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//! This query borrow-checks the MIR to (further) ensure it is not broken.
use crate::borrow_check::nll::region_infer::RegionInferenceContext;
use rustc::hir::{self, HirId};
use rustc::hir::Node;
use rustc::hir::def_id::DefId;
use rustc::infer::InferCtxt;
use rustc::lint::builtin::UNUSED_MUT;
use rustc::lint::builtin::{MUTABLE_BORROW_RESERVATION_CONFLICT};
use rustc::middle::borrowck::SignalledError;
use rustc::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
use rustc::mir::{
ClearCrossCrate, Local, Location, Body, Mutability, Operand, Place, PlaceBase, PlaceRef,
Static, StaticKind
};
use rustc::mir::{Field, Projection, ProjectionElem, Rvalue, Statement, StatementKind};
use rustc::mir::{Terminator, TerminatorKind};
use rustc::ty::query::Providers;
use rustc::ty::{self, TyCtxt};
use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, Level};
use rustc_data_structures::bit_set::BitSet;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::graph::dominators::Dominators;
use smallvec::SmallVec;
use std::collections::BTreeMap;
use std::mem;
use std::rc::Rc;
use syntax::ast::Name;
use syntax_pos::{Span, DUMMY_SP};
use crate::dataflow::indexes::{BorrowIndex, InitIndex, MoveOutIndex, MovePathIndex};
use crate::dataflow::move_paths::{HasMoveData, InitLocation, LookupResult, MoveData, MoveError};
use crate::dataflow::Borrows;
use crate::dataflow::DataflowResultsConsumer;
use crate::dataflow::FlowAtLocation;
use crate::dataflow::MoveDataParamEnv;
use crate::dataflow::{do_dataflow, DebugFormatted};
use crate::dataflow::EverInitializedPlaces;
use crate::dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
use self::borrow_set::{BorrowData, BorrowSet};
use self::flows::Flows;
use self::location::LocationTable;
use self::prefixes::PrefixSet;
use self::MutateMode::{JustWrite, WriteAndRead};
use self::mutability_errors::AccessKind;
use self::path_utils::*;
crate mod borrow_set;
mod error_reporting;
mod flows;
mod location;
mod conflict_errors;
mod move_errors;
mod mutability_errors;
mod path_utils;
crate mod place_ext;
crate mod places_conflict;
mod prefixes;
mod used_muts;
pub(crate) mod nll;
// FIXME(eddyb) perhaps move this somewhere more centrally.
#[derive(Debug)]
crate struct Upvar {
name: Name,
var_hir_id: HirId,
/// If true, the capture is behind a reference.
by_ref: bool,
mutability: Mutability,
}
pub fn provide(providers: &mut Providers<'_>) {
*providers = Providers {
mir_borrowck,
..*providers
};
}
fn mir_borrowck(tcx: TyCtxt<'_>, def_id: DefId) -> BorrowCheckResult<'_> {
let input_body = tcx.mir_validated(def_id);
debug!("run query mir_borrowck: {}", tcx.def_path_str(def_id));
let opt_closure_req = tcx.infer_ctxt().enter(|infcx| {
let input_body: &Body<'_> = &input_body.borrow();
do_mir_borrowck(&infcx, input_body, def_id)
});
debug!("mir_borrowck done");
opt_closure_req
}
fn do_mir_borrowck<'a, 'tcx>(
infcx: &InferCtxt<'a, 'tcx>,
input_body: &Body<'tcx>,
def_id: DefId,
) -> BorrowCheckResult<'tcx> {
debug!("do_mir_borrowck(def_id = {:?})", def_id);
let tcx = infcx.tcx;
let attributes = tcx.get_attrs(def_id);
let param_env = tcx.param_env(def_id);
let id = tcx
.hir()
.as_local_hir_id(def_id)
.expect("do_mir_borrowck: non-local DefId");
// Gather the upvars of a closure, if any.
