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 #![cfg_attr(bootstrap, 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::{DefiningAnchor, 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
135 .with_opaque_type_inference(DefiningAnchor::Bind(hir_owner))
137 let input_body: &Body<'_> = &input_body.borrow();
138 let promoted: &IndexVec<_, _> = &promoted.borrow();
139 do_mir_borrowck(&infcx, input_body, promoted, false).0
141 debug!("mir_borrowck done");
143 tcx.arena.alloc(opt_closure_req)
146 /// Perform the actual borrow checking.
148 /// If `return_body_with_facts` is true, then return the body with non-erased
149 /// region ids on which the borrow checking was performed together with Polonius
151 #[instrument(skip(infcx, input_body, input_promoted), fields(id=?input_body.source.with_opt_param().as_local().unwrap()), level = "debug")]
152 fn do_mir_borrowck<'a, 'tcx>(
153 infcx: &InferCtxt<'a, 'tcx>,
154 input_body: &Body<'tcx>,
155 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
156 return_body_with_facts: bool,
157 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
158 let def = input_body.source.with_opt_param().as_local().unwrap();
163 let param_env = tcx.param_env(def.did);
165 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
166 for var_debug_info in &input_body.var_debug_info {
167 if let VarDebugInfoContents::Place(place) = var_debug_info.value {
168 if let Some(local) = place.as_local() {
169 if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name {
171 var_debug_info.source_info.span,
172 "local {:?} has many names (`{}` vs `{}`)",
178 local_names[local] = Some(var_debug_info.name);
183 let mut errors = error::BorrowckErrors::new();
185 // Gather the upvars of a closure, if any.
186 let tables = tcx.typeck_opt_const_arg(def);
187 if let Some(ErrorGuaranteed { .. }) = tables.tainted_by_errors {
188 infcx.set_tainted_by_errors();
189 errors.set_tainted_by_errors();
191 let upvars: Vec<_> = tables
192 .closure_min_captures_flattened(def.did)
193 .map(|captured_place| {
194 let capture = captured_place.info.capture_kind;
195 let by_ref = match capture {
196 ty::UpvarCapture::ByValue => false,
197 ty::UpvarCapture::ByRef(..) => true,
199 Upvar { place: captured_place.clone(), by_ref }
203 // Replace all regions with fresh inference variables. This
204 // requires first making our own copy of the MIR. This copy will
205 // be modified (in place) to contain non-lexical lifetimes. It
206 // will have a lifetime tied to the inference context.
207 let mut body_owned = input_body.clone();
208 let mut promoted = input_promoted.clone();
210 nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
211 let body = &body_owned; // no further changes
213 let location_table_owned = LocationTable::new(body);
214 let location_table = &location_table_owned;
216 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
217 match MoveData::gather_moves(&body, tcx, param_env) {
218 Ok((_, move_data)) => (move_data, Vec::new()),
219 Err((move_data, move_errors)) => (move_data, move_errors),
221 let promoted_errors = promoted
223 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
225 let mdpe = MoveDataParamEnv { move_data, param_env };
227 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
228 .into_engine(tcx, &body)
229 .pass_name("borrowck")
230 .iterate_to_fixpoint()
231 .into_results_cursor(&body);
233 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def.did).is_fn_or_closure();
235 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
237 let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.unstable_opts.polonius;
239 // Compute non-lexical lifetimes.
247 } = nll::compute_regions(
261 // Dump MIR results into a file, if that is enabled. This let us
262 // write unit-tests, as well as helping with debugging.
263 nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
265 // We also have a `#[rustc_regions]` annotation that causes us to dump
267 nll::dump_annotation(
276 // The various `flow_*` structures can be large. We drop `flow_inits` here
277 // so it doesn't overlap with the others below. This reduces peak memory
278 // usage significantly on some benchmarks.
281 let regioncx = Rc::new(regioncx);
283 let flow_borrows = Borrows::new(tcx, body, ®ioncx, &borrow_set)
284 .into_engine(tcx, body)
285 .pass_name("borrowck")
286 .iterate_to_fixpoint();
287 let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &mdpe)
288 .into_engine(tcx, body)
289 .pass_name("borrowck")
290 .iterate_to_fixpoint();
291 let flow_ever_inits = EverInitializedPlaces::new(tcx, body, &mdpe)
292 .into_engine(tcx, body)
293 .pass_name("borrowck")
294 .iterate_to_fixpoint();
296 let movable_generator =
297 // The first argument is the generator type passed by value
298 if let Some(local) = body.local_decls.raw.get(1)
299 // Get the interior types and substs which typeck computed
300 && let ty::Generator(_, _, hir::Movability::Static) = local.ty.kind()
307 for (idx, move_data_results) in promoted_errors {
308 let promoted_body = &promoted[idx];
310 if let Err((move_data, move_errors)) = move_data_results {
311 let mut promoted_mbcx = MirBorrowckCtxt {
315 move_data: &move_data,
316 location_table, // no need to create a real one for the promoted, it is not used
318 fn_self_span_reported: Default::default(),
319 locals_are_invalidated_at_exit,
320 access_place_error_reported: Default::default(),
321 reservation_error_reported: Default::default(),
322 uninitialized_error_reported: Default::default(),
323 regioncx: regioncx.clone(),
324 used_mut: Default::default(),
325 used_mut_upvars: SmallVec::new(),
326 borrow_set: Rc::clone(&borrow_set),
327 dominators: Dominators::dummy(), // not used
329 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
330 region_names: RefCell::default(),
331 next_region_name: RefCell::new(1),
332 polonius_output: None,
335 promoted_mbcx.report_move_errors(move_errors);
336 errors = promoted_mbcx.errors;
340 let dominators = body.basic_blocks.dominators();
342 let mut mbcx = MirBorrowckCtxt {
346 move_data: &mdpe.move_data,
349 locals_are_invalidated_at_exit,
350 fn_self_span_reported: Default::default(),
351 access_place_error_reported: Default::default(),
352 reservation_error_reported: Default::default(),
353 uninitialized_error_reported: Default::default(),
354 regioncx: Rc::clone(®ioncx),
355 used_mut: Default::default(),
356 used_mut_upvars: SmallVec::new(),
357 borrow_set: Rc::clone(&borrow_set),
361 region_names: RefCell::default(),
362 next_region_name: RefCell::new(1),
367 // Compute and report region errors, if any.
368 mbcx.report_region_errors(nll_errors);
370 let results = BorrowckResults {
371 ever_inits: flow_ever_inits,
372 uninits: flow_uninits,
373 borrows: flow_borrows,
376 mbcx.report_move_errors(move_errors);
378 rustc_mir_dataflow::visit_results(
380 traversal::reverse_postorder(body).map(|(bb, _)| bb),
385 // For each non-user used mutable variable, check if it's been assigned from
386 // a user-declared local. If so, then put that local into the used_mut set.
