1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 #![allow(rustc::potential_query_instability)]
4 #![feature(box_patterns)]
5 #![feature(let_chains)]
7 #![feature(min_specialization)]
8 #![feature(never_type)]
9 #![feature(rustc_attrs)]
10 #![feature(stmt_expr_attributes)]
11 #![feature(trusted_step)]
12 #![feature(try_blocks)]
13 #![recursion_limit = "256"]
16 extern crate rustc_middle;
20 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
21 use rustc_data_structures::graph::dominators::Dominators;
22 use rustc_errors::{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 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>(
129 def: ty::WithOptConstParam<LocalDefId>,
130 ) -> &'tcx BorrowCheckResult<'tcx> {
131 let (input_body, promoted) = tcx.mir_promoted(def);
132 debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
133 let hir_owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;
135 let opt_closure_req = tcx
137 .with_opaque_type_inference(DefiningAnchor::Bind(hir_owner))
139 let input_body: &Body<'_> = &input_body.borrow();
140 let promoted: &IndexVec<_, _> = &promoted.borrow();
141 do_mir_borrowck(&infcx, input_body, promoted, false).0
143 debug!("mir_borrowck done");
145 tcx.arena.alloc(opt_closure_req)
148 /// Perform the actual borrow checking.
150 /// If `return_body_with_facts` is true, then return the body with non-erased
151 /// region ids on which the borrow checking was performed together with Polonius
153 #[instrument(skip(infcx, input_body, input_promoted), fields(id=?input_body.source.with_opt_param().as_local().unwrap()), level = "debug")]
154 fn do_mir_borrowck<'a, 'tcx>(
155 infcx: &InferCtxt<'a, 'tcx>,
156 input_body: &Body<'tcx>,
157 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
158 return_body_with_facts: bool,
159 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
160 let def = input_body.source.with_opt_param().as_local().unwrap();
165 let param_env = tcx.param_env(def.did);
167 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
168 for var_debug_info in &input_body.var_debug_info {
169 if let VarDebugInfoContents::Place(place) = var_debug_info.value {
170 if let Some(local) = place.as_local() {
171 if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name {
173 var_debug_info.source_info.span,
174 "local {:?} has many names (`{}` vs `{}`)",
180 local_names[local] = Some(var_debug_info.name);
185 let mut errors = error::BorrowckErrors::new();
187 // Gather the upvars of a closure, if any.
188 let tables = tcx.typeck_opt_const_arg(def);
189 if let Some(ErrorGuaranteed { .. }) = tables.tainted_by_errors {
190 infcx.set_tainted_by_errors();
191 errors.set_tainted_by_errors();
193 let upvars: Vec<_> = tables
194 .closure_min_captures_flattened(def.did)
195 .map(|captured_place| {
196 let capture = captured_place.info.capture_kind;
197 let by_ref = match capture {
198 ty::UpvarCapture::ByValue => false,
199 ty::UpvarCapture::ByRef(..) => true,
201 Upvar { place: captured_place.clone(), by_ref }
205 // Replace all regions with fresh inference variables. This
206 // requires first making our own copy of the MIR. This copy will
207 // be modified (in place) to contain non-lexical lifetimes. It
208 // will have a lifetime tied to the inference context.
209 let mut body_owned = input_body.clone();
210 let mut promoted = input_promoted.clone();
212 nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
213 let body = &body_owned; // no further changes
215 let location_table_owned = LocationTable::new(body);
216 let location_table = &location_table_owned;
218 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
219 match MoveData::gather_moves(&body, tcx, param_env) {
220 Ok((_, move_data)) => (move_data, Vec::new()),
221 Err((move_data, move_errors)) => (move_data, move_errors),
223 let promoted_errors = promoted
225 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
227 let mdpe = MoveDataParamEnv { move_data, param_env };
229 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
230 .into_engine(tcx, &body)
231 .pass_name("borrowck")
232 .iterate_to_fixpoint()
233 .into_results_cursor(&body);
235 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def.did).is_fn_or_closure();
237 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
239 let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.unstable_opts.polonius;
241 // Compute non-lexical lifetimes.
249 } = nll::compute_regions(
263 // Dump MIR results into a file, if that is enabled. This let us
264 // write unit-tests, as well as helping with debugging.
265 nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
267 // We also have a `#[rustc_regions]` annotation that causes us to dump
269 nll::dump_annotation(
278 // The various `flow_*` structures can be large. We drop `flow_inits` here
279 // so it doesn't overlap with the others below. This reduces peak memory
280 // usage significantly on some benchmarks.
283 let regioncx = Rc::new(regioncx);
285 let flow_borrows = Borrows::new(tcx, body, ®ioncx, &borrow_set)
286 .into_engine(tcx, body)
287 .pass_name("borrowck")
288 .iterate_to_fixpoint();
289 let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &mdpe)
290 .into_engine(tcx, body)
291 .pass_name("borrowck")
292 .iterate_to_fixpoint();
293 let flow_ever_inits = EverInitializedPlaces::new(tcx, body, &mdpe)
294 .into_engine(tcx, body)
295 .pass_name("borrowck")
296 .iterate_to_fixpoint();
298 let movable_generator =
299 // The first argument is the generator type passed by value
300 if let Some(local) = body.local_decls.raw.get(1)
301 // Get the interior types and substs which typeck computed
302 && let ty::Generator(_, _, hir::Movability::Static) = local.ty.kind()
309 for (idx, move_data_results) in promoted_errors {
310 let promoted_body = &promoted[idx];
312 if let Err((move_data, move_errors)) = move_data_results {
313 let mut promoted_mbcx = MirBorrowckCtxt {
317 move_data: &move_data,
318 location_table, // no need to create a real one for the promoted, it is not used
320 fn_self_span_reported: Default::default(),
321 locals_are_invalidated_at_exit,
322 access_place_error_reported: Default::default(),
323 reservation_error_reported: Default::default(),
324 uninitialized_error_reported: Default::default(),
325 regioncx: regioncx.clone(),
326 used_mut: Default::default(),
327 used_mut_upvars: SmallVec::new(),
328 borrow_set: Rc::clone(&borrow_set),
329 dominators: Dominators::dummy(), // not used
331 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
332 region_names: RefCell::default(),
333 next_region_name: RefCell::new(1),
334 polonius_output: None,
337 promoted_mbcx.report_move_errors(move_errors);
338 errors = promoted_mbcx.errors;
342 let dominators = body.basic_blocks.dominators();
344 let mut mbcx = MirBorrowckCtxt {
348 move_data: &mdpe.move_data,
351 locals_are_invalidated_at_exit,
352 fn_self_span_reported: Default::default(),
353 access_place_error_reported: Default::default(),
354 reservation_error_reported: Default::default(),
355 uninitialized_error_reported: Default::default(),
356 regioncx: Rc::clone(®ioncx),
357 used_mut: Default::default(),
358 used_mut_upvars: SmallVec::new(),
359 borrow_set: Rc::clone(&borrow_set),
363 region_names: RefCell::default(),
364 next_region_name: RefCell::new(1),
369 // Compute and report region errors, if any.
