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>(
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()));
134 if input_body.borrow().should_skip() {
135 debug!("Skipping borrowck because of injected body");
136 // Let's make up a borrowck result! Fun times!
137 let result = BorrowCheckResult {
138 concrete_opaque_types: VecMap::new(),
139 closure_requirements: None,
140 used_mut_upvars: SmallVec::new(),
141 tainted_by_errors: None,
143 return tcx.arena.alloc(result);
146 let hir_owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;
149 tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(hir_owner.def_id)).build();
150 let input_body: &Body<'_> = &input_body.borrow();
151 let promoted: &IndexVec<_, _> = &promoted.borrow();
152 let opt_closure_req = do_mir_borrowck(&infcx, input_body, promoted, false).0;
153 debug!("mir_borrowck done");
155 tcx.arena.alloc(opt_closure_req)
158 /// Perform the actual borrow checking.
160 /// If `return_body_with_facts` is true, then return the body with non-erased
161 /// region ids on which the borrow checking was performed together with Polonius
163 #[instrument(skip(infcx, input_body, input_promoted), fields(id=?input_body.source.with_opt_param().as_local().unwrap()), level = "debug")]
164 fn do_mir_borrowck<'tcx>(
165 infcx: &InferCtxt<'tcx>,
166 input_body: &Body<'tcx>,
167 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
168 return_body_with_facts: bool,
169 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
170 let def = input_body.source.with_opt_param().as_local().unwrap();
175 let param_env = tcx.param_env(def.did);
177 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
178 for var_debug_info in &input_body.var_debug_info {
179 if let VarDebugInfoContents::Place(place) = var_debug_info.value {
180 if let Some(local) = place.as_local() {
181 if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name {
183 var_debug_info.source_info.span,
184 "local {:?} has many names (`{}` vs `{}`)",
190 local_names[local] = Some(var_debug_info.name);
195 let mut errors = error::BorrowckErrors::new(infcx.tcx);
197 // Gather the upvars of a closure, if any.
198 let tables = tcx.typeck_opt_const_arg(def);
199 if let Some(e) = tables.tainted_by_errors {
200 infcx.set_tainted_by_errors(e);
201 errors.set_tainted_by_errors(e);
203 let upvars: Vec<_> = tables
204 .closure_min_captures_flattened(def.did)
205 .map(|captured_place| {
206 let capture = captured_place.info.capture_kind;
207 let by_ref = match capture {
208 ty::UpvarCapture::ByValue => false,
209 ty::UpvarCapture::ByRef(..) => true,
211 Upvar { place: captured_place.clone(), by_ref }
215 // Replace all regions with fresh inference variables. This
216 // requires first making our own copy of the MIR. This copy will
217 // be modified (in place) to contain non-lexical lifetimes. It
218 // will have a lifetime tied to the inference context.
219 let mut body_owned = input_body.clone();
220 let mut promoted = input_promoted.clone();
222 nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
223 let body = &body_owned; // no further changes
225 let location_table_owned = LocationTable::new(body);
226 let location_table = &location_table_owned;
228 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
229 match MoveData::gather_moves(&body, tcx, param_env) {
230 Ok((_, move_data)) => (move_data, Vec::new()),
231 Err((move_data, move_errors)) => (move_data, move_errors),
233 let promoted_errors = promoted
235 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
237 let mdpe = MoveDataParamEnv { move_data, param_env };
239 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
240 .into_engine(tcx, &body)
241 .pass_name("borrowck")
242 .iterate_to_fixpoint()
243 .into_results_cursor(&body);
245 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def.did).is_fn_or_closure();
247 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
249 let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.unstable_opts.polonius;
251 // Compute non-lexical lifetimes.
259 } = nll::compute_regions(
273 // Dump MIR results into a file, if that is enabled. This let us
274 // write unit-tests, as well as helping with debugging.
275 nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
277 // We also have a `#[rustc_regions]` annotation that causes us to dump
279 nll::dump_annotation(
288 // The various `flow_*` structures can be large. We drop `flow_inits` here
289 // so it doesn't overlap with the others below. This reduces peak memory
290 // usage significantly on some benchmarks.
293 let regioncx = Rc::new(regioncx);
295 let flow_borrows = Borrows::new(tcx, body, ®ioncx, &borrow_set)
296 .into_engine(tcx, body)
297 .pass_name("borrowck")
298 .iterate_to_fixpoint();
299 let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &mdpe)
300 .into_engine(tcx, body)
301 .pass_name("borrowck")
302 .iterate_to_fixpoint();
303 let flow_ever_inits = EverInitializedPlaces::new(tcx, body, &mdpe)
304 .into_engine(tcx, body)
305 .pass_name("borrowck")
306 .iterate_to_fixpoint();
308 let movable_generator =
309 // The first argument is the generator type passed by value
310 if let Some(local) = body.local_decls.raw.get(1)
311 // Get the interior types and substs which typeck computed
312 && let ty::Generator(_, _, hir::Movability::Static) = local.ty.kind()
319 for (idx, move_data_results) in promoted_errors {
320 let promoted_body = &promoted[idx];
322 if let Err((move_data, move_errors)) = move_data_results {
323 let mut promoted_mbcx = MirBorrowckCtxt {
327 move_data: &move_data,
328 location_table, // no need to create a real one for the promoted, it is not used
330 fn_self_span_reported: Default::default(),
331 locals_are_invalidated_at_exit,
332 access_place_error_reported: Default::default(),
333 reservation_error_reported: Default::default(),
334 uninitialized_error_reported: Default::default(),
335 regioncx: regioncx.clone(),
336 used_mut: Default::default(),
337 used_mut_upvars: SmallVec::new(),
338 borrow_set: Rc::clone(&borrow_set),
339 dominators: Dominators::dummy(), // not used
341 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
342 region_names: RefCell::default(),
343 next_region_name: RefCell::new(1),
344 polonius_output: None,
347 promoted_mbcx.report_move_errors(move_errors);
348 errors = promoted_mbcx.errors;
352 let dominators = body.basic_blocks.dominators();
354 let mut mbcx = MirBorrowckCtxt {
358 move_data: &mdpe.move_data,
361 locals_are_invalidated_at_exit,
362 fn_self_span_reported: Default::default(),
363 access_place_error_reported: Default::default(),
364 reservation_error_reported: Default::default(),
365 uninitialized_error_reported: Default::default(),
366 regioncx: Rc::clone(®ioncx),
367 used_mut: Default::default(),
368 used_mut_upvars: SmallVec::new(),
369 borrow_set: Rc::clone(&borrow_set),
373 region_names: RefCell::default(),
374 next_region_name: RefCell::new(1),
379 // Compute and report region errors, if any.
380 mbcx.report_region_errors(nll_errors);
382 let results = BorrowckResults {
383 ever_inits: flow_ever_inits,
384 uninits: flow_uninits,
385 borrows: flow_borrows,
388 mbcx.report_move_errors(move_errors);
390 rustc_mir_dataflow::visit_results(
392 traversal::reverse_postorder(body).map(|(bb, _)| bb),
397 // For each non-user used mutable variable, check if it's been assigned from
398 // a user-declared local. If so, then put that local into the used_mut set.
