+++ /dev/null
-//! This query borrow-checks the MIR to (further) ensure it is not broken.
-
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_data_structures::graph::dominators::Dominators;
-use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorReported};
-use rustc_hir as hir;
-use rustc_hir::def_id::LocalDefId;
-use rustc_hir::Node;
-use rustc_index::bit_set::BitSet;
-use rustc_index::vec::IndexVec;
-use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
-use rustc_middle::mir::{
- traversal, Body, ClearCrossCrate, Local, Location, Mutability, Operand, Place, PlaceElem,
- PlaceRef, VarDebugInfoContents,
-};
-use rustc_middle::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
-use rustc_middle::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
-use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
-use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::{self, CapturedPlace, ParamEnv, RegionVid, TyCtxt};
-use rustc_session::lint::builtin::{MUTABLE_BORROW_RESERVATION_CONFLICT, UNUSED_MUT};
-use rustc_span::{Span, Symbol, DUMMY_SP};
-
-use either::Either;
-use smallvec::SmallVec;
-use std::cell::RefCell;
-use std::collections::BTreeMap;
-use std::iter;
-use std::mem;
-use std::rc::Rc;
-
-use crate::dataflow;
-use crate::dataflow::impls::{
- Borrows, EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
-};
-use crate::dataflow::indexes::{BorrowIndex, InitIndex, MoveOutIndex, MovePathIndex};
-use crate::dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
-use crate::dataflow::MoveDataParamEnv;
-use crate::dataflow::{Analysis, BorrowckFlowState as Flows, BorrowckResults};
-
-use self::diagnostics::{AccessKind, RegionName};
-use self::location::LocationTable;
-use self::prefixes::PrefixSet;
-use self::MutateMode::{JustWrite, WriteAndRead};
-use facts::AllFacts;
-
-use self::path_utils::*;
-
-mod borrow_set;
-mod constraint_generation;
-mod constraints;
-pub mod consumers;
-mod def_use;
-mod diagnostics;
-mod facts;
-mod invalidation;
-mod location;
-mod member_constraints;
-mod nll;
-mod path_utils;
-mod place_ext;
-mod places_conflict;
-mod prefixes;
-mod region_infer;
-mod renumber;
-mod type_check;
-mod universal_regions;
-mod used_muts;
-
-crate use borrow_set::{BorrowData, BorrowSet};
-crate use nll::{PoloniusOutput, ToRegionVid};
-crate use place_ext::PlaceExt;
-crate use places_conflict::{places_conflict, PlaceConflictBias};
-crate use region_infer::RegionInferenceContext;
-
-// FIXME(eddyb) perhaps move this somewhere more centrally.
-#[derive(Debug)]
-crate struct Upvar<'tcx> {
- place: CapturedPlace<'tcx>,
-
- /// If true, the capture is behind a reference.
- by_ref: bool,
-}
-
-const DEREF_PROJECTION: &[PlaceElem<'_>; 1] = &[ProjectionElem::Deref];
-
-pub fn provide(providers: &mut Providers) {
- *providers = Providers {
- mir_borrowck: |tcx, did| {
- if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
- tcx.mir_borrowck_const_arg(def)
- } else {
- mir_borrowck(tcx, ty::WithOptConstParam::unknown(did))
- }
- },
- mir_borrowck_const_arg: |tcx, (did, param_did)| {
- mir_borrowck(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
- },
- ..*providers
- };
-}
-
-fn mir_borrowck<'tcx>(
- tcx: TyCtxt<'tcx>,
- def: ty::WithOptConstParam<LocalDefId>,
-) -> &'tcx BorrowCheckResult<'tcx> {
- let (input_body, promoted) = tcx.mir_promoted(def);
- debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
-
- let opt_closure_req = tcx.infer_ctxt().with_opaque_type_inference(def.did).enter(|infcx| {
- let input_body: &Body<'_> = &input_body.borrow();
- let promoted: &IndexVec<_, _> = &promoted.borrow();
- do_mir_borrowck(&infcx, input_body, promoted, false).0
- });
- debug!("mir_borrowck done");
-
- tcx.arena.alloc(opt_closure_req)
-}
-
-/// Perform the actual borrow checking.
-///
-/// If `return_body_with_facts` is true, then return the body with non-erased
-/// region ids on which the borrow checking was performed together with Polonius
-/// facts.
-fn do_mir_borrowck<'a, 'tcx>(
- infcx: &InferCtxt<'a, 'tcx>,
- input_body: &Body<'tcx>,
- input_promoted: &IndexVec<Promoted, Body<'tcx>>,
- return_body_with_facts: bool,
-) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
- let def = input_body.source.with_opt_param().as_local().unwrap();
-
- debug!("do_mir_borrowck(def = {:?})", def);
-
- assert!(
- !return_body_with_facts || infcx.tcx.sess.opts.debugging_opts.polonius,
- "borrowck facts can be requested only when Polonius is enabled"
- );
-
- let tcx = infcx.tcx;
- let param_env = tcx.param_env(def.did);
- let id = tcx.hir().local_def_id_to_hir_id(def.did);
-
- let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
- for var_debug_info in &input_body.var_debug_info {
- if let VarDebugInfoContents::Place(place) = var_debug_info.value {
- if let Some(local) = place.as_local() {
- if let Some(prev_name) = local_names[local] {
- if var_debug_info.name != prev_name {
- span_bug!(
- var_debug_info.source_info.span,
- "local {:?} has many names (`{}` vs `{}`)",
- local,
- prev_name,
- var_debug_info.name
- );
- }
- }
- local_names[local] = Some(var_debug_info.name);
- }
- }
- }
-
- // Gather the upvars of a closure, if any.
- let tables = tcx.typeck_opt_const_arg(def);
- if let Some(ErrorReported) = tables.tainted_by_errors {
- infcx.set_tainted_by_errors();
- }
- let upvars: Vec<_> = tables
- .closure_min_captures_flattened(def.did.to_def_id())
- .map(|captured_place| {
- let capture = captured_place.info.capture_kind;
- let by_ref = match capture {
- ty::UpvarCapture::ByValue(_) => false,
- ty::UpvarCapture::ByRef(..) => true,
- };
- Upvar { place: captured_place.clone(), by_ref }
- })
- .collect();
-
- // Replace all regions with fresh inference variables. This
- // requires first making our own copy of the MIR. This copy will
- // be modified (in place) to contain non-lexical lifetimes. It
- // will have a lifetime tied to the inference context.
- let mut body_owned = input_body.clone();
- let mut promoted = input_promoted.clone();
- let free_regions =
- nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
- let body = &body_owned; // no further changes
-
- let location_table_owned = LocationTable::new(body);
- let location_table = &location_table_owned;
-
- let mut errors_buffer = Vec::new();
- let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
- match MoveData::gather_moves(&body, tcx, param_env) {
- Ok(move_data) => (move_data, Vec::new()),
- Err((move_data, move_errors)) => (move_data, move_errors),
- };
- let promoted_errors = promoted
- .iter_enumerated()
- .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));
-
- let mdpe = MoveDataParamEnv { move_data, param_env };
-
- let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
- .into_engine(tcx, &body)
- .pass_name("borrowck")
- .iterate_to_fixpoint()
- .into_results_cursor(&body);
-
- let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
- let borrow_set =
- Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
-
- // Compute non-lexical lifetimes.
- let nll::NllOutput {
- regioncx,
- opaque_type_values,
- polonius_input,
- polonius_output,
- opt_closure_req,
- nll_errors,
- } = nll::compute_regions(
- infcx,
- free_regions,
- body,
- &promoted,
- location_table,
- param_env,
- &mut flow_inits,
- &mdpe.move_data,
- &borrow_set,
- &upvars,
- );
-
- // Dump MIR results into a file, if that is enabled. This let us
- // write unit-tests, as well as helping with debugging.
- nll::dump_mir_results(infcx, &body, ®ioncx, &opt_closure_req);
-
- // We also have a `#[rustc_regions]` annotation that causes us to dump
- // information.
- nll::dump_annotation(
- infcx,
- &body,
- ®ioncx,
- &opt_closure_req,
- &opaque_type_values,
- &mut errors_buffer,
- );
-
- // The various `flow_*` structures can be large. We drop `flow_inits` here
- // so it doesn't overlap with the others below. This reduces peak memory
- // usage significantly on some benchmarks.
- drop(flow_inits);
-
- let regioncx = Rc::new(regioncx);
-
- let flow_borrows = Borrows::new(tcx, &body, ®ioncx, &borrow_set)
- .into_engine(tcx, &body)
- .pass_name("borrowck")
- .iterate_to_fixpoint();
- let flow_uninits = MaybeUninitializedPlaces::new(tcx, &body, &mdpe)
- .into_engine(tcx, &body)
- .pass_name("borrowck")
- .iterate_to_fixpoint();
- let flow_ever_inits = EverInitializedPlaces::new(tcx, &body, &mdpe)
- .into_engine(tcx, &body)
- .pass_name("borrowck")
- .iterate_to_fixpoint();
-
- let movable_generator = match tcx.hir().get(id) {
- Node::Expr(&hir::Expr {
- kind: hir::ExprKind::Closure(.., Some(hir::Movability::Static)),
- ..