let tables = tcx.typeck_tables_of(def_id);
let upvars: Vec<_> = tables
.upvar_list
.get(&def_id)
.into_iter()
.flat_map(|v| v.values())
.map(|upvar_id| {
let var_hir_id = upvar_id.var_path.hir_id;
let capture = tables.upvar_capture(*upvar_id);
let by_ref = match capture {
ty::UpvarCapture::ByValue => false,
ty::UpvarCapture::ByRef(..) => true,
};
let mut upvar = Upvar {
name: tcx.hir().name(var_hir_id),
var_hir_id,
by_ref,
mutability: Mutability::Not,
};
let bm = *tables.pat_binding_modes().get(var_hir_id)
.expect("missing binding mode");
if bm == ty::BindByValue(hir::MutMutable) {
upvar.mutability = Mutability::Mut;
}
upvar
})
.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: Body<'tcx> = input_body.clone();
let free_regions = nll::replace_regions_in_mir(infcx, def_id, param_env, &mut body);
let body = &body; // no further changes
let location_table = &LocationTable::new(body);
let mut errors_buffer = Vec::new();
let (move_data, move_errors): (MoveData<'tcx>, Option<Vec<(Place<'tcx>, MoveError<'tcx>)>>) =
match MoveData::gather_moves(body, tcx) {
Ok(move_data) => (move_data, None),
Err((move_data, move_errors)) => (move_data, Some(move_errors)),
};
let mdpe = MoveDataParamEnv {
move_data: move_data,
param_env: param_env,
};
let dead_unwinds = BitSet::new_empty(body.basic_blocks().len());
let mut flow_inits = FlowAtLocation::new(do_dataflow(
tcx,
body,
def_id,
&attributes,
&dead_unwinds,
MaybeInitializedPlaces::new(tcx, body, &mdpe),
|bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
));
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));
// If we are in non-lexical mode, compute the non-lexical lifetimes.
let (regioncx, polonius_output, opt_closure_req) = nll::compute_regions(
infcx,
def_id,
free_regions,
body,
&upvars,
location_table,
param_env,
&mut flow_inits,
&mdpe.move_data,
&borrow_set,
&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 = FlowAtLocation::new(do_dataflow(
tcx,
body,
def_id,
&attributes,
&dead_unwinds,
Borrows::new(tcx, body, param_env, regioncx.clone(), &borrow_set),
|rs, i| DebugFormatted::new(&rs.location(i)),
));
let flow_uninits = FlowAtLocation::new(do_dataflow(
tcx,
body,
def_id,
&attributes,
&dead_unwinds,
MaybeUninitializedPlaces::new(tcx, body, &mdpe),
|bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
));
let flow_ever_inits = FlowAtLocation::new(do_dataflow(
tcx,
body,
def_id,
&attributes,
&dead_unwinds,
EverInitializedPlaces::new(tcx, body, &mdpe),
|bd, i| DebugFormatted::new(&bd.move_data().inits[i]),
));
let movable_generator = match tcx.hir().get(id) {
Node::Expr(&hir::Expr {
node: hir::ExprKind::Closure(.., Some(hir::GeneratorMovability::Static)),
..
}) => false,
_ => true,
};
let dominators = body.dominators();
let mut mbcx = MirBorrowckCtxt {
infcx,
body,
mir_def_id: def_id,
param_env,
move_data: &mdpe.move_data,
location_table,
movable_generator,
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,
disable_error_downgrading: false,
nonlexical_regioncx: regioncx,
used_mut: Default::default(),
used_mut_upvars: SmallVec::new(),
borrow_set,
dominators,
upvars,
};
let mut state = Flows::new(
flow_borrows,
flow_uninits,
flow_ever_inits,
polonius_output,
);
if let Some(errors) = move_errors {
mbcx.report_move_errors(errors);
}
mbcx.analyze_results(&mut state); // entry point for DataflowResultsConsumer
// 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 lint_root = if let ClearCrossCrate::Set(ref vsi) = mbcx.body.source_scope_local_data {
let scope = mbcx.body.source_info(location).scope;
vsi[scope].lint_root
} else {
id
};
// Span and message don't matter; we overwrite them below anyway
let mut diag = mbcx.infcx.tcx.struct_span_lint_hir(
MUTABLE_BORROW_RESERVATION_CONFLICT, lint_root, DUMMY_SP, "");
diag.message = initial_diag.styled_message().clone();
diag.span = initial_diag.span.clone();
initial_diag.cancel();
diag.buffer(&mut mbcx.errors_buffer);
}
// 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.is_none())
.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)) {
if let ClearCrossCrate::Set(ref vsi) = mbcx.body.source_scope_local_data {
let local_decl = &mbcx.body.local_decls[local];
// Skip implicit `self` argument for closures
if local.index() == 1 && tcx.is_closure(mbcx.mir_def_id) {
continue;
}
// Skip over locals that begin with an underscore or have no name
match local_decl.name {
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;
}
let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
tcx.struct_span_lint_hir(
UNUSED_MUT,
vsi[local_decl.source_info.scope].lint_root,
span,
"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.span.primary_span());
if !mbcx.disable_error_downgrading && tcx.migrate_borrowck() {
// When borrowck=migrate, check if AST-borrowck would
// error on the given code.
