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;
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,
14 PlaceRef, VarDebugInfoContents,
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, CapturedPlace, ParamEnv, 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};
40 use self::diagnostics::{AccessKind, RegionName};
41 use self::location::LocationTable;
42 use self::prefixes::PrefixSet;
43 use self::MutateMode::{JustWrite, WriteAndRead};
45 use self::path_utils::*;
48 mod constraint_generation;
55 mod member_constraints;
64 mod universal_regions;
67 crate use borrow_set::{BorrowData, BorrowSet};
68 crate use nll::{PoloniusOutput, ToRegionVid};
69 crate use place_ext::PlaceExt;
70 crate use places_conflict::{places_conflict, PlaceConflictBias};
71 crate use region_infer::RegionInferenceContext;
73 // FIXME(eddyb) perhaps move this somewhere more centrally.
75 crate struct Upvar<'tcx> {
76 // FIXME(project-rfc_2229#36): print capture precisely here.
79 place: CapturedPlace<'tcx>,
81 /// If true, the capture is behind a reference.
85 const DEREF_PROJECTION: &[PlaceElem<'_>; 1] = &[ProjectionElem::Deref];
87 pub fn provide(providers: &mut Providers) {
88 *providers = Providers {
89 mir_borrowck: |tcx, did| {
90 if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
91 tcx.mir_borrowck_const_arg(def)
93 mir_borrowck(tcx, ty::WithOptConstParam::unknown(did))
96 mir_borrowck_const_arg: |tcx, (did, param_did)| {
97 mir_borrowck(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
103 fn mir_borrowck<'tcx>(
105 def: ty::WithOptConstParam<LocalDefId>,
106 ) -> &'tcx BorrowCheckResult<'tcx> {
107 let (input_body, promoted) = tcx.mir_promoted(def);
108 debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
110 let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
111 let input_body: &Body<'_> = &input_body.borrow();
112 let promoted: &IndexVec<_, _> = &promoted.borrow();
113 do_mir_borrowck(&infcx, input_body, promoted)
115 debug!("mir_borrowck done");
117 tcx.arena.alloc(opt_closure_req)
120 fn do_mir_borrowck<'a, 'tcx>(
121 infcx: &InferCtxt<'a, 'tcx>,
122 input_body: &Body<'tcx>,
123 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
124 ) -> BorrowCheckResult<'tcx> {
125 let def = input_body.source.with_opt_param().as_local().unwrap();
127 debug!("do_mir_borrowck(def = {:?})", def);
130 let param_env = tcx.param_env(def.did);
131 let id = tcx.hir().local_def_id_to_hir_id(def.did);
133 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
134 for var_debug_info in &input_body.var_debug_info {
135 if let VarDebugInfoContents::Place(place) = var_debug_info.value {
136 if let Some(local) = 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);
153 // Gather the upvars of a closure, if any.
154 let tables = tcx.typeck_opt_const_arg(def);
155 if let Some(ErrorReported) = tables.tainted_by_errors {
156 infcx.set_tainted_by_errors();
158 let upvars: Vec<_> = tables
159 .closure_min_captures_flattened(def.did.to_def_id())
160 .map(|captured_place| {
161 let var_hir_id = captured_place.get_root_variable();
162 let capture = captured_place.info.capture_kind;
163 let by_ref = match capture {
164 ty::UpvarCapture::ByValue(_) => false,
165 ty::UpvarCapture::ByRef(..) => true,
167 Upvar { name: tcx.hir().name(var_hir_id), place: captured_place.clone(), by_ref }
171 // Replace all regions with fresh inference variables. This
172 // requires first making our own copy of the MIR. This copy will
173 // be modified (in place) to contain non-lexical lifetimes. It
174 // will have a lifetime tied to the inference context.
175 let mut body = input_body.clone();
176 let mut promoted = input_promoted.clone();
177 let free_regions = nll::replace_regions_in_mir(infcx, param_env, &mut body, &mut promoted);
178 let body = &body; // no further changes
180 let location_table = &LocationTable::new(&body);
182 let mut errors_buffer = Vec::new();
183 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
184 match MoveData::gather_moves(&body, tcx, param_env) {
185 Ok(move_data) => (move_data, Vec::new()),
186 Err((move_data, move_errors)) => (move_data, move_errors),
188 let promoted_errors = promoted
190 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
192 let mdpe = MoveDataParamEnv { move_data, param_env };
194 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
195 .into_engine(tcx, &body)
196 .pass_name("borrowck")
197 .iterate_to_fixpoint()
198 .into_results_cursor(&body);
200 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
202 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
204 // Compute non-lexical lifetimes.
211 } = nll::compute_regions(
224 // Dump MIR results into a file, if that is enabled. This let us
225 // write unit-tests, as well as helping with debugging.
226 nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
228 // We also have a `#[rustc_regions]` annotation that causes us to dump
230 nll::dump_annotation(
239 // The various `flow_*` structures can be large. We drop `flow_inits` here
240 // so it doesn't overlap with the others below. This reduces peak memory
241 // usage significantly on some benchmarks.
244 let regioncx = Rc::new(regioncx);
246 let flow_borrows = Borrows::new(tcx, &body, ®ioncx, &borrow_set)
247 .into_engine(tcx, &body)
248 .pass_name("borrowck")
249 .iterate_to_fixpoint();
250 let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
251 .into_engine(tcx, &body)
252 .pass_name("borrowck")
253 .iterate_to_fixpoint();
254 let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
255 .into_engine(tcx, &body)
256 .pass_name("borrowck")
257 .iterate_to_fixpoint();
259 let movable_generator = match tcx.hir().get(id) {
260 Node::Expr(&hir::Expr {
261 kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
267 for (idx, move_data_results) in promoted_errors {
268 let promoted_body = &promoted[idx];
270 if let Err((move_data, move_errors)) = move_data_results {
271 let mut promoted_mbcx = MirBorrowckCtxt {
275 move_data: &move_data,
276 location_table, // no need to create a real one for the promoted, it is not used
278 fn_self_span_reported: Default::default(),
279 locals_are_invalidated_at_exit,
280 access_place_error_reported: Default::default(),
281 reservation_error_reported: Default::default(),
282 reservation_warnings: Default::default(),
283 move_error_reported: BTreeMap::new(),
284 uninitialized_error_reported: Default::default(),
286 regioncx: regioncx.clone(),
287 used_mut: Default::default(),
288 used_mut_upvars: SmallVec::new(),
289 borrow_set: Rc::clone(&borrow_set),
290 dominators: Dominators::dummy(), // not used
292 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
293 region_names: RefCell::default(),
294 next_region_name: RefCell::new(1),
295 polonius_output: None,
297 promoted_mbcx.report_move_errors(move_errors);
298 errors_buffer = promoted_mbcx.errors_buffer;
302 let dominators = body.dominators();
304 let mut mbcx = MirBorrowckCtxt {
308 move_data: &mdpe.move_data,
311 locals_are_invalidated_at_exit,
312 fn_self_span_reported: Default::default(),
313 access_place_error_reported: Default::default(),
314 reservation_error_reported: Default::default(),
315 reservation_warnings: Default::default(),
316 move_error_reported: BTreeMap::new(),
317 uninitialized_error_reported: Default::default(),
319 regioncx: Rc::clone(®ioncx),
320 used_mut: Default::default(),
321 used_mut_upvars: SmallVec::new(),
322 borrow_set: Rc::clone(&borrow_set),
326 region_names: RefCell::default(),
327 next_region_name: RefCell::new(1),
331 // Compute and report region errors, if any.
