1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 #![allow(rustc::potential_query_instability)]
4 #![feature(box_patterns)]
5 #![feature(let_chains)]
7 #![feature(min_specialization)]
8 #![feature(never_type)]
9 #![feature(rustc_attrs)]
10 #![feature(stmt_expr_attributes)]
11 #![feature(trusted_step)]
12 #![feature(try_blocks)]
13 #![recursion_limit = "256"]
16 extern crate rustc_middle;
20 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
21 use rustc_data_structures::graph::dominators::Dominators;
22 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
24 use rustc_hir::def_id::LocalDefId;
25 use rustc_index::bit_set::ChunkedBitSet;
26 use rustc_index::vec::IndexVec;
27 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
28 use rustc_middle::mir::{
29 traversal, Body, ClearCrossCrate, Local, Location, Mutability, Operand, Place, PlaceElem,
30 PlaceRef, VarDebugInfoContents,
32 use rustc_middle::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
33 use rustc_middle::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
34 use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
35 use rustc_middle::ty::query::Providers;
36 use rustc_middle::ty::{self, CapturedPlace, ParamEnv, RegionVid, TyCtxt};
37 use rustc_session::lint::builtin::UNUSED_MUT;
38 use rustc_span::{Span, Symbol};
41 use smallvec::SmallVec;
42 use std::cell::RefCell;
43 use std::collections::BTreeMap;
46 use rustc_mir_dataflow::impls::{
47 EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
49 use rustc_mir_dataflow::move_paths::{InitIndex, MoveOutIndex, MovePathIndex};
50 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
51 use rustc_mir_dataflow::Analysis;
52 use rustc_mir_dataflow::MoveDataParamEnv;
54 use self::diagnostics::{AccessKind, RegionName};
55 use self::location::LocationTable;
56 use self::prefixes::PrefixSet;
59 use self::path_utils::*;
63 mod constraint_generation;
71 mod member_constraints;
79 mod session_diagnostics;
81 mod universal_regions;
84 // A public API provided for the Rust compiler consumers.
87 use borrow_set::{BorrowData, BorrowSet};
88 use dataflow::{BorrowIndex, BorrowckFlowState as Flows, BorrowckResults, Borrows};
89 use nll::{PoloniusOutput, ToRegionVid};
90 use place_ext::PlaceExt;
91 use places_conflict::{places_conflict, PlaceConflictBias};
92 use region_infer::RegionInferenceContext;
94 // FIXME(eddyb) perhaps move this somewhere more centrally.
97 place: CapturedPlace<'tcx>,
99 /// If true, the capture is behind a reference.
103 /// Associate some local constants with the `'tcx` lifetime
104 struct TyCtxtConsts<'tcx>(TyCtxt<'tcx>);
105 impl<'tcx> TyCtxtConsts<'tcx> {
106 const DEREF_PROJECTION: &'tcx [PlaceElem<'tcx>; 1] = &[ProjectionElem::Deref];
109 pub fn provide(providers: &mut Providers) {
110 *providers = Providers {
111 mir_borrowck: |tcx, did| {
112 if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
113 tcx.mir_borrowck_const_arg(def)
115 mir_borrowck(tcx, ty::WithOptConstParam::unknown(did))
118 mir_borrowck_const_arg: |tcx, (did, param_did)| {
119 mir_borrowck(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
125 fn mir_borrowck<'tcx>(
127 def: ty::WithOptConstParam<LocalDefId>,
128 ) -> &'tcx BorrowCheckResult<'tcx> {
129 let (input_body, promoted) = tcx.mir_promoted(def);
130 debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
131 let hir_owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;
133 let opt_closure_req = tcx.infer_ctxt().with_opaque_type_inference(hir_owner).enter(|infcx| {
134 let input_body: &Body<'_> = &input_body.borrow();
135 let promoted: &IndexVec<_, _> = &promoted.borrow();
136 do_mir_borrowck(&infcx, input_body, promoted, false).0
138 debug!("mir_borrowck done");
140 tcx.arena.alloc(opt_closure_req)
143 /// Perform the actual borrow checking.
145 /// If `return_body_with_facts` is true, then return the body with non-erased
146 /// region ids on which the borrow checking was performed together with Polonius
148 #[instrument(skip(infcx, input_body, input_promoted), fields(id=?input_body.source.with_opt_param().as_local().unwrap()), level = "debug")]
149 fn do_mir_borrowck<'a, 'tcx>(
150 infcx: &InferCtxt<'a, 'tcx>,
151 input_body: &Body<'tcx>,
152 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
153 return_body_with_facts: bool,
154 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
155 let def = input_body.source.with_opt_param().as_local().unwrap();
160 let param_env = tcx.param_env(def.did);
162 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
163 for var_debug_info in &input_body.var_debug_info {
164 if let VarDebugInfoContents::Place(place) = var_debug_info.value {
165 if let Some(local) = place.as_local() {
166 if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name {
168 var_debug_info.source_info.span,
169 "local {:?} has many names (`{}` vs `{}`)",
175 local_names[local] = Some(var_debug_info.name);
180 let mut errors = error::BorrowckErrors::new();
182 // Gather the upvars of a closure, if any.
183 let tables = tcx.typeck_opt_const_arg(def);
184 if let Some(ErrorGuaranteed { .. }) = tables.tainted_by_errors {
185 infcx.set_tainted_by_errors();
186 errors.set_tainted_by_errors();
188 let upvars: Vec<_> = tables
189 .closure_min_captures_flattened(def.did.to_def_id())
190 .map(|captured_place| {
191 let capture = captured_place.info.capture_kind;
192 let by_ref = match capture {
193 ty::UpvarCapture::ByValue => false,
194 ty::UpvarCapture::ByRef(..) => true,
196 Upvar { place: captured_place.clone(), by_ref }
200 // Replace all regions with fresh inference variables. This
201 // requires first making our own copy of the MIR. This copy will
202 // be modified (in place) to contain non-lexical lifetimes. It
203 // will have a lifetime tied to the inference context.
204 let mut body_owned = input_body.clone();
205 let mut promoted = input_promoted.clone();
207 nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
208 let body = &body_owned; // no further changes
210 let location_table_owned = LocationTable::new(body);
211 let location_table = &location_table_owned;
213 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
214 match MoveData::gather_moves(&body, tcx, param_env) {
215 Ok(move_data) => (move_data, Vec::new()),
216 Err((move_data, move_errors)) => (move_data, move_errors),
218 let promoted_errors = promoted
220 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
222 let mdpe = MoveDataParamEnv { move_data, param_env };
224 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
225 .into_engine(tcx, &body)
226 .pass_name("borrowck")
227 .iterate_to_fixpoint()
228 .into_results_cursor(&body);
230 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def.did).is_fn_or_closure();
232 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
234 let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.debugging_opts.polonius;
236 // Compute non-lexical lifetimes.
244 } = nll::compute_regions(
258 // Dump MIR results into a file, if that is enabled. This let us
259 // write unit-tests, as well as helping with debugging.
