// Copyright 2017 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! This query borrow-checks the MIR to (further) ensure it is not broken. use borrow_check::nll::region_infer::RegionInferenceContext; use rustc::hir; use rustc::hir::def_id::DefId; use rustc::hir::map::definitions::DefPathData; use rustc::infer::InferCtxt; use rustc::lint::builtin::UNUSED_MUT; use rustc::middle::borrowck::SignalledError; use rustc::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind}; use rustc::mir::{ClearCrossCrate, Local, Location, Mir, Mutability, Operand, Place}; use rustc::mir::{Field, Projection, ProjectionElem, Rvalue, Statement, StatementKind}; use rustc::mir::{Terminator, TerminatorKind}; use rustc::ty::query::Providers; use rustc::ty::{self, ParamEnv, TyCtxt}; use rustc_errors::{Diagnostic, DiagnosticBuilder, Level}; use rustc_data_structures::graph::dominators::Dominators; use rustc_data_structures::fx::FxHashSet; use rustc_data_structures::indexed_set::IdxSetBuf; use rustc_data_structures::indexed_vec::Idx; use rustc_data_structures::small_vec::SmallVec; use std::rc::Rc; use syntax_pos::Span; use dataflow::indexes::BorrowIndex; use dataflow::move_paths::{HasMoveData, LookupResult, MoveData, MoveError, MovePathIndex}; use dataflow::Borrows; use dataflow::DataflowResultsConsumer; use dataflow::FlowAtLocation; use dataflow::MoveDataParamEnv; use dataflow::{do_dataflow, DebugFormatted}; use dataflow::{EverInitializedPlaces, MovingOutStatements}; use dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces}; use 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 move_errors; mod mutability_errors; mod path_utils; crate mod place_ext; mod places_conflict; mod prefixes; mod used_muts; pub(crate) mod nll; pub fn provide(providers: &mut Providers) { *providers = Providers { mir_borrowck, ..*providers }; } fn mir_borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> BorrowCheckResult<'tcx> { let input_mir = tcx.mir_validated(def_id); debug!("run query mir_borrowck: {}", tcx.item_path_str(def_id)); let mut return_early; // Return early if we are not supposed to use MIR borrow checker for this function. return_early = !tcx.has_attr(def_id, "rustc_mir") && !tcx.use_mir_borrowck(); if tcx.is_struct_constructor(def_id) { // We are not borrow checking the automatically generated struct constructors // because we want to accept structs such as this (taken from the `linked-hash-map` // crate): // ```rust // struct Qey(Q); // ``` // MIR of this struct constructor looks something like this: // ```rust // fn Qey(_1: Q) -> Qey{ // let mut _0: Qey; // return place // // bb0: { // (_0.0: Q) = move _1; // bb0[0]: scope 0 at src/main.rs:1:1: 1:26 // return; // bb0[1]: scope 0 at src/main.rs:1:1: 1:26 // } // } // ``` // The problem here is that `(_0.0: Q) = move _1;` is valid only if `Q` is // of statically known size, which is not known to be true because of the // `Q: ?Sized` constraint. However, it is true because the constructor can be // called only when `Q` is of statically known size. return_early = true; } if return_early { return BorrowCheckResult { closure_requirements: None, used_mut_upvars: SmallVec::new(), }; } let opt_closure_req = tcx.infer_ctxt().enter(|infcx| { let input_mir: &Mir = &input_mir.borrow(); do_mir_borrowck(&infcx, input_mir, def_id) }); debug!("mir_borrowck done"); opt_closure_req } fn do_mir_borrowck<'a, 'gcx, 'tcx>( infcx: &InferCtxt<'a, 'gcx, 'tcx>, input_mir: &Mir<'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_node_id(def_id) .expect("do_mir_borrowck: non-local DefId"); // 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 mir: Mir<'tcx> = input_mir.clone(); let free_regions = nll::replace_regions_in_mir(infcx, def_id, param_env, &mut mir); let mir = &mir; // no further changes let location_table = &LocationTable::new(mir); let mut errors_buffer = Vec::new(); let (move_data, move_errors): (MoveData<'tcx>, Option>>) = match MoveData::gather_moves(mir, 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 body_id = match tcx.def_key(def_id).disambiguated_data.data { DefPathData::StructCtor | DefPathData::EnumVariant(_) => None, _ => Some(tcx.hir.body_owned_by(id)), }; let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len()); let mut flow_inits = FlowAtLocation::new(do_dataflow( tcx, mir, id, &attributes, &dead_unwinds, MaybeInitializedPlaces::new(tcx, mir, &mdpe), |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]), )); let flow_uninits = FlowAtLocation::new(do_dataflow( tcx, mir, id, &attributes, &dead_unwinds, MaybeUninitializedPlaces::new(tcx, mir, &mdpe), |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]), )); let flow_move_outs = FlowAtLocation::new(do_dataflow( tcx, mir, id, &attributes, &dead_unwinds, MovingOutStatements::new(tcx, mir, &mdpe), |bd, i| DebugFormatted::new(&bd.move_data().moves[i]), )); let flow_ever_inits = FlowAtLocation::new(do_dataflow( tcx, mir, id, &attributes, &dead_unwinds, EverInitializedPlaces::new(tcx, mir, &mdpe), |bd, i| DebugFormatted::new(&bd.move_data().inits[i]), )); let borrow_set = Rc::new(BorrowSet::build(tcx, mir)); // 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, mir, location_table, param_env, &mut flow_inits, &mdpe.move_data, &borrow_set, &mut errors_buffer, ); let regioncx = Rc::new(regioncx); let flow_borrows = FlowAtLocation::new(do_dataflow( tcx, mir, id, &attributes, &dead_unwinds, Borrows::new(tcx, mir, regioncx.clone(), def_id, body_id, &borrow_set), |rs, i| DebugFormatted::new(&rs.location(i)), )); let movable_generator = match tcx.hir.get(id) { hir::map::Node::NodeExpr(&hir::Expr { node: hir::ExprKind::Closure(.., Some(hir::GeneratorMovability::Static)), .. }) => false, _ => true, }; let dominators = mir.dominators(); let mut mbcx = MirBorrowckCtxt { tcx: tcx, mir: mir, mir_def_id: def_id, move_data: &mdpe.move_data, param_env: param_env, location_table, movable_generator, locals_are_invalidated_at_exit: match tcx.hir.body_owner_kind(id) { hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => false, hir::BodyOwnerKind::Fn => true, }, access_place_error_reported: FxHashSet(), reservation_error_reported: FxHashSet(), moved_error_reported: FxHashSet(), errors_buffer, nonlexical_regioncx: regioncx, used_mut: FxHashSet(), used_mut_upvars: SmallVec::new(), borrow_set, dominators, }; let mut state = Flows::new( flow_borrows, flow_uninits, flow_move_outs, 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 // 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.mir.local_decls[*local].is_user_variable.is_some()) .cloned() .collect(); mbcx.gather_used_muts(temporary_used_locals); debug!("mbcx.used_mut: {:?}", mbcx.used_mut); let used_mut = mbcx.used_mut; for local in mbcx .mir .mut_vars_and_args_iter() .filter(|local| !used_mut.contains(local)) { if let ClearCrossCrate::Set(ref vsi) = mbcx.mir.source_scope_local_data { let local_decl = &mbcx.mir.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; let mut_span = tcx.sess.codemap().span_until_non_whitespace(span); let mut err = tcx.struct_span_lint_node( UNUSED_MUT, vsi[local_decl.source_info.scope].lint_root, span, "variable does not need to be mutable", ); err.span_suggestion_short(mut_span, "remove this `mut`", "".to_owned()); err.buffer(&mut mbcx.errors_buffer); } } if mbcx.errors_buffer.len() > 0 { if tcx.migrate_borrowck() { match tcx.borrowck(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 &mut mbcx.errors_buffer { if err.is_error() { err.level = Level::Warning; err.warn("This error has been downgraded to a warning \ for backwards compatibility with previous releases.\n\ It represents potential unsoundness in your code.\n\ This warning will become a hard error in the future."); } } } 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.