compiler/rustc_borrowck/src/lib.rs - toolchain/rustc - Git at Google

 //! This query borrow-checks the MIR to (further) ensure it is not broken.

 #![allow(rustc::potential_query_instability)]
 #![feature(box_patterns)]
 #![feature(let_chains)]
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
 #![feature(stmt_expr_attributes)]
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]

 #[macro_use]
 extern crate rustc_middle;
 #[macro_use]
 extern crate tracing;

 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_errors::{Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_index::bit_set::ChunkedBitSet;
 use rustc_index::vec::IndexVec;
 use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
 use rustc_middle::mir::{
     traversal, Body, ClearCrossCrate, Local, Location, Mutability, NonDivergingIntrinsic, Operand,
     Place, PlaceElem, PlaceRef, VarDebugInfoContents,
 };
 use rustc_middle::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
 use rustc_middle::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
 use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, CapturedPlace, ParamEnv, RegionVid, TyCtxt};
 use rustc_session::lint::builtin::UNUSED_MUT;
 use rustc_span::{Span, Symbol};

 use either::Either;
 use smallvec::SmallVec;
 use std::cell::RefCell;
 use std::collections::BTreeMap;
 use std::rc::Rc;

 use rustc_mir_dataflow::impls::{
     EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
 };
 use rustc_mir_dataflow::move_paths::{InitIndex, MoveOutIndex, MovePathIndex};
 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult, MoveData, MoveError};
 use rustc_mir_dataflow::Analysis;
 use rustc_mir_dataflow::MoveDataParamEnv;

 use crate::session_diagnostics::VarNeedNotMut;

 use self::diagnostics::{AccessKind, RegionName};
 use self::location::LocationTable;
 use self::prefixes::PrefixSet;
 use facts::AllFacts;

 use self::path_utils::*;

 pub mod borrow_set;
 mod borrowck_errors;
 mod constraint_generation;
 mod constraints;
 mod dataflow;
 mod def_use;
 mod diagnostics;
 mod facts;
 mod invalidation;
 mod location;
 mod member_constraints;
 mod nll;
 mod path_utils;
 mod place_ext;
 mod places_conflict;
 mod prefixes;
 mod region_infer;
 mod renumber;
 mod session_diagnostics;
 mod type_check;
 mod universal_regions;
 mod used_muts;

 // A public API provided for the Rust compiler consumers.
 pub mod consumers;

 use borrow_set::{BorrowData, BorrowSet};
 use dataflow::{BorrowIndex, BorrowckFlowState as Flows, BorrowckResults, Borrows};
 use nll::{PoloniusOutput, ToRegionVid};
 use place_ext::PlaceExt;
 use places_conflict::{places_conflict, PlaceConflictBias};
 use region_infer::RegionInferenceContext;

 // FIXME(eddyb) perhaps move this somewhere more centrally.
 #[derive(Debug)]
 struct Upvar<'tcx> {
     place: CapturedPlace<'tcx>,

     /// If true, the capture is behind a reference.
     by_ref: bool,
 }

 /// Associate some local constants with the `'tcx` lifetime
 struct TyCtxtConsts<'tcx>(TyCtxt<'tcx>);
 impl<'tcx> TyCtxtConsts<'tcx> {
     const DEREF_PROJECTION: &'tcx [PlaceElem<'tcx>; 1] = &[ProjectionElem::Deref];
 }

 pub fn provide(providers: &mut Providers) {
     *providers = Providers {
         mir_borrowck: |tcx, did| {
             if let Some(def) = ty::WithOptConstParam::try_lookup(did, tcx) {
                 tcx.mir_borrowck_const_arg(def)
             } else {
                 mir_borrowck(tcx, ty::WithOptConstParam::unknown(did))
             }
         },
         mir_borrowck_const_arg: |tcx, (did, param_did)| {
             mir_borrowck(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
         },
         ..*providers
     };
 }

 fn mir_borrowck<'tcx>(
     tcx: TyCtxt<'tcx>,
     def: ty::WithOptConstParam<LocalDefId>,
 ) -> &'tcx BorrowCheckResult<'tcx> {
     let (input_body, promoted) = tcx.mir_promoted(def);
     debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
     let hir_owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;

     let infcx =
         tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(hir_owner.def_id)).build();
     let input_body: &Body<'_> = &input_body.borrow();
     let promoted: &IndexVec<_, _> = &promoted.borrow();
     let opt_closure_req = do_mir_borrowck(&infcx, input_body, promoted, false).0;
     debug!("mir_borrowck done");

