//! This query borrow-checks the MIR to (further) ensure it is not broken. // tidy-alphabetical-start #![allow(internal_features)] #![doc(rust_logo)] #![feature(assert_matches)] #![feature(box_patterns)] #![feature(file_buffered)] #![feature(if_let_guard)] #![feature(let_chains)] #![feature(never_type)] #![feature(rustc_attrs)] #![feature(rustdoc_internals)] #![feature(stmt_expr_attributes)] #![feature(try_blocks)] #![warn(unreachable_pub)] // tidy-alphabetical-end use std::borrow::Cow; use std::cell::RefCell; use std::marker::PhantomData; use std::ops::{ControlFlow, Deref}; use rustc_abi::FieldIdx; use rustc_data_structures::fx::{FxIndexMap, FxIndexSet}; use rustc_data_structures::graph::dominators::Dominators; use rustc_errors::LintDiagnostic; use rustc_hir as hir; use rustc_hir::CRATE_HIR_ID; use rustc_hir::def_id::LocalDefId; use rustc_index::bit_set::{DenseBitSet, MixedBitSet}; use rustc_index::{IndexSlice, IndexVec}; use rustc_infer::infer::{ InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin, TyCtxtInferExt, }; use rustc_middle::mir::*; use rustc_middle::query::Providers; use rustc_middle::ty::fold::fold_regions; use rustc_middle::ty::{self, ParamEnv, RegionVid, TyCtxt, TypingMode}; use rustc_middle::{bug, span_bug}; use rustc_mir_dataflow::impls::{ EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces, }; use rustc_mir_dataflow::move_paths::{ InitIndex, InitLocation, LookupResult, MoveData, MovePathIndex, }; use rustc_mir_dataflow::{Analysis, EntryStates, Results, ResultsVisitor, visit_results}; use rustc_session::lint::builtin::{TAIL_EXPR_DROP_ORDER, UNUSED_MUT}; use rustc_span::{Span, Symbol}; use smallvec::SmallVec; use tracing::{debug, instrument}; use crate::borrow_set::{BorrowData, BorrowSet}; use crate::consumers::{BodyWithBorrowckFacts, ConsumerOptions}; 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::PoloniusDiagnosticsContext; use crate::polonius::legacy::{PoloniusLocationTable, PoloniusOutput}; use crate::prefixes::PrefixSet; use crate::region_infer::RegionInferenceContext; use crate::renumber::RegionCtxt; use crate::session_diagnostics::VarNeedNotMut; mod borrow_set; mod borrowck_errors; mod constraints; mod dataflow; mod def_use; mod diagnostics; mod member_constraints; mod nll; mod path_utils; mod place_ext; mod places_conflict; mod polonius; mod prefixes; mod region_infer; mod renumber; mod session_diagnostics; mod type_check; mod universal_regions; mod used_muts; /// A public API provided for the Rust compiler consumers. pub mod consumers; rustc_fluent_macro::fluent_messages! { "../messages.ftl" } /// 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 }; } fn mir_borrowck(tcx: TyCtxt<'_>, def: LocalDefId) -> &BorrowCheckResult<'_> { let (input_body, promoted) = tcx.mir_promoted(def); debug!("run query mir_borrowck: {}", tcx.def_path_str(def)); let input_body: &Body<'_> = &input_body.borrow(); if input_body.should_skip() || input_body.tainted_by_errors.is_some() { debug!("Skipping borrowck because of injected body or tainted body"); // Let's make up a borrowck result! Fun times! let result = BorrowCheckResult { concrete_opaque_types: FxIndexMap::default(), closure_requirements: None, used_mut_upvars: SmallVec::new(), tainted_by_errors: input_body.tainted_by_errors, }; return tcx.arena.alloc(result); } let borrowck_result = do_mir_borrowck(tcx, input_body, &*promoted.borrow(), None).0; debug!("mir_borrowck done"); tcx.arena.alloc(borrowck_result) } /// Perform the actual borrow checking. /// /// Use `consumer_options: None` for the default behavior of returning /// [`BorrowCheckResult`] only. Otherwise, return [`BodyWithBorrowckFacts`] according /// to the given [`ConsumerOptions`]. #[instrument(skip(tcx, input_body, input_promoted), fields(id=?input_body.source.def_id()), level = "debug")] fn do_mir_borrowck<'tcx>( tcx: TyCtxt<'tcx>, input_body: &Body<'tcx>, input_promoted: &IndexSlice>, consumer_options: Option, ) -> (BorrowCheckResult<'tcx>, Option>>) { let def = input_body.source.def_id().expect_local(); let infcx = BorrowckInferCtxt::new(tcx, def); if let Some(e) = input_body.tainted_by_errors { infcx.set_tainted_by_errors(e); } let mut local_names = IndexVec::from_elem(None, &input_body.local_decls); for var_debug_info in &input_body.var_debug_info { if let VarDebugInfoContents::Place(place) = var_debug_info.value { if let Some(local) = place.as_local() { if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name { span_bug!