- }) => false,
- _ => true,
- };
-
- for (idx, move_data_results) in promoted_errors {
- let promoted_body = &promoted[idx];
-
- if let Err((move_data, move_errors)) = move_data_results {
- let mut promoted_mbcx = MirBorrowckCtxt {
- infcx,
- param_env,
- body: promoted_body,
- move_data: &move_data,
- location_table, // no need to create a real one for the promoted, it is not used
- movable_generator,
- fn_self_span_reported: Default::default(),
- locals_are_invalidated_at_exit,
- access_place_error_reported: Default::default(),
- reservation_error_reported: Default::default(),
- reservation_warnings: Default::default(),
- move_error_reported: BTreeMap::new(),
- uninitialized_error_reported: Default::default(),
- errors_buffer,
- regioncx: regioncx.clone(),
- used_mut: Default::default(),
- used_mut_upvars: SmallVec::new(),
- borrow_set: Rc::clone(&borrow_set),
- dominators: Dominators::dummy(), // not used
- upvars: Vec::new(),
- local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
- region_names: RefCell::default(),
- next_region_name: RefCell::new(1),
- polonius_output: None,
- };
- promoted_mbcx.report_move_errors(move_errors);
- errors_buffer = promoted_mbcx.errors_buffer;
- };
- }
-
- let dominators = body.dominators();
-
- let mut mbcx = MirBorrowckCtxt {
- infcx,
- param_env,
- body,
- move_data: &mdpe.move_data,
- location_table,
- movable_generator,
- locals_are_invalidated_at_exit,
- fn_self_span_reported: Default::default(),
- access_place_error_reported: Default::default(),
- reservation_error_reported: Default::default(),
- reservation_warnings: Default::default(),
- move_error_reported: BTreeMap::new(),
- uninitialized_error_reported: Default::default(),
- errors_buffer,
- regioncx: Rc::clone(®ioncx),
- used_mut: Default::default(),
- used_mut_upvars: SmallVec::new(),
- borrow_set: Rc::clone(&borrow_set),
- dominators,
- upvars,
- local_names,
- region_names: RefCell::default(),
- next_region_name: RefCell::new(1),
- polonius_output,
- };
-
- // Compute and report region errors, if any.
- mbcx.report_region_errors(nll_errors);
-
- let results = BorrowckResults {
- ever_inits: flow_ever_inits,
- uninits: flow_uninits,
- borrows: flow_borrows,
- };
-
- mbcx.report_move_errors(move_errors);
-
- dataflow::visit_results(
- &body,
- traversal::reverse_postorder(&body).map(|(bb, _)| bb),
- &results,
- &mut mbcx,
- );
-
- // Convert any reservation warnings into lints.
- let reservation_warnings = mem::take(&mut mbcx.reservation_warnings);
- for (_, (place, span, location, bk, borrow)) in reservation_warnings {
- let mut initial_diag = mbcx.report_conflicting_borrow(location, (place, span), bk, &borrow);
-
- let scope = mbcx.body.source_info(location).scope;
- let lint_root = match &mbcx.body.source_scopes[scope].local_data {
- ClearCrossCrate::Set(data) => data.lint_root,
- _ => id,
- };
-
- // Span and message don't matter; we overwrite them below anyway
- mbcx.infcx.tcx.struct_span_lint_hir(
- MUTABLE_BORROW_RESERVATION_CONFLICT,
- lint_root,
- DUMMY_SP,
- |lint| {
- let mut diag = lint.build("");
-
- diag.message = initial_diag.styled_message().clone();
- diag.span = initial_diag.span.clone();
-
- diag.buffer(&mut mbcx.errors_buffer);
- },
- );
- initial_diag.cancel();
- }
-
- // For each non-user used mutable variable, check if it's been assigned from
- // a user-declared local. If so, then put that local into the used_mut set.
- // Note that this set is expected to be small - only upvars from closures
- // would have a chance of erroneously adding non-user-defined mutable vars
- // to the set.
- let temporary_used_locals: FxHashSet<Local> = mbcx
- .used_mut
- .iter()
- .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
- .cloned()
- .collect();
- // For the remaining unused locals that are marked as mutable, we avoid linting any that
- // were never initialized. These locals may have been removed as unreachable code; or will be
- // linted as unused variables.
- let unused_mut_locals =
- mbcx.body.mut_vars_iter().filter(|local| !mbcx.used_mut.contains(local)).collect();
- mbcx.gather_used_muts(temporary_used_locals, unused_mut_locals);
-
- debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
- let used_mut = mbcx.used_mut;
- for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
- let local_decl = &mbcx.body.local_decls[local];
- let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
- ClearCrossCrate::Set(data) => data.lint_root,
- _ => continue,
- };
-
- // Skip over locals that begin with an underscore or have no name
- match mbcx.local_names[local] {
- Some(name) => {
- if name.as_str().starts_with('_') {
- continue;
- }
- }
- None => continue,
- }
-
- let span = local_decl.source_info.span;
- if span.desugaring_kind().is_some() {
- // If the `mut` arises as part of a desugaring, we should ignore it.
- continue;
- }
-
- tcx.struct_span_lint_hir(UNUSED_MUT, lint_root, span, |lint| {
- let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
- lint.build("variable does not need to be mutable")
- .span_suggestion_short(
- mut_span,
- "remove this `mut`",
- String::new(),
- Applicability::MachineApplicable,
- )
- .emit();
- })
- }
-
- // Buffer any move errors that we collected and de-duplicated.
- for (_, (_, diag)) in mbcx.move_error_reported {
- diag.buffer(&mut mbcx.errors_buffer);
- }
-
- if !mbcx.errors_buffer.is_empty() {
- mbcx.errors_buffer.sort_by_key(|diag| diag.sort_span);
-
- for diag in mbcx.errors_buffer.drain(..) {
- mbcx.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
- }
- }
-
- let result = BorrowCheckResult {
- concrete_opaque_types: opaque_type_values,
- closure_requirements: opt_closure_req,
- used_mut_upvars: mbcx.used_mut_upvars,
- };
-
- let body_with_facts = if return_body_with_facts {
- let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
- Some(Box::new(BodyWithBorrowckFacts {
- body: body_owned,
- input_facts: *polonius_input.expect("Polonius input facts were not generated"),
- output_facts,
- location_table: location_table_owned,
- }))
- } else {
- None
- };
-
- debug!("do_mir_borrowck: result = {:#?}", result);
-
- (result, body_with_facts)
-}
-
-/// A `Body` with information computed by the borrow checker. This struct is
-/// intended to be consumed by compiler consumers.
-///
-/// We need to include the MIR body here because the region identifiers must
-/// match the ones in the Polonius facts.
-pub struct BodyWithBorrowckFacts<'tcx> {
- /// A mir body that contains region identifiers.
- pub body: Body<'tcx>,
- /// Polonius input facts.
- pub input_facts: AllFacts,
- /// Polonius output facts.
- pub output_facts: Rc<self::nll::PoloniusOutput>,
- /// The table that maps Polonius points to locations in the table.
- pub location_table: LocationTable,
-}
-
-crate struct MirBorrowckCtxt<'cx, 'tcx> {
- crate infcx: &'cx InferCtxt<'cx, 'tcx>,
- param_env: ParamEnv<'tcx>,
- body: &'cx Body<'tcx>,
- move_data: &'cx MoveData<'tcx>,
-
- /// Map from MIR `Location` to `LocationIndex`; created
- /// when MIR borrowck begins.
- location_table: &'cx LocationTable,
-
- movable_generator: bool,
- /// This keeps track of whether local variables are free-ed when the function
- /// exits even without a `StorageDead`, which appears to be the case for
- /// constants.
- ///
- /// I'm not sure this is the right approach - @eddyb could you try and
- /// figure this out?
- locals_are_invalidated_at_exit: bool,
- /// This field keeps track of when borrow errors are reported in the access_place function
- /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
- /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
- /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
- /// errors.
- access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
- /// This field keeps track of when borrow conflict errors are reported
- /// for reservations, so that we don't report seemingly duplicate
- /// errors for corresponding activations.
- //
- // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
- // but it is currently inconvenient to track down the `BorrowIndex`
- // at the time we detect and report a reservation error.
- reservation_error_reported: FxHashSet<Place<'tcx>>,
- /// This fields keeps track of the `Span`s that we have
- /// used to report extra information for `FnSelfUse`, to avoid
- /// unnecessarily verbose errors.
- fn_self_span_reported: FxHashSet<Span>,
- /// Migration warnings to be reported for #56254. We delay reporting these
- /// so that we can suppress the warning if there's a corresponding error
- /// for the activation of the borrow.