387 // Note that this set is expected to be small - only upvars from closures
388 // would have a chance of erroneously adding non-user-defined mutable vars
390 let temporary_used_locals: FxHashSet<Local> = mbcx
393 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
396 // For the remaining unused locals that are marked as mutable, we avoid linting any that
397 // were never initialized. These locals may have been removed as unreachable code; or will be
398 // linted as unused variables.
399 let unused_mut_locals =
400 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
401 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
403 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
404 let used_mut = std::mem::take(&mut mbcx.used_mut);
405 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
406 let local_decl = &mbcx.body.local_decls[local];
407 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
408 ClearCrossCrate::Set(data) => data.lint_root,
412 // Skip over locals that begin with an underscore or have no name
413 match mbcx.local_names[local] {
415 if name.as_str().starts_with('_') {
422 let span = local_decl.source_info.span;
423 if span.desugaring_kind().is_some() {
424 // If the `mut` arises as part of a desugaring, we should ignore it.
428 tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
429 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
430 lint.build("variable does not need to be mutable")
431 .span_suggestion_short(
435 Applicability::MachineApplicable,
441 let tainted_by_errors = mbcx.emit_errors();
443 let result = BorrowCheckResult {
444 concrete_opaque_types: opaque_type_values,
445 closure_requirements: opt_closure_req,
446 used_mut_upvars: mbcx.used_mut_upvars,
450 let body_with_facts = if return_body_with_facts {
451 let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
452 Some(Box::new(BodyWithBorrowckFacts {
454 input_facts: *polonius_input.expect("Polonius input facts were not generated"),
456 location_table: location_table_owned,
462 debug!("do_mir_borrowck: result = {:#?}", result);
464 (result, body_with_facts)
467 /// A `Body` with information computed by the borrow checker. This struct is
468 /// intended to be consumed by compiler consumers.
470 /// We need to include the MIR body here because the region identifiers must
471 /// match the ones in the Polonius facts.
472 pub struct BodyWithBorrowckFacts<'tcx> {
473 /// A mir body that contains region identifiers.
474 pub body: Body<'tcx>,
475 /// Polonius input facts.
476 pub input_facts: AllFacts,
477 /// Polonius output facts.
478 pub output_facts: Rc<self::nll::PoloniusOutput>,
479 /// The table that maps Polonius points to locations in the table.
480 pub location_table: LocationTable,
483 struct MirBorrowckCtxt<'cx, 'tcx> {
484 infcx: &'cx InferCtxt<'cx, 'tcx>,
485 param_env: ParamEnv<'tcx>,
486 body: &'cx Body<'tcx>,
487 move_data: &'cx MoveData<'tcx>,
489 /// Map from MIR `Location` to `LocationIndex`; created
490 /// when MIR borrowck begins.
491 location_table: &'cx LocationTable,
493 movable_generator: bool,
494 /// This keeps track of whether local variables are free-ed when the function
495 /// exits even without a `StorageDead`, which appears to be the case for
498 /// I'm not sure this is the right approach - @eddyb could you try and
500 locals_are_invalidated_at_exit: bool,
501 /// This field keeps track of when borrow errors are reported in the access_place function
502 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
503 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
504 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
506 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
507 /// This field keeps track of when borrow conflict errors are reported
508 /// for reservations, so that we don't report seemingly duplicate
509 /// errors for corresponding activations.
511 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
512 // but it is currently inconvenient to track down the `BorrowIndex`
513 // at the time we detect and report a reservation error.
514 reservation_error_reported: FxHashSet<Place<'tcx>>,
515 /// This fields keeps track of the `Span`s that we have
516 /// used to report extra information for `FnSelfUse`, to avoid
517 /// unnecessarily verbose errors.
518 fn_self_span_reported: FxHashSet<Span>,
519 /// This field keeps track of errors reported in the checking of uninitialized variables,
520 /// so that we don't report seemingly duplicate errors.
521 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
522 /// This field keeps track of all the local variables that are declared mut and are mutated.
523 /// Used for the warning issued by an unused mutable local variable.
524 used_mut: FxHashSet<Local>,
525 /// If the function we're checking is a closure, then we'll need to report back the list of
526 /// mutable upvars that have been used. This field keeps track of them.
527 used_mut_upvars: SmallVec<[Field; 8]>,
528 /// Region inference context. This contains the results from region inference and lets us e.g.
529 /// find out which CFG points are contained in each borrow region.
530 regioncx: Rc<RegionInferenceContext<'tcx>>,
532 /// The set of borrows extracted from the MIR
533 borrow_set: Rc<BorrowSet<'tcx>>,
535 /// Dominators for MIR
536 dominators: Dominators<BasicBlock>,
538 /// Information about upvars not necessarily preserved in types or MIR
539 upvars: Vec<Upvar<'tcx>>,
541 /// Names of local (user) variables (extracted from `var_debug_info`).
542 local_names: IndexVec<Local, Option<Symbol>>,
544 /// Record the region names generated for each region in the given
545 /// MIR def so that we can reuse them later in help/error messages.
546 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
548 /// The counter for generating new region names.
549 next_region_name: RefCell<usize>,
551 /// Results of Polonius analysis.
552 polonius_output: Option<Rc<PoloniusOutput>>,
554 errors: error::BorrowckErrors<'tcx>,
558 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
559 // 2. loans made in overlapping scopes do not conflict
560 // 3. assignments do not affect things loaned out as immutable
561 // 4. moves do not affect things loaned out in any way
562 impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
563 type FlowState = Flows<'cx, 'tcx>;
565 fn visit_statement_before_primary_effect(
567 flow_state: &Flows<'cx, 'tcx>,
568 stmt: &'cx Statement<'tcx>,
571 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
572 let span = stmt.source_info.span;
574 self.check_activations(location, span, flow_state);
577 StatementKind::Assign(box (lhs, ref rhs)) => {
578 self.consume_rvalue(location, (rhs, span), flow_state);
580 self.mutate_place(location, (*lhs, span), Shallow(None), flow_state);
582 StatementKind::FakeRead(box (_, ref place)) => {
583 // Read for match doesn't access any memory and is used to
584 // assert that a place is safe and live. So we don't have to
585 // do any checks here.
587 // FIXME: Remove check that the place is initialized. This is
588 // needed for now because matches don't have never patterns yet.
589 // So this is the only place we prevent
593 self.check_if_path_or_subpath_is_moved(
595 InitializationRequiringAction::Use,
596 (place.as_ref(), span),
600 StatementKind::CopyNonOverlapping(box rustc_middle::mir::CopyNonOverlapping {
605 "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
609 | StatementKind::Coverage(..)
610 | StatementKind::AscribeUserType(..)
