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];
269 let dominators = promoted_body.dominators();
271 if let Err((move_data, move_errors)) = move_data_results {
272 let mut promoted_mbcx = MirBorrowckCtxt {
276 move_data: &move_data,
277 location_table: &LocationTable::new(promoted_body),
279 fn_self_span_reported: Default::default(),
280 locals_are_invalidated_at_exit,
281 access_place_error_reported: Default::default(),
282 reservation_error_reported: Default::default(),
283 reservation_warnings: Default::default(),
284 move_error_reported: BTreeMap::new(),
285 uninitialized_error_reported: Default::default(),
287 regioncx: regioncx.clone(),
288 used_mut: Default::default(),
289 used_mut_upvars: SmallVec::new(),
290 borrow_set: Rc::clone(&borrow_set),
293 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
294 region_names: RefCell::default(),
295 next_region_name: RefCell::new(1),
296 polonius_output: None,
298 promoted_mbcx.report_move_errors(move_errors);
299 errors_buffer = promoted_mbcx.errors_buffer;
303 let dominators = body.dominators();
305 let mut mbcx = MirBorrowckCtxt {
309 move_data: &mdpe.move_data,
312 locals_are_invalidated_at_exit,
313 fn_self_span_reported: Default::default(),
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: Rc::clone(®ioncx),
321 used_mut: Default::default(),
322 used_mut_upvars: SmallVec::new(),
323 borrow_set: Rc::clone(&borrow_set),
327 region_names: RefCell::default(),
328 next_region_name: RefCell::new(1),
332 // Compute and report region errors, if any.
333 mbcx.report_region_errors(nll_errors);
335 let results = BorrowckResults {
336 ever_inits: flow_ever_inits,
337 uninits: flow_uninits,
338 borrows: flow_borrows,
341 mbcx.report_move_errors(move_errors);
343 dataflow::visit_results(
345 traversal::reverse_postorder(&body).map(|(bb, _)| bb),
350 // Convert any reservation warnings into lints.
351 let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
352 for (_, (place, span, location, bk, borrow)) in reservation_warnings {
353 let mut initial_diag = mbcx.report_conflicting_borrow(location, (place, span), bk, &borrow);
355 let scope = mbcx.body.source_info(location).scope;
356 let lint_root = match &mbcx.body.source_scopes[scope].local_data {
357 ClearCrossCrate::Set(data) => data.lint_root,
361 // Span and message don't matter; we overwrite them below anyway
362 mbcx.infcx.tcx.struct_span_lint_hir(
363 MUTABLE_BORROW_RESERVATION_CONFLICT,
367 let mut diag = lint.build("");
369 diag.message = initial_diag.styled_message().clone();
370 diag.span = initial_diag.span.clone();
372 diag.buffer(&mut mbcx.errors_buffer);
375 initial_diag.cancel();
378 // For each non-user used mutable variable, check if it's been assigned from
379 // a user-declared local. If so, then put that local into the used_mut set.
380 // Note that this set is expected to be small - only upvars from closures
381 // would have a chance of erroneously adding non-user-defined mutable vars
383 let temporary_used_locals: FxHashSet<Local> = mbcx
386 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
389 // For the remaining unused locals that are marked as mutable, we avoid linting any that
390 // were never initialized. These locals may have been removed as unreachable code; or will be
391 // linted as unused variables.
392 let unused_mut_locals =
393 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
394 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
396 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
397 let used_mut = mbcx.used_mut;
398 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
399 let local_decl = &mbcx.body.local_decls[local];
400 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
401 ClearCrossCrate::Set(data) => data.lint_root,
405 // Skip over locals that begin with an underscore or have no name
406 match mbcx.local_names[local] {
408 if name.as_str().starts_with('_') {
415 let span = local_decl.source_info.span;
416 if span.desugaring_kind().is_some() {
417 // If the `mut` arises as part of a desugaring, we should ignore it.
421 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
422 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
423 lint.build("variable does not need to be mutable")
424 .span_suggestion_short(
428 Applicability::MachineApplicable,
434 // Buffer any move errors that we collected and de-duplicated.
435 for (_, (_, diag)) in mbcx.move_error_reported {
436 diag.buffer(&mut mbcx.errors_buffer);
439 if !mbcx.errors_buffer.is_empty() {
440 mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
442 for diag in mbcx.errors_buffer.drain(..) {
443 mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
447 let result = BorrowCheckResult {
448 concrete_opaque_types: opaque_type_values,
449 closure_requirements: opt_closure_req,
450 used_mut_upvars: mbcx.used_mut_upvars,
453 debug!("do_mir_borrowck: result = {:#?}", result);
458 crate struct MirBorrowckCtxt<'cx, 'tcx> {
459 crate infcx: &'cx InferCtxt<'cx, 'tcx>,
460 param_env: ParamEnv<'tcx>,
461 body: &'cx Body<'tcx>,
462 move_data: &'cx MoveData<'tcx>,
464 /// Map from MIR `Location` to `LocationIndex`; created
465 /// when MIR borrowck begins.
466 location_table: &'cx LocationTable,
468 movable_generator: bool,
469 /// This keeps track of whether local variables are free-ed when the function
470 /// exits even without a `StorageDead`, which appears to be the case for
473 /// I'm not sure this is the right approach - @eddyb could you try and
475 locals_are_invalidated_at_exit: bool,
476 /// This field keeps track of when borrow errors are reported in the access_place function
477 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
478 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
479 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
481 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
482 /// This field keeps track of when borrow conflict errors are reported
483 /// for reservations, so that we don't report seemingly duplicate
484 /// errors for corresponding activations.
486 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
487 // but it is currently inconvenient to track down the `BorrowIndex`
488 // at the time we detect and report a reservation error.
489 reservation_error_reported: FxHashSet<Place<'tcx>>,
490 /// This fields keeps track of the `Span`s that we have
491 /// used to report extra information for `FnSelfUse`, to avoid
492 /// unnecessarily verbose errors.
493 fn_self_span_reported: FxHashSet<Span>,
494 /// Migration warnings to be reported for #56254. We delay reporting these
495 /// so that we can suppress the warning if there's a corresponding error
496 /// for the activation of the borrow.
497 reservation_warnings:
498 FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
499 /// This field keeps track of move errors that are to be reported for given move indices.