- reservation_warnings:
- FxHashMap<BorrowIndex, (Place<'tcx>, Span, Location, BorrowKind, BorrowData<'tcx>)>,
- /// This field keeps track of move errors that are to be reported for given move indices.
- ///
- /// There are situations where many errors can be reported for a single move out (see #53807)
- /// and we want only the best of those errors.
- ///
- /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
- /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of the
- /// `Place` of the previous most diagnostic. This happens instead of buffering the error. Once
- /// all move errors have been reported, any diagnostics in this map are added to the buffer
- /// to be emitted.
- ///
- /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
- /// when errors in the map are being re-added to the error buffer so that errors with the
- /// same primary span come out in a consistent order.
- move_error_reported: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'cx>)>,
- /// This field keeps track of errors reported in the checking of uninitialized variables,
- /// so that we don't report seemingly duplicate errors.
- uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
- /// Errors to be reported buffer
- errors_buffer: Vec<Diagnostic>,
- /// This field keeps track of all the local variables that are declared mut and are mutated.
- /// Used for the warning issued by an unused mutable local variable.
- used_mut: FxHashSet<Local>,
- /// If the function we're checking is a closure, then we'll need to report back the list of
- /// mutable upvars that have been used. This field keeps track of them.
- used_mut_upvars: SmallVec<[Field; 8]>,
- /// Region inference context. This contains the results from region inference and lets us e.g.
- /// find out which CFG points are contained in each borrow region.
- regioncx: Rc<RegionInferenceContext<'tcx>>,
-
- /// The set of borrows extracted from the MIR
- borrow_set: Rc<BorrowSet<'tcx>>,
-
- /// Dominators for MIR
- dominators: Dominators<BasicBlock>,
-
- /// Information about upvars not necessarily preserved in types or MIR
- upvars: Vec<Upvar<'tcx>>,
-
- /// Names of local (user) variables (extracted from `var_debug_info`).
- local_names: IndexVec<Local, Option<Symbol>>,
-
- /// Record the region names generated for each region in the given
- /// MIR def so that we can reuse them later in help/error messages.
- region_names: RefCell<FxHashMap<RegionVid, RegionName>>,
-
- /// The counter for generating new region names.
- next_region_name: RefCell<usize>,
-
- /// Results of Polonius analysis.
- polonius_output: Option<Rc<PoloniusOutput>>,
-}
-
-// Check that:
-// 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
-// 2. loans made in overlapping scopes do not conflict
-// 3. assignments do not affect things loaned out as immutable
-// 4. moves do not affect things loaned out in any way
-impl<'cx, 'tcx> dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
- type FlowState = Flows<'cx, 'tcx>;
-
- fn visit_statement_before_primary_effect(
- &mut self,
- flow_state: &Flows<'cx, 'tcx>,
- stmt: &'cx Statement<'tcx>,
- location: Location,
- ) {
- debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, flow_state);
- let span = stmt.source_info.span;
-
- self.check_activations(location, span, flow_state);
-
- match &stmt.kind {
- StatementKind::Assign(box (lhs, ref rhs)) => {
- self.consume_rvalue(location, (rhs, span), flow_state);
-
- self.mutate_place(location, (*lhs, span), Shallow(None), JustWrite, flow_state);
- }
- StatementKind::FakeRead(box (_, ref place)) => {
- // Read for match doesn't access any memory and is used to
- // assert that a place is safe and live. So we don't have to
- // do any checks here.
- //
- // FIXME: Remove check that the place is initialized. This is
- // needed for now because matches don't have never patterns yet.
- // So this is the only place we prevent
- // let x: !;
- // match x {};
- // from compiling.
- self.check_if_path_or_subpath_is_moved(
- location,
- InitializationRequiringAction::Use,
- (place.as_ref(), span),
- flow_state,
- );
- }
- StatementKind::SetDiscriminant { place, variant_index: _ } => {
- self.mutate_place(location, (**place, span), Shallow(None), JustWrite, flow_state);
- }
- StatementKind::LlvmInlineAsm(ref asm) => {
- for (o, output) in iter::zip(&asm.asm.outputs, &*asm.outputs) {
- if o.is_indirect {
- // FIXME(eddyb) indirect inline asm outputs should
- // be encoded through MIR place derefs instead.
- self.access_place(
- location,
- (*output, o.span),
- (Deep, Read(ReadKind::Copy)),
- LocalMutationIsAllowed::No,
- flow_state,
- );
- self.check_if_path_or_subpath_is_moved(
- location,
- InitializationRequiringAction::Use,
- (output.as_ref(), o.span),
- flow_state,
- );
- } else {
- self.mutate_place(
- location,
- (*output, o.span),
- if o.is_rw { Deep } else { Shallow(None) },
- if o.is_rw { WriteAndRead } else { JustWrite },
- flow_state,
- );
- }
- }
- for (_, input) in asm.inputs.iter() {
- self.consume_operand(location, (input, span), flow_state);
- }
- }
-
- StatementKind::CopyNonOverlapping(box rustc_middle::mir::CopyNonOverlapping {
- ..
- }) => {
- span_bug!(
- span,
- "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
- )
- }
- StatementKind::Nop
- | StatementKind::Coverage(..)
- | StatementKind::AscribeUserType(..)
- | StatementKind::Retag { .. }
- | StatementKind::StorageLive(..) => {
- // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
- // to borrow check.
- }
- StatementKind::StorageDead(local) => {
- self.access_place(
- location,
- (Place::from(*local), span),
- (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
- LocalMutationIsAllowed::Yes,
- flow_state,
- );
- }
- }
- }
-
- fn visit_terminator_before_primary_effect(
- &mut self,
- flow_state: &Flows<'cx, 'tcx>,
- term: &'cx Terminator<'tcx>,
- loc: Location,
- ) {
- debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
- let span = term.source_info.span;
-
- self.check_activations(loc, span, flow_state);
-
- match term.kind {
- TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
- self.consume_operand(loc, (discr, span), flow_state);
- }
- TerminatorKind::Drop { place, target: _, unwind: _ } => {
- debug!(
- "visit_terminator_drop \
- loc: {:?} term: {:?} place: {:?} span: {:?}",
- loc, term, place, span
- );
-
- self.access_place(
- loc,
- (place, span),
- (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
- LocalMutationIsAllowed::Yes,
- flow_state,
- );
- }
- TerminatorKind::DropAndReplace {
- place: drop_place,
- value: ref new_value,
- target: _,
- unwind: _,
- } => {
- self.mutate_place(loc, (drop_place, span), Deep, JustWrite, flow_state);
- self.consume_operand(loc, (new_value, span), flow_state);
- }
- TerminatorKind::Call {
- ref func,
- ref args,
- ref destination,
- cleanup: _,
- from_hir_call: _,
- fn_span: _,
- } => {
- self.consume_operand(loc, (func, span), flow_state);
- for arg in args {
- self.consume_operand(loc, (arg, span), flow_state);
- }
- if let Some((dest, _ /*bb*/)) = *destination {
- self.mutate_place(loc, (dest, span), Deep, JustWrite, flow_state);
- }
- }
- TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
- self.consume_operand(loc, (cond, span), flow_state);
- use rustc_middle::mir::AssertKind;
- if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
- self.consume_operand(loc, (len, span), flow_state);
- self.consume_operand(loc, (index, span), flow_state);
- }
- }
-
- TerminatorKind::Yield { ref value, resume: _, resume_arg, drop: _ } => {
- self.consume_operand(loc, (value, span), flow_state);
- self.mutate_place(loc, (resume_arg, span), Deep, JustWrite, flow_state);
- }
-
- TerminatorKind::InlineAsm {
- template: _,
- ref operands,
- options: _,
- line_spans: _,
- destination: _,
- } => {
- for op in operands {
- match *op {
- InlineAsmOperand::In { reg: _, ref value } => {
- self.consume_operand(loc, (value, span), flow_state);
- }
- InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
- if let Some(place) = place {
- self.mutate_place(
- loc,
- (place, span),
- Shallow(None),
- JustWrite,
- flow_state,
- );
- }
- }
- InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
- self.consume_operand(loc, (in_value, span), flow_state);
- if let Some(out_place) = out_place {
- self.mutate_place(
- loc,
- (out_place, span),
- Shallow(None),
- JustWrite,
- flow_state,
- );
- }
- }
- InlineAsmOperand::Const { value: _ }
- | InlineAsmOperand::SymFn { value: _ }
- | InlineAsmOperand::SymStatic { def_id: _ } => {}
- }
- }
- }
-
- TerminatorKind::Goto { target: _ }
- | TerminatorKind::Abort
- | TerminatorKind::Unreachable
- | TerminatorKind::Resume
- | TerminatorKind::Return
- | TerminatorKind::GeneratorDrop
- | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
- | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
- // no data used, thus irrelevant to borrowck
- }
- }
- }
-
- fn visit_terminator_after_primary_effect(
- &mut self,
- flow_state: &Flows<'cx, 'tcx>,
- term: &'cx Terminator<'tcx>,
- loc: Location,
- ) {
- let span = term.source_info.span;
-
- match term.kind {
- TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
- if self.movable_generator {
- // Look for any active borrows to locals
- let borrow_set = self.borrow_set.clone();
- for i in flow_state.borrows.iter() {
- let borrow = &borrow_set[i];
- self.check_for_local_borrow(borrow, span);
- }
- }
- }
-
- TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
- // Returning from the function implicitly kills storage for all locals and statics.