611 | StatementKind::Retag { .. }
612 | StatementKind::StorageLive(..) => {
613 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
616 StatementKind::StorageDead(local) => {
619 (Place::from(*local), span),
620 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
621 LocalMutationIsAllowed::Yes,
625 StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
626 bug!("Statement not allowed in this MIR phase")
631 fn visit_terminator_before_primary_effect(
633 flow_state: &Flows<'cx, 'tcx>,
634 term: &'cx Terminator<'tcx>,
637 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
638 let span = term.source_info.span;
640 self.check_activations(loc, span, flow_state);
643 TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
644 self.consume_operand(loc, (discr, span), flow_state);
646 TerminatorKind::Drop { place, target: _, unwind: _ } => {
648 "visit_terminator_drop \
649 loc: {:?} term: {:?} place: {:?} span: {:?}",
650 loc, term, place, span
656 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
657 LocalMutationIsAllowed::Yes,
661 TerminatorKind::DropAndReplace {
663 value: ref new_value,
667 self.mutate_place(loc, (drop_place, span), Deep, flow_state);
668 self.consume_operand(loc, (new_value, span), flow_state);
670 TerminatorKind::Call {
679 self.consume_operand(loc, (func, span), flow_state);
681 self.consume_operand(loc, (arg, span), flow_state);
683 self.mutate_place(loc, (destination, span), Deep, flow_state);
685 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
686 self.consume_operand(loc, (cond, span), flow_state);
687 use rustc_middle::mir::AssertKind;
688 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
689 self.consume_operand(loc, (len, span), flow_state);
690 self.consume_operand(loc, (index, span), flow_state);
694 TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
695 self.consume_operand(loc, (value, span), flow_state);
696 self.mutate_place(loc, (resume_arg, span), Deep, flow_state);
699 TerminatorKind::InlineAsm {
709 InlineAsmOperand::In { reg: _, ref value } => {
710 self.consume_operand(loc, (value, span), flow_state);
712 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
713 if let Some(place) = place {
714 self.mutate_place(loc, (place, span), Shallow(None), flow_state);
717 InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
718 self.consume_operand(loc, (in_value, span), flow_state);
719 if let Some(out_place) = out_place {
728 InlineAsmOperand::Const { value: _ }
729 | InlineAsmOperand::SymFn { value: _ }
730 | InlineAsmOperand::SymStatic { def_id: _ } => {}
735 TerminatorKind::Goto { target: _ }
736 | TerminatorKind::Abort
737 | TerminatorKind::Unreachable
738 | TerminatorKind::Resume
739 | TerminatorKind::Return
740 | TerminatorKind::GeneratorDrop
741 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
742 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
743 // no data used, thus irrelevant to borrowck
748 fn visit_terminator_after_primary_effect(
750 flow_state: &Flows<'cx, 'tcx>,
751 term: &'cx Terminator<'tcx>,
754 let span = term.source_info.span;
757 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
758 if self.movable_generator {
759 // Look for any active borrows to locals
760 let borrow_set = self.borrow_set.clone();
761 for i in flow_state.borrows.iter() {
762 let borrow = &borrow_set[i];
763 self.check_for_local_borrow(borrow, span);
768 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
769 // Returning from the function implicitly kills storage for all locals and statics.
770 // Often, the storage will already have been killed by an explicit
771 // StorageDead, but we don't always emit those (notably on unwind paths),
772 // so this "extra check" serves as a kind of backup.
773 let borrow_set = self.borrow_set.clone();
774 for i in flow_state.borrows.iter() {
775 let borrow = &borrow_set[i];
776 self.check_for_invalidation_at_exit(loc, borrow, span);
780 TerminatorKind::Abort
781 | TerminatorKind::Assert { .. }
782 | TerminatorKind::Call { .. }
783 | TerminatorKind::Drop { .. }
784 | TerminatorKind::DropAndReplace { .. }
785 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
786 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
787 | TerminatorKind::Goto { .. }
788 | TerminatorKind::SwitchInt { .. }
789 | TerminatorKind::Unreachable
790 | TerminatorKind::InlineAsm { .. } => {}
795 use self::AccessDepth::{Deep, Shallow};
796 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
798 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
799 enum ArtificialField {
804 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
806 /// From the RFC: "A *shallow* access means that the immediate
807 /// fields reached at P are accessed, but references or pointers
808 /// found within are not dereferenced. Right now, the only access
809 /// that is shallow is an assignment like `x = ...;`, which would
810 /// be a *shallow write* of `x`."
811 Shallow(Option<ArtificialField>),
813 /// From the RFC: "A *deep* access means that all data reachable
814 /// through the given place may be invalidated or accesses by
818 /// Access is Deep only when there is a Drop implementation that
819 /// can reach the data behind the reference.
823 /// Kind of access to a value: read or write
824 /// (For informational purposes only)
825 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
827 /// From the RFC: "A *read* means that the existing data may be
828 /// read, but will not be changed."
831 /// From the RFC: "A *write* means that the data may be mutated to
832 /// new values or otherwise invalidated (for example, it could be
833 /// de-initialized, as in a move operation).
836 /// For two-phase borrows, we distinguish a reservation (which is treated
837 /// like a Read) from an activation (which is treated like a write), and
838 /// each of those is furthermore distinguished from Reads/Writes above.
839 Reservation(WriteKind),
840 Activation(WriteKind, BorrowIndex),
843 /// Kind of read access to a value
844 /// (For informational purposes only)
845 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
851 /// Kind of write access to a value
852 /// (For informational purposes only)
853 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
856 MutableBorrow(BorrowKind),
861 /// When checking permissions for a place access, this flag is used to indicate that an immutable
862 /// local place can be mutated.
864 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
865 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
866 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
867 // `is_declared_mutable()`.
868 // - Take flow state into consideration in `is_assignable()` for local variables.
869 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
870 enum LocalMutationIsAllowed {
872 /// We want use of immutable upvars to cause a "write to immutable upvar"
873 /// error, not an "reassignment" error.
878 #[derive(Copy, Clone, Debug)]
879 enum InitializationRequiringAction {
887 struct RootPlace<'tcx> {
889 place_projection: &'tcx [PlaceElem<'tcx>],
890 is_local_mutation_allowed: LocalMutationIsAllowed,
893 impl InitializationRequiringAction {
894 fn as_noun(self) -> &'static str {
896 InitializationRequiringAction::Borrow => "borrow",
897 InitializationRequiringAction::MatchOn => "use", // no good noun
898 InitializationRequiringAction::Use => "use",
899 InitializationRequiringAction::Assignment => "assign",
900 InitializationRequiringAction::PartialAssignment => "assign to part",
904 fn as_verb_in_past_tense(self) -> &'static str {
906 InitializationRequiringAction::Borrow => "borrowed",
907 InitializationRequiringAction::MatchOn => "matched on",
908 InitializationRequiringAction::Use => "used",
909 InitializationRequiringAction::Assignment => "assigned",
910 InitializationRequiringAction::PartialAssignment => "partially assigned",
914 fn as_general_verb_in_past_tense(self) -> &'static str {
916 InitializationRequiringAction::Borrow
917 | InitializationRequiringAction::MatchOn
918 | InitializationRequiringAction::Use => "used",
919 InitializationRequiringAction::Assignment => "assigned",
920 InitializationRequiringAction::PartialAssignment => "partially assigned",
925 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
926 fn body(&self) -> &'cx Body<'tcx> {
930 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
931 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
932 /// place is initialized and (b) it is not borrowed in some way that would prevent this
935 /// Returns `true` if an error is reported.