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 } pub struct MirBorrowckCtxt<'cx, 'gcx: 'tcx, 'tcx: 'cx> { tcx: TyCtxt<'cx, 'gcx, 'tcx>, mir: &'cx Mir<'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, param_env: ParamEnv<'gcx>, 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 Places, /// but it is currently inconvenient to track down the BorrowIndex /// at the time we detect and report a reservation error. reservation_error_reported: FxHashSet>, /// This field keeps track of errors reported in the checking of moved variables, /// so that we don't report seemingly duplicate errors. moved_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, } // 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 mir(&self) -> &'cx Mir<'tcx> { self.mir } 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( ContextKind::AssignRhs.new(location), (rhs, span), location, flow_state, ); self.mutate_place( ContextKind::AssignLhs.new(location), (lhs, span), Shallow(None), JustWrite, flow_state, ); } StatementKind::ReadForMatch(ref place) => { self.access_place( ContextKind::ReadForMatch.new(location), (place, span), (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))), LocalMutationIsAllowed::No, flow_state, ); } StatementKind::SetDiscriminant { ref place, variant_index: _, } => { self.mutate_place( ContextKind::SetDiscrim.new(location), (place, span), Shallow(Some(ArtificialField::Discriminant)), JustWrite, flow_state, ); } StatementKind::InlineAsm { ref asm, ref outputs, ref inputs, } => { let context = ContextKind::InlineAsm.new(location); for (o, output) in asm.outputs.iter().zip(outputs) { if o.is_indirect { // FIXME(eddyb) indirect inline asm outputs should // be encoeded through MIR place derefs instead. self.access_place( context, (output, span), (Deep, Read(ReadKind::Copy)), LocalMutationIsAllowed::No, flow_state, ); self.check_if_path_or_subpath_is_moved( context, InitializationRequiringAction::Use, (output, span), flow_state, ); } else { self.mutate_place( context, (output, span), if o.is_rw { Deep } else { Shallow(None) }, if o.is_rw { WriteAndRead } else { JustWrite }, flow_state, ); } } for input in inputs { self.consume_operand(context, (input, span), flow_state); } } StatementKind::EndRegion(ref _rgn) => { // ignored when consuming results (update to // flow_state already handled). } StatementKind::Nop | StatementKind::UserAssertTy(..) | StatementKind::Validate(..) | StatementKind::StorageLive(..) => { // `Nop`, `UserAssertTy`, `Validate`, and `StorageLive` are irrelevant // to borrow check. } StatementKind::StorageDead(local) => { self.access_place( ContextKind::StorageDead.new(location), (&Place::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(ContextKind::SwitchInt.new(loc), (discr, span), flow_state); } TerminatorKind::Drop { location: ref drop_place, target: _, unwind: _, } => { let gcx = self.tcx.global_tcx(); // Compute the type with accurate region information. let drop_place_ty = drop_place.ty(self.mir, self.tcx); // Erase the regions. let drop_place_ty = self.tcx.erase_regions(&drop_place_ty).to_ty(self.tcx); // "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(); self.visit_terminator_drop(loc, term, flow_state, drop_place, drop_place_ty, span); } TerminatorKind::DropAndReplace { location: ref drop_place, value: ref new_value, target: _, unwind: _, } => { self.mutate_place( ContextKind::DropAndReplace.new(loc), (drop_place, span), Deep, JustWrite, flow_state, ); self.consume_operand( ContextKind::DropAndReplace.new(loc), (new_value, span), flow_state, ); } TerminatorKind::Call { ref func, ref args, ref destination, cleanup: _, } => { self.consume_operand(ContextKind::CallOperator.new(loc), (func, span), flow_state); for arg in args { self.consume_operand( ContextKind::CallOperand.new(loc), (arg, span), flow_state, ); } if let Some((ref dest, _ /*bb*/)) = *destination { self.mutate_place( ContextKind::CallDest.new(loc), (dest, span), Deep, JustWrite, flow_state, ); } } TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _, } => { self.consume_operand(ContextKind::Assert.new(loc), (cond, span), flow_state); use rustc::mir::interpret::EvalErrorKind::BoundsCheck; if let BoundsCheck { ref len, ref index } = *msg { self.consume_operand(ContextKind::Assert.new(loc), (len, span), flow_state); self.consume_operand(ContextKind::Assert.new(loc), (index, span), flow_state); } } TerminatorKind::Yield { ref value, resume: _, drop: _, } => { self.consume_operand(ContextKind::Yield.new(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]; let context = ContextKind::StorageDead.new(loc); self.check_for_invalidation_at_exit(context, 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::ShallowOrDeep::{Deep, Shallow}; #[derive(Copy, Clone, PartialEq, Eq, Debug)] enum ArtificialField { Discriminant, ArrayLength, } #[derive(Copy, Clone, PartialEq, Eq, Debug)] enum ShallowOrDeep { /// 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, } /// 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, } struct AccessErrorsReported { mutability_error: bool, #[allow(dead_code)] conflict_error: bool, } #[derive(Copy, Clone)] enum InitializationRequiringAction { Update, Borrow, Use, Assignment, } 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::Use => "use", InitializationRequiringAction::Assignment => "assign", } } fn as_verb_in_past_tense(self) -> &'static str { match self { InitializationRequiringAction::Update => "updated", InitializationRequiringAction::Borrow => "borrowed", InitializationRequiringAction::Use => "used", InitializationRequiringAction::Assignment => "assigned", } } } impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> { /// Invokes `access_place` as appropriate for dropping the value /// at `drop_place`. Note that the *actual* `Drop` in the MIR is /// always for a variable (e.g., `Drop(x)`) -- but we recursively /// break this variable down into subpaths (e.g., `Drop(x.foo)`) /// to indicate more precisely which fields might actually be /// accessed by a destructor. fn visit_terminator_drop( &mut self, loc: Location, term: &Terminator<'tcx>, flow_state: &Flows<'cx, 'gcx, 'tcx>, drop_place: &Place<'tcx>, erased_drop_place_ty: ty::Ty<'gcx>, span: Span, ) { let gcx = self.tcx.global_tcx(); let drop_field = |mir: &mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>, (index, field): (usize, ty::Ty<'gcx>)| { let field_ty = gcx.normalize_erasing_regions(mir.param_env, field); let place = drop_place.clone().field(Field::new(index), field_ty); mir.visit_terminator_drop(loc, term, flow_state, &place, field_ty, span); }; match erased_drop_place_ty.sty { // When a struct is being dropped, we need to check // whether it has a destructor, if it does, then we can // call it, if it does not then we need to check the // individual fields instead. This way if `foo` has a // destructor but `bar` does not, we will only check for // borrows of `x.foo` and not `x.bar`. See #47703. ty::TyAdt(def, substs) if def.is_struct() && !def.has_dtor(self.tcx) => { def.all_fields() .map(|field| field.ty(gcx, substs)) .enumerate() .for_each(|field| drop_field(self, field)); } // Same as above, but for tuples. ty::TyTuple(tys) => { tys.iter() .cloned() .enumerate() .for_each(|field| drop_field(self, field)); } // Closures also have disjoint fields, but they are only // directly accessed in the body of the closure. ty::TyClosure(def, substs) if *drop_place == Place::Local(Local::new(1)) && !self.mir.upvar_decls.is_empty() => { substs .upvar_tys(def, self.tcx) .enumerate() .for_each(|field| drop_field(self, field)); } // Generators also have disjoint fields, but they are only // directly accessed in the body of the generator. ty::TyGenerator(def, substs, _) if *drop_place == Place::Local(Local::new(1)) && !self.mir.upvar_decls.is_empty() => { substs .upvar_tys(def, self.tcx) .enumerate() .for_each(|field| drop_field(self, field)); } _ => { // We have now refined the type of the value being // dropped (potentially) to just the type of a // subfield; so check whether that field's type still // "needs drop". If so, we assume that the destructor // may access any data it likes (i.e., a Deep Write). if erased_drop_place_ty.needs_drop(gcx, self.param_env) { self.access_place( ContextKind::Drop.new(loc), (drop_place, span), (Deep, Write(WriteKind::StorageDeadOrDrop)), LocalMutationIsAllowed::Yes, flow_state, ); } } } } /// 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, false otherwise. fn access_place( &mut self, context: Context, place_span: (&Place<'tcx>, Span), kind: (ShallowOrDeep, ReadOrWrite), is_local_mutation_allowed: LocalMutationIsAllowed, flow_state: &Flows<'cx, 'gcx, 'tcx>, ) -> AccessErrorsReported { 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 AccessErrorsReported { mutability_error: false, conflict_error: true, }; } } if 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 AccessErrorsReported { mutability_error: false, conflict_error: true, }; } let mutability_error = self.check_access_permissions( place_span, rw, is_local_mutation_allowed, flow_state, context.loc, ); let conflict_error = self.check_access_for_conflict(context, place_span, sd, rw, flow_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.clone(), place_span.1)); } AccessErrorsReported { mutability_error, conflict_error, } } fn check_access_for_conflict( &mut self, context: Context, place_span: (&Place<'tcx>, Span), sd: ShallowOrDeep, rw: ReadOrWrite, flow_state: &Flows<'cx, 'gcx, 'tcx>, ) -> bool { debug!( "check_access_for_conflict(context={:?}, place_span={:?}, sd={:?}, rw={:?})", context, place_span, sd, rw, ); let mut error_reported = false; let tcx = self.tcx; let mir = self.mir; let location = self.location_table.start_index(context.loc); let borrow_set = self.borrow_set.clone(); each_borrow_involving_path( self, tcx, mir, context, (sd, place_span.0), &borrow_set, flow_state.borrows_in_scope(location), |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) | (Reservation(..), BorrowKind::Shared) => { 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, context.loc) { assert!(allow_two_phase_borrow(&this.tcx, borrow.kind)); return Control::Continue; } match kind { ReadKind::Copy => { error_reported = true; this.report_use_while_mutably_borrowed(context, place_span, borrow) } ReadKind::Borrow(bk) => { error_reported = true; this.report_conflicting_borrow(context, place_span, bk, &borrow) } } Control::Break } (Reservation(kind), BorrowKind::Unique) | (Reservation(kind), BorrowKind::Mut { .. }) | (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(..) => {} } match kind { WriteKind::MutableBorrow(bk) => { error_reported = true; this.report_conflicting_borrow(context, place_span, bk, &borrow) } WriteKind::StorageDeadOrDrop => { error_reported = true; this.report_borrowed_value_does_not_live_long_enough( context, borrow, place_span, Some(kind), ); } WriteKind::Mutate => { error_reported = true; this.report_illegal_mutation_of_borrowed(context, place_span, borrow) } WriteKind::Move => { error_reported = true; this.report_move_out_while_borrowed(context, place_span, &borrow) } } Control::Break } }, ); error_reported } fn mutate_place( &mut self, context: Context, place_span: (&Place<'tcx>, Span), kind: ShallowOrDeep, 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( context, InitializationRequiringAction::Update, place_span, flow_state, ); } MutateMode::JustWrite => { self.check_if_assigned_path_is_moved(context, place_span, flow_state); } } let errors_reported = self.access_place( context, place_span, (kind, Write(WriteKind::Mutate)), // We want immutable upvars to cause an "assignment to immutable var" // error, not an "reassignment of immutable var" error, because the // latter can't find a good previous assignment span. // // There's probably a better way to do this. LocalMutationIsAllowed::ExceptUpvars, flow_state, ); if !errors_reported.mutability_error { // check for reassignments to immutable local variables self.check_if_reassignment_to_immutable_state(context, place_span, flow_state); } } fn consume_rvalue( &mut self, context: Context, (rvalue, span): (&Rvalue<'tcx>, Span), _location: Location, flow_state: &Flows<'cx, 'gcx, 'tcx>, ) { match *rvalue { Rvalue::Ref(_ /*rgn*/, bk, ref place) => { let access_kind = match bk { BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))), BorrowKind::Unique | BorrowKind::Mut { .. } => { let wk = WriteKind::MutableBorrow(bk); if allow_two_phase_borrow(&self.tcx, bk) { (Deep, Reservation(wk)) } else { (Deep, Write(wk)) } } }; self.access_place( context, (place, span), access_kind, LocalMutationIsAllowed::No, flow_state, ); self.check_if_path_or_subpath_is_moved( context, InitializationRequiringAction::Borrow, (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(context, (operand, span), flow_state) } Rvalue::Len(ref place) | Rvalue::Discriminant(ref place) => { let af = match *rvalue { Rvalue::Len(..) => ArtificialField::ArrayLength, Rvalue::Discriminant(..) => ArtificialField::Discriminant, _ => unreachable!