// rust-lang/rust#55492, rust-lang/rust#58776 check the base def id
// for errors. AST borrowck is responsible for aggregating
// `signalled_any_error` from all of the nested closures here.
let base_def_id = tcx.closure_base_def_id(def_id);
match tcx.borrowck(base_def_id).signalled_any_error {
SignalledError::NoErrorsSeen => {
// if AST-borrowck signalled no errors, then
// downgrade all the buffered MIR-borrowck errors
// to warnings.
for err in mbcx.errors_buffer.iter_mut() {
downgrade_if_error(err);
}
}
SignalledError::SawSomeError => {
// if AST-borrowck signalled a (cancelled) error,
// then we will just emit the buffered
// MIR-borrowck errors as normal.
}
}
}
for diag in mbcx.errors_buffer.drain(..) {
DiagnosticBuilder::new_diagnostic(mbcx.infcx.tcx.sess.diagnostic(), diag).emit();
}
}
let result = BorrowCheckResult {
closure_requirements: opt_closure_req,
used_mut_upvars: mbcx.used_mut_upvars,
};
debug!("do_mir_borrowck: result = {:#?}", result);
result
}
fn downgrade_if_error(diag: &mut Diagnostic) {
if diag.is_error() {
diag.level = Level::Warning;
diag.warn(
"this error has been downgraded to a warning for backwards \
compatibility with previous releases",
).warn(
"this represents potential undefined behavior in your code and \
this warning will become a hard error in the future",
).note(
"for more information, try `rustc --explain E0729`"
);
}
}
crate struct MirBorrowckCtxt<'cx, 'tcx> {
crate infcx: &'cx InferCtxt<'cx, 'tcx>,
body: &'cx Body<'tcx>,
mir_def_id: DefId,
param_env: ty::ParamEnv<'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>>,
/// 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 indicies.
///
/// 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<'cx, '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<'cx, 'tcx>>,
/// Errors to be reported buffer
errors_buffer: Vec<Diagnostic>,
/// If there are no errors reported by the HIR borrow checker, we downgrade
/// all NLL errors to warnings. Setting this flag disables downgrading.
disable_error_downgrading: bool,
/// 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]>,
/// Non-lexical region inference context, if NLL is enabled. This
/// contains the results from region inference and lets us e.g.
/// find out which CFG points are contained in each borrow region.
