1 //! This query borrow-checks the MIR to (further) ensure it is not broken.
3 #![allow(rustc::potential_query_instability)]
4 #![feature(box_patterns)]
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_errors::{Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
23 use rustc_hir::def_id::LocalDefId;
24 use rustc_index::bit_set::ChunkedBitSet;
25 use rustc_index::vec::IndexVec;
26 use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
27 use rustc_middle::mir::{
28 traversal, Body, ClearCrossCrate, Local, Location, Mutability, Operand, Place, PlaceElem,
29 PlaceRef, VarDebugInfoContents,
31 use rustc_middle::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
32 use rustc_middle::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
33 use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
34 use rustc_middle::ty::query::Providers;
35 use rustc_middle::ty::{self, CapturedPlace, ParamEnv, RegionVid, TyCtxt};
36 use rustc_session::lint::builtin::UNUSED_MUT;
37 use rustc_span::{Span, Symbol};
40 use smallvec::SmallVec;
41 use std::cell::RefCell;
42 use std::collections::BTreeMap;
45 use rustc_mir_dataflow::impls::{
46 EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
48 use rustc_mir_dataflow::move_paths::{InitIndex, MoveOutIndex, MovePathIndex};
49 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
50 use rustc_mir_dataflow::Analysis;
51 use rustc_mir_dataflow::MoveDataParamEnv;
53 use crate::session_diagnostics::VarNeedNotMut;
55 use self::diagnostics::{AccessKind, RegionName};
56 use self::location::LocationTable;
57 use self::prefixes::PrefixSet;
60 use self::path_utils::*;
64 mod constraint_generation;
72 mod member_constraints;
80 mod session_diagnostics;
82 mod universal_regions;
85 // A public API provided for the Rust compiler consumers.
88 use borrow_set::{BorrowData, BorrowSet};
89 use dataflow::{BorrowIndex, BorrowckFlowState as Flows, BorrowckResults, Borrows};
90 use nll::{PoloniusOutput, ToRegionVid};
91 use place_ext::PlaceExt;
92 use places_conflict::{places_conflict, PlaceConflictBias};
93 use region_infer::RegionInferenceContext;
95 // FIXME(eddyb) perhaps move this somewhere more centrally.
98 place: CapturedPlace<'tcx>,
100 /// If true, the capture is behind a reference.
104 /// Associate some local constants with the `'tcx` lifetime
105 struct TyCtxtConsts<'tcx>(TyCtxt<'tcx>);
106 impl<'tcx> TyCtxtConsts<'tcx> {
107 const DEREF_PROJECTION: &'tcx [PlaceElem<'tcx>; 1] = &[ProjectionElem::Deref];
110 pub fn provide(providers: &mut Providers) {
111 *providers = Providers {
112 mir_borrowck: |tcx, did| {
113 if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
114 tcx.mir_borrowck_const_arg(def)
116 mir_borrowck(tcx, ty::WithOptConstParam::unknown(did))
119 mir_borrowck_const_arg: |tcx, (did, param_did)| {
120 mir_borrowck(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
126 fn mir_borrowck<'tcx>(
128 def: ty::WithOptConstParam<LocalDefId>,
129 ) -> &'tcx BorrowCheckResult<'tcx> {
130 let (input_body, promoted) = tcx.mir_promoted(def);
131 debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
132 let hir_owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;
134 let opt_closure_req = tcx
136 .with_opaque_type_inference(DefiningAnchor::Bind(hir_owner))
138 let input_body: &Body<'_> = &input_body.borrow();
139 let promoted: &IndexVec<_, _> = &promoted.borrow();
140 do_mir_borrowck(&infcx, input_body, promoted, false).0
142 debug!("mir_borrowck done");
144 tcx.arena.alloc(opt_closure_req)
147 /// Perform the actual borrow checking.
149 /// If `return_body_with_facts` is true, then return the body with non-erased
150 /// region ids on which the borrow checking was performed together with Polonius
152 #[instrument(skip(infcx, input_body, input_promoted), fields(id=?input_body.source.with_opt_param().as_local().unwrap()), level = "debug")]
153 fn do_mir_borrowck<'a, 'tcx>(
154 infcx: &InferCtxt<'a, 'tcx>,
155 input_body: &Body<'tcx>,
156 input_promoted: &IndexVec<Promoted, Body<'tcx>>,
157 return_body_with_facts: bool,
158 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
159 let def = input_body.source.with_opt_param().as_local().unwrap();
164 let param_env = tcx.param_env(def.did);
166 let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
167 for var_debug_info in &input_body.var_debug_info {
168 if let VarDebugInfoContents::Place(place) = var_debug_info.value {
169 if let Some(local) = place.as_local() {
170 if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name {
172 var_debug_info.source_info.span,
173 "local {:?} has many names (`{}` vs `{}`)",
179 local_names[local] = Some(var_debug_info.name);
184 let mut errors = error::BorrowckErrors::new();
186 // Gather the upvars of a closure, if any.
187 let tables = tcx.typeck_opt_const_arg(def);
188 if let Some(ErrorGuaranteed { .. }) = tables.tainted_by_errors {
189 infcx.set_tainted_by_errors();
190 errors.set_tainted_by_errors();
192 let upvars: Vec<_> = tables
193 .closure_min_captures_flattened(def.did)
194 .map(|captured_place| {
195 let capture = captured_place.info.capture_kind;
196 let by_ref = match capture {
197 ty::UpvarCapture::ByValue => false,
198 ty::UpvarCapture::ByRef(..) => true,
200 Upvar { place: captured_place.clone(), by_ref }
204 // Replace all regions with fresh inference variables. This
205 // requires first making our own copy of the MIR. This copy will
206 // be modified (in place) to contain non-lexical lifetimes. It
207 // will have a lifetime tied to the inference context.
208 let mut body_owned = input_body.clone();
209 let mut promoted = input_promoted.clone();
211 nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
212 let body = &body_owned; // no further changes
214 let location_table_owned = LocationTable::new(body);
215 let location_table = &location_table_owned;
217 let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
218 match MoveData::gather_moves(&body, tcx, param_env) {
219 Ok((_, move_data)) => (move_data, Vec::new()),
220 Err((move_data, move_errors)) => (move_data, move_errors),
222 let promoted_errors = promoted
224 .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
226 let mdpe = MoveDataParamEnv { move_data, param_env };
228 let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
229 .into_engine(tcx, &body)
230 .pass_name("borrowck")
231 .iterate_to_fixpoint()
232 .into_results_cursor(&body);
234 let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def.did).is_fn_or_closure();
236 Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
238 let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.unstable_opts.polonius;
240 // Compute non-lexical lifetimes.
248 } = nll::compute_regions(
262 // Dump MIR results into a file, if that is enabled. This let us
263 // write unit-tests, as well as helping with debugging.
264 nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
266 // We also have a `#[rustc_regions]` annotation that causes us to dump
268 nll::dump_annotation(
277 // The various `flow_*` structures can be large. We drop `flow_inits` here
278 // so it doesn't overlap with the others below. This reduces peak memory
279 // usage significantly on some benchmarks.