332 mbcx.report_region_errors(nll_errors);
334 let results = BorrowckResults {
335 ever_inits: flow_ever_inits,
336 uninits: flow_uninits,
337 borrows: flow_borrows,
340 mbcx.report_move_errors(move_errors);
342 dataflow::visit_results(
344 traversal::reverse_postorder(&body).map(|(bb, _)| bb),
349 // Convert any reservation warnings into lints.
350 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
351 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
352 let mut initial_diag = mbcx.report_conflicting_borrow(location, (place, span), bk, &borrow);
354 let scope = mbcx.body.source_info(location).scope;
355 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
356 ClearCrossCrate::Set(data) => data.lint_root,
360 // Span and message don't matter; we overwrite them below anyway
361 mbcx.infcx.tcx.struct_span_lint_hir(
362 MUTABLE_BORROW_RESERVATION_CONFLICT,
366 let mut diag = lint.build("");
368 diag.message = initial_diag.styled_message().clone();
369 diag.span = initial_diag.span.clone();
371 diag.buffer(&mut mbcx.errors_buffer);
374 initial_diag.cancel();
377 // For each non-user used mutable variable, check if it's been assigned from
378 // a user-declared local. If so, then put that local into the used_mut set.
379 // Note that this set is expected to be small - only upvars from closures
380 // would have a chance of erroneously adding non-user-defined mutable vars
382 let temporary_used_locals: FxHashSet<Local> = mbcx
385 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
388 // For the remaining unused locals that are marked as mutable, we avoid linting any that
389 // were never initialized. These locals may have been removed as unreachable code; or will be
390 // linted as unused variables.
391 let unused_mut_locals =
392 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
393 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
395 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
396 let used_mut = mbcx.used_mut;
397 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
398 let local_decl = &mbcx.body.local_decls[local];
399 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
400 ClearCrossCrate::Set(data) => data.lint_root,
404 // Skip over locals that begin with an underscore or have no name
405 match mbcx.local_names[local] {
407 if name.as_str().starts_with('_') {
414 let span = local_decl.source_info.span;
415 if span.desugaring_kind().is_some() {
416 // If the `mut` arises as part of a desugaring, we should ignore it.
420 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
421 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
422 lint.build("variable does not need to be mutable")
423 .span_suggestion_short(
427 Applicability::MachineApplicable,
433 // Buffer any move errors that we collected and de-duplicated.
434 for (_, (_, diag)) in mbcx.move_error_reported {
435 diag.buffer(&mut mbcx.errors_buffer);
438 if !mbcx.errors_buffer.is_empty() {
439 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
441 for diag in mbcx.errors_buffer.drain(..) {
442 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
446 let result = BorrowCheckResult {
447 concrete_opaque_types: opaque_type_values,
448 closure_requirements: opt_closure_req,
449 used_mut_upvars: mbcx.used_mut_upvars,
452 debug!("do_mir_borrowck: result = {:#?}", result);
457 crate struct MirBorrowckCtxt<'cx, 'tcx> {
458 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
459 param_env: ParamEnv<'tcx>,
460 body: &'cx Body<'tcx>,
461 move_data: &'cx MoveData<'tcx>,
463 /// Map from MIR `Location` to `LocationIndex`; created
464 /// when MIR borrowck begins.
465 location_table: &'cx LocationTable,
467 movable_generator: bool,
468 /// This keeps track of whether local variables are free-ed when the function
469 /// exits even without a `StorageDead`, which appears to be the case for
472 /// I'm not sure this is the right approach - @eddyb could you try and
474 locals_are_invalidated_at_exit: bool,
475 /// This field keeps track of when borrow errors are reported in the access_place function
476 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
477 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
478 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
480 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
481 /// This field keeps track of when borrow conflict errors are reported
482 /// for reservations, so that we don't report seemingly duplicate
483 /// errors for corresponding activations.
485 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
486 // but it is currently inconvenient to track down the `BorrowIndex`
487 // at the time we detect and report a reservation error.
488 reservation_error_reported: FxHashSet<Place<'tcx>>,
489 /// This fields keeps track of the `Span`s that we have
490 /// used to report extra information for `FnSelfUse`, to avoid
491 /// unnecessarily verbose errors.
492 fn_self_span_reported: FxHashSet<Span>,
493 /// Migration warnings to be reported for #56254. We delay reporting these
494 /// so that we can suppress the warning if there's a corresponding error
495 /// for the activation of the borrow.
496 reservation_warnings:
497 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
498 /// This field keeps track of move errors that are to be reported for given move indices.
500 /// There are situations where many errors can be reported for a single move out (see #53807)
501 /// and we want only the best of those errors.
503 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
504 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
505 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
506 /// all move errors have been reported, any diagnostics in this map are added to the buffer
509 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
510 /// when errors in the map are being re-added to the error buffer so that errors with the
511 /// same primary span come out in a consistent order.
512 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'cx>)>,
513 /// This field keeps track of errors reported in the checking of uninitialized variables,
514 /// so that we don't report seemingly duplicate errors.
515 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
516 /// Errors to be reported buffer
517 errors_buffer: Vec<Diagnostic>,
518 /// This field keeps track of all the local variables that are declared mut and are mutated.
519 /// Used for the warning issued by an unused mutable local variable.
520 used_mut: FxHashSet<Local>,
521 /// If the function we're checking is a closure, then we'll need to report back the list of
522 /// mutable upvars that have been used. This field keeps track of them.
523 used_mut_upvars: SmallVec<[Field; 8]>,
524 /// Region inference context. This contains the results from region inference and lets us e.g.
525 /// find out which CFG points are contained in each borrow region.
526 regioncx: Rc<RegionInferenceContext<'tcx>>,
528 /// The set of borrows extracted from the MIR
529 borrow_set: Rc<BorrowSet<'tcx>>,
531 /// Dominators for MIR
532 dominators: Dominators<BasicBlock>,
534 /// Information about upvars not necessarily preserved in types or MIR
535 upvars: Vec<Upvar<'tcx>>,
537 /// Names of local (user) variables (extracted from `var_debug_info`).
538 local_names: IndexVec<Local, Option<Symbol>>,
540 /// Record the region names generated for each region in the given
541 /// MIR def so that we can reuse them later in help/error messages.
542 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
544 /// The counter for generating new region names.
545 next_region_name: RefCell<usize>,
547 /// Results of Polonius analysis.