939 place_span: (Place<'tcx>, Span),
940 kind: (AccessDepth, ReadOrWrite),
941 is_local_mutation_allowed: LocalMutationIsAllowed,
942 flow_state: &Flows<'cx, 'tcx>,
946 if let Activation(_, borrow_index) = rw {
947 if self.reservation_error_reported.contains(&place_span.0) {
949 "skipping access_place for activation of invalid reservation \
950 place: {:?} borrow_index: {:?}",
951 place_span.0, borrow_index
957 // Check is_empty() first because it's the common case, and doing that
958 // way we avoid the clone() call.
959 if !self.access_place_error_reported.is_empty()
960 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
963 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
969 let mutability_error = self.check_access_permissions(
972 is_local_mutation_allowed,
977 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
979 if conflict_error || mutability_error {
980 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
981 self.access_place_error_reported.insert((place_span.0, place_span.1));
985 fn check_access_for_conflict(
988 place_span: (Place<'tcx>, Span),
991 flow_state: &Flows<'cx, 'tcx>,
994 "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
995 location, place_span, sd, rw,
998 let mut error_reported = false;
999 let tcx = self.infcx.tcx;
1000 let body = self.body;
1001 let borrow_set = self.borrow_set.clone();
1003 // Use polonius output if it has been enabled.
1004 let polonius_output = self.polonius_output.clone();
1005 let borrows_in_scope = if let Some(polonius) = &polonius_output {
1006 let location = self.location_table.start_index(location);
1007 Either::Left(polonius.errors_at(location).iter().copied())
1009 Either::Right(flow_state.borrows.iter())
1012 each_borrow_involving_path(
1020 |this, borrow_index, borrow| match (rw, borrow.kind) {
1021 // Obviously an activation is compatible with its own
1022 // reservation (or even prior activating uses of same
1023 // borrow); so don't check if they interfere.
1025 // NOTE: *reservations* do conflict with themselves;
1026 // thus aren't injecting unsoundness w/ this check.)
1027 (Activation(_, activating), _) if activating == borrow_index => {
1029 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1030 skipping {:?} b/c activation of same borrow_index",
1034 (borrow_index, borrow),
1039 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1041 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1042 BorrowKind::Unique | BorrowKind::Mut { .. },
1043 ) => Control::Continue,
1045 (Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
1046 // This used to be a future compatibility warning (to be
1047 // disallowed on NLL). See rust-lang/rust#56254
1051 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1052 // Handled by initialization checks.
1056 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1057 // Reading from mere reservations of mutable-borrows is OK.
1058 if !is_active(&this.dominators, borrow, location) {
1059 assert!(allow_two_phase_borrow(borrow.kind));
1060 return Control::Continue;
1063 error_reported = true;
1067 .report_use_while_mutably_borrowed(location, place_span, borrow);
1068 this.buffer_error(err);
1070 ReadKind::Borrow(bk) => {
1072 this.report_conflicting_borrow(location, place_span, bk, borrow);
1073 this.buffer_error(err);
1079 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1081 Reservation(..) => {
1083 "recording invalid reservation of \
1087 this.reservation_error_reported.insert(place_span.0);
1089 Activation(_, activating) => {
1091 "observing check_place for activation of \
1092 borrow_index: {:?}",
1096 Read(..) | Write(..) => {}
1099 error_reported = true;
1101 WriteKind::MutableBorrow(bk) => {
1103 this.report_conflicting_borrow(location, place_span, bk, borrow);
1104 this.buffer_error(err);
1106 WriteKind::StorageDeadOrDrop => this
1107 .report_borrowed_value_does_not_live_long_enough(
1113 WriteKind::Mutate => {
1114 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1116 WriteKind::Move => {
1117 this.report_move_out_while_borrowed(location, place_span, borrow)
1131 place_span: (Place<'tcx>, Span),
1133 flow_state: &Flows<'cx, 'tcx>,
1135 // Write of P[i] or *P requires P init'd.
1136 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1138 // Special case: you can assign an immutable local variable
1139 // (e.g., `x = ...`) so long as it has never been initialized
1140 // before (at this point in the flow).
1141 if let Some(local) = place_span.0.as_local() {
1142 if let Mutability::Not = self.body.local_decls[local].mutability {
1143 // check for reassignments to immutable local variables
1144 self.check_if_reassignment_to_immutable_state(
1145 location, local, place_span, flow_state,
1151 // Otherwise, use the normal access permission rules.
1155 (kind, Write(WriteKind::Mutate)),
1156 LocalMutationIsAllowed::No,
1164 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1165 flow_state: &Flows<'cx, 'tcx>,
1168 Rvalue::Ref(_ /*rgn*/, bk, place) => {
1169 let access_kind = match bk {
1170 BorrowKind::Shallow => {
1171 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1173 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1174 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1175 let wk = WriteKind::MutableBorrow(bk);
1176 if allow_two_phase_borrow(bk) {
1177 (Deep, Reservation(wk))
1188 LocalMutationIsAllowed::No,
1192 let action = if bk == BorrowKind::Shallow {
1193 InitializationRequiringAction::MatchOn
1195 InitializationRequiringAction::Borrow
1198 self.check_if_path_or_subpath_is_moved(
1201 (place.as_ref(), span),
1206 Rvalue::AddressOf(mutability, place) => {
1207 let access_kind = match mutability {
1208 Mutability::Mut => (
1210 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1211 allow_two_phase_borrow: false,
1214 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1221 LocalMutationIsAllowed::No,
1225 self.check_if_path_or_subpath_is_moved(
1227 InitializationRequiringAction::Borrow,
1228 (place.as_ref(), span),
1233 Rvalue::ThreadLocalRef(_) => {}
1235 Rvalue::Use(ref operand)
1236 | Rvalue::Repeat(ref operand, _)
1237 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1238 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/)
1239 | Rvalue::ShallowInitBox(ref operand, _ /*ty*/) => {
1240 self.consume_operand(location, (operand, span), flow_state)
1242 Rvalue::CopyForDeref(place) => {
1246 (Deep, Read(ReadKind::Copy)),
1247 LocalMutationIsAllowed::No,
1251 // Finally, check if path was already moved.
1252 self.check_if_path_or_subpath_is_moved(
1254 InitializationRequiringAction::Use,
1255 (place.as_ref(), span),
1260 Rvalue::Len(place) | Rvalue::Discriminant(place) => {
1261 let af = match *rvalue {
1262 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1263 Rvalue::Discriminant(..) => None,
1264 _ => unreachable!(),
1269 (Shallow(af), Read(ReadKind::Copy)),
1270 LocalMutationIsAllowed::No,
1273 self.check_if_path_or_subpath_is_moved(
1275 InitializationRequiringAction::Use,
1276 (place.as_ref(), span),
1281 Rvalue::BinaryOp(_bin_op, box (ref operand1, ref operand2))
1282 | Rvalue::CheckedBinaryOp(_bin_op, box (ref operand1, ref operand2)) => {
1283 self.consume_operand(location, (operand1, span), flow_state);
1284 self.consume_operand(location, (operand2, span), flow_state);
1287 Rvalue::NullaryOp(_op, _ty) => {
1288 // nullary ops take no dynamic input; no borrowck effect.
