.check_if_path_or_subpath_is_moved(
1565 InitializationRequiringAction::Use,
1566 (place.as_ref(), span),
1570 Operand::Constant(_) => {}
1574 /// Checks whether a borrow of this place is invalidated when the function
1576 fn check_for_invalidation_at_exit(
1579 borrow: &BorrowData<'tcx>,
1582 debug!("check_for_invalidation_at_exit({:?})", borrow);
1583 let place = borrow.borrowed_place;
1584 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1586 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1587 // we just know that all locals are dropped at function exit (otherwise
1588 // we'll have a memory leak) and assume that all statics have a destructor.
1590 // FIXME: allow thread-locals to borrow other thread locals?
1592 let (might_be_alive, will_be_dropped) =
1593 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1594 // Thread-locals might be dropped after the function exits
1595 // We have to dereference the outer reference because
1596 // borrows don't conflict behind shared references.
1597 root_place.projection = DEREF_PROJECTION;
1600 (false, self.locals_are_invalidated_at_exit)
1603 if !will_be_dropped {
1604 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1608 let sd = if might_be_alive { Deep } else { Shallow(None) };
1610 if places_conflict::borrow_conflicts_with_place(
1617 places_conflict::PlaceConflictBias::Overlap,
1619 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1620 // FIXME: should be talking about the region lifetime instead
1621 // of just a span here.
1622 let span = self.infcx.tcx.sess.source_map().end_point(span);
1623 self.report_borrowed_value_does_not_live_long_enough(
1632 /// Reports an error if this is a borrow of local data.
1633 /// This is called for all Yield expressions on movable generators
1634 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1635 debug!("check_for_local_borrow({:?})", borrow);
1637 if borrow_of_local_data(borrow.borrowed_place) {
1638 let err = self.cannot_borrow_across_generator_yield(
1639 self.retrieve_borrow_spans(borrow).var_or_use(),
1643 err.buffer(&mut self.errors_buffer);
1647 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1648 // Two-phase borrow support: For each activation that is newly
1649 // generated at this statement, check if it interferes with
1651 let borrow_set = self.borrow_set.clone();
1652 for &borrow_index in borrow_set.activations_at_location(location) {
1653 let borrow = &borrow_set[borrow_index];
1655 // only mutable borrows should be 2-phase
1656 assert!(match borrow.kind {
1657 BorrowKind::Shared | BorrowKind::Shallow => false,
1658 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1663 (borrow.borrowed_place, span),
1664 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1665 LocalMutationIsAllowed::No,
1668 // We do not need to call `check_if_path_or_subpath_is_moved`
1669 // again, as we already called it when we made the
1670 // initial reservation.
1674 fn check_if_reassignment_to_immutable_state(
1678 place_span: (Place<'tcx>, Span),
1679 flow_state: &Flows<'cx, 'tcx>,
1681 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1683 // Check if any of the initializiations of `local` have happened yet:
1684 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1685 // And, if so, report an error.
1686 let init = &self.move_data.inits[init_index];
1687 let span = init.span(&self.body);
1688 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1692 fn check_if_full_path_is_moved(
1695 desired_action: InitializationRequiringAction,
1696 place_span: (PlaceRef<'tcx>, Span),
1697 flow_state: &Flows<'cx, 'tcx>,
1699 let maybe_uninits = &flow_state.uninits;
1703 // 1. Move of `a.b.c`, use of `a.b.c`
1704 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1705 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1706 // partial initialization support, one might have `a.x`
1707 // initialized but not `a.b`.
1711 // 4. Move of `a.b.c`, use of `a.b.d`
1712 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1713 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1714 // must have been initialized for the use to be sound.
1715 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1717 // The dataflow tracks shallow prefixes distinctly (that is,
1718 // field-accesses on P distinctly from P itself), in order to
1719 // track substructure initialization separately from the whole
1722 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1723 // which we have a MovePath is `a.b`, then that means that the
1724 // initialization state of `a.b` is all we need to inspect to
1725 // know if `a.b.c` is valid (and from that we infer that the
1726 // dereference and `.d` access is also valid, since we assume
1727 // `a.b.c` is assigned a reference to an initialized and
1728 // well-formed record structure.)