399 // Note that this set is expected to be small - only upvars from closures
400 // would have a chance of erroneously adding non-user-defined mutable vars
402 let temporary_used_locals: FxHashSet<Local> = mbcx
405 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
408 // For the remaining unused locals that are marked as mutable, we avoid linting any that
409 // were never initialized. These locals may have been removed as unreachable code; or will be
410 // linted as unused variables.
411 let unused_mut_locals =
412 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
413 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
415 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
416 let used_mut = std::mem::take(&mut mbcx.used_mut);
417 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
418 let local_decl = &mbcx.body.local_decls[local];
419 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
420 ClearCrossCrate::Set(data) => data.lint_root,
424 // Skip over locals that begin with an underscore or have no name
425 match mbcx.local_names[local] {
427 if name.as_str().starts_with('_') {
434 let span = local_decl.source_info.span;
435 if span.desugaring_kind().is_some() {
436 // If the `mut` arises as part of a desugaring, we should ignore it.
440 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
442 tcx.emit_spanned_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
445 let tainted_by_errors = mbcx.emit_errors();
447 let result = BorrowCheckResult {
448 concrete_opaque_types: opaque_type_values,
449 closure_requirements: opt_closure_req,
450 used_mut_upvars: mbcx.used_mut_upvars,
454 let body_with_facts = if return_body_with_facts {
455 let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
456 Some(Box::new(BodyWithBorrowckFacts {
458 input_facts: *polonius_input.expect("Polonius input facts were not generated"),
460 location_table: location_table_owned,
466 debug!("do_mir_borrowck: result = {:#?}", result);
468 (result, body_with_facts)
471 /// A `Body` with information computed by the borrow checker. This struct is
472 /// intended to be consumed by compiler consumers.
474 /// We need to include the MIR body here because the region identifiers must
475 /// match the ones in the Polonius facts.
476 pub struct BodyWithBorrowckFacts<'tcx> {
477 /// A mir body that contains region identifiers.
478 pub body: Body<'tcx>,
479 /// Polonius input facts.
480 pub input_facts: AllFacts,
481 /// Polonius output facts.
482 pub output_facts: Rc<self::nll::PoloniusOutput>,
483 /// The table that maps Polonius points to locations in the table.
484 pub location_table: LocationTable,
487 struct MirBorrowckCtxt<'cx, 'tcx> {
488 infcx: &'cx InferCtxt<'tcx>,
489 param_env: ParamEnv<'tcx>,
490 body: &'cx Body<'tcx>,
491 move_data: &'cx MoveData<'tcx>,
493 /// Map from MIR `Location` to `LocationIndex`; created
494 /// when MIR borrowck begins.
495 location_table: &'cx LocationTable,
497 movable_generator: bool,
498 /// This keeps track of whether local variables are free-ed when the function
499 /// exits even without a `StorageDead`, which appears to be the case for
502 /// I'm not sure this is the right approach - @eddyb could you try and
504 locals_are_invalidated_at_exit: bool,
505 /// This field keeps track of when borrow errors are reported in the access_place function
506 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
507 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
508 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
510 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
511 /// This field keeps track of when borrow conflict errors are reported
512 /// for reservations, so that we don't report seemingly duplicate
513 /// errors for corresponding activations.
515 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
516 // but it is currently inconvenient to track down the `BorrowIndex`
517 // at the time we detect and report a reservation error.
518 reservation_error_reported: FxHashSet<Place<'tcx>>,
519 /// This fields keeps track of the `Span`s that we have
520 /// used to report extra information for `FnSelfUse`, to avoid
521 /// unnecessarily verbose errors.
522 fn_self_span_reported: FxHashSet<Span>,
523 /// This field keeps track of errors reported in the checking of uninitialized variables,
524 /// so that we don't report seemingly duplicate errors.
525 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
526 /// This field keeps track of all the local variables that are declared mut and are mutated.
527 /// Used for the warning issued by an unused mutable local variable.
528 used_mut: FxHashSet<Local>,
529 /// If the function we're checking is a closure, then we'll need to report back the list of
530 /// mutable upvars that have been used. This field keeps track of them.
531 used_mut_upvars: SmallVec<[Field; 8]>,
532 /// Region inference context. This contains the results from region inference and lets us e.g.
533 /// find out which CFG points are contained in each borrow region.
534 regioncx: Rc<RegionInferenceContext<'tcx>>,
536 /// The set of borrows extracted from the MIR
537 borrow_set: Rc<BorrowSet<'tcx>>,
539 /// Dominators for MIR
540 dominators: Dominators<BasicBlock>,
542 /// Information about upvars not necessarily preserved in types or MIR
543 upvars: Vec<Upvar<'tcx>>,
545 /// Names of local (user) variables (extracted from `var_debug_info`).
546 local_names: IndexVec<Local, Option<Symbol>>,
548 /// Record the region names generated for each region in the given
549 /// MIR def so that we can reuse them later in help/error messages.
550 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
552 /// The counter for generating new region names.
553 next_region_name: RefCell<usize>,
555 /// Results of Polonius analysis.
556 polonius_output: Option<Rc<PoloniusOutput>>,
558 errors: error::BorrowckErrors<'tcx>,
562 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
563 // 2. loans made in overlapping scopes do not conflict
564 // 3. assignments do not affect things loaned out as immutable
565 // 4. moves do not affect things loaned out in any way
566 impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
567 type FlowState = Flows<'cx, 'tcx>;
569 fn visit_statement_before_primary_effect(
571 flow_state: &Flows<'cx, 'tcx>,
572 stmt: &'cx Statement<'tcx>,
575 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
576 let span = stmt.source_info.span;
578 self.check_activations(location, span, flow_state);
581 StatementKind::Assign(box (lhs, rhs)) => {
582 self.consume_rvalue(location, (rhs, span), flow_state);
584 self.mutate_place(location, (*lhs, span), Shallow(None), flow_state);
586 StatementKind::FakeRead(box (_, place)) => {
587 // Read for match doesn't access any memory and is used to
588 // assert that a place is safe and live. So we don't have to
589 // do any checks here.
591 // FIXME: Remove check that the place is initialized. This is
592 // needed for now because matches don't have never patterns yet.
593 // So this is the only place we prevent
597 self.check_if_path_or_subpath_is_moved(
599 InitializationRequiringAction::Use,
600 (place.as_ref(), span),
604 StatementKind::Intrinsic(box kind) => match kind {
605 NonDivergingIntrinsic::Assume(op) => self.consume_operand(location, (op, span), flow_state),
606 NonDivergingIntrinsic::CopyNonOverlapping(..) => span_bug!(
608 "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
611 // Only relevant for mir typeck
612 StatementKind::AscribeUserType(..)
613 // Doesn't have any language semantics
614 | StatementKind::Coverage(..)
615 // Does not actually affect borrowck
616 | StatementKind::StorageLive(..) => {}
617 StatementKind::StorageDead(local) => {
620 (Place::from(*local), span),
621 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
622 LocalMutationIsAllowed::Yes,
627 | StatementKind::Retag { .. }
628 | StatementKind::Deinit(..)