282 let regioncx = Rc::new(regioncx);
284 let flow_borrows = Borrows::new(tcx, body, ®ioncx, &borrow_set)
285 .into_engine(tcx, body)
286 .pass_name("borrowck")
287 .iterate_to_fixpoint();
288 let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &mdpe)
289 .into_engine(tcx, body)
290 .pass_name("borrowck")
291 .iterate_to_fixpoint();
292 let flow_ever_inits = EverInitializedPlaces::new(tcx, body, &mdpe)
293 .into_engine(tcx, body)
294 .pass_name("borrowck")
295 .iterate_to_fixpoint();
297 let movable_generator =
298 // The first argument is the generator type passed by value
299 if let Some(local) = body.local_decls.raw.get(1)
300 // Get the interior types and substs which typeck computed
301 && let ty::Generator(_, _, hir::Movability::Static) = local.ty.kind()
308 for (idx, move_data_results) in promoted_errors {
309 let promoted_body = &promoted[idx];
311 if let Err((move_data, move_errors)) = move_data_results {
312 let mut promoted_mbcx = MirBorrowckCtxt {
316 move_data: &move_data,
317 location_table, // no need to create a real one for the promoted, it is not used
319 fn_self_span_reported: Default::default(),
320 locals_are_invalidated_at_exit,
321 access_place_error_reported: Default::default(),
322 reservation_error_reported: Default::default(),
323 uninitialized_error_reported: Default::default(),
324 regioncx: regioncx.clone(),
325 used_mut: Default::default(),
326 used_mut_upvars: SmallVec::new(),
327 borrow_set: Rc::clone(&borrow_set),
328 dominators: Dominators::dummy(), // not used
330 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
331 region_names: RefCell::default(),
332 next_region_name: RefCell::new(1),
333 polonius_output: None,
336 promoted_mbcx.report_move_errors(move_errors);
337 errors = promoted_mbcx.errors;
341 let dominators = body.basic_blocks.dominators();
343 let mut mbcx = MirBorrowckCtxt {
347 move_data: &mdpe.move_data,
350 locals_are_invalidated_at_exit,
351 fn_self_span_reported: Default::default(),
352 access_place_error_reported: Default::default(),
353 reservation_error_reported: Default::default(),
354 uninitialized_error_reported: Default::default(),
355 regioncx: Rc::clone(®ioncx),
356 used_mut: Default::default(),
357 used_mut_upvars: SmallVec::new(),
358 borrow_set: Rc::clone(&borrow_set),
362 region_names: RefCell::default(),
363 next_region_name: RefCell::new(1),
368 // Compute and report region errors, if any.
369 mbcx.report_region_errors(nll_errors);
371 let results = BorrowckResults {
372 ever_inits: flow_ever_inits,
373 uninits: flow_uninits,
374 borrows: flow_borrows,
377 mbcx.report_move_errors(move_errors);
379 rustc_mir_dataflow::visit_results(
381 traversal::reverse_postorder(body).map(|(bb, _)| bb),
386 // For each non-user used mutable variable, check if it's been assigned from
387 // a user-declared local. If so, then put that local into the used_mut set.
388 // Note that this set is expected to be small - only upvars from closures
389 // would have a chance of erroneously adding non-user-defined mutable vars
391 let temporary_used_locals: FxHashSet<Local> = mbcx
394 .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
397 // For the remaining unused locals that are marked as mutable, we avoid linting any that
398 // were never initialized. These locals may have been removed as unreachable code; or will be
399 // linted as unused variables.
400 let unused_mut_locals =
401 mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
402 mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
404 debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
405 let used_mut = std::mem::take(&mut mbcx.used_mut);
406 for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
407 let local_decl = &mbcx.body.local_decls[local];
408 let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
409 ClearCrossCrate::Set(data) => data.lint_root,
413 // Skip over locals that begin with an underscore or have no name
414 match mbcx.local_names[local] {
416 if name.as_str().starts_with('_') {
423 let span = local_decl.source_info.span;
424 if span.desugaring_kind().is_some() {
425 // If the `mut` arises as part of a desugaring, we should ignore it.
429 let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
431 tcx.emit_spanned_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
434 let tainted_by_errors = mbcx.emit_errors();
436 let result = BorrowCheckResult {
437 concrete_opaque_types: opaque_type_values,
438 closure_requirements: opt_closure_req,
439 used_mut_upvars: mbcx.used_mut_upvars,
443 let body_with_facts = if return_body_with_facts {
444 let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
445 Some(Box::new(BodyWithBorrowckFacts {
447 input_facts: *polonius_input.expect("Polonius input facts were not generated"),
449 location_table: location_table_owned,
455 debug!("do_mir_borrowck: result = {:#?}", result);
457 (result, body_with_facts)
460 /// A `Body` with information computed by the borrow checker. This struct is
461 /// intended to be consumed by compiler consumers.
463 /// We need to include the MIR body here because the region identifiers must
464 /// match the ones in the Polonius facts.
465 pub struct BodyWithBorrowckFacts<'tcx> {
466 /// A mir body that contains region identifiers.
467 pub body: Body<'tcx>,
468 /// Polonius input facts.
469 pub input_facts: AllFacts,
470 /// Polonius output facts.
471 pub output_facts: Rc<self::nll::PoloniusOutput>,
472 /// The table that maps Polonius points to locations in the table.
473 pub location_table: LocationTable,
476 struct MirBorrowckCtxt<'cx, 'tcx> {
477 infcx: &'cx InferCtxt<'cx, 'tcx>,
478 param_env: ParamEnv<'tcx>,
479 body: &'cx Body<'tcx>,
480 move_data: &'cx MoveData<'tcx>,
482 /// Map from MIR `Location` to `LocationIndex`; created
483 /// when MIR borrowck begins.
484 location_table: &'cx LocationTable,
486 movable_generator: bool,
487 /// This keeps track of whether local variables are free-ed when the function
488 /// exits even without a `StorageDead`, which appears to be the case for
491 /// I'm not sure this is the right approach - @eddyb could you try and
493 locals_are_invalidated_at_exit: bool,
494 /// This field keeps track of when borrow errors are reported in the access_place function
495 /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
496 /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
497 /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
499 access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
500 /// This field keeps track of when borrow conflict errors are reported
501 /// for reservations, so that we don't report seemingly duplicate
502 /// errors for corresponding activations.
504 // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
505 // but it is currently inconvenient to track down the `BorrowIndex`
506 // at the time we detect and report a reservation error.
507 reservation_error_reported: FxHashSet<Place<'tcx>>,
508 /// This fields keeps track of the `Span`s that we have
509 /// used to report extra information for `FnSelfUse`, to avoid
510 /// unnecessarily verbose errors.
511 fn_self_span_reported: FxHashSet<Span>,
512 /// This field keeps track of errors reported in the checking of uninitialized variables,
513 /// so that we don't report seemingly duplicate errors.
514 uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
515 /// This field keeps track of all the local variables that are declared mut and are mutated.
516 /// Used for the warning issued by an unused mutable local variable.
517 used_mut: FxHashSet<Local>,
518 /// If the function we're checking is a closure, then we'll need to report back the list of
519 /// mutable upvars that have been used. This field keeps track of them.
520 used_mut_upvars: SmallVec<[Field; 8]>,
521 /// Region inference context. This contains the results from region inference and lets us e.g.
522 /// find out which CFG points are contained in each borrow region.
523 regioncx: Rc<RegionInferenceContext<'tcx>>,
525 /// The set of borrows extracted from the MIR
526 borrow_set: Rc<BorrowSet<'tcx>>,
528 /// Dominators for MIR
529 dominators: Dominators<BasicBlock>,
531 /// Information about upvars not necessarily preserved in types or MIR
532 upvars: Vec<Upvar<'tcx>>,
534 /// Names of local (user) variables (extracted from `var_debug_info`).
535 local_names: IndexVec<Local, Option<Symbol>>,
537 /// Record the region names generated for each region in the given
538 /// MIR def so that we can reuse them later in help/error messages.
539 region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
541 /// The counter for generating new region names.
542 next_region_name: RefCell<usize>,
544 /// Results of Polonius analysis.
