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rust/rust/f9ddd9fdbb2b0df76216dfafebc843e46e7ebd08/./compiler/rustc_borrowck/src/lib.rs
blob: acdeea91a189f4ed076dfd3914ab7e90fb6a7676 [file]
//! This crate implemens MIR typeck and MIR borrowck.
// tidy-alphabetical-start
#![allow(internal_features)]
#![feature(box_patterns)]
#![feature(default_field_values)]
#![feature(file_buffered)]
#![feature(negative_impls)]
#![feature(never_type)]
#![feature(rustc_attrs)]
#![feature(stmt_expr_attributes)]
#![feature(try_blocks)]
// tidy-alphabetical-end
use std::borrow::Cow;
use std::cell::{OnceCell, RefCell};
use std::marker::PhantomData;
use std::ops::{ControlFlow, Deref};
use std::rc::Rc;
use borrow_set::LocalsStateAtExit;
use polonius_engine::AllFacts;
use root_cx::BorrowCheckRootCtxt;
use rustc_abi::FieldIdx;
use rustc_data_structures::frozen::Frozen;
use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
use rustc_data_structures::graph::dominators::Dominators;
use rustc_hir as hir;
use rustc_hir::CRATE_HIR_ID;
use rustc_hir::def_id::LocalDefId;
use rustc_index::bit_set::MixedBitSet;
use rustc_index::{IndexSlice, IndexVec};
use rustc_infer::infer::outlives::env::RegionBoundPairs;
use rustc_infer::infer::{
InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin, TyCtxtInferExt,
};
use rustc_middle::mir::*;
use rustc_middle::query::Providers;
use rustc_middle::ty::{
self, ParamEnv, RegionVid, Ty, TyCtxt, TypeFoldable, TypeVisitable, TypingMode, fold_regions,
};
use rustc_middle::{bug, span_bug};
use rustc_mir_dataflow::impls::{EverInitializedPlaces, MaybeUninitializedPlaces};
use rustc_mir_dataflow::move_paths::{
InitIndex, InitLocation, LookupResult, MoveData, MovePathIndex,
};
use rustc_mir_dataflow::points::DenseLocationMap;
use rustc_mir_dataflow::{Analysis, EntryStates, Results, ResultsVisitor, visit_results};
use rustc_session::lint::builtin::{TAIL_EXPR_DROP_ORDER, UNUSED_MUT};
use rustc_span::{ErrorGuaranteed, Span, Symbol};
use smallvec::SmallVec;
use tracing::{debug, instrument};
use crate::borrow_set::{BorrowData, BorrowSet};
use crate::consumers::{BodyWithBorrowckFacts, RustcFacts};
use crate::dataflow::{BorrowIndex, Borrowck, BorrowckDomain, Borrows};
use crate::diagnostics::{
AccessKind, BorrowckDiagnosticsBuffer, IllegalMoveOriginKind, MoveError, RegionName,
};
use crate::path_utils::*;
use crate::place_ext::PlaceExt;
use crate::places_conflict::{PlaceConflictBias, places_conflict};
use crate::polonius::PoloniusContext;
use crate::polonius::legacy::{
PoloniusFacts, PoloniusFactsExt, PoloniusLocationTable, PoloniusOutput,
};
use crate::prefixes::PrefixSet;
use crate::region_infer::RegionInferenceContext;
use crate::region_infer::opaque_types::DeferredOpaqueTypeError;
use crate::renumber::RegionCtxt;
use crate::session_diagnostics::VarNeedNotMut;
use crate::type_check::free_region_relations::UniversalRegionRelations;
use crate::type_check::{Locations, MirTypeckRegionConstraints, MirTypeckResults};
mod borrow_set;
mod borrowck_errors;
mod constraints;
mod dataflow;
mod def_use;
mod diagnostics;
mod handle_placeholders;
mod nll;
mod path_utils;
mod place_ext;
mod places_conflict;
mod polonius;
mod prefixes;
mod region_infer;
mod renumber;
mod root_cx;
mod session_diagnostics;
mod type_check;
mod universal_regions;
mod used_muts;
/// A public API provided for the Rust compiler consumers.
pub mod consumers;
/// Associate some local constants with the `'tcx` lifetime
struct TyCtxtConsts<'tcx>(PhantomData<&'tcx ()>);
impl<'tcx> TyCtxtConsts<'tcx> {
const DEREF_PROJECTION: &'tcx [PlaceElem<'tcx>; 1] = &[ProjectionElem::Deref];
}
pub fn provide(providers: &mut Providers) {
*providers = Providers { mir_borrowck, ..*providers };
}
/// Provider for `query mir_borrowck`. Unlike `typeck`, this must
/// only be called for typeck roots which *similar* to `typeck` will
/// then borrowck all nested bodies as well.
fn mir_borrowck(
tcx: TyCtxt<'_>,
def: LocalDefId,
) -> Result<&FxIndexMap<LocalDefId, ty::DefinitionSiteHiddenType<'_>>, ErrorGuaranteed> {
assert!(!tcx.is_typeck_child(def.to_def_id()));
let (input_body, _) = tcx.mir_promoted(def);
debug!("run query mir_borrowck: {}", tcx.def_path_str(def));
// We should eagerly check stalled coroutine obligations from HIR typeck.
// Not doing so leads to silent normalization failures later, which will
// fail to register opaque types in the next solver.
tcx.ensure_result().check_coroutine_obligations(def)?;
let input_body: &Body<'_> = &input_body.borrow();
if let Some(guar) = input_body.tainted_by_errors {
debug!("Skipping borrowck because of tainted body");
Err(guar)
} else if input_body.should_skip() {
debug!("Skipping borrowck because of injected body");
let opaque_types = Default::default();
Ok(tcx.arena.alloc(opaque_types))
} else {
let mut root_cx = BorrowCheckRootCtxt::new(tcx, def, None);
root_cx.do_mir_borrowck();
root_cx.finalize()
}
}
/// Data propagated to the typeck parent by nested items.
/// This should always be empty for the typeck root.
#[derive(Debug)]
struct PropagatedBorrowCheckResults<'tcx> {
closure_requirements: Option<ClosureRegionRequirements<'tcx>>,
used_mut_upvars: SmallVec<[FieldIdx; 8]>,
}
type DeferredClosureRequirements<'tcx> = Vec<(LocalDefId, ty::GenericArgsRef<'tcx>, Locations)>;
/// After we borrow check a closure, we are left with various
/// requirements that we have inferred between the free regions that
/// appear in the closure's signature or on its field types. These
/// requirements are then verified and proved by the closure's
/// creating function. This struct encodes those requirements.
///
/// The requirements are listed as being between various `RegionVid`. The 0th
/// region refers to `'static`; subsequent region vids refer to the free
/// regions that appear in the closure (or coroutine's) type, in order of
/// appearance. (This numbering is actually defined by the `UniversalRegions`
/// struct in the NLL region checker. See for example
/// `UniversalRegions::closure_mapping`.) Note the free regions in the
/// closure's signature and captures are erased.