501 /// There are situations where many errors can be reported for a single move out (see #53807)
502 /// and we want only the best of those errors.
504 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
505 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
506 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
507 /// all move errors have been reported, any diagnostics in this map are added to the buffer
510 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
511 /// when errors in the map are being re-added to the error buffer so that errors with the
512 /// same primary span come out in a consistent order.
513 move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'cx>)>,
514 /// This field keeps track of errors reported in the checking of uninitialized variables,
515 /// so that we don't report seemingly duplicate errors.
516 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
517 /// Errors to be reported buffer
518 errors_buffer: Vec<Diagnostic>,
519 /// This field keeps track of all the local variables that are declared mut and are mutated.
520 /// Used for the warning issued by an unused mutable local variable.
521 used_mut: FxHashSet<Local>,
522 /// If the function we're checking is a closure, then we'll need to report back the list of
523 /// mutable upvars that have been used. This field keeps track of them.
524 used_mut_upvars: SmallVec<[Field; 8]>,
525 /// Region inference context. This contains the results from region inference and lets us e.g.
526 /// find out which CFG points are contained in each borrow region.
527 regioncx: Rc<RegionInferenceContext<'tcx>>,
529 /// The set of borrows extracted from the MIR
530 borrow_set: Rc<BorrowSet<'tcx>>,
532 /// Dominators for MIR
533 dominators: Dominators<BasicBlock>,
535 /// Information about upvars not necessarily preserved in types or MIR
536 upvars: Vec<Upvar<'tcx>>,
538 /// Names of local (user) variables (extracted from `var_debug_info`).
539 local_names: IndexVec<Local, Option<Symbol>>,
541 /// Record the region names generated for each region in the given
542 /// MIR def so that we can reuse them later in help/error messages.
543 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
545 /// The counter for generating new region names.
546 next_region_name: RefCell<usize>,
548 /// Results of Polonius analysis.
549 polonius_output: Option<Rc<PoloniusOutput>>,
553 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
554 // 2. loans made in overlapping scopes do not conflict
555 // 3. assignments do not affect things loaned out as immutable
556 // 4. moves do not affect things loaned out in any way
557 impl<'cx, 'tcx> dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
558 type FlowState = Flows<'cx, 'tcx>;
560 fn visit_statement_before_primary_effect(
562 flow_state: &Flows<'cx, 'tcx>,
563 stmt: &'cx Statement<'tcx>,
566 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
567 let span = stmt.source_info.span;
569 self.check_activations(location, span, flow_state);
572 StatementKind::Assign(box (lhs, ref rhs)) => {
573 self.consume_rvalue(location, (rhs, span), flow_state);
575 self.mutate_place(location, (*lhs, span), Shallow(None), JustWrite, flow_state);
577 StatementKind::FakeRead(_, box ref place) => {
578 // Read for match doesn't access any memory and is used to
579 // assert that a place is safe and live. So we don't have to
580 // do any checks here.
582 // FIXME: Remove check that the place is initialized. This is
583 // needed for now because matches don't have never patterns yet.
584 // So this is the only place we prevent
588 self.check_if_path_or_subpath_is_moved(
590 InitializationRequiringAction::Use,
591 (place.as_ref(), span),
595 StatementKind::SetDiscriminant { place, variant_index: _ } => {
596 self.mutate_place(location, (**place, span), Shallow(None), JustWrite, flow_state);
598 StatementKind::LlvmInlineAsm(ref asm) => {
599 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
601 // FIXME(eddyb) indirect inline asm outputs should
602 // be encoded through MIR place derefs instead.
606 (Deep, Read(ReadKind::Copy)),
607 LocalMutationIsAllowed::No,
610 self.check_if_path_or_subpath_is_moved(
612 InitializationRequiringAction::Use,
613 (output.as_ref(), o.span),
620 if o.is_rw { Deep } else { Shallow(None) },
621 if o.is_rw { WriteAndRead } else { JustWrite },
626 for (_, input) in asm.inputs.iter() {
627 self.consume_operand(location, (input, span), flow_state);
631 | StatementKind::Coverage(..)
632 | StatementKind::AscribeUserType(..)
633 | StatementKind::Retag { .. }
634 | StatementKind::StorageLive(..) => {
635 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
638 StatementKind::StorageDead(local) => {
641 (Place::from(*local), span),
642 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
643 LocalMutationIsAllowed::Yes,
650 fn visit_terminator_before_primary_effect(
652 flow_state: &Flows<'cx, 'tcx>,
653 term: &'cx Terminator<'tcx>,
656 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
657 let span = term.source_info.span;
659 self.check_activations(loc, span, flow_state);
662 TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
663 self.consume_operand(loc, (discr, span), flow_state);
665 TerminatorKind::Drop { place, target: _, unwind: _ } => {
667 "visit_terminator_drop \
668 loc: {:?} term: {:?} place: {:?} span: {:?}",
669 loc, term, place, span
675 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
676 LocalMutationIsAllowed::Yes,
680 TerminatorKind::DropAndReplace {
682 value: ref new_value,
686 self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
687 self.consume_operand(loc, (new_value, span), flow_state);
689 TerminatorKind::Call {
697 self.consume_operand(loc, (func, span), flow_state);
699 self.consume_operand(loc, (arg, span), flow_state);
701 if let Some((dest, _ /*bb*/)) = *destination {
702 self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
705 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
706 self.consume_operand(loc, (cond, span), flow_state);
707 use rustc_middle::mir::AssertKind;
708 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
709 self.consume_operand(loc, (len, span), flow_state);
710 self.consume_operand(loc, (index, span), flow_state);
714 TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
715 self.consume_operand(loc, (value, span), flow_state);
716 self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
719 TerminatorKind::InlineAsm {
728 InlineAsmOperand::In { reg: _, ref value }
729 | InlineAsmOperand::Const { ref value } => {
730 self.consume_operand(loc, (value, span), flow_state);
732 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
733 if let Some(place) = place {
743 InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
744 self.consume_operand(loc, (in_value, span), flow_state);
745 if let Some(out_place) = out_place {
755 InlineAsmOperand::SymFn { value: _ }
756 | InlineAsmOperand::SymStatic { def_id: _ } => {}
761 TerminatorKind::Goto { target: _ }
762 | TerminatorKind::Abort
763 | TerminatorKind::Unreachable
764 | TerminatorKind::Resume
765 | TerminatorKind::Return
766 | TerminatorKind::GeneratorDrop
767 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
768 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
769 // no data used, thus irrelevant to borrowck
774 fn visit_terminator_after_primary_effect(
776 flow_state: &Flows<'cx, 'tcx>,
777 term: &'cx Terminator<'tcx>,
780 let span = term.source_info.span;
783 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
784 if self.movable_generator {
785 // Look for any active borrows to locals
786 let borrow_set = self.borrow_set.clone();
787 for i in flow_state.borrows.iter() {
788 let borrow = &borrow_set[i];
789 self.check_for_local_borrow(borrow, span);
794 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
795 // Returning from the function implicitly kills storage for all locals and statics.