629 | StatementKind::SetDiscriminant { .. } => {
630 bug!("Statement not allowed in this MIR phase")
635 fn visit_terminator_before_primary_effect(
637 flow_state: &Flows<'cx, 'tcx>,
638 term: &'cx Terminator<'tcx>,
641 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
642 let span = term.source_info.span;
644 self.check_activations(loc, span, flow_state);
647 TerminatorKind::SwitchInt { discr, targets: _ } => {
648 self.consume_operand(loc, (discr, span), flow_state);
650 TerminatorKind::Drop { place, target: _, unwind: _ } => {
652 "visit_terminator_drop \
653 loc: {:?} term: {:?} place: {:?} span: {:?}",
654 loc, term, place, span
660 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
661 LocalMutationIsAllowed::Yes,
665 TerminatorKind::DropAndReplace {
671 self.mutate_place(loc, (*drop_place, span), Deep, flow_state);
672 self.consume_operand(loc, (new_value, span), flow_state);
674 TerminatorKind::Call {
683 self.consume_operand(loc, (func, span), flow_state);
685 self.consume_operand(loc, (arg, span), flow_state);
687 self.mutate_place(loc, (*destination, span), Deep, flow_state);
689 TerminatorKind::Assert { cond, expected: _, msg, target: _, cleanup: _ } => {
690 self.consume_operand(loc, (cond, span), flow_state);
691 use rustc_middle::mir::AssertKind;
692 if let AssertKind::BoundsCheck { len, index } = msg {
693 self.consume_operand(loc, (len, span), flow_state);
694 self.consume_operand(loc, (index, span), flow_state);
698 TerminatorKind::Yield { value, resume: _, resume_arg, drop: _ } => {
699 self.consume_operand(loc, (value, span), flow_state);
700 self.mutate_place(loc, (*resume_arg, span), Deep, flow_state);
703 TerminatorKind::InlineAsm {
713 InlineAsmOperand::In { reg: _, value } => {
714 self.consume_operand(loc, (value, span), flow_state);
716 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
717 if let Some(place) = place {
718 self.mutate_place(loc, (*place, span), Shallow(None), flow_state);
721 InlineAsmOperand::InOut { reg: _, late: _, in_value, out_place } => {
722 self.consume_operand(loc, (in_value, span), flow_state);
723 if let &Some(out_place) = out_place {
732 InlineAsmOperand::Const { value: _ }
733 | InlineAsmOperand::SymFn { value: _ }
734 | InlineAsmOperand::SymStatic { def_id: _ } => {}
739 TerminatorKind::Goto { target: _ }
740 | TerminatorKind::Abort
741 | TerminatorKind::Unreachable
742 | TerminatorKind::Resume
743 | TerminatorKind::Return
744 | TerminatorKind::GeneratorDrop
745 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
746 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
747 // no data used, thus irrelevant to borrowck
752 fn visit_terminator_after_primary_effect(
754 flow_state: &Flows<'cx, 'tcx>,
755 term: &'cx Terminator<'tcx>,
758 let span = term.source_info.span;
761 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
762 if self.movable_generator {
763 // Look for any active borrows to locals
764 let borrow_set = self.borrow_set.clone();
765 for i in flow_state.borrows.iter() {
766 let borrow = &borrow_set[i];
767 self.check_for_local_borrow(borrow, span);
772 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
773 // Returning from the function implicitly kills storage for all locals and statics.
774 // Often, the storage will already have been killed by an explicit
775 // StorageDead, but we don't always emit those (notably on unwind paths),
776 // so this "extra check" serves as a kind of backup.
777 let borrow_set = self.borrow_set.clone();
778 for i in flow_state.borrows.iter() {
779 let borrow = &borrow_set[i];
780 self.check_for_invalidation_at_exit(loc, borrow, span);
784 TerminatorKind::Abort
785 | TerminatorKind::Assert { .. }
786 | TerminatorKind::Call { .. }
787 | TerminatorKind::Drop { .. }
788 | TerminatorKind::DropAndReplace { .. }
789 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
790 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
791 | TerminatorKind::Goto { .. }
792 | TerminatorKind::SwitchInt { .. }
793 | TerminatorKind::Unreachable
794 | TerminatorKind::InlineAsm { .. } => {}
799 use self::AccessDepth::{Deep, Shallow};
800 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
802 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
803 enum ArtificialField {
808 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
810 /// From the RFC: "A *shallow* access means that the immediate
811 /// fields reached at P are accessed, but references or pointers
812 /// found within are not dereferenced. Right now, the only access
813 /// that is shallow is an assignment like `x = ...;`, which would
814 /// be a *shallow write* of `x`."
815 Shallow(Option<ArtificialField>),
817 /// From the RFC: "A *deep* access means that all data reachable
818 /// through the given place may be invalidated or accesses by
822 /// Access is Deep only when there is a Drop implementation that
823 /// can reach the data behind the reference.
827 /// Kind of access to a value: read or write
828 /// (For informational purposes only)
829 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
831 /// From the RFC: "A *read* means that the existing data may be
832 /// read, but will not be changed."
835 /// From the RFC: "A *write* means that the data may be mutated to
836 /// new values or otherwise invalidated (for example, it could be
837 /// de-initialized, as in a move operation).
840 /// For two-phase borrows, we distinguish a reservation (which is treated
841 /// like a Read) from an activation (which is treated like a write), and
842 /// each of those is furthermore distinguished from Reads/Writes above.
843 Reservation(WriteKind),
844 Activation(WriteKind, BorrowIndex),
847 /// Kind of read access to a value
848 /// (For informational purposes only)
849 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
855 /// Kind of write access to a value
856 /// (For informational purposes only)
857 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
860 MutableBorrow(BorrowKind),
865 /// When checking permissions for a place access, this flag is used to indicate that an immutable
866 /// local place can be mutated.
868 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
869 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
870 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
871 // `is_declared_mutable()`.
872 // - Take flow state into consideration in `is_assignable()` for local variables.
873 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
874 enum LocalMutationIsAllowed {
876 /// We want use of immutable upvars to cause a "write to immutable upvar"
877 /// error, not an "reassignment" error.
882 #[derive(Copy, Clone, Debug)]
883 enum InitializationRequiringAction {
891 struct RootPlace<'tcx> {
893 place_projection: &'tcx [PlaceElem<'tcx>],
894 is_local_mutation_allowed: LocalMutationIsAllowed,
897 impl InitializationRequiringAction {
898 fn as_noun(self) -> &'static str {
900 InitializationRequiringAction::Borrow => "borrow",
901 InitializationRequiringAction::MatchOn => "use", // no good noun
902 InitializationRequiringAction::Use => "use",
903 InitializationRequiringAction::Assignment => "assign",
904 InitializationRequiringAction::PartialAssignment => "assign to part",
908 fn as_verb_in_past_tense(self) -> &'static str {
910 InitializationRequiringAction::Borrow => "borrowed",
911 InitializationRequiringAction::MatchOn => "matched on",
912 InitializationRequiringAction::Use => "used",
913 InitializationRequiringAction::Assignment => "assigned",
914 InitializationRequiringAction::PartialAssignment => "partially assigned",
918 fn as_general_verb_in_past_tense(self) -> &'static str {
920 InitializationRequiringAction::Borrow
921 | InitializationRequiringAction::MatchOn
922 | InitializationRequiringAction::Use => "used",
923 InitializationRequiringAction::Assignment => "assigned",
924 InitializationRequiringAction::PartialAssignment => "partially assigned",
929 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
930 fn body(&self) -> &'cx Body<'tcx> {
934 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
935 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
936 /// place is initialized and (b) it is not borrowed in some way that would prevent this
939 /// Returns `true` if an error is reported.