545 polonius_output: Option<Rc<PoloniusOutput>>,
547 errors: error::BorrowckErrors<'tcx>,
551 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
552 // 2. loans made in overlapping scopes do not conflict
553 // 3. assignments do not affect things loaned out as immutable
554 // 4. moves do not affect things loaned out in any way
555 impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
556 type FlowState = Flows<'cx, 'tcx>;
558 fn visit_statement_before_primary_effect(
560 flow_state: &Flows<'cx, 'tcx>,
561 stmt: &'cx Statement<'tcx>,
564 debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
565 let span = stmt.source_info.span;
567 self.check_activations(location, span, flow_state);
570 StatementKind::Assign(box (lhs, ref rhs)) => {
571 self.consume_rvalue(location, (rhs, span), flow_state);
573 self.mutate_place(location, (*lhs, span), Shallow(None), flow_state);
575 StatementKind::FakeRead(box (_, ref place)) => {
576 // Read for match doesn't access any memory and is used to
577 // assert that a place is safe and live. So we don't have to
578 // do any checks here.
580 // FIXME: Remove check that the place is initialized. This is
581 // needed for now because matches don't have never patterns yet.
582 // So this is the only place we prevent
586 self.check_if_path_or_subpath_is_moved(
588 InitializationRequiringAction::Use,
589 (place.as_ref(), span),
593 StatementKind::CopyNonOverlapping(box rustc_middle::mir::CopyNonOverlapping {
598 "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
602 | StatementKind::Coverage(..)
603 | StatementKind::AscribeUserType(..)
604 | StatementKind::Retag { .. }
605 | StatementKind::StorageLive(..) => {
606 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
609 StatementKind::StorageDead(local) => {
612 (Place::from(*local), span),
613 (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
614 LocalMutationIsAllowed::Yes,
618 StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
619 bug!("Statement not allowed in this MIR phase")
624 fn visit_terminator_before_primary_effect(
626 flow_state: &Flows<'cx, 'tcx>,
627 term: &'cx Terminator<'tcx>,
630 debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
631 let span = term.source_info.span;
633 self.check_activations(loc, span, flow_state);
636 TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
637 self.consume_operand(loc, (discr, span), flow_state);
639 TerminatorKind::Drop { place, target: _, unwind: _ } => {
641 "visit_terminator_drop \
642 loc: {:?} term: {:?} place: {:?} span: {:?}",
643 loc, term, place, span
649 (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
650 LocalMutationIsAllowed::Yes,
654 TerminatorKind::DropAndReplace {
656 value: ref new_value,
660 self.mutate_place(loc, (drop_place, span), Deep, flow_state);
661 self.consume_operand(loc, (new_value, span), flow_state);
663 TerminatorKind::Call {
672 self.consume_operand(loc, (func, span), flow_state);
674 self.consume_operand(loc, (arg, span), flow_state);
676 self.mutate_place(loc, (destination, span), Deep, flow_state);
678 TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
679 self.consume_operand(loc, (cond, span), flow_state);
680 use rustc_middle::mir::AssertKind;
681 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
682 self.consume_operand(loc, (len, span), flow_state);
683 self.consume_operand(loc, (index, span), flow_state);
687 TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
688 self.consume_operand(loc, (value, span), flow_state);
689 self.mutate_place(loc, (resume_arg, span), Deep, flow_state);
692 TerminatorKind::InlineAsm {
702 InlineAsmOperand::In { reg: _, ref value } => {
703 self.consume_operand(loc, (value, span), flow_state);
705 InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
706 if let Some(place) = place {
707 self.mutate_place(loc, (place, span), Shallow(None), flow_state);
710 InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
711 self.consume_operand(loc, (in_value, span), flow_state);
712 if let Some(out_place) = out_place {
721 InlineAsmOperand::Const { value: _ }
722 | InlineAsmOperand::SymFn { value: _ }
723 | InlineAsmOperand::SymStatic { def_id: _ } => {}
728 TerminatorKind::Goto { target: _ }
729 | TerminatorKind::Abort
730 | TerminatorKind::Unreachable
731 | TerminatorKind::Resume
732 | TerminatorKind::Return
733 | TerminatorKind::GeneratorDrop
734 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
735 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
736 // no data used, thus irrelevant to borrowck
741 fn visit_terminator_after_primary_effect(
743 flow_state: &Flows<'cx, 'tcx>,
744 term: &'cx Terminator<'tcx>,
747 let span = term.source_info.span;
750 TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
751 if self.movable_generator {
752 // Look for any active borrows to locals
753 let borrow_set = self.borrow_set.clone();
754 for i in flow_state.borrows.iter() {
755 let borrow = &borrow_set[i];
756 self.check_for_local_borrow(borrow, span);
761 TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
762 // Returning from the function implicitly kills storage for all locals and statics.
763 // Often, the storage will already have been killed by an explicit
764 // StorageDead, but we don't always emit those (notably on unwind paths),
765 // so this "extra check" serves as a kind of backup.
766 let borrow_set = self.borrow_set.clone();
767 for i in flow_state.borrows.iter() {
768 let borrow = &borrow_set[i];
769 self.check_for_invalidation_at_exit(loc, borrow, span);
773 TerminatorKind::Abort
774 | TerminatorKind::Assert { .. }
775 | TerminatorKind::Call { .. }
776 | TerminatorKind::Drop { .. }
777 | TerminatorKind::DropAndReplace { .. }
778 | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
779 | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
780 | TerminatorKind::Goto { .. }
781 | TerminatorKind::SwitchInt { .. }
782 | TerminatorKind::Unreachable
783 | TerminatorKind::InlineAsm { .. } => {}
788 use self::AccessDepth::{Deep, Shallow};
789 use self::ReadOrWrite::{Activation, Read, Reservation, Write};
791 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
792 enum ArtificialField {
797 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
799 /// From the RFC: "A *shallow* access means that the immediate
800 /// fields reached at P are accessed, but references or pointers
801 /// found within are not dereferenced. Right now, the only access
802 /// that is shallow is an assignment like `x = ...;`, which would
803 /// be a *shallow write* of `x`."
804 Shallow(Option<ArtificialField>),
806 /// From the RFC: "A *deep* access means that all data reachable
807 /// through the given place may be invalidated or accesses by
811 /// Access is Deep only when there is a Drop implementation that
812 /// can reach the data behind the reference.
816 /// Kind of access to a value: read or write
817 /// (For informational purposes only)
818 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
820 /// From the RFC: "A *read* means that the existing data may be
821 /// read, but will not be changed."
824 /// From the RFC: "A *write* means that the data may be mutated to
825 /// new values or otherwise invalidated (for example, it could be
826 /// de-initialized, as in a move operation).
829 /// For two-phase borrows, we distinguish a reservation (which is treated
830 /// like a Read) from an activation (which is treated like a write), and
831 /// each of those is furthermore distinguished from Reads/Writes above.
832 Reservation(WriteKind),
833 Activation(WriteKind, BorrowIndex),
836 /// Kind of read access to a value
837 /// (For informational purposes only)
838 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
844 /// Kind of write access to a value
845 /// (For informational purposes only)
846 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
849 MutableBorrow(BorrowKind),
854 /// When checking permissions for a place access, this flag is used to indicate that an immutable
855 /// local place can be mutated.
857 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
858 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
859 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
860 // `is_declared_mutable()`.
861 // - Take flow state into consideration in `is_assignable()` for local variables.
862 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
863 enum LocalMutationIsAllowed {
865 /// We want use of immutable upvars to cause a "write to immutable upvar"
866 /// error, not an "reassignment" error.