///
/// Example: If type check produces a closure with the closure args:
///
/// ```text
/// ClosureArgs = [
/// 'a, // From the parent.
/// 'b,
/// i8, // the "closure kind"
/// for<'x> fn(&'<erased> &'x u32) -> &'x u32, // the "closure signature"
/// &'<erased> String, // some upvar
/// ]
/// ```
///
/// We would "renumber" each free region to a unique vid, as follows:
///
/// ```text
/// ClosureArgs = [
/// '1, // From the parent.
/// '2,
/// i8, // the "closure kind"
/// for<'x> fn(&'3 &'x u32) -> &'x u32, // the "closure signature"
/// &'4 String, // some upvar
/// ]
/// ```
///
/// Now the code might impose a requirement like `'1: '2`. When an
/// instance of the closure is created, the corresponding free regions
/// can be extracted from its type and constrained to have the given
/// outlives relationship.
#[derive(Clone, Debug)]
pub struct ClosureRegionRequirements<'tcx> {
/// The number of external regions defined on the closure. In our
/// example above, it would be 3 -- one for `'static`, then `'1`
/// and `'2`. This is just used for a sanity check later on, to
/// make sure that the number of regions we see at the callsite
/// matches.
pub num_external_vids: usize,
/// Requirements between the various free regions defined in
/// indices.
pub outlives_requirements: Vec<ClosureOutlivesRequirement<'tcx>>,
}
/// Indicates an outlives-constraint between a type or between two
/// free regions declared on the closure.
#[derive(Copy, Clone, Debug)]
pub struct ClosureOutlivesRequirement<'tcx> {
// This region or type ...
pub subject: ClosureOutlivesSubject<'tcx>,
// ... must outlive this one.
pub outlived_free_region: ty::RegionVid,
// If not, report an error here ...
pub blame_span: Span,
// ... due to this reason.
pub category: ConstraintCategory<'tcx>,
}
// Make sure this enum doesn't unintentionally grow
#[cfg(target_pointer_width = "64")]
rustc_data_structures::static_assert_size!(ConstraintCategory<'_>, 16);
/// The subject of a `ClosureOutlivesRequirement` -- that is, the thing
/// that must outlive some region.
#[derive(Copy, Clone, Debug)]
pub enum ClosureOutlivesSubject<'tcx> {
/// Subject is a type, typically a type parameter, but could also
/// be a projection. Indicates a requirement like `T: 'a` being
/// passed to the caller, where the type here is `T`.
Ty(ClosureOutlivesSubjectTy<'tcx>),
/// Subject is a free region from the closure. Indicates a requirement
/// like `'a: 'b` being passed to the caller; the region here is `'a`.
Region(ty::RegionVid),
}
/// Represents a `ty::Ty` for use in [`ClosureOutlivesSubject`].
///
/// This abstraction is necessary because the type may include `ReVar` regions,
/// which is what we use internally within NLL code, and they can't be used in
/// a query response.
#[derive(Copy, Clone, Debug)]
pub struct ClosureOutlivesSubjectTy<'tcx> {
inner: Ty<'tcx>,
}
// DO NOT implement `TypeVisitable` or `TypeFoldable` traits, because this
// type is not recognized as a binder for late-bound region.
impl<'tcx, I> !TypeVisitable<I> for ClosureOutlivesSubjectTy<'tcx> {}
impl<'tcx, I> !TypeFoldable<I> for ClosureOutlivesSubjectTy<'tcx> {}
impl<'tcx> ClosureOutlivesSubjectTy<'tcx> {
/// All regions of `ty` must be of kind `ReVar` and must represent
/// universal regions *external* to the closure.
pub fn bind(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Self {
let inner = fold_regions(tcx, ty, |r, depth| match r.kind() {
ty::ReVar(vid) => {
let br = ty::BoundRegion {
var: ty::BoundVar::from_usize(vid.index()),
kind: ty::BoundRegionKind::Anon,
};
ty::Region::new_bound(tcx, depth, br)
}
_ => bug!("unexpected region in ClosureOutlivesSubjectTy: {r:?}"),
});
Self { inner }
}
pub fn instantiate(
self,
tcx: TyCtxt<'tcx>,
mut map: impl FnMut(ty::RegionVid) -> ty::Region<'tcx>,
) -> Ty<'tcx> {
fold_regions(tcx, self.inner, |r, depth| match r.kind() {
ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn), br) => {
debug_assert_eq!(debruijn, depth);
map(ty::RegionVid::from_usize(br.var.index()))
}
_ => bug!("unexpected region {r:?}"),
})
}
}
struct CollectRegionConstraintsResult<'tcx> {
infcx: BorrowckInferCtxt<'tcx>,
body_owned: Body<'tcx>,
promoted: IndexVec<Promoted, Body<'tcx>>,
move_data: MoveData<'tcx>,
borrow_set: BorrowSet<'tcx>,
location_table: PoloniusLocationTable,
location_map: Rc<DenseLocationMap>,
universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
region_bound_pairs: Frozen<RegionBoundPairs<'tcx>>,
known_type_outlives_obligations: Frozen<Vec<ty::PolyTypeOutlivesPredicate<'tcx>>>,
constraints: MirTypeckRegionConstraints<'tcx>,
deferred_closure_requirements: DeferredClosureRequirements<'tcx>,
deferred_opaque_type_errors: Vec<DeferredOpaqueTypeError<'tcx>>,
polonius_facts: Option<AllFacts<RustcFacts>>,
polonius_context: Option<PoloniusContext>,
}
/// Start borrow checking by collecting the region constraints for
/// the current body. This initializes the relevant data structures
/// and then type checks the MIR body.
fn borrowck_collect_region_constraints<'tcx>(
root_cx: &mut BorrowCheckRootCtxt<'tcx>,
def: LocalDefId,
) -> CollectRegionConstraintsResult<'tcx> {
let tcx = root_cx.tcx;
let infcx = BorrowckInferCtxt::new(tcx, def, root_cx.root_def_id());
let (input_body, promoted) = tcx.mir_promoted(def);
let input_body: &Body<'_> = &input_body.borrow();
let input_promoted: &IndexSlice<_, _> = &promoted.borrow();
if let Some(e) = input_body.tainted_by_errors {
infcx.set_tainted_by_errors(e);
root_cx.set_tainted_by_errors(e);
}
// 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.to_owned();
let universal_regions = nll::replace_regions_in_mir(&infcx, &mut body_owned, &mut promoted);
let body = &body_owned; // no further changes
let location_table = PoloniusLocationTable::new(body);
let move_data = MoveData::gather_moves(body, tcx, |_| true);
let locals_are_invalidated_at_exit = tcx.hir_body_owner_kind(def).is_fn_or_closure();
let borrow_set = BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &move_data);
let location_map = Rc::new(DenseLocationMap::new(body));
let polonius_input = root_cx.consumer.as_ref().map_or(false, |c| c.polonius_input())
|| infcx.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled();
let mut polonius_facts =
(polonius_input || PoloniusFacts::enabled(infcx.tcx)).then_some(PoloniusFacts::default());
// Run the MIR type-checker.