nonlexical_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>,
}
// 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> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
type FlowState = Flows<'cx, 'tcx>;
fn body(&self) -> &'cx Body<'tcx> {
self.body
}
fn visit_block_entry(&mut self, bb: BasicBlock, flow_state: &Self::FlowState) {
debug!("MirBorrowckCtxt::process_block({:?}): {}", bb, flow_state);
}
fn visit_statement_entry(
&mut self,
location: Location,
stmt: &'cx Statement<'tcx>,
flow_state: &Self::FlowState,
) {
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(ref lhs, ref rhs) => {
self.consume_rvalue(
location,
(rhs, span),
flow_state,
);
self.mutate_place(
location,
(lhs, span),
Shallow(None),
JustWrite,
flow_state,
);
}
StatementKind::FakeRead(_, 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 {
ref place,
variant_index: _,
} => {
self.mutate_place(
location,
(place, span),
Shallow(None),
JustWrite,
flow_state,
);
}
StatementKind::InlineAsm(ref asm) => {
for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
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::Nop
| 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_entry(
&mut self,
location: Location,
term: &'cx Terminator<'tcx>,
flow_state: &Self::FlowState,
) {
let loc = location;
debug!(
"MirBorrowckCtxt::process_terminator({:?}, {:?}): {}",
location, term, flow_state
);
let span = term.source_info.span;
self.check_activations(location, span, flow_state);
match term.kind {
TerminatorKind::SwitchInt {
ref discr,
switch_ty: _,
values: _,
targets: _,
} => {
self.consume_operand(loc, (discr, span), flow_state);
}
TerminatorKind::Drop {
location: ref drop_place,
target: _,
unwind: _,
} => {
let gcx = self.infcx.tcx.global_tcx();
// Compute the type with accurate region information.
let drop_place_ty = drop_place.ty(self.body, self.infcx.tcx);
// Erase the regions.
let drop_place_ty = self.infcx.tcx.erase_regions(&drop_place_ty).ty;
// "Lift" into the gcx -- once regions are erased, this type should be in the
// global arenas; this "lift" operation basically just asserts that is true, but
// that is useful later.
gcx.lift_to_global(&drop_place_ty).unwrap();
debug!("visit_terminator_drop \
loc: {:?} term: {:?} drop_place: {:?} drop_place_ty: {:?} span: {:?}",
loc, term, drop_place, drop_place_ty, span);
self.access_place(
loc,
(drop_place, span),
(AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
LocalMutationIsAllowed::Yes,
flow_state,
);
}
TerminatorKind::DropAndReplace {
location: ref 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: _,
} => {
self.consume_operand(loc, (func, span), flow_state);
for arg in args {
self.consume_operand(
loc,
(arg, span),
flow_state,
);
}
if let Some((ref 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::mir::interpret::PanicInfo;
if let PanicInfo::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: _,
drop: _,
} => {
self.consume_operand(loc, (value, span), flow_state);
if self.movable_generator {
// Look for any active borrows to locals
let borrow_set = self.borrow_set.clone();
flow_state.with_outgoing_borrows(|borrows| {
for i in borrows {
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();
flow_state.with_outgoing_borrows(|borrows| {
for i in borrows {
let borrow = &borrow_set[i];
self.check_for_invalidation_at_exit(loc, borrow, span);
}
});
}
TerminatorKind::Goto { target: _ }
| TerminatorKind::Abort
| TerminatorKind::Unreachable
| TerminatorKind::FalseEdges {
real_target: _,
imaginary_target: _,
}
| TerminatorKind::FalseUnwind {
real_target: _,
unwind: _,
} => {
// no data used, thus irrelevant to borrowck
}
}
}
}
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum MutateMode {
JustWrite,
WriteAndRead,
}
use self::ReadOrWrite::{Activation, Read, Reservation, Write};
use self::AccessDepth::{Deep, Shallow};
#[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<'d, 'tcx> {
place_base: &'d PlaceBase<'tcx>,
place_projection: &'d Option<Box<Projection<'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> {
/// If there are no errors reported by the HIR borrow checker, we downgrade
/// all NLL errors to warnings. Calling this disables downgrading.
crate fn disable_error_downgrading(&mut self) {
self.disable_error_downgrading = true;
}
/// 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.clone(), 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 emited 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.clone(), 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 param_env = self.param_env;
let location_table = self.location_table.start_index(location);
let borrow_set = self.borrow_set.clone();
each_borrow_involving_path(
self,
tcx,
param_env,
body,
location,
(sd, place_span.0),
&borrow_set,
flow_state.borrows_in_scope(location_table),
|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)
| (Read(_), BorrowKind::Shallow)
| (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
| (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
Control::Continue
}
(Write(WriteKind::Move), BorrowKind::Shallow) => {
// Handled by initialization checks.