370 mbcx.report_region_errors(nll_errors);
372 let results = BorrowckResults {
373 ever_inits: flow_ever_inits,
374 uninits: flow_uninits,
375 borrows: flow_borrows,
378 mbcx.report_move_errors(move_errors);
380 rustc_mir_dataflow::visit_results(
382 traversal::reverse_postorder(body).map(|(bb, _)| bb),
387 // For each non-user used mutable variable, check if it's been assigned from
388 // a user-declared local. If so, then put that local into the used_mut set.
389 // Note that this set is expected to be small - only upvars from closures
390 // would have a chance of erroneously adding non-user-defined mutable vars
392 let temporary_used_locals: FxHashSet<Local> = mbcx
395 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
398 // For the remaining unused locals that are marked as mutable, we avoid linting any that
399 // were never initialized. These locals may have been removed as unreachable code; or will be
400 // linted as unused variables.
401 let unused_mut_locals =
402 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
403 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
405 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
406 let used_mut = std::mem::take(&mut mbcx.used_mut);
407 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
408 let local_decl = &mbcx.body.local_decls[local];
409 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
410 ClearCrossCrate::Set(data) => data.lint_root,
414 // Skip over locals that begin with an underscore or have no name
415 match mbcx.local_names[local] {
417 if name.as_str().starts_with('_') {
424 let span = local_decl.source_info.span;
425 if span.desugaring_kind().is_some() {
426 // If the `mut` arises as part of a desugaring, we should ignore it.
430 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
432 tcx.emit_spanned_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
435 let tainted_by_errors = mbcx.emit_errors();
437 let result = BorrowCheckResult {
438 concrete_opaque_types: opaque_type_values,
439 closure_requirements: opt_closure_req,
440 used_mut_upvars: mbcx.used_mut_upvars,
444 let body_with_facts = if return_body_with_facts {
445 let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
446 Some(Box::new(BodyWithBorrowckFacts {
448 input_facts: *polonius_input.expect("Polonius input facts were not generated"),
450 location_table: location_table_owned,
456 debug!("do_mir_borrowck: result = {:#?}", result);
458 (result, body_with_facts)
461 /// A `Body` with information computed by the borrow checker. This struct is
462 /// intended to be consumed by compiler consumers.
464 /// We need to include the MIR body here because the region identifiers must
465 /// match the ones in the Polonius facts.
466 pub struct BodyWithBorrowckFacts<'tcx> {
467 /// A mir body that contains region identifiers.
468 pub body: Body<'tcx>,
469 /// Polonius input facts.
470 pub input_facts: AllFacts,
471 /// Polonius output facts.
472 pub output_facts: Rc<self::nll::PoloniusOutput>,
473 /// The table that maps Polonius points to locations in the table.
474 pub location_table: LocationTable,
477 struct MirBorrowckCtxt<'cx, 'tcx> {
478 infcx: &'cx InferCtxt<'cx, 'tcx>,
479 param_env: ParamEnv<'tcx>,
480 body: &'cx Body<'tcx>,
481 move_data: &'cx MoveData<'tcx>,
483 /// Map from MIR `Location` to `LocationIndex`; created
484 /// when MIR borrowck begins.
485 location_table: &'cx LocationTable,
487 movable_generator: bool,
488 /// This keeps track of whether local variables are free-ed when the function
489 /// exits even without a `StorageDead`, which appears to be the case for
492 /// I'm not sure this is the right approach - @eddyb could you try and
494 locals_are_invalidated_at_exit: bool,
495 /// This field keeps track of when borrow errors are reported in the access_place function
496 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
497 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
498 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
500 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
501 /// This field keeps track of when borrow conflict errors are reported
502 /// for reservations, so that we don't report seemingly duplicate
503 /// errors for corresponding activations.
505 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
506 // but it is currently inconvenient to track down the `BorrowIndex`
507 // at the time we detect and report a reservation error.
508 reservation_error_reported: FxHashSet<Place<'tcx>>,
509 /// This fields keeps track of the `Span`s that we have
510 /// used to report extra information for `FnSelfUse`, to avoid
511 /// unnecessarily verbose errors.
512 fn_self_span_reported: FxHashSet<Span>,
513 /// This field keeps track of errors reported in the checking of uninitialized variables,
514 /// so that we don't report seemingly duplicate errors.
515 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
516 /// This field keeps track of all the local variables that are declared mut and are mutated.
517 /// Used for the warning issued by an unused mutable local variable.
518 used_mut: FxHashSet<Local>,
519 /// If the function we're checking is a closure, then we'll need to report back the list of
520 /// mutable upvars that have been used. This field keeps track of them.
521 used_mut_upvars: SmallVec<[Field; 8]>,
522 /// Region inference context. This contains the results from region inference and lets us e.g.
523 /// find out which CFG points are contained in each borrow region.
524 regioncx: Rc<RegionInferenceContext<'tcx>>,
526 /// The set of borrows extracted from the MIR
527 borrow_set: Rc<BorrowSet<'tcx>>,
529 /// Dominators for MIR
530 dominators: Dominators<BasicBlock>,
532 /// Information about upvars not necessarily preserved in types or MIR
533 upvars: Vec<Upvar<'tcx>>,
535 /// Names of local (user) variables (extracted from `var_debug_info`).
536 local_names: IndexVec<Local, Option<Symbol>>,
538 /// Record the region names generated for each region in the given
539 /// MIR def so that we can reuse them later in help/error messages.
540 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
542 /// The counter for generating new region names.
543 next_region_name: RefCell<usize>,
545 /// Results of Polonius analysis.
546 polonius_output: Option<Rc<PoloniusOutput>>,
548 errors: error::BorrowckErrors<'tcx>,
552 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
553 // 2. loans made in overlapping scopes do not conflict
554 // 3. assignments do not affect things loaned out as immutable
555 // 4. moves do not affect things loaned out in any way
556 impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
557 type FlowState = Flows<'cx, 'tcx>;
559 fn visit_statement_before_primary_effect(
561 flow_state: &Flows<'cx, 'tcx>,
562 stmt: &'cx Statement<'tcx>,
565 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
566 let span = stmt.source_info.span;
568 self.check_activations(location, span, flow_state);
571 StatementKind::Assign(box (lhs, ref rhs)) => {
572 self.consume_rvalue(location, (rhs, span), flow_state);
574 self.mutate_place(location, (*lhs, span), Shallow(None), flow_state);
576 StatementKind::FakeRead(box (_, ref place)) => {
577 // Read for match doesn't access any memory and is used to
578 // assert that a place is safe and live. So we don't have to
579 // do any checks here.
581 // FIXME: Remove check that the place is initialized. This is
582 // needed for now because matches don't have never patterns yet.
583 // So this is the only place we prevent
587 self.check_if_path_or_subpath_is_moved(
589 InitializationRequiringAction::Use,
590 (place.as_ref(), span),
594 StatementKind::CopyNonOverlapping(box rustc_middle::mir::CopyNonOverlapping {
599 "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
603 | StatementKind::Coverage(..)