let MirTypeckResults {
constraints,
universal_region_relations,
region_bound_pairs,
known_type_outlives_obligations,
deferred_closure_requirements,
polonius_context,
} = type_check::type_check(
root_cx,
&infcx,
body,
&promoted,
universal_regions,
&location_table,
&borrow_set,
&mut polonius_facts,
&move_data,
Rc::clone(&location_map),
);
CollectRegionConstraintsResult {
infcx,
body_owned,
promoted,
move_data,
borrow_set,
location_table,
location_map,
universal_region_relations,
region_bound_pairs,
known_type_outlives_obligations,
constraints,
deferred_closure_requirements,
deferred_opaque_type_errors: Default::default(),
polonius_facts,
polonius_context,
}
}
/// Using the region constraints computed by [borrowck_collect_region_constraints]
/// and the additional constraints from [BorrowCheckRootCtxt::handle_opaque_type_uses],
/// compute the region graph and actually check for any borrowck errors.
fn borrowck_check_region_constraints<'tcx>(
root_cx: &mut BorrowCheckRootCtxt<'tcx>,
CollectRegionConstraintsResult {
infcx,
body_owned,
promoted,
move_data,
borrow_set,
location_table,
location_map,
universal_region_relations,
region_bound_pairs: _,
known_type_outlives_obligations: _,
constraints,
deferred_closure_requirements,
deferred_opaque_type_errors,
polonius_facts,
polonius_context,
}: CollectRegionConstraintsResult<'tcx>,
) -> PropagatedBorrowCheckResults<'tcx> {
assert!(!infcx.has_opaque_types_in_storage());
assert!(deferred_closure_requirements.is_empty());
let tcx = root_cx.tcx;
let body = &body_owned;
let def = body.source.def_id().expect_local();
// Compute non-lexical lifetimes using the constraints computed
// by typechecking the MIR body.
let nll::NllOutput {
regioncx,
polonius_input,
polonius_output,
opt_closure_req,
nll_errors,
polonius_context,
} = nll::compute_regions(
root_cx,
&infcx,
body,
&location_table,
&move_data,
&borrow_set,
location_map,
universal_region_relations,
constraints,
polonius_facts,
polonius_context,
);
// Dump MIR results into a file, if that is enabled. This lets us
// write unit-tests, as well as helping with debugging.
nll::dump_nll_mir(&infcx, body, &regioncx, &opt_closure_req, &borrow_set);
polonius::dump_polonius_mir(
&infcx,
body,
&regioncx,
&opt_closure_req,
&borrow_set,
polonius_context.as_ref(),
);
// We also have a `#[rustc_regions]` annotation that causes us to dump
// information.
nll::dump_annotation(&infcx, body, &regioncx, &opt_closure_req);
let movable_coroutine = body.coroutine.is_some()
&& tcx.coroutine_movability(def.to_def_id()) == hir::Movability::Movable;
let diags_buffer = &mut BorrowckDiagnosticsBuffer::default();
// While promoteds should mostly be correct by construction, we need to check them for
// invalid moves to detect moving out of arrays:`struct S; fn main() { &([S][0]); }`.
for promoted_body in &promoted {
use rustc_middle::mir::visit::Visitor;
// This assumes that we won't use some of the fields of the `promoted_mbcx`
// when detecting and reporting move errors. While it would be nice to move
// this check out of `MirBorrowckCtxt`, actually doing so is far from trivial.
let move_data = MoveData::gather_moves(promoted_body, tcx, |_| true);
let mut promoted_mbcx = MirBorrowckCtxt {
root_cx,
infcx: &infcx,
body: promoted_body,
move_data: &move_data,
// no need to create a real location table for the promoted, it is not used
location_table: &location_table,
movable_coroutine,
fn_self_span_reported: Default::default(),
access_place_error_reported: Default::default(),
reservation_error_reported: Default::default(),
uninitialized_error_reported: Default::default(),
regioncx: &regioncx,
used_mut: Default::default(),
used_mut_upvars: SmallVec::new(),
borrow_set: &borrow_set,
upvars: &[],
local_names: OnceCell::from(IndexVec::from_elem(None, &promoted_body.local_decls)),
region_names: RefCell::default(),
next_region_name: RefCell::new(1),
polonius_output: None,
move_errors: Vec::new(),
diags_buffer,
polonius_context: polonius_context.as_ref(),
};
struct MoveVisitor<'a, 'b, 'infcx, 'tcx> {
ctxt: &'a mut MirBorrowckCtxt<'b, 'infcx, 'tcx>,
}
impl<'tcx> Visitor<'tcx> for MoveVisitor<'_, '_, '_, 'tcx> {
fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
if let Operand::Move(place) = operand {
self.ctxt.check_movable_place(location, *place);
}
}
}
MoveVisitor { ctxt: &mut promoted_mbcx }.visit_body(promoted_body);
promoted_mbcx.report_move_errors();
}
let mut mbcx = MirBorrowckCtxt {
root_cx,
infcx: &infcx,
body,
move_data: &move_data,
location_table: &location_table,
movable_coroutine,
fn_self_span_reported: Default::default(),
access_place_error_reported: Default::default(),
reservation_error_reported: Default::default(),
uninitialized_error_reported: Default::default(),
regioncx: &regioncx,
used_mut: Default::default(),
used_mut_upvars: SmallVec::new(),
borrow_set: &borrow_set,
upvars: tcx.closure_captures(def),
local_names: OnceCell::new(),
region_names: RefCell::default(),
next_region_name: RefCell::new(1),
move_errors: Vec::new(),
diags_buffer,
polonius_output: polonius_output.as_deref(),
polonius_context: polonius_context.as_ref(),
};
// Compute and report region errors, if any.
if nll_errors.is_empty() {
mbcx.report_opaque_type_errors(deferred_opaque_type_errors);
} else {
mbcx.report_region_errors(nll_errors);
}
let flow_results = get_flow_results(tcx, body, &move_data, &borrow_set, &regioncx);
visit_results(
body,
traversal::reverse_postorder(body).map(|(bb, _)| bb),
&flow_results,
&mut mbcx,
);
mbcx.report_move_errors();
// 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: FxIndexSet<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);
mbcx.lint_unused_mut();
if let Some(guar) = mbcx.emit_errors() {
mbcx.root_cx.set_tainted_by_errors(guar);
}
let result = PropagatedBorrowCheckResults {
closure_requirements: opt_closure_req,
used_mut_upvars: mbcx.used_mut_upvars,
};
if let Some(consumer) = &mut root_cx.consumer {
consumer.insert_body(
def,
BodyWithBorrowckFacts {
body: body_owned,
promoted,
borrow_set,
region_inference_context: regioncx,
location_table: polonius_input.as_ref().map(|_| location_table),
input_facts: polonius_input,
output_facts: polonius_output,
},
);
}
debug!("do_mir_borrowck: result = {:#?}", result);
result
}
fn get_flow_results<'a, 'tcx>(
tcx: TyCtxt<'tcx>,
body: &'a Body<'tcx>,
move_data: &'a MoveData<'tcx>,
borrow_set: &'a BorrowSet<'tcx>,
regioncx: &RegionInferenceContext<'tcx>,
) -> Results<'tcx, Borrowck<'a, 'tcx>> {
// We compute these three analyses individually, but them combine them into
// a single results so that `mbcx` can visit them all together.