871 #[derive(Copy, Clone, Debug)]
872 enum InitializationRequiringAction {
880 struct RootPlace<'tcx> {
882 place_projection: &'tcx [PlaceElem<'tcx>],
883 is_local_mutation_allowed: LocalMutationIsAllowed,
886 impl InitializationRequiringAction {
887 fn as_noun(self) -> &'static str {
889 InitializationRequiringAction::Borrow => "borrow",
890 InitializationRequiringAction::MatchOn => "use", // no good noun
891 InitializationRequiringAction::Use => "use",
892 InitializationRequiringAction::Assignment => "assign",
893 InitializationRequiringAction::PartialAssignment => "assign to part",
897 fn as_verb_in_past_tense(self) -> &'static str {
899 InitializationRequiringAction::Borrow => "borrowed",
900 InitializationRequiringAction::MatchOn => "matched on",
901 InitializationRequiringAction::Use => "used",
902 InitializationRequiringAction::Assignment => "assigned",
903 InitializationRequiringAction::PartialAssignment => "partially assigned",
907 fn as_general_verb_in_past_tense(self) -> &'static str {
909 InitializationRequiringAction::Borrow
910 | InitializationRequiringAction::MatchOn
911 | InitializationRequiringAction::Use => "used",
912 InitializationRequiringAction::Assignment => "assigned",
913 InitializationRequiringAction::PartialAssignment => "partially assigned",
918 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
919 fn body(&self) -> &'cx Body<'tcx> {
923 /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
924 /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
925 /// place is initialized and (b) it is not borrowed in some way that would prevent this
928 /// Returns `true` if an error is reported.
932 place_span: (Place<'tcx>, Span),
933 kind: (AccessDepth, ReadOrWrite),
934 is_local_mutation_allowed: LocalMutationIsAllowed,
935 flow_state: &Flows<'cx, 'tcx>,
939 if let Activation(_, borrow_index) = rw {
940 if self.reservation_error_reported.contains(&place_span.0) {
942 "skipping access_place for activation of invalid reservation \
943 place: {:?} borrow_index: {:?}",
944 place_span.0, borrow_index
950 // Check is_empty() first because it's the common case, and doing that
951 // way we avoid the clone() call.
952 if !self.access_place_error_reported.is_empty()
953 && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
956 "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
962 let mutability_error = self.check_access_permissions(
965 is_local_mutation_allowed,
970 self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
972 if conflict_error || mutability_error {
973 debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
974 self.access_place_error_reported.insert((place_span.0, place_span.1));
978 #[instrument(level = "debug", skip(self, flow_state))]
979 fn check_access_for_conflict(
982 place_span: (Place<'tcx>, Span),
985 flow_state: &Flows<'cx, 'tcx>,
987 let mut error_reported = false;
988 let tcx = self.infcx.tcx;
989 let body = self.body;
990 let borrow_set = self.borrow_set.clone();
992 // Use polonius output if it has been enabled.
993 let polonius_output = self.polonius_output.clone();
994 let borrows_in_scope = if let Some(polonius) = &polonius_output {
995 let location = self.location_table.start_index(location);
996 Either::Left(polonius.errors_at(location).iter().copied())
998 Either::Right(flow_state.borrows.iter())
1001 each_borrow_involving_path(
1009 |this, borrow_index, borrow| match (rw, borrow.kind) {
1010 // Obviously an activation is compatible with its own
1011 // reservation (or even prior activating uses of same
1012 // borrow); so don't check if they interfere.
1014 // NOTE: *reservations* do conflict with themselves;
1015 // thus aren't injecting unsoundness w/ this check.)
1016 (Activation(_, activating), _) if activating == borrow_index => {
1018 "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
1019 skipping {:?} b/c activation of same borrow_index",
1023 (borrow_index, borrow),
1028 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
1030 Read(ReadKind::Borrow(BorrowKind::Shallow)),
1031 BorrowKind::Unique | BorrowKind::Mut { .. },
1032 ) => Control::Continue,
1034 (Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
1035 // This used to be a future compatibility warning (to be
1036 // disallowed on NLL). See rust-lang/rust#56254
1040 (Write(WriteKind::Move), BorrowKind::Shallow) => {
1041 // Handled by initialization checks.
1045 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
1046 // Reading from mere reservations of mutable-borrows is OK.
1047 if !is_active(&this.dominators, borrow, location) {
1048 assert!(allow_two_phase_borrow(borrow.kind));
1049 return Control::Continue;
1052 error_reported = true;
1056 .report_use_while_mutably_borrowed(location, place_span, borrow);
1057 this.buffer_error(err);
1059 ReadKind::Borrow(bk) => {
1061 this.report_conflicting_borrow(location, place_span, bk, borrow);
1062 this.buffer_error(err);
1068 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
1070 Reservation(..) => {
1072 "recording invalid reservation of \
1076 this.reservation_error_reported.insert(place_span.0);
1078 Activation(_, activating) => {
1080 "observing check_place for activation of \
1081 borrow_index: {:?}",
1085 Read(..) | Write(..) => {}
1088 error_reported = true;
1090 WriteKind::MutableBorrow(bk) => {
1092 this.report_conflicting_borrow(location, place_span, bk, borrow);
1093 this.buffer_error(err);
1095 WriteKind::StorageDeadOrDrop => this
1096 .report_borrowed_value_does_not_live_long_enough(
1102 WriteKind::Mutate => {
1103 this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
1105 WriteKind::Move => {
1106 this.report_move_out_while_borrowed(location, place_span, borrow)
1120 place_span: (Place<'tcx>, Span),
1122 flow_state: &Flows<'cx, 'tcx>,
1124 // Write of P[i] or *P requires P init'd.
1125 self.check_if_assigned_path_is_moved(location, place_span, flow_state);
1127 // Special case: you can assign an immutable local variable
1128 // (e.g., `x = ...`) so long as it has never been initialized
1129 // before (at this point in the flow).
1130 if let Some(local) = place_span.0.as_local() {
1131 if let Mutability::Not = self.body.local_decls[local].mutability {
1132 // check for reassignments to immutable local variables
1133 self.check_if_reassignment_to_immutable_state(
1134 location, local, place_span, flow_state,
1140 // Otherwise, use the normal access permission rules.
1144 (kind, Write(WriteKind::Mutate)),
1145 LocalMutationIsAllowed::No,
1153 (rvalue, span): (&'cx Rvalue<'tcx>, Span),
1154 flow_state: &Flows<'cx, 'tcx>,
1157 Rvalue::Ref(_ /*rgn*/, bk, place) => {
1158 let access_kind = match bk {
1159 BorrowKind::Shallow => {
1160 (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
1162 BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
1163 BorrowKind::Unique | BorrowKind::Mut { .. } => {
1164 let wk = WriteKind::MutableBorrow(bk);
1165 if allow_two_phase_borrow(bk) {
1166 (Deep, Reservation(wk))
1177 LocalMutationIsAllowed::No,
1181 let action = if bk == BorrowKind::Shallow {
1182 InitializationRequiringAction::MatchOn
1184 InitializationRequiringAction::Borrow
1187 self.check_if_path_or_subpath_is_moved(
1190 (place.as_ref(), span),
1195 Rvalue::AddressOf(mutability, place) => {
1196 let access_kind = match mutability {
1197 Mutability::Mut => (
1199 Write(WriteKind::MutableBorrow(BorrowKind::Mut {
1200 allow_two_phase_borrow: false,
1203 Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
1210 LocalMutationIsAllowed::No,
1214 self.check_if_path_or_subpath_is_moved(
1216 InitializationRequiringAction::Borrow,
1217 (place.as_ref(), span),
1222 Rvalue::ThreadLocalRef(_) => {}
1224 Rvalue::Use(ref operand)
1225 | Rvalue::Repeat(ref operand, _)
1226 | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
1227 | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/)
1228 | Rvalue::ShallowInitBox(ref operand, _ /*ty*/) => {
1229 self.consume_operand(location, (operand, span), flow_state)
1231 Rvalue::CopyForDeref(place) => {
1235 (Deep, Read(ReadKind::Copy)),
1236 LocalMutationIsAllowed::No,
1240 // Finally, check if path was already moved.