548 polonius_output: Option<Rc<PoloniusOutput>>,
552 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
553 // 2. loans made in overlapping scopes do not conflict
554 // 3. assignments do not affect things loaned out as immutable
555 // 4. moves do not affect things loaned out in any way
556 impl<'cx, 'tcx> dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
557 type FlowState = Flows<'cx, 'tcx>;
559 fn visit_statement_before_primary_effect(
561 flow_state: &Flows<'cx, 'tcx>,
562 stmt: &'cx Statement<'tcx>,
565 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
566 let span = stmt.source_info.span;
568 self.check_activations(location, span, flow_state);
571 StatementKind::Assign(box (lhs, ref rhs)) => {
572 self.consume_rvalue(location, (rhs, span), flow_state);
574 self.mutate_place(location, (*lhs, span), Shallow(None), JustWrite, flow_state);
576 StatementKind::FakeRead(_, box ref place) => {
577 // Read for match doesn't access any memory and is used to
578 // assert that a place is safe and live. So we don't have to
579 // do any checks here.
581 // FIXME: Remove check that the place is initialized. This is
582 // needed for now because matches don't have never patterns yet.
583 // So this is the only place we prevent
587 self.check_if_path_or_subpath_is_moved(
589 InitializationRequiringAction::Use,
590 (place.as_ref(), span),
594 StatementKind::SetDiscriminant { place, variant_index: _ } => {
595 self.mutate_place(location, (**place, span), Shallow(None), JustWrite, flow_state);
597 StatementKind::LlvmInlineAsm(ref asm) => {
598 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
600 // FIXME(eddyb) indirect inline asm outputs should
601 // be encoded through MIR place derefs instead.
605 (Deep, Read(ReadKind::Copy)),
606 LocalMutationIsAllowed::No,
609 self.check_if_path_or_subpath_is_moved(
611 InitializationRequiringAction::Use,
612 (output.as_ref(), o.span),
619 if o.is_rw { Deep } else { Shallow(None) },
620 if o.is_rw { WriteAndRead } else { JustWrite },
625 for (_, input) in asm.inputs.iter() {
626 self.consume_operand(location, (input, span), flow_state);
630 | StatementKind::Coverage(..)
631 | StatementKind::AscribeUserType(..)
632 | StatementKind::Retag { .. }
633 | StatementKind::StorageLive(..) => {
634 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
637 StatementKind::StorageDead(local) => {
640 (Place::from(*local), span),
641 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
642 LocalMutationIsAllowed::Yes,
649 fn visit_terminator_before_primary_effect(
651 flow_state: &Flows<'cx, 'tcx>,
652 term: &'cx Terminator<'tcx>,
655 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
656 let span = term.source_info.span;
658 self.check_activations(loc, span, flow_state);
661 TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
662 self.consume_operand(loc, (discr, span), flow_state);
664 TerminatorKind::Drop { place, target: _, unwind: _ } => {
666 "visit_terminator_drop \
667 loc: {:?} term: {:?} place: {:?} span: {:?}",
668 loc, term, place, span
674 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
675 LocalMutationIsAllowed::Yes,
679 TerminatorKind::DropAndReplace {
681 value: ref new_value,
685 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
686 self.consume_operand(loc, (new_value, span), flow_state);
688 TerminatorKind::Call {
696 self.consume_operand(loc, (func, span), flow_state);
698 self.consume_operand(loc, (arg, span), flow_state);
700 if let Some((dest, _ /*bb*/)) = *destination {
701 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
704 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
705 self.consume_operand(loc, (cond, span), flow_state);
706 use rustc_middle::mir::AssertKind;
707 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
708 self.consume_operand(loc, (len, span), flow_state);
709 self.consume_operand(loc, (index, span), flow_state);
713 TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
714 self.consume_operand(loc, (value, span), flow_state);
715 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
718 TerminatorKind::InlineAsm {
727 InlineAsmOperand::In { reg: _, ref value }
728 | InlineAsmOperand::Const { ref value } => {
729 self.consume_operand(loc, (value, span), flow_state);
731 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
732 if let Some(place) = place {
742 InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
743 self.consume_operand(loc, (in_value, span), flow_state);
744 if let Some(out_place) = out_place {
754 InlineAsmOperand::SymFn { value: _ }
755 | InlineAsmOperand::SymStatic { def_id: _ } => {}
760 TerminatorKind::Goto { target: _ }
761 | TerminatorKind::Abort
762 | TerminatorKind::Unreachable
763 | TerminatorKind::Resume
764 | TerminatorKind::Return
765 | TerminatorKind::GeneratorDrop
766 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
767 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
768 // no data used, thus irrelevant to borrowck
773 fn visit_terminator_after_primary_effect(
775 flow_state: &Flows<'cx, 'tcx>,
776 term: &'cx Terminator<'tcx>,
779 let span = term.source_info.span;
782 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
783 if self.movable_generator {
784 // Look for any active borrows to locals
785 let borrow_set = self.borrow_set.clone();
786 for i in flow_state.borrows.iter() {
787 let borrow = &borrow_set[i];
788 self.check_for_local_borrow(borrow, span);
793 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
794 // Returning from the function implicitly kills storage for all locals and statics.
795 // Often, the storage will already have been killed by an explicit
796 // StorageDead, but we don't always emit those (notably on unwind paths),
797 // so this "extra check" serves as a kind of backup.
798 let borrow_set = self.borrow_set.clone();
799 for i in flow_state.borrows.iter() {
800 let borrow = &borrow_set[i];
801 self.check_for_invalidation_at_exit(loc, borrow, span);
805 TerminatorKind::Abort
806 | TerminatorKind::Assert { .. }
807 | TerminatorKind::Call { .. }
808 | TerminatorKind::Drop { .. }
809 | TerminatorKind::DropAndReplace { .. }
810 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
811 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
812 | TerminatorKind::Goto { .. }
813 | TerminatorKind::SwitchInt { .. }
814 | TerminatorKind::Unreachable
815 | TerminatorKind::InlineAsm { .. } => {}
820 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
826 use self::AccessDepth::{Deep, Shallow};
827 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
829 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
830 enum ArtificialField {
835 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
837 /// From the RFC: "A *shallow* access means that the immediate
838 /// fields reached at P are accessed, but references or pointers
839 /// found within are not dereferenced. Right now, the only access
840 /// that is shallow is an assignment like `x = ...;`, which would
841 /// be a *shallow write* of `x`."
842 Shallow(Option<ArtificialField>),
844 /// From the RFC: "A *deep* access means that all data reachable
845 /// through the given place may be invalidated or accesses by
849 /// Access is Deep only when there is a Drop implementation that
850 /// can reach the data behind the reference.
854 /// Kind of access to a value: read or write
855 /// (For informational purposes only)
856 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
858 /// From the RFC: "A *read* means that the existing data may be
859 /// read, but will not be changed."
862 /// From the RFC: "A *write* means that the data may be mutated to
863 /// new values or otherwise invalidated (for example, it could be
864 /// de-initialized, as in a move operation).