let borrows = Borrows::new(tcx, body, regioncx, borrow_set).iterate_to_fixpoint(
tcx,
body,
Some("borrowck"),
);
let uninits = MaybeUninitializedPlaces::new(tcx, body, move_data).iterate_to_fixpoint(
tcx,
body,
Some("borrowck"),
);
let ever_inits = EverInitializedPlaces::new(body, move_data).iterate_to_fixpoint(
tcx,
body,
Some("borrowck"),
);
let analysis = Borrowck {
borrows: borrows.analysis,
uninits: uninits.analysis,
ever_inits: ever_inits.analysis,
};
assert_eq!(borrows.entry_states.len(), uninits.entry_states.len());
assert_eq!(borrows.entry_states.len(), ever_inits.entry_states.len());
let entry_states: EntryStates<_> =
itertools::izip!(borrows.entry_states, uninits.entry_states, ever_inits.entry_states)
.map(|(borrows, uninits, ever_inits)| BorrowckDomain { borrows, uninits, ever_inits })
.collect();
Results { analysis, entry_states }
}
pub(crate) struct BorrowckInferCtxt<'tcx> {
pub(crate) infcx: InferCtxt<'tcx>,
pub(crate) root_def_id: LocalDefId,
pub(crate) param_env: ParamEnv<'tcx>,
pub(crate) reg_var_to_origin: RefCell<FxIndexMap<ty::RegionVid, RegionCtxt>>,
}
impl<'tcx> BorrowckInferCtxt<'tcx> {
pub(crate) fn new(tcx: TyCtxt<'tcx>, def_id: LocalDefId, root_def_id: LocalDefId) -> Self {
let typing_mode = if tcx.use_typing_mode_borrowck() {
TypingMode::borrowck(tcx, def_id)
} else {
TypingMode::analysis_in_body(tcx, def_id)
};
let infcx = tcx.infer_ctxt().build(typing_mode);
let param_env = tcx.param_env(def_id);
BorrowckInferCtxt {
infcx,
root_def_id,
reg_var_to_origin: RefCell::new(Default::default()),
param_env,
}
}
pub(crate) fn next_region_var<F>(
&self,
origin: RegionVariableOrigin<'tcx>,
get_ctxt_fn: F,
) -> ty::Region<'tcx>
where
F: Fn() -> RegionCtxt,
{
let next_region = self.infcx.next_region_var(origin);
let vid = next_region.as_var();
if cfg!(debug_assertions) {
debug!("inserting vid {:?} with origin {:?} into var_to_origin", vid, origin);
let ctxt = get_ctxt_fn();
let mut var_to_origin = self.reg_var_to_origin.borrow_mut();
assert_eq!(var_to_origin.insert(vid, ctxt), None);
}
next_region
}
#[instrument(skip(self, get_ctxt_fn), level = "debug")]
pub(crate) fn next_nll_region_var<F>(
&self,
origin: NllRegionVariableOrigin<'tcx>,
get_ctxt_fn: F,
) -> ty::Region<'tcx>
where
F: Fn() -> RegionCtxt,
{
let next_region = self.infcx.next_nll_region_var(origin);
let vid = next_region.as_var();
if cfg!(debug_assertions) {
debug!("inserting vid {:?} with origin {:?} into var_to_origin", vid, origin);
let ctxt = get_ctxt_fn();
let mut var_to_origin = self.reg_var_to_origin.borrow_mut();
assert_eq!(var_to_origin.insert(vid, ctxt), None);
}
next_region
}
}
impl<'tcx> Deref for BorrowckInferCtxt<'tcx> {
type Target = InferCtxt<'tcx>;
fn deref(&self) -> &Self::Target {
&self.infcx
}
}
pub(crate) struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
root_cx: &'a mut BorrowCheckRootCtxt<'tcx>,
infcx: &'infcx BorrowckInferCtxt<'tcx>,
body: &'a Body<'tcx>,
move_data: &'a MoveData<'tcx>,
/// Map from MIR `Location` to `LocationIndex`; created
/// when MIR borrowck begins.
location_table: &'a PoloniusLocationTable,
movable_coroutine: 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: FxIndexSet<(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: FxIndexSet<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: FxIndexSet<Span>,
/// 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: FxIndexSet<Local>,
/// 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: FxIndexSet<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<[FieldIdx; 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: &'a RegionInferenceContext<'tcx>,
/// The set of borrows extracted from the MIR
borrow_set: &'a BorrowSet<'tcx>,
/// Information about upvars not necessarily preserved in types or MIR
upvars: &'tcx [&'tcx ty::CapturedPlace<'tcx>],
/// Names of local (user) variables (extracted from `var_debug_info`).
local_names: OnceCell<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<FxIndexMap<RegionVid, RegionName>>,
/// The counter for generating new region names.
next_region_name: RefCell<usize>,
diags_buffer: &'a mut BorrowckDiagnosticsBuffer<'infcx, 'tcx>,
move_errors: Vec<MoveError<'tcx>>,
/// Results of Polonius analysis.
polonius_output: Option<&'a PoloniusOutput>,
/// When using `-Zpolonius=next`: the data used to compute errors and diagnostics.
polonius_context: Option<&'a PoloniusContext>,
}
// 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<'a, 'tcx> ResultsVisitor<'tcx, Borrowck<'a, 'tcx>> for MirBorrowckCtxt<'a, '_, 'tcx> {
fn visit_after_early_statement_effect(
&mut self,
_analysis: &Borrowck<'a, 'tcx>,
state: &BorrowckDomain,
stmt: &Statement<'tcx>,
location: Location,
) {
debug!("MirBorrowckCtxt::process_statement({:?}, {:?}): {:?}", location, stmt, state);
let span = stmt.source_info.span;
self.check_activations(location, span, state);
match &stmt.kind {
StatementKind::Assign(box (lhs, rhs)) => {
self.consume_rvalue(location, (rhs, span), state);
self.mutate_place(location, (*lhs, span), Shallow(None), state);
}
StatementKind::FakeRead(box (_, 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),
state,
);
}
StatementKind::Intrinsic(box kind) => match kind {
NonDivergingIntrinsic::Assume(op) => {
self.consume_operand(location, (op, span), state);
}
NonDivergingIntrinsic::CopyNonOverlapping(..) => span_bug!(
span,
"Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
)
}
// Only relevant for mir typeck
StatementKind::AscribeUserType(..)
// Only relevant for liveness and unsafeck
| StatementKind::PlaceMention(..)
// Doesn't have any language semantics
| StatementKind::Coverage(..)