796 // Often, the storage will already have been killed by an explicit
797 // StorageDead, but we don't always emit those (notably on unwind paths),
798 // so this "extra check" serves as a kind of backup.
799 let borrow_set = self.borrow_set.clone();
800 for i in flow_state.borrows.iter() {
801 let borrow = &borrow_set[i];
802 self.check_for_invalidation_at_exit(loc, borrow, span);
806 TerminatorKind::Abort
807 | TerminatorKind::Assert { .. }
808 | TerminatorKind::Call { .. }
809 | TerminatorKind::Drop { .. }
810 | TerminatorKind::DropAndReplace { .. }
811 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
812 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
813 | TerminatorKind::Goto { .. }
814 | TerminatorKind::SwitchInt { .. }
815 | TerminatorKind::Unreachable
816 | TerminatorKind::InlineAsm { .. } => {}
821 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
827 use self::AccessDepth::{Deep, Shallow};
828 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
830 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
831 enum ArtificialField {
836 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
838 /// From the RFC: "A *shallow* access means that the immediate
839 /// fields reached at P are accessed, but references or pointers
840 /// found within are not dereferenced. Right now, the only access
841 /// that is shallow is an assignment like `x = ...;`, which would
842 /// be a *shallow write* of `x`."
843 Shallow(Option<ArtificialField>),
845 /// From the RFC: "A *deep* access means that all data reachable
846 /// through the given place may be invalidated or accesses by
850 /// Access is Deep only when there is a Drop implementation that
851 /// can reach the data behind the reference.
855 /// Kind of access to a value: read or write
856 /// (For informational purposes only)
857 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
859 /// From the RFC: "A *read* means that the existing data may be
860 /// read, but will not be changed."
863 /// From the RFC: "A *write* means that the data may be mutated to
864 /// new values or otherwise invalidated (for example, it could be
865 /// de-initialized, as in a move operation).
868 /// For two-phase borrows, we distinguish a reservation (which is treated
869 /// like a Read) from an activation (which is treated like a write), and
870 /// each of those is furthermore distinguished from Reads/Writes above.
871 Reservation(WriteKind),
872 Activation(WriteKind, BorrowIndex),
875 /// Kind of read access to a value
876 /// (For informational purposes only)
877 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
883 /// Kind of write access to a value
884 /// (For informational purposes only)
885 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
888 MutableBorrow(BorrowKind),
893 /// When checking permissions for a place access, this flag is used to indicate that an immutable
894 /// local place can be mutated.
896 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
897 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
898 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
899 // `is_declared_mutable()`.
900 // - Take flow state into consideration in `is_assignable()` for local variables.
901 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
902 enum LocalMutationIsAllowed {
904 /// We want use of immutable upvars to cause a "write to immutable upvar"
905 /// error, not an "reassignment" error.
910 #[derive(Copy, Clone, Debug)]
911 enum InitializationRequiringAction {
920 struct RootPlace<'tcx> {
922 place_projection: &'tcx [PlaceElem<'tcx>],
923 is_local_mutation_allowed: LocalMutationIsAllowed,
926 impl InitializationRequiringAction {
927 fn as_noun(self) -> &'static str {
929 InitializationRequiringAction::Update => "update",
930 InitializationRequiringAction::Borrow => "borrow",
931 InitializationRequiringAction::MatchOn => "use", // no good noun
932 InitializationRequiringAction::Use => "use",
933 InitializationRequiringAction::Assignment => "assign",
934 InitializationRequiringAction::PartialAssignment => "assign to part",
938 fn as_verb_in_past_tense(self) -> &'static str {
940 InitializationRequiringAction::Update => "updated",
941 InitializationRequiringAction::Borrow => "borrowed",
942 InitializationRequiringAction::MatchOn => "matched on",
943 InitializationRequiringAction::Use => "used",
944 InitializationRequiringAction::Assignment => "assigned",
945 InitializationRequiringAction::PartialAssignment => "partially assigned",
950 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
951 fn body(&self) -> &'cx Body<'tcx> {
955 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
956 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
957 /// place is initialized and (b) it is not borrowed in some way that would prevent this
960 /// Returns `true` if an error is reported.
964 place_span: (Place<'tcx>, Span),
965 kind: (AccessDepth, ReadOrWrite),
966 is_local_mutation_allowed: LocalMutationIsAllowed,
967 flow_state: &Flows<'cx, 'tcx>,
971 if let Activation(_, borrow_index) = rw {
972 if self.reservation_error_reported.contains(&place_span.0) {
974 "skipping access_place for activation of invalid reservation \
975 place: {:?} borrow_index: {:?}",
976 place_span.0, borrow_index
982 // Check is_empty() first because it's the common case, and doing that
983 // way we avoid the clone() call.
984 if !self.access_place_error_reported.is_empty()
985 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
988 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
994 let mutability_error = self.check_access_permissions(
997 is_local_mutation_allowed,
1001 let conflict_error =
1002 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
1004 if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
1005 // Suppress this warning when there's an error being emitted for the
1006 // same borrow: fixing the error is likely to fix the warning.
1007 self.reservation_warnings.remove(&borrow_idx);
1010 if conflict_error || mutability_error {
1011 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
1013 self.access_place_error_reported.insert((place_span.0, place_span.1));
1017 fn check_access_for_conflict(
1020 place_span: (Place<'tcx>, Span),
1023 flow_state: &Flows<'cx, 'tcx>,
1026 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
1027 location, place_span, sd, rw,
1030 let mut error_reported = false;
1031 let tcx = self.infcx.tcx;
1032 let body = self.body;
1033 let borrow_set = self.borrow_set.clone();
1035 // Use polonius output if it has been enabled.