867 /// For two-phase borrows, we distinguish a reservation (which is treated
868 /// like a Read) from an activation (which is treated like a write), and
869 /// each of those is furthermore distinguished from Reads/Writes above.
870 Reservation(WriteKind),
871 Activation(WriteKind, BorrowIndex),
874 /// Kind of read access to a value
875 /// (For informational purposes only)
876 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
882 /// Kind of write access to a value
883 /// (For informational purposes only)
884 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
887 MutableBorrow(BorrowKind),
892 /// When checking permissions for a place access, this flag is used to indicate that an immutable
893 /// local place can be mutated.
895 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
896 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
897 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
898 // `is_declared_mutable()`.
899 // - Take flow state into consideration in `is_assignable()` for local variables.
900 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
901 enum LocalMutationIsAllowed {
903 /// We want use of immutable upvars to cause a "write to immutable upvar"
904 /// error, not an "reassignment" error.
909 #[derive(Copy, Clone, Debug)]
910 enum InitializationRequiringAction {
919 struct RootPlace<'tcx> {
921 place_projection: &'tcx [PlaceElem<'tcx>],
922 is_local_mutation_allowed: LocalMutationIsAllowed,
925 impl InitializationRequiringAction {
926 fn as_noun(self) -> &'static str {
928 InitializationRequiringAction::Update => "update",
929 InitializationRequiringAction::Borrow => "borrow",
930 InitializationRequiringAction::MatchOn => "use", // no good noun
931 InitializationRequiringAction::Use => "use",
932 InitializationRequiringAction::Assignment => "assign",
933 InitializationRequiringAction::PartialAssignment => "assign to part",
937 fn as_verb_in_past_tense(self) -> &'static str {
939 InitializationRequiringAction::Update => "updated",
940 InitializationRequiringAction::Borrow => "borrowed",
941 InitializationRequiringAction::MatchOn => "matched on",
942 InitializationRequiringAction::Use => "used",
943 InitializationRequiringAction::Assignment => "assigned",
944 InitializationRequiringAction::PartialAssignment => "partially assigned",
949 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
950 fn body(&self) -> &'cx Body<'tcx> {
954 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
955 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
956 /// place is initialized and (b) it is not borrowed in some way that would prevent this
959 /// Returns `true` if an error is reported.
963 place_span: (Place<'tcx>, Span),
964 kind: (AccessDepth, ReadOrWrite),
965 is_local_mutation_allowed: LocalMutationIsAllowed,
966 flow_state: &Flows<'cx, 'tcx>,
970 if let Activation(_, borrow_index) = rw {
971 if self.reservation_error_reported.contains(&place_span.0) {
973 "skipping access_place for activation of invalid reservation \
974 place: {:?} borrow_index: {:?}",
975 place_span.0, borrow_index
981 // Check is_empty() first because it's the common case, and doing that
982 // way we avoid the clone() call.
983 if !self.access_place_error_reported.is_empty()
984 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
987 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
993 let mutability_error = self.check_access_permissions(
996 is_local_mutation_allowed,
1000 let conflict_error =
1001 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
1003 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
1004 // Suppress this warning when there's an error being emitted for the
1005 // same borrow: fixing the error is likely to fix the warning.
1006 self.reservation_warnings.remove(&borrow_idx);
1009 if conflict_error || mutability_error {
1010 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
1012 self.access_place_error_reported.insert((place_span.0, place_span.1));
1016 fn check_access_for_conflict(
1019 place_span: (Place<'tcx>, Span),
1022 flow_state: &Flows<'cx, 'tcx>,
1025 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
1026 location, place_span, sd, rw,
1029 let mut error_reported = false;
1030 let tcx = self.infcx.tcx;
1031 let body = self.body;
1032 let borrow_set = self.borrow_set.clone();
1034 // Use polonius output if it has been enabled.
1035 let polonius_output = self.polonius_output.clone();
1036 let borrows_in_scope = if let Some(polonius) = &polonius_output {
1037 let location = self.location_table.start_index(location);
1038 Either::Left(polonius.errors_at(location).iter().copied())
1040 Either::Right(flow_state.borrows.iter())
1043 each_borrow_involving_path(
1051 |this, borrow_index, borrow| match (rw, borrow.kind) {
1052 // Obviously an activation is compatible with its own
1053 // reservation (or even prior activating uses of same
1054 // borrow); so don't check if they interfere.
1056 // NOTE: *reservations* do conflict with themselves;
1057 // thus aren't injecting unsoundenss w/ this check.)
1058 (Activation(_, activating), _) if activating == borrow_index => {
1060 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1061 skipping {:?} b/c activation of same borrow_index",
1065 (borrow_index, borrow),
1070 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1072 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1073 BorrowKind::Unique | BorrowKind::Mut { .. },
1074 ) => Control::Continue,
1076 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1077 // Handled by initialization checks.
1081 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1082 // Reading from mere reservations of mutable-borrows is OK.
1083 if !is_active(&this.dominators, borrow, location) {
1084 assert!(allow_two_phase_borrow(borrow.kind));
1085 return Control::Continue;
1088 error_reported = true;
1091 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1092 .buffer(&mut this.errors_buffer);
1094 ReadKind::Borrow(bk) => {
1095 this.report_conflicting_borrow(location, place_span, bk, borrow)
1096 .buffer(&mut this.errors_buffer);
1103 Reservation(WriteKind::MutableBorrow(bk)),
1104 BorrowKind::Shallow | BorrowKind::Shared,
1105 ) if { tcx.migrate_borrowck() && this.borrow_set.contains(&location) } => {
1106 let bi = this.borrow_set.get_index_of(&location).unwrap();
1108 "recording invalid reservation of place: {:?} with \
1109 borrow index {:?} as warning",
1112 // rust-lang/rust#56254 - This was previously permitted on
1113 // the 2018 edition so we emit it as a warning. We buffer
1114 // these sepately so that we only emit a warning if borrow
1115 // checking was otherwise successful.
1116 this.reservation_warnings
1117 .insert(bi, (place_span.0, place_span.1, location, bk, borrow.clone()));
1119 // Don't suppress actual errors.
1123 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1125 Reservation(..) => {
1127 "recording invalid reservation of \
1131 this.reservation_error_reported.insert(place_span.0);
1133 Activation(_, activating) => {
1135 "observing check_place for activation of \
1136 borrow_index: {:?}",
1140 Read(..) | Write(..) => {}
1143 error_reported = true;
1145 WriteKind::MutableBorrow(bk) => {
1146 this.report_conflicting_borrow(location, place_span, bk, borrow)
1147 .buffer(&mut this.errors_buffer);
1149 WriteKind::StorageDeadOrDrop => this
1150 .report_borrowed_value_does_not_live_long_enough(
1156 WriteKind::Mutate => {
1157 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1159 WriteKind::Move => {
1160 this.report_move_out_while_borrowed(location, place_span, borrow)
1174 place_span: (Place<'tcx>, Span),
1177 flow_state: &Flows<'cx, 'tcx>,
1179 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1181 MutateMode::WriteAndRead => {
1182 self.check_if_path_or_subpath_is_moved(
1184 InitializationRequiringAction::Update,
1185 (place_span.0.as_ref(), place_span.1),
1189 MutateMode::JustWrite => {
1190 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1194 // Special case: you can assign a immutable local variable
1195 // (e.g., `x = ...`) so long as it has never been initialized
1196 // before (at this point in the flow).