Control::Continue
}
(Read(kind), BorrowKind::Unique) | (Read(kind), 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)
| (Reservation(WriteKind::MutableBorrow(bk)), BorrowKind::Shared) if {
tcx.migrate_borrowck() && this.borrow_set.location_map.contains_key(&location)
} => {
let bi = this.borrow_set.location_map[&location];
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.clone(), 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.clone());
}
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: (&'cx 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 a immutable local variable
// (e.g., `x = ...`) so long as it has never been initialized
// before (at this point in the flow).
if let Place {
base: PlaceBase::Local(local),
projection: None,
} = place_span.0 {
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, ref 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::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(ref place) | Rvalue::Discriminant(ref 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, ref operand1, ref operand2)
| Rvalue::CheckedBinaryOp(_bin_op, 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);
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>| {
if place.projection.is_some() {
if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
this.used_mut_upvars.push(field);
}
} else if let PlaceBase::Local(local) = place.base {
this.used_mut.insert(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 {
base: PlaceBase::Local(local),
projection: None,
}) |
Operand::Copy(Place {
base: PlaceBase::Local(local),
projection: None,
}) if self.body.local_decls[local].is_user_variable.is_none() => {
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 bbd = &self.body[loc.block];
let stmt = &bbd.statements[loc.statement_index];
debug!("temporary assigned in: stmt={:?}", stmt);
if let StatementKind::Assign(_, box Rvalue::Ref(_, _, ref source)) = stmt.kind {
propagate_closure_used_mut_place(self, source);
} else {
bug!("closures should only capture user variables \
or references to user variables");
}
}
Operand::Move(ref place)
| Operand::Copy(ref place) => {
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(ref 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(ref 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 root_place = self.prefixes(place.as_ref(), PrefixSet::All).last().unwrap();
// 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?
assert!(root_place.projection.is_none());
let (might_be_alive, will_be_dropped) = match root_place.base {
PlaceBase::Static(box Static {
kind: StaticKind::Promoted(_),
..
}) => {
(true, false)
}
PlaceBase::Static(box Static {
kind: StaticKind::Static(_),
..
}) => {
// Thread-locals might be dropped after the function exits, but
// "true" statics will never be.
(true, self.is_place_thread_local(root_place))
}
PlaceBase::Local(_) => {
// Locals are always dropped at function exit, and if they
// have a destructor it would've been called already.
(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.param_env,
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 statements 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.
}
}
}
impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
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<'cx, '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 a 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);
match self.move_path_closest_to(place_span.0) {
Ok((prefix, mpi)) => {
if maybe_uninits.contains(mpi) {
self.report_use_of_moved_or_uninitialized(
location,
desired_action,
(prefix, place_span.0, place_span.1),
mpi,
);
return; // don't bother finding other problems.
}
}
Err(NoMovePathFound::ReachedStatic) => {
// Okay: we do not build MoveData for static variables
} // 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.)
}
}
fn check_if_path_or_subpath_is_moved(
&mut self,
location: Location,
desired_action: InitializationRequiringAction,
place_span: (PlaceRef<'cx, '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);
// 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) {
if let Some(child_mpi) = maybe_uninits.has_any_child_of(mpi) {
self.report_use_of_moved_or_uninitialized(
location,
desired_action,
(place_span.0, place_span.0, place_span.1),
child_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<'cx, 'tcx>,
) -> Result<(PlaceRef<'cx, 'tcx>, MovePathIndex), NoMovePathFound> {
let mut last_prefix = place.base;
for prefix in self.prefixes(place, PrefixSet::All) {
if let Some(mpi) = self.move_path_for_place(prefix) {
return Ok((prefix, mpi));
}
last_prefix = prefix.base;
}
match last_prefix {
PlaceBase::Local(_) => panic!("should have move path for every Local"),
PlaceBase::Static(_) => Err(NoMovePathFound::ReachedStatic),
}
}
fn move_path_for_place(&mut self, place: PlaceRef<'cx, '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): (&'cx Place<'tcx>, Span),
flow_state: &Flows<'cx, 'tcx>,
) {
debug!("check_if_assigned_path_is_moved place: {:?}", place);
// recur down place; dispatch to external checks when necessary
let mut place_projection = &place.projection;
// None case => assigning to `x` does not require `x` be initialized.
while let Some(proj) = place_projection {
let Projection { ref base, ref elem } = **proj;
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 a adt with a dtor?