604 | StatementKind::AscribeUserType(..)
605 | StatementKind::Retag { .. }
606 | StatementKind::StorageLive(..) => {
607 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
610 StatementKind::StorageDead(local) => {
613 (Place::from(*local), span),
614 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
615 LocalMutationIsAllowed::Yes,
619 StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
620 bug!("Statement not allowed in this MIR phase")
625 fn visit_terminator_before_primary_effect(
627 flow_state: &Flows<'cx, 'tcx>,
628 term: &'cx Terminator<'tcx>,
631 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
632 let span = term.source_info.span;
634 self.check_activations(loc, span, flow_state);
637 TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
638 self.consume_operand(loc, (discr, span), flow_state);
640 TerminatorKind::Drop { place, target: _, unwind: _ } => {
642 "visit_terminator_drop \
643 loc: {:?} term: {:?} place: {:?} span: {:?}",
644 loc, term, place, span
650 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
651 LocalMutationIsAllowed::Yes,
655 TerminatorKind::DropAndReplace {
657 value: ref new_value,
661 self.mutate_place(loc, (drop_place, span), Deep, flow_state);
662 self.consume_operand(loc, (new_value, span), flow_state);
664 TerminatorKind::Call {
673 self.consume_operand(loc, (func, span), flow_state);
675 self.consume_operand(loc, (arg, span), flow_state);
677 self.mutate_place(loc, (destination, span), Deep, flow_state);
679 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
680 self.consume_operand(loc, (cond, span), flow_state);
681 use rustc_middle::mir::AssertKind;
682 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
683 self.consume_operand(loc, (len, span), flow_state);
684 self.consume_operand(loc, (index, span), flow_state);
688 TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
689 self.consume_operand(loc, (value, span), flow_state);
690 self.mutate_place(loc, (resume_arg, span), Deep, flow_state);
693 TerminatorKind::InlineAsm {
703 InlineAsmOperand::In { reg: _, ref value } => {
704 self.consume_operand(loc, (value, span), flow_state);
706 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
707 if let Some(place) = place {
708 self.mutate_place(loc, (place, span), Shallow(None), flow_state);
711 InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
712 self.consume_operand(loc, (in_value, span), flow_state);
713 if let Some(out_place) = out_place {
722 InlineAsmOperand::Const { value: _ }
723 | InlineAsmOperand::SymFn { value: _ }
724 | InlineAsmOperand::SymStatic { def_id: _ } => {}
729 TerminatorKind::Goto { target: _ }
730 | TerminatorKind::Abort
731 | TerminatorKind::Unreachable
732 | TerminatorKind::Resume
733 | TerminatorKind::Return
734 | TerminatorKind::GeneratorDrop
735 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
736 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
737 // no data used, thus irrelevant to borrowck
742 fn visit_terminator_after_primary_effect(
744 flow_state: &Flows<'cx, 'tcx>,
745 term: &'cx Terminator<'tcx>,
748 let span = term.source_info.span;
751 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
752 if self.movable_generator {
753 // Look for any active borrows to locals
754 let borrow_set = self.borrow_set.clone();
755 for i in flow_state.borrows.iter() {
756 let borrow = &borrow_set[i];
757 self.check_for_local_borrow(borrow, span);
762 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
763 // Returning from the function implicitly kills storage for all locals and statics.
764 // Often, the storage will already have been killed by an explicit
765 // StorageDead, but we don't always emit those (notably on unwind paths),
766 // so this "extra check" serves as a kind of backup.
767 let borrow_set = self.borrow_set.clone();
768 for i in flow_state.borrows.iter() {
769 let borrow = &borrow_set[i];
770 self.check_for_invalidation_at_exit(loc, borrow, span);
774 TerminatorKind::Abort
775 | TerminatorKind::Assert { .. }
776 | TerminatorKind::Call { .. }
777 | TerminatorKind::Drop { .. }
778 | TerminatorKind::DropAndReplace { .. }
779 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
780 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
781 | TerminatorKind::Goto { .. }
782 | TerminatorKind::SwitchInt { .. }
783 | TerminatorKind::Unreachable
784 | TerminatorKind::InlineAsm { .. } => {}
789 use self::AccessDepth::{Deep, Shallow};
790 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
792 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
793 enum ArtificialField {
798 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
800 /// From the RFC: "A *shallow* access means that the immediate
801 /// fields reached at P are accessed, but references or pointers
802 /// found within are not dereferenced. Right now, the only access
803 /// that is shallow is an assignment like `x = ...;`, which would
804 /// be a *shallow write* of `x`."
805 Shallow(Option<ArtificialField>),
807 /// From the RFC: "A *deep* access means that all data reachable
808 /// through the given place may be invalidated or accesses by
812 /// Access is Deep only when there is a Drop implementation that
813 /// can reach the data behind the reference.
817 /// Kind of access to a value: read or write
818 /// (For informational purposes only)
819 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
821 /// From the RFC: "A *read* means that the existing data may be
822 /// read, but will not be changed."
825 /// From the RFC: "A *write* means that the data may be mutated to
826 /// new values or otherwise invalidated (for example, it could be
827 /// de-initialized, as in a move operation).
830 /// For two-phase borrows, we distinguish a reservation (which is treated
831 /// like a Read) from an activation (which is treated like a write), and
832 /// each of those is furthermore distinguished from Reads/Writes above.
833 Reservation(WriteKind),
834 Activation(WriteKind, BorrowIndex),
837 /// Kind of read access to a value
838 /// (For informational purposes only)
839 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
845 /// Kind of write access to a value
846 /// (For informational purposes only)
847 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
850 MutableBorrow(BorrowKind),
855 /// When checking permissions for a place access, this flag is used to indicate that an immutable
856 /// local place can be mutated.
858 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
859 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
860 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
861 // `is_declared_mutable()`.
862 // - Take flow state into consideration in `is_assignable()` for local variables.
863 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
864 enum LocalMutationIsAllowed {
866 /// We want use of immutable upvars to cause a "write to immutable upvar"
867 /// error, not an "reassignment" error.
872 #[derive(Copy, Clone, Debug)]
873 enum InitializationRequiringAction {
881 struct RootPlace<'tcx> {
883 place_projection: &'tcx [PlaceElem<'tcx>],
884 is_local_mutation_allowed: LocalMutationIsAllowed,
887 impl InitializationRequiringAction {
888 fn as_noun(self) -> &'static str {
890 InitializationRequiringAction::Borrow => "borrow",
891 InitializationRequiringAction::MatchOn => "use", // no good noun
892 InitializationRequiringAction::Use => "use",
893 InitializationRequiringAction::Assignment => "assign",
894 InitializationRequiringAction::PartialAssignment => "assign to part",
898 fn as_verb_in_past_tense(self) -> &'static str {
900 InitializationRequiringAction::Borrow => "borrowed",
901 InitializationRequiringAction::MatchOn => "matched on",
902 InitializationRequiringAction::Use => "used",
903 InitializationRequiringAction::Assignment => "assigned",
904 InitializationRequiringAction::PartialAssignment => "partially assigned",
908 fn as_general_verb_in_past_tense(self) -> &'static str {
910 InitializationRequiringAction::Borrow
911 | InitializationRequiringAction::MatchOn
912 | InitializationRequiringAction::Use => "used",
913 InitializationRequiringAction::Assignment => "assigned",
914 InitializationRequiringAction::PartialAssignment => "partially assigned",
919 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
920 fn body(&self) -> &'cx Body<'tcx> {
924 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
925 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
926 /// place is initialized and (b) it is not borrowed in some way that would prevent this
929 /// Returns `true` if an error is reported.
