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)]
6 #![feature(min_specialization)]
7 #![feature(never_type)]
8 #![feature(rustc_attrs)]
9 #![feature(stmt_expr_attributes)]
10 #![feature(trusted_step)]
11 #![feature(try_blocks)]
12 #![recursion_limit = "256"]
15 extern crate rustc_middle;
19 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
20 use rustc_data_structures::graph::dominators::Dominators;
21 use rustc_data_structures::vec_map::VecMap;
22 use rustc_errors::{Diagnostic, DiagnosticBuilder};
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, NonDivergingIntrinsic, Operand,
30 Place, PlaceElem, 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 crate::session_diagnostics::VarNeedNotMut;
56 use self::diagnostics::{AccessKind, RegionName};
57 use self::location::LocationTable;
58 use self::prefixes::PrefixSet;
61 use self::path_utils::*;
65 mod constraint_generation;
73 mod member_constraints;
81 mod session_diagnostics;
83 mod universal_regions;
86 /// A public API provided for the Rust compiler consumers.
89 use borrow_set::{BorrowData, BorrowSet};
90 use dataflow::{BorrowIndex, BorrowckFlowState as Flows, BorrowckResults, Borrows};
91 use nll::{PoloniusOutput, ToRegionVid};
92 use place_ext::PlaceExt;
93 use places_conflict::{places_conflict, PlaceConflictBias};
94 use region_infer::RegionInferenceContext;
96 // FIXME(eddyb) perhaps move this somewhere more centrally.
99 place: CapturedPlace<'tcx>,
101 /// If true, the capture is behind a reference.
105 /// Associate some local constants with the `'tcx` lifetime
106 struct TyCtxtConsts<'tcx>(TyCtxt<'tcx>);
107 impl<'tcx> TyCtxtConsts<'tcx> {
108 const DEREF_PROJECTION: &'tcx [PlaceElem<'tcx>; 1] = &[ProjectionElem::Deref];
111 pub fn provide(providers: &mut Providers) {
112 *providers = Providers {
113 mir_borrowck: |tcx, did| {
114 if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
115 tcx.mir_borrowck_const_arg(def)
117 mir_borrowck(tcx, ty::WithOptConstParam::unknown(did))
120 mir_borrowck_const_arg: |tcx, (did, param_did)| {
121 mir_borrowck(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
127 fn mir_borrowck(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> &BorrowCheckResult<'_> {
128 let (input_body, promoted) = tcx.mir_promoted(def);
129 debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
131 if input_body.borrow().should_skip() {
132 debug!("Skipping borrowck because of injected body");
133 // Let's make up a borrowck result! Fun times!
134 let result = BorrowCheckResult {
135 concrete_opaque_types: VecMap::new(),
136 closure_requirements: None,
137 used_mut_upvars: SmallVec::new(),
138 tainted_by_errors: None,
140 return tcx.arena.alloc(result);
143 let hir_owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;
146 tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(hir_owner.def_id)).build();
147 let input_body: &Body<'_> = &input_body.borrow();
148 let promoted: &IndexVec<_, _> = &promoted.borrow();
149 let opt_closure_req = do_mir_borrowck(&infcx, input_body, promoted, false).0;
150 debug!("mir_borrowck done");
152 tcx.arena.alloc(opt_closure_req)
155 /// Perform the actual borrow checking.
157 /// If `return_body_with_facts` is true, then return the body with non-erased
158 /// region ids on which the borrow checking was performed together with Polonius
160 #[instrument(skip(infcx, input_body, input_promoted), fields(id=?input_body.source.with_opt_param().as_local().unwrap()), level = "debug")]
161 fn do_mir_borrowck<'tcx>(
162 infcx: &InferCtxt<'tcx>,
163 input_body: &Body<'tcx>,
164 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
165 return_body_with_facts: bool,
166 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
167 let def = input_body.source.with_opt_param().as_local().unwrap();
172 let param_env = tcx.param_env(def.did);
174 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
175 for var_debug_info in &input_body.var_debug_info {
176 if let VarDebugInfoContents::Place(place) = var_debug_info.value {
177 if let Some(local) = place.as_local() {
178 if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name {
180 var_debug_info.source_info.span,
181 "local {:?} has many names (`{}` vs `{}`)",
187 local_names[local] = Some(var_debug_info.name);
192 let mut errors = error::BorrowckErrors::new(infcx.tcx);
194 // Gather the upvars of a closure, if any.
195 let tables = tcx.typeck_opt_const_arg(def);
196 if let Some(e) = tables.tainted_by_errors {
197 infcx.set_tainted_by_errors(e);
198 errors.set_tainted_by_errors(e);
200 let upvars: Vec<_> = tables
201 .closure_min_captures_flattened(def.did)
202 .map(|captured_place| {
203 let capture = captured_place.info.capture_kind;
204 let by_ref = match capture {
205 ty::UpvarCapture::ByValue => false,
206 ty::UpvarCapture::ByRef(..) => true,
208 Upvar { place: captured_place.clone(), by_ref }
212 // Replace all regions with fresh inference variables. This
213 // requires first making our own copy of the MIR. This copy will
214 // be modified (in place) to contain non-lexical lifetimes. It
215 // will have a lifetime tied to the inference context.
216 let mut body_owned = input_body.clone();
217 let mut promoted = input_promoted.clone();
219 nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
220 let body = &body_owned; // no further changes
222 let location_table_owned = LocationTable::new(body);
223 let location_table = &location_table_owned;
225 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
226 match MoveData::gather_moves(&body, tcx, param_env) {
227 Ok((_, move_data)) => (move_data, Vec::new()),
228 Err((move_data, move_errors)) => (move_data, move_errors),
230 let promoted_errors = promoted
232 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
234 let mdpe = MoveDataParamEnv { move_data, param_env };
236 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
237 .into_engine(tcx, &body)
238 .pass_name("borrowck")
239 .iterate_to_fixpoint()
240 .into_results_cursor(&body);
242 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def.did).is_fn_or_closure();
244 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
246 let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.unstable_opts.polonius;
248 // Compute non-lexical lifetimes.
256 } = nll::compute_regions(
270 // Dump MIR results into a file, if that is enabled. This let us
271 // write unit-tests, as well as helping with debugging.
272 nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
274 // We also have a `#[rustc_regions]` annotation that causes us to dump
276 nll::dump_annotation(
285 // The various `flow_*` structures can be large. We drop `flow_inits` here
286 // so it doesn't overlap with the others below. This reduces peak memory
287 // usage significantly on some benchmarks.