1036 let polonius_output = self.polonius_output.clone();
1037 let borrows_in_scope = if let Some(polonius) = &polonius_output {
1038 let location = self.location_table.start_index(location);
1039 Either::Left(polonius.errors_at(location).iter().copied())
1041 Either::Right(flow_state.borrows.iter())
1044 each_borrow_involving_path(
1052 |this, borrow_index, borrow| match (rw, borrow.kind) {
1053 // Obviously an activation is compatible with its own
1054 // reservation (or even prior activating uses of same
1055 // borrow); so don't check if they interfere.
1057 // NOTE: *reservations* do conflict with themselves;
1058 // thus aren't injecting unsoundenss w/ this check.)
1059 (Activation(_, activating), _) if activating == borrow_index => {
1061 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1062 skipping {:?} b/c activation of same borrow_index",
1066 (borrow_index, borrow),
1071 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1073 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1074 BorrowKind::Unique | BorrowKind::Mut { .. },
1075 ) => Control::Continue,
1077 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1078 // Handled by initialization checks.
1082 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1083 // Reading from mere reservations of mutable-borrows is OK.
1084 if !is_active(&this.dominators, borrow, location) {
1085 assert!(allow_two_phase_borrow(borrow.kind));
1086 return Control::Continue;
1089 error_reported = true;
1092 this.report_use_while_mutably_borrowed(location, place_span, borrow)
1093 .buffer(&mut this.errors_buffer);
1095 ReadKind::Borrow(bk) => {
1096 this.report_conflicting_borrow(location, place_span, bk, borrow)
1097 .buffer(&mut this.errors_buffer);
1104 Reservation(WriteKind::MutableBorrow(bk)),
1105 BorrowKind::Shallow | BorrowKind::Shared,
1106 ) if { tcx.migrate_borrowck() && this.borrow_set.contains(&location) } => {
1107 let bi = this.borrow_set.get_index_of(&location).unwrap();
1109 "recording invalid reservation of place: {:?} with \
1110 borrow index {:?} as warning",
1113 // rust-lang/rust#56254 - This was previously permitted on
1114 // the 2018 edition so we emit it as a warning. We buffer
1115 // these sepately so that we only emit a warning if borrow
1116 // checking was otherwise successful.
1117 this.reservation_warnings
1118 .insert(bi, (place_span.0, place_span.1, location, bk, borrow.clone()));
1120 // Don't suppress actual errors.
1124 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1126 Reservation(..) => {
1128 "recording invalid reservation of \
1132 this.reservation_error_reported.insert(place_span.0);
1134 Activation(_, activating) => {
1136 "observing check_place for activation of \
1137 borrow_index: {:?}",
1141 Read(..) | Write(..) => {}
1144 error_reported = true;
1146 WriteKind::MutableBorrow(bk) => {
1147 this.report_conflicting_borrow(location, place_span, bk, borrow)
1148 .buffer(&mut this.errors_buffer);
1150 WriteKind::StorageDeadOrDrop => this
1151 .report_borrowed_value_does_not_live_long_enough(
1157 WriteKind::Mutate => {
1158 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1160 WriteKind::Move => {
1161 this.report_move_out_while_borrowed(location, place_span, borrow)
1175 place_span: (Place<'tcx>, Span),
1178 flow_state: &Flows<'cx, 'tcx>,
1180 // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
1182 MutateMode::WriteAndRead => {
1183 self.check_if_path_or_subpath_is_moved(
1185 InitializationRequiringAction::Update,
1186 (place_span.0.as_ref(), place_span.1),
1190 MutateMode::JustWrite => {
1191 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1195 // Special case: you can assign a immutable local variable
1196 // (e.g., `x = ...`) so long as it has never been initialized
1197 // before (at this point in the flow).
1198 if let Some(local) = place_span.0.as_local() {
1199 if let Mutability::Not = self.body.local_decls[local].mutability {
1200 // check for reassignments to immutable local variables
1201 self.check_if_reassignment_to_immutable_state(
1202 location, local, place_span, flow_state,
1208 // Otherwise, use the normal access permission rules.
1212 (kind, Write(WriteKind::Mutate)),
1213 LocalMutationIsAllowed::No,
1221 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1222 flow_state: &Flows<'cx, 'tcx>,
1225 Rvalue::Ref(_ /*rgn*/, bk, place) => {
1226 let access_kind = match bk {
1227 BorrowKind::Shallow => {
1228 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1230 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1231 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1232 let wk = WriteKind::MutableBorrow(bk);
1233 if allow_two_phase_borrow(bk) {
1234 (Deep, Reservation(wk))
1245 LocalMutationIsAllowed::No,
1249 let action = if bk == BorrowKind::Shallow {
1250 InitializationRequiringAction::MatchOn
1252 InitializationRequiringAction::Borrow
1255 self.check_if_path_or_subpath_is_moved(
1258 (place.as_ref(), span),
1263 Rvalue::AddressOf(mutability, place) => {
1264 let access_kind = match mutability {
1265 Mutability::Mut => (
1267 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1268 allow_two_phase_borrow: false,
1271 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1278 LocalMutationIsAllowed::No,
1282 self.check_if_path_or_subpath_is_moved(
1284 InitializationRequiringAction::Borrow,
1285 (place.as_ref(), span),
1290 Rvalue::ThreadLocalRef(_) => {}
1292 Rvalue::Use(ref operand)
1293 | Rvalue::Repeat(ref operand, _)
1294 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1295 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
1296 self.consume_operand(location, (operand, span), flow_state)
1299 Rvalue::Len(place) | Rvalue::Discriminant(place) => {
1300 let af = match *rvalue {
1301 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1302 Rvalue::Discriminant(..) => None,
1303 _ => unreachable!(),
1308 (Shallow(af), Read(ReadKind::Copy)),
1309 LocalMutationIsAllowed::No,
1312 self.check_if_path_or_subpath_is_moved(
1314 InitializationRequiringAction::Use,
1315 (place.as_ref(), span),
1320 Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
1321 | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
1322 self.consume_operand(location, (operand1, span), flow_state);
1323 self.consume_operand(location, (operand2, span), flow_state);
1326 Rvalue::NullaryOp(_op, _ty) => {
1327 // nullary ops take no dynamic input; no borrowck effect.