{ }
// assigning to (*P) requires P to be initialized
ProjectionElem::Deref => {
self.check_if_full_path_is_moved(
location, InitializationRequiringAction::Use,
(PlaceRef {
base: &place.base,
projection: 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::ty_from(&place.base, base, self.body, tcx).ty;
match base_ty.sty {
ty::Adt(def, _) if def.has_dtor(tcx) => {
self.check_if_path_or_subpath_is_moved(
location, InitializationRequiringAction::Assignment,
(PlaceRef {
base: &place.base,
projection: 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, PlaceRef {
base: &place.base,
projection: base,
}, span, flow_state);
if let PlaceBase::Local(local) = place.base {
// 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(local);
}
}
_ => {}
}
}
}
place_projection = base;
}
fn check_parent_of_field<'cx, 'tcx>(
this: &mut MirBorrowckCtxt<'cx, 'tcx>,
location: Location,
base: PlaceRef<'cx, '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 a uninitialized field of a union (for example,
// after a move out). In this case, do not report a 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 let ty::Adt(def, _) =
Place::ty_from(base.base, base.projection, this.body, tcx).ty.sty
{
if def.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;
// 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 = if let PlaceBase::Local(local) = place.base {
self.is_local_ever_initialized(local, flow_state).is_some()
} else {
true
};
match kind {
Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
| Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
| Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Unique))
| Write(WriteKind::MutableBorrow(borrow_kind @ 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(wk @ WriteKind::Move)
| Write(wk @ WriteKind::Move)
| Reservation(wk @ WriteKind::StorageDeadOrDrop)
| Reservation(wk @ WriteKind::MutableBorrow(BorrowKind::Shared))
| Reservation(wk @ WriteKind::MutableBorrow(BorrowKind::Shallow))
| Write(wk @ WriteKind::StorageDeadOrDrop)
| Write(wk @ WriteKind::MutableBorrow(BorrowKind::Shared))
| Write(wk @ WriteKind::MutableBorrow(BorrowKind::Shallow)) => {
if let (Err(place_err), true) = (
self.is_mutable(place.as_ref(), is_local_mutation_allowed),
self.errors_buffer.is_empty()
) {
if self.infcx.tcx.migrate_borrowck() {
// rust-lang/rust#46908: In pure NLL mode this
// code path should be unreachable (and thus
// we signal an ICE in the else branch
// here). But we can legitimately get here
// under borrowck=migrate mode, so instead of
// ICE'ing we instead report a legitimate
// error (which will then be downgraded to a
// warning by the migrate machinery).
error_access = match wk {
WriteKind::MutableBorrow(_) => AccessKind::MutableBorrow,
WriteKind::Move => AccessKind::Move,
WriteKind::StorageDeadOrDrop |
WriteKind::Mutate => AccessKind::Mutate,
};
self.report_mutability_error(
place,
span,
place_err,
error_access,
location,
);
} else {
span_bug!(
span,
"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))
| Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
| Read(ReadKind::Borrow(BorrowKind::Shared))
| Read(ReadKind::Borrow(BorrowKind::Shallow))
| Read(ReadKind::Copy) => {
// Access authorized
return false;
}
}
// at this point, we have set up the error reporting state.
return 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<'d>(&mut self, root_place: RootPlace<'d, 'tcx>, flow_state: &Flows<'cx, 'tcx>) {
match root_place {
RootPlace {
place_base: PlaceBase::Local(local),
place_projection: None,
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_base: _,
place_projection: _,
is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
} => {}
RootPlace {
place_base,
place_projection: place_projection @ Some(_),
is_local_mutation_allowed: _,
} => {
if let Some(field) = self.is_upvar_field_projection(PlaceRef {
base: &place_base,
projection: &place_projection,
}) {
self.used_mut_upvars.push(field);
}
}
RootPlace {
place_base: PlaceBase::Static(..),
place_projection: None,
is_local_mutation_allowed: _,
} => {}
}
}
/// Whether this value can be written or borrowed mutably.