290 let regioncx = Rc::new(regioncx);
292 let flow_borrows = Borrows::new(tcx, body, ®ioncx, &borrow_set)
293 .into_engine(tcx, body)
294 .pass_name("borrowck")
295 .iterate_to_fixpoint();
296 let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &mdpe)
297 .into_engine(tcx, body)
298 .pass_name("borrowck")
299 .iterate_to_fixpoint();
300 let flow_ever_inits = EverInitializedPlaces::new(tcx, body, &mdpe)
301 .into_engine(tcx, body)
302 .pass_name("borrowck")
303 .iterate_to_fixpoint();
305 let movable_generator =
306 // The first argument is the generator type passed by value
307 if let Some(local) = body.local_decls.raw.get(1)
308 // Get the interior types and substs which typeck computed
309 && let ty::Generator(_, _, hir::Movability::Static) = local.ty.kind()
316 for (idx, move_data_results) in promoted_errors {
317 let promoted_body = &promoted[idx];
319 if let Err((move_data, move_errors)) = move_data_results {
320 let mut promoted_mbcx = MirBorrowckCtxt {
324 move_data: &move_data,
325 location_table, // no need to create a real one for the promoted, it is not used
327 fn_self_span_reported: Default::default(),
328 locals_are_invalidated_at_exit,
329 access_place_error_reported: Default::default(),
330 reservation_error_reported: Default::default(),
331 uninitialized_error_reported: Default::default(),
332 regioncx: regioncx.clone(),
333 used_mut: Default::default(),
334 used_mut_upvars: SmallVec::new(),
335 borrow_set: Rc::clone(&borrow_set),
336 dominators: Dominators::dummy(), // not used
338 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
339 region_names: RefCell::default(),
340 next_region_name: RefCell::new(1),
341 polonius_output: None,
344 promoted_mbcx.report_move_errors(move_errors);
345 errors = promoted_mbcx.errors;
349 let dominators = body.basic_blocks.dominators();
351 let mut mbcx = MirBorrowckCtxt {
355 move_data: &mdpe.move_data,
358 locals_are_invalidated_at_exit,
359 fn_self_span_reported: Default::default(),
360 access_place_error_reported: Default::default(),
361 reservation_error_reported: Default::default(),
362 uninitialized_error_reported: Default::default(),
363 regioncx: Rc::clone(®ioncx),
364 used_mut: Default::default(),
365 used_mut_upvars: SmallVec::new(),
366 borrow_set: Rc::clone(&borrow_set),
370 region_names: RefCell::default(),
371 next_region_name: RefCell::new(1),
376 // Compute and report region errors, if any.
377 mbcx.report_region_errors(nll_errors);
379 let results = BorrowckResults {
380 ever_inits: flow_ever_inits,
381 uninits: flow_uninits,
382 borrows: flow_borrows,
385 mbcx.report_move_errors(move_errors);
387 rustc_mir_dataflow::visit_results(
389 traversal::reverse_postorder(body).map(|(bb, _)| bb),
394 // For each non-user used mutable variable, check if it's been assigned from
395 // a user-declared local. If so, then put that local into the used_mut set.
396 // Note that this set is expected to be small - only upvars from closures
397 // would have a chance of erroneously adding non-user-defined mutable vars
399 let temporary_used_locals: FxHashSet<Local> = mbcx
402 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
405 // For the remaining unused locals that are marked as mutable, we avoid linting any that
406 // were never initialized. These locals may have been removed as unreachable code; or will be
407 // linted as unused variables.
408 let unused_mut_locals =
409 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
410 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
412 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
413 let used_mut = std::mem::take(&mut mbcx.used_mut);
414 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
415 let local_decl = &mbcx.body.local_decls[local];
416 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
417 ClearCrossCrate::Set(data) => data.lint_root,
421 // Skip over locals that begin with an underscore or have no name
422 match mbcx.local_names[local] {
424 if name.as_str().starts_with('_') {
431 let span = local_decl.source_info.span;
432 if span.desugaring_kind().is_some() {
433 // If the `mut` arises as part of a desugaring, we should ignore it.
437 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
439 tcx.emit_spanned_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
442 let tainted_by_errors = mbcx.emit_errors();
444 let result = BorrowCheckResult {
445 concrete_opaque_types: opaque_type_values,
446 closure_requirements: opt_closure_req,
447 used_mut_upvars: mbcx.used_mut_upvars,
451 let body_with_facts = if return_body_with_facts {
452 let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
453 Some(Box::new(BodyWithBorrowckFacts {
455 input_facts: *polonius_input.expect("Polonius input facts were not generated"),
457 location_table: location_table_owned,
463 debug!("do_mir_borrowck: result = {:#?}", result);
465 (result, body_with_facts)
468 /// A `Body` with information computed by the borrow checker. This struct is
469 /// intended to be consumed by compiler consumers.
471 /// We need to include the MIR body here because the region identifiers must
472 /// match the ones in the Polonius facts.
473 pub struct BodyWithBorrowckFacts<'tcx> {
474 /// A mir body that contains region identifiers.
475 pub body: Body<'tcx>,
476 /// Polonius input facts.
477 pub input_facts: AllFacts,
478 /// Polonius output facts.
479 pub output_facts: Rc<self::nll::PoloniusOutput>,
480 /// The table that maps Polonius points to locations in the table.
481 pub location_table: LocationTable,
484 struct MirBorrowckCtxt<'cx, 'tcx> {
485 infcx: &'cx InferCtxt<'tcx>,
486 param_env: ParamEnv<'tcx>,
487 body: &'cx Body<'tcx>,
488 move_data: &'cx MoveData<'tcx>,
490 /// Map from MIR `Location` to `LocationIndex`; created
491 /// when MIR borrowck begins.
492 location_table: &'cx LocationTable,
494 movable_generator: bool,
495 /// This keeps track of whether local variables are free-ed when the function
496 /// exits even without a `StorageDead`, which appears to be the case for
499 /// I'm not sure this is the right approach - @eddyb could you try and
501 locals_are_invalidated_at_exit: bool,
502 /// This field keeps track of when borrow errors are reported in the access_place function
503 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
504 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
505 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
507 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
508 /// This field keeps track of when borrow conflict errors are reported
509 /// for reservations, so that we don't report seemingly duplicate
510 /// errors for corresponding activations.
512 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
513 // but it is currently inconvenient to track down the `BorrowIndex`
514 // at the time we detect and report a reservation error.
515 reservation_error_reported: FxHashSet<Place<'tcx>>,
516 /// This fields keeps track of the `Span`s that we have
517 /// used to report extra information for `FnSelfUse`, to avoid
518 /// unnecessarily verbose errors.
519 fn_self_span_reported: FxHashSet<Span>,
520 /// This field keeps track of errors reported in the checking of uninitialized variables,
521 /// so that we don't report seemingly duplicate errors.
522 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
523 /// This field keeps track of all the local variables that are declared mut and are mutated.
524 /// Used for the warning issued by an unused mutable local variable.
525 used_mut: FxHashSet<Local>,
526 /// If the function we're checking is a closure, then we'll need to report back the list of
527 /// mutable upvars that have been used. This field keeps track of them.
528 used_mut_upvars: SmallVec<[Field; 8]>,
529 /// Region inference context. This contains the results from region inference and lets us e.g.
530 /// find out which CFG points are contained in each borrow region.
531 regioncx: Rc<RegionInferenceContext<'tcx>>,
533 /// The set of borrows extracted from the MIR
534 borrow_set: Rc<BorrowSet<'tcx>>,
536 /// Dominators for MIR
537 dominators: Dominators<BasicBlock>,
539 /// Information about upvars not necessarily preserved in types or MIR
540 upvars: Vec<Upvar<'tcx>>,
542 /// Names of local (user) variables (extracted from `var_debug_info`).