1241 self.check_if_path_or_subpath_is_moved(
1243 InitializationRequiringAction::Use,
1244 (place.as_ref(), span),
1249 Rvalue::Len(place) | Rvalue::Discriminant(place) => {
1250 let af = match *rvalue {
1251 Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1252 Rvalue::Discriminant(..) => None,
1253 _ => unreachable!(),
1258 (Shallow(af), Read(ReadKind::Copy)),
1259 LocalMutationIsAllowed::No,
1262 self.check_if_path_or_subpath_is_moved(
1264 InitializationRequiringAction::Use,
1265 (place.as_ref(), span),
1270 Rvalue::BinaryOp(_bin_op, box (ref operand1, ref operand2))
1271 | Rvalue::CheckedBinaryOp(_bin_op, box (ref operand1, ref operand2)) => {
1272 self.consume_operand(location, (operand1, span), flow_state);
1273 self.consume_operand(location, (operand2, span), flow_state);
1276 Rvalue::NullaryOp(_op, _ty) => {
1277 // nullary ops take no dynamic input; no borrowck effect.
1280 Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
1281 // We need to report back the list of mutable upvars that were
1282 // moved into the closure and subsequently used by the closure,
1283 // in order to populate our used_mut set.
1284 match **aggregate_kind {
1285 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
1286 let BorrowCheckResult { used_mut_upvars, .. } =
1287 self.infcx.tcx.mir_borrowck(def_id);
1288 debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
1289 for field in used_mut_upvars {
1290 self.propagate_closure_used_mut_upvar(&operands[field.index()]);
1293 AggregateKind::Adt(..)
1294 | AggregateKind::Array(..)
1295 | AggregateKind::Tuple { .. } => (),
1298 for operand in operands {
1299 self.consume_operand(location, (operand, span), flow_state);
1305 fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
1306 let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
1307 // We have three possibilities here:
1308 // a. We are modifying something through a mut-ref
1309 // b. We are modifying something that is local to our parent
1310 // c. Current body is a nested closure, and we are modifying path starting from
1311 // a Place captured by our parent closure.
1313 // Handle (c), the path being modified is exactly the path captured by our parent
1314 if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
1315 this.used_mut_upvars.push(field);
1319 for (place_ref, proj) in place.iter_projections().rev() {
1321 if proj == ProjectionElem::Deref {
1322 match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
1323 // We aren't modifying a variable directly
1324 ty::Ref(_, _, hir::Mutability::Mut) => return,
1331 if let Some(field) = this.is_upvar_field_projection(place_ref) {
1332 this.used_mut_upvars.push(field);
1338 this.used_mut.insert(place.local);
1341 // This relies on the current way that by-value
1342 // captures of a closure are copied/moved directly
1343 // when generating MIR.
1345 Operand::Move(place) | Operand::Copy(place) => {
1346 match place.as_local() {
1347 Some(local) if !self.body.local_decls[local].is_user_variable() => {
1348 if self.body.local_decls[local].ty.is_mutable_ptr() {
1349 // The variable will be marked as mutable by the borrow.
1352 // This is an edge case where we have a `move` closure
1353 // inside a non-move closure, and the inner closure
1354 // contains a mutation:
1357 // || { move || { i += 1; }; };
1359 // In this case our usual strategy of assuming that the
1360 // variable will be captured by mutable reference is
1361 // wrong, since `i` can be copied into the inner
1362 // closure from a shared reference.
1364 // As such we have to search for the local that this
1365 // capture comes from and mark it as being used as mut.
1367 let temp_mpi = self.move_data.rev_lookup.find_local(local);
1368 let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
1369 &self.move_data.inits[init_index]
1371 bug!("temporary should be initialized exactly once")
1374 let InitLocation::Statement(loc) = init.location else {
1375 bug!("temporary initialized in arguments")
1378 let body = self.body;
1379 let bbd = &body[loc.block];
1380 let stmt = &bbd.statements[loc.statement_index];
1381 debug!("temporary assigned in: stmt={:?}", stmt);
1383 if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
1385 propagate_closure_used_mut_place(self, source);
1388 "closures should only capture user variables \
1389 or references to user variables"
1393 _ => propagate_closure_used_mut_place(self, place),
1396 Operand::Constant(..) => {}
1403 (operand, span): (&'cx Operand<'tcx>, Span),
1404 flow_state: &Flows<'cx, 'tcx>,
1407 Operand::Copy(place) => {
1408 // copy of place: check if this is "copy of frozen path"
1409 // (FIXME: see check_loans.rs)
1413 (Deep, Read(ReadKind::Copy)),
1414 LocalMutationIsAllowed::No,
1418 // Finally, check if path was already moved.
1419 self.check_if_path_or_subpath_is_moved(
1421 InitializationRequiringAction::Use,
1422 (place.as_ref(), span),
1426 Operand::Move(place) => {
1427 // move of place: check if this is move of already borrowed path
1431 (Deep, Write(WriteKind::Move)),
1432 LocalMutationIsAllowed::Yes,
1436 // Finally, check if path was already moved.
1437 self.check_if_path_or_subpath_is_moved(
1439 InitializationRequiringAction::Use,
1440 (place.as_ref(), span),
1444 Operand::Constant(_) => {}
1448 /// Checks whether a borrow of this place is invalidated when the function
1450 #[instrument(level = "debug", skip(self))]
1451 fn check_for_invalidation_at_exit(
1454 borrow: &BorrowData<'tcx>,
1457 let place = borrow.borrowed_place;
1458 let mut root_place = PlaceRef { local: place.local, projection: &[] };
1460 // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
1461 // we just know that all locals are dropped at function exit (otherwise
1462 // we'll have a memory leak) and assume that all statics have a destructor.
1464 // FIXME: allow thread-locals to borrow other thread locals?
1466 let (might_be_alive, will_be_dropped) =
1467 if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
1468 // Thread-locals might be dropped after the function exits
1469 // We have to dereference the outer reference because
1470 // borrows don't conflict behind shared references.
1471 root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
1474 (false, self.locals_are_invalidated_at_exit)
1477 if !will_be_dropped {
1478 debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
1482 let sd = if might_be_alive { Deep } else { Shallow(None) };
1484 if places_conflict::borrow_conflicts_with_place(
1491 places_conflict::PlaceConflictBias::Overlap,
1493 debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
1494 // FIXME: should be talking about the region lifetime instead
1495 // of just a span here.
1496 let span = self.infcx.tcx.sess.source_map().end_point(span);
1497 self.report_borrowed_value_does_not_live_long_enough(
1506 /// Reports an error if this is a borrow of local data.
1507 /// This is called for all Yield expressions on movable generators
1508 fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
1509 debug!("check_for_local_borrow({:?})", borrow);
1511 if borrow_of_local_data(borrow.borrowed_place) {
1512 let err = self.cannot_borrow_across_generator_yield(
1513 self.retrieve_borrow_spans(borrow).var_or_use(),
1517 self.buffer_error(err);
1521 fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
1522 // Two-phase borrow support: For each activation that is newly
1523 // generated at this statement, check if it interferes with
1525 let borrow_set = self.borrow_set.clone();
1526 for &borrow_index in borrow_set.activations_at_location(location) {
1527 let borrow = &borrow_set[borrow_index];
1529 // only mutable borrows should be 2-phase
1530 assert!(match borrow.kind {
1531 BorrowKind::Shared | BorrowKind::Shallow => false,
1532 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
1537 (borrow.borrowed_place, span),
1538 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
1539 LocalMutationIsAllowed::No,
1542 // We do not need to call `check_if_path_or_subpath_is_moved`
1543 // again, as we already called it when we made the
1544 // initial reservation.