/// Returns the root place if the place passed in is a projection.
fn is_mutable<'d>(
&self,
place: PlaceRef<'d, 'tcx>,
is_local_mutation_allowed: LocalMutationIsAllowed,
) -> Result<RootPlace<'d, 'tcx>, PlaceRef<'d, 'tcx>> {
match place {
PlaceRef {
base: PlaceBase::Local(local),
projection: None,
} => {
let local = &self.body.local_decls[*local];
match local.mutability {
Mutability::Not => match is_local_mutation_allowed {
LocalMutationIsAllowed::Yes => Ok(RootPlace {
place_base: place.base,
place_projection: place.projection,
is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
}),
LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
place_base: place.base,
place_projection: place.projection,
is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
}),
LocalMutationIsAllowed::No => Err(place),
},
Mutability::Mut => Ok(RootPlace {
place_base: place.base,
place_projection: place.projection,
is_local_mutation_allowed,
}),
}
}
// The rules for promotion are made by `qualify_consts`, there wouldn't even be a
// `Place::Promoted` if the promotion weren't 100% legal. So we just forward this
PlaceRef {
base: PlaceBase::Static(box Static {
kind: StaticKind::Promoted(_),
..
}),
projection: None,
} =>
Ok(RootPlace {
place_base: place.base,
place_projection: place.projection,
is_local_mutation_allowed,
}),
PlaceRef {
base: PlaceBase::Static(box Static {
kind: StaticKind::Static(def_id),
..
}),
projection: None,
} => {
if !self.infcx.tcx.is_mutable_static(*def_id) {
Err(place)
} else {
Ok(RootPlace {
place_base: place.base,
place_projection: place.projection,
is_local_mutation_allowed,
})
}
}
PlaceRef {
base: _,
projection: Some(proj),
} => {
match proj.elem {
ProjectionElem::Deref => {
let base_ty =
Place::ty_from(place.base, &proj.base, self.body, self.infcx.tcx).ty;
// Check the kind of deref to decide
match base_ty.sty {
ty::Ref(_, _, mutbl) => {
match mutbl {
// Shared borrowed data is never mutable
hir::MutImmutable => Err(place),
// Mutably borrowed data is mutable, but only if we have a
// unique path to the `&mut`
hir::MutMutable => {
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(PlaceRef {
base: place.base,
projection: &proj.base,
}, mode)
}
}
}
ty::RawPtr(tnm) => {
match tnm.mutbl {
// `*const` raw pointers are not mutable
hir::MutImmutable => Err(place),
// `*mut` raw pointers are always mutable, regardless of
// context. The users have to check by themselves.
hir::MutMutable => {
Ok(RootPlace {
place_base: place.base,
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(PlaceRef {
base: place.base,
projection: &proj.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!(
"upvar.mutability={:?} local_mutation_is_allowed={:?} \
place={:?}",
upvar, is_local_mutation_allowed, place
);
match (upvar.mutability, is_local_mutation_allowed) {
(Mutability::Not, LocalMutationIsAllowed::No)
| (Mutability::Not, 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(PlaceRef {
base: place.base,
projection: &proj.base,
}, is_local_mutation_allowed)?;
Ok(RootPlace {
place_base: place.base,
place_projection: place.projection,
is_local_mutation_allowed,
})
}
}
} else {
self.is_mutable(PlaceRef {
base: place.base,
projection: &proj.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<'cx, 'tcx>) -> Option<Field> {
let mut place_projection = place_ref.projection;
let mut by_ref = false;
if let Some(box Projection {
base,
elem: ProjectionElem::Deref,
}) = place_projection {
place_projection = &base;
by_ref = true;
}
match place_projection {
Some(box Projection {
base,
elem: ProjectionElem::Field(field, _ty),
}) => {
let tcx = self.infcx.tcx;
let base_ty = Place::ty_from(place_ref.base, &base, self.body, tcx).ty;
if (base_ty.is_closure() || base_ty.is_generator()) &&
(!by_ref || self.upvars[field.index()].by_ref) {
Some(*field)
} else {
None
}
}
_ => None,
}
}
}
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum NoMovePathFound {
ReachedStatic,
}
/// 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,
}
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