543 local_names: IndexVec<Local, Option<Symbol>>,
545 /// Record the region names generated for each region in the given
546 /// MIR def so that we can reuse them later in help/error messages.
547 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
549 /// The counter for generating new region names.
550 next_region_name: RefCell<usize>,
552 /// Results of Polonius analysis.
553 polonius_output: Option<Rc<PoloniusOutput>>,
555 errors: error::BorrowckErrors<'tcx>,
559 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
560 // 2. loans made in overlapping scopes do not conflict
561 // 3. assignments do not affect things loaned out as immutable
562 // 4. moves do not affect things loaned out in any way
563 impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
564 type FlowState = Flows<'cx, 'tcx>;
566 fn visit_statement_before_primary_effect(
568 flow_state: &Flows<'cx, 'tcx>,
569 stmt: &'cx Statement<'tcx>,
572 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
573 let span = stmt.source_info.span;
575 self.check_activations(location, span, flow_state);
578 StatementKind::Assign(box (lhs, rhs)) => {
579 self.consume_rvalue(location, (rhs, span), flow_state);
581 self.mutate_place(location, (*lhs, span), Shallow(None), flow_state);
583 StatementKind::FakeRead(box (_, place)) => {
584 // Read for match doesn't access any memory and is used to
585 // assert that a place is safe and live. So we don't have to
586 // do any checks here.
588 // FIXME: Remove check that the place is initialized. This is
589 // needed for now because matches don't have never patterns yet.
590 // So this is the only place we prevent
594 self.check_if_path_or_subpath_is_moved(
596 InitializationRequiringAction::Use,
597 (place.as_ref(), span),
601 StatementKind::Intrinsic(box kind) => match kind {
602 NonDivergingIntrinsic::Assume(op) => self.consume_operand(location, (op, span), flow_state),
603 NonDivergingIntrinsic::CopyNonOverlapping(..) => span_bug!(
605 "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
608 // Only relevant for mir typeck
609 StatementKind::AscribeUserType(..)
610 // Doesn't have any language semantics
611 | StatementKind::Coverage(..)
612 // Does not actually affect borrowck
613 | StatementKind::StorageLive(..) => {}
614 StatementKind::StorageDead(local) => {
617 (Place::from(*local), span),
618 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
619 LocalMutationIsAllowed::Yes,
624 | StatementKind::Retag { .. }
625 | StatementKind::Deinit(..)
626 | StatementKind::SetDiscriminant { .. } => {
627 bug!("Statement not allowed in this MIR phase")
632 fn visit_terminator_before_primary_effect(
634 flow_state: &Flows<'cx, 'tcx>,
635 term: &'cx Terminator<'tcx>,
638 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
639 let span = term.source_info.span;
641 self.check_activations(loc, span, flow_state);
644 TerminatorKind::SwitchInt { discr, targets: _ } => {
645 self.consume_operand(loc, (discr, span), flow_state);
647 TerminatorKind::Drop { place, target: _, unwind: _ } => {
649 "visit_terminator_drop \
650 loc: {:?} term: {:?} place: {:?} span: {:?}",
651 loc, term, place, span
657 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
658 LocalMutationIsAllowed::Yes,
662 TerminatorKind::DropAndReplace {
668 self.mutate_place(loc, (*drop_place, span), Deep, flow_state);
669 self.consume_operand(loc, (new_value, span), flow_state);
671 TerminatorKind::Call {
680 self.consume_operand(loc, (func, span), flow_state);
682 self.consume_operand(loc, (arg, span), flow_state);
684 self.mutate_place(loc, (*destination, span), Deep, flow_state);
686 TerminatorKind::Assert { cond, expected: _, msg, target: _, cleanup: _ } => {
687 self.consume_operand(loc, (cond, span), flow_state);
688 use rustc_middle::mir::AssertKind;
689 if let AssertKind::BoundsCheck { len, index } = msg {
690 self.consume_operand(loc, (len, span), flow_state);
691 self.consume_operand(loc, (index, span), flow_state);
695 TerminatorKind::Yield { value, resume: _, resume_arg, drop: _ } => {
696 self.consume_operand(loc, (value, span), flow_state);
697 self.mutate_place(loc, (*resume_arg, span), Deep, flow_state);
700 TerminatorKind::InlineAsm {
710 InlineAsmOperand::In { reg: _, value } => {
711 self.consume_operand(loc, (value, span), flow_state);
713 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
714 if let Some(place) = place {
715 self.mutate_place(loc, (*place, span), Shallow(None), flow_state);
718 InlineAsmOperand::InOut { reg: _, late: _, in_value, out_place } => {
719 self.consume_operand(loc, (in_value, span), flow_state);
720 if let &Some(out_place) = out_place {
729 InlineAsmOperand::Const { value: _ }
730 | InlineAsmOperand::SymFn { value: _ }
731 | InlineAsmOperand::SymStatic { def_id: _ } => {}
736 TerminatorKind::Goto { target: _ }
737 | TerminatorKind::Abort
738 | TerminatorKind::Unreachable
739 | TerminatorKind::Resume
740 | TerminatorKind::Return
741 | TerminatorKind::GeneratorDrop
742 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
743 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
744 // no data used, thus irrelevant to borrowck
749 fn visit_terminator_after_primary_effect(
751 flow_state: &Flows<'cx, 'tcx>,
752 term: &'cx Terminator<'tcx>,
755 let span = term.source_info.span;
758 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
759 if self.movable_generator {
760 // Look for any active borrows to locals
761 let borrow_set = self.borrow_set.clone();
762 for i in flow_state.borrows.iter() {
763 let borrow = &borrow_set[i];
764 self.check_for_local_borrow(borrow, span);
769 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
770 // Returning from the function implicitly kills storage for all locals and statics.
771 // Often, the storage will already have been killed by an explicit
772 // StorageDead, but we don't always emit those (notably on unwind paths),
773 // so this "extra check" serves as a kind of backup.
774 let borrow_set = self.borrow_set.clone();
775 for i in flow_state.borrows.iter() {
776 let borrow = &borrow_set[i];
777 self.check_for_invalidation_at_exit(loc, borrow, span);
781 TerminatorKind::Abort
782 | TerminatorKind::Assert { .. }
783 | TerminatorKind::Call { .. }
784 | TerminatorKind::Drop { .. }
785 | TerminatorKind::DropAndReplace { .. }
786 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
787 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
788 | TerminatorKind::Goto { .. }
789 | TerminatorKind::SwitchInt { .. }
790 | TerminatorKind::Unreachable
791 | TerminatorKind::InlineAsm { .. } => {}
796 use self::AccessDepth::{Deep, Shallow};
797 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
799 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
800 enum ArtificialField {
805 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
807 /// From the RFC: "A *shallow* access means that the immediate
808 /// fields reached at P are accessed, but references or pointers
809 /// found within are not dereferenced. Right now, the only access
810 /// that is shallow is an assignment like `x = ...;`, which would
811 /// be a *shallow write* of `x`."