943 place_span: (Place<'tcx>, Span),
944 kind: (AccessDepth, ReadOrWrite),
945 is_local_mutation_allowed: LocalMutationIsAllowed,
946 flow_state: &Flows<'cx, 'tcx>,
950 if let Activation(_, borrow_index) = rw {
951 if self.reservation_error_reported.contains(&place_span.0) {
953 "skipping access_place for activation of invalid reservation \
954 place: {:?} borrow_index: {:?}",
955 place_span.0, borrow_index
961 // Check is_empty() first because it's the common case, and doing that
962 // way we avoid the clone() call.
963 if !self.access_place_error_reported.is_empty()
964 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
967 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
973 let mutability_error = self.check_access_permissions(
976 is_local_mutation_allowed,
981 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
983 if conflict_error || mutability_error {
984 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
985 self.access_place_error_reported.insert((place_span.0, place_span.1));
989 #[instrument(level = "debug", skip(self, flow_state))]
990 fn check_access_for_conflict(
993 place_span: (Place<'tcx>, Span),
996 flow_state: &Flows<'cx, 'tcx>,
998 let mut error_reported = false;
999 let tcx = self.infcx.tcx;
1000 let body = self.body;
1001 let borrow_set = self.borrow_set.clone();
1003 // Use polonius output if it has been enabled.
1004 let polonius_output = self.polonius_output.clone();
1005 let borrows_in_scope = if let Some(polonius) = &polonius_output {
1006 let location = self.location_table.start_index(location);
1007 Either::Left(polonius.errors_at(location).iter().copied())
1009 Either::Right(flow_state.borrows.iter())
1012 each_borrow_involving_path(
1020 |this, borrow_index, borrow| match (rw, borrow.kind) {
1021 // Obviously an activation is compatible with its own
1022 // reservation (or even prior activating uses of same
1023 // borrow); so don't check if they interfere.
1025 // NOTE: *reservations* do conflict with themselves;
1026 // thus aren't injecting unsoundness w/ this check.)
1027 (Activation(_, activating), _) if activating == borrow_index => {
1029 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1030 skipping {:?} b/c activation of same borrow_index",
1034 (borrow_index, borrow),
1039 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1041 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1042 BorrowKind::Unique | BorrowKind::Mut { .. },
1043 ) => Control::Continue,
1045 (Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
1046 // This used to be a future compatibility warning (to be
1047 // disallowed on NLL). See rust-lang/rust#56254
1051 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1052 // Handled by initialization checks.
1056 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1057 // Reading from mere reservations of mutable-borrows is OK.
1058 if !is_active(&this.dominators, borrow, location) {
1059 assert!(allow_two_phase_borrow(borrow.kind));
1060 return Control::Continue;
1063 error_reported = true;
1067 .report_use_while_mutably_borrowed(location, place_span, borrow);
1068 this.buffer_error(err);
1070 ReadKind::Borrow(bk) => {
1072 this.report_conflicting_borrow(location, place_span, bk, borrow);
1073 this.buffer_error(err);
1079 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1081 Reservation(..) => {
1083 "recording invalid reservation of \
1087 this.reservation_error_reported.insert(place_span.0);
1089 Activation(_, activating) => {
1091 "observing check_place for activation of \
1092 borrow_index: {:?}",
1096 Read(..) | Write(..) => {}
1099 error_reported = true;
1101 WriteKind::MutableBorrow(bk) => {
1103 this.report_conflicting_borrow(location, place_span, bk, borrow);
1104 this.buffer_error(err);
1106 WriteKind::StorageDeadOrDrop => this
1107 .report_borrowed_value_does_not_live_long_enough(
1113 WriteKind::Mutate => {
1114 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1116 WriteKind::Move => {
1117 this.report_move_out_while_borrowed(location, place_span, borrow)
1131 place_span: (Place<'tcx>, Span),
1133 flow_state: &Flows<'cx, 'tcx>,
1135 // Write of P[i] or *P requires P init'd.
1136 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1138 // Special case: you can assign an immutable local variable
1139 // (e.g., `x = ...`) so long as it has never been initialized
1140 // before (at this point in the flow).
1141 if let Some(local) = place_span.0.as_local() {
1142 if let Mutability::Not = self.body.local_decls[local].mutability {
1143 // check for reassignments to immutable local variables
1144 self.check_if_reassignment_to_immutable_state(
1145 location, local, place_span, flow_state,
1151 // Otherwise, use the normal access permission rules.
1155 (kind, Write(WriteKind::Mutate)),
1156 LocalMutationIsAllowed::No,
1164 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1165 flow_state: &Flows<'cx, 'tcx>,
1168 &Rvalue::Ref(_ /*rgn*/, bk, place) => {
1169 let access_kind = match bk {
1170 BorrowKind::Shallow => {
1171 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1173 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1174 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1175 let wk = WriteKind::MutableBorrow(bk);
1176 if allow_two_phase_borrow(bk) {
1177 (Deep, Reservation(wk))
1188 LocalMutationIsAllowed::No,
1192 let action = if bk == BorrowKind::Shallow {
1193 InitializationRequiringAction::MatchOn
1195 InitializationRequiringAction::Borrow
1198 self.check_if_path_or_subpath_is_moved(
1201 (place.as_ref(), span),
1206 &Rvalue::AddressOf(mutability, place) => {
1207 let access_kind = match mutability {
1208 Mutability::Mut => (
1210 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1211 allow_two_phase_borrow: false,
1214 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1221 LocalMutationIsAllowed::No,
1225 self.check_if_path_or_subpath_is_moved(
1227 InitializationRequiringAction::Borrow,
1228 (place.as_ref(), span),
1233 Rvalue::ThreadLocalRef(_) => {}
1235 Rvalue::Use(operand)
1236 | Rvalue::Repeat(operand, _)
1237 | Rvalue::UnaryOp(_ /*un_op*/, operand)
1238 | Rvalue::Cast(_ /*cast_kind*/, operand, _ /*ty*/)
1239 | Rvalue::ShallowInitBox(operand, _ /*ty*/) => {
1240 self.consume_operand(location, (operand, span), flow_state)
1243 &Rvalue::CopyForDeref(place) => {
1247 (Deep, Read(ReadKind::Copy)),
1248 LocalMutationIsAllowed::No,
1252 // Finally, check if path was already moved.