260 nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
262 // We also have a `#[rustc_regions]` annotation that causes us to dump
264 nll::dump_annotation(
273 // The various `flow_*` structures can be large. We drop `flow_inits` here
274 // so it doesn't overlap with the others below. This reduces peak memory
275 // usage significantly on some benchmarks.
278 let regioncx = Rc::new(regioncx);
280 let flow_borrows = Borrows::new(tcx, body, ®ioncx, &borrow_set)
281 .into_engine(tcx, body)
282 .pass_name("borrowck")
283 .iterate_to_fixpoint();
284 let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &mdpe)
285 .into_engine(tcx, body)
286 .pass_name("borrowck")
287 .iterate_to_fixpoint();
288 let flow_ever_inits = EverInitializedPlaces::new(tcx, body, &mdpe)
289 .into_engine(tcx, body)
290 .pass_name("borrowck")
291 .iterate_to_fixpoint();
293 let movable_generator =
294 // The first argument is the generator type passed by value
295 if let Some(local) = body.local_decls.raw.get(1)
296 // Get the interior types and substs which typeck computed
297 && let ty::Generator(_, _, hir::Movability::Static) = local.ty.kind()
304 for (idx, move_data_results) in promoted_errors {
305 let promoted_body = &promoted[idx];
307 if let Err((move_data, move_errors)) = move_data_results {
308 let mut promoted_mbcx = MirBorrowckCtxt {
312 move_data: &move_data,
313 location_table, // no need to create a real one for the promoted, it is not used
315 fn_self_span_reported: Default::default(),
316 locals_are_invalidated_at_exit,
317 access_place_error_reported: Default::default(),
318 reservation_error_reported: Default::default(),
319 uninitialized_error_reported: Default::default(),
320 regioncx: regioncx.clone(),
321 used_mut: Default::default(),
322 used_mut_upvars: SmallVec::new(),
323 borrow_set: Rc::clone(&borrow_set),
324 dominators: Dominators::dummy(), // not used
326 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
327 region_names: RefCell::default(),
328 next_region_name: RefCell::new(1),
329 polonius_output: None,
332 promoted_mbcx.report_move_errors(move_errors);
333 errors = promoted_mbcx.errors;
337 let dominators = body.dominators();
339 let mut mbcx = MirBorrowckCtxt {
343 move_data: &mdpe.move_data,
346 locals_are_invalidated_at_exit,
347 fn_self_span_reported: Default::default(),
348 access_place_error_reported: Default::default(),
349 reservation_error_reported: Default::default(),
350 uninitialized_error_reported: Default::default(),
351 regioncx: Rc::clone(®ioncx),
352 used_mut: Default::default(),
353 used_mut_upvars: SmallVec::new(),
354 borrow_set: Rc::clone(&borrow_set),
358 region_names: RefCell::default(),
359 next_region_name: RefCell::new(1),
364 // Compute and report region errors, if any.
365 mbcx.report_region_errors(nll_errors);
367 let results = BorrowckResults {
368 ever_inits: flow_ever_inits,
369 uninits: flow_uninits,
370 borrows: flow_borrows,
373 mbcx.report_move_errors(move_errors);
375 rustc_mir_dataflow::visit_results(
377 traversal::reverse_postorder(body).map(|(bb, _)| bb),
382 // For each non-user used mutable variable, check if it's been assigned from
383 // a user-declared local. If so, then put that local into the used_mut set.
384 // Note that this set is expected to be small - only upvars from closures
385 // would have a chance of erroneously adding non-user-defined mutable vars
387 let temporary_used_locals: FxHashSet<Local> = mbcx
390 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
393 // For the remaining unused locals that are marked as mutable, we avoid linting any that
394 // were never initialized. These locals may have been removed as unreachable code; or will be
395 // linted as unused variables.
396 let unused_mut_locals =
397 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
398 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
400 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
401 let used_mut = std::mem::take(&mut mbcx.used_mut);
402 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
403 let local_decl = &mbcx.body.local_decls[local];
404 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
405 ClearCrossCrate::Set(data) => data.lint_root,
409 // Skip over locals that begin with an underscore or have no name
410 match mbcx.local_names[local] {
412 if name.as_str().starts_with('_') {
419 let span = local_decl.source_info.span;
420 if span.desugaring_kind().is_some() {
421 // If the `mut` arises as part of a desugaring, we should ignore it.
425 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
426 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
427 lint.build("variable does not need to be mutable")
428 .span_suggestion_short(
432 Applicability::MachineApplicable,
438 let tainted_by_errors = mbcx.emit_errors();
440 let result = BorrowCheckResult {
441 concrete_opaque_types: opaque_type_values,
442 closure_requirements: opt_closure_req,
443 used_mut_upvars: mbcx.used_mut_upvars,
447 let body_with_facts = if return_body_with_facts {
448 let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
449 Some(Box::new(BodyWithBorrowckFacts {
451 input_facts: *polonius_input.expect("Polonius input facts were not generated"),
453 location_table: location_table_owned,
459 debug!("do_mir_borrowck: result = {:#?}", result);
461 (result, body_with_facts)
464 /// A `Body` with information computed by the borrow checker. This struct is
465 /// intended to be consumed by compiler consumers.
467 /// We need to include the MIR body here because the region identifiers must
468 /// match the ones in the Polonius facts.
469 pub struct BodyWithBorrowckFacts<'tcx> {
470 /// A mir body that contains region identifiers.
471 pub body: Body<'tcx>,
472 /// Polonius input facts.
473 pub input_facts: AllFacts,
474 /// Polonius output facts.
475 pub output_facts: Rc<self::nll::PoloniusOutput>,
476 /// The table that maps Polonius points to locations in the table.
477 pub location_table: LocationTable,
480 struct MirBorrowckCtxt<'cx, 'tcx> {
481 infcx: &'cx InferCtxt<'cx, 'tcx>,
482 param_env: ParamEnv<'tcx>,
483 body: &'cx Body<'tcx>,
484 move_data: &'cx MoveData<'tcx>,
486 /// Map from MIR `Location` to `LocationIndex`; created
487 /// when MIR borrowck begins.
488 location_table: &'cx LocationTable,
490 movable_generator: bool,
491 /// This keeps track of whether local variables are free-ed when the function
492 /// exits even without a `StorageDead`, which appears to be the case for
495 /// I'm not sure this is the right approach - @eddyb could you try and
497 locals_are_invalidated_at_exit: bool,
498 /// This field keeps track of when borrow errors are reported in the access_place function
499 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
500 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
501 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
503 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
504 /// This field keeps track of when borrow conflict errors are reported
505 /// for reservations, so that we don't report seemingly duplicate
506 /// errors for corresponding activations.
508 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
509 // but it is currently inconvenient to track down the `BorrowIndex`
510 // at the time we detect and report a reservation error.
511 reservation_error_reported: FxHashSet<Place<'tcx>>,
512 /// This fields keeps track of the `Span`s that we have
513 /// used to report extra information for `FnSelfUse`, to avoid
514 /// unnecessarily verbose errors.
515 fn_self_span_reported: FxHashSet<Span>,
516 /// This field keeps track of errors reported in the checking of uninitialized variables,
517 /// so that we don't report seemingly duplicate errors.