812 Shallow(Option<ArtificialField>),
814 /// From the RFC: "A *deep* access means that all data reachable
815 /// through the given place may be invalidated or accesses by
819 /// Access is Deep only when there is a Drop implementation that
820 /// can reach the data behind the reference.
824 /// Kind of access to a value: read or write
825 /// (For informational purposes only)
826 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
828 /// From the RFC: "A *read* means that the existing data may be
829 /// read, but will not be changed."
832 /// From the RFC: "A *write* means that the data may be mutated to
833 /// new values or otherwise invalidated (for example, it could be
834 /// de-initialized, as in a move operation).
837 /// For two-phase borrows, we distinguish a reservation (which is treated
838 /// like a Read) from an activation (which is treated like a write), and
839 /// each of those is furthermore distinguished from Reads/Writes above.
840 Reservation(WriteKind),
841 Activation(WriteKind, BorrowIndex),
844 /// Kind of read access to a value
845 /// (For informational purposes only)
846 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
852 /// Kind of write access to a value
853 /// (For informational purposes only)
854 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
857 MutableBorrow(BorrowKind),
862 /// When checking permissions for a place access, this flag is used to indicate that an immutable
863 /// local place can be mutated.
865 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
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 #[instrument(level = "debug", skip(self, flow_state))]
986 fn check_access_for_conflict(
989 place_span: (Place<'tcx>, Span),
992 flow_state: &Flows<'cx, 'tcx>,
994 let mut error_reported = false;
995 let tcx = self.infcx.tcx;
996 let body = self.body;
997 let borrow_set = self.borrow_set.clone();
999 // Use polonius output if it has been enabled.
1000 let polonius_output = self.polonius_output.clone();
1001 let borrows_in_scope = if let Some(polonius) = &polonius_output {
1002 let location = self.location_table.start_index(location);
1003 Either::Left(polonius.errors_at(location).iter().copied())
1005 Either::Right(flow_state.borrows.iter())
1008 each_borrow_involving_path(
1016 |this, borrow_index, borrow| match (rw, borrow.kind) {
1017 // Obviously an activation is compatible with its own
1018 // reservation (or even prior activating uses of same
1019 // borrow); so don't check if they interfere.
1021 // NOTE: *reservations* do conflict with themselves;
1022 // thus aren't injecting unsoundness w/ this check.)
1023 (Activation(_, activating), _) if activating == borrow_index => {
1025 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1026 skipping {:?} b/c activation of same borrow_index",
1030 (borrow_index, borrow),
1035 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1037 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1038 BorrowKind::Unique | BorrowKind::Mut { .. },
1039 ) => Control::Continue,
1041 (Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
1042 // This used to be a future compatibility warning (to be
1043 // disallowed on NLL). See rust-lang/rust#56254
1047 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1048 // Handled by initialization checks.
1052 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1053 // Reading from mere reservations of mutable-borrows is OK.
1054 if !is_active(&this.dominators, borrow, location) {
1055 assert!(allow_two_phase_borrow(borrow.kind));
1056 return Control::Continue;
1059 error_reported = true;
1063 .report_use_while_mutably_borrowed(location, place_span, borrow);
1064 this.buffer_error(err);
1066 ReadKind::Borrow(bk) => {
1068 this.report_conflicting_borrow(location, place_span, bk, borrow);
1069 this.buffer_error(err);
1075 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1077 Reservation(..) => {
1079 "recording invalid reservation of \
1083 this.reservation_error_reported.insert(place_span.0);
1085 Activation(_, activating) => {
1087 "observing check_place for activation of \
1088 borrow_index: {:?}",
1092 Read(..) | Write(..) => {}
1095 error_reported = true;
1097 WriteKind::MutableBorrow(bk) => {
1099 this.report_conflicting_borrow(location, place_span, bk, borrow);
1100 this.buffer_error(err);
1102 WriteKind::StorageDeadOrDrop => this
1103 .report_borrowed_value_does_not_live_long_enough(
1109 WriteKind::Mutate => {
1110 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1112 WriteKind::Move => {
1113 this.report_move_out_while_borrowed(location, place_span, borrow)
1127 place_span: (Place<'tcx>, Span),
1129 flow_state: &Flows<'cx, 'tcx>,
1131 // Write of P[i] or *P requires P init'd.
1132 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1137 (kind, Write(WriteKind::Mutate)),
1138 LocalMutationIsAllowed::No,
1146 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1147 flow_state: &Flows<'cx, 'tcx>,
1150 &Rvalue::Ref(_ /*rgn*/, bk, place) => {
1151 let access_kind = match bk {
1152 BorrowKind::Shallow => {
1153 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1155 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1156 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1157 let wk = WriteKind::MutableBorrow(bk);
1158 if allow_two_phase_borrow(bk) {
1159 (Deep, Reservation(wk))
1170 LocalMutationIsAllowed::No,
1174 let action = if bk == BorrowKind::Shallow {
1175 InitializationRequiringAction::MatchOn
1177 InitializationRequiringAction::Borrow
1180 self.check_if_path_or_subpath_is_moved(
1183 (place.as_ref(), span),
1188 &Rvalue::AddressOf(mutability, place) => {
1189 let access_kind = match mutability {
1190 Mutability::Mut => (
1192 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1193 allow_two_phase_borrow: false,
1196 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1203 LocalMutationIsAllowed::No,
1207 self.check_if_path_or_subpath_is_moved(
1209 InitializationRequiringAction::Borrow,
1210 (place.as_ref(), span),
1215 Rvalue::ThreadLocalRef(_) => {}
1217 Rvalue::Use(operand)
1218 | Rvalue::Repeat(operand, _)
1219 | Rvalue::UnaryOp(_ /*un_op*/, operand)
1220 | Rvalue::Cast(_ /*cast_kind*/, operand, _ /*ty*/)
1221 | Rvalue::ShallowInitBox(operand, _ /*ty*/) => {
1222 self.consume_operand(location, (operand, span), flow_state)
1225 &Rvalue::CopyForDeref(place) => {
1229 (Deep, Read(ReadKind::Copy)),
1230 LocalMutationIsAllowed::No,
1234 // Finally, check if path was already moved.
1235 self.check_if_path_or_subpath_is_moved(
1237 InitializationRequiringAction::Use,
1238 (place.as_ref(), span),
1243 &(Rvalue::Len(place) | Rvalue::Discriminant(place)) => {
1244 let af = match *rvalue {
1245 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1246 Rvalue::Discriminant(..) => None,
1247 _ => unreachable!(),
1252 (Shallow(af), Read(ReadKind::Copy)),
1253 LocalMutationIsAllowed::No,
1256 self.check_if_path_or_subpath_is_moved(
1258 InitializationRequiringAction::Use,
1259 (place.as_ref(), span),
1264 Rvalue::BinaryOp(_bin_op, box (operand1, operand2))
1265 | Rvalue::CheckedBinaryOp(_bin_op, box (operand1, operand2)) => {
1266 self.consume_operand(location, (operand1, span), flow_state);
1267 self.consume_operand(location, (operand2, span), flow_state);
1270 Rvalue::NullaryOp(_op, _ty) => {
1271 // nullary ops take no dynamic input; no borrowck effect.