1548 fn check_if_reassignment_to_immutable_state(
1552 place_span: (Place<'tcx>, Span),
1553 flow_state: &Flows<'cx, 'tcx>,
1555 debug!("check_if_reassignment_to_immutable_state({:?})", local);
1557 // Check if any of the initializations of `local` have happened yet:
1558 if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
1559 // And, if so, report an error.
1560 let init = &self.move_data.inits[init_index];
1561 let span = init.span(&self.body);
1562 self.report_illegal_reassignment(location, place_span, span, place_span.0);
1566 fn check_if_full_path_is_moved(
1569 desired_action: InitializationRequiringAction,
1570 place_span: (PlaceRef<'tcx>, Span),
1571 flow_state: &Flows<'cx, 'tcx>,
1573 let maybe_uninits = &flow_state.uninits;
1577 // 1. Move of `a.b.c`, use of `a.b.c`
1578 // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
1579 // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
1580 // partial initialization support, one might have `a.x`
1581 // initialized but not `a.b`.
1585 // 4. Move of `a.b.c`, use of `a.b.d`
1586 // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1587 // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1588 // must have been initialized for the use to be sound.
1589 // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1591 // The dataflow tracks shallow prefixes distinctly (that is,
1592 // field-accesses on P distinctly from P itself), in order to
1593 // track substructure initialization separately from the whole
1596 // E.g., when looking at (*a.b.c).d, if the closest prefix for
1597 // which we have a MovePath is `a.b`, then that means that the
1598 // initialization state of `a.b` is all we need to inspect to
1599 // know if `a.b.c` is valid (and from that we infer that the
1600 // dereference and `.d` access is also valid, since we assume
1601 // `a.b.c` is assigned a reference to an initialized and
1602 // well-formed record structure.)
1604 // Therefore, if we seek out the *closest* prefix for which we
1605 // have a MovePath, that should capture the initialization
1606 // state for the place scenario.
1608 // This code covers scenarios 1, 2, and 3.
1610 debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
1611 let (prefix, mpi) = self.move_path_closest_to(place_span.0);
1612 if maybe_uninits.contains(mpi) {
1613 self.report_use_of_moved_or_uninitialized(
1616 (prefix, place_span.0, place_span.1),
1619 } // Only query longest prefix with a MovePath, not further
1620 // ancestors; dataflow recurs on children when parents
1621 // move (to support partial (re)inits).
1623 // (I.e., querying parents breaks scenario 7; but may want
1624 // to do such a query based on partial-init feature-gate.)
1627 /// Subslices correspond to multiple move paths, so we iterate through the
1628 /// elements of the base array. For each element we check
1630 /// * Does this element overlap with our slice.
1631 /// * Is any part of it uninitialized.
1632 fn check_if_subslice_element_is_moved(
1635 desired_action: InitializationRequiringAction,
1636 place_span: (PlaceRef<'tcx>, Span),
1637 maybe_uninits: &ChunkedBitSet<MovePathIndex>,
1641 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1642 let move_paths = &self.move_data.move_paths;
1644 let root_path = &move_paths[mpi];
1645 for (child_mpi, child_move_path) in root_path.children(move_paths) {
1646 let last_proj = child_move_path.place.projection.last().unwrap();
1647 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
1648 debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
1650 if (from..to).contains(offset) {
1652 self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
1653 maybe_uninits.contains(mpi)
1656 if let Some(uninit_child) = uninit_child {
1657 self.report_use_of_moved_or_uninitialized(
1660 (place_span.0, place_span.0, place_span.1),
1663 return; // don't bother finding other problems.
1671 fn check_if_path_or_subpath_is_moved(
1674 desired_action: InitializationRequiringAction,
1675 place_span: (PlaceRef<'tcx>, Span),
1676 flow_state: &Flows<'cx, 'tcx>,
1678 let maybe_uninits = &flow_state.uninits;
1682 // 1. Move of `a.b.c`, use of `a` or `a.b`
1683 // partial initialization support, one might have `a.x`
1684 // initialized but not `a.b`.
1685 // 2. All bad scenarios from `check_if_full_path_is_moved`
1689 // 3. Move of `a.b.c`, use of `a.b.d`
1690 // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
1691 // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
1692 // must have been initialized for the use to be sound.
1693 // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
1695 self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
1697 if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
1698 place_span.0.last_projection()
1700 let place_ty = place_base.ty(self.body(), self.infcx.tcx);
1701 if let ty::Array(..) = place_ty.ty.kind() {
1702 self.check_if_subslice_element_is_moved(
1705 (place_base, place_span.1),
1714 // A move of any shallow suffix of `place` also interferes
1715 // with an attempt to use `place`. This is scenario 3 above.
1717 // (Distinct from handling of scenarios 1+2+4 above because
1718 // `place` does not interfere with suffixes of its prefixes,
1719 // e.g., `a.b.c` does not interfere with `a.b.d`)
1721 // This code covers scenario 1.
1723 debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
1724 if let Some(mpi) = self.move_path_for_place(place_span.0) {
1725 let uninit_mpi = self
1727 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
1729 if let Some(uninit_mpi) = uninit_mpi {
1730 self.report_use_of_moved_or_uninitialized(
1733 (place_span.0, place_span.0, place_span.1),
1736 return; // don't bother finding other problems.
1741 /// Currently MoveData does not store entries for all places in
1742 /// the input MIR. For example it will currently filter out
1743 /// places that are Copy; thus we do not track places of shared
1744 /// reference type. This routine will walk up a place along its
1745 /// prefixes, searching for a foundational place that *is*
1746 /// tracked in the MoveData.
1748 /// An Err result includes a tag indicated why the search failed.
1749 /// Currently this can only occur if the place is built off of a
1750 /// static variable, as we do not track those in the MoveData.
1751 fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
1752 match self.move_data.rev_lookup.find(place) {
1753 LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
1754 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
1756 LookupResult::Parent(None) => panic!("should have move path for every Local"),
1760 fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
1761 // If returns None, then there is no move path corresponding
1762 // to a direct owner of `place` (which means there is nothing
1763 // that borrowck tracks for its analysis).
1765 match self.move_data.rev_lookup.find(place) {
1766 LookupResult::Parent(_) => None,
1767 LookupResult::Exact(mpi) => Some(mpi),
1771 fn check_if_assigned_path_is_moved(
1774 (place, span): (Place<'tcx>, Span),
1775 flow_state: &Flows<'cx, 'tcx>,
1777 debug!("check_if_assigned_path_is_moved place: {:?}", place);
1779 // None case => assigning to `x` does not require `x` be initialized.
1780 for (place_base, elem) in place.iter_projections().rev() {
1782 ProjectionElem::Index(_/*operand*/) |
1783 ProjectionElem::ConstantIndex { .. } |
1784 // assigning to P[i] requires P to be valid.
1785 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
1786 // assigning to (P->variant) is okay if assigning to `P` is okay
1788 // FIXME: is this true even if P is an adt with a dtor?