// These do not actually affect borrowck
| StatementKind::ConstEvalCounter
| StatementKind::StorageLive(..) => {}
// This does not affect borrowck
StatementKind::BackwardIncompatibleDropHint { place, reason: BackwardIncompatibleDropReason::Edition2024 } => {
self.check_backward_incompatible_drop(location, **place, state);
}
StatementKind::StorageDead(local) => {
self.access_place(
location,
(Place::from(*local), span),
(Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
LocalMutationIsAllowed::Yes,
state,
);
}
StatementKind::Nop
| StatementKind::SetDiscriminant { .. } => {
bug!("Statement not allowed in this MIR phase")
}
}
}
fn visit_after_early_terminator_effect(
&mut self,
_analysis: &Borrowck<'a, 'tcx>,
state: &BorrowckDomain,
term: &Terminator<'tcx>,
loc: Location,
) {
debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, state);
let span = term.source_info.span;
self.check_activations(loc, span, state);
match &term.kind {
TerminatorKind::SwitchInt { discr, targets: _ } => {
self.consume_operand(loc, (discr, span), state);
}
TerminatorKind::Drop {
place,
target: _,
unwind: _,
replace,
drop: _,
async_fut: _,
} => {
debug!(
"visit_terminator_drop \
loc: {:?} term: {:?} place: {:?} span: {:?}",
loc, term, place, span
);
let write_kind =
if *replace { WriteKind::Replace } else { WriteKind::StorageDeadOrDrop };
self.access_place(
loc,
(*place, span),
(AccessDepth::Drop, Write(write_kind)),
LocalMutationIsAllowed::Yes,
state,
);
}
TerminatorKind::Call {
func,
args,
destination,
target: _,
unwind: _,
call_source: _,
fn_span: _,
} => {
self.consume_operand(loc, (func, span), state);
for arg in args {
self.consume_operand(loc, (&arg.node, arg.span), state);
}
self.mutate_place(loc, (*destination, span), Deep, state);
}
TerminatorKind::TailCall { func, args, fn_span: _ } => {
self.consume_operand(loc, (func, span), state);
for arg in args {
self.consume_operand(loc, (&arg.node, arg.span), state);
}
}
TerminatorKind::Assert { cond, expected: _, msg, target: _, unwind: _ } => {
self.consume_operand(loc, (cond, span), state);
if let AssertKind::BoundsCheck { len, index } = &**msg {
self.consume_operand(loc, (len, span), state);
self.consume_operand(loc, (index, span), state);
}
}
TerminatorKind::Yield { value, resume: _, resume_arg, drop: _ } => {
self.consume_operand(loc, (value, span), state);
self.mutate_place(loc, (*resume_arg, span), Deep, state);
}
TerminatorKind::InlineAsm {
asm_macro: _,
template: _,
operands,
options: _,
line_spans: _,
targets: _,
unwind: _,
} => {
for op in operands {
match op {
InlineAsmOperand::In { reg: _, value } => {
self.consume_operand(loc, (value, span), state);
}
InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
if let Some(place) = place {
self.mutate_place(loc, (*place, span), Shallow(None), state);
}
}
InlineAsmOperand::InOut { reg: _, late: _, in_value, out_place } => {
self.consume_operand(loc, (in_value, span), state);
if let &Some(out_place) = out_place {
self.mutate_place(loc, (out_place, span), Shallow(None), state);
}
}
InlineAsmOperand::Const { value: _ }
| InlineAsmOperand::SymFn { value: _ }
| InlineAsmOperand::SymStatic { def_id: _ }
| InlineAsmOperand::Label { target_index: _ } => {}
}
}
}
TerminatorKind::Goto { target: _ }
| TerminatorKind::UnwindTerminate(_)
| TerminatorKind::Unreachable
| TerminatorKind::UnwindResume
| TerminatorKind::Return
| TerminatorKind::CoroutineDrop
| TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
| TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
// no data used, thus irrelevant to borrowck
}
}
}
fn visit_after_primary_terminator_effect(
&mut self,
_analysis: &Borrowck<'a, 'tcx>,
state: &BorrowckDomain,
term: &Terminator<'tcx>,
loc: Location,
) {
let span = term.source_info.span;
match term.kind {
TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
if self.movable_coroutine {
// Look for any active borrows to locals
for i in state.borrows.iter() {
let borrow = &self.borrow_set[i];
self.check_for_local_borrow(borrow, span);
}
}
}
TerminatorKind::UnwindResume
| TerminatorKind::Return
| TerminatorKind::TailCall { .. }
| TerminatorKind::CoroutineDrop => {
match self.borrow_set.locals_state_at_exit() {
LocalsStateAtExit::AllAreInvalidated => {
// 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.
for i in state.borrows.iter() {
let borrow = &self.borrow_set[i];
self.check_for_invalidation_at_exit(loc, borrow, span);
}
}
// If we do not implicitly invalidate all locals on exit,
// we check for conflicts when dropping or moving this local.
LocalsStateAtExit::SomeAreInvalidated { has_storage_dead_or_moved: _ } => {}
}
}
TerminatorKind::UnwindTerminate(_)
| TerminatorKind::Assert { .. }
| TerminatorKind::Call { .. }
| TerminatorKind::Drop { .. }
| TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
| TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
| TerminatorKind::Goto { .. }
| TerminatorKind::SwitchInt { .. }
| TerminatorKind::Unreachable
| TerminatorKind::InlineAsm { .. } => {}
}
}
}
use self::AccessDepth::{Deep, Shallow};
use self::ReadOrWrite::{Activation, Read, Reservation, Write};
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum ArtificialField {
ArrayLength,
FakeBorrow,
}
#[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,
Replace,
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:
// - 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 {
Borrow,
MatchOn,
Use,
Assignment,
PartialAssignment,
}
#[derive(Debug)]
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::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::Borrow => "borrowed",
InitializationRequiringAction::MatchOn => "matched on",
InitializationRequiringAction::Use => "used",
InitializationRequiringAction::Assignment => "assigned",
InitializationRequiringAction::PartialAssignment => "partially assigned",
}
}
fn as_general_verb_in_past_tense(self) -> &'static str {
match self {
InitializationRequiringAction::Borrow
| InitializationRequiringAction::MatchOn
| InitializationRequiringAction::Use => "used",
InitializationRequiringAction::Assignment => "assigned",
InitializationRequiringAction::PartialAssignment => "partially assigned",
}
}
}
impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
fn body(&self) -> &'a 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,
state: &BorrowckDomain,
) {
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
);
// If the place is being mutated, then mark it as such anyway in order to suppress the
// `unused_mut` lint, which is likely incorrect once the access place error has been
// resolved.
if rw == ReadOrWrite::Write(WriteKind::Mutate)
&& let Ok(root_place) =
self.is_mutable(place_span.0.as_ref(), is_local_mutation_allowed)
{
self.add_used_mut(root_place, state);
}
return;
}
let mutability_error = self.check_access_permissions(
place_span,
rw,
is_local_mutation_allowed,
state,
location,
);
let conflict_error = self.check_access_for_conflict(location, place_span, sd, rw, state);
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 borrows_in_scope<'s>(
&self,
location: Location,
state: &'s BorrowckDomain,
) -> Cow<'s, MixedBitSet<BorrowIndex>> {
if let Some(polonius) = &self.polonius_output {
// Use polonius output if it has been enabled.