( var_debug_info.source_info.span, "local {:?} has many names (`{}` vs `{}`)", local, prev_name, var_debug_info.name ); } local_names[local] = Some(var_debug_info.name); } } } // 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 free_regions = nll::replace_regions_in_mir(&infcx, &mut body_owned, &mut promoted); let body = &body_owned; // no further changes // FIXME(-Znext-solver): A bit dubious that we're only registering // predefined opaques in the typeck root. if infcx.next_trait_solver() && !infcx.tcx.is_typeck_child(body.source.def_id()) { infcx.register_predefined_opaques_for_next_solver(def); } let location_table = PoloniusLocationTable::new(body); let move_data = MoveData::gather_moves(body, tcx, |_| true); let flow_inits = MaybeInitializedPlaces::new(tcx, body, &move_data) .iterate_to_fixpoint(tcx, body, Some("borrowck")) .into_results_cursor(body); 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); // Compute non-lexical lifetimes. let nll::NllOutput { regioncx, opaque_type_values, polonius_input, polonius_output, opt_closure_req, nll_errors, polonius_diagnostics, } = nll::compute_regions( &infcx, free_regions, body, &promoted, &location_table, flow_inits, &move_data, &borrow_set, consumer_options, ); // 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, ®ioncx, &opt_closure_req, &borrow_set); // We also have a `#[rustc_regions]` annotation that causes us to dump // information. let diags_buffer = &mut BorrowckDiagnosticsBuffer::default(); nll::dump_annotation( &infcx, body, ®ioncx, &opt_closure_req, &opaque_type_values, diags_buffer, ); let movable_coroutine = // The first argument is the coroutine type passed by value if let Some(local) = body.local_decls.raw.get(1) // Get the interior types and args which typeck computed && let ty::Coroutine(def_id, _) = *local.ty.kind() && tcx.coroutine_movability(def_id) == hir::Movability::Movable { true } else { false }; // 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 { 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(), locals_are_invalidated_at_exit, access_place_error_reported: Default::default(), reservation_error_reported: Default::default(), uninitialized_error_reported: Default::default(), regioncx: ®ioncx, used_mut: Default::default(), used_mut_upvars: SmallVec::new(), borrow_set: &borrow_set, upvars: &[], local_names: 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_diagnostics: polonius_diagnostics.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 { infcx: &infcx, body, move_data: &move_data, location_table: &location_table, movable_coroutine, locals_are_invalidated_at_exit, fn_self_span_reported: Default::default(), access_place_error_reported: Default::default(), reservation_error_reported: Default::default(), uninitialized_error_reported: Default::default(), regioncx: ®ioncx, used_mut: Default::default(), used_mut_upvars: SmallVec::new(), borrow_set: &borrow_set, upvars: tcx.closure_captures(def), local_names, region_names: RefCell::default(), next_region_name: RefCell::new(1), polonius_output, move_errors: Vec::new(), diags_buffer, polonius_diagnostics: polonius_diagnostics.as_ref(), }; // Compute and report region errors, if any. mbcx.report_region_errors(nll_errors); let mut flow_results = get_flow_results(tcx, body, &move_data, &borrow_set, ®ioncx); visit_results( body, traversal::reverse_postorder(body).map(|(bb, _)| bb), &mut flow_results, &mut mbcx, ); mbcx.report_move_errors(); // If requested, dump polonius MIR. polonius::dump_polonius_mir( &infcx, body, ®ioncx, &borrow_set, polonius_diagnostics.as_ref(), &opt_closure_req, ); // 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 = 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(); let tainted_by_errors = mbcx.emit_errors(); let result = BorrowCheckResult { concrete_opaque_types: opaque_type_values, closure_requirements: opt_closure_req, used_mut_upvars: mbcx.used_mut_upvars, tainted_by_errors, }; let body_with_facts = if consumer_options.is_some() { let output_facts = mbcx.polonius_output; Some(Box::new(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, })) } else { None }; debug!("do_mir_borrowck: result = {:#?