1791 // assigning to (*P) requires P to be initialized
1792 ProjectionElem::Deref => {
1793 self.check_if_full_path_is_moved(
1794 location, InitializationRequiringAction::Use,
1795 (place_base, span), flow_state);
1796 // (base initialized; no need to
1801 ProjectionElem::Subslice { .. } => {
1802 panic!("we don't allow assignments to subslices, location: {:?}",
1806 ProjectionElem::Field(..) => {
1807 // if type of `P` has a dtor, then
1808 // assigning to `P.f` requires `P` itself
1809 // be already initialized
1810 let tcx = self.infcx.tcx;
1811 let base_ty = place_base.ty(self.body(), tcx).ty;
1812 match base_ty.kind() {
1813 ty::Adt(def, _) if def.has_dtor(tcx) => {
1814 self.check_if_path_or_subpath_is_moved(
1815 location, InitializationRequiringAction::Assignment,
1816 (place_base, span), flow_state);
1818 // (base initialized; no need to
1823 // Once `let s; s.x = V; read(s.x);`,
1824 // is allowed, remove this match arm.
1825 ty::Adt(..) | ty::Tuple(..) => {
1826 check_parent_of_field(self, location, place_base, span, flow_state);
1828 // rust-lang/rust#21232, #54499, #54986: during period where we reject
1829 // partial initialization, do not complain about unnecessary `mut` on
1830 // an attempt to do a partial initialization.
1831 self.used_mut.insert(place.local);
1840 fn check_parent_of_field<'cx, 'tcx>(
1841 this: &mut MirBorrowckCtxt<'cx, 'tcx>,
1843 base: PlaceRef<'tcx>,
1845 flow_state: &Flows<'cx, 'tcx>,
1847 // rust-lang/rust#21232: Until Rust allows reads from the
1848 // initialized parts of partially initialized structs, we
1849 // will, starting with the 2018 edition, reject attempts
1850 // to write to structs that are not fully initialized.
1852 // In other words, *until* we allow this:
1854 // 1. `let mut s; s.x = Val; read(s.x);`
1856 // we will for now disallow this:
1858 // 2. `let mut s; s.x = Val;`
1862 // 3. `let mut s = ...; drop(s); s.x=Val;`
1864 // This does not use check_if_path_or_subpath_is_moved,
1865 // because we want to *allow* reinitializations of fields:
1866 // e.g., want to allow
1868 // `let mut s = ...; drop(s.x); s.x=Val;`
1870 // This does not use check_if_full_path_is_moved on
1871 // `base`, because that would report an error about the
1872 // `base` as a whole, but in this scenario we *really*
1873 // want to report an error about the actual thing that was
1874 // moved, which may be some prefix of `base`.
1876 // Shallow so that we'll stop at any dereference; we'll
1877 // report errors about issues with such bases elsewhere.
1878 let maybe_uninits = &flow_state.uninits;
1880 // Find the shortest uninitialized prefix you can reach
1881 // without going over a Deref.
1882 let mut shortest_uninit_seen = None;
1883 for prefix in this.prefixes(base, PrefixSet::Shallow) {
1884 let Some(mpi) = this.move_path_for_place(prefix) else { continue };
1886 if maybe_uninits.contains(mpi) {
1888 "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
1889 shortest_uninit_seen,
1892 shortest_uninit_seen = Some((prefix, mpi));
1894 debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
1898 if let Some((prefix, mpi)) = shortest_uninit_seen {
1899 // Check for a reassignment into an uninitialized field of a union (for example,
1900 // after a move out). In this case, do not report an error here. There is an
1901 // exception, if this is the first assignment into the union (that is, there is
1902 // no move out from an earlier location) then this is an attempt at initialization
1903 // of the union - we should error in that case.
1904 let tcx = this.infcx.tcx;
1905 if base.ty(this.body(), tcx).ty.is_union() {
1906 if this.move_data.path_map[mpi].iter().any(|moi| {
1907 this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
1913 this.report_use_of_moved_or_uninitialized(
1915 InitializationRequiringAction::PartialAssignment,
1916 (prefix, base, span),
1923 /// Checks the permissions for the given place and read or write kind
1925 /// Returns `true` if an error is reported.
1926 fn check_access_permissions(
1928 (place, span): (Place<'tcx>, Span),
1930 is_local_mutation_allowed: LocalMutationIsAllowed,
1931 flow_state: &Flows<'cx, 'tcx>,
1935 "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
1936 place, kind, is_local_mutation_allowed
1943 Reservation(WriteKind::MutableBorrow(
1944 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1946 | Write(WriteKind::MutableBorrow(
1947 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
1949 let is_local_mutation_allowed = match borrow_kind {
1950 BorrowKind::Unique => LocalMutationIsAllowed::Yes,
1951 BorrowKind::Mut { .. } => is_local_mutation_allowed,
1952 BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
1954 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1956 self.add_used_mut(root_place, flow_state);
1960 error_access = AccessKind::MutableBorrow;
1961 the_place_err = place_err;
1965 Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
1966 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
1968 self.add_used_mut(root_place, flow_state);
1972 error_access = AccessKind::Mutate;
1973 the_place_err = place_err;
1980 | WriteKind::StorageDeadOrDrop
1981 | WriteKind::MutableBorrow(BorrowKind::Shared)
1982 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1986 | WriteKind::StorageDeadOrDrop
1987 | WriteKind::MutableBorrow(BorrowKind::Shared)
1988 | WriteKind::MutableBorrow(BorrowKind::Shallow),
1990 if self.is_mutable(place.as_ref(), is_local_mutation_allowed).is_err()
1991 && !self.has_buffered_errors()
1993 // rust-lang/rust#46908: In pure NLL mode this code path should be
1994 // unreachable, but we use `delay_span_bug` because we can hit this when
1995 // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
1996 // enabled. We don't want to ICE for that case, as other errors will have
1997 // been emitted (#52262).
1998 self.infcx.tcx.sess.delay_span_bug(
2001 "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
2009 // permission checks are done at Reservation point.
2015 | BorrowKind::Mut { .. }
2016 | BorrowKind::Shared
2017 | BorrowKind::Shallow,
2021 // Access authorized
2026 // rust-lang/rust#21232, #54986: during period where we reject
2027 // partial initialization, do not complain about mutability
2028 // errors except for actual mutation (as opposed to an attempt
2029 // to do a partial initialization).
2030 let previously_initialized =
2031 self.is_local_ever_initialized(place.local, flow_state).is_some();
2033 // at this point, we have set up the error reporting state.
2034 if previously_initialized {
2035 self.report_mutability_error(place, span, the_place_err, error_access, location);
2042 fn is_local_ever_initialized(
2045 flow_state: &Flows<'cx, 'tcx>,
2046 ) -> Option<InitIndex> {
2047 let mpi = self.move_data.rev_lookup.find_local(local);
2048 let ii = &self.move_data.init_path_map[mpi];
2050 if flow_state.ever_inits.contains(index) {
2057 /// Adds the place into the used mutable variables set
2058 fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
2060 RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
2061 // If the local may have been initialized, and it is now currently being
2062 // mutated, then it is justified to be annotated with the `mut`
2063 // keyword, since the mutation may be a possible reassignment.
2064 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
2065 && self.is_local_ever_initialized(local, flow_state).is_some()
2067 self.used_mut.insert(local);
2072 place_projection: _,
2073 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2077 place_projection: place_projection @ [.., _],
2078 is_local_mutation_allowed: _,
2080 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
2082 projection: place_projection,
2084 self.used_mut_upvars.push(field);
2090 /// Whether this value can be written or borrowed mutably.
2091 /// Returns the root place if the place passed in is a projection.