let location = self.location_table.start_index(location);
let mut polonius_output = MixedBitSet::new_empty(self.borrow_set.len());
for &idx in polonius.errors_at(location) {
polonius_output.insert(idx);
}
Cow::Owned(polonius_output)
} else {
Cow::Borrowed(&state.borrows)
}
}
#[instrument(level = "debug", skip(self, state))]
fn check_access_for_conflict(
&mut self,
location: Location,
place_span: (Place<'tcx>, Span),
sd: AccessDepth,
rw: ReadOrWrite,
state: &BorrowckDomain,
) -> bool {
let mut error_reported = false;
let borrows_in_scope = self.borrows_in_scope(location, state);
each_borrow_involving_path(
self,
self.infcx.tcx,
self.body,
(sd, place_span.0),
self.borrow_set,
|borrow_index| borrows_in_scope.contains(borrow_index),
|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 unsoundness 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),
);
ControlFlow::Continue(())
}
(Read(_), BorrowKind::Shared | BorrowKind::Fake(_))
| (
Read(ReadKind::Borrow(BorrowKind::Fake(FakeBorrowKind::Shallow))),
BorrowKind::Mut { .. },
) => ControlFlow::Continue(()),
(Reservation(_), BorrowKind::Fake(_) | BorrowKind::Shared) => {
// This used to be a future compatibility warning (to be
// disallowed on NLL). See rust-lang/rust#56254
ControlFlow::Continue(())
}
(Write(WriteKind::Move), BorrowKind::Fake(FakeBorrowKind::Shallow)) => {
// Handled by initialization checks.
ControlFlow::Continue(())
}
(Read(kind), BorrowKind::Mut { .. }) => {
// Reading from mere reservations of mutable-borrows is OK.
if !is_active(this.dominators(), borrow, location) {
assert!(borrow.kind.is_two_phase_borrow());
return ControlFlow::Continue(());
}
error_reported = true;
match kind {
ReadKind::Copy => {
let err = this
.report_use_while_mutably_borrowed(location, place_span, borrow);
this.buffer_error(err);
}
ReadKind::Borrow(bk) => {
let err =
this.report_conflicting_borrow(location, place_span, bk, borrow);
this.buffer_error(err);
}
}
ControlFlow::Break(())
}
(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) => {
let err =
this.report_conflicting_borrow(location, place_span, bk, borrow);
this.buffer_error(err);
}
WriteKind::StorageDeadOrDrop => this
.report_borrowed_value_does_not_live_long_enough(
location,
borrow,
place_span,
Some(WriteKind::StorageDeadOrDrop),
),
WriteKind::Mutate => {
this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
}
WriteKind::Move => {
this.report_move_out_while_borrowed(location, place_span, borrow)
}
WriteKind::Replace => {
this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
}
}
ControlFlow::Break(())
}
},
);
error_reported
}
/// Through #123739, `BackwardIncompatibleDropHint`s (BIDs) are introduced.
/// We would like to emit lints whether borrow checking fails at these future drop locations.
#[instrument(level = "debug", skip(self, state))]
fn check_backward_incompatible_drop(
&mut self,
location: Location,
place: Place<'tcx>,
state: &BorrowckDomain,
) {
let tcx = self.infcx.tcx;
// If this type does not need `Drop`, then treat it like a `StorageDead`.
// This is needed because we track the borrows of refs to thread locals,
// and we'll ICE because we don't track borrows behind shared references.
let sd = if place.ty(self.body, tcx).ty.needs_drop(tcx, self.body.typing_env(tcx)) {
AccessDepth::Drop
} else {
AccessDepth::Shallow(None)
};
let borrows_in_scope = self.borrows_in_scope(location, state);
// This is a very simplified version of `Self::check_access_for_conflict`.
// We are here checking on BIDs and specifically still-live borrows of data involving the BIDs.
each_borrow_involving_path(
self,
self.infcx.tcx,
self.body,
(sd, place),
self.borrow_set,
|borrow_index| borrows_in_scope.contains(borrow_index),
|this, _borrow_index, borrow| {
if matches!(borrow.kind, BorrowKind::Fake(_)) {
return ControlFlow::Continue(());
}
let borrowed = this.retrieve_borrow_spans(borrow).var_or_use_path_span();
let explain = this.explain_why_borrow_contains_point(
location,
borrow,
Some((WriteKind::StorageDeadOrDrop, place)),
);
this.infcx.tcx.emit_node_span_lint(
TAIL_EXPR_DROP_ORDER,
CRATE_HIR_ID,
borrowed,
session_diagnostics::TailExprDropOrder {
borrowed,
callback: |diag| {
explain.add_explanation_to_diagnostic(&this, diag, "", None, None);
},
},
);
// We may stop at the first case
ControlFlow::Break(())
},
);
}
fn mutate_place(
&mut self,
location: Location,
place_span: (Place<'tcx>, Span),
kind: AccessDepth,
state: &BorrowckDomain,
) {
// Write of P[i] or *P requires P init'd.
self.check_if_assigned_path_is_moved(location, place_span, state);
self.access_place(
location,
place_span,
(kind, Write(WriteKind::Mutate)),
LocalMutationIsAllowed::No,
state,
);
}
fn consume_rvalue(
&mut self,
location: Location,
(rvalue, span): (&Rvalue<'tcx>, Span),
state: &BorrowckDomain,
) {
match rvalue {
&Rvalue::Ref(_ /*rgn*/, bk, place) => {
let access_kind = match bk {
BorrowKind::Fake(FakeBorrowKind::Shallow) => {
(Shallow(Some(ArtificialField::FakeBorrow)), Read(ReadKind::Borrow(bk)))
}
BorrowKind::Shared | BorrowKind::Fake(FakeBorrowKind::Deep) => {
(Deep, Read(ReadKind::Borrow(bk)))
}
BorrowKind::Mut { .. } => {
let wk = WriteKind::MutableBorrow(bk);
if bk.is_two_phase_borrow() {
(Deep, Reservation(wk))
} else {
(Deep, Write(wk))
}
}
};
self.access_place(
location,
(place, span),
access_kind,
LocalMutationIsAllowed::No,
state,
);
let action = if bk == BorrowKind::Fake(FakeBorrowKind::Shallow) {
InitializationRequiringAction::MatchOn
} else {
InitializationRequiringAction::Borrow
};
self.check_if_path_or_subpath_is_moved(
location,
action,
(place.as_ref(), span),
state,
);
}
&Rvalue::RawPtr(kind, place) => {
let access_kind = match kind {
RawPtrKind::Mut => (
Deep,
Write(WriteKind::MutableBorrow(BorrowKind::Mut {
kind: MutBorrowKind::Default,
})),
),
RawPtrKind::Const => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
RawPtrKind::FakeForPtrMetadata => {
(Shallow(Some(ArtificialField::ArrayLength)), Read(ReadKind::Copy))
}
};
self.access_place(
location,
(place, span),
access_kind,
LocalMutationIsAllowed::No,
state,
);
self.check_if_path_or_subpath_is_moved(
location,
InitializationRequiringAction::Borrow,
(place.as_ref(), span),
state,
);
}
Rvalue::ThreadLocalRef(_) => {}
Rvalue::Use(operand, _)
| Rvalue::Repeat(operand, _)
| Rvalue::UnaryOp(_ /*un_op*/, operand)
| Rvalue::Cast(_ /*cast_kind*/, operand, _ /*ty*/) => {
self.consume_operand(location, (operand, span), state)
}
&Rvalue::Discriminant(place) => {
let af = match *rvalue {
Rvalue::Discriminant(..) => None,
_ => unreachable!(),
};
self.access_place(
location,
(place, span),
(Shallow(af), Read(ReadKind::Copy)),
LocalMutationIsAllowed::No,
state,
);
self.check_if_path_or_subpath_is_moved(
location,
InitializationRequiringAction::Use,
(place.as_ref(), span),
state,
);
}
Rvalue::BinaryOp(_bin_op, box (operand1, operand2)) => {
self.consume_operand(location, (operand1, span), state);
self.consume_operand(location, (operand2, span), state);
}
Rvalue::Aggregate(aggregate_kind, 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::CoroutineClosure(def_id, _)
| AggregateKind::Coroutine(def_id, _) => {
let def_id = def_id.expect_local();
let used_mut_upvars = self.root_cx.used_mut_upvars(def_id);
debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
// FIXME: We're cloning the `SmallVec` here to avoid borrowing `root_cx`
// when calling `propagate_closure_used_mut_upvar`. This should ideally
// be unnecessary.