933 place_span: (Place<'tcx>, Span),
934 kind: (AccessDepth, ReadOrWrite),
935 is_local_mutation_allowed: LocalMutationIsAllowed,
936 flow_state: &Flows<'cx, 'tcx>,
940 if let Activation(_, borrow_index) = rw {
941 if self.reservation_error_reported.contains(&place_span.0) {
943 "skipping access_place for activation of invalid reservation \
944 place: {:?} borrow_index: {:?}",
945 place_span.0, borrow_index
951 // Check is_empty() first because it's the common case, and doing that
952 // way we avoid the clone() call.
953 if !self.access_place_error_reported.is_empty()
954 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
957 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
963 let mutability_error = self.check_access_permissions(
966 is_local_mutation_allowed,
971 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
973 if conflict_error || mutability_error {
974 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
975 self.access_place_error_reported.insert((place_span.0, place_span.1));
979 #[instrument(level = "debug", skip(self, flow_state))]
980 fn check_access_for_conflict(
983 place_span: (Place<'tcx>, Span),
986 flow_state: &Flows<'cx, 'tcx>,
988 let mut error_reported = false;
989 let tcx = self.infcx.tcx;
990 let body = self.body;
991 let borrow_set = self.borrow_set.clone();
993 // Use polonius output if it has been enabled.
994 let polonius_output = self.polonius_output.clone();
995 let borrows_in_scope = if let Some(polonius) = &polonius_output {
996 let location = self.location_table.start_index(location);
997 Either::Left(polonius.errors_at(location).iter().copied())
999 Either::Right(flow_state.borrows.iter())
1002 each_borrow_involving_path(
1010 |this, borrow_index, borrow| match (rw, borrow.kind) {
1011 // Obviously an activation is compatible with its own
1012 // reservation (or even prior activating uses of same
1013 // borrow); so don't check if they interfere.
1015 // NOTE: *reservations* do conflict with themselves;
1016 // thus aren't injecting unsoundness w/ this check.)
1017 (Activation(_, activating), _) if activating == borrow_index => {
1019 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1020 skipping {:?} b/c activation of same borrow_index",
1024 (borrow_index, borrow),
1029 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1031 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1032 BorrowKind::Unique | BorrowKind::Mut { .. },
1033 ) => Control::Continue,
1035 (Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
1036 // This used to be a future compatibility warning (to be
1037 // disallowed on NLL). See rust-lang/rust#56254
1041 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1042 // Handled by initialization checks.
1046 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1047 // Reading from mere reservations of mutable-borrows is OK.
1048 if !is_active(&this.dominators, borrow, location) {
1049 assert!(allow_two_phase_borrow(borrow.kind));
1050 return Control::Continue;
1053 error_reported = true;
1057 .report_use_while_mutably_borrowed(location, place_span, borrow);
1058 this.buffer_error(err);
1060 ReadKind::Borrow(bk) => {
1062 this.report_conflicting_borrow(location, place_span, bk, borrow);
1063 this.buffer_error(err);
1069 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1071 Reservation(..) => {
1073 "recording invalid reservation of \
1077 this.reservation_error_reported.insert(place_span.0);
1079 Activation(_, activating) => {
1081 "observing check_place for activation of \
1082 borrow_index: {:?}",
1086 Read(..) | Write(..) => {}
1089 error_reported = true;
1091 WriteKind::MutableBorrow(bk) => {
1093 this.report_conflicting_borrow(location, place_span, bk, borrow);
1094 this.buffer_error(err);
1096 WriteKind::StorageDeadOrDrop => this
1097 .report_borrowed_value_does_not_live_long_enough(
1103 WriteKind::Mutate => {
1104 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1106 WriteKind::Move => {
1107 this.report_move_out_while_borrowed(location, place_span, borrow)
1121 place_span: (Place<'tcx>, Span),
1123 flow_state: &Flows<'cx, 'tcx>,
1125 // Write of P[i] or *P requires P init'd.
1126 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1128 // Special case: you can assign an immutable local variable
1129 // (e.g., `x = ...`) so long as it has never been initialized
1130 // before (at this point in the flow).
1131 if let Some(local) = place_span.0.as_local() {
1132 if let Mutability::Not = self.body.local_decls[local].mutability {
1133 // check for reassignments to immutable local variables
1134 self.check_if_reassignment_to_immutable_state(
1135 location, local, place_span, flow_state,
1141 // Otherwise, use the normal access permission rules.
1145 (kind, Write(WriteKind::Mutate)),
1146 LocalMutationIsAllowed::No,
1154 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1155 flow_state: &Flows<'cx, 'tcx>,
1158 Rvalue::Ref(_ /*rgn*/, bk, place) => {
1159 let access_kind = match bk {
1160 BorrowKind::Shallow => {
1161 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1163 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1164 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1165 let wk = WriteKind::MutableBorrow(bk);
1166 if allow_two_phase_borrow(bk) {
1167 (Deep, Reservation(wk))
1178 LocalMutationIsAllowed::No,
1182 let action = if bk == BorrowKind::Shallow {
1183 InitializationRequiringAction::MatchOn
1185 InitializationRequiringAction::Borrow
1188 self.check_if_path_or_subpath_is_moved(
1191 (place.as_ref(), span),
1196 Rvalue::AddressOf(mutability, place) => {
1197 let access_kind = match mutability {
1198 Mutability::Mut => (
1200 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1201 allow_two_phase_borrow: false,
1204 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1211 LocalMutationIsAllowed::No,
1215 self.check_if_path_or_subpath_is_moved(
1217 InitializationRequiringAction::Borrow,
1218 (place.as_ref(), span),
1223 Rvalue::ThreadLocalRef(_) => {}
1225 Rvalue::Use(ref operand)
1226 | Rvalue::Repeat(ref operand, _)
1227 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1228 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/)
1229 | Rvalue::ShallowInitBox(ref operand, _ /*ty*/) => {
1230 self.consume_operand(location, (operand, span), flow_state)
1232 Rvalue::CopyForDeref(place) => {
1236 (Deep, Read(ReadKind::Copy)),
1237 LocalMutationIsAllowed::No,
1241 // Finally, check if path was already moved.