1730 // Therefore, if we seek out the *closest* prefix for which we
1731 // have a MovePath, that should capture the initialization
1732 // state for the place scenario.
1734 // This code covers scenarios 1, 2, and 3.
1736 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1737 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1738 if maybe_uninits.contains(mpi) {
1739 self.report_use_of_moved_or_uninitialized(
1742 (prefix, place_span.0, place_span.1),
1745 } // Only query longest prefix with a MovePath, not further
1746 // ancestors; dataflow recurs on children when parents
1747 // move (to support partial (re)inits).
1749 // (I.e., querying parents breaks scenario 7; but may want
1750 // to do such a query based on partial-init feature-gate.)
1753 /// Subslices correspond to multiple move paths, so we iterate through the
1754 /// elements of the base array. For each element we check
1756 /// * Does this element overlap with our slice.
1757 /// * Is any part of it uninitialized.
1758 fn check_if_subslice_element_is_moved(
1761 desired_action: InitializationRequiringAction,
1762 place_span: (PlaceRef<'tcx>, Span),
1763 maybe_uninits: &BitSet<MovePathIndex>,
1767 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1768 let move_paths = &self.move_data.move_paths;
1770 let root_path = &move_paths[mpi];
1771 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1772 let last_proj = child_move_path.place.projection.last().unwrap();
1773 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1774 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1776 if (from..to).contains(offset) {
1778 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1779 maybe_uninits.contains(mpi)
1782 if let Some(uninit_child) = uninit_child {
1783 self.report_use_of_moved_or_uninitialized(
1786 (place_span.0, place_span.0, place_span.1),
1789 return; // don't bother finding other problems.
1797 fn check_if_path_or_subpath_is_moved(
1800 desired_action: InitializationRequiringAction,
1801 place_span: (PlaceRef<'tcx>, Span),
1802 flow_state: &Flows<'cx, 'tcx>,
1804 let maybe_uninits = &flow_state.uninits;
1808 // 1. Move of `a.b.c`, use of `a` or `a.b`
1809 // partial initialization support, one might have `a.x`
1810 // initialized but not `a.b`.
1811 // 2. All bad scenarios from `check_if_full_path_is_moved`
1815 // 3. Move of `a.b.c`, use of `a.b.d`
1816 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1817 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1818 // must have been initialized for the use to be sound.
1819 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1821 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1823 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1824 place_span.0.last_projection()
1826 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1827 if let ty::Array(..) = place_ty.ty.kind() {
1828 self.check_if_subslice_element_is_moved(
1831 (place_base, place_span.1),
1840 // A move of any shallow suffix of `place` also interferes
1841 // with an attempt to use `place`. This is scenario 3 above.
1843 // (Distinct from handling of scenarios 1+2+4 above because
1844 // `place` does not interfere with suffixes of its prefixes,
1845 // e.g., `a.b.c` does not interfere with `a.b.d`)
1847 // This code covers scenario 1.
1849 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1850 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1851 let uninit_mpi = self
1853 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1855 if let Some(uninit_mpi) = uninit_mpi {
1856 self.report_use_of_moved_or_uninitialized(
1859 (place_span.0, place_span.0, place_span.1),
1862 return; // don't bother finding other problems.
1867 /// Currently MoveData does not store entries for all places in
1868 /// the input MIR. For example it will currently filter out
1869 /// places that are Copy; thus we do not track places of shared
1870 /// reference type. This routine will walk up a place along its
1871 /// prefixes, searching for a foundational place that *is*
1872 /// tracked in the MoveData.
1874 /// An Err result includes a tag indicated why the search failed.
1875 /// Currently this can only occur if the place is built off of a
1876 /// static variable, as we do not track those in the MoveData.
1877 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1878 match self.move_data.rev_lookup.find(place) {
1879 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1880 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1882 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1886 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1887 // If returns None, then there is no move path corresponding
1888 // to a direct owner of `place` (which means there is nothing
1889 // that borrowck tracks for its analysis).
1891 match self.move_data.rev_lookup.find(place) {
1892 LookupResult::Parent(_) => None,
1893 LookupResult::Exact(mpi) => Some(mpi),
1897 fn check_if_assigned_path_is_moved(
1900 (place, span): (Place<'tcx>, Span),
1901 flow_state: &Flows<'cx, 'tcx>,
1903 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1905 // None case => assigning to `x` does not require `x` be initialized.