     tcx.arena.alloc(opt_closure_req)
 }

 /// Perform the actual borrow checking.
 ///
 /// If `return_body_with_facts` is true, then return the body with non-erased
 /// region ids on which the borrow checking was performed together with Polonius
 /// facts.
 #[instrument(skip(infcx, input_body, input_promoted), fields(id=?input_body.source.with_opt_param().as_local().unwrap()), level = "debug")]
 fn do_mir_borrowck<'tcx>(
     infcx: &InferCtxt<'tcx>,
     input_body: &Body<'tcx>,
     input_promoted: &IndexVec<Promoted, Body<'tcx>>,
     return_body_with_facts: bool,
 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
     let def = input_body.source.with_opt_param().as_local().unwrap();

     debug!(?def);

     let tcx = infcx.tcx;
     let param_env = tcx.param_env(def.did);

     let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
     for var_debug_info in &input_body.var_debug_info {
         if let VarDebugInfoContents::Place(place) = var_debug_info.value {
             if let Some(local) = place.as_local() {
                 if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name {
                     span_bug!(
                         var_debug_info.source_info.span,
                         "local {:?} has many names (`{}` vs `{}`)",
                         local,
                         prev_name,
                         var_debug_info.name
                     );
                 }
                 local_names[local] = Some(var_debug_info.name);
             }
         }
     }

     let mut errors = error::BorrowckErrors::new();

     // Gather the upvars of a closure, if any.
     let tables = tcx.typeck_opt_const_arg(def);
     if let Some(ErrorGuaranteed { .. }) = tables.tainted_by_errors {
         infcx.set_tainted_by_errors();
         errors.set_tainted_by_errors();
     }
     let upvars: Vec<_> = tables
         .closure_min_captures_flattened(def.did)
         .map(|captured_place| {
             let capture = captured_place.info.capture_kind;
             let by_ref = match capture {
                 ty::UpvarCapture::ByValue => false,
                 ty::UpvarCapture::ByRef(..) => true,
             };
             Upvar { place: captured_place.clone(), by_ref }
         })
         .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_owned = input_body.clone();
     let mut promoted = input_promoted.clone();
     let free_regions =
         nll::replace_regions_in_mir(infcx, param_env, &mut body_owned, &mut promoted);
     let body = &body_owned; // no further changes

     let location_table_owned = LocationTable::new(body);
     let location_table = &location_table_owned;

     let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
         match MoveData::gather_moves(&body, tcx, param_env) {
             Ok((_, move_data)) => (move_data, Vec::new()),
             Err((move_data, move_errors)) => (move_data, move_errors),
         };
     let promoted_errors = promoted
         .iter_enumerated()
         .map(|(idx, body)| (idx, MoveData::gather_moves(&body, tcx, param_env)));

     let mdpe = MoveDataParamEnv { move_data, param_env };

     let mut flow_inits = MaybeInitializedPlaces::new(tcx, &body, &mdpe)
         .into_engine(tcx, &body)
         .pass_name("borrowck")
         .iterate_to_fixpoint()
         .into_results_cursor(&body);

     let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def.did).is_fn_or_closure();
     let borrow_set =
         Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));

     let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.unstable_opts.polonius;

     // Compute non-lexical lifetimes.
     let nll::NllOutput {
         regioncx,
         opaque_type_values,
         polonius_input,
         polonius_output,
         opt_closure_req,
         nll_errors,
     } = nll::compute_regions(
         infcx,
         free_regions,
         body,
         &promoted,
         location_table,
         param_env,
         &mut flow_inits,
         &mdpe.move_data,
         &borrow_set,
         &upvars,
         use_polonius,
     );

     // Dump MIR results into a file, if that is enabled. This let us
     // write unit-tests, as well as helping with debugging.
     nll::dump_mir_results(infcx, &body, &regioncx, &opt_closure_req);

     // We also have a `#[rustc_regions]` annotation that causes us to dump
     // information.
     nll::dump_annotation(
         infcx,
         &body,
         &regioncx,
         &opt_closure_req,
         &opaque_type_values,
         &mut errors,
     );