1274 Rvalue::Aggregate(aggregate_kind, operands) => {
1275 // We need to report back the list of mutable upvars that were
1276 // moved into the closure and subsequently used by the closure,
1277 // in order to populate our used_mut set.
1278 match **aggregate_kind {
1279 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1280 let BorrowCheckResult { used_mut_upvars, .. } =
1281 self.infcx.tcx.mir_borrowck(def_id);
1282 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1283 for field in used_mut_upvars {
1284 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1287 AggregateKind::Adt(..)
1288 | AggregateKind::Array(..)
1289 | AggregateKind::Tuple { .. } => (),
1292 for operand in operands {
1293 self.consume_operand(location, (operand, span), flow_state);
1299 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1300 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1301 // We have three possibilities here:
1302 // a. We are modifying something through a mut-ref
1303 // b. We are modifying something that is local to our parent
1304 // c. Current body is a nested closure, and we are modifying path starting from
1305 // a Place captured by our parent closure.
1307 // Handle (c), the path being modified is exactly the path captured by our parent
1308 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1309 this.used_mut_upvars.push(field);
1313 for (place_ref, proj) in place.iter_projections().rev() {
1315 if proj == ProjectionElem::Deref {
1316 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1317 // We aren't modifying a variable directly
1318 ty::Ref(_, _, hir::Mutability::Mut) => return,
1325 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1326 this.used_mut_upvars.push(field);
1332 this.used_mut.insert(place.local);
1335 // This relies on the current way that by-value
1336 // captures of a closure are copied/moved directly
1337 // when generating MIR.
1339 Operand::Move(place) | Operand::Copy(place) => {
1340 match place.as_local() {
1341 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1342 if self.body.local_decls[local].ty.is_mutable_ptr() {
1343 // The variable will be marked as mutable by the borrow.
1346 // This is an edge case where we have a `move` closure
1347 // inside a non-move closure, and the inner closure
1348 // contains a mutation:
1351 // || { move || { i += 1; }; };
1353 // In this case our usual strategy of assuming that the
1354 // variable will be captured by mutable reference is
1355 // wrong, since `i` can be copied into the inner
1356 // closure from a shared reference.
1358 // As such we have to search for the local that this
1359 // capture comes from and mark it as being used as mut.
1361 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1362 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1363 &self.move_data.inits[init_index]
1365 bug!("temporary should be initialized exactly once")
1368 let InitLocation::Statement(loc) = init.location else {
1369 bug!("temporary initialized in arguments")
1372 let body = self.body;
1373 let bbd = &body[loc.block];
1374 let stmt = &bbd.statements[loc.statement_index];
1375 debug!("temporary assigned in: stmt={:?}", stmt);
1377 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1379 propagate_closure_used_mut_place(self, source);
1382 "closures should only capture user variables \
1383 or references to user variables"
1387 _ => propagate_closure_used_mut_place(self, place),
1390 Operand::Constant(..) => {}
1397 (operand, span): (&'cx Operand<'tcx>, Span),
1398 flow_state: &Flows<'cx, 'tcx>,
1401 Operand::Copy(place) => {
1402 // copy of place: check if this is "copy of frozen path"
1403 // (FIXME: see check_loans.rs)
1407 (Deep, Read(ReadKind::Copy)),
1408 LocalMutationIsAllowed::No,
1412 // Finally, check if path was already moved.
1413 self.check_if_path_or_subpath_is_moved(
1415 InitializationRequiringAction::Use,
1416 (place.as_ref(), span),
1420 Operand::Move(place) => {
1421 // move of place: check if this is move of already borrowed path
1425 (Deep, Write(WriteKind::Move)),
1426 LocalMutationIsAllowed::Yes,
1430 // Finally, check if path was already moved.
1431 self.check_if_path_or_subpath_is_moved(
1433 InitializationRequiringAction::Use,
1434 (place.as_ref(), span),
1438 Operand::Constant(_) => {}
1442 /// Checks whether a borrow of this place is invalidated when the function
1444 #[instrument(level = "debug", skip(self))]
1445 fn check_for_invalidation_at_exit(
1448 borrow: &BorrowData<'tcx>,
1451 let place = borrow.borrowed_place;
1452 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1454 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1455 // we just know that all locals are dropped at function exit (otherwise
1456 // we'll have a memory leak) and assume that all statics have a destructor.
1458 // FIXME: allow thread-locals to borrow other thread locals?
1460 let (might_be_alive, will_be_dropped) =
1461 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1462 // Thread-locals might be dropped after the function exits
1463 // We have to dereference the outer reference because
1464 // borrows don't conflict behind shared references.
1465 root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
1468 (false, self.locals_are_invalidated_at_exit)
1471 if !will_be_dropped {
1472 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1476 let sd = if might_be_alive { Deep } else { Shallow(None) };
1478 if places_conflict::borrow_conflicts_with_place(
1485 places_conflict::PlaceConflictBias::Overlap,
1487 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1488 // FIXME: should be talking about the region lifetime instead
1489 // of just a span here.
1490 let span = self.infcx.tcx.sess.source_map().end_point(span);
1491 self.report_borrowed_value_does_not_live_long_enough(
1500 /// Reports an error if this is a borrow of local data.
1501 /// This is called for all Yield expressions on movable generators
1502 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1503 debug!("check_for_local_borrow({:?})", borrow);
1505 if borrow_of_local_data(borrow.borrowed_place) {
1506 let err = self.cannot_borrow_across_generator_yield(
1507 self.retrieve_borrow_spans(borrow).var_or_use(),
1511 self.buffer_error(err);
1515 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1516 // Two-phase borrow support: For each activation that is newly
1517 // generated at this statement, check if it interferes with
1519 let borrow_set = self.borrow_set.clone();
1520 for &borrow_index in borrow_set.activations_at_location(location) {
1521 let borrow = &borrow_set[borrow_index];
1523 // only mutable borrows should be 2-phase
1524 assert!(match borrow.kind {
1525 BorrowKind::Shared | BorrowKind::Shallow => false,
1526 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1531 (borrow.borrowed_place, span),
1532 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1533 LocalMutationIsAllowed::No,
1536 // We do not need to call `check_if_path_or_subpath_is_moved`
1537 // again, as we already called it when we made the
1538 // initial reservation.
1542 fn check_if_full_path_is_moved(
1545 desired_action: InitializationRequiringAction,
1546 place_span: (PlaceRef<'tcx>, Span),
1547 flow_state: &Flows<'cx, 'tcx>,
1549 let maybe_uninits = &flow_state.uninits;
1553 // 1. Move of `a.b.c`, use of `a.b.c`
1554 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1555 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1556 // partial initialization support, one might have `a.x`
1557 // initialized but not `a.b`.
1561 // 4. Move of `a.b.c`, use of `a.b.d`
1562 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1563 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1564 // must have been initialized for the use to be sound.