518 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
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>>,
551 errors: error::BorrowckErrors<'tcx>,
555 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
556 // 2. loans made in overlapping scopes do not conflict
557 // 3. assignments do not affect things loaned out as immutable
558 // 4. moves do not affect things loaned out in any way
559 impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
560 type FlowState = Flows<'cx, 'tcx>;
562 fn visit_statement_before_primary_effect(
564 flow_state: &Flows<'cx, 'tcx>,
565 stmt: &'cx Statement<'tcx>,
568 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
569 let span = stmt.source_info.span;
571 self.check_activations(location, span, flow_state);
574 StatementKind::Assign(box (lhs, ref rhs)) => {
575 self.consume_rvalue(location, (rhs, span), flow_state);
577 self.mutate_place(location, (*lhs, span), Shallow(None), flow_state);
579 StatementKind::FakeRead(box (_, ref place)) => {
580 // Read for match doesn't access any memory and is used to
581 // assert that a place is safe and live. So we don't have to
582 // do any checks here.
584 // FIXME: Remove check that the place is initialized. This is
585 // needed for now because matches don't have never patterns yet.
586 // So this is the only place we prevent
590 self.check_if_path_or_subpath_is_moved(
592 InitializationRequiringAction::Use,
593 (place.as_ref(), span),
597 StatementKind::CopyNonOverlapping(box rustc_middle::mir::CopyNonOverlapping {
602 "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
606 | StatementKind::Coverage(..)
607 | StatementKind::AscribeUserType(..)
608 | StatementKind::Retag { .. }
609 | StatementKind::StorageLive(..) => {
610 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
613 StatementKind::StorageDead(local) => {
616 (Place::from(*local), span),
617 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
618 LocalMutationIsAllowed::Yes,
622 StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
623 bug!("Statement not allowed in this MIR phase")
628 fn visit_terminator_before_primary_effect(
630 flow_state: &Flows<'cx, 'tcx>,
631 term: &'cx Terminator<'tcx>,
634 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
635 let span = term.source_info.span;
637 self.check_activations(loc, span, flow_state);
640 TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
641 self.consume_operand(loc, (discr, span), flow_state);
643 TerminatorKind::Drop { place, target: _, unwind: _ } => {
645 "visit_terminator_drop \
646 loc: {:?} term: {:?} place: {:?} span: {:?}",
647 loc, term, place, span
653 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
654 LocalMutationIsAllowed::Yes,
658 TerminatorKind::DropAndReplace {
660 value: ref new_value,
664 self.mutate_place(loc, (drop_place, span), Deep, flow_state);
665 self.consume_operand(loc, (new_value, span), flow_state);
667 TerminatorKind::Call {
676 self.consume_operand(loc, (func, span), flow_state);
678 self.consume_operand(loc, (arg, span), flow_state);
680 self.mutate_place(loc, (destination, span), Deep, flow_state);
682 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
683 self.consume_operand(loc, (cond, span), flow_state);
684 use rustc_middle::mir::AssertKind;
685 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
686 self.consume_operand(loc, (len, span), flow_state);
687 self.consume_operand(loc, (index, span), flow_state);
691 TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
692 self.consume_operand(loc, (value, span), flow_state);
693 self.mutate_place(loc, (resume_arg, span), Deep, flow_state);
696 TerminatorKind::InlineAsm {
706 InlineAsmOperand::In { reg: _, ref value } => {
707 self.consume_operand(loc, (value, span), flow_state);
709 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
710 if let Some(place) = place {
711 self.mutate_place(loc, (place, span), Shallow(None), flow_state);
714 InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
715 self.consume_operand(loc, (in_value, span), flow_state);
716 if let Some(out_place) = out_place {
725 InlineAsmOperand::Const { value: _ }
726 | InlineAsmOperand::SymFn { value: _ }
727 | InlineAsmOperand::SymStatic { def_id: _ } => {}
732 TerminatorKind::Goto { target: _ }
733 | TerminatorKind::Abort
734 | TerminatorKind::Unreachable
735 | TerminatorKind::Resume
736 | TerminatorKind::Return
737 | TerminatorKind::GeneratorDrop
738 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
739 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
740 // no data used, thus irrelevant to borrowck
745 fn visit_terminator_after_primary_effect(
747 flow_state: &Flows<'cx, 'tcx>,
748 term: &'cx Terminator<'tcx>,
751 let span = term.source_info.span;
754 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
755 if self.movable_generator {
756 // Look for any active borrows to locals
757 let borrow_set = self.borrow_set.clone();
758 for i in flow_state.borrows.iter() {
759 let borrow = &borrow_set[i];
760 self.check_for_local_borrow(borrow, span);
765 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
766 // Returning from the function implicitly kills storage for all locals and statics.
767 // Often, the storage will already have been killed by an explicit
768 // StorageDead, but we don't always emit those (notably on unwind paths),
769 // so this "extra check" serves as a kind of backup.
770 let borrow_set = self.borrow_set.clone();
771 for i in flow_state.borrows.iter() {
772 let borrow = &borrow_set[i];
773 self.check_for_invalidation_at_exit(loc, borrow, span);
777 TerminatorKind::Abort
778 | TerminatorKind::Assert { .. }
779 | TerminatorKind::Call { .. }
780 | TerminatorKind::Drop { .. }
781 | TerminatorKind::DropAndReplace { .. }
782 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
783 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
784 | TerminatorKind::Goto { .. }
785 | TerminatorKind::SwitchInt { .. }
786 | TerminatorKind::Unreachable
787 | TerminatorKind::InlineAsm { .. } => {}
792 use self::AccessDepth::{Deep, Shallow};
793 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
795 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
796 enum ArtificialField {
801 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
803 /// From the RFC: "A *shallow* access means that the immediate
804 /// fields reached at P are accessed, but references or pointers
805 /// found within are not dereferenced. Right now, the only access
806 /// that is shallow is an assignment like `x = ...;`, which would
807 /// be a *shallow write* of `x`."
808 Shallow(Option<ArtificialField>),
810 /// From the RFC: "A *deep* access means that all data reachable
811 /// through the given place may be invalidated or accesses by
815 /// Access is Deep only when there is a Drop implementation that
816 /// can reach the data behind the reference.
820 /// Kind of access to a value: read or write
821 /// (For informational purposes only)
822 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
824 /// From the RFC: "A *read* means that the existing data may be
825 /// read, but will not be changed."
828 /// From the RFC: "A *write* means that the data may be mutated to
829 /// new values or otherwise invalidated (for example, it could be
830 /// de-initialized, as in a move operation).
833 /// For two-phase borrows, we distinguish a reservation (which is treated
834 /// like a Read) from an activation (which is treated like a write), and
835 /// each of those is furthermore distinguished from Reads/Writes above.
836 Reservation(WriteKind),
837 Activation(WriteKind, BorrowIndex),
840 /// Kind of read access to a value
841 /// (For informational purposes only)
842 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
848 /// Kind of write access to a value
849 /// (For informational purposes only)
850 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
853 MutableBorrow(BorrowKind),
858 /// When checking permissions for a place access, this flag is used to indicate that an immutable
859 /// local place can be mutated.