     // 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 = Borrows::new(tcx, body, &regioncx, &borrow_set)
         .into_engine(tcx, body)
         .pass_name("borrowck")
         .iterate_to_fixpoint();
     let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &mdpe)
         .into_engine(tcx, body)
         .pass_name("borrowck")
         .iterate_to_fixpoint();
     let flow_ever_inits = EverInitializedPlaces::new(tcx, body, &mdpe)
         .into_engine(tcx, body)
         .pass_name("borrowck")
         .iterate_to_fixpoint();

     let movable_generator =
         // The first argument is the generator type passed by value
         if let Some(local) = body.local_decls.raw.get(1)
         // Get the interior types and substs which typeck computed
         && let ty::Generator(_, _, hir::Movability::Static) = local.ty.kind()
     {
         false
     } else {
         true
     };

     for (idx, move_data_results) in promoted_errors {
         let promoted_body = &promoted[idx];

         if let Err((move_data, move_errors)) = move_data_results {
             let mut promoted_mbcx = MirBorrowckCtxt {
                 infcx,
                 param_env,
                 body: promoted_body,
                 move_data: &move_data,
                 location_table, // no need to create a real one for the promoted, it is not used
                 movable_generator,
                 fn_self_span_reported: Default::default(),
                 locals_are_invalidated_at_exit,
                 access_place_error_reported: Default::default(),
                 reservation_error_reported: Default::default(),
                 uninitialized_error_reported: Default::default(),
                 regioncx: regioncx.clone(),
                 used_mut: Default::default(),
                 used_mut_upvars: SmallVec::new(),
                 borrow_set: Rc::clone(&borrow_set),
                 dominators: Dominators::dummy(), // not used
                 upvars: Vec::new(),
                 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
                 region_names: RefCell::default(),
                 next_region_name: RefCell::new(1),
                 polonius_output: None,
                 errors,
             };
             promoted_mbcx.report_move_errors(move_errors);
             errors = promoted_mbcx.errors;
         };
     }

     let dominators = body.basic_blocks.dominators();

     let mut mbcx = MirBorrowckCtxt {
         infcx,
         param_env,
         body,
         move_data: &mdpe.move_data,
         location_table,
         movable_generator,
         locals_are_invalidated_at_exit,
         fn_self_span_reported: Default::default(),
         access_place_error_reported: Default::default(),
         reservation_error_reported: Default::default(),
         uninitialized_error_reported: Default::default(),
         regioncx: Rc::clone(&regioncx),
         used_mut: Default::default(),
         used_mut_upvars: SmallVec::new(),
         borrow_set: Rc::clone(&borrow_set),
         dominators,
         upvars,
         local_names,
         region_names: RefCell::default(),
         next_region_name: RefCell::new(1),
         polonius_output,
         errors,
     };

     // Compute and report region errors, if any.
     mbcx.report_region_errors(nll_errors);

     let results = BorrowckResults {
         ever_inits: flow_ever_inits,
         uninits: flow_uninits,
         borrows: flow_borrows,
     };

     mbcx.report_move_errors(move_errors);

     rustc_mir_dataflow::visit_results(
         body,
         traversal::reverse_postorder(body).map(|(bb, _)| bb),
         &results,
         &mut mbcx,
     );

     // For each non-user used mutable variable, check if it's been assigned from
     // a user-declared local. If so, then put that local into the used_mut set.
     // Note that this set is expected to be small - only upvars from closures
     // would have a chance of erroneously adding non-user-defined mutable vars
     // to the set.
     let temporary_used_locals: FxHashSet<Local> = mbcx
         .used_mut
         .iter()
         .filter(|&local| !mbcx.body.local_decls[*local].is_user_variable())
         .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 = std::mem::take(&mut mbcx.used_mut);
     for local in mbcx.body.mut_vars_and_args_iter().filter(|local| !used_mut.contains(local)) {
         let local_decl = &mbcx.body.local_decls[local];
         let lint_root = match &mbcx.body.source_scopes[local_decl.source_info.scope].local_data {
             ClearCrossCrate::Set(data) => data.lint_root,
             _ => continue,
         };

         // Skip over locals that begin with an underscore or have no name
         match mbcx.local_names[local] {
             Some(name) => {
                 if name.as_str().starts_with('_') {
                     continue;
                 }
             }
             None => continue,
         }

         let span = local_decl.source_info.span;
         if span.desugaring_kind().is_some() {
             // If the `mut` arises as part of a desugaring, we should ignore it.
             continue;
         }

         let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);

         tcx.emit_spanned_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
     }

     let tainted_by_errors = mbcx.emit_errors();

     let result = BorrowCheckResult {
         concrete_opaque_types: opaque_type_values,
         closure_requirements: opt_closure_req,
         used_mut_upvars: mbcx.used_mut_upvars,
         tainted_by_errors,
     };

     let body_with_facts = if return_body_with_facts {
         let output_facts = mbcx.polonius_output.expect("Polonius output was not computed");
         Some(Box::new(BodyWithBorrowckFacts {
             body: body_owned,
             input_facts: *polonius_input.expect("Polonius input facts were not generated"),
             output_facts,
             location_table: location_table_owned,
         }))
     } else {
         None
     };

     debug!("do_mir_borrowck: result = {:#?}", result);