1197 if let Some(local) = place_span.0.as_local() {
1198 if let Mutability::Not = self.body.local_decls[local].mutability {
1199 // check for reassignments to immutable local variables
1200 self.check_if_reassignment_to_immutable_state(
1201 location, local, place_span, flow_state,
1207 // Otherwise, use the normal access permission rules.
1211 (kind, Write(WriteKind::Mutate)),
1212 LocalMutationIsAllowed::No,
1220 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1221 flow_state: &Flows<'cx, 'tcx>,
1224 Rvalue::Ref(_ /*rgn*/, bk, place) => {
1225 let access_kind = match bk {
1226 BorrowKind::Shallow => {
1227 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1229 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1230 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1231 let wk = WriteKind::MutableBorrow(bk);
1232 if allow_two_phase_borrow(bk) {
1233 (Deep, Reservation(wk))
1244 LocalMutationIsAllowed::No,
1248 let action = if bk == BorrowKind::Shallow {
1249 InitializationRequiringAction::MatchOn
1251 InitializationRequiringAction::Borrow
1254 self.check_if_path_or_subpath_is_moved(
1257 (place.as_ref(), span),
1262 Rvalue::AddressOf(mutability, place) => {
1263 let access_kind = match mutability {
1264 Mutability::Mut => (
1266 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1267 allow_two_phase_borrow: false,
1270 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1277 LocalMutationIsAllowed::No,
1281 self.check_if_path_or_subpath_is_moved(
1283 InitializationRequiringAction::Borrow,
1284 (place.as_ref(), span),
1289 Rvalue::ThreadLocalRef(_) => {}
1291 Rvalue::Use(ref operand)
1292 | Rvalue::Repeat(ref operand, _)
1293 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1294 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1295 self.consume_operand(location, (operand, span), flow_state)
1298 Rvalue::Len(place) | Rvalue::Discriminant(place) => {
1299 let af = match *rvalue {
1300 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1301 Rvalue::Discriminant(..) => None,
1302 _ => unreachable!(),
1307 (Shallow(af), Read(ReadKind::Copy)),
1308 LocalMutationIsAllowed::No,
1311 self.check_if_path_or_subpath_is_moved(
1313 InitializationRequiringAction::Use,
1314 (place.as_ref(), span),
1319 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1320 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1321 self.consume_operand(location, (operand1, span), flow_state);
1322 self.consume_operand(location, (operand2, span), flow_state);
1325 Rvalue::NullaryOp(_op, _ty) => {
1326 // nullary ops take no dynamic input; no borrowck effect.
1328 // FIXME: is above actually true? Do we want to track
1329 // the fact that uninitialized data can be created via
1333 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1334 // We need to report back the list of mutable upvars that were
1335 // moved into the closure and subsequently used by the closure,
1336 // in order to populate our used_mut set.
1337 match **aggregate_kind {
1338 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1339 let BorrowCheckResult { used_mut_upvars, .. } =
1340 self.infcx.tcx.mir_borrowck(def_id.expect_local());
1341 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1342 for field in used_mut_upvars {
1343 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1346 AggregateKind::Adt(..)
1347 | AggregateKind::Array(..)
1348 | AggregateKind::Tuple { .. } => (),
1351 for operand in operands {
1352 self.consume_operand(location, (operand, span), flow_state);
1358 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1359 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1360 // We have three possibilities here:
1361 // a. We are modifying something through a mut-ref
1362 // b. We are modifying something that is local to our parent
1363 // c. Current body is a nested closure, and we are modifying path starting from
1364 // a Place captured by our parent closure.
1366 // Handle (c), the path being modified is exactly the path captured by our parent
1367 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1368 this.used_mut_upvars.push(field);
1372 for (place_ref, proj) in place.iter_projections().rev() {
1374 if proj == ProjectionElem::Deref {
1375 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1376 // We aren't modifying a variable directly
1377 ty::Ref(_, _, hir::Mutability::Mut) => return,
1384 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1385 this.used_mut_upvars.push(field);
1391 this.used_mut.insert(place.local);
1394 // This relies on the current way that by-value
1395 // captures of a closure are copied/moved directly
1396 // when generating MIR.
1398 Operand::Move(place) | Operand::Copy(place) => {
1399 match place.as_local() {
1400 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1401 if self.body.local_decls[local].ty.is_mutable_ptr() {
1402 // The variable will be marked as mutable by the borrow.
1405 // This is an edge case where we have a `move` closure
1406 // inside a non-move closure, and the inner closure
1407 // contains a mutation:
1410 // || { move || { i += 1; }; };
1412 // In this case our usual strategy of assuming that the
1413 // variable will be captured by mutable reference is
1414 // wrong, since `i` can be copied into the inner
1415 // closure from a shared reference.
1417 // As such we have to search for the local that this
1418 // capture comes from and mark it as being used as mut.
1420 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1421 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1422 &self.move_data.inits[init_index]
1424 bug!("temporary should be initialized exactly once")
1427 let loc = match init.location {
1428 InitLocation::Statement(stmt) => stmt,
1429 _ => bug!("temporary initialized in arguments"),
1432 let body = self.body;
1433 let bbd = &body[loc.block];
1434 let stmt = &bbd.statements[loc.statement_index];
1435 debug!("temporary assigned in: stmt={:?}", stmt);
1437 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1439 propagate_closure_used_mut_place(self, source);
1442 "closures should only capture user variables \
1443 or references to user variables"
1447 _ => propagate_closure_used_mut_place(self, place),
1450 Operand::Constant(..) => {}
1457 (operand, span): (&'cx Operand<'tcx>, Span),
1458 flow_state: &Flows<'cx, 'tcx>,
1461 Operand::Copy(place) => {
1462 // copy of place: check if this is "copy of frozen path"
1463 // (FIXME: see check_loans.rs)
1467 (Deep, Read(ReadKind::Copy)),
1468 LocalMutationIsAllowed::No,
1472 // Finally, check if path was already moved.
1473 self.check_if_path_or_subpath_is_moved(
1475 InitializationRequiringAction::Use,
1476 (place.as_ref(), span),
1480 Operand::Move(place) => {
1481 // move of place: check if this is move of already borrowed path
1485 (Deep, Write(WriteKind::Move)),
1486 LocalMutationIsAllowed::Yes,
1490 // Finally, check if path was already moved.