2094 place: PlaceRef<'tcx>,
2095 is_local_mutation_allowed: LocalMutationIsAllowed,
2096 ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
2097 debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
2098 match place.last_projection() {
2100 let local = &self.body.local_decls[place.local];
2101 match local.mutability {
2102 Mutability::Not => match is_local_mutation_allowed {
2103 LocalMutationIsAllowed::Yes => Ok(RootPlace {
2104 place_local: place.local,
2105 place_projection: place.projection,
2106 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
2108 LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
2109 place_local: place.local,
2110 place_projection: place.projection,
2111 is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
2113 LocalMutationIsAllowed::No => Err(place),
2115 Mutability::Mut => Ok(RootPlace {
2116 place_local: place.local,
2117 place_projection: place.projection,
2118 is_local_mutation_allowed,
2122 Some((place_base, elem)) => {
2124 ProjectionElem::Deref => {
2125 let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
2127 // Check the kind of deref to decide
2128 match base_ty.kind() {
2129 ty::Ref(_, _, mutbl) => {
2131 // Shared borrowed data is never mutable
2132 hir::Mutability::Not => Err(place),
2133 // Mutably borrowed data is mutable, but only if we have a
2134 // unique path to the `&mut`
2135 hir::Mutability::Mut => {
2136 let mode = match self.is_upvar_field_projection(place) {
2137 Some(field) if self.upvars[field.index()].by_ref => {
2138 is_local_mutation_allowed
2140 _ => LocalMutationIsAllowed::Yes,
2143 self.is_mutable(place_base, mode)
2147 ty::RawPtr(tnm) => {
2149 // `*const` raw pointers are not mutable
2150 hir::Mutability::Not => Err(place),
2151 // `*mut` raw pointers are always mutable, regardless of
2152 // context. The users have to check by themselves.
2153 hir::Mutability::Mut => Ok(RootPlace {
2154 place_local: place.local,
2155 place_projection: place.projection,
2156 is_local_mutation_allowed,
2160 // `Box<T>` owns its content, so mutable if its location is mutable
2161 _ if base_ty.is_box() => {
2162 self.is_mutable(place_base, is_local_mutation_allowed)
2164 // Deref should only be for reference, pointers or boxes
2165 _ => bug!("Deref of unexpected type: {:?}", base_ty),
2168 // All other projections are owned by their base path, so mutable if
2169 // base path is mutable
2170 ProjectionElem::Field(..)
2171 | ProjectionElem::Index(..)
2172 | ProjectionElem::ConstantIndex { .. }
2173 | ProjectionElem::Subslice { .. }
2174 | ProjectionElem::Downcast(..) => {
2175 let upvar_field_projection = self.is_upvar_field_projection(place);
2176 if let Some(field) = upvar_field_projection {
2177 let upvar = &self.upvars[field.index()];
2179 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
2180 place={:?}, place_base={:?}",
2181 upvar, is_local_mutation_allowed, place, place_base
2183 match (upvar.place.mutability, is_local_mutation_allowed) {
2186 LocalMutationIsAllowed::No
2187 | LocalMutationIsAllowed::ExceptUpvars,
2189 (Mutability::Not, LocalMutationIsAllowed::Yes)
2190 | (Mutability::Mut, _) => {
2191 // Subtle: this is an upvar
2192 // reference, so it looks like
2193 // `self.foo` -- we want to double
2194 // check that the location `*self`
2195 // is mutable (i.e., this is not a
2196 // `Fn` closure). But if that
2197 // check succeeds, we want to
2198 // *blame* the mutability on
2199 // `place` (that is,
2200 // `self.foo`). This is used to
2201 // propagate the info about
2202 // whether mutability declarations
2203 // are used outwards, so that we register
2204 // the outer variable as mutable. Otherwise a
2205 // test like this fails to record the `mut`
2209 // fn foo<F: FnOnce()>(_f: F) { }
2211 // let var = Vec::new();
2218 self.is_mutable(place_base, is_local_mutation_allowed)?;
2220 place_local: place.local,
2221 place_projection: place.projection,
2222 is_local_mutation_allowed,
2227 self.is_mutable(place_base, is_local_mutation_allowed)
2235 /// If `place` is a field projection, and the field is being projected from a closure type,
2236 /// then returns the index of the field being projected. Note that this closure will always
2237 /// be `self` in the current MIR, because that is the only time we directly access the fields
2238 /// of a closure type.
2239 fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
2240 path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
2245 use rustc_errors::ErrorGuaranteed;
2249 pub struct BorrowckErrors<'tcx> {
2250 /// This field keeps track of move errors that are to be reported for given move indices.
2252 /// There are situations where many errors can be reported for a single move out (see #53807)
2253 /// and we want only the best of those errors.
2255 /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
2256 /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
2257 /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
2258 /// all move errors have been reported, any diagnostics in this map are added to the buffer
2261 /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
2262 /// when errors in the map are being re-added to the error buffer so that errors with the
2263 /// same primary span come out in a consistent order.
2264 buffered_move_errors:
2265 BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>)>,
2266 /// Diagnostics to be reported buffer.
2267 buffered: Vec<Diagnostic>,
2268 /// Set to Some if we emit an error during borrowck
2269 tainted_by_errors: Option<ErrorGuaranteed>,
2272 impl BorrowckErrors<'_> {
2273 pub fn new() -> Self {
2275 buffered_move_errors: BTreeMap::new(),
2276 buffered: Default::default(),
2277 tainted_by_errors: None,
2281 // FIXME(eddyb) this is a suboptimal API because `tainted_by_errors` is
2282 // set before any emission actually happens (weakening the guarantee).
2283 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2284 self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
2285 t.buffer(&mut self.buffered);
2288 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2289 t.buffer(&mut self.buffered);
2292 pub fn set_tainted_by_errors(&mut self) {
2293 self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
2297 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
2298 pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
2299 self.errors.buffer_error(t);
2302 pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
2303 self.errors.buffer_non_error_diag(t);
2306 pub fn buffer_move_error(
2308 move_out_indices: Vec<MoveOutIndex>,
2309 place_and_err: (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>),
2311 if let Some((_, diag)) =
2312 self.errors.buffered_move_errors.insert(move_out_indices, place_and_err)
2314 // Cancel the old diagnostic so we don't ICE
2322 pub fn emit_errors(&mut self) -> Option<ErrorGuaranteed> {
2323 // Buffer any move errors that we collected and de-duplicated.
2324 for (_, (_, diag)) in std::mem::take(&mut self.errors.buffered_move_errors) {
2325 // We have already set tainted for this error, so just buffer it.
2326 diag.buffer(&mut self.errors.buffered);
2329 if !self.errors.buffered.is_empty() {
2330 self.errors.buffered.sort_by_key(|diag| diag.sort_span);
2332 for mut diag in self.errors.buffered.drain(..) {
2333 self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
2337 self.errors.tainted_by_errors
2340 pub fn has_buffered_errors(&self) -> bool {
2341 self.errors.buffered.is_empty()
2344 pub fn has_move_error(
2346 move_out_indices: &[MoveOutIndex],
2347 ) -> Option<&(PlaceRef<'tcx>, DiagnosticBuilder<'cx, ErrorGuaranteed>)> {
2348 self.errors.buffered_move_errors.get(move_out_indices)
2353 /// The degree of overlap between 2 places for borrow-checking.
2355 /// The places might partially overlap - in this case, we give
2356 /// up and say that they might conflict. This occurs when
2357 /// different fields of a union are borrowed. For example,
2358 /// if `u` is a union, we have no way of telling how disjoint
2359 /// `u.a.x` and `a.b.y` are.
2361 /// The places have the same type, and are either completely disjoint
2362 /// or equal - i.e., they can't "partially" overlap as can occur with
2363 /// unions. This is the "base case" on which we recur for extensions
2366 /// The places are disjoint, so we know all extensions of them
2367 /// will also be disjoint.