for field in used_mut_upvars.clone() {
self.propagate_closure_used_mut_upvar(&operands[field]);
}
}
AggregateKind::Adt(..)
| AggregateKind::Array(..)
| AggregateKind::Tuple { .. }
| AggregateKind::RawPtr(..) => (),
}
for operand in operands {
self.consume_operand(location, (operand, span), state);
}
}
Rvalue::WrapUnsafeBinder(op, _) => {
self.consume_operand(location, (op, span), state);
}
Rvalue::CopyForDeref(_) => bug!("`CopyForDeref` in borrowck"),
}
}
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 Some(temp_mpi) = self.move_data.rev_lookup.find_local(local) else {
bug!("temporary should be tracked");
};
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 InitLocation::Statement(loc) = init.location else {
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);
match stmt.kind {
StatementKind::Assign(box (
_,
Rvalue::Ref(_, _, source)
| Rvalue::Use(Operand::Copy(source) | Operand::Move(source), _),
)) => {
propagate_closure_used_mut_place(self, source);
}
_ => {
bug!(
"closures should only capture user variables \
or references to user variables"
);
}
}
}
_ => propagate_closure_used_mut_place(self, place),
}
}
Operand::Constant(..) | Operand::RuntimeChecks(_) => {}
}
}
fn consume_operand(
&mut self,
location: Location,
(operand, span): (&Operand<'tcx>, Span),
state: &BorrowckDomain,
) {
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,
state,
);
// Finally, check if path was already moved.
self.check_if_path_or_subpath_is_moved(
location,
InitializationRequiringAction::Use,
(place.as_ref(), span),
state,
);
}
Operand::Move(place) => {
// Check if moving from this place makes sense.
self.check_movable_place(location, 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,
state,
);
// Finally, check if path was already moved.
self.check_if_path_or_subpath_is_moved(
location,
InitializationRequiringAction::Use,
(place.as_ref(), span),
state,
);
}
Operand::Constant(_) | Operand::RuntimeChecks(_) => {}
}
}
/// Checks whether a borrow of this place is invalidated when the function
/// exits
#[instrument(level = "debug", skip(self))]
fn check_for_invalidation_at_exit(
&mut self,
location: Location,
borrow: &BorrowData<'tcx>,
span: Span,
) {
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 = 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 = TyCtxtConsts::DEREF_PROJECTION;
true
} else {
false
};
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 coroutines
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_coroutine_yield(
self.retrieve_borrow_spans(borrow).var_or_use(),
yield_span,
);
self.buffer_error(err);
}
}
fn check_activations(&mut self, location: Location, span: Span, state: &BorrowckDomain) {
// Two-phase borrow support: For each activation that is newly
// generated at this statement, check if it interferes with
// another borrow.
for &borrow_index in self.borrow_set.activations_at_location(location) {
let borrow = &self.borrow_set[borrow_index];
// only mutable borrows should be 2-phase
assert!(match borrow.kind {
BorrowKind::Shared | BorrowKind::Fake(_) => false,
BorrowKind::Mut { .. } => true,
});
self.access_place(
location,
(borrow.borrowed_place, span),
(Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
LocalMutationIsAllowed::No,
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_movable_place(&mut self, location: Location, place: Place<'tcx>) {
use IllegalMoveOriginKind::*;
let body = self.body;
let tcx = self.infcx.tcx;
let mut place_ty = PlaceTy::from_ty(body.local_decls[place.local].ty);
for (place_ref, elem) in place.iter_projections() {
match elem {
ProjectionElem::Deref => match place_ty.ty.kind() {
ty::Ref(..) | ty::RawPtr(..) => {
self.move_errors.push(MoveError::new(
place,
location,
BorrowedContent {
target_place: place_ref.project_deeper(&[elem], tcx),
},
));
return;
}
ty::Adt(adt, _) => {
if !adt.is_box() {
bug!("Adt should be a box type when Place is deref");
}
}
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Foreign(_)
| ty::Str
| ty::Array(_, _)
| ty::Pat(_, _)
| ty::Slice(_)
| ty::FnDef(_, _)
| ty::FnPtr(..)
| ty::Dynamic(_, _)
| ty::Closure(_, _)
| ty::CoroutineClosure(_, _)
| ty::Coroutine(_, _)
| ty::CoroutineWitness(..)
| ty::Never
| ty::Tuple(_)
| ty::UnsafeBinder(_)
| ty::Alias(_)
| ty::Param(_)
| ty::Bound(_, _)
| ty::Infer(_)
| ty::Error(_)
| ty::Placeholder(_) => {
bug!("When Place is Deref it's type shouldn't be {place_ty:#?}")
}
},
ProjectionElem::Field(_, _) => match place_ty.ty.kind() {
ty::Adt(adt, _) => {
if adt.has_dtor(tcx) {
self.move_errors.push(MoveError::new(
place,
location,
InteriorOfTypeWithDestructor { container_ty: place_ty.ty },
));
return;
}
}
ty::Closure(..)
| ty::CoroutineClosure(..)
| ty::Coroutine(_, _)
| ty::Tuple(_) => (),
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Foreign(_)
| ty::Str
| ty::Array(_, _)
| ty::Pat(_, _)
| ty::Slice(_)
| ty::RawPtr(_, _)
| ty::Ref(_, _, _)
| ty::FnDef(_, _)
| ty::FnPtr(..)
| ty::Dynamic(_, _)
| ty::CoroutineWitness(..)
| ty::Never
| ty::UnsafeBinder(_)
| ty::Alias(_)
| ty::Param(_)
| ty::Bound(_, _)
| ty::Infer(_)
| ty::Error(_)
| ty::Placeholder(_) => bug!(
"When Place contains ProjectionElem::Field it's type shouldn't be {place_ty:#?}"
),
},
ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
match place_ty.ty.kind() {
ty::Slice(_) => {
self.move_errors.push(MoveError::new(
place,
location,
InteriorOfSliceOrArray { ty: place_ty.ty, is_index: false },
));
return;
}
ty::Array(_, _) => (),
_ => bug!("Unexpected type {:#?}", place_ty.ty),
}
}
ProjectionElem::Index(_) => match place_ty.ty.kind() {
ty::Array(..) | ty::Slice(..) => {
self.move_errors.push(MoveError::new(
place,
location,
InteriorOfSliceOrArray { ty: place_ty.ty, is_index: true },
));
return;
}
_ => bug!("Unexpected type {place_ty:#?}"),
},
// `OpaqueCast`: only transmutes the type, so no moves there.