1491 self.check_if_path_or_subpath_is_moved(
1493 InitializationRequiringAction::Use,
1494 (place.as_ref(), span),
1498 Operand::Constant(_) => {}
1502 /// Checks whether a borrow of this place is invalidated when the function
1504 fn check_for_invalidation_at_exit(
1507 borrow: &BorrowData<'tcx>,
1510 debug!("check_for_invalidation_at_exit({:?})", borrow);
1511 let place = borrow.borrowed_place;
1512 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1514 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1515 // we just know that all locals are dropped at function exit (otherwise
1516 // we'll have a memory leak) and assume that all statics have a destructor.
1518 // FIXME: allow thread-locals to borrow other thread locals?
1520 let (might_be_alive, will_be_dropped) =
1521 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1522 // Thread-locals might be dropped after the function exits
1523 // We have to dereference the outer reference because
1524 // borrows don't conflict behind shared references.
1525 root_place.projection = DEREF_PROJECTION;
1528 (false, self.locals_are_invalidated_at_exit)
1531 if !will_be_dropped {
1532 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1536 let sd = if might_be_alive { Deep } else { Shallow(None) };
1538 if places_conflict::borrow_conflicts_with_place(
1545 places_conflict::PlaceConflictBias::Overlap,
1547 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1548 // FIXME: should be talking about the region lifetime instead
1549 // of just a span here.
1550 let span = self.infcx.tcx.sess.source_map().end_point(span);
1551 self.report_borrowed_value_does_not_live_long_enough(
1560 /// Reports an error if this is a borrow of local data.
1561 /// This is called for all Yield expressions on movable generators
1562 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1563 debug!("check_for_local_borrow({:?})", borrow);
1565 if borrow_of_local_data(borrow.borrowed_place) {
1566 let err = self.cannot_borrow_across_generator_yield(
1567 self.retrieve_borrow_spans(borrow).var_or_use(),
1571 err.buffer(&mut self.errors_buffer);
1575 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1576 // Two-phase borrow support: For each activation that is newly
1577 // generated at this statement, check if it interferes with
1579 let borrow_set = self.borrow_set.clone();
1580 for &borrow_index in borrow_set.activations_at_location(location) {
1581 let borrow = &borrow_set[borrow_index];
1583 // only mutable borrows should be 2-phase
1584 assert!(match borrow.kind {
1585 BorrowKind::Shared | BorrowKind::Shallow => false,
1586 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1591 (borrow.borrowed_place, span),
1592 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1593 LocalMutationIsAllowed::No,
1596 // We do not need to call `check_if_path_or_subpath_is_moved`
1597 // again, as we already called it when we made the
1598 // initial reservation.
1602 fn check_if_reassignment_to_immutable_state(
1606 place_span: (Place<'tcx>, Span),
1607 flow_state: &Flows<'cx, 'tcx>,
1609 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1611 // Check if any of the initializiations of `local` have happened yet:
1612 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1613 // And, if so, report an error.
1614 let init = &self.move_data.inits[init_index];
1615 let span = init.span(&self.body);
1616 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1620 fn check_if_full_path_is_moved(
1623 desired_action: InitializationRequiringAction,
1624 place_span: (PlaceRef<'tcx>, Span),
1625 flow_state: &Flows<'cx, 'tcx>,
1627 let maybe_uninits = &flow_state.uninits;
1631 // 1. Move of `a.b.c`, use of `a.b.c`
1632 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1633 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1634 // partial initialization support, one might have `a.x`
1635 // initialized but not `a.b`.
1639 // 4. Move of `a.b.c`, use of `a.b.d`
1640 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1641 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1642 // must have been initialized for the use to be sound.
1643 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1645 // The dataflow tracks shallow prefixes distinctly (that is,
1646 // field-accesses on P distinctly from P itself), in order to
1647 // track substructure initialization separately from the whole
1650 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1651 // which we have a MovePath is `a.b`, then that means that the
1652 // initialization state of `a.b` is all we need to inspect to
1653 // know if `a.b.c` is valid (and from that we infer that the
1654 // dereference and `.d` access is also valid, since we assume
1655 // `a.b.c` is assigned a reference to a initialized and
1656 // well-formed record structure.)
1658 // Therefore, if we seek out the *closest* prefix for which we
1659 // have a MovePath, that should capture the initialization
1660 // state for the place scenario.
1662 // This code covers scenarios 1, 2, and 3.
1664 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1665 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1666 if maybe_uninits.contains(mpi) {
1667 self.report_use_of_moved_or_uninitialized(
1670 (prefix, place_span.0, place_span.1),
1673 } // Only query longest prefix with a MovePath, not further
1674 // ancestors; dataflow recurs on children when parents
1675 // move (to support partial (re)inits).
1677 // (I.e., querying parents breaks scenario 7; but may want
1678 // to do such a query based on partial-init feature-gate.)
1681 /// Subslices correspond to multiple move paths, so we iterate through the
1682 /// elements of the base array. For each element we check
1684 /// * Does this element overlap with our slice.
1685 /// * Is any part of it uninitialized.
1686 fn check_if_subslice_element_is_moved(
1689 desired_action: InitializationRequiringAction,
1690 place_span: (PlaceRef<'tcx>, Span),
1691 maybe_uninits: &BitSet<MovePathIndex>,
1695 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1696 let move_paths = &self.move_data.move_paths;
1698 let root_path = &move_paths[mpi];
1699 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1700 let last_proj = child_move_path.place.projection.last().unwrap();
1701 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1702 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1704 if (from..to).contains(offset) {
1706 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1707 maybe_uninits.contains(mpi)
1710 if let Some(uninit_child) = uninit_child {
1711 self.report_use_of_moved_or_uninitialized(
1714 (place_span.0, place_span.0, place_span.1),
1717 return; // don't bother finding other problems.
1725 fn check_if_path_or_subpath_is_moved(
1728 desired_action: InitializationRequiringAction,
1729 place_span: (PlaceRef<'tcx>, Span),
1730 flow_state: &Flows<'cx, 'tcx>,
1732 let maybe_uninits = &flow_state.uninits;
1736 // 1. Move of `a.b.c`, use of `a` or `a.b`
1737 // partial initialization support, one might have `a.x`
1738 // initialized but not `a.b`.
1739 // 2. All bad scenarios from `check_if_full_path_is_moved`
1743 // 3. Move of `a.b.c`, use of `a.b.d`
1744 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1745 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1746 // must have been initialized for the use to be sound.
1747 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1749 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1751 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1752 place_span.0.last_projection()
1754 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1755 if let ty::Array(..) = place_ty.ty.kind() {
1756 self.check_if_subslice_element_is_moved(
1759 (place_base, place_span.1),
1768 // A move of any shallow suffix of `place` also interferes
1769 // with an attempt to use `place`. This is scenario 3 above.
1771 // (Distinct from handling of scenarios 1+2+4 above because
1772 // `place` does not interfere with suffixes of its prefixes,
1773 // e.g., `a.b.c` does not interfere with `a.b.d`)
1775 // This code covers scenario 1.