     (result, body_with_facts)
 }

 /// A `Body` with information computed by the borrow checker. This struct is
 /// intended to be consumed by compiler consumers.
 ///
 /// We need to include the MIR body here because the region identifiers must
 /// match the ones in the Polonius facts.
 pub struct BodyWithBorrowckFacts<'tcx> {
     /// A mir body that contains region identifiers.
     pub body: Body<'tcx>,
     /// Polonius input facts.
     pub input_facts: AllFacts,
     /// Polonius output facts.
     pub output_facts: Rc<self::nll::PoloniusOutput>,
     /// The table that maps Polonius points to locations in the table.
     pub location_table: LocationTable,
 }

 struct MirBorrowckCtxt<'cx, 'tcx> {
     infcx: &'cx InferCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
     body: &'cx Body<'tcx>,
     move_data: &'cx MoveData<'tcx>,

     /// Map from MIR `Location` to `LocationIndex`; created
     /// when MIR borrowck begins.
     location_table: &'cx LocationTable,

     movable_generator: bool,
     /// This keeps track of whether local variables are free-ed when the function
     /// exits even without a `StorageDead`, which appears to be the case for
     /// constants.
     ///
     /// I'm not sure this is the right approach - @eddyb could you try and
     /// figure this out?
     locals_are_invalidated_at_exit: bool,
     /// This field keeps track of when borrow errors are reported in the access_place function
     /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
     /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
     /// of the `Span` type (while required to mute some errors) stops the muting of the reservation
     /// errors.
     access_place_error_reported: FxHashSet<(Place<'tcx>, Span)>,
     /// This field keeps track of when borrow conflict errors are reported
     /// for reservations, so that we don't report seemingly duplicate
     /// errors for corresponding activations.
     //
     // FIXME: ideally this would be a set of `BorrowIndex`, not `Place`s,
     // but it is currently inconvenient to track down the `BorrowIndex`
     // at the time we detect and report a reservation error.
     reservation_error_reported: FxHashSet<Place<'tcx>>,
     /// This fields keeps track of the `Span`s that we have
     /// used to report extra information for `FnSelfUse`, to avoid
     /// unnecessarily verbose errors.
     fn_self_span_reported: FxHashSet<Span>,
     /// This field keeps track of errors reported in the checking of uninitialized variables,
     /// so that we don't report seemingly duplicate errors.
     uninitialized_error_reported: FxHashSet<PlaceRef<'tcx>>,
     /// This field keeps track of all the local variables that are declared mut and are mutated.
     /// Used for the warning issued by an unused mutable local variable.
     used_mut: FxHashSet<Local>,
     /// If the function we're checking is a closure, then we'll need to report back the list of
     /// mutable upvars that have been used. This field keeps track of them.
     used_mut_upvars: SmallVec<[Field; 8]>,
     /// Region inference context. This contains the results from region inference and lets us e.g.
     /// find out which CFG points are contained in each borrow region.
     regioncx: Rc<RegionInferenceContext<'tcx>>,

     /// The set of borrows extracted from the MIR
     borrow_set: Rc<BorrowSet<'tcx>>,

     /// Dominators for MIR
     dominators: Dominators<BasicBlock>,

     /// Information about upvars not necessarily preserved in types or MIR
     upvars: Vec<Upvar<'tcx>>,

     /// Names of local (user) variables (extracted from `var_debug_info`).
     local_names: IndexVec<Local, Option<Symbol>>,

     /// Record the region names generated for each region in the given
     /// MIR def so that we can reuse them later in help/error messages.
     region_names: RefCell<FxHashMap<RegionVid, RegionName>>,

     /// The counter for generating new region names.
     next_region_name: RefCell<usize>,