}", result); (result, body_with_facts) } 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<'_, Borrowck<'_, '_>> = 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) reg_var_to_origin: RefCell>, pub(crate) param_env: ParamEnv<'tcx>, } impl<'tcx> BorrowckInferCtxt<'tcx> { pub(crate) fn new(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self { let infcx = tcx.infer_ctxt().build(TypingMode::analysis_in_body(tcx, def_id)); let param_env = tcx.param_env(def_id); BorrowckInferCtxt { infcx, reg_var_to_origin: RefCell::new(Default::default()), param_env } } pub(crate) fn next_region_var( &self, origin: RegionVariableOrigin, 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( &self, origin: NllRegionVariableOrigin, 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 } /// With the new solver we prepopulate the opaque type storage during /// MIR borrowck with the hidden types from HIR typeck. This is necessary /// to avoid ambiguities as earlier goals can rely on the hidden type /// of an opaque which is only constrained by a later goal. fn register_predefined_opaques_for_next_solver(&self, def_id: LocalDefId) { let tcx = self.tcx; // OK to use the identity arguments for each opaque type key, since // we remap opaques from HIR typeck back to their definition params. for data in tcx.typeck(def_id).concrete_opaque_types.iter().map(|(k, v)| (*k, *v)) { // HIR typeck did not infer the regions of the opaque, so we instantiate // them with fresh inference variables. let (key, hidden_ty) = fold_regions(tcx, data, |_, _| { self.next_nll_region_var_in_universe( NllRegionVariableOrigin::Existential { from_forall: false }, ty::UniverseIndex::ROOT, ) }); self.inject_new_hidden_type_unchecked(key, hidden_ty); } } } impl<'tcx> Deref for BorrowckInferCtxt<'tcx> { type Target = InferCtxt<'tcx>; fn deref(&self) -> &Self::Target { &self.infcx } } struct MirBorrowckCtxt<'a, 'infcx, '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 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: 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>, /// 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, /// 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, /// 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, /// 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: IndexVec>, /// 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>, /// The counter for generating new region names. next_region_name: RefCell, /// Results of Polonius analysis. polonius_output: Option>, diags_buffer: &'a mut BorrowckDiagnosticsBuffer<'infcx, 'tcx>, move_errors: Vec>, /// When using `-Zpolonius=next`: the data used to compute errors and diagnostics. polonius_diagnostics: Option<&'a PoloniusDiagnosticsContext>, } // 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<'a, 'tcx, Borrowck<'a, 'tcx>> for MirBorrowckCtxt<'a, '_, 'tcx> { fn visit_after_early_statement_effect( &mut self, _results: &mut Results<'tcx, Borrowck<'a, 'tcx>>, state: &BorrowckDomain, stmt: &'a 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, span), state); } StatementKind::StorageDead(local) => { self.access_place( location, (Place::from(*local), span), (Shallow(None), Write(WriteKind::StorageDeadOrDrop)), LocalMutationIsAllowed::Yes, state, ); } StatementKind::Nop | StatementKind::Retag { .. } | StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => { bug!("Statement not allowed in this MIR phase") } } } fn visit_after_early_terminator_effect( &mut self, _results: &mut Results<'tcx, Borrowck<'a, 'tcx>>, state: &BorrowckDomain, term: &'a 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 } => { 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, _results: &mut Results<'tcx, Borrowck<'a, 'tcx>>, state: &BorrowckDomain, term: &'a 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 => { // 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); } } 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), /// 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 ); 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, DenseBitSet> { 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 = DenseBitSet::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.allows_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, backward incompatible drops (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_span): (Place<'tcx>, Span), 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.node_span_lint( TAIL_EXPR_DROP_ORDER, CRATE_HIR_ID, borrowed, |diag| { session_diagnostics::TailExprDropOrder { borrowed }.decorate_lint(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): (&'a 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.allows_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*/) | Rvalue::ShallowInitBox(operand, _ /*ty*/) => { self.consume_operand(location, (operand, span), state) } &Rvalue::CopyForDeref(place) => { 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, ); } &(Rvalue::Len(place) | Rvalue::Discriminant(place)) => { let af = match *rvalue { Rvalue::Len(..) => Some(ArtificialField::ArrayLength), Rvalue::Discriminant(..) => None, _ => unreachable!