1777 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1778 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1779 let uninit_mpi = self
1781 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1783 if let Some(uninit_mpi) = uninit_mpi {
1784 self.report_use_of_moved_or_uninitialized(
1787 (place_span.0, place_span.0, place_span.1),
1790 return; // don't bother finding other problems.
1795 /// Currently MoveData does not store entries for all places in
1796 /// the input MIR. For example it will currently filter out
1797 /// places that are Copy; thus we do not track places of shared
1798 /// reference type. This routine will walk up a place along its
1799 /// prefixes, searching for a foundational place that *is*
1800 /// tracked in the MoveData.
1802 /// An Err result includes a tag indicated why the search failed.
1803 /// Currently this can only occur if the place is built off of a
1804 /// static variable, as we do not track those in the MoveData.
1805 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1806 match self.move_data.rev_lookup.find(place) {
1807 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1808 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1810 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1814 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1815 // If returns None, then there is no move path corresponding
1816 // to a direct owner of `place` (which means there is nothing
1817 // that borrowck tracks for its analysis).
1819 match self.move_data.rev_lookup.find(place) {
1820 LookupResult::Parent(_) => None,
1821 LookupResult::Exact(mpi) => Some(mpi),
1825 fn check_if_assigned_path_is_moved(
1828 (place, span): (Place<'tcx>, Span),
1829 flow_state: &Flows<'cx, 'tcx>,
1831 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1833 // None case => assigning to `x` does not require `x` be initialized.
1834 for (place_base, elem) in place.iter_projections().rev() {
1836 ProjectionElem::Index(_/*operand*/) |
1837 ProjectionElem::ConstantIndex { .. } |
1838 // assigning to P[i] requires P to be valid.
1839 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1840 // assigning to (P->variant) is okay if assigning to `P` is okay
1842 // FIXME: is this true even if P is a adt with a dtor?
1845 // assigning to (*P) requires P to be initialized
1846 ProjectionElem::Deref => {
1847 self.check_if_full_path_is_moved(
1848 location, InitializationRequiringAction::Use,
1849 (place_base, span), flow_state);
1850 // (base initialized; no need to
1855 ProjectionElem::Subslice { .. } => {
1856 panic!("we don't allow assignments to subslices, location: {:?}",
1860 ProjectionElem::Field(..) => {
1861 // if type of `P` has a dtor, then
1862 // assigning to `P.f` requires `P` itself
1863 // be already initialized
1864 let tcx = self.infcx.tcx;
1865 let base_ty = place_base.ty(self.body(), tcx).ty;
1866 match base_ty.kind() {
1867 ty::Adt(def, _) if def.has_dtor(tcx) => {
1868 self.check_if_path_or_subpath_is_moved(
1869 location, InitializationRequiringAction::Assignment,
1870 (place_base, span), flow_state);
1872 // (base initialized; no need to
1877 // Once `let s; s.x = V; read(s.x);`,
1878 // is allowed, remove this match arm.
1879 ty::Adt(..) | ty::Tuple(..) => {
1880 check_parent_of_field(self, location, place_base, span, flow_state);
1882 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1883 // partial initialization, do not complain about unnecessary `mut` on
1884 // an attempt to do a partial initialization.
1885 self.used_mut.insert(place.local);
1894 fn check_parent_of_field<'cx, 'tcx>(
1895 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1897 base: PlaceRef<'tcx>,
1899 flow_state: &Flows<'cx, 'tcx>,
1901 // rust-lang/rust#21232: Until Rust allows reads from the
1902 // initialized parts of partially initialized structs, we
1903 // will, starting with the 2018 edition, reject attempts
1904 // to write to structs that are not fully initialized.
1906 // In other words, *until* we allow this:
1908 // 1. `let mut s; s.x = Val; read(s.x);`
1910 // we will for now disallow this:
1912 // 2. `let mut s; s.x = Val;`
1916 // 3. `let mut s = ...; drop(s); s.x=Val;`
1918 // This does not use check_if_path_or_subpath_is_moved,
1919 // because we want to *allow* reinitializations of fields:
1920 // e.g., want to allow
1922 // `let mut s = ...; drop(s.x); s.x=Val;`
1924 // This does not use check_if_full_path_is_moved on
1925 // `base`, because that would report an error about the
1926 // `base` as a whole, but in this scenario we *really*
1927 // want to report an error about the actual thing that was
1928 // moved, which may be some prefix of `base`.
1930 // Shallow so that we'll stop at any dereference; we'll
1931 // report errors about issues with such bases elsewhere.
1932 let maybe_uninits = &flow_state.uninits;
1934 // Find the shortest uninitialized prefix you can reach
1935 // without going over a Deref.
1936 let mut shortest_uninit_seen = None;
1937 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1938 let mpi = match this.move_path_for_place(prefix) {
1943 if maybe_uninits.contains(mpi) {
1945 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1946 shortest_uninit_seen,
1949 shortest_uninit_seen = Some((prefix, mpi));
1951 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1955 if let Some((prefix, mpi)) = shortest_uninit_seen {
1956 // Check for a reassignment into a uninitialized field of a union (for example,
1957 // after a move out). In this case, do not report a error here. There is an
1958 // exception, if this is the first assignment into the union (that is, there is
1959 // no move out from an earlier location) then this is an attempt at initialization
1960 // of the union - we should error in that case.
1961 let tcx = this.infcx.tcx;
1962 if let ty::Adt(def, _) = base.ty(this.body(), tcx).ty.kind() {
1964 if this.move_data.path_map[mpi].iter().any(|moi| {
1965 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1972 this.report_use_of_moved_or_uninitialized(
1974 InitializationRequiringAction::PartialAssignment,
1975 (prefix, base, span),
1982 /// Checks the permissions for the given place and read or write kind
1984 /// Returns `true` if an error is reported.
1985 fn check_access_permissions(
1987 (place, span): (Place<'tcx>, Span),
1989 is_local_mutation_allowed: LocalMutationIsAllowed,
1990 flow_state: &Flows<'cx, 'tcx>,
1994 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1995 place, kind, is_local_mutation_allowed
2002 Reservation(WriteKind::MutableBorrow(
2003 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
2005 | Write(WriteKind::MutableBorrow(
2006 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
2008 let is_local_mutation_allowed = match borrow_kind {
2009 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
2010 BorrowKind::Mut { .. } => is_local_mutation_allowed,
2011 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
2013 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
2015 self.add_used_mut(root_place, flow_state);
2019 error_access = AccessKind::MutableBorrow;
2020 the_place_err = place_err;
2024 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
2025 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
2027 self.add_used_mut(root_place, flow_state);
2031 error_access = AccessKind::Mutate;
2032 the_place_err = place_err;
2039 | WriteKind::StorageDeadOrDrop
2040 | WriteKind::MutableBorrow(BorrowKind::Shared)
2041 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2045 | WriteKind::StorageDeadOrDrop
2046 | WriteKind::MutableBorrow(BorrowKind::Shared)
2047 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2049 if let (Err(_), true) = (
2050 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
2051 self.errors_buffer.is_empty(),
2053 // rust-lang/rust#46908: In pure NLL mode this code path should be
2054 // unreachable, but we use `delay_span_bug` because we can hit this when
2055 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
2056 // enabled. We don't want to ICE for that case, as other errors will have
2057 // been emitted (#52262).