1329 // FIXME: is above actually true? Do we want to track
1330 // the fact that uninitialized data can be created via
1334 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1335 // We need to report back the list of mutable upvars that were
1336 // moved into the closure and subsequently used by the closure,
1337 // in order to populate our used_mut set.
1338 match **aggregate_kind {
1339 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1340 let BorrowCheckResult { used_mut_upvars, .. } =
1341 self.infcx.tcx.mir_borrowck(def_id.expect_local());
1342 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1343 for field in used_mut_upvars {
1344 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1347 AggregateKind::Adt(..)
1348 | AggregateKind::Array(..)
1349 | AggregateKind::Tuple { .. } => (),
1352 for operand in operands {
1353 self.consume_operand(location, (operand, span), flow_state);
1359 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1360 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1361 // We have three possibilities here:
1362 // a. We are modifying something through a mut-ref
1363 // b. We are modifying something that is local to our parent
1364 // c. Current body is a nested closure, and we are modifying path starting from
1365 // a Place captured by our parent closure.
1367 // Handle (c), the path being modified is exactly the path captured by our parent
1368 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1369 this.used_mut_upvars.push(field);
1373 for (place_ref, proj) in place.iter_projections().rev() {
1375 if proj == ProjectionElem::Deref {
1376 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1377 // We aren't modifying a variable directly
1378 ty::Ref(_, _, hir::Mutability::Mut) => return,
1385 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1386 this.used_mut_upvars.push(field);
1392 this.used_mut.insert(place.local);
1395 // This relies on the current way that by-value
1396 // captures of a closure are copied/moved directly
1397 // when generating MIR.
1399 Operand::Move(place) | Operand::Copy(place) => {
1400 match place.as_local() {
1401 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1402 if self.body.local_decls[local].ty.is_mutable_ptr() {
1403 // The variable will be marked as mutable by the borrow.
1406 // This is an edge case where we have a `move` closure
1407 // inside a non-move closure, and the inner closure
1408 // contains a mutation:
1411 // || { move || { i += 1; }; };
1413 // In this case our usual strategy of assuming that the
1414 // variable will be captured by mutable reference is
1415 // wrong, since `i` can be copied into the inner
1416 // closure from a shared reference.
1418 // As such we have to search for the local that this
1419 // capture comes from and mark it as being used as mut.
1421 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1422 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1423 &self.move_data.inits[init_index]
1425 bug!("temporary should be initialized exactly once")
1428 let loc = match init.location {
1429 InitLocation::Statement(stmt) => stmt,
1430 _ => bug!("temporary initialized in arguments"),
1433 let body = self.body;
1434 let bbd = &body[loc.block];
1435 let stmt = &bbd.statements[loc.statement_index];
1436 debug!("temporary assigned in: stmt={:?}", stmt);
1438 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1440 propagate_closure_used_mut_place(self, source);
1443 "closures should only capture user variables \
1444 or references to user variables"
1448 _ => propagate_closure_used_mut_place(self, place),
1451 Operand::Constant(..) => {}
1458 (operand, span): (&'cx Operand<'tcx>, Span),
1459 flow_state: &Flows<'cx, 'tcx>,
1462 Operand::Copy(place) => {
1463 // copy of place: check if this is "copy of frozen path"
1464 // (FIXME: see check_loans.rs)
1468 (Deep, Read(ReadKind::Copy)),
1469 LocalMutationIsAllowed::No,
1473 // Finally, check if path was already moved.
1474 self.check_if_path_or_subpath_is_moved(
1476 InitializationRequiringAction::Use,
1477 (place.as_ref(), span),
1481 Operand::Move(place) => {
1482 // move of place: check if this is move of already borrowed path
1486 (Deep, Write(WriteKind::Move)),
1487 LocalMutationIsAllowed::Yes,
1491 // Finally, check if path was already moved.
1492 self.check_if_path_or_subpath_is_moved(
1494 InitializationRequiringAction::Use,
1495 (place.as_ref(), span),
1499 Operand::Constant(_) => {}
1503 /// Checks whether a borrow of this place is invalidated when the function
1505 fn check_for_invalidation_at_exit(
1508 borrow: &BorrowData<'tcx>,
1511 debug!("check_for_invalidation_at_exit({:?})", borrow);
1512 let place = borrow.borrowed_place;
1513 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1515 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1516 // we just know that all locals are dropped at function exit (otherwise
1517 // we'll have a memory leak) and assume that all statics have a destructor.
1519 // FIXME: allow thread-locals to borrow other thread locals?
1521 let (might_be_alive, will_be_dropped) =
1522 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1523 // Thread-locals might be dropped after the function exits
1524 // We have to dereference the outer reference because
1525 // borrows don't conflict behind shared references.
1526 root_place.projection = DEREF_PROJECTION;
1529 (false, self.locals_are_invalidated_at_exit)
1532 if !will_be_dropped {
1533 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1537 let sd = if might_be_alive { Deep } else { Shallow(None) };
1539 if places_conflict::borrow_conflicts_with_place(
1546 places_conflict::PlaceConflictBias::Overlap,
1548 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1549 // FIXME: should be talking about the region lifetime instead
1550 // of just a span here.
1551 let span = self.infcx.tcx.sess.source_map().end_point(span);
1552 self.report_borrowed_value_does_not_live_long_enough(
1561 /// Reports an error if this is a borrow of local data.
1562 /// This is called for all Yield expressions on movable generators
1563 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1564 debug!("check_for_local_borrow({:?})", borrow);
1566 if borrow_of_local_data(borrow.borrowed_place) {
1567 let err = self.cannot_borrow_across_generator_yield(
1568 self.retrieve_borrow_spans(borrow).var_or_use(),
1572 err.buffer(&mut self.errors_buffer);
1576 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1577 // Two-phase borrow support: For each activation that is newly
1578 // generated at this statement, check if it interferes with
1580 let borrow_set = self.borrow_set.clone();
1581 for &borrow_index in borrow_set.activations_at_location(location) {
1582 let borrow = &borrow_set[borrow_index];
1584 // only mutable borrows should be 2-phase
1585 assert!(match borrow.kind {
1586 BorrowKind::Shared | BorrowKind::Shallow => false,
1587 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1592 (borrow.borrowed_place, span),
1593 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1594 LocalMutationIsAllowed::No,
1597 // We do not need to call `check_if_path_or_subpath_is_moved`
1598 // again, as we already called it when we made the
1599 // initial reservation.