- // Often, the storage will already have been killed by an explicit
- // StorageDead, but we don't always emit those (notably on unwind paths),
- // so this "extra check" serves as a kind of backup.
- let borrow_set = self.borrow_set.clone();
- for i in flow_state.borrows.iter() {
- let borrow = &borrow_set[i];
- self.check_for_invalidation_at_exit(loc, borrow, span);
- }
- }
-
- TerminatorKind::Abort
- | TerminatorKind::Assert { .. }
- | TerminatorKind::Call { .. }
- | TerminatorKind::Drop { .. }
- | TerminatorKind::DropAndReplace { .. }
- | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
- | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
- | TerminatorKind::Goto { .. }
- | TerminatorKind::SwitchInt { .. }
- | TerminatorKind::Unreachable
- | TerminatorKind::InlineAsm { .. } => {}
- }
- }
-}
-
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-enum MutateMode {
- JustWrite,
- WriteAndRead,
-}
-
-use self::AccessDepth::{Deep, Shallow};
-use self::ReadOrWrite::{Activation, Read, Reservation, Write};
-
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-enum ArtificialField {
- ArrayLength,
- ShallowBorrow,
-}
-
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-enum AccessDepth {
- /// From the RFC: "A *shallow* access means that the immediate
- /// fields reached at P are accessed, but references or pointers
- /// found within are not dereferenced. Right now, the only access
- /// that is shallow is an assignment like `x = ...;`, which would
- /// be a *shallow write* of `x`."
- Shallow(Option<ArtificialField>),
-
- /// From the RFC: "A *deep* access means that all data reachable
- /// through the given place may be invalidated or accesses by
- /// this action."
- Deep,
-
- /// Access is Deep only when there is a Drop implementation that
- /// can reach the data behind the reference.
- Drop,
-}
-
-/// Kind of access to a value: read or write
-/// (For informational purposes only)
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-enum ReadOrWrite {
- /// From the RFC: "A *read* means that the existing data may be
- /// read, but will not be changed."
- Read(ReadKind),
-
- /// From the RFC: "A *write* means that the data may be mutated to
- /// new values or otherwise invalidated (for example, it could be
- /// de-initialized, as in a move operation).
- Write(WriteKind),
-
- /// For two-phase borrows, we distinguish a reservation (which is treated
- /// like a Read) from an activation (which is treated like a write), and
- /// each of those is furthermore distinguished from Reads/Writes above.
- Reservation(WriteKind),
- Activation(WriteKind, BorrowIndex),
-}
-
-/// Kind of read access to a value
-/// (For informational purposes only)
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-enum ReadKind {
- Borrow(BorrowKind),
- Copy,
-}
-
-/// Kind of write access to a value
-/// (For informational purposes only)
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-enum WriteKind {
- StorageDeadOrDrop,
- MutableBorrow(BorrowKind),
- Mutate,
- Move,
-}
-
-/// When checking permissions for a place access, this flag is used to indicate that an immutable
-/// local place can be mutated.
-//
-// FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
-// - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
-// - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
-// `is_declared_mutable()`.
-// - Take flow state into consideration in `is_assignable()` for local variables.
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-enum LocalMutationIsAllowed {
- Yes,
- /// We want use of immutable upvars to cause a "write to immutable upvar"
- /// error, not an "reassignment" error.
- ExceptUpvars,
- No,
-}
-
-#[derive(Copy, Clone, Debug)]
-enum InitializationRequiringAction {
- Update,
- Borrow,
- MatchOn,
- Use,
- Assignment,
- PartialAssignment,
-}
-
-struct RootPlace<'tcx> {
- place_local: Local,
- place_projection: &'tcx [PlaceElem<'tcx>],
- is_local_mutation_allowed: LocalMutationIsAllowed,
-}
-
-impl InitializationRequiringAction {
- fn as_noun(self) -> &'static str {
- match self {
- InitializationRequiringAction::Update => "update",
- InitializationRequiringAction::Borrow => "borrow",
- InitializationRequiringAction::MatchOn => "use", // no good noun
- InitializationRequiringAction::Use => "use",
- InitializationRequiringAction::Assignment => "assign",
- InitializationRequiringAction::PartialAssignment => "assign to part",
- }
- }
-
- fn as_verb_in_past_tense(self) -> &'static str {
- match self {
- InitializationRequiringAction::Update => "updated",
- InitializationRequiringAction::Borrow => "borrowed",
- InitializationRequiringAction::MatchOn => "matched on",
- InitializationRequiringAction::Use => "used",
- InitializationRequiringAction::Assignment => "assigned",
- InitializationRequiringAction::PartialAssignment => "partially assigned",
- }
- }
-}
-
-impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
- fn body(&self) -> &'cx Body<'tcx> {
- self.body
- }
-
- /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
- /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
- /// place is initialized and (b) it is not borrowed in some way that would prevent this
- /// access.
- ///
- /// Returns `true` if an error is reported.
- fn access_place(
- &mut self,
- location: Location,
- place_span: (Place<'tcx>, Span),
- kind: (AccessDepth, ReadOrWrite),
- is_local_mutation_allowed: LocalMutationIsAllowed,
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- let (sd, rw) = kind;
-
- if let Activation(_, borrow_index) = rw {
- if self.reservation_error_reported.contains(&place_span.0) {
- debug!(
- "skipping access_place for activation of invalid reservation \
- place: {:?} borrow_index: {:?}",
- place_span.0, borrow_index
- );
- return;
- }
- }
-
- // Check is_empty() first because it's the common case, and doing that
- // way we avoid the clone() call.
- if !self.access_place_error_reported.is_empty()
- && self.access_place_error_reported.contains(&(place_span.0, place_span.1))
- {
- debug!(
- "access_place: suppressing error place_span=`{:?}` kind=`{:?}`",
- place_span, kind
- );
- return;
- }
-
- let mutability_error = self.check_access_permissions(
- place_span,
- rw,
- is_local_mutation_allowed,
- flow_state,
- location,
- );
- let conflict_error =
- self.check_access_for_conflict(location, place_span, sd, rw, flow_state);
-
- if let (Activation(_, borrow_idx), true) = (kind.1, conflict_error) {
- // Suppress this warning when there's an error being emitted for the
- // same borrow: fixing the error is likely to fix the warning.
- self.reservation_warnings.remove(&borrow_idx);
- }
-
- if conflict_error || mutability_error {
- debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
-
- self.access_place_error_reported.insert((place_span.0, place_span.1));
- }
- }
-
- fn check_access_for_conflict(
- &mut self,
- location: Location,
- place_span: (Place<'tcx>, Span),
- sd: AccessDepth,
- rw: ReadOrWrite,
- flow_state: &Flows<'cx, 'tcx>,
- ) -> bool {
- debug!(
- "check_access_for_conflict(location={:?}, place_span={:?}, sd={:?}, rw={:?})",
- location, place_span, sd, rw,
- );
-
- let mut error_reported = false;
- let tcx = self.infcx.tcx;
- let body = self.body;
- let borrow_set = self.borrow_set.clone();
-
- // Use polonius output if it has been enabled.
- let polonius_output = self.polonius_output.clone();
- let borrows_in_scope = if let Some(polonius) = &polonius_output {
- let location = self.location_table.start_index(location);
- Either::Left(polonius.errors_at(location).iter().copied())
- } else {
- Either::Right(flow_state.borrows.iter())
- };
-
- each_borrow_involving_path(
- self,
- tcx,
- body,
- location,
- (sd, place_span.0),
- &borrow_set,
- borrows_in_scope,
- |this, borrow_index, borrow| match (rw, borrow.kind) {
- // Obviously an activation is compatible with its own
- // reservation (or even prior activating uses of same
- // borrow); so don't check if they interfere.
- //
- // NOTE: *reservations* do conflict with themselves;
- // thus aren't injecting unsoundenss w/ this check.)
- (Activation(_, activating), _) if activating == borrow_index => {
- debug!(
- "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
- skipping {:?} b/c activation of same borrow_index",
- place_span,
- sd,
- rw,
- (borrow_index, borrow),
- );
- Control::Continue
- }
-
- (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
- | (
- Read(ReadKind::Borrow(BorrowKind::Shallow)),
- BorrowKind::Unique | BorrowKind::Mut { .. },
- ) => Control::Continue,
-
- (Write(WriteKind::Move), BorrowKind::Shallow) => {
- // Handled by initialization checks.