1242 self.check_if_path_or_subpath_is_moved(
1244 InitializationRequiringAction::Use,
1245 (place.as_ref(), span),
1250 Rvalue::Len(place) | Rvalue::Discriminant(place) => {
1251 let af = match *rvalue {
1252 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1253 Rvalue::Discriminant(..) => None,
1254 _ => unreachable!(),
1259 (Shallow(af), Read(ReadKind::Copy)),
1260 LocalMutationIsAllowed::No,
1263 self.check_if_path_or_subpath_is_moved(
1265 InitializationRequiringAction::Use,
1266 (place.as_ref(), span),
1271 Rvalue::BinaryOp(_bin_op, box (ref operand1, ref operand2))
1272 | Rvalue::CheckedBinaryOp(_bin_op, box (ref operand1, ref operand2)) => {
1273 self.consume_operand(location, (operand1, span), flow_state);
1274 self.consume_operand(location, (operand2, span), flow_state);
1277 Rvalue::NullaryOp(_op, _ty) => {
1278 // nullary ops take no dynamic input; no borrowck effect.
1281 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1282 // We need to report back the list of mutable upvars that were
1283 // moved into the closure and subsequently used by the closure,
1284 // in order to populate our used_mut set.
1285 match **aggregate_kind {
1286 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1287 let BorrowCheckResult { used_mut_upvars, .. } =
1288 self.infcx.tcx.mir_borrowck(def_id);
1289 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1290 for field in used_mut_upvars {
1291 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1294 AggregateKind::Adt(..)
1295 | AggregateKind::Array(..)
1296 | AggregateKind::Tuple { .. } => (),
1299 for operand in operands {
1300 self.consume_operand(location, (operand, span), flow_state);
1306 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1307 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1308 // We have three possibilities here:
1309 // a. We are modifying something through a mut-ref
1310 // b. We are modifying something that is local to our parent
1311 // c. Current body is a nested closure, and we are modifying path starting from
1312 // a Place captured by our parent closure.
1314 // Handle (c), the path being modified is exactly the path captured by our parent
1315 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1316 this.used_mut_upvars.push(field);
1320 for (place_ref, proj) in place.iter_projections().rev() {
1322 if proj == ProjectionElem::Deref {
1323 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1324 // We aren't modifying a variable directly
1325 ty::Ref(_, _, hir::Mutability::Mut) => return,
1332 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1333 this.used_mut_upvars.push(field);
1339 this.used_mut.insert(place.local);
1342 // This relies on the current way that by-value
1343 // captures of a closure are copied/moved directly
1344 // when generating MIR.
1346 Operand::Move(place) | Operand::Copy(place) => {
1347 match place.as_local() {
1348 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1349 if self.body.local_decls[local].ty.is_mutable_ptr() {
1350 // The variable will be marked as mutable by the borrow.
1353 // This is an edge case where we have a `move` closure
1354 // inside a non-move closure, and the inner closure
1355 // contains a mutation:
1358 // || { move || { i += 1; }; };
1360 // In this case our usual strategy of assuming that the
1361 // variable will be captured by mutable reference is
1362 // wrong, since `i` can be copied into the inner
1363 // closure from a shared reference.
1365 // As such we have to search for the local that this
1366 // capture comes from and mark it as being used as mut.
1368 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1369 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1370 &self.move_data.inits[init_index]
1372 bug!("temporary should be initialized exactly once")
1375 let InitLocation::Statement(loc) = init.location else {
1376 bug!("temporary initialized in arguments")
1379 let body = self.body;
1380 let bbd = &body[loc.block];
1381 let stmt = &bbd.statements[loc.statement_index];
1382 debug!("temporary assigned in: stmt={:?}", stmt);
1384 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1386 propagate_closure_used_mut_place(self, source);
1389 "closures should only capture user variables \
1390 or references to user variables"
1394 _ => propagate_closure_used_mut_place(self, place),
1397 Operand::Constant(..) => {}
1404 (operand, span): (&'cx Operand<'tcx>, Span),
1405 flow_state: &Flows<'cx, 'tcx>,
1408 Operand::Copy(place) => {
1409 // copy of place: check if this is "copy of frozen path"
1410 // (FIXME: see check_loans.rs)
1414 (Deep, Read(ReadKind::Copy)),
1415 LocalMutationIsAllowed::No,
1419 // Finally, check if path was already moved.
1420 self.check_if_path_or_subpath_is_moved(
1422 InitializationRequiringAction::Use,
1423 (place.as_ref(), span),
1427 Operand::Move(place) => {
1428 // move of place: check if this is move of already borrowed path
1432 (Deep, Write(WriteKind::Move)),
1433 LocalMutationIsAllowed::Yes,
1437 // Finally, check if path was already moved.
1438 self.check_if_path_or_subpath_is_moved(
1440 InitializationRequiringAction::Use,
1441 (place.as_ref(), span),
1445 Operand::Constant(_) => {}
1449 /// Checks whether a borrow of this place is invalidated when the function
1451 #[instrument(level = "debug", skip(self))]
1452 fn check_for_invalidation_at_exit(
1455 borrow: &BorrowData<'tcx>,
1458 let place = borrow.borrowed_place;
1459 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1461 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1462 // we just know that all locals are dropped at function exit (otherwise
1463 // we'll have a memory leak) and assume that all statics have a destructor.
1465 // FIXME: allow thread-locals to borrow other thread locals?
1467 let (might_be_alive, will_be_dropped) =
1468 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1469 // Thread-locals might be dropped after the function exits
1470 // We have to dereference the outer reference because
1471 // borrows don't conflict behind shared references.
1472 root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
1475 (false, self.locals_are_invalidated_at_exit)
1478 if !will_be_dropped {
1479 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1483 let sd = if might_be_alive { Deep } else { Shallow(None) };
1485 if places_conflict::borrow_conflicts_with_place(
1492 places_conflict::PlaceConflictBias::Overlap,
1494 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1495 // FIXME: should be talking about the region lifetime instead
1496 // of just a span here.
1497 let span = self.infcx.tcx.sess.source_map().end_point(span);
1498 self.report_borrowed_value_does_not_live_long_enough(
1507 /// Reports an error if this is a borrow of local data.
1508 /// This is called for all Yield expressions on movable generators
1509 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1510 debug!("check_for_local_borrow({:?})", borrow);
1512 if borrow_of_local_data(borrow.borrowed_place) {
1513 let err = self.cannot_borrow_across_generator_yield(
1514 self.retrieve_borrow_spans(borrow).var_or_use(),
1518 self.buffer_error(err);
1522 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1523 // Two-phase borrow support: For each activation that is newly
1524 // generated at this statement, check if it interferes with
1526 let borrow_set = self.borrow_set.clone();
1527 for &borrow_index in borrow_set.activations_at_location(location) {
1528 let borrow = &borrow_set[borrow_index];
1530 // only mutable borrows should be 2-phase
1531 assert!(match borrow.kind {
1532 BorrowKind::Shared | BorrowKind::Shallow => false,
1533 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1538 (borrow.borrowed_place, span),
1539 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1540 LocalMutationIsAllowed::No,
1543 // We do not need to call `check_if_path_or_subpath_is_moved`
1544 // again, as we already called it when we made the
1545 // initial reservation.