(), }; self.access_place( context, (place, span), (Shallow(Some(af)), Read(ReadKind::Copy)), LocalMutationIsAllowed::No, flow_state, ); self.check_if_path_or_subpath_is_moved( context, 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(context, (operand1, span), flow_state); self.consume_operand(context, (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.tcx.mir_borrowck(def_id); debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars); for field in used_mut_upvars { // This relies on the current way that by-value // captures of a closure are copied/moved directly // when generating MIR. match operands[field.index()] { Operand::Move(Place::Local(local)) | Operand::Copy(Place::Local(local)) => { self.used_mut.insert(local); } Operand::Move(ref place @ Place::Projection(_)) | Operand::Copy(ref place @ Place::Projection(_)) => { if let Some(field) = place.is_upvar_field_projection( self.mir, &self.tcx) { self.used_mut_upvars.push(field); } } Operand::Move(Place::Static(..)) | Operand::Copy(Place::Static(..)) | Operand::Move(Place::Promoted(..)) | Operand::Copy(Place::Promoted(..)) | Operand::Constant(..) => {} } } } AggregateKind::Adt(..) | AggregateKind::Array(..) | AggregateKind::Tuple { .. } => (), } for operand in operands { self.consume_operand(context, (operand, span), flow_state); } } } } fn consume_operand( &mut self, context: Context, (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( context, (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( context, 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( context, (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( context, InitializationRequiringAction::Use, (place, span), flow_state, ); } Operand::Constant(_) => {} } } /// Returns whether a borrow of this place is invalidated when the function /// exits fn check_for_invalidation_at_exit( &mut self, context: Context, 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::Promoted(_) => (true, false), Place::Static(statik) => { // Thread-locals might be dropped after the function exits, but // "true" statics will never be. let is_thread_local = self .tcx .get_attrs(statik.def_id) .iter() .any(|attr| attr.check_name("thread_local")); (true, is_thread_local) } Place::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; } // FIXME: replace this with a proper borrow_conflicts_with_place when // that is merged. let sd = if might_be_alive { Deep } else { Shallow(None) }; if places_conflict::places_conflict(self.tcx, self.mir, place, root_place, sd) { 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.tcx.sess.codemap().end_point(span); self.report_borrowed_value_does_not_live_long_enough( context, 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.tcx .cannot_borrow_across_generator_yield( self.retrieve_borrow_span(borrow), 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>, ) { if !self.tcx.two_phase_borrows() { return; } // 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 => false, BorrowKind::Unique | BorrowKind::Mut { .. } => true, }); self.access_place( ContextKind::Activation.new(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, context: Context, (place, span): (&Place<'tcx>, Span), flow_state: &Flows<'cx, 'gcx, 'tcx>, ) { debug!("check_if_reassignment_to_immutable_state({:?})", place); // determine if this path has a non-mut owner (and thus needs checking). let err_place = match self.is_mutable(place, LocalMutationIsAllowed::No) { Ok(..) => return, Err(place) => place, }; debug!( "check_if_reassignment_to_immutable_state({:?