     /// Results of Polonius analysis.
     polonius_output: Option<Rc<PoloniusOutput>>,

     errors: error::BorrowckErrors<'tcx>,
 }

 // Check that:
 // 1. assignments are always made to mutable locations (FIXME: does that still really go here?)
 // 2. loans made in overlapping scopes do not conflict
 // 3. assignments do not affect things loaned out as immutable
 // 4. moves do not affect things loaned out in any way
 impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx> {
     type FlowState = Flows<'cx, 'tcx>;

     fn visit_statement_before_primary_effect(
         &mut self,
         flow_state: &Flows<'cx, 'tcx>,
         stmt: &'cx Statement<'tcx>,
         location: Location,
     ) {
         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(box (lhs, ref rhs)) => {
                 self.consume_rvalue(location, (rhs, span), flow_state);

                 self.mutate_place(location, (*lhs, span), Shallow(None), flow_state);
             }
             StatementKind::FakeRead(box (_, ref place)) => {
                 // Read for match doesn't access any memory and is used to
                 // assert that a place is safe and live. So we don't have to
                 // do any checks here.
                 //
                 // FIXME: Remove check that the place is initialized. This is
                 // needed for now because matches don't have never patterns yet.
                 // So this is the only place we prevent
                 //      let x: !;
                 //      match x {};
                 // from compiling.
                 self.check_if_path_or_subpath_is_moved(
                     location,
                     InitializationRequiringAction::Use,
                     (place.as_ref(), span),
                     flow_state,
                 );
             }
             StatementKind::Intrinsic(box ref kind) => match kind {
                 NonDivergingIntrinsic::Assume(op) => self.consume_operand(location, (op, span), flow_state),
                 NonDivergingIntrinsic::CopyNonOverlapping(..) => span_bug!(
                     span,
                     "Unexpected CopyNonOverlapping, should only appear after lower_intrinsics",
                 )
             }
             // Only relevant for mir typeck
             StatementKind::AscribeUserType(..)
             // Doesn't have any language semantics
             | StatementKind::Coverage(..)
             // Does not actually affect borrowck
             | StatementKind::StorageLive(..) => {}
             StatementKind::StorageDead(local) => {
                 self.access_place(
                     location,
                     (Place::from(*local), span),
                     (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
                     LocalMutationIsAllowed::Yes,
                     flow_state,
                 );
             }
             StatementKind::Nop
             | StatementKind::Retag { .. }
             | StatementKind::Deinit(..)
             | StatementKind::SetDiscriminant { .. } => {
                 bug!("Statement not allowed in this MIR phase")
             }
         }
     }

     fn visit_terminator_before_primary_effect(
         &mut self,
         flow_state: &Flows<'cx, 'tcx>,
         term: &'cx Terminator<'tcx>,
         loc: Location,
     ) {
         debug!("MirBorrowckCtxt::process_terminator({:?}, {:?}): {:?}", loc, term, flow_state);
         let span = term.source_info.span;

         self.check_activations(loc, span, flow_state);

         match term.kind {
             TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
                 self.consume_operand(loc, (discr, span), flow_state);
             }
             TerminatorKind::Drop { place, target: _, unwind: _ } => {
                 debug!(
                     "visit_terminator_drop \
                      loc: {:?} term: {:?} place: {:?} span: {:?}",
                     loc, term, place, span
                 );

                 self.access_place(
                     loc,
                     (place, span),
                     (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
                     LocalMutationIsAllowed::Yes,
                     flow_state,
                 );
             }
             TerminatorKind::DropAndReplace {
                 place: drop_place,
                 value: ref new_value,
                 target: _,
                 unwind: _,
             } => {
                 self.mutate_place(loc, (drop_place, span), Deep, flow_state);
                 self.consume_operand(loc, (new_value, span), flow_state);
             }
             TerminatorKind::Call {
                 ref func,
                 ref args,
                 destination,
                 target: _,
                 cleanup: _,
                 from_hir_call: _,
                 fn_span: _,
             } => {
                 self.consume_operand(loc, (func, span), flow_state);
                 for arg in args {
                     self.consume_operand(loc, (arg, span), flow_state);
                 }
                 self.mutate_place(loc, (destination, span), Deep, flow_state);
             }
             TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
                 self.consume_operand(loc, (cond, span), flow_state);
                 use rustc_middle::mir::AssertKind;
                 if let AssertKind::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: _, resume_arg, drop: _ } => {
                 self.consume_operand(loc, (value, span), flow_state);
                 self.mutate_place(loc, (resume_arg, span), Deep, flow_state);
             }