1603 fn check_if_reassignment_to_immutable_state(
1607 place_span: (Place<'tcx>, Span),
1608 flow_state: &Flows<'cx, 'tcx>,
1610 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1612 // Check if any of the initializiations of `local` have happened yet:
1613 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1614 // And, if so, report an error.
1615 let init = &self.move_data.inits[init_index];
1616 let span = init.span(&self.body);
1617 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1621 fn check_if_full_path_is_moved(
1624 desired_action: InitializationRequiringAction,
1625 place_span: (PlaceRef<'tcx>, Span),
1626 flow_state: &Flows<'cx, 'tcx>,
1628 let maybe_uninits = &flow_state.uninits;
1632 // 1. Move of `a.b.c`, use of `a.b.c`
1633 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1634 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1635 // partial initialization support, one might have `a.x`
1636 // initialized but not `a.b`.
1640 // 4. Move of `a.b.c`, use of `a.b.d`
1641 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1642 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1643 // must have been initialized for the use to be sound.
1644 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1646 // The dataflow tracks shallow prefixes distinctly (that is,
1647 // field-accesses on P distinctly from P itself), in order to
1648 // track substructure initialization separately from the whole
1651 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1652 // which we have a MovePath is `a.b`, then that means that the
1653 // initialization state of `a.b` is all we need to inspect to
1654 // know if `a.b.c` is valid (and from that we infer that the
1655 // dereference and `.d` access is also valid, since we assume
1656 // `a.b.c` is assigned a reference to a initialized and
1657 // well-formed record structure.)
1659 // Therefore, if we seek out the *closest* prefix for which we
1660 // have a MovePath, that should capture the initialization
1661 // state for the place scenario.
1663 // This code covers scenarios 1, 2, and 3.
1665 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1666 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1667 if maybe_uninits.contains(mpi) {
1668 self.report_use_of_moved_or_uninitialized(
1671 (prefix, place_span.0, place_span.1),
1674 } // Only query longest prefix with a MovePath, not further
1675 // ancestors; dataflow recurs on children when parents
1676 // move (to support partial (re)inits).
1678 // (I.e., querying parents breaks scenario 7; but may want
1679 // to do such a query based on partial-init feature-gate.)
1682 /// Subslices correspond to multiple move paths, so we iterate through the
1683 /// elements of the base array. For each element we check
1685 /// * Does this element overlap with our slice.
1686 /// * Is any part of it uninitialized.
1687 fn check_if_subslice_element_is_moved(
1690 desired_action: InitializationRequiringAction,
1691 place_span: (PlaceRef<'tcx>, Span),
1692 maybe_uninits: &BitSet<MovePathIndex>,
1696 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1697 let move_paths = &self.move_data.move_paths;
1699 let root_path = &move_paths[mpi];
1700 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1701 let last_proj = child_move_path.place.projection.last().unwrap();
1702 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1703 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1705 if (from..to).contains(offset) {
1707 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1708 maybe_uninits.contains(mpi)
1711 if let Some(uninit_child) = uninit_child {
1712 self.report_use_of_moved_or_uninitialized(
1715 (place_span.0, place_span.0, place_span.1),
1718 return; // don't bother finding other problems.
1726 fn check_if_path_or_subpath_is_moved(
1729 desired_action: InitializationRequiringAction,
1730 place_span: (PlaceRef<'tcx>, Span),
1731 flow_state: &Flows<'cx, 'tcx>,
1733 let maybe_uninits = &flow_state.uninits;
1737 // 1. Move of `a.b.c`, use of `a` or `a.b`
1738 // partial initialization support, one might have `a.x`
1739 // initialized but not `a.b`.
1740 // 2. All bad scenarios from `check_if_full_path_is_moved`
1744 // 3. Move of `a.b.c`, use of `a.b.d`
1745 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1746 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1747 // must have been initialized for the use to be sound.
1748 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1750 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1752 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1753 place_span.0.last_projection()
1755 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1756 if let ty::Array(..) = place_ty.ty.kind() {
1757 self.check_if_subslice_element_is_moved(
1760 (place_base, place_span.1),
1769 // A move of any shallow suffix of `place` also interferes
1770 // with an attempt to use `place`. This is scenario 3 above.
1772 // (Distinct from handling of scenarios 1+2+4 above because
1773 // `place` does not interfere with suffixes of its prefixes,
1774 // e.g., `a.b.c` does not interfere with `a.b.d`)
1776 // This code covers scenario 1.
1778 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1779 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1780 let uninit_mpi = self
1782 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1784 if let Some(uninit_mpi) = uninit_mpi {
1785 self.report_use_of_moved_or_uninitialized(
1788 (place_span.0, place_span.0, place_span.1),
1791 return; // don't bother finding other problems.
1796 /// Currently MoveData does not store entries for all places in
1797 /// the input MIR. For example it will currently filter out
1798 /// places that are Copy; thus we do not track places of shared
1799 /// reference type. This routine will walk up a place along its
1800 /// prefixes, searching for a foundational place that *is*
1801 /// tracked in the MoveData.
1803 /// An Err result includes a tag indicated why the search failed.
1804 /// Currently this can only occur if the place is built off of a
1805 /// static variable, as we do not track those in the MoveData.
1806 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1807 match self.move_data.rev_lookup.find(place) {
1808 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1809 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1811 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1815 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1816 // If returns None, then there is no move path corresponding
1817 // to a direct owner of `place` (which means there is nothing
1818 // that borrowck tracks for its analysis).
1820 match self.move_data.rev_lookup.find(place) {
1821 LookupResult::Parent(_) => None,
1822 LookupResult::Exact(mpi) => Some(mpi),
1826 fn check_if_assigned_path_is_moved(
1829 (place, span): (Place<'tcx>, Span),
1830 flow_state: &Flows<'cx, 'tcx>,
1832 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1834 // None case => assigning to `x` does not require `x` be initialized.