1906 for (place_base, elem) in place.iter_projections().rev() {
1908 ProjectionElem::Index(_/*operand*/) |
1909 ProjectionElem::ConstantIndex { .. } |
1910 // assigning to P[i] requires P to be valid.
1911 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1912 // assigning to (P->variant) is okay if assigning to `P` is okay
1914 // FIXME: is this true even if P is an adt with a dtor?
1917 // assigning to (*P) requires P to be initialized
1918 ProjectionElem::Deref => {
1919 self.check_if_full_path_is_moved(
1920 location, InitializationRequiringAction::Use,
1921 (place_base, span), flow_state);
1922 // (base initialized; no need to
1927 ProjectionElem::Subslice { .. } => {
1928 panic!("we don't allow assignments to subslices, location: {:?}",
1932 ProjectionElem::Field(..) => {
1933 // if type of `P` has a dtor, then
1934 // assigning to `P.f` requires `P` itself
1935 // be already initialized
1936 let tcx = self.infcx.tcx;
1937 let base_ty = place_base.ty(self.body(), tcx).ty;
1938 match base_ty.kind() {
1939 ty::Adt(def, _) if def.has_dtor(tcx) => {
1940 self.check_if_path_or_subpath_is_moved(
1941 location, InitializationRequiringAction::Assignment,
1942 (place_base, span), flow_state);
1944 // (base initialized; no need to
1949 // Once `let s; s.x = V; read(s.x);`,
1950 // is allowed, remove this match arm.
1951 ty::Adt(..) | ty::Tuple(..) => {
1952 check_parent_of_field(self, location, place_base, span, flow_state);
1954 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1955 // partial initialization, do not complain about unnecessary `mut` on
1956 // an attempt to do a partial initialization.
1957 self.used_mut.insert(place.local);
1966 fn check_parent_of_field<'cx, 'tcx>(
1967 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1969 base: PlaceRef<'tcx>,
1971 flow_state: &Flows<'cx, 'tcx>,
1973 // rust-lang/rust#21232: Until Rust allows reads from the
1974 // initialized parts of partially initialized structs, we
1975 // will, starting with the 2018 edition, reject attempts
1976 // to write to structs that are not fully initialized.
1978 // In other words, *until* we allow this:
1980 // 1. `let mut s; s.x = Val; read(s.x);`
1982 // we will for now disallow this:
1984 // 2. `let mut s; s.x = Val;`
1988 // 3. `let mut s = ...; drop(s); s.x=Val;`
1990 // This does not use check_if_path_or_subpath_is_moved,
1991 // because we want to *allow* reinitializations of fields:
1992 // e.g., want to allow
1994 // `let mut s = ...; drop(s.x); s.x=Val;`
1996 // This does not use check_if_full_path_is_moved on
1997 // `base`, because that would report an error about the
1998 // `base` as a whole, but in this scenario we *really*
1999 // want to report an error about the actual thing that was
2000 // moved, which may be some prefix of `base`.
2002 // Shallow so that we'll stop at any dereference; we'll
2003 // report errors about issues with such bases elsewhere.
2004 let maybe_uninits = &flow_state.uninits;
2006 // Find the shortest uninitialized prefix you can reach
2007 // without going over a Deref.
2008 let mut shortest_uninit_seen = None;
2009 for prefix in this.prefixes(base, PrefixSet::Shallow) {
2010 let mpi = match this.move_path_for_place(prefix) {
2015 if maybe_uninits.contains(mpi) {
2017 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
2018 shortest_uninit_seen,
2021 shortest_uninit_seen = Some((prefix, mpi));
2023 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
2027 if let Some((prefix, mpi)) = shortest_uninit_seen {
2028 // Check for a reassignment into an uninitialized field of a union (for example,
2029 // after a move out). In this case, do not report an error here. There is an
2030 // exception, if this is the first assignment into the union (that is, there is
2031 // no move out from an earlier location) then this is an attempt at initialization
2032 // of the union - we should error in that case.