}) - is an imm local", place ); for i in flow_state.ever_inits.iter_incoming() { let init = self.move_data.inits[i]; let init_place = &self.move_data.move_paths[init.path].place; if places_conflict::places_conflict(self.tcx, self.mir, &init_place, place, Deep) { self.report_illegal_reassignment(context, (place, span), init.span, err_place); break; } } } fn check_if_full_path_is_moved( &mut self, context: Context, desired_action: InitializationRequiringAction, place_span: (&Place<'tcx>, Span), flow_state: &Flows<'cx, 'gcx, 'tcx>, ) { // FIXME: analogous code in check_loans first maps `place` to // its base_path ... but is that what we want here? let place = self.base_path(place_span.0); let maybe_uninits = &flow_state.uninits; let curr_move_outs = &flow_state.move_outs; // 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); match self.move_path_closest_to(place) { Ok(mpi) => { if maybe_uninits.contains(&mpi) { self.report_use_of_moved_or_uninitialized( context, desired_action, place_span, mpi, curr_move_outs, ); 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, context: Context, desired_action: InitializationRequiringAction, place_span: (&Place<'tcx>, Span), flow_state: &Flows<'cx, 'gcx, 'tcx>, ) { // FIXME: analogous code in check_loans first maps `place` to // its base_path ... but is that what we want here? let place = self.base_path(place_span.0); let maybe_uninits = &flow_state.uninits; let curr_move_outs = &flow_state.move_outs; // 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(context, 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); if let Some(mpi) = self.move_path_for_place(place) { if let Some(child_mpi) = maybe_uninits.has_any_child_of(mpi) { self.report_use_of_moved_or_uninitialized( context, desired_action, place_span, child_mpi, curr_move_outs, ); 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: &Place<'tcx>, ) -> Result { 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(mpi); } last_prefix = prefix; } match *last_prefix { Place::Local(_) => panic!("should have move path for every Local"), Place::Projection(_) => panic!("PrefixSet::All meant don't stop for Projection"), Place::Promoted(_) | Place::Static(_) => return 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, context: Context, (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::Promoted(_) | Place::Local(_) | Place::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( context, InitializationRequiringAction::Use, (base, span), flow_state); // (base initialized; no need to // recur further) break; } ProjectionElem::Subslice { .. } => { panic!("we don't allow assignments to subslices, context: {:?}", context); } ProjectionElem::Field(..) => { // if type of `P` has a dtor, then // assigning to `P.f` requires `P` itself // be already initialized let tcx = self.tcx; match base.ty(self.mir, tcx).to_ty(tcx).sty { ty::TyAdt(def, _) if def.has_dtor(tcx) => { // FIXME: analogous code in // check_loans.rs first maps // `base` to its base_path. self.check_if_path_or_subpath_is_moved( context, InitializationRequiringAction::Assignment, (base, span), flow_state); // (base initialized; no need to // recur further) break; } _ => {} } } } place = base; continue; } } } } /// Check the permissions for the given place and read or write kind /// /// Returns true if an error is reported, false otherwise. 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({:?}, {:?}, {:?})", place, kind, is_local_mutation_allowed ); let error_access; let the_place_err; 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 => 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)) | Write(wk @ WriteKind::StorageDeadOrDrop) | Write(wk @ WriteKind::MutableBorrow(BorrowKind::Shared)) => { if let Err(_place_err) = self.is_mutable(place, is_local_mutation_allowed) { if self.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 { self.tcx.sess.delay_span_bug( span, &format!( "Accessing `{:?}` with the kind `{:?