1253 self.check_if_path_or_subpath_is_moved(
1255 InitializationRequiringAction::Use,
1256 (place.as_ref(), span),
1261 &(Rvalue::Len(place) | Rvalue::Discriminant(place)) => {
1262 let af = match *rvalue {
1263 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1264 Rvalue::Discriminant(..) => None,
1265 _ => unreachable!(),
1270 (Shallow(af), Read(ReadKind::Copy)),
1271 LocalMutationIsAllowed::No,
1274 self.check_if_path_or_subpath_is_moved(
1276 InitializationRequiringAction::Use,
1277 (place.as_ref(), span),
1282 Rvalue::BinaryOp(_bin_op, box (operand1, operand2))
1283 | Rvalue::CheckedBinaryOp(_bin_op, box (operand1, operand2)) => {
1284 self.consume_operand(location, (operand1, span), flow_state);
1285 self.consume_operand(location, (operand2, span), flow_state);
1288 Rvalue::NullaryOp(_op, _ty) => {
1289 // nullary ops take no dynamic input; no borrowck effect.
1292 Rvalue::Aggregate(aggregate_kind, operands) => {
1293 // We need to report back the list of mutable upvars that were
1294 // moved into the closure and subsequently used by the closure,
1295 // in order to populate our used_mut set.
1296 match **aggregate_kind {
1297 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1298 let BorrowCheckResult { used_mut_upvars, .. } =
1299 self.infcx.tcx.mir_borrowck(def_id);
1300 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1301 for field in used_mut_upvars {
1302 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1305 AggregateKind::Adt(..)
1306 | AggregateKind::Array(..)
1307 | AggregateKind::Tuple { .. } => (),
1310 for operand in operands {
1311 self.consume_operand(location, (operand, span), flow_state);
1317 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1318 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1319 // We have three possibilities here:
1320 // a. We are modifying something through a mut-ref
1321 // b. We are modifying something that is local to our parent
1322 // c. Current body is a nested closure, and we are modifying path starting from
1323 // a Place captured by our parent closure.
1325 // Handle (c), the path being modified is exactly the path captured by our parent
1326 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1327 this.used_mut_upvars.push(field);
1331 for (place_ref, proj) in place.iter_projections().rev() {
1333 if proj == ProjectionElem::Deref {
1334 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1335 // We aren't modifying a variable directly
1336 ty::Ref(_, _, hir::Mutability::Mut) => return,
1343 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1344 this.used_mut_upvars.push(field);
1350 this.used_mut.insert(place.local);
1353 // This relies on the current way that by-value
1354 // captures of a closure are copied/moved directly
1355 // when generating MIR.
1357 Operand::Move(place) | Operand::Copy(place) => {
1358 match place.as_local() {
1359 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1360 if self.body.local_decls[local].ty.is_mutable_ptr() {
1361 // The variable will be marked as mutable by the borrow.
1364 // This is an edge case where we have a `move` closure
1365 // inside a non-move closure, and the inner closure
1366 // contains a mutation:
1369 // || { move || { i += 1; }; };
1371 // In this case our usual strategy of assuming that the
1372 // variable will be captured by mutable reference is
1373 // wrong, since `i` can be copied into the inner
1374 // closure from a shared reference.
1376 // As such we have to search for the local that this
1377 // capture comes from and mark it as being used as mut.
1379 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1380 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1381 &self.move_data.inits[init_index]
1383 bug!("temporary should be initialized exactly once")
1386 let InitLocation::Statement(loc) = init.location else {
1387 bug!("temporary initialized in arguments")
1390 let body = self.body;
1391 let bbd = &body[loc.block];
1392 let stmt = &bbd.statements[loc.statement_index];
1393 debug!("temporary assigned in: stmt={:?}", stmt);
1395 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1397 propagate_closure_used_mut_place(self, source);
1400 "closures should only capture user variables \
1401 or references to user variables"
1405 _ => propagate_closure_used_mut_place(self, place),
1408 Operand::Constant(..) => {}
1415 (operand, span): (&'cx Operand<'tcx>, Span),
1416 flow_state: &Flows<'cx, 'tcx>,
1419 Operand::Copy(place) => {
1420 // copy of place: check if this is "copy of frozen path"
1421 // (FIXME: see check_loans.rs)
1425 (Deep, Read(ReadKind::Copy)),
1426 LocalMutationIsAllowed::No,
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::Move(place) => {
1439 // move of place: check if this is move of already borrowed path
1443 (Deep, Write(WriteKind::Move)),
1444 LocalMutationIsAllowed::Yes,
1448 // Finally, check if path was already moved.
1449 self.check_if_path_or_subpath_is_moved(
1451 InitializationRequiringAction::Use,
1452 (place.as_ref(), span),
1456 Operand::Constant(_) => {}
1460 /// Checks whether a borrow of this place is invalidated when the function
1462 #[instrument(level = "debug", skip(self))]
1463 fn check_for_invalidation_at_exit(
1466 borrow: &BorrowData<'tcx>,
1469 let place = borrow.borrowed_place;
1470 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1472 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1473 // we just know that all locals are dropped at function exit (otherwise
1474 // we'll have a memory leak) and assume that all statics have a destructor.
1476 // FIXME: allow thread-locals to borrow other thread locals?
1478 let (might_be_alive, will_be_dropped) =
1479 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1480 // Thread-locals might be dropped after the function exits
1481 // We have to dereference the outer reference because
1482 // borrows don't conflict behind shared references.
1483 root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
1486 (false, self.locals_are_invalidated_at_exit)
1489 if !will_be_dropped {
1490 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1494 let sd = if might_be_alive { Deep } else { Shallow(None) };
1496 if places_conflict::borrow_conflicts_with_place(
1503 places_conflict::PlaceConflictBias::Overlap,
1505 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1506 // FIXME: should be talking about the region lifetime instead
1507 // of just a span here.
1508 let span = self.infcx.tcx.sess.source_map().end_point(span);
1509 self.report_borrowed_value_does_not_live_long_enough(
1518 /// Reports an error if this is a borrow of local data.
1519 /// This is called for all Yield expressions on movable generators
1520 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1521 debug!("check_for_local_borrow({:?})", borrow);
1523 if borrow_of_local_data(borrow.borrowed_place) {
1524 let err = self.cannot_borrow_across_generator_yield(
1525 self.retrieve_borrow_spans(borrow).var_or_use(),
1529 self.buffer_error(err);
1533 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1534 // Two-phase borrow support: For each activation that is newly
1535 // generated at this statement, check if it interferes with
1537 let borrow_set = self.borrow_set.clone();
1538 for &borrow_index in borrow_set.activations_at_location(location) {
1539 let borrow = &borrow_set[borrow_index];
1541 // only mutable borrows should be 2-phase
1542 assert!(match borrow.kind {
1543 BorrowKind::Shared | BorrowKind::Shallow => false,
1544 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1549 (borrow.borrowed_place, span),
1550 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1551 LocalMutationIsAllowed::No,
1554 // We do not need to call `check_if_path_or_subpath_is_moved`
1555 // again, as we already called it when we made the
1556 // initial reservation.
1560 fn check_if_reassignment_to_immutable_state(
1564 place_span: (Place<'tcx>, Span),
1565 flow_state: &Flows<'cx, 'tcx>,
1567 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1569 // Check if any of the initializations of `local` have happened yet:
1570 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1571 // And, if so, report an error.