1549 fn check_if_reassignment_to_immutable_state(
1553 place_span: (Place<'tcx>, Span),
1554 flow_state: &Flows<'cx, 'tcx>,
1556 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1558 // Check if any of the initializations of `local` have happened yet:
1559 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1560 // And, if so, report an error.
1561 let init = &self.move_data.inits[init_index];
1562 let span = init.span(&self.body);
1563 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1567 fn check_if_full_path_is_moved(
1570 desired_action: InitializationRequiringAction,
1571 place_span: (PlaceRef<'tcx>, Span),
1572 flow_state: &Flows<'cx, 'tcx>,
1574 let maybe_uninits = &flow_state.uninits;
1578 // 1. Move of `a.b.c`, use of `a.b.c`
1579 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1580 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1581 // partial initialization support, one might have `a.x`
1582 // initialized but not `a.b`.
1586 // 4. Move of `a.b.c`, use of `a.b.d`
1587 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1588 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1589 // must have been initialized for the use to be sound.
1590 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1592 // The dataflow tracks shallow prefixes distinctly (that is,
1593 // field-accesses on P distinctly from P itself), in order to
1594 // track substructure initialization separately from the whole
1597 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1598 // which we have a MovePath is `a.b`, then that means that the
1599 // initialization state of `a.b` is all we need to inspect to
1600 // know if `a.b.c` is valid (and from that we infer that the
1601 // dereference and `.d` access is also valid, since we assume
1602 // `a.b.c` is assigned a reference to an initialized and
1603 // well-formed record structure.)
1605 // Therefore, if we seek out the *closest* prefix for which we
1606 // have a MovePath, that should capture the initialization
1607 // state for the place scenario.
1609 // This code covers scenarios 1, 2, and 3.
1611 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1612 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1613 if maybe_uninits.contains(mpi) {
1614 self.report_use_of_moved_or_uninitialized(
1617 (prefix, place_span.0, place_span.1),
1620 } // Only query longest prefix with a MovePath, not further
1621 // ancestors; dataflow recurs on children when parents
1622 // move (to support partial (re)inits).
1624 // (I.e., querying parents breaks scenario 7; but may want
1625 // to do such a query based on partial-init feature-gate.)
1628 /// Subslices correspond to multiple move paths, so we iterate through the
1629 /// elements of the base array. For each element we check
1631 /// * Does this element overlap with our slice.
1632 /// * Is any part of it uninitialized.
1633 fn check_if_subslice_element_is_moved(
1636 desired_action: InitializationRequiringAction,
1637 place_span: (PlaceRef<'tcx>, Span),
1638 maybe_uninits: &ChunkedBitSet<MovePathIndex>,
1642 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1643 let move_paths = &self.move_data.move_paths;
1645 let root_path = &move_paths[mpi];
1646 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1647 let last_proj = child_move_path.place.projection.last().unwrap();
1648 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1649 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1651 if (from..to).contains(offset) {
1653 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1654 maybe_uninits.contains(mpi)
1657 if let Some(uninit_child) = uninit_child {
1658 self.report_use_of_moved_or_uninitialized(
1661 (place_span.0, place_span.0, place_span.1),
1664 return; // don't bother finding other problems.
1672 fn check_if_path_or_subpath_is_moved(
1675 desired_action: InitializationRequiringAction,
1676 place_span: (PlaceRef<'tcx>, Span),
1677 flow_state: &Flows<'cx, 'tcx>,
1679 let maybe_uninits = &flow_state.uninits;
1683 // 1. Move of `a.b.c`, use of `a` or `a.b`
1684 // partial initialization support, one might have `a.x`
1685 // initialized but not `a.b`.
1686 // 2. All bad scenarios from `check_if_full_path_is_moved`
1690 // 3. Move of `a.b.c`, use of `a.b.d`
1691 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1692 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1693 // must have been initialized for the use to be sound.
1694 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1696 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1698 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1699 place_span.0.last_projection()
1701 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1702 if let ty::Array(..) = place_ty.ty.kind() {
1703 self.check_if_subslice_element_is_moved(
1706 (place_base, place_span.1),
1715 // A move of any shallow suffix of `place` also interferes
1716 // with an attempt to use `place`. This is scenario 3 above.
1718 // (Distinct from handling of scenarios 1+2+4 above because
1719 // `place` does not interfere with suffixes of its prefixes,
1720 // e.g., `a.b.c` does not interfere with `a.b.d`)
1722 // This code covers scenario 1.
1724 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1725 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1726 let uninit_mpi = self
1728 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1730 if let Some(uninit_mpi) = uninit_mpi {
1731 self.report_use_of_moved_or_uninitialized(
1734 (place_span.0, place_span.0, place_span.1),
1737 return; // don't bother finding other problems.
1742 /// Currently MoveData does not store entries for all places in
1743 /// the input MIR. For example it will currently filter out
1744 /// places that are Copy; thus we do not track places of shared
1745 /// reference type. This routine will walk up a place along its
1746 /// prefixes, searching for a foundational place that *is*
1747 /// tracked in the MoveData.
1749 /// An Err result includes a tag indicated why the search failed.
1750 /// Currently this can only occur if the place is built off of a
1751 /// static variable, as we do not track those in the MoveData.
1752 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1753 match self.move_data.rev_lookup.find(place) {
1754 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1755 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1757 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1761 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1762 // If returns None, then there is no move path corresponding
1763 // to a direct owner of `place` (which means there is nothing
1764 // that borrowck tracks for its analysis).
1766 match self.move_data.rev_lookup.find(place) {
1767 LookupResult::Parent(_) => None,
1768 LookupResult::Exact(mpi) => Some(mpi),
1772 fn check_if_assigned_path_is_moved(
1775 (place, span): (Place<'tcx>, Span),
1776 flow_state: &Flows<'cx, 'tcx>,
1778 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1780 // None case => assigning to `x` does not require `x` be initialized.
1781 for (place_base, elem) in place.iter_projections().rev() {
1783 ProjectionElem::Index(_/*operand*/) |
1784 ProjectionElem::ConstantIndex { .. } |
1785 // assigning to P[i] requires P to be valid.
1786 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1787 // assigning to (P->variant) is okay if assigning to `P` is okay
1789 // FIXME: is this true even if P is an adt with a dtor?
1792 // assigning to (*P) requires P to be initialized
1793 ProjectionElem::Deref => {
1794 self.check_if_full_path_is_moved(
1795 location, InitializationRequiringAction::Use,
1796 (place_base, span), flow_state);
1797 // (base initialized; no need to
1802 ProjectionElem::Subslice { .. } => {
1803 panic!("we don't allow assignments to subslices, location: {:?}",
1807 ProjectionElem::Field(..) => {
1808 // if type of `P` has a dtor, then
1809 // assigning to `P.f` requires `P` itself
1810 // be already initialized
1811 let tcx = self.infcx.tcx;
1812 let base_ty = place_base.ty(self.body(), tcx).ty;
1813 match base_ty.kind() {
1814 ty::Adt(def, _) if def.has_dtor(tcx) => {
1815 self.check_if_path_or_subpath_is_moved(
1816 location, InitializationRequiringAction::Assignment,
1817 (place_base, span), flow_state);
1819 // (base initialized; no need to
1824 // Once `let s; s.x = V; read(s.x);`,
1825 // is allowed, remove this match arm.