1291 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1292 // We need to report back the list of mutable upvars that were
1293 // moved into the closure and subsequently used by the closure,
1294 // in order to populate our used_mut set.
1295 match **aggregate_kind {
1296 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1297 let BorrowCheckResult { used_mut_upvars, .. } =
1298 self.infcx.tcx.mir_borrowck(def_id);
1299 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1300 for field in used_mut_upvars {
1301 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1304 AggregateKind::Adt(..)
1305 | AggregateKind::Array(..)
1306 | AggregateKind::Tuple { .. } => (),
1309 for operand in operands {
1310 self.consume_operand(location, (operand, span), flow_state);
1316 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1317 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1318 // We have three possibilities here:
1319 // a. We are modifying something through a mut-ref
1320 // b. We are modifying something that is local to our parent
1321 // c. Current body is a nested closure, and we are modifying path starting from
1322 // a Place captured by our parent closure.
1324 // Handle (c), the path being modified is exactly the path captured by our parent
1325 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1326 this.used_mut_upvars.push(field);
1330 for (place_ref, proj) in place.iter_projections().rev() {
1332 if proj == ProjectionElem::Deref {
1333 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1334 // We aren't modifying a variable directly
1335 ty::Ref(_, _, hir::Mutability::Mut) => return,
1342 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1343 this.used_mut_upvars.push(field);
1349 this.used_mut.insert(place.local);
1352 // This relies on the current way that by-value
1353 // captures of a closure are copied/moved directly
1354 // when generating MIR.
1356 Operand::Move(place) | Operand::Copy(place) => {
1357 match place.as_local() {
1358 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1359 if self.body.local_decls[local].ty.is_mutable_ptr() {
1360 // The variable will be marked as mutable by the borrow.
1363 // This is an edge case where we have a `move` closure
1364 // inside a non-move closure, and the inner closure
1365 // contains a mutation:
1368 // || { move || { i += 1; }; };
1370 // In this case our usual strategy of assuming that the
1371 // variable will be captured by mutable reference is
1372 // wrong, since `i` can be copied into the inner
1373 // closure from a shared reference.
1375 // As such we have to search for the local that this
1376 // capture comes from and mark it as being used as mut.
1378 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1379 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1380 &self.move_data.inits[init_index]
1382 bug!("temporary should be initialized exactly once")
1385 let InitLocation::Statement(loc) = init.location else {
1386 bug!("temporary initialized in arguments")
1389 let body = self.body;
1390 let bbd = &body[loc.block];
1391 let stmt = &bbd.statements[loc.statement_index];
1392 debug!("temporary assigned in: stmt={:?}", stmt);
1394 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1396 propagate_closure_used_mut_place(self, source);
1399 "closures should only capture user variables \
1400 or references to user variables"
1404 _ => propagate_closure_used_mut_place(self, place),
1407 Operand::Constant(..) => {}
1414 (operand, span): (&'cx Operand<'tcx>, Span),
1415 flow_state: &Flows<'cx, 'tcx>,
1418 Operand::Copy(place) => {
1419 // copy of place: check if this is "copy of frozen path"
1420 // (FIXME: see check_loans.rs)
1424 (Deep, Read(ReadKind::Copy)),
1425 LocalMutationIsAllowed::No,
1429 // Finally, check if path was already moved.
1430 self.check_if_path_or_subpath_is_moved(
1432 InitializationRequiringAction::Use,
1433 (place.as_ref(), span),
1437 Operand::Move(place) => {
1438 // move of place: check if this is move of already borrowed path
1442 (Deep, Write(WriteKind::Move)),
1443 LocalMutationIsAllowed::Yes,
1447 // Finally, check if path was already moved.
1448 self.check_if_path_or_subpath_is_moved(
1450 InitializationRequiringAction::Use,
1451 (place.as_ref(), span),
1455 Operand::Constant(_) => {}
1459 /// Checks whether a borrow of this place is invalidated when the function
1461 fn check_for_invalidation_at_exit(
1464 borrow: &BorrowData<'tcx>,
1467 debug!("check_for_invalidation_at_exit({:?})", borrow);
1468 let place = borrow.borrowed_place;
1469 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1471 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1472 // we just know that all locals are dropped at function exit (otherwise
1473 // we'll have a memory leak) and assume that all statics have a destructor.
1475 // FIXME: allow thread-locals to borrow other thread locals?
1477 let (might_be_alive, will_be_dropped) =
1478 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1479 // Thread-locals might be dropped after the function exits
1480 // We have to dereference the outer reference because
1481 // borrows don't conflict behind shared references.
1482 root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
1485 (false, self.locals_are_invalidated_at_exit)
1488 if !will_be_dropped {
1489 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1493 let sd = if might_be_alive { Deep } else { Shallow(None) };
1495 if places_conflict::borrow_conflicts_with_place(
1502 places_conflict::PlaceConflictBias::Overlap,
1504 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1505 // FIXME: should be talking about the region lifetime instead
1506 // of just a span here.
1507 let span = self.infcx.tcx.sess.source_map().end_point(span);
1508 self.report_borrowed_value_does_not_live_long_enough(
1517 /// Reports an error if this is a borrow of local data.
1518 /// This is called for all Yield expressions on movable generators
1519 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1520 debug!("check_for_local_borrow({:?})", borrow);
1522 if borrow_of_local_data(borrow.borrowed_place) {
1523 let err = self.cannot_borrow_across_generator_yield(
1524 self.retrieve_borrow_spans(borrow).var_or_use(),
1528 self.buffer_error(err);
1532 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1533 // Two-phase borrow support: For each activation that is newly
1534 // generated at this statement, check if it interferes with
1536 let borrow_set = self.borrow_set.clone();
1537 for &borrow_index in borrow_set.activations_at_location(location) {
1538 let borrow = &borrow_set[borrow_index];
1540 // only mutable borrows should be 2-phase
1541 assert!(match borrow.kind {
1542 BorrowKind::Shared | BorrowKind::Shallow => false,
1543 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1548 (borrow.borrowed_place, span),
1549 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1550 LocalMutationIsAllowed::No,
1553 // We do not need to call `check_if_path_or_subpath_is_moved`
1554 // again, as we already called it when we made the
1555 // initial reservation.
1559 fn check_if_reassignment_to_immutable_state(
1563 place_span: (Place<'tcx>, Span),
1564 flow_state: &Flows<'cx, 'tcx>,
1566 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1568 // Check if any of the initializations of `local` have happened yet:
1569 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1570 // And, if so, report an error.