- Control::Continue
- }
-
- (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
- // Reading from mere reservations of mutable-borrows is OK.
- if !is_active(&this.dominators, borrow, location) {
- assert!(allow_two_phase_borrow(borrow.kind));
- return Control::Continue;
- }
-
- error_reported = true;
- match kind {
- ReadKind::Copy => {
- this.report_use_while_mutably_borrowed(location, place_span, borrow)
- .buffer(&mut this.errors_buffer);
- }
- ReadKind::Borrow(bk) => {
- this.report_conflicting_borrow(location, place_span, bk, borrow)
- .buffer(&mut this.errors_buffer);
- }
- }
- Control::Break
- }
-
- (
- Reservation(WriteKind::MutableBorrow(bk)),
- BorrowKind::Shallow | BorrowKind::Shared,
- ) if { tcx.migrate_borrowck() && this.borrow_set.contains(&location) } => {
- let bi = this.borrow_set.get_index_of(&location).unwrap();
- debug!(
- "recording invalid reservation of place: {:?} with \
- borrow index {:?} as warning",
- place_span.0, bi,
- );
- // rust-lang/rust#56254 - This was previously permitted on
- // the 2018 edition so we emit it as a warning. We buffer
- // these sepately so that we only emit a warning if borrow
- // checking was otherwise successful.
- this.reservation_warnings
- .insert(bi, (place_span.0, place_span.1, location, bk, borrow.clone()));
-
- // Don't suppress actual errors.
- Control::Continue
- }
-
- (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
- match rw {
- Reservation(..) => {
- debug!(
- "recording invalid reservation of \
- place: {:?}",
- place_span.0
- );
- this.reservation_error_reported.insert(place_span.0);
- }
- Activation(_, activating) => {
- debug!(
- "observing check_place for activation of \
- borrow_index: {:?}",
- activating
- );
- }
- Read(..) | Write(..) => {}
- }
-
- error_reported = true;
- match kind {
- WriteKind::MutableBorrow(bk) => {
- this.report_conflicting_borrow(location, place_span, bk, borrow)
- .buffer(&mut this.errors_buffer);
- }
- WriteKind::StorageDeadOrDrop => this
- .report_borrowed_value_does_not_live_long_enough(
- location,
- borrow,
- place_span,
- Some(kind),
- ),
- WriteKind::Mutate => {
- this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
- }
- WriteKind::Move => {
- this.report_move_out_while_borrowed(location, place_span, borrow)
- }
- }
- Control::Break
- }
- },
- );
-
- error_reported
- }
-
- fn mutate_place(
- &mut self,
- location: Location,
- place_span: (Place<'tcx>, Span),
- kind: AccessDepth,
- mode: MutateMode,
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- // Write of P[i] or *P, or WriteAndRead of any P, requires P init'd.
- match mode {
- MutateMode::WriteAndRead => {
- self.check_if_path_or_subpath_is_moved(
- location,
- InitializationRequiringAction::Update,
- (place_span.0.as_ref(), place_span.1),
- flow_state,
- );
- }
- MutateMode::JustWrite => {
- self.check_if_assigned_path_is_moved(location, place_span, flow_state);
- }
- }
-
- // Special case: you can assign an immutable local variable
- // (e.g., `x = ...`) so long as it has never been initialized
- // before (at this point in the flow).
- if let Some(local) = place_span.0.as_local() {
- if let Mutability::Not = self.body.local_decls[local].mutability {
- // check for reassignments to immutable local variables
- self.check_if_reassignment_to_immutable_state(
- location, local, place_span, flow_state,
- );
- return;
- }
- }
-
- // Otherwise, use the normal access permission rules.
- self.access_place(
- location,
- place_span,
- (kind, Write(WriteKind::Mutate)),
- LocalMutationIsAllowed::No,
- flow_state,
- );
- }
-
- fn consume_rvalue(
- &mut self,
- location: Location,
- (rvalue, span): (&'cx Rvalue<'tcx>, Span),
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- match *rvalue {
- Rvalue::Ref(_ /*rgn*/, bk, place) => {
- let access_kind = match bk {
- BorrowKind::Shallow => {
- (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
- }
- BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
- BorrowKind::Unique | BorrowKind::Mut { .. } => {
- let wk = WriteKind::MutableBorrow(bk);
- if allow_two_phase_borrow(bk) {
- (Deep, Reservation(wk))
- } else {
- (Deep, Write(wk))
- }
- }
- };
-
- self.access_place(
- location,
- (place, span),
- access_kind,
- LocalMutationIsAllowed::No,
- flow_state,
- );
-
- let action = if bk == BorrowKind::Shallow {
- InitializationRequiringAction::MatchOn
- } else {
- InitializationRequiringAction::Borrow
- };
-
- self.check_if_path_or_subpath_is_moved(
- location,
- action,
- (place.as_ref(), span),
- flow_state,
- );
- }
-
- Rvalue::AddressOf(mutability, place) => {
- let access_kind = match mutability {
- Mutability::Mut => (
- Deep,
- Write(WriteKind::MutableBorrow(BorrowKind::Mut {
- allow_two_phase_borrow: false,
- })),
- ),
- Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
- };
-
- self.access_place(
- location,
- (place, span),
- access_kind,
- LocalMutationIsAllowed::No,
- flow_state,
- );
-
- self.check_if_path_or_subpath_is_moved(
- location,
- InitializationRequiringAction::Borrow,
- (place.as_ref(), span),
- flow_state,
- );
- }
-
- Rvalue::ThreadLocalRef(_) => {}
-
- Rvalue::Use(ref operand)
- | Rvalue::Repeat(ref operand, _)
- | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
- | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
- self.consume_operand(location, (operand, span), flow_state)
- }
-
- Rvalue::Len(place) | Rvalue::Discriminant(place) => {
- let af = match *rvalue {
- Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
- Rvalue::Discriminant(..) => None,
- _ => unreachable!(),
- };
- self.access_place(
- location,
- (place, span),
- (Shallow(af), Read(ReadKind::Copy)),
- LocalMutationIsAllowed::No,
- flow_state,
- );
- self.check_if_path_or_subpath_is_moved(
- location,
- InitializationRequiringAction::Use,
- (place.as_ref(), span),
- flow_state,
- );
- }
-
- Rvalue::BinaryOp(_bin_op, box (ref operand1, ref operand2))
- | Rvalue::CheckedBinaryOp(_bin_op, box (ref operand1, ref operand2)) => {
- self.consume_operand(location, (operand1, span), flow_state);
- self.consume_operand(location, (operand2, span), flow_state);
- }
-
- Rvalue::NullaryOp(_op, _ty) => {
- // nullary ops take no dynamic input; no borrowck effect.
- //
- // FIXME: is above actually true? Do we want to track
- // the fact that uninitialized data can be created via
- // `NullOp::Box`?
- }
-
- Rvalue::Aggregate(ref aggregate_kind, ref operands) => {
- // We need to report back the list of mutable upvars that were
- // moved into the closure and subsequently used by the closure,
- // in order to populate our used_mut set.
- match **aggregate_kind {
- AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
- let BorrowCheckResult { used_mut_upvars, .. } =
- self.infcx.tcx.mir_borrowck(def_id.expect_local());
- debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
- for field in used_mut_upvars {
- self.propagate_closure_used_mut_upvar(&operands[field.index()]);
- }
- }
- AggregateKind::Adt(..)
- | AggregateKind::Array(..)
- | AggregateKind::Tuple { .. } => (),
- }
-
- for operand in operands {
- self.consume_operand(location, (operand, span), flow_state);
- }
- }
- }
- }
-
- fn propagate_closure_used_mut_upvar(&mut self, operand: &Operand<'tcx>) {
- let propagate_closure_used_mut_place = |this: &mut Self, place: Place<'tcx>| {
- // We have three possibilities here:
- // a. We are modifying something through a mut-ref
- // b. We are modifying something that is local to our parent
- // c. Current body is a nested closure, and we are modifying path starting from
- // a Place captured by our parent closure.
-
- // Handle (c), the path being modified is exactly the path captured by our parent
- if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
- this.used_mut_upvars.push(field);
- return;
- }
-
- for (place_ref, proj) in place.iter_projections().rev() {
- // Handle (a)
- if proj == ProjectionElem::Deref {
- match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
- // We aren't modifying a variable directly
- ty::Ref(_, _, hir::Mutability::Mut) => return,
-
- _ => {}
- }
- }
-
- // Handle (c)
- if let Some(field) = this.is_upvar_field_projection(place_ref) {
- this.used_mut_upvars.push(field);
- return;
- }
- }
-
- // Handle(b)
- this.used_mut.insert(place.local);
- };
-
- // This relies on the current way that by-value
- // captures of a closure are copied/moved directly
- // when generating MIR.
- match *operand {
- Operand::Move(place) | Operand::Copy(place) => {
- match place.as_local() {
- Some(local) if !self.body.local_decls[local].is_user_variable() => {
- if self.body.local_decls[local].ty.is_mutable_ptr() {
- // The variable will be marked as mutable by the borrow.