1835 for (place_base, elem) in place.iter_projections().rev() {
1837 ProjectionElem::Index(_/*operand*/) |
1838 ProjectionElem::ConstantIndex { .. } |
1839 // assigning to P[i] requires P to be valid.
1840 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1841 // assigning to (P->variant) is okay if assigning to `P` is okay
1843 // FIXME: is this true even if P is a adt with a dtor?
1846 // assigning to (*P) requires P to be initialized
1847 ProjectionElem::Deref => {
1848 self.check_if_full_path_is_moved(
1849 location, InitializationRequiringAction::Use,
1850 (place_base, span), flow_state);
1851 // (base initialized; no need to
1856 ProjectionElem::Subslice { .. } => {
1857 panic!("we don't allow assignments to subslices, location: {:?}",
1861 ProjectionElem::Field(..) => {
1862 // if type of `P` has a dtor, then
1863 // assigning to `P.f` requires `P` itself
1864 // be already initialized
1865 let tcx = self.infcx.tcx;
1866 let base_ty = place_base.ty(self.body(), tcx).ty;
1867 match base_ty.kind() {
1868 ty::Adt(def, _) if def.has_dtor(tcx) => {
1869 self.check_if_path_or_subpath_is_moved(
1870 location, InitializationRequiringAction::Assignment,
1871 (place_base, span), flow_state);
1873 // (base initialized; no need to
1878 // Once `let s; s.x = V; read(s.x);`,
1879 // is allowed, remove this match arm.
1880 ty::Adt(..) | ty::Tuple(..) => {
1881 check_parent_of_field(self, location, place_base, span, flow_state);
1883 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1884 // partial initialization, do not complain about unnecessary `mut` on
1885 // an attempt to do a partial initialization.
1886 self.used_mut.insert(place.local);
1895 fn check_parent_of_field<'cx, 'tcx>(
1896 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1898 base: PlaceRef<'tcx>,
1900 flow_state: &Flows<'cx, 'tcx>,
1902 // rust-lang/rust#21232: Until Rust allows reads from the
1903 // initialized parts of partially initialized structs, we
1904 // will, starting with the 2018 edition, reject attempts
1905 // to write to structs that are not fully initialized.
1907 // In other words, *until* we allow this:
1909 // 1. `let mut s; s.x = Val; read(s.x);`
1911 // we will for now disallow this:
1913 // 2. `let mut s; s.x = Val;`
1917 // 3. `let mut s = ...; drop(s); s.x=Val;`
1919 // This does not use check_if_path_or_subpath_is_moved,
1920 // because we want to *allow* reinitializations of fields:
1921 // e.g., want to allow
1923 // `let mut s = ...; drop(s.x); s.x=Val;`
1925 // This does not use check_if_full_path_is_moved on
1926 // `base`, because that would report an error about the
1927 // `base` as a whole, but in this scenario we *really*
1928 // want to report an error about the actual thing that was
1929 // moved, which may be some prefix of `base`.
1931 // Shallow so that we'll stop at any dereference; we'll
1932 // report errors about issues with such bases elsewhere.
1933 let maybe_uninits = &flow_state.uninits;
1935 // Find the shortest uninitialized prefix you can reach
1936 // without going over a Deref.
1937 let mut shortest_uninit_seen = None;
1938 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1939 let mpi = match this.move_path_for_place(prefix) {
1944 if maybe_uninits.contains(mpi) {
1946 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1947 shortest_uninit_seen,
1950 shortest_uninit_seen = Some((prefix, mpi));
1952 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1956 if let Some((prefix, mpi)) = shortest_uninit_seen {
1957 // Check for a reassignment into a uninitialized field of a union (for example,
1958 // after a move out). In this case, do not report a error here. There is an
1959 // exception, if this is the first assignment into the union (that is, there is
1960 // no move out from an earlier location) then this is an attempt at initialization
1961 // of the union - we should error in that case.
1962 let tcx = this.infcx.tcx;
1963 if let ty::Adt(def, _) = base.ty(this.body(), tcx).ty.kind() {
1965 if this.move_data.path_map[mpi].iter().any(|moi| {
1966 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1973 this.report_use_of_moved_or_uninitialized(
1975 InitializationRequiringAction::PartialAssignment,
1976 (prefix, base, span),
1983 /// Checks the permissions for the given place and read or write kind
1985 /// Returns `true` if an error is reported.
1986 fn check_access_permissions(
1988 (place, span): (Place<'tcx>, Span),
1990 is_local_mutation_allowed: LocalMutationIsAllowed,
1991 flow_state: &Flows<'cx, 'tcx>,
1995 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1996 place, kind, is_local_mutation_allowed
2003 Reservation(WriteKind::MutableBorrow(
2004 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
2006 | Write(WriteKind::MutableBorrow(
2007 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
2009 let is_local_mutation_allowed = match borrow_kind {
2010 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
2011 BorrowKind::Mut { .. } => is_local_mutation_allowed,
2012 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
2014 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
2016 self.add_used_mut(root_place, flow_state);
2020 error_access = AccessKind::MutableBorrow;
2021 the_place_err = place_err;
2025 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
2026 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
2028 self.add_used_mut(root_place, flow_state);
2032 error_access = AccessKind::Mutate;
2033 the_place_err = place_err;
2040 | WriteKind::StorageDeadOrDrop
2041 | WriteKind::MutableBorrow(BorrowKind::Shared)
2042 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2046 | WriteKind::StorageDeadOrDrop
2047 | WriteKind::MutableBorrow(BorrowKind::Shared)
2048 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2050 if let (Err(_), true) = (
2051 self.is_mutable(place.as_ref(), is_local_mutation_allowed),
2052 self.errors_buffer.is_empty(),
2054 // rust-lang/rust#46908: In pure NLL mode this code path should be
2055 // unreachable, but we use `delay_span_bug` because we can hit this when
2056 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
2057 // enabled. We don't want to ICE for that case, as other errors will have
2058 // been emitted (#52262).
2059 self.infcx.tcx.sess.delay_span_bug(
2062 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2070 // permission checks are done at Reservation point.
2076 | BorrowKind::Mut { .. }
2077 | BorrowKind::Shared
2078 | BorrowKind::Shallow,
2082 // Access authorized
2087 // rust-lang/rust#21232, #54986: during period where we reject
2088 // partial initialization, do not complain about mutability
2089 // errors except for actual mutation (as opposed to an attempt
2090 // to do a partial initialization).