861 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
862 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
863 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
864 // `is_declared_mutable()`.
865 // - Take flow state into consideration in `is_assignable()` for local variables.
866 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
867 enum LocalMutationIsAllowed {
869 /// We want use of immutable upvars to cause a "write to immutable upvar"
870 /// error, not an "reassignment" error.
875 #[derive(Copy, Clone, Debug)]
876 enum InitializationRequiringAction {
884 struct RootPlace<'tcx> {
886 place_projection: &'tcx [PlaceElem<'tcx>],
887 is_local_mutation_allowed: LocalMutationIsAllowed,
890 impl InitializationRequiringAction {
891 fn as_noun(self) -> &'static str {
893 InitializationRequiringAction::Borrow => "borrow",
894 InitializationRequiringAction::MatchOn => "use", // no good noun
895 InitializationRequiringAction::Use => "use",
896 InitializationRequiringAction::Assignment => "assign",
897 InitializationRequiringAction::PartialAssignment => "assign to part",
901 fn as_verb_in_past_tense(self) -> &'static str {
903 InitializationRequiringAction::Borrow => "borrowed",
904 InitializationRequiringAction::MatchOn => "matched on",
905 InitializationRequiringAction::Use => "used",
906 InitializationRequiringAction::Assignment => "assigned",
907 InitializationRequiringAction::PartialAssignment => "partially assigned",
912 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
913 fn body(&self) -> &'cx Body<'tcx> {
917 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
918 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
919 /// place is initialized and (b) it is not borrowed in some way that would prevent this
922 /// Returns `true` if an error is reported.
926 place_span: (Place<'tcx>, Span),
927 kind: (AccessDepth, ReadOrWrite),
928 is_local_mutation_allowed: LocalMutationIsAllowed,
929 flow_state: &Flows<'cx, 'tcx>,
933 if let Activation(_, borrow_index) = rw {
934 if self.reservation_error_reported.contains(&place_span.0) {
936 "skipping access_place for activation of invalid reservation \
937 place: {:?} borrow_index: {:?}",
938 place_span.0, borrow_index
944 // Check is_empty() first because it's the common case, and doing that
945 // way we avoid the clone() call.
946 if !self.access_place_error_reported.is_empty()
947 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
950 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
956 let mutability_error = self.check_access_permissions(
959 is_local_mutation_allowed,
964 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
966 if conflict_error || mutability_error {
967 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
968 self.access_place_error_reported.insert((place_span.0, place_span.1));
972 fn check_access_for_conflict(
975 place_span: (Place<'tcx>, Span),
978 flow_state: &Flows<'cx, 'tcx>,
981 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
982 location, place_span, sd, rw,
985 let mut error_reported = false;
986 let tcx = self.infcx.tcx;
987 let body = self.body;
988 let borrow_set = self.borrow_set.clone();
990 // Use polonius output if it has been enabled.
991 let polonius_output = self.polonius_output.clone();
992 let borrows_in_scope = if let Some(polonius) = &polonius_output {
993 let location = self.location_table.start_index(location);
994 Either::Left(polonius.errors_at(location).iter().copied())
996 Either::Right(flow_state.borrows.iter())
999 each_borrow_involving_path(
1007 |this, borrow_index, borrow| match (rw, borrow.kind) {
1008 // Obviously an activation is compatible with its own
1009 // reservation (or even prior activating uses of same
1010 // borrow); so don't check if they interfere.
1012 // NOTE: *reservations* do conflict with themselves;
1013 // thus aren't injecting unsoundness w/ this check.)
1014 (Activation(_, activating), _) if activating == borrow_index => {
1016 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1017 skipping {:?} b/c activation of same borrow_index",
1021 (borrow_index, borrow),
1026 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1028 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1029 BorrowKind::Unique | BorrowKind::Mut { .. },
1030 ) => Control::Continue,
1032 (Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
1033 // This used to be a future compatibility warning (to be
1034 // disallowed on NLL). See rust-lang/rust#56254
1038 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1039 // Handled by initialization checks.
1043 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1044 // Reading from mere reservations of mutable-borrows is OK.
1045 if !is_active(&this.dominators, borrow, location) {
1046 assert!(allow_two_phase_borrow(borrow.kind));
1047 return Control::Continue;
1050 error_reported = true;
1054 .report_use_while_mutably_borrowed(location, place_span, borrow);
1055 this.buffer_error(err);
1057 ReadKind::Borrow(bk) => {
1059 this.report_conflicting_borrow(location, place_span, bk, borrow);
1060 this.buffer_error(err);
1066 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1068 Reservation(..) => {
1070 "recording invalid reservation of \
1074 this.reservation_error_reported.insert(place_span.0);
1076 Activation(_, activating) => {
1078 "observing check_place for activation of \
1079 borrow_index: {:?}",
1083 Read(..) | Write(..) => {}
1086 error_reported = true;
1088 WriteKind::MutableBorrow(bk) => {
1090 this.report_conflicting_borrow(location, place_span, bk, borrow);
1091 this.buffer_error(err);
1093 WriteKind::StorageDeadOrDrop => this
1094 .report_borrowed_value_does_not_live_long_enough(
1100 WriteKind::Mutate => {
1101 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1103 WriteKind::Move => {
1104 this.report_move_out_while_borrowed(location, place_span, borrow)
1118 place_span: (Place<'tcx>, Span),
1120 flow_state: &Flows<'cx, 'tcx>,
1122 // Write of P[i] or *P requires P init'd.
1123 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1125 // Special case: you can assign an immutable local variable
1126 // (e.g., `x = ...`) so long as it has never been initialized
1127 // before (at this point in the flow).
1128 if let Some(local) = place_span.0.as_local() {
1129 if let Mutability::Not = self.body.local_decls[local].mutability {
1130 // check for reassignments to immutable local variables
1131 self.check_if_reassignment_to_immutable_state(
1132 location, local, place_span, flow_state,
1138 // Otherwise, use the normal access permission rules.