- return;
- }
- // This is an edge case where we have a `move` closure
- // inside a non-move closure, and the inner closure
- // contains a mutation:
- //
- // let mut i = 0;
- // || { move || { i += 1; }; };
- //
- // In this case our usual strategy of assuming that the
- // variable will be captured by mutable reference is
- // wrong, since `i` can be copied into the inner
- // closure from a shared reference.
- //
- // As such we have to search for the local that this
- // capture comes from and mark it as being used as mut.
-
- let temp_mpi = self.move_data.rev_lookup.find_local(local);
- let init = if let [init_index] = *self.move_data.init_path_map[temp_mpi] {
- &self.move_data.inits[init_index]
- } else {
- bug!("temporary should be initialized exactly once")
- };
-
- let loc = match init.location {
- InitLocation::Statement(stmt) => stmt,
- _ => bug!("temporary initialized in arguments"),
- };
-
- let body = self.body;
- let bbd = &body[loc.block];
- let stmt = &bbd.statements[loc.statement_index];
- debug!("temporary assigned in: stmt={:?}", stmt);
-
- if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
- {
- propagate_closure_used_mut_place(self, source);
- } else {
- bug!(
- "closures should only capture user variables \
- or references to user variables"
- );
- }
- }
- _ => propagate_closure_used_mut_place(self, place),
- }
- }
- Operand::Constant(..) => {}
- }
- }
-
- fn consume_operand(
- &mut self,
- location: Location,
- (operand, span): (&'cx Operand<'tcx>, Span),
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- match *operand {
- Operand::Copy(place) => {
- // copy of place: check if this is "copy of frozen path"
- // (FIXME: see check_loans.rs)
- self.access_place(
- location,
- (place, span),
- (Deep, Read(ReadKind::Copy)),
- LocalMutationIsAllowed::No,
- flow_state,
- );
-
- // Finally, check if path was already moved.
- self.check_if_path_or_subpath_is_moved(
- location,
- InitializationRequiringAction::Use,
- (place.as_ref(), span),
- flow_state,
- );
- }
- Operand::Move(place) => {
- // move of place: check if this is move of already borrowed path
- self.access_place(
- location,
- (place, span),
- (Deep, Write(WriteKind::Move)),
- LocalMutationIsAllowed::Yes,
- flow_state,
- );
-
- // Finally, check if path was already moved.
- self.check_if_path_or_subpath_is_moved(
- location,
- InitializationRequiringAction::Use,
- (place.as_ref(), span),
- flow_state,
- );
- }
- Operand::Constant(_) => {}
- }
- }
-
- /// Checks whether a borrow of this place is invalidated when the function
- /// exits
- fn check_for_invalidation_at_exit(
- &mut self,
- location: Location,
- borrow: &BorrowData<'tcx>,
- span: Span,
- ) {
- debug!("check_for_invalidation_at_exit({:?})", borrow);
- let place = borrow.borrowed_place;
- let mut root_place = PlaceRef { local: place.local, projection: &[] };
-
- // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
- // we just know that all locals are dropped at function exit (otherwise
- // we'll have a memory leak) and assume that all statics have a destructor.
- //
- // FIXME: allow thread-locals to borrow other thread locals?
-
- let (might_be_alive, will_be_dropped) =
- if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
- // Thread-locals might be dropped after the function exits
- // We have to dereference the outer reference because
- // borrows don't conflict behind shared references.
- root_place.projection = DEREF_PROJECTION;
- (true, true)
- } else {
- (false, self.locals_are_invalidated_at_exit)
- };
-
- if !will_be_dropped {
- debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
- return;
- }
-
- let sd = if might_be_alive { Deep } else { Shallow(None) };
-
- if places_conflict::borrow_conflicts_with_place(
- self.infcx.tcx,
- &self.body,
- place,
- borrow.kind,
- root_place,
- sd,
- places_conflict::PlaceConflictBias::Overlap,
- ) {
- debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
- // FIXME: should be talking about the region lifetime instead
- // of just a span here.
- let span = self.infcx.tcx.sess.source_map().end_point(span);
- self.report_borrowed_value_does_not_live_long_enough(
- location,
- borrow,
- (place, span),
- None,
- )
- }
- }
-
- /// Reports an error if this is a borrow of local data.
- /// This is called for all Yield expressions on movable generators
- fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
- debug!("check_for_local_borrow({:?})", borrow);
-
- if borrow_of_local_data(borrow.borrowed_place) {
- let err = self.cannot_borrow_across_generator_yield(
- self.retrieve_borrow_spans(borrow).var_or_use(),
- yield_span,
- );
-
- err.buffer(&mut self.errors_buffer);
- }
- }
-
- fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
- // Two-phase borrow support: For each activation that is newly
- // generated at this statement, check if it interferes with
- // another borrow.
- let borrow_set = self.borrow_set.clone();
- for &borrow_index in borrow_set.activations_at_location(location) {
- let borrow = &borrow_set[borrow_index];
-
- // only mutable borrows should be 2-phase
- assert!(match borrow.kind {
- BorrowKind::Shared | BorrowKind::Shallow => false,
- BorrowKind::Unique | BorrowKind::Mut { .. } => true,
- });
-
- self.access_place(
- location,
- (borrow.borrowed_place, span),
- (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
- LocalMutationIsAllowed::No,
- flow_state,
- );
- // We do not need to call `check_if_path_or_subpath_is_moved`
- // again, as we already called it when we made the
- // initial reservation.
- }
- }
-
- fn check_if_reassignment_to_immutable_state(
- &mut self,
- location: Location,
- local: Local,
- place_span: (Place<'tcx>, Span),
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- debug!("check_if_reassignment_to_immutable_state({:?})", local);
-
- // Check if any of the initializiations of `local` have happened yet:
- if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
- // And, if so, report an error.
- let init = &self.move_data.inits[init_index];
- let span = init.span(&self.body);
- self.report_illegal_reassignment(location, place_span, span, place_span.0);
- }
- }
-
- fn check_if_full_path_is_moved(
- &mut self,
- location: Location,
- desired_action: InitializationRequiringAction,
- place_span: (PlaceRef<'tcx>, Span),
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- let maybe_uninits = &flow_state.uninits;
-
- // Bad scenarios:
- //
- // 1. Move of `a.b.c`, use of `a.b.c`
- // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
- // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
- // partial initialization support, one might have `a.x`
- // initialized but not `a.b`.
- //
- // OK scenarios:
- //
- // 4. Move of `a.b.c`, use of `a.b.d`
- // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
- // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
- // must have been initialized for the use to be sound.
- // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
-
- // The dataflow tracks shallow prefixes distinctly (that is,
- // field-accesses on P distinctly from P itself), in order to
- // track substructure initialization separately from the whole
- // structure.
- //
- // E.g., when looking at (*a.b.c).d, if the closest prefix for
- // which we have a MovePath is `a.b`, then that means that the
- // initialization state of `a.b` is all we need to inspect to
- // know if `a.b.c` is valid (and from that we infer that the
- // dereference and `.d` access is also valid, since we assume
- // `a.b.c` is assigned a reference to an initialized and
- // well-formed record structure.)
-
- // Therefore, if we seek out the *closest* prefix for which we
- // have a MovePath, that should capture the initialization
- // state for the place scenario.
- //
- // This code covers scenarios 1, 2, and 3.
-
- debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
- let (prefix, mpi) = self.move_path_closest_to(place_span.0);
- if maybe_uninits.contains(mpi) {
- self.report_use_of_moved_or_uninitialized(
- location,
- desired_action,
- (prefix, place_span.0, place_span.1),
- mpi,
- );
- } // Only query longest prefix with a MovePath, not further
- // ancestors; dataflow recurs on children when parents
- // move (to support partial (re)inits).
- //
- // (I.e., querying parents breaks scenario 7; but may want
- // to do such a query based on partial-init feature-gate.)
- }
-
- /// Subslices correspond to multiple move paths, so we iterate through the
- /// elements of the base array. For each element we check
- ///
- /// * Does this element overlap with our slice.
- /// * Is any part of it uninitialized.
- fn check_if_subslice_element_is_moved(
- &mut self,
- location: Location,
- desired_action: InitializationRequiringAction,
- place_span: (PlaceRef<'tcx>, Span),
- maybe_uninits: &BitSet<MovePathIndex>,
- from: u64,
- to: u64,
- ) {
- if let Some(mpi) = self.move_path_for_place(place_span.0) {
- let move_paths = &self.move_data.move_paths;
-
- let root_path = &move_paths[mpi];
- for (child_mpi, child_move_path) in root_path.children(move_paths) {
- let last_proj = child_move_path.place.projection.last().unwrap();
- if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
- debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");
-
- if (from..to).contains(offset) {
- let uninit_child =
- self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
- maybe_uninits.contains(mpi)
- });
-
- if let Some(uninit_child) = uninit_child {
- self.report_use_of_moved_or_uninitialized(
- location,
- desired_action,
- (place_span.0, place_span.0, place_span.1),
- uninit_child,
- );
- return; // don't bother finding other problems.