1572 let init = &self.move_data.inits[init_index];
1573 let span = init.span(&self.body);
1574 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1578 fn check_if_full_path_is_moved(
1581 desired_action: InitializationRequiringAction,
1582 place_span: (PlaceRef<'tcx>, Span),
1583 flow_state: &Flows<'cx, 'tcx>,
1585 let maybe_uninits = &flow_state.uninits;
1589 // 1. Move of `a.b.c`, use of `a.b.c`
1590 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1591 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1592 // partial initialization support, one might have `a.x`
1593 // initialized but not `a.b`.
1597 // 4. Move of `a.b.c`, use of `a.b.d`
1598 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1599 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1600 // must have been initialized for the use to be sound.
1601 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1603 // The dataflow tracks shallow prefixes distinctly (that is,
1604 // field-accesses on P distinctly from P itself), in order to
1605 // track substructure initialization separately from the whole
1608 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1609 // which we have a MovePath is `a.b`, then that means that the
1610 // initialization state of `a.b` is all we need to inspect to
1611 // know if `a.b.c` is valid (and from that we infer that the
1612 // dereference and `.d` access is also valid, since we assume
1613 // `a.b.c` is assigned a reference to an initialized and
1614 // well-formed record structure.)
1616 // Therefore, if we seek out the *closest* prefix for which we
1617 // have a MovePath, that should capture the initialization
1618 // state for the place scenario.
1620 // This code covers scenarios 1, 2, and 3.
1622 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1623 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1624 if maybe_uninits.contains(mpi) {
1625 self.report_use_of_moved_or_uninitialized(
1628 (prefix, place_span.0, place_span.1),
1631 } // Only query longest prefix with a MovePath, not further
1632 // ancestors; dataflow recurs on children when parents
1633 // move (to support partial (re)inits).
1635 // (I.e., querying parents breaks scenario 7; but may want
1636 // to do such a query based on partial-init feature-gate.)
1639 /// Subslices correspond to multiple move paths, so we iterate through the
1640 /// elements of the base array. For each element we check
1642 /// * Does this element overlap with our slice.
1643 /// * Is any part of it uninitialized.
1644 fn check_if_subslice_element_is_moved(
1647 desired_action: InitializationRequiringAction,
1648 place_span: (PlaceRef<'tcx>, Span),
1649 maybe_uninits: &ChunkedBitSet<MovePathIndex>,
1653 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1654 let move_paths = &self.move_data.move_paths;
1656 let root_path = &move_paths[mpi];
1657 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1658 let last_proj = child_move_path.place.projection.last().unwrap();
1659 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1660 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1662 if (from..to).contains(offset) {
1664 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1665 maybe_uninits.contains(mpi)
1668 if let Some(uninit_child) = uninit_child {
1669 self.report_use_of_moved_or_uninitialized(
1672 (place_span.0, place_span.0, place_span.1),
1675 return; // don't bother finding other problems.
1683 fn check_if_path_or_subpath_is_moved(
1686 desired_action: InitializationRequiringAction,
1687 place_span: (PlaceRef<'tcx>, Span),
1688 flow_state: &Flows<'cx, 'tcx>,
1690 let maybe_uninits = &flow_state.uninits;
1694 // 1. Move of `a.b.c`, use of `a` or `a.b`
1695 // partial initialization support, one might have `a.x`
1696 // initialized but not `a.b`.
1697 // 2. All bad scenarios from `check_if_full_path_is_moved`
1701 // 3. Move of `a.b.c`, use of `a.b.d`
1702 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1703 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1704 // must have been initialized for the use to be sound.
1705 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1707 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1709 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1710 place_span.0.last_projection()
1712 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1713 if let ty::Array(..) = place_ty.ty.kind() {
1714 self.check_if_subslice_element_is_moved(
1717 (place_base, place_span.1),
1726 // A move of any shallow suffix of `place` also interferes
1727 // with an attempt to use `place`. This is scenario 3 above.
1729 // (Distinct from handling of scenarios 1+2+4 above because
1730 // `place` does not interfere with suffixes of its prefixes,
1731 // e.g., `a.b.c` does not interfere with `a.b.d`)
1733 // This code covers scenario 1.
1735 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1736 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1737 let uninit_mpi = self
1739 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1741 if let Some(uninit_mpi) = uninit_mpi {
1742 self.report_use_of_moved_or_uninitialized(
1745 (place_span.0, place_span.0, place_span.1),
1748 return; // don't bother finding other problems.
1753 /// Currently MoveData does not store entries for all places in
1754 /// the input MIR. For example it will currently filter out
1755 /// places that are Copy; thus we do not track places of shared
1756 /// reference type. This routine will walk up a place along its
1757 /// prefixes, searching for a foundational place that *is*
1758 /// tracked in the MoveData.
1760 /// An Err result includes a tag indicated why the search failed.
1761 /// Currently this can only occur if the place is built off of a
1762 /// static variable, as we do not track those in the MoveData.
1763 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1764 match self.move_data.rev_lookup.find(place) {
1765 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1766 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1768 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1772 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1773 // If returns None, then there is no move path corresponding
1774 // to a direct owner of `place` (which means there is nothing
1775 // that borrowck tracks for its analysis).
1777 match self.move_data.rev_lookup.find(place) {
1778 LookupResult::Parent(_) => None,
1779 LookupResult::Exact(mpi) => Some(mpi),
1783 fn check_if_assigned_path_is_moved(
1786 (place, span): (Place<'tcx>, Span),
1787 flow_state: &Flows<'cx, 'tcx>,
1789 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1791 // None case => assigning to `x` does not require `x` be initialized.
1792 for (place_base, elem) in place.iter_projections().rev() {
1794 ProjectionElem::Index(_/*operand*/) |
1795 ProjectionElem::OpaqueCast(_) |
1796 ProjectionElem::ConstantIndex { .. } |
1797 // assigning to P[i] requires P to be valid.
1798 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1799 // assigning to (P->variant) is okay if assigning to `P` is okay
1801 // FIXME: is this true even if P is an adt with a dtor?
1804 // assigning to (*P) requires P to be initialized
1805 ProjectionElem::Deref => {
1806 self.check_if_full_path_is_moved(
1807 location, InitializationRequiringAction::Use,
1808 (place_base, span), flow_state);
1809 // (base initialized; no need to
1814 ProjectionElem::Subslice { .. } => {
1815 panic!("we don't allow assignments to subslices, location: {:?}",
1819 ProjectionElem::Field(..) => {
1820 // if type of `P` has a dtor, then
1821 // assigning to `P.f` requires `P` itself
1822 // be already initialized
1823 let tcx = self.infcx.tcx;
1824 let base_ty = place_base.ty(self.body(), tcx).ty;
1825 match base_ty.kind() {
1826 ty::Adt(def, _) if def.has_dtor(tcx) => {
1827 self.check_if_path_or_subpath_is_moved(
1828 location, InitializationRequiringAction::Assignment,
1829 (place_base, span), flow_state);
1831 // (base initialized; no need to
1836 // Once `let s; s.x = V; read(s.x);`,
1837 // is allowed, remove this match arm.