2058 self.infcx.tcx.sess.delay_span_bug(
2061 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2069 // permission checks are done at Reservation point.
2075 | BorrowKind::Mut { .. }
2076 | BorrowKind::Shared
2077 | BorrowKind::Shallow,
2081 // Access authorized
2086 // rust-lang/rust#21232, #54986: during period where we reject
2087 // partial initialization, do not complain about mutability
2088 // errors except for actual mutation (as opposed to an attempt
2089 // to do a partial initialization).
2090 let previously_initialized =
2091 self.is_local_ever_initialized(place.local, flow_state).is_some();
2093 // at this point, we have set up the error reporting state.
2094 if previously_initialized {
2095 self.report_mutability_error(place, span, the_place_err, error_access, location);
2102 fn is_local_ever_initialized(
2105 flow_state: &Flows<'cx, 'tcx>,
2106 ) -> Option<InitIndex> {
2107 let mpi = self.move_data.rev_lookup.find_local(local);
2108 let ii = &self.move_data.init_path_map[mpi];
2110 if flow_state.ever_inits.contains(index) {
2117 /// Adds the place into the used mutable variables set
2118 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2120 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2121 // If the local may have been initialized, and it is now currently being
2122 // mutated, then it is justified to be annotated with the `mut`
2123 // keyword, since the mutation may be a possible reassignment.
2124 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2125 && self.is_local_ever_initialized(local, flow_state).is_some()
2127 self.used_mut.insert(local);
2132 place_projection: _,
2133 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2137 place_projection: place_projection @ [.., _],
2138 is_local_mutation_allowed: _,
2140 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2142 projection: place_projection,
2144 self.used_mut_upvars.push(field);
2150 /// Whether this value can be written or borrowed mutably.
2151 /// Returns the root place if the place passed in is a projection.
2154 place: PlaceRef<'tcx>,
2155 is_local_mutation_allowed: LocalMutationIsAllowed,
2156 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2157 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2158 match place.last_projection() {
2160 let local = &self.body.local_decls[place.local];
2161 match local.mutability {
2162 Mutability::Not => match is_local_mutation_allowed {
2163 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2164 place_local: place.local,
2165 place_projection: place.projection,
2166 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2168 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2169 place_local: place.local,
2170 place_projection: place.projection,
2171 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2173 LocalMutationIsAllowed::No => Err(place),
2175 Mutability::Mut => Ok(RootPlace {
2176 place_local: place.local,
2177 place_projection: place.projection,
2178 is_local_mutation_allowed,
2182 Some((place_base, elem)) => {
2184 ProjectionElem::Deref => {
2185 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2187 // Check the kind of deref to decide
2188 match base_ty.kind() {
2189 ty::Ref(_, _, mutbl) => {
2191 // Shared borrowed data is never mutable
2192 hir::Mutability::Not => Err(place),
2193 // Mutably borrowed data is mutable, but only if we have a
2194 // unique path to the `&mut`
2195 hir::Mutability::Mut => {
2196 let mode = match self.is_upvar_field_projection(place) {
2197 Some(field) if self.upvars[field.index()].by_ref => {
2198 is_local_mutation_allowed
2200 _ => LocalMutationIsAllowed::Yes,
2203 self.is_mutable(place_base, mode)
2207 ty::RawPtr(tnm) => {
2209 // `*const` raw pointers are not mutable
2210 hir::Mutability::Not => Err(place),
2211 // `*mut` raw pointers are always mutable, regardless of
2212 // context. The users have to check by themselves.
2213 hir::Mutability::Mut => Ok(RootPlace {
2214 place_local: place.local,
2215 place_projection: place.projection,
2216 is_local_mutation_allowed,
2220 // `Box<T>` owns its content, so mutable if its location is mutable
2221 _ if base_ty.is_box() => {
2222 self.is_mutable(place_base, is_local_mutation_allowed)
2224 // Deref should only be for reference, pointers or boxes
2225 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2228 // All other projections are owned by their base path, so mutable if
2229 // base path is mutable
2230 ProjectionElem::Field(..)
2231 | ProjectionElem::Index(..)
2232 | ProjectionElem::ConstantIndex { .. }
2233 | ProjectionElem::Subslice { .. }
2234 | ProjectionElem::Downcast(..) => {
2235 let upvar_field_projection = self.is_upvar_field_projection(place);
2236 if let Some(field) = upvar_field_projection {
2237 let upvar = &self.upvars[field.index()];
2239 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2240 place={:?}, place_base={:?}",
2241 upvar, is_local_mutation_allowed, place, place_base
2243 match (upvar.place.mutability, is_local_mutation_allowed) {
2246 LocalMutationIsAllowed::No
2247 | LocalMutationIsAllowed::ExceptUpvars,
2249 (Mutability::Not, LocalMutationIsAllowed::Yes)
2250 | (Mutability::Mut, _) => {
2251 // Subtle: this is an upvar
2252 // reference, so it looks like
2253 // `self.foo` -- we want to double
2254 // check that the location `*self`
2255 // is mutable (i.e., this is not a
2256 // `Fn` closure). But if that
2257 // check succeeds, we want to
2258 // *blame* the mutability on
2259 // `place` (that is,
2260 // `self.foo`). This is used to
2261 // propagate the info about
2262 // whether mutability declarations
2263 // are used outwards, so that we register
2264 // the outer variable as mutable. Otherwise a
2265 // test like this fails to record the `mut`
2269 // fn foo<F: FnOnce()>(_f: F) { }
2271 // let var = Vec::new();
2278 self.is_mutable(place_base, is_local_mutation_allowed)?;
2280 place_local: place.local,
2281 place_projection: place.projection,
2282 is_local_mutation_allowed,
2287 self.is_mutable(place_base, is_local_mutation_allowed)
2295 /// If `place` is a field projection, and the field is being projected from a closure type,
2296 /// then returns the index of the field being projected. Note that this closure will always
2297 /// be `self` in the current MIR, because that is the only time we directly access the fields
2298 /// of a closure type.
2299 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2300 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2304 /// The degree of overlap between 2 places for borrow-checking.
2306 /// The places might partially overlap - in this case, we give
2307 /// up and say that they might conflict. This occurs when
2308 /// different fields of a union are borrowed. For example,
2309 /// if `u` is a union, we have no way of telling how disjoint
2310 /// `u.a.x` and `a.b.y` are.
2312 /// The places have the same type, and are either completely disjoint
2313 /// or equal - i.e., they can't "partially" overlap as can occur with
2314 /// unions. This is the "base case" on which we recur for extensions
2317 /// The places are disjoint, so we know all extensions of them
2318 /// will also be disjoint.