// `Downcast` : only changes information about a `Place` without moving.
// So it's safe to skip these.
ProjectionElem::OpaqueCast(_)
| ProjectionElem::Downcast(_, _)
| ProjectionElem::UnwrapUnsafeBinder(_) => (),
}
place_ty = place_ty.projection_ty(tcx, elem);
}
}
fn check_if_full_path_is_moved(
&mut self,
location: Location,
desired_action: InitializationRequiringAction,
place_span: (PlaceRef<'tcx>, Span),
state: &BorrowckDomain,
) {
let maybe_uninits = &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: &MixedBitSet<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),
state: &BorrowckDomain,
) {
let maybe_uninits = &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, 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),
state: &BorrowckDomain,
) {
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::OpaqueCast(_) |
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?
{ }
ProjectionElem::UnwrapUnsafeBinder(_) => {
check_parent_of_field(self, location, place_base, span, state);
}
// assigning to (*P) requires P to be initialized
ProjectionElem::Deref => {
self.check_if_full_path_is_moved(
location, InitializationRequiringAction::Use,
(place_base, span), 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), 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, state);
}
_ => {}
}
}
}
}
fn check_parent_of_field<'a, 'tcx>(
this: &mut MirBorrowckCtxt<'a, '_, 'tcx>,
location: Location,
base: PlaceRef<'tcx>,
span: Span,
state: &BorrowckDomain,
) {
// 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 = &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 Some(mpi) = this.move_path_for_place(prefix) else { 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()
&& 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,
);
// 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.
this.used_mut.insert(base.local);
}
}
}
/// 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,
state: &BorrowckDomain,
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(BorrowKind::Mut { kind: mut_borrow_kind }))
| Write(WriteKind::MutableBorrow(BorrowKind::Mut { kind: mut_borrow_kind })) => {
let is_local_mutation_allowed = match mut_borrow_kind {
// `ClosureCapture` is used for mutable variable with an immutable binding.
// This is only behaviour difference between `ClosureCapture` and mutable
// borrows.
MutBorrowKind::ClosureCapture => LocalMutationIsAllowed::Yes,
MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow => {
is_local_mutation_allowed
}
};
match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
Ok(root_place) => {
self.add_used_mut(root_place, 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, state);
return false;
}
Err(place_err) => {
error_access = AccessKind::Mutate;
the_place_err = place_err;
}
}
}
Reservation(
WriteKind::Move
| WriteKind::Replace
| WriteKind::StorageDeadOrDrop
| WriteKind::MutableBorrow(BorrowKind::Shared)
| WriteKind::MutableBorrow(BorrowKind::Fake(_)),
)
| Write(
WriteKind::Move
| WriteKind::Replace
| WriteKind::StorageDeadOrDrop
| WriteKind::MutableBorrow(BorrowKind::Shared)
| WriteKind::MutableBorrow(BorrowKind::Fake(_)),
) => {
if self.is_mutable(place.as_ref(), is_local_mutation_allowed).is_err()
&& !self.has_buffered_diags()
{
// rust-lang/rust#46908: In pure NLL mode this code path should be
// unreachable, but we use `span_delayed_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.dcx().span_delayed_bug(
span,
format!(
"Accessing `{place:?}` with the kind `{kind:?}` shouldn't be possible",
),
);
}
return false;
}
Activation(..) => {
// permission checks are done at Reservation point.
return false;
}
Read(
ReadKind::Borrow(BorrowKind::Mut { .. } | BorrowKind::Shared | BorrowKind::Fake(_))
| 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, state);
// at this point, we have set up the error reporting state.
if let Some(init_index) = previously_initialized {
if let (AccessKind::Mutate, Some(_)) = (error_access, place.as_local()) {
// If this is a mutate access to an immutable local variable with no projections
// report the error as an illegal reassignment
let init = &self.move_data.inits[init_index];
let assigned_span = init.span(self.body);
self.report_illegal_reassignment((place, span), assigned_span, place);
} else {
self.report_mutability_error(place, span, the_place_err, error_access, location)
}
true
} else {
false
}
}
fn is_local_ever_initialized(&self, local: Local, state: &BorrowckDomain) -> Option<InitIndex> {
let mpi = self.move_data.rev_lookup.find_local(local)?;
let ii = &self.move_data.init_path_map[mpi];
ii.into_iter().find(|&&index| state.ever_inits.contains(index)).copied()
}
/// Adds the place into the used mutable variables set
fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, state: &BorrowckDomain) {
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, 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()].is_by_ref() =>
{
is_local_mutation_allowed
}
_ => LocalMutationIsAllowed::Yes,
};
self.is_mutable(place_base, mode)
}
}
}
ty::RawPtr(_, mutbl) => {
match 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),
}
}
// Check as the inner reference type if it is a field projection
// from the `&pin` pattern
ProjectionElem::Field(FieldIdx::ZERO, _)
if let Some(adt) =
place_base.ty(self.body(), self.infcx.tcx).ty.ty_adt_def()
&& adt.is_pin()
&& self.infcx.tcx.features().pin_ergonomics() =>
{
self.is_mutable(place_base, is_local_mutation_allowed)
}
// 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::OpaqueCast { .. }
| ProjectionElem::Downcast(..)
| ProjectionElem::UnwrapUnsafeBinder(_) => {
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.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.
fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<FieldIdx> {
path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
}
fn dominators(&self) -> &Dominators<BasicBlock> {
// `BasicBlocks` computes dominators on-demand and caches them.
self.body.basic_blocks.dominators()
}
fn lint_unused_mut(&self) {
let tcx = self.infcx.tcx;
let body = self.body;
for local in body.mut_vars_and_args_iter().filter(|local| !self.used_mut.contains(local)) {
let local_decl = &body.local_decls[local];
let ClearCrossCrate::Set(SourceScopeLocalData { lint_root, .. }) =
body.source_scopes[local_decl.source_info.scope].local_data
else {
continue;
};
// Skip over locals that begin with an underscore or have no name
if self.local_excluded_from_unused_mut_lint(local) {
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;
}
let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
tcx.emit_node_span_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
}
}
}
/// 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,
}