1838 ty::Adt(..) | ty::Tuple(..) => {
1839 check_parent_of_field(self, location, place_base, span, flow_state);
1841 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1842 // partial initialization, do not complain about unnecessary `mut` on
1843 // an attempt to do a partial initialization.
1844 self.used_mut.insert(place.local);
1853 fn check_parent_of_field<'cx, 'tcx>(
1854 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1856 base: PlaceRef<'tcx>,
1858 flow_state: &Flows<'cx, 'tcx>,
1860 // rust-lang/rust#21232: Until Rust allows reads from the
1861 // initialized parts of partially initialized structs, we
1862 // will, starting with the 2018 edition, reject attempts
1863 // to write to structs that are not fully initialized.
1865 // In other words, *until* we allow this:
1867 // 1. `let mut s; s.x = Val; read(s.x);`
1869 // we will for now disallow this:
1871 // 2. `let mut s; s.x = Val;`
1875 // 3. `let mut s = ...; drop(s); s.x=Val;`
1877 // This does not use check_if_path_or_subpath_is_moved,
1878 // because we want to *allow* reinitializations of fields:
1879 // e.g., want to allow
1881 // `let mut s = ...; drop(s.x); s.x=Val;`
1883 // This does not use check_if_full_path_is_moved on
1884 // `base`, because that would report an error about the
1885 // `base` as a whole, but in this scenario we *really*
1886 // want to report an error about the actual thing that was
1887 // moved, which may be some prefix of `base`.
1889 // Shallow so that we'll stop at any dereference; we'll
1890 // report errors about issues with such bases elsewhere.
1891 let maybe_uninits = &flow_state.uninits;
1893 // Find the shortest uninitialized prefix you can reach
1894 // without going over a Deref.
1895 let mut shortest_uninit_seen = None;
1896 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1897 let Some(mpi) = this.move_path_for_place(prefix) else { continue };
1899 if maybe_uninits.contains(mpi) {
1901 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1902 shortest_uninit_seen,
1905 shortest_uninit_seen = Some((prefix, mpi));
1907 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1911 if let Some((prefix, mpi)) = shortest_uninit_seen {
1912 // Check for a reassignment into an uninitialized field of a union (for example,
1913 // after a move out). In this case, do not report an error here. There is an
1914 // exception, if this is the first assignment into the union (that is, there is
1915 // no move out from an earlier location) then this is an attempt at initialization
1916 // of the union - we should error in that case.
1917 let tcx = this.infcx.tcx;
1918 if base.ty(this.body(), tcx).ty.is_union() {
1919 if this.move_data.path_map[mpi].iter().any(|moi| {
1920 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1926 this.report_use_of_moved_or_uninitialized(
1928 InitializationRequiringAction::PartialAssignment,
1929 (prefix, base, span),
1936 /// Checks the permissions for the given place and read or write kind
1938 /// Returns `true` if an error is reported.
1939 fn check_access_permissions(
1941 (place, span): (Place<'tcx>, Span),
1943 is_local_mutation_allowed: LocalMutationIsAllowed,
1944 flow_state: &Flows<'cx, 'tcx>,
1948 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1949 place, kind, is_local_mutation_allowed
1956 Reservation(WriteKind::MutableBorrow(
1957 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1959 | Write(WriteKind::MutableBorrow(
1960 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1962 let is_local_mutation_allowed = match borrow_kind {
1963 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1964 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1965 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
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::MutableBorrow;
1974 the_place_err = place_err;
1978 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1979 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1981 self.add_used_mut(root_place, flow_state);
1985 error_access = AccessKind::Mutate;
1986 the_place_err = place_err;
1993 | WriteKind::StorageDeadOrDrop
1994 | WriteKind::MutableBorrow(BorrowKind::Shared)
1995 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1999 | WriteKind::StorageDeadOrDrop
2000 | WriteKind::MutableBorrow(BorrowKind::Shared)
2001 | WriteKind::MutableBorrow(BorrowKind::Shallow),
2003 if self.is_mutable(place.as_ref(), is_local_mutation_allowed).is_err()
2004 && !self.has_buffered_errors()
2006 // rust-lang/rust#46908: In pure NLL mode this code path should be
2007 // unreachable, but we use `delay_span_bug` because we can hit this when
2008 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
2009 // enabled. We don't want to ICE for that case, as other errors will have
2010 // been emitted (#52262).
2011 self.infcx.tcx.sess.delay_span_bug(
2014 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2022 // permission checks are done at Reservation point.
2028 | BorrowKind::Mut { .. }
2029 | BorrowKind::Shared
2030 | BorrowKind::Shallow,
2034 // Access authorized
2039 // rust-lang/rust#21232, #54986: during period where we reject
2040 // partial initialization, do not complain about mutability
2041 // errors except for actual mutation (as opposed to an attempt
2042 // to do a partial initialization).
2043 let previously_initialized =
2044 self.is_local_ever_initialized(place.local, flow_state).is_some();
2046 // at this point, we have set up the error reporting state.
2047 if previously_initialized {
2048 self.report_mutability_error(place, span, the_place_err, error_access, location);
2055 fn is_local_ever_initialized(
2058 flow_state: &Flows<'cx, 'tcx>,
2059 ) -> Option<InitIndex> {
2060 let mpi = self.move_data.rev_lookup.find_local(local);
2061 let ii = &self.move_data.init_path_map[mpi];
2062 ii.into_iter().find(|&&index| flow_state.ever_inits.contains(index)).copied()
2065 /// Adds the place into the used mutable variables set
2066 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2068 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2069 // If the local may have been initialized, and it is now currently being
2070 // mutated, then it is justified to be annotated with the `mut`
2071 // keyword, since the mutation may be a possible reassignment.
2072 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2073 && self.is_local_ever_initialized(local, flow_state).is_some()
2075 self.used_mut.insert(local);
2080 place_projection: _,
2081 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2085 place_projection: place_projection @ [.., _],
2086 is_local_mutation_allowed: _,
2088 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2090 projection: place_projection,
2092 self.used_mut_upvars.push(field);
2098 /// Whether this value can be written or borrowed mutably.
2099 /// Returns the root place if the place passed in is a projection.