1826 ty::Adt(..) | ty::Tuple(..) => {
1827 check_parent_of_field(self, location, place_base, span, flow_state);
1829 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1830 // partial initialization, do not complain about unnecessary `mut` on
1831 // an attempt to do a partial initialization.
1832 self.used_mut.insert(place.local);
1841 fn check_parent_of_field<'cx, 'tcx>(
1842 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1844 base: PlaceRef<'tcx>,
1846 flow_state: &Flows<'cx, 'tcx>,
1848 // rust-lang/rust#21232: Until Rust allows reads from the
1849 // initialized parts of partially initialized structs, we
1850 // will, starting with the 2018 edition, reject attempts
1851 // to write to structs that are not fully initialized.
1853 // In other words, *until* we allow this:
1855 // 1. `let mut s; s.x = Val; read(s.x);`
1857 // we will for now disallow this:
1859 // 2. `let mut s; s.x = Val;`
1863 // 3. `let mut s = ...; drop(s); s.x=Val;`
1865 // This does not use check_if_path_or_subpath_is_moved,
1866 // because we want to *allow* reinitializations of fields:
1867 // e.g., want to allow
1869 // `let mut s = ...; drop(s.x); s.x=Val;`
1871 // This does not use check_if_full_path_is_moved on
1872 // `base`, because that would report an error about the
1873 // `base` as a whole, but in this scenario we *really*
1874 // want to report an error about the actual thing that was
1875 // moved, which may be some prefix of `base`.
1877 // Shallow so that we'll stop at any dereference; we'll
1878 // report errors about issues with such bases elsewhere.
1879 let maybe_uninits = &flow_state.uninits;
1881 // Find the shortest uninitialized prefix you can reach
1882 // without going over a Deref.
1883 let mut shortest_uninit_seen = None;
1884 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1885 let Some(mpi) = this.move_path_for_place(prefix) else { continue };
1887 if maybe_uninits.contains(mpi) {
1889 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1890 shortest_uninit_seen,
1893 shortest_uninit_seen = Some((prefix, mpi));
1895 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1899 if let Some((prefix, mpi)) = shortest_uninit_seen {
1900 // Check for a reassignment into an uninitialized field of a union (for example,
1901 // after a move out). In this case, do not report an error here. There is an
1902 // exception, if this is the first assignment into the union (that is, there is
1903 // no move out from an earlier location) then this is an attempt at initialization
1904 // of the union - we should error in that case.
1905 let tcx = this.infcx.tcx;
1906 if base.ty(this.body(), tcx).ty.is_union() {
1907 if this.move_data.path_map[mpi].iter().any(|moi| {
1908 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1914 this.report_use_of_moved_or_uninitialized(
1916 InitializationRequiringAction::PartialAssignment,
1917 (prefix, base, span),
1924 /// Checks the permissions for the given place and read or write kind
1926 /// Returns `true` if an error is reported.
1927 fn check_access_permissions(
1929 (place, span): (Place<'tcx>, Span),
1931 is_local_mutation_allowed: LocalMutationIsAllowed,
1932 flow_state: &Flows<'cx, 'tcx>,
1936 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1937 place, kind, is_local_mutation_allowed
1944 Reservation(WriteKind::MutableBorrow(
1945 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1947 | Write(WriteKind::MutableBorrow(
1948 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1950 let is_local_mutation_allowed = match borrow_kind {
1951 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1952 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1953 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1955 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1957 self.add_used_mut(root_place, flow_state);
1961 error_access = AccessKind::MutableBorrow;
1962 the_place_err = place_err;
1966 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1967 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1969 self.add_used_mut(root_place, flow_state);
1973 error_access = AccessKind::Mutate;
1974 the_place_err = place_err;
1981 | WriteKind::StorageDeadOrDrop
1982 | WriteKind::MutableBorrow(BorrowKind::Shared)
1983 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1987 | WriteKind::StorageDeadOrDrop
1988 | WriteKind::MutableBorrow(BorrowKind::Shared)
1989 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1991 if self.is_mutable(place.as_ref(), is_local_mutation_allowed).is_err()
1992 && !self.has_buffered_errors()
1994 // rust-lang/rust#46908: In pure NLL mode this code path should be
1995 // unreachable, but we use `delay_span_bug` because we can hit this when
1996 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1997 // enabled. We don't want to ICE for that case, as other errors will have
1998 // been emitted (#52262).
1999 self.infcx.tcx.sess.delay_span_bug(
2002 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2010 // permission checks are done at Reservation point.
2016 | BorrowKind::Mut { .. }
2017 | BorrowKind::Shared
2018 | BorrowKind::Shallow,
2022 // Access authorized
2027 // rust-lang/rust#21232, #54986: during period where we reject
2028 // partial initialization, do not complain about mutability
2029 // errors except for actual mutation (as opposed to an attempt
2030 // to do a partial initialization).
2031 let previously_initialized =
2032 self.is_local_ever_initialized(place.local, flow_state).is_some();
2034 // at this point, we have set up the error reporting state.
2035 if previously_initialized {
2036 self.report_mutability_error(place, span, the_place_err, error_access, location);
2043 fn is_local_ever_initialized(
2046 flow_state: &Flows<'cx, 'tcx>,
2047 ) -> Option<InitIndex> {
2048 let mpi = self.move_data.rev_lookup.find_local(local);
2049 let ii = &self.move_data.init_path_map[mpi];
2051 if flow_state.ever_inits.contains(index) {
2058 /// Adds the place into the used mutable variables set
2059 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2061 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2062 // If the local may have been initialized, and it is now currently being
2063 // mutated, then it is justified to be annotated with the `mut`
2064 // keyword, since the mutation may be a possible reassignment.
2065 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2066 && self.is_local_ever_initialized(local, flow_state).is_some()
2068 self.used_mut.insert(local);
2073 place_projection: _,
2074 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2078 place_projection: place_projection @ [.., _],
2079 is_local_mutation_allowed: _,
2081 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2083 projection: place_projection,
2085 self.used_mut_upvars.push(field);
2091 /// Whether this value can be written or borrowed mutably.
2092 /// Returns the root place if the place passed in is a projection.