2033 let tcx = this.infcx.tcx;
2034 if base.ty(this.body(), tcx).ty.is_union() {
2035 if this.move_data.path_map[mpi].iter().any(|moi| {
2036 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
2042 this.report_use_of_moved_or_uninitialized(
2044 InitializationRequiringAction::PartialAssignment,
2045 (prefix, base, span),
2052 /// Checks the permissions for the given place and read or write kind
2054 /// Returns `true` if an error is reported.
2055 fn check_access_permissions(
2057 (place, span): (Place<'tcx>, Span),
2059 is_local_mutation_allowed: LocalMutationIsAllowed,
2060 flow_state: &Flows<'cx, 'tcx>,
2064 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
2065 place, kind, is_local_mutation_allowed
2072 Reservation(WriteKind::MutableBorrow(
2073 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
2075 | Write(WriteKind::MutableBorrow(
2076 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
2078 let is_local_mutation_allowed = match borrow_kind {
2079 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
2080 BorrowKind::Mut { .. } => is_local_mutation_allowed,
2081 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
2083 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
2085 self.add_used_mut(root_place, flow_state);
2089 error_access = AccessKind::MutableBorrow;
2090 the_place_err = place_err;
2094 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
2095 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
2097 self.add_used_mut(root_place, flow_state);
2101 error_access = AccessKind::Mutate;
2102 the_place_err = place_err;
2109 | WriteKind::StorageDeadOrDrop
2110 | WriteKind::MutableBorrow(BorrowKind::Shared)
2111 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2115 | WriteKind::StorageDeadOrDrop
2116 | WriteKind::MutableBorrow(BorrowKind::Shared)
2117 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2119 if let (Err(_), true) = (
2120 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
2121 self.errors_buffer.is_empty(),
2123 // rust-lang/rust#46908: In pure NLL mode this code path should be
2124 // unreachable, but we use `delay_span_bug` because we can hit this when
2125 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
2126 // enabled. We don't want to ICE for that case, as other errors will have
2127 // been emitted (#52262).
2128 self.infcx.tcx.sess.delay_span_bug(
2131 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2139 // permission checks are done at Reservation point.
2145 | BorrowKind::Mut { .. }
2146 | BorrowKind::Shared
2147 | BorrowKind::Shallow,
2151 // Access authorized
2156 // rust-lang/rust#21232, #54986: during period where we reject
2157 // partial initialization, do not complain about mutability
2158 // errors except for actual mutation (as opposed to an attempt
2159 // to do a partial initialization).
2160 let previously_initialized =
2161 self.is_local_ever_initialized(place.local, flow_state).is_some();
2163 // at this point, we have set up the error reporting state.
2164 if previously_initialized {
2165 self.report_mutability_error(place, span, the_place_err, error_access, location);
2172 fn is_local_ever_initialized(
2175 flow_state: &Flows<'cx, 'tcx>,
2176 ) -> Option<InitIndex> {
2177 let mpi = self.move_data.rev_lookup.find_local(local);
2178 let ii = &self.move_data.init_path_map[mpi];
2180 if flow_state.ever_inits.contains(index) {
2187 /// Adds the place into the used mutable variables set
2188 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2190 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2191 // If the local may have been initialized, and it is now currently being
2192 // mutated, then it is justified to be annotated with the `mut`
2193 // keyword, since the mutation may be a possible reassignment.
2194 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2195 && self.is_local_ever_initialized(local, flow_state).is_some()
2197 self.used_mut.insert(local);
2202 place_projection: _,
2203 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2207 place_projection: place_projection @ [.., _],
2208 is_local_mutation_allowed: _,
2210 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2212 projection: place_projection,
2214 self.used_mut_upvars.push(field);
2220 /// Whether this value can be written or borrowed mutably.
2221 /// Returns the root place if the place passed in is a projection.