}` shouldn't be possible", place, kind ), ); } } return false; } Activation(..) => { // permission checks are done at Reservation point. return false; } Read(ReadKind::Borrow(BorrowKind::Unique)) | Read(ReadKind::Borrow(BorrowKind::Mut { .. })) | Read(ReadKind::Borrow(BorrowKind::Shared)) | Read(ReadKind::Copy) => { // Access authorized return false; } } // at this point, we have set up the error reporting state. self.report_mutability_error( place, span, the_place_err, error_access, location, ); return true; } /// 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::Local(local), is_local_mutation_allowed, } => { if is_local_mutation_allowed != LocalMutationIsAllowed::Yes { // If the local may be 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. 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) { self.used_mut.insert(*local); break; } } } } RootPlace { place: _, is_local_mutation_allowed: LocalMutationIsAllowed::Yes, } => {} RootPlace { place: place @ Place::Projection(_), is_local_mutation_allowed: _, } => { if let Some(field) = place.is_upvar_field_projection(self.mir, &self.tcx) { self.used_mut_upvars.push(field); } } RootPlace { place: Place::Promoted(..), is_local_mutation_allowed: _, } => {} RootPlace { place: Place::Static(..), is_local_mutation_allowed: _, } => {} } } /// Whether this value 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::Local(local) => { let local = &self.mir.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::Promoted(_) => Ok(RootPlace { place, is_local_mutation_allowed, }), Place::Static(ref static_) => { if self.tcx.is_static(static_.def_id) != Some(hir::Mutability::MutMutable) { 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.mir, self.tcx).to_ty(self.tcx); // Check the kind of deref to decide match base_ty.sty { ty::TyRef(_, _, 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 place.is_upvar_field_projection( self.mir, &self.tcx) { Some(field) if { self.mir.upvar_decls[field.index()].by_ref } => { is_local_mutation_allowed } _ => LocalMutationIsAllowed::Yes, }; self.is_mutable(&proj.base, mode) } } } ty::TyRawPtr(tnm) => { match tnm.mutbl { // `*const` raw pointers are not mutable hir::MutImmutable => return Err(place), // `*mut` raw pointers are always mutable, regardless of // context. The users have to check by themselves. hir::MutMutable => { return 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 = place.is_upvar_field_projection( self.mir, &self.tcx); if let Some(field) = upvar_field_projection { let decl = &self.mir.upvar_decls[field.index()]; debug!( "decl.mutability={:?} local_mutation_is_allowed={:?} place={:?}", decl, is_local_mutation_allowed, place ); match (decl.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 context `*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) } } } } } } } #[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, } impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> { // FIXME (#16118): function intended to allow the borrow checker // to be less precise in its handling of Box while still allowing // moves out of a Box. They should be removed when/if we stop // treating Box specially (e.g. when/if DerefMove is added...) fn base_path<'d>(&self, place: &'d Place<'tcx>) -> &'d Place<'tcx> { //! Returns the base of the leftmost (deepest) dereference of an //! Box in `place`. If there is no dereference of an Box //! in `place`, then it just returns `place` itself. let mut cursor = place; let mut deepest = place; loop { let proj = match *cursor { Place::Promoted(_) | Place::Local(..) | Place::Static(..) => return deepest, Place::Projection(ref proj) => proj, }; if proj.elem == ProjectionElem::Deref && place.ty(self.mir, self.tcx).to_ty(self.tcx).is_box() { deepest = &proj.base; } cursor = &proj.base; } } } #[derive(Copy, Clone, PartialEq, Eq, Debug)] struct Context { kind: ContextKind, loc: Location, } #[derive(Copy, Clone, PartialEq, Eq, Debug)] enum ContextKind { Activation, AssignLhs, AssignRhs, SetDiscrim, InlineAsm, SwitchInt, Drop, DropAndReplace, CallOperator, CallOperand, CallDest, Assert, Yield, ReadForMatch, StorageDead, } impl ContextKind { fn new(self, loc: Location) -> Context { Context { kind: self, loc: loc, } } }