1571 let init = &self.move_data.inits[init_index];
1572 let span = init.span(&self.body);
1573 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1577 fn check_if_full_path_is_moved(
1580 desired_action: InitializationRequiringAction,
1581 place_span: (PlaceRef<'tcx>, Span),
1582 flow_state: &Flows<'cx, 'tcx>,
1584 let maybe_uninits = &flow_state.uninits;
1588 // 1. Move of `a.b.c`, use of `a.b.c`
1589 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1590 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1591 // partial initialization support, one might have `a.x`
1592 // initialized but not `a.b`.
1596 // 4. Move of `a.b.c`, use of `a.b.d`
1597 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1598 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1599 // must have been initialized for the use to be sound.
1600 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1602 // The dataflow tracks shallow prefixes distinctly (that is,
1603 // field-accesses on P distinctly from P itself), in order to
1604 // track substructure initialization separately from the whole
1607 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1608 // which we have a MovePath is `a.b`, then that means that the
1609 // initialization state of `a.b` is all we need to inspect to
1610 // know if `a.b.c` is valid (and from that we infer that the
1611 // dereference and `.d` access is also valid, since we assume
1612 // `a.b.c` is assigned a reference to an initialized and
1613 // well-formed record structure.)
1615 // Therefore, if we seek out the *closest* prefix for which we
1616 // have a MovePath, that should capture the initialization
1617 // state for the place scenario.
1619 // This code covers scenarios 1, 2, and 3.
1621 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1622 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1623 if maybe_uninits.contains(mpi) {
1624 self.report_use_of_moved_or_uninitialized(
1627 (prefix, place_span.0, place_span.1),
1630 } // Only query longest prefix with a MovePath, not further
1631 // ancestors; dataflow recurs on children when parents
1632 // move (to support partial (re)inits).
1634 // (I.e., querying parents breaks scenario 7; but may want
1635 // to do such a query based on partial-init feature-gate.)
1638 /// Subslices correspond to multiple move paths, so we iterate through the
1639 /// elements of the base array. For each element we check
1641 /// * Does this element overlap with our slice.
1642 /// * Is any part of it uninitialized.
1643 fn check_if_subslice_element_is_moved(
1646 desired_action: InitializationRequiringAction,
1647 place_span: (PlaceRef<'tcx>, Span),
1648 maybe_uninits: &ChunkedBitSet<MovePathIndex>,
1652 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1653 let move_paths = &self.move_data.move_paths;
1655 let root_path = &move_paths[mpi];
1656 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1657 let last_proj = child_move_path.place.projection.last().unwrap();
1658 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1659 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1661 if (from..to).contains(offset) {
1663 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1664 maybe_uninits.contains(mpi)
1667 if let Some(uninit_child) = uninit_child {
1668 self.report_use_of_moved_or_uninitialized(
1671 (place_span.0, place_span.0, place_span.1),
1674 return; // don't bother finding other problems.
1682 fn check_if_path_or_subpath_is_moved(
1685 desired_action: InitializationRequiringAction,
1686 place_span: (PlaceRef<'tcx>, Span),
1687 flow_state: &Flows<'cx, 'tcx>,
1689 let maybe_uninits = &flow_state.uninits;
1693 // 1. Move of `a.b.c`, use of `a` or `a.b`
1694 // partial initialization support, one might have `a.x`
1695 // initialized but not `a.b`.
1696 // 2. All bad scenarios from `check_if_full_path_is_moved`
1700 // 3. Move of `a.b.c`, use of `a.b.d`
1701 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1702 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1703 // must have been initialized for the use to be sound.
1704 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1706 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1708 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1709 place_span.0.last_projection()
1711 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1712 if let ty::Array(..) = place_ty.ty.kind() {
1713 self.check_if_subslice_element_is_moved(
1716 (place_base, place_span.1),
1725 // A move of any shallow suffix of `place` also interferes
1726 // with an attempt to use `place`. This is scenario 3 above.
1728 // (Distinct from handling of scenarios 1+2+4 above because
1729 // `place` does not interfere with suffixes of its prefixes,
1730 // e.g., `a.b.c` does not interfere with `a.b.d`)
1732 // This code covers scenario 1.
1734 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1735 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1736 let uninit_mpi = self
1738 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1740 if let Some(uninit_mpi) = uninit_mpi {
1741 self.report_use_of_moved_or_uninitialized(
1744 (place_span.0, place_span.0, place_span.1),
1747 return; // don't bother finding other problems.
1752 /// Currently MoveData does not store entries for all places in
1753 /// the input MIR. For example it will currently filter out
1754 /// places that are Copy; thus we do not track places of shared
1755 /// reference type. This routine will walk up a place along its
1756 /// prefixes, searching for a foundational place that *is*
1757 /// tracked in the MoveData.
1759 /// An Err result includes a tag indicated why the search failed.
1760 /// Currently this can only occur if the place is built off of a
1761 /// static variable, as we do not track those in the MoveData.
1762 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1763 match self.move_data.rev_lookup.find(place) {
1764 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1765 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1767 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1771 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1772 // If returns None, then there is no move path corresponding
1773 // to a direct owner of `place` (which means there is nothing
1774 // that borrowck tracks for its analysis).
1776 match self.move_data.rev_lookup.find(place) {
1777 LookupResult::Parent(_) => None,
1778 LookupResult::Exact(mpi) => Some(mpi),
1782 fn check_if_assigned_path_is_moved(
1785 (place, span): (Place<'tcx>, Span),
1786 flow_state: &Flows<'cx, 'tcx>,
1788 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1790 // None case => assigning to `x` does not require `x` be initialized.
1791 for (place_base, elem) in place.iter_projections().rev() {
1793 ProjectionElem::Index(_/*operand*/) |
1794 ProjectionElem::ConstantIndex { .. } |
1795 // assigning to P[i] requires P to be valid.
1796 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1797 // assigning to (P->variant) is okay if assigning to `P` is okay
1799 // FIXME: is this true even if P is an adt with a dtor?
1802 // assigning to (*P) requires P to be initialized
1803 ProjectionElem::Deref => {
1804 self.check_if_full_path_is_moved(
1805 location, InitializationRequiringAction::Use,
1806 (place_base, span), flow_state);
1807 // (base initialized; no need to
1812 ProjectionElem::Subslice { .. } => {
1813 panic!("we don't allow assignments to subslices, location: {:?}",
1817 ProjectionElem::Field(..) => {
1818 // if type of `P` has a dtor, then
1819 // assigning to `P.f` requires `P` itself
1820 // be already initialized
1821 let tcx = self.infcx.tcx;
1822 let base_ty = place_base.ty(self.body(), tcx).ty;
1823 match base_ty.kind() {
1824 ty::Adt(def, _) if def.has_dtor(tcx) => {
1825 self.check_if_path_or_subpath_is_moved(
1826 location, InitializationRequiringAction::Assignment,
1827 (place_base, span), flow_state);
1829 // (base initialized; no need to
1834 // Once `let s; s.x = V; read(s.x);`,
1835 // is allowed, remove this match arm.