2224 place: PlaceRef<'tcx>,
2225 is_local_mutation_allowed: LocalMutationIsAllowed,
2226 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2227 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2228 match place.last_projection() {
2230 let local = &self.body.local_decls[place.local];
2231 match local.mutability {
2232 Mutability::Not => match is_local_mutation_allowed {
2233 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2234 place_local: place.local,
2235 place_projection: place.projection,
2236 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2238 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2239 place_local: place.local,
2240 place_projection: place.projection,
2241 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2243 LocalMutationIsAllowed::No => Err(place),
2245 Mutability::Mut => Ok(RootPlace {
2246 place_local: place.local,
2247 place_projection: place.projection,
2248 is_local_mutation_allowed,
2252 Some((place_base, elem)) => {
2254 ProjectionElem::Deref => {
2255 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2257 // Check the kind of deref to decide
2258 match base_ty.kind() {
2259 ty::Ref(_, _, mutbl) => {
2261 // Shared borrowed data is never mutable
2262 hir::Mutability::Not => Err(place),
2263 // Mutably borrowed data is mutable, but only if we have a
2264 // unique path to the `&mut`
2265 hir::Mutability::Mut => {
2266 let mode = match self.is_upvar_field_projection(place) {
2267 Some(field) if self.upvars[field.index()].by_ref => {
2268 is_local_mutation_allowed
2270 _ => LocalMutationIsAllowed::Yes,
2273 self.is_mutable(place_base, mode)
2277 ty::RawPtr(tnm) => {
2279 // `*const` raw pointers are not mutable
2280 hir::Mutability::Not => Err(place),
2281 // `*mut` raw pointers are always mutable, regardless of
2282 // context. The users have to check by themselves.
2283 hir::Mutability::Mut => Ok(RootPlace {
2284 place_local: place.local,
2285 place_projection: place.projection,
2286 is_local_mutation_allowed,
2290 // `Box<T>` owns its content, so mutable if its location is mutable
2291 _ if base_ty.is_box() => {
2292 self.is_mutable(place_base, is_local_mutation_allowed)
2294 // Deref should only be for reference, pointers or boxes
2295 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2298 // All other projections are owned by their base path, so mutable if
2299 // base path is mutable
2300 ProjectionElem::Field(..)
2301 | ProjectionElem::Index(..)
2302 | ProjectionElem::ConstantIndex { .. }
2303 | ProjectionElem::Subslice { .. }
2304 | ProjectionElem::Downcast(..) => {
2305 let upvar_field_projection = self.is_upvar_field_projection(place);
2306 if let Some(field) = upvar_field_projection {
2307 let upvar = &self.upvars[field.index()];
2309 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2310 place={:?}, place_base={:?}",
2311 upvar, is_local_mutation_allowed, place, place_base
2313 match (upvar.place.mutability, is_local_mutation_allowed) {
2316 LocalMutationIsAllowed::No
2317 | LocalMutationIsAllowed::ExceptUpvars,
2319 (Mutability::Not, LocalMutationIsAllowed::Yes)
2320 | (Mutability::Mut, _) => {
2321 // Subtle: this is an upvar
2322 // reference, so it looks like
2323 // `self.foo` -- we want to double
2324 // check that the location `*self`
2325 // is mutable (i.e., this is not a
2326 // `Fn` closure). But if that
2327 // check succeeds, we want to
2328 // *blame* the mutability on
2329 // `place` (that is,
2330 // `self.foo`). This is used to
2331 // propagate the info about
2332 // whether mutability declarations
2333 // are used outwards, so that we register
2334 // the outer variable as mutable. Otherwise a
2335 // test like this fails to record the `mut`
2339 // fn foo<F: FnOnce()>(_f: F) { }
2341 // let var = Vec::new();
2348 self.is_mutable(place_base, is_local_mutation_allowed)?;
2350 place_local: place.local,
2351 place_projection: place.projection,
2352 is_local_mutation_allowed,
2357 self.is_mutable(place_base, is_local_mutation_allowed)
2365 /// If `place` is a field projection, and the field is being projected from a closure type,
2366 /// then returns the index of the field being projected. Note that this closure will always
2367 /// be `self` in the current MIR, because that is the only time we directly access the fields
2368 /// of a closure type.
2369 fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2370 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2374 /// The degree of overlap between 2 places for borrow-checking.
2376 /// The places might partially overlap - in this case, we give
2377 /// up and say that they might conflict. This occurs when
2378 /// different fields of a union are borrowed. For example,
2379 /// if `u` is a union, we have no way of telling how disjoint
2380 /// `u.a.x` and `a.b.y` are.
2382 /// The places have the same type, and are either completely disjoint
2383 /// or equal - i.e., they can't "partially" overlap as can occur with
2384 /// unions. This is the "base case" on which we recur for extensions
2387 /// The places are disjoint, so we know all extensions of them
2388 /// will also be disjoint.