2091 let previously_initialized =
2092 self.is_local_ever_initialized(place.local, flow_state).is_some();
2094 // at this point, we have set up the error reporting state.
2095 if previously_initialized {
2096 self.report_mutability_error(place, span, the_place_err, error_access, location);
2103 fn is_local_ever_initialized(
2106 flow_state: &Flows<'cx, 'tcx>,
2107 ) -> Option<InitIndex> {
2108 let mpi = self.move_data.rev_lookup.find_local(local);
2109 let ii = &self.move_data.init_path_map[mpi];
2111 if flow_state.ever_inits.contains(index) {
2118 /// Adds the place into the used mutable variables set
2119 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2121 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2122 // If the local may have been initialized, and it is now currently being
2123 // mutated, then it is justified to be annotated with the `mut`
2124 // keyword, since the mutation may be a possible reassignment.
2125 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2126 && self.is_local_ever_initialized(local, flow_state).is_some()
2128 self.used_mut.insert(local);
2133 place_projection: _,
2134 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2138 place_projection: place_projection @ [.., _],
2139 is_local_mutation_allowed: _,
2141 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2143 projection: place_projection,
2145 self.used_mut_upvars.push(field);
2151 /// Whether this value can be written or borrowed mutably.
2152 /// Returns the root place if the place passed in is a projection.
2155 place: PlaceRef<'tcx>,
2156 is_local_mutation_allowed: LocalMutationIsAllowed,
2157 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2158 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2159 match place.last_projection() {
2161 let local = &self.body.local_decls[place.local];
2162 match local.mutability {
2163 Mutability::Not => match is_local_mutation_allowed {
2164 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2165 place_local: place.local,
2166 place_projection: place.projection,
2167 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2169 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2170 place_local: place.local,
2171 place_projection: place.projection,
2172 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2174 LocalMutationIsAllowed::No => Err(place),
2176 Mutability::Mut => Ok(RootPlace {
2177 place_local: place.local,
2178 place_projection: place.projection,
2179 is_local_mutation_allowed,
2183 Some((place_base, elem)) => {
2185 ProjectionElem::Deref => {
2186 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2188 // Check the kind of deref to decide
2189 match base_ty.kind() {
2190 ty::Ref(_, _, mutbl) => {
2192 // Shared borrowed data is never mutable
2193 hir::Mutability::Not => Err(place),
2194 // Mutably borrowed data is mutable, but only if we have a
2195 // unique path to the `&mut`
2196 hir::Mutability::Mut => {
2197 let mode = match self.is_upvar_field_projection(place) {
2198 Some(field) if self.upvars[field.index()].by_ref => {
2199 is_local_mutation_allowed
2201 _ => LocalMutationIsAllowed::Yes,
2204 self.is_mutable(place_base, mode)
2208 ty::RawPtr(tnm) => {
2210 // `*const` raw pointers are not mutable
2211 hir::Mutability::Not => Err(place),
2212 // `*mut` raw pointers are always mutable, regardless of
2213 // context. The users have to check by themselves.
2214 hir::Mutability::Mut => Ok(RootPlace {
2215 place_local: place.local,
2216 place_projection: place.projection,
2217 is_local_mutation_allowed,
2221 // `Box<T>` owns its content, so mutable if its location is mutable
2222 _ if base_ty.is_box() => {
2223 self.is_mutable(place_base, is_local_mutation_allowed)
2225 // Deref should only be for reference, pointers or boxes
2226 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2229 // All other projections are owned by their base path, so mutable if
2230 // base path is mutable
2231 ProjectionElem::Field(..)
2232 | ProjectionElem::Index(..)
2233 | ProjectionElem::ConstantIndex { .. }
2234 | ProjectionElem::Subslice { .. }
2235 | ProjectionElem::Downcast(..) => {
2236 let upvar_field_projection = self.is_upvar_field_projection(place);
2237 if let Some(field) = upvar_field_projection {
2238 let upvar = &self.upvars[field.index()];
2240 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2241 place={:?}, place_base={:?}",
2242 upvar, is_local_mutation_allowed, place, place_base
2244 match (upvar.place.mutability, is_local_mutation_allowed) {
2247 LocalMutationIsAllowed::No
2248 | LocalMutationIsAllowed::ExceptUpvars,
2250 (Mutability::Not, LocalMutationIsAllowed::Yes)
2251 | (Mutability::Mut, _) => {
2252 // Subtle: this is an upvar
2253 // reference, so it looks like
2254 // `self.foo` -- we want to double
2255 // check that the location `*self`
2256 // is mutable (i.e., this is not a
2257 // `Fn` closure). But if that
2258 // check succeeds, we want to
2259 // *blame* the mutability on
2260 // `place` (that is,
2261 // `self.foo`). This is used to
2262 // propagate the info about
2263 // whether mutability declarations
2264 // are used outwards, so that we register
2265 // the outer variable as mutable. Otherwise a
2266 // test like this fails to record the `mut`
2270 // fn foo<F: FnOnce()>(_f: F) { }
2272 // let var = Vec::new();
2279 self.is_mutable(place_base, is_local_mutation_allowed)?;
2281 place_local: place.local,
2282 place_projection: place.projection,
2283 is_local_mutation_allowed,
2288 self.is_mutable(place_base, is_local_mutation_allowed)
2296 /// If `place` is a field projection, and the field is being projected from a closure type,
2297 /// then returns the index of the field being projected. Note that this closure will always
2298 /// be `self` in the current MIR, because that is the only time we directly access the fields
2299 /// of a closure type.
2300 pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2301 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2305 /// The degree of overlap between 2 places for borrow-checking.
2307 /// The places might partially overlap - in this case, we give
2308 /// up and say that they might conflict. This occurs when
2309 /// different fields of a union are borrowed. For example,
2310 /// if `u` is a union, we have no way of telling how disjoint
2311 /// `u.a.x` and `a.b.y` are.
2313 /// The places have the same type, and are either completely disjoint
2314 /// or equal - i.e., they can't "partially" overlap as can occur with
2315 /// unions. This is the "base case" on which we recur for extensions
2318 /// The places are disjoint, so we know all extensions of them
2319 /// will also be disjoint.