1836 ty::Adt(..) | ty::Tuple(..) => {
1837 check_parent_of_field(self, location, place_base, span, flow_state);
1839 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1840 // partial initialization, do not complain about unnecessary `mut` on
1841 // an attempt to do a partial initialization.
1842 self.used_mut.insert(place.local);
1851 fn check_parent_of_field<'cx, 'tcx>(
1852 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1854 base: PlaceRef<'tcx>,
1856 flow_state: &Flows<'cx, 'tcx>,
1858 // rust-lang/rust#21232: Until Rust allows reads from the
1859 // initialized parts of partially initialized structs, we
1860 // will, starting with the 2018 edition, reject attempts
1861 // to write to structs that are not fully initialized.
1863 // In other words, *until* we allow this:
1865 // 1. `let mut s; s.x = Val; read(s.x);`
1867 // we will for now disallow this:
1869 // 2. `let mut s; s.x = Val;`
1873 // 3. `let mut s = ...; drop(s); s.x=Val;`
1875 // This does not use check_if_path_or_subpath_is_moved,
1876 // because we want to *allow* reinitializations of fields:
1877 // e.g., want to allow
1879 // `let mut s = ...; drop(s.x); s.x=Val;`
1881 // This does not use check_if_full_path_is_moved on
1882 // `base`, because that would report an error about the
1883 // `base` as a whole, but in this scenario we *really*
1884 // want to report an error about the actual thing that was
1885 // moved, which may be some prefix of `base`.
1887 // Shallow so that we'll stop at any dereference; we'll
1888 // report errors about issues with such bases elsewhere.
1889 let maybe_uninits = &flow_state.uninits;
1891 // Find the shortest uninitialized prefix you can reach
1892 // without going over a Deref.
1893 let mut shortest_uninit_seen = None;
1894 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1895 let Some(mpi) = this.move_path_for_place(prefix) else { continue };
1897 if maybe_uninits.contains(mpi) {
1899 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1900 shortest_uninit_seen,
1903 shortest_uninit_seen = Some((prefix, mpi));
1905 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1909 if let Some((prefix, mpi)) = shortest_uninit_seen {
1910 // Check for a reassignment into an uninitialized field of a union (for example,
1911 // after a move out). In this case, do not report an error here. There is an
1912 // exception, if this is the first assignment into the union (that is, there is
1913 // no move out from an earlier location) then this is an attempt at initialization
1914 // of the union - we should error in that case.
1915 let tcx = this.infcx.tcx;
1916 if base.ty(this.body(), tcx).ty.is_union() {
1917 if this.move_data.path_map[mpi].iter().any(|moi| {
1918 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1924 this.report_use_of_moved_or_uninitialized(
1926 InitializationRequiringAction::PartialAssignment,
1927 (prefix, base, span),
1934 /// Checks the permissions for the given place and read or write kind
1936 /// Returns `true` if an error is reported.
1937 fn check_access_permissions(
1939 (place, span): (Place<'tcx>, Span),
1941 is_local_mutation_allowed: LocalMutationIsAllowed,
1942 flow_state: &Flows<'cx, 'tcx>,
1946 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1947 place, kind, is_local_mutation_allowed
1954 Reservation(WriteKind::MutableBorrow(
1955 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1957 | Write(WriteKind::MutableBorrow(
1958 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1960 let is_local_mutation_allowed = match borrow_kind {
1961 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1962 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1963 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1965 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1967 self.add_used_mut(root_place, flow_state);
1971 error_access = AccessKind::MutableBorrow;
1972 the_place_err = place_err;
1976 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1977 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1979 self.add_used_mut(root_place, flow_state);
1983 error_access = AccessKind::Mutate;
1984 the_place_err = place_err;
1991 | WriteKind::StorageDeadOrDrop
1992 | WriteKind::MutableBorrow(BorrowKind::Shared)
1993 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1997 | WriteKind::StorageDeadOrDrop
1998 | WriteKind::MutableBorrow(BorrowKind::Shared)
1999 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2001 if self.is_mutable(place.as_ref(), is_local_mutation_allowed).is_err()
2002 && !self.has_buffered_errors()
2004 // rust-lang/rust#46908: In pure NLL mode this code path should be
2005 // unreachable, but we use `delay_span_bug` because we can hit this when
2006 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
2007 // enabled. We don't want to ICE for that case, as other errors will have
2008 // been emitted (#52262).
2009 self.infcx.tcx.sess.delay_span_bug(
2012 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2020 // permission checks are done at Reservation point.
2026 | BorrowKind::Mut { .. }
2027 | BorrowKind::Shared
2028 | BorrowKind::Shallow,
2032 // Access authorized
2037 // rust-lang/rust#21232, #54986: during period where we reject
2038 // partial initialization, do not complain about mutability
2039 // errors except for actual mutation (as opposed to an attempt
2040 // to do a partial initialization).
2041 let previously_initialized =
2042 self.is_local_ever_initialized(place.local, flow_state).is_some();
2044 // at this point, we have set up the error reporting state.
2045 if previously_initialized {
2046 self.report_mutability_error(place, span, the_place_err, error_access, location);
2053 fn is_local_ever_initialized(
2056 flow_state: &Flows<'cx, 'tcx>,
2057 ) -> Option<InitIndex> {
2058 let mpi = self.move_data.rev_lookup.find_local(local);
2059 let ii = &self.move_data.init_path_map[mpi];
2061 if flow_state.ever_inits.contains(index) {
2068 /// Adds the place into the used mutable variables set
2069 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2071 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2072 // If the local may have been initialized, and it is now currently being
2073 // mutated, then it is justified to be annotated with the `mut`
2074 // keyword, since the mutation may be a possible reassignment.
2075 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2076 && self.is_local_ever_initialized(local, flow_state).is_some()
2078 self.used_mut.insert(local);
2083 place_projection: _,
2084 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2088 place_projection: place_projection @ [.., _],
2089 is_local_mutation_allowed: _,
2091 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2093 projection: place_projection,
2095 self.used_mut_upvars.push(field);
2101 /// Whether this value can be written or borrowed mutably.
2102 /// Returns the root place if the place passed in is a projection.