(), }; self.access_place( location, (place, span), (Shallow(af), Read(ReadKind::Copy)), LocalMutationIsAllowed::No, 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::NullaryOp(_op, _ty) => { // nullary ops take no dynamic input; no borrowck effect. } 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 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]); } } 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); } } } 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); if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind { propagate_closure_used_mut_place(self, source); } else { bug!( "closures should only capture user variables \ or references to user variables" ); } } _ => propagate_closure_used_mut_place(self, place), } } Operand::Constant(..) => {} } } fn consume_operand( &mut self, location: Location, (operand, span): (&'a 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(_) => {} } } /// 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, will_be_dropped) = if self.body.local_decls[root_place.local].is_ref_to_thread_local() { // Thread-locals might be dropped after the function exits // We have to dereference the outer reference because // borrows don't conflict behind shared references. root_place.projection = TyCtxtConsts::DEREF_PROJECTION; (true, true) } else { (false, self.locals_are_invalidated_at_exit) }; if !will_be_dropped { debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place); return; } let sd = if might_be_alive { Deep } else { Shallow(None) }; if places_conflict::borrow_conflicts_with_place( self.infcx.tcx, self.body, place, borrow.kind, root_place, sd, places_conflict::PlaceConflictBias::Overlap, ) { debug!("check_for_invalidation_at_exit({:?}): INVALID", place); // FIXME: should be talking about the region lifetime instead // of just a span here. let span = self.infcx.tcx.sess.source_map().end_point(span); self.report_borrowed_value_does_not_live_long_enough( location, borrow, (place, span), None, ) } } /// Reports an error if this is a borrow of local data. /// This is called for all Yield expressions on movable 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. // `Subtype` : only transmutes the type, so no moves. // So it's safe to skip these. ProjectionElem::OpaqueCast(_) | ProjectionElem::Subtype(_) | 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, 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 { // 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::Subtype(_) | 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 { 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, 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` owns its content, so mutable if its location is mutable _ if base_ty.is_box() => { self.is_mutable(place_base, is_local_mutation_allowed) } // Deref should only be for reference, pointers or boxes _ => bug!("Deref of unexpected type: {:?}", base_ty), } } // All other projections are owned by their base path, so mutable if // base path is mutable ProjectionElem::Field(..) | ProjectionElem::Index(..) | ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } | ProjectionElem::Subtype(..) | 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: 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 { path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body()) } fn dominators(&self) -> &Dominators { // `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 lint_root = match &body.source_scopes[local_decl.source_info.scope].local_data { ClearCrossCrate::Set(data) => data.lint_root, _ => continue, }; // Skip over locals that begin with an underscore or have no name match self.local_names[local] { Some(name) => { if name.as_str().starts_with('_') { continue; } } None => continue, } let span = local_decl.source_info.span; if span.desugaring_kind().is_some() { // If the `mut` arises as part of a desugaring, we should ignore it. continue; } 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, }