2102 place: PlaceRef<'tcx>,
2103 is_local_mutation_allowed: LocalMutationIsAllowed,
2104 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2105 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2106 match place.last_projection() {
2108 let local = &self.body.local_decls[place.local];
2109 match local.mutability {
2110 Mutability::Not => match is_local_mutation_allowed {
2111 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2112 place_local: place.local,
2113 place_projection: place.projection,
2114 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2116 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2117 place_local: place.local,
2118 place_projection: place.projection,
2119 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2121 LocalMutationIsAllowed::No => Err(place),
2123 Mutability::Mut => Ok(RootPlace {
2124 place_local: place.local,
2125 place_projection: place.projection,
2126 is_local_mutation_allowed,
2130 Some((place_base, elem)) => {
2132 ProjectionElem::Deref => {
2133 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2135 // Check the kind of deref to decide
2136 match base_ty.kind() {
2137 ty::Ref(_, _, mutbl) => {
2139 // Shared borrowed data is never mutable
2140 hir::Mutability::Not => Err(place),
2141 // Mutably borrowed data is mutable, but only if we have a
2142 // unique path to the `&mut`
2143 hir::Mutability::Mut => {
2144 let mode = match self.is_upvar_field_projection(place) {
2145 Some(field) if self.upvars[field.index()].by_ref => {
2146 is_local_mutation_allowed
2148 _ => LocalMutationIsAllowed::Yes,
2151 self.is_mutable(place_base, mode)
2155 ty::RawPtr(tnm) => {
2157 // `*const` raw pointers are not mutable
2158 hir::Mutability::Not => Err(place),
2159 // `*mut` raw pointers are always mutable, regardless of
2160 // context. The users have to check by themselves.
2161 hir::Mutability::Mut => Ok(RootPlace {
2162 place_local: place.local,
2163 place_projection: place.projection,
2164 is_local_mutation_allowed,
2168 // `Box<T>` owns its content, so mutable if its location is mutable
2169 _ if base_ty.is_box() => {
2170 self.is_mutable(place_base, is_local_mutation_allowed)
2172 // Deref should only be for reference, pointers or boxes
2173 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2176 // All other projections are owned by their base path, so mutable if
2177 // base path is mutable
2178 ProjectionElem::Field(..)
2179 | ProjectionElem::Index(..)
2180 | ProjectionElem::ConstantIndex { .. }
2181 | ProjectionElem::Subslice { .. }
2182 | ProjectionElem::OpaqueCast { .. }
2183 | ProjectionElem::Downcast(..) => {
2184 let upvar_field_projection = self.is_upvar_field_projection(place);
2185 if let Some(field) = upvar_field_projection {
2186 let upvar = &self.upvars[field.index()];
2188 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2189 place={:?}, place_base={:?}",
2190 upvar, is_local_mutation_allowed, place, place_base
2192 match (upvar.place.mutability, is_local_mutation_allowed) {
2195 LocalMutationIsAllowed::No
2196 | LocalMutationIsAllowed::ExceptUpvars,
2198 (Mutability::Not, LocalMutationIsAllowed::Yes)
2199 | (Mutability::Mut, _) => {
2200 // Subtle: this is an upvar
2201 // reference, so it looks like
2202 // `self.foo` -- we want to double
2203 // check that the location `*self`
2204 // is mutable (i.e., this is not a
2205 // `Fn` closure). But if that
2206 // check succeeds, we want to
2207 // *blame* the mutability on
2208 // `place` (that is,
2209 // `self.foo`). This is used to
2210 // propagate the info about
2211 // whether mutability declarations
2212 // are used outwards, so that we register
2213 // the outer variable as mutable. Otherwise a
2214 // test like this fails to record the `mut`
2218 // fn foo<F: FnOnce()>(_f: F) { }
2220 // let var = Vec::new();
2227 self.is_mutable(place_base, is_local_mutation_allowed)?;
2229 place_local: place.local,
2230 place_projection: place.projection,
2231 is_local_mutation_allowed,
2236 self.is_mutable(place_base, is_local_mutation_allowed)
2244 /// If `place` is a field projection, and the field is being projected from a closure type,
2245 /// then returns the index of the field being projected. Note that this closure will always
2246 /// be `self` in the current MIR, because that is the only time we directly access the fields
2247 /// of a closure type.
2248 fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2249 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2254 use rustc_errors::ErrorGuaranteed;
2258 pub struct BorrowckErrors<'tcx> {
2260 /// This field keeps track of move errors that are to be reported for given move indices.
2262 /// There are situations where many errors can be reported for a single move out (see #53807)
2263 /// and we want only the best of those errors.
2265 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
2266 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
2267 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
2268 /// all move errors have been reported, any diagnostics in this map are added to the buffer
2271 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
2272 /// when errors in the map are being re-added to the error buffer so that errors with the
2273 /// same primary span come out in a consistent order.
2274 buffered_move_errors:
2275 BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>)>,
2276 /// Diagnostics to be reported buffer.
2277 buffered: Vec<Diagnostic>,
2278 /// Set to Some if we emit an error during borrowck
2279 tainted_by_errors: Option<ErrorGuaranteed>,
2282 impl<'tcx> BorrowckErrors<'tcx> {
2283 pub fn new(tcx: TyCtxt<'tcx>) -> Self {
2286 buffered_move_errors: BTreeMap::new(),
2287 buffered: Default::default(),
2288 tainted_by_errors: None,
2292 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2293 if let None = self.tainted_by_errors {
2294 self.tainted_by_errors = Some(
2297 .delay_span_bug(t.span.clone(), "diagnostic buffered but not emitted"),
2300 t.buffer(&mut self.buffered);
2303 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2304 t.buffer(&mut self.buffered);
2307 pub fn set_tainted_by_errors(&mut self, e: ErrorGuaranteed) {
2308 self.tainted_by_errors = Some(e);
2312 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
2313 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2314 self.errors.buffer_error(t);
2317 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2318 self.errors.buffer_non_error_diag(t);
2321 pub fn buffer_move_error(
2323 move_out_indices: Vec<MoveOutIndex>,
2324 place_and_err: (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>),
2326 if let Some((_, diag)) =
2327 self.errors.buffered_move_errors.insert(move_out_indices, place_and_err)
2329 // Cancel the old diagnostic so we don't ICE
2337 pub fn emit_errors(&mut self) -> Option<ErrorGuaranteed> {
2338 // Buffer any move errors that we collected and de-duplicated.
2339 for (_, (_, diag)) in std::mem::take(&mut self.errors.buffered_move_errors) {
2340 // We have already set tainted for this error, so just buffer it.
2341 diag.buffer(&mut self.errors.buffered);
2344 if !self.errors.buffered.is_empty() {
2345 self.errors.buffered.sort_by_key(|diag| diag.sort_span);
2347 for mut diag in self.errors.buffered.drain(..) {
2348 self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
2352 self.errors.tainted_by_errors
2355 pub fn has_buffered_errors(&self) -> bool {
2356 self.errors.buffered.is_empty()
2359 pub fn has_move_error(
2361 move_out_indices: &[MoveOutIndex],
2362 ) -> Option<&(PlaceRef<'tcx>, DiagnosticBuilder<'cx, ErrorGuaranteed>)> {
2363 self.errors.buffered_move_errors.get(move_out_indices)
2368 /// The degree of overlap between 2 places for borrow-checking.
2370 /// The places might partially overlap - in this case, we give
2371 /// up and say that they might conflict. This occurs when
2372 /// different fields of a union are borrowed. For example,
2373 /// if `u` is a union, we have no way of telling how disjoint
2374 /// `u.a.x` and `a.b.y` are.
2376 /// The places have the same type, and are either completely disjoint
2377 /// or equal - i.e., they can't "partially" overlap as can occur with
2378 /// unions. This is the "base case" on which we recur for extensions
2381 /// The places are disjoint, so we know all extensions of them
2382 /// will also be disjoint.