1565 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1567 // The dataflow tracks shallow prefixes distinctly (that is,
1568 // field-accesses on P distinctly from P itself), in order to
1569 // track substructure initialization separately from the whole
1572 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1573 // which we have a MovePath is `a.b`, then that means that the
1574 // initialization state of `a.b` is all we need to inspect to
1575 // know if `a.b.c` is valid (and from that we infer that the
1576 // dereference and `.d` access is also valid, since we assume
1577 // `a.b.c` is assigned a reference to an initialized and
1578 // well-formed record structure.)
1580 // Therefore, if we seek out the *closest* prefix for which we
1581 // have a MovePath, that should capture the initialization
1582 // state for the place scenario.
1584 // This code covers scenarios 1, 2, and 3.
1586 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1587 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1588 if maybe_uninits.contains(mpi) {
1589 self.report_use_of_moved_or_uninitialized(
1592 (prefix, place_span.0, place_span.1),
1595 } // Only query longest prefix with a MovePath, not further
1596 // ancestors; dataflow recurs on children when parents
1597 // move (to support partial (re)inits).
1599 // (I.e., querying parents breaks scenario 7; but may want
1600 // to do such a query based on partial-init feature-gate.)
1603 /// Subslices correspond to multiple move paths, so we iterate through the
1604 /// elements of the base array. For each element we check
1606 /// * Does this element overlap with our slice.
1607 /// * Is any part of it uninitialized.
1608 fn check_if_subslice_element_is_moved(
1611 desired_action: InitializationRequiringAction,
1612 place_span: (PlaceRef<'tcx>, Span),
1613 maybe_uninits: &ChunkedBitSet<MovePathIndex>,
1617 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1618 let move_paths = &self.move_data.move_paths;
1620 let root_path = &move_paths[mpi];
1621 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1622 let last_proj = child_move_path.place.projection.last().unwrap();
1623 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1624 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1626 if (from..to).contains(offset) {
1628 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1629 maybe_uninits.contains(mpi)
1632 if let Some(uninit_child) = uninit_child {
1633 self.report_use_of_moved_or_uninitialized(
1636 (place_span.0, place_span.0, place_span.1),
1639 return; // don't bother finding other problems.
1647 fn check_if_path_or_subpath_is_moved(
1650 desired_action: InitializationRequiringAction,
1651 place_span: (PlaceRef<'tcx>, Span),
1652 flow_state: &Flows<'cx, 'tcx>,
1654 let maybe_uninits = &flow_state.uninits;
1658 // 1. Move of `a.b.c`, use of `a` or `a.b`
1659 // partial initialization support, one might have `a.x`
1660 // initialized but not `a.b`.
1661 // 2. All bad scenarios from `check_if_full_path_is_moved`
1665 // 3. Move of `a.b.c`, use of `a.b.d`
1666 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1667 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1668 // must have been initialized for the use to be sound.
1669 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1671 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1673 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1674 place_span.0.last_projection()
1676 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1677 if let ty::Array(..) = place_ty.ty.kind() {
1678 self.check_if_subslice_element_is_moved(
1681 (place_base, place_span.1),
1690 // A move of any shallow suffix of `place` also interferes
1691 // with an attempt to use `place`. This is scenario 3 above.
1693 // (Distinct from handling of scenarios 1+2+4 above because
1694 // `place` does not interfere with suffixes of its prefixes,
1695 // e.g., `a.b.c` does not interfere with `a.b.d`)
1697 // This code covers scenario 1.
1699 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1700 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1701 let uninit_mpi = self
1703 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1705 if let Some(uninit_mpi) = uninit_mpi {
1706 self.report_use_of_moved_or_uninitialized(
1709 (place_span.0, place_span.0, place_span.1),
1712 return; // don't bother finding other problems.
1717 /// Currently MoveData does not store entries for all places in
1718 /// the input MIR. For example it will currently filter out
1719 /// places that are Copy; thus we do not track places of shared
1720 /// reference type. This routine will walk up a place along its
1721 /// prefixes, searching for a foundational place that *is*
1722 /// tracked in the MoveData.
1724 /// An Err result includes a tag indicated why the search failed.
1725 /// Currently this can only occur if the place is built off of a
1726 /// static variable, as we do not track those in the MoveData.
1727 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1728 match self.move_data.rev_lookup.find(place) {
1729 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1730 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1732 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1736 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1737 // If returns None, then there is no move path corresponding
1738 // to a direct owner of `place` (which means there is nothing
1739 // that borrowck tracks for its analysis).
1741 match self.move_data.rev_lookup.find(place) {
1742 LookupResult::Parent(_) => None,
1743 LookupResult::Exact(mpi) => Some(mpi),
1747 fn check_if_assigned_path_is_moved(
1750 (place, span): (Place<'tcx>, Span),
1751 flow_state: &Flows<'cx, 'tcx>,
1753 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1755 // None case => assigning to `x` does not require `x` be initialized.
1756 for (place_base, elem) in place.iter_projections().rev() {
1758 ProjectionElem::Index(_/*operand*/) |
1759 ProjectionElem::OpaqueCast(_) |
1760 ProjectionElem::ConstantIndex { .. } |
1761 // assigning to P[i] requires P to be valid.
1762 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1763 // assigning to (P->variant) is okay if assigning to `P` is okay
1765 // FIXME: is this true even if P is an adt with a dtor?
1768 // assigning to (*P) requires P to be initialized
1769 ProjectionElem::Deref => {
1770 self.check_if_full_path_is_moved(
1771 location, InitializationRequiringAction::Use,
1772 (place_base, span), flow_state);
1773 // (base initialized; no need to
1778 ProjectionElem::Subslice { .. } => {
1779 panic!("we don't allow assignments to subslices, location: {:?}",
1783 ProjectionElem::Field(..) => {
1784 // if type of `P` has a dtor, then
1785 // assigning to `P.f` requires `P` itself
1786 // be already initialized
1787 let tcx = self.infcx.tcx;
1788 let base_ty = place_base.ty(self.body(), tcx).ty;
1789 match base_ty.kind() {
1790 ty::Adt(def, _) if def.has_dtor(tcx) => {
1791 self.check_if_path_or_subpath_is_moved(
1792 location, InitializationRequiringAction::Assignment,
1793 (place_base, span), flow_state);
1795 // (base initialized; no need to
1800 // Once `let s; s.x = V; read(s.x);`,
1801 // is allowed, remove this match arm.
1802 ty::Adt(..) | ty::Tuple(..) => {
1803 check_parent_of_field(self, location, place_base, span, flow_state);
1805 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1806 // partial initialization, do not complain about unnecessary `mut` on
1807 // an attempt to do a partial initialization.
1808 self.used_mut.insert(place.local);
1817 fn check_parent_of_field<'cx, 'tcx>(
1818 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1820 base: PlaceRef<'tcx>,
1822 flow_state: &Flows<'cx, 'tcx>,
1824 // rust-lang/rust#21232: Until Rust allows reads from the
1825 // initialized parts of partially initialized structs, we
1826 // will, starting with the 2018 edition, reject attempts
1827 // to write to structs that are not fully initialized.
