//! 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, 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 crate::util::borrowck_errors::{BorrowckErrors, Origin}; 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>(tcx: TyCtxt<'tcx, 'tcx>, def_id: DefId) -> BorrowCheckResult<'tcx> { 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, 'gcx, 'tcx>( infcx: &InferCtxt<'a, 'gcx, 'tcx>, input_body: &Body<'gcx>, def_id: DefId, ) -> BorrowCheckResult<'gcx> { 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 var_node_id = tcx.hir().hir_to_node_id(var_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_node_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, 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_by_hir_id(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, 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_by_hir_id(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, 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, 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::replace(&mut mbcx.reservation_warnings, Default::default()); 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 = 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.compiler_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 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`" ); } } pub struct MirBorrowckCtxt<'cx, 'gcx: 'tcx, 'tcx: 'cx> { infcx: &'cx InferCtxt<'cx, 'gcx, 'tcx>, body: &'cx Body<'tcx>, mir_def_id: DefId, 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>, /// 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, (Place<'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>, /// Errors to be reported buffer errors_buffer: Vec, /// 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, /// 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>, /// The set of borrows extracted from the MIR borrow_set: Rc>, /// Dominators for MIR dominators: Dominators, /// Information about upvars not necessarily preserved in types or MIR upvars: Vec, } // 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, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'gcx, 'tcx> { type FlowState = Flows<'cx, 'gcx, '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: &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, 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, 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::Base(PlaceBase::Local(local)), span), (Shallow(None), Write(WriteKind::StorageDeadOrDrop)), LocalMutationIsAllowed::Yes, flow_state, ); } } } fn visit_terminator_entry( &mut self, location: Location, term: &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. let drop_place_ty = gcx.lift(&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::InterpError::BoundsCheck; if let 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_targets: _, } | 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), /// 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: 'd> { place: &'d Place<'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, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> { /// 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, 'gcx, '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, 'gcx, '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 location_table = self.location_table.start_index(location); let borrow_set = self.borrow_set.clone(); each_borrow_involving_path( self, tcx, 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() } => { 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: (&Place<'tcx>, Span), kind: AccessDepth, mode: MutateMode, flow_state: &Flows<'cx, 'gcx, '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, 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)) = 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): (&Rvalue<'tcx>, Span), flow_state: &Flows<'cx, 'gcx, '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, 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, 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>| { match *place { Place::Projection { .. } => { if let Some(field) = this.is_upvar_field_projection(place) { this.used_mut_upvars.push(field); } } Place::Base(PlaceBase::Local(local)) => { this.used_mut.insert(local); } Place::Base(PlaceBase::Static(_)) => {} } }; // 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))) | Operand::Copy(Place::Base(PlaceBase::Local(local))) if self.body.local_decls[local].is_user_variable.is_none() => { if self.body.local_decls[local].ty.is_mutable_pointer() { // 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): (&Operand<'tcx>, Span), flow_state: &Flows<'cx, 'gcx, '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, 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, 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, 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? let (might_be_alive, will_be_dropped) = match root_place { Place::Base(PlaceBase::Static(box Static{ kind: StaticKind::Promoted(_), .. })) => { (true, false) } Place::Base(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)) } Place::Base(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) } Place::Projection(..) => { bug!("root of {:?} is a projection ({:?