1142 (kind, Write(WriteKind::Mutate)),
1143 LocalMutationIsAllowed::No,
1151 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1152 flow_state: &Flows<'cx, 'tcx>,
1155 Rvalue::Ref(_ /*rgn*/, bk, place) => {
1156 let access_kind = match bk {
1157 BorrowKind::Shallow => {
1158 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1160 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1161 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1162 let wk = WriteKind::MutableBorrow(bk);
1163 if allow_two_phase_borrow(bk) {
1164 (Deep, Reservation(wk))
1175 LocalMutationIsAllowed::No,
1179 let action = if bk == BorrowKind::Shallow {
1180 InitializationRequiringAction::MatchOn
1182 InitializationRequiringAction::Borrow
1185 self.check_if_path_or_subpath_is_moved(
1188 (place.as_ref(), span),
1193 Rvalue::AddressOf(mutability, place) => {
1194 let access_kind = match mutability {
1195 Mutability::Mut => (
1197 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1198 allow_two_phase_borrow: false,
1201 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1208 LocalMutationIsAllowed::No,
1212 self.check_if_path_or_subpath_is_moved(
1214 InitializationRequiringAction::Borrow,
1215 (place.as_ref(), span),
1220 Rvalue::ThreadLocalRef(_) => {}
1222 Rvalue::Use(ref operand)
1223 | Rvalue::Repeat(ref operand, _)
1224 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1225 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/)
1226 | Rvalue::ShallowInitBox(ref operand, _ /*ty*/) => {
1227 self.consume_operand(location, (operand, span), flow_state)
1230 Rvalue::Len(place) | Rvalue::Discriminant(place) => {
1231 let af = match *rvalue {
1232 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1233 Rvalue::Discriminant(..) => None,
1234 _ => unreachable!(),
1239 (Shallow(af), Read(ReadKind::Copy)),
1240 LocalMutationIsAllowed::No,
1243 self.check_if_path_or_subpath_is_moved(
1245 InitializationRequiringAction::Use,
1246 (place.as_ref(), span),
1251 Rvalue::BinaryOp(_bin_op, box (ref operand1, ref operand2))
1252 | Rvalue::CheckedBinaryOp(_bin_op, box (ref operand1, ref operand2)) => {
1253 self.consume_operand(location, (operand1, span), flow_state);
1254 self.consume_operand(location, (operand2, span), flow_state);
1257 Rvalue::NullaryOp(_op, _ty) => {
1258 // nullary ops take no dynamic input; no borrowck effect.
1261 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1262 // We need to report back the list of mutable upvars that were
1263 // moved into the closure and subsequently used by the closure,
1264 // in order to populate our used_mut set.
1265 match **aggregate_kind {
1266 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1267 let BorrowCheckResult { used_mut_upvars, .. } =
1268 self.infcx.tcx.mir_borrowck(def_id.expect_local());
1269 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1270 for field in used_mut_upvars {
1271 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1274 AggregateKind::Adt(..)
1275 | AggregateKind::Array(..)
1276 | AggregateKind::Tuple { .. } => (),
1279 for operand in operands {
1280 self.consume_operand(location, (operand, span), flow_state);
1286 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1287 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1288 // We have three possibilities here:
1289 // a. We are modifying something through a mut-ref
1290 // b. We are modifying something that is local to our parent
1291 // c. Current body is a nested closure, and we are modifying path starting from
1292 // a Place captured by our parent closure.
1294 // Handle (c), the path being modified is exactly the path captured by our parent
1295 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1296 this.used_mut_upvars.push(field);
1300 for (place_ref, proj) in place.iter_projections().rev() {
1302 if proj == ProjectionElem::Deref {
1303 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1304 // We aren't modifying a variable directly
1305 ty::Ref(_, _, hir::Mutability::Mut) => return,
1312 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1313 this.used_mut_upvars.push(field);
1319 this.used_mut.insert(place.local);
1322 // This relies on the current way that by-value
1323 // captures of a closure are copied/moved directly
1324 // when generating MIR.
1326 Operand::Move(place) | Operand::Copy(place) => {
1327 match place.as_local() {
1328 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1329 if self.body.local_decls[local].ty.is_mutable_ptr() {
1330 // The variable will be marked as mutable by the borrow.
1333 // This is an edge case where we have a `move` closure
1334 // inside a non-move closure, and the inner closure
1335 // contains a mutation:
1338 // || { move || { i += 1; }; };
1340 // In this case our usual strategy of assuming that the
1341 // variable will be captured by mutable reference is
1342 // wrong, since `i` can be copied into the inner
1343 // closure from a shared reference.
1345 // As such we have to search for the local that this
1346 // capture comes from and mark it as being used as mut.
1348 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1349 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1350 &self.move_data.inits[init_index]
1352 bug!("temporary should be initialized exactly once")
1355 let InitLocation::Statement(loc) = init.location else {
1356 bug!("temporary initialized in arguments")
1359 let body = self.body;
1360 let bbd = &body[loc.block];
1361 let stmt = &bbd.statements[loc.statement_index];
1362 debug!("temporary assigned in: stmt={:?}", stmt);
1364 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1366 propagate_closure_used_mut_place(self, source);
1369 "closures should only capture user variables \
1370 or references to user variables"
1374 _ => propagate_closure_used_mut_place(self, place),
1377 Operand::Constant(..) => {}
1384 (operand, span): (&'cx Operand<'tcx>, Span),
1385 flow_state: &Flows<'cx, 'tcx>,
1388 Operand::Copy(place) => {
1389 // copy of place: check if this is "copy of frozen path"
1390 // (FIXME: see check_loans.rs)
1394 (Deep, Read(ReadKind::Copy)),
1395 LocalMutationIsAllowed::No,
1399 // Finally, check if path was already moved.
1400 self.check_if_path_or_subpath_is_moved(
1402 InitializationRequiringAction::Use,
1403 (place.as_ref(), span),
1407 Operand::Move(place) => {
1408 // move of place: check if this is move of already borrowed path
1412 (Deep, Write(WriteKind::Move)),
1413 LocalMutationIsAllowed::Yes,
1417 // Finally, check if path was already moved.
1418 self.check_if_path_or_subpath_is_moved(
1420 InitializationRequiringAction::Use,
1421 (place.as_ref(), span),
1425 Operand::Constant(_) => {}
1429 /// Checks whether a borrow of this place is invalidated when the function
1431 fn check_for_invalidation_at_exit(
1434 borrow: &BorrowData<'tcx>,
1437 debug!("check_for_invalidation_at_exit({:?})", borrow);
1438 let place = borrow.borrowed_place;
1439 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1441 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1442 // we just know that all locals are dropped at function exit (otherwise
1443 // we'll have a memory leak) and assume that all statics have a destructor.
1445 // FIXME: allow thread-locals to borrow other thread locals?
1447 let (might_be_alive, will_be_dropped) =
1448 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1449 // Thread-locals might be dropped after the function exits
1450 // We have to dereference the outer reference because
1451 // borrows don't conflict behind shared references.
1452 root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
1455 (false, self.locals_are_invalidated_at_exit)
1458 if !will_be_dropped {
1459 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1463 let sd = if might_be_alive { Deep } else { Shallow(None) };
1465 if places_conflict::borrow_conflicts_with_place(
1472 places_conflict::PlaceConflictBias::Overlap,
1474 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1475 // FIXME: should be talking about the region lifetime instead
1476 // of just a span here.
1477 let span = self.infcx.tcx.sess.source_map().end_point(span);
1478 self.report_borrowed_value_does_not_live_long_enough(
1487 /// Reports an error if this is a borrow of local data.
1488 /// This is called for all Yield expressions on movable generators
1489 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1490 debug!("check_for_local_borrow({:?})", borrow);
1492 if borrow_of_local_data(borrow.borrowed_place) {
1493 let err = self.cannot_borrow_across_generator_yield(
1494 self.retrieve_borrow_spans(borrow).var_or_use(),
1498 self.buffer_error(err);
1502 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1503 // Two-phase borrow support: For each activation that is newly
1504 // generated at this statement, check if it interferes with
1506 let borrow_set = self.borrow_set.clone();
1507 for &borrow_index in borrow_set.activations_at_location(location) {
1508 let borrow = &borrow_set[borrow_index];
1510 // only mutable borrows should be 2-phase
1511 assert!(match borrow.kind {
1512 BorrowKind::Shared | BorrowKind::Shallow => false,
1513 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1518 (borrow.borrowed_place, span),
1519 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1520 LocalMutationIsAllowed::No,
1523 // We do not need to call `check_if_path_or_subpath_is_moved`
1524 // again, as we already called it when we made the
1525 // initial reservation.