1829 // In other words, *until* we allow this:
1831 // 1. `let mut s; s.x = Val; read(s.x);`
1833 // we will for now disallow this:
1835 // 2. `let mut s; s.x = Val;`
1839 // 3. `let mut s = ...; drop(s); s.x=Val;`
1841 // This does not use check_if_path_or_subpath_is_moved,
1842 // because we want to *allow* reinitializations of fields:
1843 // e.g., want to allow
1845 // `let mut s = ...; drop(s.x); s.x=Val;`
1847 // This does not use check_if_full_path_is_moved on
1848 // `base`, because that would report an error about the
1849 // `base` as a whole, but in this scenario we *really*
1850 // want to report an error about the actual thing that was
1851 // moved, which may be some prefix of `base`.
1853 // Shallow so that we'll stop at any dereference; we'll
1854 // report errors about issues with such bases elsewhere.
1855 let maybe_uninits = &flow_state.uninits;
1857 // Find the shortest uninitialized prefix you can reach
1858 // without going over a Deref.
1859 let mut shortest_uninit_seen = None;
1860 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1861 let Some(mpi) = this.move_path_for_place(prefix) else { continue };
1863 if maybe_uninits.contains(mpi) {
1865 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1866 shortest_uninit_seen,
1869 shortest_uninit_seen = Some((prefix, mpi));
1871 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1875 if let Some((prefix, mpi)) = shortest_uninit_seen {
1876 // Check for a reassignment into an uninitialized field of a union (for example,
1877 // after a move out). In this case, do not report an error here. There is an
1878 // exception, if this is the first assignment into the union (that is, there is
1879 // no move out from an earlier location) then this is an attempt at initialization
1880 // of the union - we should error in that case.
1881 let tcx = this.infcx.tcx;
1882 if base.ty(this.body(), tcx).ty.is_union() {
1883 if this.move_data.path_map[mpi].iter().any(|moi| {
1884 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1890 this.report_use_of_moved_or_uninitialized(
1892 InitializationRequiringAction::PartialAssignment,
1893 (prefix, base, span),
1900 /// Checks the permissions for the given place and read or write kind
1902 /// Returns `true` if an error is reported.
1903 fn check_access_permissions(
1905 (place, span): (Place<'tcx>, Span),
1907 is_local_mutation_allowed: LocalMutationIsAllowed,
1908 flow_state: &Flows<'cx, 'tcx>,
1912 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1913 place, kind, is_local_mutation_allowed
1920 Reservation(WriteKind::MutableBorrow(
1921 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1923 | Write(WriteKind::MutableBorrow(
1924 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1926 let is_local_mutation_allowed = match borrow_kind {
1927 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1928 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1929 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1931 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1933 self.add_used_mut(root_place, flow_state);
1937 error_access = AccessKind::MutableBorrow;
1938 the_place_err = place_err;
1942 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1943 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1945 self.add_used_mut(root_place, flow_state);
1949 error_access = AccessKind::Mutate;
1950 the_place_err = place_err;
1957 | WriteKind::StorageDeadOrDrop
1958 | WriteKind::MutableBorrow(BorrowKind::Shared)
1959 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1963 | WriteKind::StorageDeadOrDrop
1964 | WriteKind::MutableBorrow(BorrowKind::Shared)
1965 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1967 if self.is_mutable(place.as_ref(), is_local_mutation_allowed).is_err()
1968 && !self.has_buffered_errors()
1970 // rust-lang/rust#46908: In pure NLL mode this code path should be
1971 // unreachable, but we use `delay_span_bug` because we can hit this when
1972 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1973 // enabled. We don't want to ICE for that case, as other errors will have
1974 // been emitted (#52262).
1975 self.infcx.tcx.sess.delay_span_bug(
1978 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
1986 // permission checks are done at Reservation point.
1992 | BorrowKind::Mut { .. }
1993 | BorrowKind::Shared
1994 | BorrowKind::Shallow,
1998 // Access authorized
2003 // rust-lang/rust#21232, #54986: during period where we reject
2004 // partial initialization, do not complain about mutability
2005 // errors except for actual mutation (as opposed to an attempt
2006 // to do a partial initialization).
2007 let previously_initialized = self.is_local_ever_initialized(place.local, flow_state);
2009 // at this point, we have set up the error reporting state.
2010 if let Some(init_index) = previously_initialized {
2011 if let (AccessKind::Mutate, Some(_)) = (error_access, place.as_local()) {
2012 // If this is a mutate access to an immutable local variable with no projections
2013 // report the error as an illegal reassignment
2014 let init = &self.move_data.inits[init_index];
2015 let assigned_span = init.span(&self.body);
2016 self.report_illegal_reassignment(location, (place, span), assigned_span, place);
2018 self.report_mutability_error(place, span, the_place_err, error_access, location)
2026 fn is_local_ever_initialized(
2029 flow_state: &Flows<'cx, 'tcx>,
2030 ) -> Option<InitIndex> {
2031 let mpi = self.move_data.rev_lookup.find_local(local);
2032 let ii = &self.move_data.init_path_map[mpi];
2033 ii.into_iter().find(|&&index| flow_state.ever_inits.contains(index)).copied()
2036 /// Adds the place into the used mutable variables set
2037 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2039 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2040 // If the local may have been initialized, and it is now currently being
2041 // mutated, then it is justified to be annotated with the `mut`
2042 // keyword, since the mutation may be a possible reassignment.
2043 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2044 && self.is_local_ever_initialized(local, flow_state).is_some()
2046 self.used_mut.insert(local);
2051 place_projection: _,
2052 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2056 place_projection: place_projection @ [.., _],
2057 is_local_mutation_allowed: _,
2059 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2061 projection: place_projection,
2063 self.used_mut_upvars.push(field);
2069 /// Whether this value can be written or borrowed mutably.
2070 /// Returns the root place if the place passed in is a projection.
2073 place: PlaceRef<'tcx>,
2074 is_local_mutation_allowed: LocalMutationIsAllowed,
2075 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2076 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2077 match place.last_projection() {
2079 let local = &self.body.local_decls[place.local];
2080 match local.mutability {
2081 Mutability::Not => match is_local_mutation_allowed {
2082 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2083 place_local: place.local,
2084 place_projection: place.projection,
2085 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2087 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2088 place_local: place.local,
2089 place_projection: place.projection,
2090 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2092 LocalMutationIsAllowed::No => Err(place),
2094 Mutability::Mut => Ok(RootPlace {
2095 place_local: place.local,
2096 place_projection: place.projection,
2097 is_local_mutation_allowed,
2101 Some((place_base, elem)) => {
2103 ProjectionElem::Deref => {
2104 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2106 // Check the kind of deref to decide
2107 match base_ty.kind() {
2108 ty::Ref(_, _, mutbl) => {
2110 // Shared borrowed data is never mutable
2111 hir::Mutability::Not => Err(place),
2112 // Mutably borrowed data is mutable, but only if we have a
2113 // unique path to the `&mut`
2114 hir::Mutability::Mut => {
2115 let mode = match self.is_upvar_field_projection(place) {
2116 Some(field) if self.upvars[field.index()].by_ref => {
2117 is_local_mutation_allowed
2119 _ => LocalMutationIsAllowed::Yes,
2122 self.is_mutable(place_base, mode)
2126 ty::RawPtr(tnm) => {
2128 // `*const` raw pointers are not mutable
2129 hir::Mutability::Not => Err(place),
2130 // `*mut` raw pointers are always mutable, regardless of
2131 // context. The users have to check by themselves.