- }
- }
- }
- }
- }
- }
-
- fn check_if_path_or_subpath_is_moved(
- &mut self,
- location: Location,
- desired_action: InitializationRequiringAction,
- place_span: (PlaceRef<'tcx>, Span),
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- let maybe_uninits = &flow_state.uninits;
-
- // Bad scenarios:
- //
- // 1. Move of `a.b.c`, use of `a` or `a.b`
- // partial initialization support, one might have `a.x`
- // initialized but not `a.b`.
- // 2. All bad scenarios from `check_if_full_path_is_moved`
- //
- // OK scenarios:
- //
- // 3. Move of `a.b.c`, use of `a.b.d`
- // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
- // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
- // must have been initialized for the use to be sound.
- // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`
-
- self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);
-
- if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
- place_span.0.last_projection()
- {
- let place_ty = place_base.ty(self.body(), self.infcx.tcx);
- if let ty::Array(..) = place_ty.ty.kind() {
- self.check_if_subslice_element_is_moved(
- location,
- desired_action,
- (place_base, place_span.1),
- maybe_uninits,
- from,
- to,
- );
- return;
- }
- }
-
- // A move of any shallow suffix of `place` also interferes
- // with an attempt to use `place`. This is scenario 3 above.
- //
- // (Distinct from handling of scenarios 1+2+4 above because
- // `place` does not interfere with suffixes of its prefixes,
- // e.g., `a.b.c` does not interfere with `a.b.d`)
- //
- // This code covers scenario 1.
-
- debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
- if let Some(mpi) = self.move_path_for_place(place_span.0) {
- let uninit_mpi = self
- .move_data
- .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));
-
- if let Some(uninit_mpi) = uninit_mpi {
- self.report_use_of_moved_or_uninitialized(
- location,
- desired_action,
- (place_span.0, place_span.0, place_span.1),
- uninit_mpi,
- );
- return; // don't bother finding other problems.
- }
- }
- }
-
- /// Currently MoveData does not store entries for all places in
- /// the input MIR. For example it will currently filter out
- /// places that are Copy; thus we do not track places of shared
- /// reference type. This routine will walk up a place along its
- /// prefixes, searching for a foundational place that *is*
- /// tracked in the MoveData.
- ///
- /// An Err result includes a tag indicated why the search failed.
- /// Currently this can only occur if the place is built off of a
- /// static variable, as we do not track those in the MoveData.
- fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
- match self.move_data.rev_lookup.find(place) {
- LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
- (self.move_data.move_paths[mpi].place.as_ref(), mpi)
- }
- LookupResult::Parent(None) => panic!("should have move path for every Local"),
- }
- }
-
- fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
- // If returns None, then there is no move path corresponding
- // to a direct owner of `place` (which means there is nothing
- // that borrowck tracks for its analysis).
-
- match self.move_data.rev_lookup.find(place) {
- LookupResult::Parent(_) => None,
- LookupResult::Exact(mpi) => Some(mpi),
- }
- }
-
- fn check_if_assigned_path_is_moved(
- &mut self,
- location: Location,
- (place, span): (Place<'tcx>, Span),
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- debug!("check_if_assigned_path_is_moved place: {:?}", place);
-
- // None case => assigning to `x` does not require `x` be initialized.
- for (place_base, elem) in place.iter_projections().rev() {
- match elem {
- ProjectionElem::Index(_/*operand*/) |
- ProjectionElem::ConstantIndex { .. } |
- // assigning to P[i] requires P to be valid.
- ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
- // assigning to (P->variant) is okay if assigning to `P` is okay
- //
- // FIXME: is this true even if P is an adt with a dtor?
- { }
-
- // assigning to (*P) requires P to be initialized
- ProjectionElem::Deref => {
- self.check_if_full_path_is_moved(
- location, InitializationRequiringAction::Use,
- (place_base, span), flow_state);
- // (base initialized; no need to
- // recur further)
- break;
- }
-
- ProjectionElem::Subslice { .. } => {
- panic!("we don't allow assignments to subslices, location: {:?}",
- location);
- }
-
- ProjectionElem::Field(..) => {
- // if type of `P` has a dtor, then
- // assigning to `P.f` requires `P` itself
- // be already initialized
- let tcx = self.infcx.tcx;
- let base_ty = place_base.ty(self.body(), tcx).ty;
- match base_ty.kind() {
- ty::Adt(def, _) if def.has_dtor(tcx) => {
- self.check_if_path_or_subpath_is_moved(
- location, InitializationRequiringAction::Assignment,
- (place_base, span), flow_state);
-
- // (base initialized; no need to
- // recur further)
- break;
- }
-
- // Once `let s; s.x = V; read(s.x);`,
- // is allowed, remove this match arm.
- ty::Adt(..) | ty::Tuple(..) => {
- check_parent_of_field(self, location, place_base, span, flow_state);
-
- // rust-lang/rust#21232, #54499, #54986: during period where we reject
- // partial initialization, do not complain about unnecessary `mut` on
- // an attempt to do a partial initialization.
- self.used_mut.insert(place.local);
- }
-
- _ => {}
- }
- }
- }
- }
-
- fn check_parent_of_field<'cx, 'tcx>(
- this: &mut MirBorrowckCtxt<'cx, 'tcx>,
- location: Location,
- base: PlaceRef<'tcx>,
- span: Span,
- flow_state: &Flows<'cx, 'tcx>,
- ) {
- // rust-lang/rust#21232: Until Rust allows reads from the
- // initialized parts of partially initialized structs, we
- // will, starting with the 2018 edition, reject attempts
- // to write to structs that are not fully initialized.
- //
- // In other words, *until* we allow this:
- //
- // 1. `let mut s; s.x = Val; read(s.x);`
- //
- // we will for now disallow this:
- //
- // 2. `let mut s; s.x = Val;`
- //
- // and also this:
- //
- // 3. `let mut s = ...; drop(s); s.x=Val;`
- //
- // This does not use check_if_path_or_subpath_is_moved,
- // because we want to *allow* reinitializations of fields:
- // e.g., want to allow
- //
- // `let mut s = ...; drop(s.x); s.x=Val;`
- //
- // This does not use check_if_full_path_is_moved on
- // `base`, because that would report an error about the
- // `base` as a whole, but in this scenario we *really*
- // want to report an error about the actual thing that was
- // moved, which may be some prefix of `base`.
-
- // Shallow so that we'll stop at any dereference; we'll
- // report errors about issues with such bases elsewhere.
- let maybe_uninits = &flow_state.uninits;
-
- // Find the shortest uninitialized prefix you can reach
- // without going over a Deref.
- let mut shortest_uninit_seen = None;
- for prefix in this.prefixes(base, PrefixSet::Shallow) {
- let mpi = match this.move_path_for_place(prefix) {
- Some(mpi) => mpi,
- None => continue,
- };
-
- if maybe_uninits.contains(mpi) {
- debug!(
- "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
- shortest_uninit_seen,
- Some((prefix, mpi))
- );
- shortest_uninit_seen = Some((prefix, mpi));
- } else {
- debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
- }
- }
-
- if let Some((prefix, mpi)) = shortest_uninit_seen {
- // Check for a reassignment into an uninitialized field of a union (for example,
- // after a move out). In this case, do not report an error here. There is an
- // exception, if this is the first assignment into the union (that is, there is
- // no move out from an earlier location) then this is an attempt at initialization
- // of the union - we should error in that case.
- let tcx = this.infcx.tcx;
- if base.ty(this.body(), tcx).ty.is_union() {
- if this.move_data.path_map[mpi].iter().any(|moi| {
- this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
- }) {
- return;
- }
- }
-
- this.report_use_of_moved_or_uninitialized(
- location,
- InitializationRequiringAction::PartialAssignment,
- (prefix, base, span),
- mpi,
- );
- }
- }
- }
-
- /// Checks the permissions for the given place and read or write kind
- ///
- /// Returns `true` if an error is reported.