})?", place, root_place) } }; 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 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.infcx.tcx .cannot_borrow_across_generator_yield( self.retrieve_borrow_spans(borrow).var_or_use(), yield_span, Origin::Mir, ); err.buffer(&mut self.errors_buffer); } } fn check_activations( &mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'gcx, '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, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> { fn check_if_reassignment_to_immutable_state( &mut self, location: Location, local: Local, place_span: (&Place<'tcx>, Span), flow_state: &Flows<'cx, 'gcx, '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: (&Place<'tcx>, Span), flow_state: &Flows<'cx, 'gcx, '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: (&Place<'tcx>, Span), flow_state: &Flows<'cx, 'gcx, '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<'a>( &mut self, place: &'a Place<'tcx>, ) -> Result<(&'a Place<'tcx>, MovePathIndex), NoMovePathFound> where 'cx: 'a { let mut last_prefix = place; 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; } match *last_prefix { Place::Base(PlaceBase::Local(_)) => panic!("should have move path for every Local"), Place::Projection(_) => panic!("PrefixSet::All meant don't stop for Projection"), Place::Base(PlaceBase::Static(_)) => Err(NoMovePathFound::ReachedStatic), } } fn move_path_for_place(&mut self, place: &Place<'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), flow_state: &Flows<'cx, 'gcx, 'tcx>, ) { debug!("check_if_assigned_path_is_moved place: {:?}", place); // recur down place; dispatch to external checks when necessary let mut place = place; loop { match *place { Place::Base(PlaceBase::Local(_)) | Place::Base(PlaceBase::Static(_)) => { // assigning to `x` does not require `x` be initialized. break; } Place::Projection(ref proj) => { 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, (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; match base.ty(self.body, tcx).ty.sty { ty::Adt(def, _) if def.has_dtor(tcx) => { self.check_if_path_or_subpath_is_moved( location, InitializationRequiringAction::Assignment, (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, base, span, flow_state); if let Some(local) = place.base_local() { // 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 = base; } } } fn check_parent_of_field<'cx, 'gcx, 'tcx>( this: &mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>, location: Location, base: &Place<'tcx>, span: Span, flow_state: &Flows<'cx, 'gcx, '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, _) = base.ty(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, 'gcx, '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 Some(local) = place.base_local() { 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, 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, 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, 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, 'gcx, 'tcx>) -> Option { 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, 'gcx, 'tcx>, ) { match root_place { RootPlace { place: Place::Base(PlaceBase::Local(local)), 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: _, is_local_mutation_allowed: LocalMutationIsAllowed::Yes, } => {} RootPlace { place: place @ Place::Projection(_), is_local_mutation_allowed: _, } => { if let Some(field) = self.is_upvar_field_projection(place) { self.used_mut_upvars.push(field); } } RootPlace { place: Place::Base(PlaceBase::Static(..)), 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: &'d Place<'tcx>, is_local_mutation_allowed: LocalMutationIsAllowed, ) -> Result, &'d Place<'tcx>> { match *place { Place::Base(PlaceBase::Local(local)) => { let local = &self.body.local_decls[local]; match local.mutability { Mutability::Not => match is_local_mutation_allowed { LocalMutationIsAllowed::Yes => Ok(RootPlace { place, is_local_mutation_allowed: LocalMutationIsAllowed::Yes, }), LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace { place, is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars, }), LocalMutationIsAllowed::No => Err(place), }, Mutability::Mut => Ok(RootPlace { place, 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 Place::Base(PlaceBase::Static(box Static{kind: StaticKind::Promoted(_), ..})) => Ok(RootPlace { place, is_local_mutation_allowed, }), Place::Base(PlaceBase::Static(box Static{ kind: StaticKind::Static(def_id), .. })) => { if !self.infcx.tcx.is_mutable_static(def_id) { Err(place) } else { Ok(RootPlace { place, is_local_mutation_allowed, }) } } Place::Projection(ref proj) => { match proj.elem { ProjectionElem::Deref => { let base_ty = proj.base.ty(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(&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, is_local_mutation_allowed, }) } } } // `Box` owns its content, so mutable if its location is mutable _ if base_ty.is_box() => { self.is_mutable(&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: F) { } // fn main() { // let var = Vec::new(); // foo(move || { // var.push(1); // }); // } // ``` let _ = self.is_mutable(&proj.base, is_local_mutation_allowed)?; Ok(RootPlace { place, is_local_mutation_allowed, }) } } } else { self.is_mutable(&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: &Place<'tcx>) -> Option { let (place, by_ref) = if let Place::Projection(ref proj) = place { if let ProjectionElem::Deref = proj.elem { (&proj.base, true) } else { (place, false) } } else { (place, false) }; match place { Place::Projection(ref proj) => match proj.elem { ProjectionElem::Field(field, _ty) => { let tcx = self.infcx.tcx; let base_ty = proj.base.ty(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, } _ => 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, }