2132 hir::Mutability::Mut => Ok(RootPlace {
2133 place_local: place.local,
2134 place_projection: place.projection,
2135 is_local_mutation_allowed,
2139 // `Box<T>` owns its content, so mutable if its location is mutable
2140 _ if base_ty.is_box() => {
2141 self.is_mutable(place_base, is_local_mutation_allowed)
2143 // Deref should only be for reference, pointers or boxes
2144 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2147 // All other projections are owned by their base path, so mutable if
2148 // base path is mutable
2149 ProjectionElem::Field(..)
2150 | ProjectionElem::Index(..)
2151 | ProjectionElem::ConstantIndex { .. }
2152 | ProjectionElem::Subslice { .. }
2153 | ProjectionElem::OpaqueCast { .. }
2154 | ProjectionElem::Downcast(..) => {
2155 let upvar_field_projection = self.is_upvar_field_projection(place);
2156 if let Some(field) = upvar_field_projection {
2157 let upvar = &self.upvars[field.index()];
2159 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2160 place={:?}, place_base={:?}",
2161 upvar, is_local_mutation_allowed, place, place_base
2163 match (upvar.place.mutability, is_local_mutation_allowed) {
2166 LocalMutationIsAllowed::No
2167 | LocalMutationIsAllowed::ExceptUpvars,
2169 (Mutability::Not, LocalMutationIsAllowed::Yes)
2170 | (Mutability::Mut, _) => {
2171 // Subtle: this is an upvar
2172 // reference, so it looks like
2173 // `self.foo` -- we want to double
2174 // check that the location `*self`
2175 // is mutable (i.e., this is not a
2176 // `Fn` closure). But if that
2177 // check succeeds, we want to
2178 // *blame* the mutability on
2179 // `place` (that is,
2180 // `self.foo`). This is used to
2181 // propagate the info about
2182 // whether mutability declarations
2183 // are used outwards, so that we register
2184 // the outer variable as mutable. Otherwise a
2185 // test like this fails to record the `mut`
2189 // fn foo<F: FnOnce()>(_f: F) { }
2191 // let var = Vec::new();
2198 self.is_mutable(place_base, is_local_mutation_allowed)?;
2200 place_local: place.local,
2201 place_projection: place.projection,
2202 is_local_mutation_allowed,
2207 self.is_mutable(place_base, is_local_mutation_allowed)
2215 /// If `place` is a field projection, and the field is being projected from a closure type,
2216 /// then returns the index of the field being projected. Note that this closure will always
2217 /// be `self` in the current MIR, because that is the only time we directly access the fields
2218 /// of a closure type.
2219 fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2220 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2225 use rustc_errors::ErrorGuaranteed;
2229 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 buffered_mut_errors: FxHashMap<Span, (DiagnosticBuilder<'tcx, ErrorGuaranteed>, usize)>,
2248 /// Diagnostics to be reported buffer.
2249 buffered: Vec<Diagnostic>,
2250 /// Set to Some if we emit an error during borrowck
2251 tainted_by_errors: Option<ErrorGuaranteed>,
2254 impl<'tcx> BorrowckErrors<'tcx> {
2255 pub fn new(tcx: TyCtxt<'tcx>) -> Self {
2258 buffered_move_errors: BTreeMap::new(),
2259 buffered_mut_errors: Default::default(),
2260 buffered: Default::default(),
2261 tainted_by_errors: None,
2265 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2266 if let None = self.tainted_by_errors {
2267 self.tainted_by_errors = Some(
2270 .delay_span_bug(t.span.clone(), "diagnostic buffered but not emitted"),
2273 t.buffer(&mut self.buffered);
2276 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2277 t.buffer(&mut self.buffered);
2280 pub fn set_tainted_by_errors(&mut self, e: ErrorGuaranteed) {
2281 self.tainted_by_errors = Some(e);
2285 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
2286 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2287 self.errors.buffer_error(t);
2290 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2291 self.errors.buffer_non_error_diag(t);
2294 pub fn buffer_move_error(
2296 move_out_indices: Vec<MoveOutIndex>,
2297 place_and_err: (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>),
2299 if let Some((_, diag)) =
2300 self.errors.buffered_move_errors.insert(move_out_indices, place_and_err)
2302 // Cancel the old diagnostic so we don't ICE
2310 pub fn get_buffered_mut_error(
2313 ) -> Option<(DiagnosticBuilder<'tcx, ErrorGuaranteed>, usize)> {
2314 self.errors.buffered_mut_errors.remove(&span)
2317 pub fn buffer_mut_error(
2320 t: DiagnosticBuilder<'tcx, ErrorGuaranteed>,
2323 self.errors.buffered_mut_errors.insert(span, (t, count));
2326 pub fn emit_errors(&mut self) -> Option<ErrorGuaranteed> {
2327 // Buffer any move errors that we collected and de-duplicated.
2328 for (_, (_, diag)) in std::mem::take(&mut self.errors.buffered_move_errors) {
2329 // We have already set tainted for this error, so just buffer it.
2330 diag.buffer(&mut self.errors.buffered);
2332 for (_, (mut diag, count)) in std::mem::take(&mut self.errors.buffered_mut_errors) {
2334 diag.note(&format!("...and {} other attempted mutable borrows", count - 10));
2336 diag.buffer(&mut self.errors.buffered);
2339 if !self.errors.buffered.is_empty() {
2340 self.errors.buffered.sort_by_key(|diag| diag.sort_span);
2342 for mut diag in self.errors.buffered.drain(..) {
2343 self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
2347 self.errors.tainted_by_errors
2350 pub fn has_buffered_errors(&self) -> bool {
2351 self.errors.buffered.is_empty()
2354 pub fn has_move_error(
2356 move_out_indices: &[MoveOutIndex],
2357 ) -> Option<&(PlaceRef<'tcx>, DiagnosticBuilder<'cx, ErrorGuaranteed>)> {
2358 self.errors.buffered_move_errors.get(move_out_indices)
2363 /// The degree of overlap between 2 places for borrow-checking.
2365 /// The places might partially overlap - in this case, we give
2366 /// up and say that they might conflict. This occurs when
2367 /// different fields of a union are borrowed. For example,
2368 /// if `u` is a union, we have no way of telling how disjoint
2369 /// `u.a.x` and `a.b.y` are.
2371 /// The places have the same type, and are either completely disjoint
2372 /// or equal - i.e., they can't "partially" overlap as can occur with
2373 /// unions. This is the "base case" on which we recur for extensions
2376 /// The places are disjoint, so we know all extensions of them
2377 /// will also be disjoint.