1529 fn check_if_reassignment_to_immutable_state(
1533 place_span: (Place<'tcx>, Span),
1534 flow_state: &Flows<'cx, 'tcx>,
1536 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1538 // Check if any of the initializations of `local` have happened yet:
1539 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1540 // And, if so, report an error.
1541 let init = &self.move_data.inits[init_index];
1542 let span = init.span(&self.body);
1543 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1547 fn check_if_full_path_is_moved(
1550 desired_action: InitializationRequiringAction,
1551 place_span: (PlaceRef<'tcx>, Span),
1552 flow_state: &Flows<'cx, 'tcx>,
1554 let maybe_uninits = &flow_state.uninits;
1558 // 1. Move of `a.b.c`, use of `a.b.c`
1559 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1560 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1561 // partial initialization support, one might have `a.x`
1562 // initialized but not `a.b`.
1566 // 4. Move of `a.b.c`, use of `a.b.d`
1567 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1568 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1569 // must have been initialized for the use to be sound.
1570 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1572 // The dataflow tracks shallow prefixes distinctly (that is,
1573 // field-accesses on P distinctly from P itself), in order to
1574 // track substructure initialization separately from the whole
1577 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1578 // which we have a MovePath is `a.b`, then that means that the
1579 // initialization state of `a.b` is all we need to inspect to
1580 // know if `a.b.c` is valid (and from that we infer that the
1581 // dereference and `.d` access is also valid, since we assume
1582 // `a.b.c` is assigned a reference to an initialized and
1583 // well-formed record structure.)
1585 // Therefore, if we seek out the *closest* prefix for which we
1586 // have a MovePath, that should capture the initialization
1587 // state for the place scenario.
1589 // This code covers scenarios 1, 2, and 3.
1591 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1592 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1593 if maybe_uninits.contains(mpi) {
1594 self.report_use_of_moved_or_uninitialized(
1597 (prefix, place_span.0, place_span.1),
1600 } // Only query longest prefix with a MovePath, not further
1601 // ancestors; dataflow recurs on children when parents
1602 // move (to support partial (re)inits).
1604 // (I.e., querying parents breaks scenario 7; but may want
1605 // to do such a query based on partial-init feature-gate.)
1608 /// Subslices correspond to multiple move paths, so we iterate through the
1609 /// elements of the base array. For each element we check
1611 /// * Does this element overlap with our slice.
1612 /// * Is any part of it uninitialized.
1613 fn check_if_subslice_element_is_moved(
1616 desired_action: InitializationRequiringAction,
1617 place_span: (PlaceRef<'tcx>, Span),
1618 maybe_uninits: &ChunkedBitSet<MovePathIndex>,
1622 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1623 let move_paths = &self.move_data.move_paths;
1625 let root_path = &move_paths[mpi];
1626 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1627 let last_proj = child_move_path.place.projection.last().unwrap();
1628 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1629 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1631 if (from..to).contains(offset) {
1633 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1634 maybe_uninits.contains(mpi)
1637 if let Some(uninit_child) = uninit_child {
1638 self.report_use_of_moved_or_uninitialized(
1641 (place_span.0, place_span.0, place_span.1),
1644 return; // don't bother finding other problems.
1652 fn check_if_path_or_subpath_is_moved(
1655 desired_action: InitializationRequiringAction,
1656 place_span: (PlaceRef<'tcx>, Span),
1657 flow_state: &Flows<'cx, 'tcx>,
1659 let maybe_uninits = &flow_state.uninits;
1663 // 1. Move of `a.b.c`, use of `a` or `a.b`
1664 // partial initialization support, one might have `a.x`
1665 // initialized but not `a.b`.
1666 // 2. All bad scenarios from `check_if_full_path_is_moved`
1670 // 3. Move of `a.b.c`, use of `a.b.d`
1671 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1672 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1673 // must have been initialized for the use to be sound.
1674 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1676 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1678 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1679 place_span.0.last_projection()
1681 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1682 if let ty::Array(..) = place_ty.ty.kind() {
1683 self.check_if_subslice_element_is_moved(
1686 (place_base, place_span.1),
1695 // A move of any shallow suffix of `place` also interferes
1696 // with an attempt to use `place`. This is scenario 3 above.
1698 // (Distinct from handling of scenarios 1+2+4 above because
1699 // `place` does not interfere with suffixes of its prefixes,
1700 // e.g., `a.b.c` does not interfere with `a.b.d`)
1702 // This code covers scenario 1.
1704 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1705 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1706 let uninit_mpi = self
1708 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1710 if let Some(uninit_mpi) = uninit_mpi {
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.
1722 /// Currently MoveData does not store entries for all places in
1723 /// the input MIR. For example it will currently filter out
1724 /// places that are Copy; thus we do not track places of shared
1725 /// reference type. This routine will walk up a place along its
1726 /// prefixes, searching for a foundational place that *is*
1727 /// tracked in the MoveData.
1729 /// An Err result includes a tag indicated why the search failed.
1730 /// Currently this can only occur if the place is built off of a
1731 /// static variable, as we do not track those in the MoveData.
1732 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1733 match self.move_data.rev_lookup.find(place) {
1734 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1735 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1737 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1741 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1742 // If returns None, then there is no move path corresponding
1743 // to a direct owner of `place` (which means there is nothing
1744 // that borrowck tracks for its analysis).
1746 match self.move_data.rev_lookup.find(place) {
1747 LookupResult::Parent(_) => None,
1748 LookupResult::Exact(mpi) => Some(mpi),
1752 fn check_if_assigned_path_is_moved(
1755 (place, span): (Place<'tcx>, Span),
1756 flow_state: &Flows<'cx, 'tcx>,
1758 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1760 // None case => assigning to `x` does not require `x` be initialized.
1761 for (place_base, elem) in place.iter_projections().rev() {
1763 ProjectionElem::Index(_/*operand*/) |
1764 ProjectionElem::ConstantIndex { .. } |
1765 // assigning to P[i] requires P to be valid.
1766 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1767 // assigning to (P->variant) is okay if assigning to `P` is okay
1769 // FIXME: is this true even if P is an adt with a dtor?
1772 // assigning to (*P) requires P to be initialized
1773 ProjectionElem::Deref => {
1774 self.check_if_full_path_is_moved(
1775 location, InitializationRequiringAction::Use,
1776 (place_base, span), flow_state);
1777 // (base initialized; no need to
1782 ProjectionElem::Subslice { .. } => {
1783 panic!("we don't allow assignments to subslices, location: {:?}",
1787 ProjectionElem::Field(..) => {
1788 // if type of `P` has a dtor, then
1789 // assigning to `P.f` requires `P` itself
1790 // be already initialized
1791 let tcx = self.infcx.tcx;
1792 let base_ty = place_base.ty(self.body(), tcx).ty;
1793 match base_ty.kind() {
1794 ty::Adt(def, _) if def.has_dtor(tcx) => {
1795 self.check_if_path_or_subpath_is_moved(
1796 location, InitializationRequiringAction::Assignment,
1797 (place_base, span), flow_state);
1799 // (base initialized; no need to
1804 // Once `let s; s.x = V; read(s.x);`,
1805 // is allowed, remove this match arm.