2105 place: PlaceRef<'tcx>,
2106 is_local_mutation_allowed: LocalMutationIsAllowed,
2107 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2108 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2109 match place.last_projection() {
2111 let local = &self.body.local_decls[place.local];
2112 match local.mutability {
2113 Mutability::Not => match is_local_mutation_allowed {
2114 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2115 place_local: place.local,
2116 place_projection: place.projection,
2117 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2119 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2120 place_local: place.local,
2121 place_projection: place.projection,
2122 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2124 LocalMutationIsAllowed::No => Err(place),
2126 Mutability::Mut => Ok(RootPlace {
2127 place_local: place.local,
2128 place_projection: place.projection,
2129 is_local_mutation_allowed,
2133 Some((place_base, elem)) => {
2135 ProjectionElem::Deref => {
2136 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2138 // Check the kind of deref to decide
2139 match base_ty.kind() {
2140 ty::Ref(_, _, mutbl) => {
2142 // Shared borrowed data is never mutable
2143 hir::Mutability::Not => Err(place),
2144 // Mutably borrowed data is mutable, but only if we have a
2145 // unique path to the `&mut`
2146 hir::Mutability::Mut => {
2147 let mode = match self.is_upvar_field_projection(place) {
2148 Some(field) if self.upvars[field.index()].by_ref => {
2149 is_local_mutation_allowed
2151 _ => LocalMutationIsAllowed::Yes,
2154 self.is_mutable(place_base, mode)
2158 ty::RawPtr(tnm) => {
2160 // `*const` raw pointers are not mutable
2161 hir::Mutability::Not => Err(place),
2162 // `*mut` raw pointers are always mutable, regardless of
2163 // context. The users have to check by themselves.
2164 hir::Mutability::Mut => Ok(RootPlace {
2165 place_local: place.local,
2166 place_projection: place.projection,
2167 is_local_mutation_allowed,
2171 // `Box<T>` owns its content, so mutable if its location is mutable
2172 _ if base_ty.is_box() => {
2173 self.is_mutable(place_base, is_local_mutation_allowed)
2175 // Deref should only be for reference, pointers or boxes
2176 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2179 // All other projections are owned by their base path, so mutable if
2180 // base path is mutable
2181 ProjectionElem::Field(..)
2182 | ProjectionElem::Index(..)
2183 | ProjectionElem::ConstantIndex { .. }
2184 | ProjectionElem::Subslice { .. }
2185 | ProjectionElem::Downcast(..) => {
2186 let upvar_field_projection = self.is_upvar_field_projection(place);
2187 if let Some(field) = upvar_field_projection {
2188 let upvar = &self.upvars[field.index()];
2190 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2191 place={:?}, place_base={:?}",
2192 upvar, is_local_mutation_allowed, place, place_base
2194 match (upvar.place.mutability, is_local_mutation_allowed) {
2197 LocalMutationIsAllowed::No
2198 | LocalMutationIsAllowed::ExceptUpvars,
2200 (Mutability::Not, LocalMutationIsAllowed::Yes)
2201 | (Mutability::Mut, _) => {
2202 // Subtle: this is an upvar
2203 // reference, so it looks like
2204 // `self.foo` -- we want to double
2205 // check that the location `*self`
2206 // is mutable (i.e., this is not a
2207 // `Fn` closure). But if that
2208 // check succeeds, we want to
2209 // *blame* the mutability on
2210 // `place` (that is,
2211 // `self.foo`). This is used to
2212 // propagate the info about
2213 // whether mutability declarations
2214 // are used outwards, so that we register
2215 // the outer variable as mutable. Otherwise a
2216 // test like this fails to record the `mut`
2220 // fn foo<F: FnOnce()>(_f: F) { }
2222 // let var = Vec::new();
2229 self.is_mutable(place_base, is_local_mutation_allowed)?;
2231 place_local: place.local,
2232 place_projection: place.projection,
2233 is_local_mutation_allowed,
2238 self.is_mutable(place_base, is_local_mutation_allowed)
2246 /// If `place` is a field projection, and the field is being projected from a closure type,
2247 /// then returns the index of the field being projected. Note that this closure will always
2248 /// be `self` in the current MIR, because that is the only time we directly access the fields
2249 /// of a closure type.
2250 fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2251 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2256 use rustc_errors::ErrorGuaranteed;
2260 pub struct BorrowckErrors<'tcx> {
2261 /// This field keeps track of move errors that are to be reported for given move indices.
2263 /// There are situations where many errors can be reported for a single move out (see #53807)
2264 /// and we want only the best of those errors.
2266 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
2267 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
2268 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
2269 /// all move errors have been reported, any diagnostics in this map are added to the buffer
2272 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
2273 /// when errors in the map are being re-added to the error buffer so that errors with the
2274 /// same primary span come out in a consistent order.
2275 buffered_move_errors:
2276 BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>)>,
2277 /// Diagnostics to be reported buffer.
2278 buffered: Vec<Diagnostic>,
2279 /// Set to Some if we emit an error during borrowck
2280 tainted_by_errors: Option<ErrorGuaranteed>,
2283 impl BorrowckErrors<'_> {
2284 pub fn new() -> Self {
2286 buffered_move_errors: BTreeMap::new(),
2287 buffered: Default::default(),
2288 tainted_by_errors: None,
2292 // FIXME(eddyb) this is a suboptimal API because `tainted_by_errors` is
2293 // set before any emission actually happens (weakening the guarantee).
2294 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2295 self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
2296 t.buffer(&mut self.buffered);
2299 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2300 t.buffer(&mut self.buffered);
2303 pub fn set_tainted_by_errors(&mut self) {
2304 self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
2308 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
2309 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2310 self.errors.buffer_error(t);
2313 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2314 self.errors.buffer_non_error_diag(t);
2317 pub fn buffer_move_error(
2319 move_out_indices: Vec<MoveOutIndex>,
2320 place_and_err: (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>),
2322 if let Some((_, diag)) =
2323 self.errors.buffered_move_errors.insert(move_out_indices, place_and_err)
2325 // Cancel the old diagnostic so we don't ICE
2333 pub fn emit_errors(&mut self) -> Option<ErrorGuaranteed> {
2334 // Buffer any move errors that we collected and de-duplicated.
2335 for (_, (_, diag)) in std::mem::take(&mut self.errors.buffered_move_errors) {
2336 // We have already set tainted for this error, so just buffer it.
2337 diag.buffer(&mut self.errors.buffered);
2340 if !self.errors.buffered.is_empty() {
2341 self.errors.buffered.sort_by_key(|diag| diag.sort_span);
2343 for mut diag in self.errors.buffered.drain(..) {
2344 self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
2348 self.errors.tainted_by_errors
2351 pub fn has_buffered_errors(&self) -> bool {
2352 self.errors.buffered.is_empty()
2355 pub fn has_move_error(
2357 move_out_indices: &[MoveOutIndex],
2358 ) -> Option<&(PlaceRef<'tcx>, DiagnosticBuilder<'cx, ErrorGuaranteed>)> {
2359 self.errors.buffered_move_errors.get(move_out_indices)
2364 /// The degree of overlap between 2 places for borrow-checking.
2366 /// The places might partially overlap - in this case, we give
2367 /// up and say that they might conflict. This occurs when
2368 /// different fields of a union are borrowed. For example,
2369 /// if `u` is a union, we have no way of telling how disjoint
2370 /// `u.a.x` and `a.b.y` are.
2372 /// The places have the same type, and are either completely disjoint
2373 /// or equal - i.e., they can't "partially" overlap as can occur with
2374 /// unions. This is the "base case" on which we recur for extensions
2377 /// The places are disjoint, so we know all extensions of them
2378 /// will also be disjoint.