- fn check_access_permissions(
- &mut self,
- (place, span): (Place<'tcx>, Span),
- kind: ReadOrWrite,
- is_local_mutation_allowed: LocalMutationIsAllowed,
- flow_state: &Flows<'cx, 'tcx>,
- location: Location,
- ) -> bool {
- debug!(
- "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
- place, kind, is_local_mutation_allowed
- );
-
- let error_access;
- let the_place_err;
-
- match kind {
- Reservation(WriteKind::MutableBorrow(
- borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
- ))
- | Write(WriteKind::MutableBorrow(
- borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
- )) => {
- let is_local_mutation_allowed = match borrow_kind {
- BorrowKind::Unique => LocalMutationIsAllowed::Yes,
- BorrowKind::Mut { .. } => is_local_mutation_allowed,
- BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
- };
- match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
- Ok(root_place) => {
- self.add_used_mut(root_place, flow_state);
- return false;
- }
- Err(place_err) => {
- error_access = AccessKind::MutableBorrow;
- the_place_err = place_err;
- }
- }
- }
- Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
- match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
- Ok(root_place) => {
- self.add_used_mut(root_place, flow_state);
- return false;
- }
- Err(place_err) => {
- error_access = AccessKind::Mutate;
- the_place_err = place_err;
- }
- }
- }
-
- Reservation(
- WriteKind::Move
- | WriteKind::StorageDeadOrDrop
- | WriteKind::MutableBorrow(BorrowKind::Shared)
- | WriteKind::MutableBorrow(BorrowKind::Shallow),
- )
- | Write(
- WriteKind::Move
- | WriteKind::StorageDeadOrDrop
- | WriteKind::MutableBorrow(BorrowKind::Shared)
- | WriteKind::MutableBorrow(BorrowKind::Shallow),
- ) => {
- if let (Err(_), true) = (
- self.is_mutable(place.as_ref(), is_local_mutation_allowed),
- self.errors_buffer.is_empty(),
- ) {
- // rust-lang/rust#46908: In pure NLL mode this code path should be
- // unreachable, but we use `delay_span_bug` because we can hit this when
- // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
- // enabled. We don't want to ICE for that case, as other errors will have
- // been emitted (#52262).
- self.infcx.tcx.sess.delay_span_bug(
- span,
- &format!(
- "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
- place, kind,
- ),
- );
- }
- return false;
- }
- Activation(..) => {
- // permission checks are done at Reservation point.
- return false;
- }
- Read(
- ReadKind::Borrow(
- BorrowKind::Unique
- | BorrowKind::Mut { .. }
- | BorrowKind::Shared
- | BorrowKind::Shallow,
- )
- | ReadKind::Copy,
- ) => {
- // Access authorized
- return false;
- }
- }
-
- // rust-lang/rust#21232, #54986: during period where we reject
- // partial initialization, do not complain about mutability
- // errors except for actual mutation (as opposed to an attempt
- // to do a partial initialization).
- let previously_initialized =
- self.is_local_ever_initialized(place.local, flow_state).is_some();
-
- // at this point, we have set up the error reporting state.
- if previously_initialized {
- self.report_mutability_error(place, span, the_place_err, error_access, location);
- true
- } else {
- false
- }
- }
-
- fn is_local_ever_initialized(
- &self,
- local: Local,
- flow_state: &Flows<'cx, 'tcx>,
- ) -> Option<InitIndex> {
- let mpi = self.move_data.rev_lookup.find_local(local);
- let ii = &self.move_data.init_path_map[mpi];
- for &index in ii {
- if flow_state.ever_inits.contains(index) {
- return Some(index);
- }
- }
- None
- }
-
- /// Adds the place into the used mutable variables set
- fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
- match root_place {
- RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
- // If the local may have been initialized, and it is now currently being
- // mutated, then it is justified to be annotated with the `mut`
- // keyword, since the mutation may be a possible reassignment.
- if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
- && self.is_local_ever_initialized(local, flow_state).is_some()
- {
- self.used_mut.insert(local);
- }
- }
- RootPlace {
- place_local: _,
- place_projection: _,
- is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
- } => {}
- RootPlace {
- place_local,
- place_projection: place_projection @ [.., _],
- is_local_mutation_allowed: _,
- } => {
- if let Some(field) = self.is_upvar_field_projection(PlaceRef {
- local: place_local,
- projection: place_projection,
- }) {
- self.used_mut_upvars.push(field);
- }
- }
- }
- }
-
- /// Whether this value can be written or borrowed mutably.
- /// Returns the root place if the place passed in is a projection.
- fn is_mutable(
- &self,
- place: PlaceRef<'tcx>,
- is_local_mutation_allowed: LocalMutationIsAllowed,
- ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
- debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
- match place.last_projection() {
- None => {
- let local = &self.body.local_decls[place.local];
- match local.mutability {
- Mutability::Not => match is_local_mutation_allowed {
- LocalMutationIsAllowed::Yes => Ok(RootPlace {
- place_local: place.local,
- place_projection: place.projection,
- is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
- }),
- LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
- place_local: place.local,
- place_projection: place.projection,
- is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
- }),
- LocalMutationIsAllowed::No => Err(place),
- },
- Mutability::Mut => Ok(RootPlace {
- place_local: place.local,
- place_projection: place.projection,
- is_local_mutation_allowed,
- }),
- }
- }
- Some((place_base, elem)) => {
- match elem {
- ProjectionElem::Deref => {
- let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;
-
- // Check the kind of deref to decide
- match base_ty.kind() {
- ty::Ref(_, _, mutbl) => {
- match mutbl {
- // Shared borrowed data is never mutable
- hir::Mutability::Not => Err(place),
- // Mutably borrowed data is mutable, but only if we have a
- // unique path to the `&mut`
- hir::Mutability::Mut => {
- let mode = match self.is_upvar_field_projection(place) {
- Some(field) if self.upvars[field.index()].by_ref => {
- is_local_mutation_allowed
- }
- _ => LocalMutationIsAllowed::Yes,
- };
-
- self.is_mutable(place_base, mode)
- }
- }
- }
- ty::RawPtr(tnm) => {
- match tnm.mutbl {
- // `*const` raw pointers are not mutable
- hir::Mutability::Not => Err(place),
- // `*mut` raw pointers are always mutable, regardless of
- // context. The users have to check by themselves.
- hir::Mutability::Mut => Ok(RootPlace {
- place_local: place.local,
- place_projection: place.projection,
- is_local_mutation_allowed,
- }),
- }
- }
- // `Box<T>` owns its content, so mutable if its location is mutable
- _ if base_ty.is_box() => {
- self.is_mutable(place_base, is_local_mutation_allowed)
- }
- // Deref should only be for reference, pointers or boxes
- _ => bug!("Deref of unexpected type: {:?}", base_ty),
- }
- }
- // All other projections are owned by their base path, so mutable if
- // base path is mutable
- ProjectionElem::Field(..)
- | ProjectionElem::Index(..)
- | ProjectionElem::ConstantIndex { .. }
- | ProjectionElem::Subslice { .. }
- | ProjectionElem::Downcast(..) => {
- let upvar_field_projection = self.is_upvar_field_projection(place);
- if let Some(field) = upvar_field_projection {
- let upvar = &self.upvars[field.index()];
- debug!(
- "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
- place={:?}, place_base={:?}",
- upvar, is_local_mutation_allowed, place, place_base
- );
- match (upvar.place.mutability, is_local_mutation_allowed) {
- (
- Mutability::Not,
- LocalMutationIsAllowed::No
- | LocalMutationIsAllowed::ExceptUpvars,
- ) => Err(place),
- (Mutability::Not, LocalMutationIsAllowed::Yes)
- | (Mutability::Mut, _) => {
- // Subtle: this is an upvar
- // reference, so it looks like
- // `self.foo` -- we want to double
- // check that the location `*self`
- // is mutable (i.e., this is not a
- // `Fn` closure). But if that
- // check succeeds, we want to
- // *blame* the mutability on
- // `place` (that is,
- // `self.foo`). This is used to
- // propagate the info about
- // whether mutability declarations
- // are used outwards, so that we register
- // the outer variable as mutable. Otherwise a
- // test like this fails to record the `mut`
- // as needed:
- //
- // ```
- // fn foo<F: FnOnce()>(_f: F) { }
- // fn main() {
- // let var = Vec::new();
- // foo(move || {
- // var.push(1);
- // });
- // }
- // ```
- let _ =
- self.is_mutable(place_base, is_local_mutation_allowed)?;
- Ok(RootPlace {
- place_local: place.local,
- place_projection: place.projection,
- is_local_mutation_allowed,
- })
- }
- }
- } else {
- self.is_mutable(place_base, is_local_mutation_allowed)
- }
- }
- }
- }
- }
- }
-
- /// If `place` is a field projection, and the field is being projected from a closure type,
- /// then returns the index of the field being projected. Note that this closure will always
- /// be `self` in the current MIR, because that is the only time we directly access the fields
- /// of a closure type.
- pub fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
- path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
- }
-}
-
-/// The degree of overlap between 2 places for borrow-checking.
-enum Overlap {
- /// The places might partially overlap - in this case, we give
- /// up and say that they might conflict. This occurs when
- /// different fields of a union are borrowed. For example,
- /// if `u` is a union, we have no way of telling how disjoint
- /// `u.a.x` and `a.b.y` are.
- Arbitrary,
- /// The places have the same type, and are either completely disjoint
- /// or equal - i.e., they can't "partially" overlap as can occur with
- /// unions. This is the "base case" on which we recur for extensions
- /// of the place.
- EqualOrDisjoint,
- /// The places are disjoint, so we know all extensions of them
- /// will also be disjoint.
- Disjoint,
-}
projects / rustc.git / blobdiff