1806 ty::Adt(..) | ty::Tuple(..) => {
1807 check_parent_of_field(self, location, place_base, span, flow_state);
1809 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1810 // partial initialization, do not complain about unnecessary `mut` on
1811 // an attempt to do a partial initialization.
1812 self.used_mut.insert(place.local);
1821 fn check_parent_of_field<'cx, 'tcx>(
1822 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1824 base: PlaceRef<'tcx>,
1826 flow_state: &Flows<'cx, 'tcx>,
1828 // rust-lang/rust#21232: Until Rust allows reads from the
1829 // initialized parts of partially initialized structs, we
1830 // will, starting with the 2018 edition, reject attempts
1831 // to write to structs that are not fully initialized.
1833 // In other words, *until* we allow this:
1835 // 1. `let mut s; s.x = Val; read(s.x);`
1837 // we will for now disallow this:
1839 // 2. `let mut s; s.x = Val;`
1843 // 3. `let mut s = ...; drop(s); s.x=Val;`
1845 // This does not use check_if_path_or_subpath_is_moved,
1846 // because we want to *allow* reinitializations of fields:
1847 // e.g., want to allow
1849 // `let mut s = ...; drop(s.x); s.x=Val;`
1851 // This does not use check_if_full_path_is_moved on
1852 // `base`, because that would report an error about the
1853 // `base` as a whole, but in this scenario we *really*
1854 // want to report an error about the actual thing that was
1855 // moved, which may be some prefix of `base`.
1857 // Shallow so that we'll stop at any dereference; we'll
1858 // report errors about issues with such bases elsewhere.
1859 let maybe_uninits = &flow_state.uninits;
1861 // Find the shortest uninitialized prefix you can reach
1862 // without going over a Deref.
1863 let mut shortest_uninit_seen = None;
1864 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1865 let Some(mpi) = this.move_path_for_place(prefix) else { continue };
1867 if maybe_uninits.contains(mpi) {
1869 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1870 shortest_uninit_seen,
1873 shortest_uninit_seen = Some((prefix, mpi));
1875 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1879 if let Some((prefix, mpi)) = shortest_uninit_seen {
1880 // Check for a reassignment into an uninitialized field of a union (for example,
1881 // after a move out). In this case, do not report an error here. There is an
1882 // exception, if this is the first assignment into the union (that is, there is
1883 // no move out from an earlier location) then this is an attempt at initialization
1884 // of the union - we should error in that case.
1885 let tcx = this.infcx.tcx;
1886 if base.ty(this.body(), tcx).ty.is_union() {
1887 if this.move_data.path_map[mpi].iter().any(|moi| {
1888 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1894 this.report_use_of_moved_or_uninitialized(
1896 InitializationRequiringAction::PartialAssignment,
1897 (prefix, base, span),
1904 /// Checks the permissions for the given place and read or write kind
1906 /// Returns `true` if an error is reported.
1907 fn check_access_permissions(
1909 (place, span): (Place<'tcx>, Span),
1911 is_local_mutation_allowed: LocalMutationIsAllowed,
1912 flow_state: &Flows<'cx, 'tcx>,
1916 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1917 place, kind, is_local_mutation_allowed
1924 Reservation(WriteKind::MutableBorrow(
1925 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1927 | Write(WriteKind::MutableBorrow(
1928 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1930 let is_local_mutation_allowed = match borrow_kind {
1931 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1932 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1933 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1935 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1937 self.add_used_mut(root_place, flow_state);
1941 error_access = AccessKind::MutableBorrow;
1942 the_place_err = place_err;
1946 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1947 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1949 self.add_used_mut(root_place, flow_state);
1953 error_access = AccessKind::Mutate;
1954 the_place_err = place_err;
1961 | WriteKind::StorageDeadOrDrop
1962 | WriteKind::MutableBorrow(BorrowKind::Shared)
1963 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1967 | WriteKind::StorageDeadOrDrop
1968 | WriteKind::MutableBorrow(BorrowKind::Shared)
1969 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1971 if self.is_mutable(place.as_ref(), is_local_mutation_allowed).is_err()
1972 && !self.has_buffered_errors()
1974 // rust-lang/rust#46908: In pure NLL mode this code path should be
1975 // unreachable, but we use `delay_span_bug` because we can hit this when
1976 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1977 // enabled. We don't want to ICE for that case, as other errors will have
1978 // been emitted (#52262).
1979 self.infcx.tcx.sess.delay_span_bug(
1982 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1990 // permission checks are done at Reservation point.
1996 | BorrowKind::Mut { .. }
1997 | BorrowKind::Shared
1998 | BorrowKind::Shallow,
2002 // Access authorized
2007 // rust-lang/rust#21232, #54986: during period where we reject
2008 // partial initialization, do not complain about mutability
2009 // errors except for actual mutation (as opposed to an attempt
2010 // to do a partial initialization).
2011 let previously_initialized =
2012 self.is_local_ever_initialized(place.local, flow_state).is_some();
2014 // at this point, we have set up the error reporting state.
2015 if previously_initialized {
2016 self.report_mutability_error(place, span, the_place_err, error_access, location);
2023 fn is_local_ever_initialized(
2026 flow_state: &Flows<'cx, 'tcx>,
2027 ) -> Option<InitIndex> {
2028 let mpi = self.move_data.rev_lookup.find_local(local);
2029 let ii = &self.move_data.init_path_map[mpi];
2031 if flow_state.ever_inits.contains(index) {
2038 /// Adds the place into the used mutable variables set
2039 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2041 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2042 // If the local may have been initialized, and it is now currently being
2043 // mutated, then it is justified to be annotated with the `mut`
2044 // keyword, since the mutation may be a possible reassignment.
2045 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2046 && self.is_local_ever_initialized(local, flow_state).is_some()
2048 self.used_mut.insert(local);
2053 place_projection: _,
2054 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2058 place_projection: place_projection @ [.., _],
2059 is_local_mutation_allowed: _,
2061 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2063 projection: place_projection,
2065 self.used_mut_upvars.push(field);
2071 /// Whether this value can be written or borrowed mutably.
2072 /// Returns the root place if the place passed in is a projection.