2095 place: PlaceRef<'tcx>,
2096 is_local_mutation_allowed: LocalMutationIsAllowed,
2097 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2098 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2099 match place.last_projection() {
2101 let local = &self.body.local_decls[place.local];
2102 match local.mutability {
2103 Mutability::Not => match is_local_mutation_allowed {
2104 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2105 place_local: place.local,
2106 place_projection: place.projection,
2107 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2109 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2110 place_local: place.local,
2111 place_projection: place.projection,
2112 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2114 LocalMutationIsAllowed::No => Err(place),
2116 Mutability::Mut => Ok(RootPlace {
2117 place_local: place.local,
2118 place_projection: place.projection,
2119 is_local_mutation_allowed,
2123 Some((place_base, elem)) => {
2125 ProjectionElem::Deref => {
2126 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2128 // Check the kind of deref to decide
2129 match base_ty.kind() {
2130 ty::Ref(_, _, mutbl) => {
2132 // Shared borrowed data is never mutable
2133 hir::Mutability::Not => Err(place),
2134 // Mutably borrowed data is mutable, but only if we have a
2135 // unique path to the `&mut`
2136 hir::Mutability::Mut => {
2137 let mode = match self.is_upvar_field_projection(place) {
2138 Some(field) if self.upvars[field.index()].by_ref => {
2139 is_local_mutation_allowed
2141 _ => LocalMutationIsAllowed::Yes,
2144 self.is_mutable(place_base, mode)
2148 ty::RawPtr(tnm) => {
2150 // `*const` raw pointers are not mutable
2151 hir::Mutability::Not => Err(place),
2152 // `*mut` raw pointers are always mutable, regardless of
2153 // context. The users have to check by themselves.
2154 hir::Mutability::Mut => Ok(RootPlace {
2155 place_local: place.local,
2156 place_projection: place.projection,
2157 is_local_mutation_allowed,
2161 // `Box<T>` owns its content, so mutable if its location is mutable
2162 _ if base_ty.is_box() => {
2163 self.is_mutable(place_base, is_local_mutation_allowed)
2165 // Deref should only be for reference, pointers or boxes
2166 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2169 // All other projections are owned by their base path, so mutable if
2170 // base path is mutable
2171 ProjectionElem::Field(..)
2172 | ProjectionElem::Index(..)
2173 | ProjectionElem::ConstantIndex { .. }
2174 | ProjectionElem::Subslice { .. }
2175 | ProjectionElem::Downcast(..) => {
2176 let upvar_field_projection = self.is_upvar_field_projection(place);
2177 if let Some(field) = upvar_field_projection {
2178 let upvar = &self.upvars[field.index()];
2180 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2181 place={:?}, place_base={:?}",
2182 upvar, is_local_mutation_allowed, place, place_base
2184 match (upvar.place.mutability, is_local_mutation_allowed) {
2187 LocalMutationIsAllowed::No
2188 | LocalMutationIsAllowed::ExceptUpvars,
2190 (Mutability::Not, LocalMutationIsAllowed::Yes)
2191 | (Mutability::Mut, _) => {
2192 // Subtle: this is an upvar
2193 // reference, so it looks like
2194 // `self.foo` -- we want to double
2195 // check that the location `*self`
2196 // is mutable (i.e., this is not a
2197 // `Fn` closure). But if that
2198 // check succeeds, we want to
2199 // *blame* the mutability on
2200 // `place` (that is,
2201 // `self.foo`). This is used to
2202 // propagate the info about
2203 // whether mutability declarations
2204 // are used outwards, so that we register
2205 // the outer variable as mutable. Otherwise a
2206 // test like this fails to record the `mut`
2210 // fn foo<F: FnOnce()>(_f: F) { }
2212 // let var = Vec::new();
2219 self.is_mutable(place_base, is_local_mutation_allowed)?;
2221 place_local: place.local,
2222 place_projection: place.projection,
2223 is_local_mutation_allowed,
2228 self.is_mutable(place_base, is_local_mutation_allowed)
2236 /// If `place` is a field projection, and the field is being projected from a closure type,
2237 /// then returns the index of the field being projected. Note that this closure will always
2238 /// be `self` in the current MIR, because that is the only time we directly access the fields
2239 /// of a closure type.
2240 fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2241 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2246 use rustc_errors::ErrorGuaranteed;
2250 pub struct BorrowckErrors<'tcx> {
2251 /// This field keeps track of move errors that are to be reported for given move indices.
2253 /// There are situations where many errors can be reported for a single move out (see #53807)
2254 /// and we want only the best of those errors.
2256 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
2257 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
2258 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
2259 /// all move errors have been reported, any diagnostics in this map are added to the buffer
2262 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
2263 /// when errors in the map are being re-added to the error buffer so that errors with the
2264 /// same primary span come out in a consistent order.
2265 buffered_move_errors:
2266 BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>)>,
2267 /// Diagnostics to be reported buffer.
2268 buffered: Vec<Diagnostic>,
2269 /// Set to Some if we emit an error during borrowck
2270 tainted_by_errors: Option<ErrorGuaranteed>,
2273 impl BorrowckErrors<'_> {
2274 pub fn new() -> Self {
2276 buffered_move_errors: BTreeMap::new(),
2277 buffered: Default::default(),
2278 tainted_by_errors: None,
2282 // FIXME(eddyb) this is a suboptimal API because `tainted_by_errors` is
2283 // set before any emission actually happens (weakening the guarantee).
2284 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2285 self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
2286 t.buffer(&mut self.buffered);
2289 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2290 t.buffer(&mut self.buffered);
2293 pub fn set_tainted_by_errors(&mut self) {
2294 self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
2298 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
2299 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2300 self.errors.buffer_error(t);
2303 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2304 self.errors.buffer_non_error_diag(t);
2307 pub fn buffer_move_error(
2309 move_out_indices: Vec<MoveOutIndex>,
2310 place_and_err: (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>),
2312 if let Some((_, diag)) =
2313 self.errors.buffered_move_errors.insert(move_out_indices, place_and_err)
2315 // Cancel the old diagnostic so we don't ICE
2323 pub fn emit_errors(&mut self) -> Option<ErrorGuaranteed> {
2324 // Buffer any move errors that we collected and de-duplicated.
2325 for (_, (_, diag)) in std::mem::take(&mut self.errors.buffered_move_errors) {
2326 // We have already set tainted for this error, so just buffer it.
2327 diag.buffer(&mut self.errors.buffered);
2330 if !self.errors.buffered.is_empty() {
2331 self.errors.buffered.sort_by_key(|diag| diag.sort_span);
2333 for mut diag in self.errors.buffered.drain(..) {
2334 self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
2338 self.errors.tainted_by_errors
2341 pub fn has_buffered_errors(&self) -> bool {
2342 self.errors.buffered.is_empty()
2345 pub fn has_move_error(
2347 move_out_indices: &[MoveOutIndex],
2348 ) -> Option<&(PlaceRef<'tcx>, DiagnosticBuilder<'cx, ErrorGuaranteed>)> {
2349 self.errors.buffered_move_errors.get(move_out_indices)
2354 /// The degree of overlap between 2 places for borrow-checking.
2356 /// The places might partially overlap - in this case, we give
2357 /// up and say that they might conflict. This occurs when
2358 /// different fields of a union are borrowed. For example,
2359 /// if `u` is a union, we have no way of telling how disjoint
2360 /// `u.a.x` and `a.b.y` are.
2362 /// The places have the same type, and are either completely disjoint
2363 /// or equal - i.e., they can't "partially" overlap as can occur with
2364 /// unions. This is the "base case" on which we recur for extensions
2367 /// The places are disjoint, so we know all extensions of them
2368 /// will also be disjoint.