2075 place: PlaceRef<'tcx>,
2076 is_local_mutation_allowed: LocalMutationIsAllowed,
2077 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2078 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2079 match place.last_projection() {
2081 let local = &self.body.local_decls[place.local];
2082 match local.mutability {
2083 Mutability::Not => match is_local_mutation_allowed {
2084 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2085 place_local: place.local,
2086 place_projection: place.projection,
2087 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2089 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2090 place_local: place.local,
2091 place_projection: place.projection,
2092 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2094 LocalMutationIsAllowed::No => Err(place),
2096 Mutability::Mut => Ok(RootPlace {
2097 place_local: place.local,
2098 place_projection: place.projection,
2099 is_local_mutation_allowed,
2103 Some((place_base, elem)) => {
2105 ProjectionElem::Deref => {
2106 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2108 // Check the kind of deref to decide
2109 match base_ty.kind() {
2110 ty::Ref(_, _, mutbl) => {
2112 // Shared borrowed data is never mutable
2113 hir::Mutability::Not => Err(place),
2114 // Mutably borrowed data is mutable, but only if we have a
2115 // unique path to the `&mut`
2116 hir::Mutability::Mut => {
2117 let mode = match self.is_upvar_field_projection(place) {
2118 Some(field) if self.upvars[field.index()].by_ref => {
2119 is_local_mutation_allowed
2121 _ => LocalMutationIsAllowed::Yes,
2124 self.is_mutable(place_base, mode)
2128 ty::RawPtr(tnm) => {
2130 // `*const` raw pointers are not mutable
2131 hir::Mutability::Not => Err(place),
2132 // `*mut` raw pointers are always mutable, regardless of
2133 // context. The users have to check by themselves.
2134 hir::Mutability::Mut => Ok(RootPlace {
2135 place_local: place.local,
2136 place_projection: place.projection,
2137 is_local_mutation_allowed,
2141 // `Box<T>` owns its content, so mutable if its location is mutable
2142 _ if base_ty.is_box() => {
2143 self.is_mutable(place_base, is_local_mutation_allowed)
2145 // Deref should only be for reference, pointers or boxes
2146 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2149 // All other projections are owned by their base path, so mutable if
2150 // base path is mutable
2151 ProjectionElem::Field(..)
2152 | ProjectionElem::Index(..)
2153 | ProjectionElem::ConstantIndex { .. }
2154 | ProjectionElem::Subslice { .. }
2155 | ProjectionElem::Downcast(..) => {
2156 let upvar_field_projection = self.is_upvar_field_projection(place);
2157 if let Some(field) = upvar_field_projection {
2158 let upvar = &self.upvars[field.index()];
2160 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2161 place={:?}, place_base={:?}",
2162 upvar, is_local_mutation_allowed, place, place_base
2164 match (upvar.place.mutability, is_local_mutation_allowed) {
2167 LocalMutationIsAllowed::No
2168 | LocalMutationIsAllowed::ExceptUpvars,
2170 (Mutability::Not, LocalMutationIsAllowed::Yes)
2171 | (Mutability::Mut, _) => {
2172 // Subtle: this is an upvar
2173 // reference, so it looks like
2174 // `self.foo` -- we want to double
2175 // check that the location `*self`
2176 // is mutable (i.e., this is not a
2177 // `Fn` closure). But if that
2178 // check succeeds, we want to
2179 // *blame* the mutability on
2180 // `place` (that is,
2181 // `self.foo`). This is used to
2182 // propagate the info about
2183 // whether mutability declarations
2184 // are used outwards, so that we register
2185 // the outer variable as mutable. Otherwise a
2186 // test like this fails to record the `mut`
2190 // fn foo<F: FnOnce()>(_f: F) { }
2192 // let var = Vec::new();
2199 self.is_mutable(place_base, is_local_mutation_allowed)?;
2201 place_local: place.local,
2202 place_projection: place.projection,
2203 is_local_mutation_allowed,
2208 self.is_mutable(place_base, is_local_mutation_allowed)
2216 /// If `place` is a field projection, and the field is being projected from a closure type,
2217 /// then returns the index of the field being projected. Note that this closure will always
2218 /// be `self` in the current MIR, because that is the only time we directly access the fields
2219 /// of a closure type.
2220 fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2221 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2226 use rustc_errors::ErrorGuaranteed;
2230 pub struct BorrowckErrors<'tcx> {
2231 /// This field keeps track of move errors that are to be reported for given move indices.
2233 /// There are situations where many errors can be reported for a single move out (see #53807)
2234 /// and we want only the best of those errors.
2236 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
2237 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
2238 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
2239 /// all move errors have been reported, any diagnostics in this map are added to the buffer
2242 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
2243 /// when errors in the map are being re-added to the error buffer so that errors with the
2244 /// same primary span come out in a consistent order.
2245 buffered_move_errors:
2246 BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>)>,
2247 /// Diagnostics to be reported buffer.
2248 buffered: Vec<Diagnostic>,
2249 /// Set to Some if we emit an error during borrowck
2250 tainted_by_errors: Option<ErrorGuaranteed>,
2253 impl BorrowckErrors<'_> {
2254 pub fn new() -> Self {
2256 buffered_move_errors: BTreeMap::new(),
2257 buffered: Default::default(),
2258 tainted_by_errors: None,
2262 // FIXME(eddyb) this is a suboptimal API because `tainted_by_errors` is
2263 // set before any emission actually happens (weakening the guarantee).
2264 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2265 self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
2266 t.buffer(&mut self.buffered);
2269 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2270 t.buffer(&mut self.buffered);
2273 pub fn set_tainted_by_errors(&mut self) {
2274 self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
2278 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
2279 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2280 self.errors.buffer_error(t);
2283 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2284 self.errors.buffer_non_error_diag(t);
2287 pub fn buffer_move_error(
2289 move_out_indices: Vec<MoveOutIndex>,
2290 place_and_err: (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>),
2292 if let Some((_, diag)) =
2293 self.errors.buffered_move_errors.insert(move_out_indices, place_and_err)
2295 // Cancel the old diagnostic so we don't ICE
2303 pub fn emit_errors(&mut self) -> Option<ErrorGuaranteed> {
2304 // Buffer any move errors that we collected and de-duplicated.
2305 for (_, (_, diag)) in std::mem::take(&mut self.errors.buffered_move_errors) {
2306 // We have already set tainted for this error, so just buffer it.
2307 diag.buffer(&mut self.errors.buffered);
2310 if !self.errors.buffered.is_empty() {
2311 self.errors.buffered.sort_by_key(|diag| diag.sort_span);
2313 for mut diag in self.errors.buffered.drain(..) {
2314 self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
2318 self.errors.tainted_by_errors
2321 pub fn has_buffered_errors(&self) -> bool {
2322 self.errors.buffered.is_empty()
2325 pub fn has_move_error(
2327 move_out_indices: &[MoveOutIndex],
2328 ) -> Option<&(PlaceRef<'tcx>, DiagnosticBuilder<'cx, ErrorGuaranteed>)> {
2329 self.errors.buffered_move_errors.get(move_out_indices)
2334 /// The degree of overlap between 2 places for borrow-checking.
2336 /// The places might partially overlap - in this case, we give
2337 /// up and say that they might conflict. This occurs when
2338 /// different fields of a union are borrowed. For example,
2339 /// if `u` is a union, we have no way of telling how disjoint
2340 /// `u.a.x` and `a.b.y` are.
2342 /// The places have the same type, and are either completely disjoint
2343 /// or equal - i.e., they can't "partially" overlap as can occur with
2344 /// unions. This is the "base case" on which we recur for extensions
2347 /// The places are disjoint, so we know all extensions of them
2348 /// will also be disjoint.