             TerminatorKind::InlineAsm {
                 template: _,
                 ref operands,
                 options: _,
                 line_spans: _,
                 destination: _,
                 cleanup: _,
             } => {
                 for op in operands {
                     match *op {
                         InlineAsmOperand::In { reg: _, ref value } => {
                             self.consume_operand(loc, (value, span), flow_state);
                         }
                         InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
                             if let Some(place) = place {
                                 self.mutate_place(loc, (place, span), Shallow(None), flow_state);
                             }
                         }
                         InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
                             self.consume_operand(loc, (in_value, span), flow_state);
                             if let Some(out_place) = out_place {
                                 self.mutate_place(
                                     loc,
                                     (out_place, span),
                                     Shallow(None),
                                     flow_state,
                                 );
                             }
                         }
                         InlineAsmOperand::Const { value: _ }
                         | InlineAsmOperand::SymFn { value: _ }
                         | InlineAsmOperand::SymStatic { def_id: _ } => {}
                     }
                 }
             }

             TerminatorKind::Goto { target: _ }
             | TerminatorKind::Abort
             | TerminatorKind::Unreachable
             | TerminatorKind::Resume
             | TerminatorKind::Return
             | TerminatorKind::GeneratorDrop
             | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
             | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
                 // no data used, thus irrelevant to borrowck
             }
         }
     }

     fn visit_terminator_after_primary_effect(
         &mut self,
         flow_state: &Flows<'cx, 'tcx>,
         term: &'cx Terminator<'tcx>,
         loc: Location,
     ) {
         let span = term.source_info.span;

         match term.kind {
             TerminatorKind::Yield { value: _, resume: _, resume_arg: _, drop: _ } => {
                 if self.movable_generator {
                     // Look for any active borrows to locals
                     let borrow_set = self.borrow_set.clone();
                     for i in flow_state.borrows.iter() {
                         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();
                 for i in flow_state.borrows.iter() {
                     let borrow = &borrow_set[i];
                     self.check_for_invalidation_at_exit(loc, borrow, span);
                 }
             }

             TerminatorKind::Abort
             | TerminatorKind::Assert { .. }
             | TerminatorKind::Call { .. }
             | TerminatorKind::Drop { .. }
             | TerminatorKind::DropAndReplace { .. }
             | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
             | TerminatorKind::FalseUnwind { real_target: _, unwind: _ }
             | TerminatorKind::Goto { .. }
             | TerminatorKind::SwitchInt { .. }
             | TerminatorKind::Unreachable
             | TerminatorKind::InlineAsm { .. } => {}
         }
     }
 }

 use self::AccessDepth::{Deep, Shallow};
 use self::ReadOrWrite::{Activation, Read, Reservation, Write};

 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 enum ArtificialField {
     ArrayLength,
     ShallowBorrow,
 }

 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 enum AccessDepth {
     /// From the RFC: "A *shallow* access means that the immediate
     /// fields reached at P are accessed, but references or pointers
     /// found within are not dereferenced. Right now, the only access
     /// that is shallow is an assignment like `x = ...;`, which would
     /// be a *shallow write* of `x`."
     Shallow(Option<ArtificialField>),

     /// From the RFC: "A *deep* access means that all data reachable
     /// through the given place may be invalidated or accesses by
     /// this action."
     Deep,

     /// Access is Deep only when there is a Drop implementation that
     /// can reach the data behind the reference.
     Drop,
 }

 /// Kind of access to a value: read or write
 /// (For informational purposes only)
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 enum ReadOrWrite {
     /// From the RFC: "A *read* means that the existing data may be
     /// read, but will not be changed."
     Read(ReadKind),

     /// From the RFC: "A *write* means that the data may be mutated to
     /// new values or otherwise invalidated (for example, it could be
     /// de-initialized, as in a move operation).
     Write(WriteKind),

     /// For two-phase borrows, we distinguish a reservation (which is treated
     /// like a Read) from an activation (which is treated like a write), and
     /// each of those is furthermore distinguished from Reads/Writes above.
     Reservation(WriteKind),
     Activation(WriteKind, BorrowIndex),
 }

 /// Kind of read access to a value
 /// (For informational purposes only)
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 enum ReadKind {
     Borrow(BorrowKind),
     Copy,
 }

 /// Kind of write access to a value
 /// (For informational purposes only)
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 enum WriteKind {
     StorageDeadOrDrop,
     MutableBorrow(BorrowKind),
     Mutate,
     Move,
 }

 /// When checking permissions for a place access, this flag is used to indicate that an immutable
 /// local place can be mutated.
 //
 // FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
 // - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
 // - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
 //   `is_declared_mutable()`.
 // - Take flow state into consideration in `is_assignable()` for local variables.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 enum LocalMutationIsAllowed {
     Yes,
     /// We want use of immutable upvars to cause a "write to immutable upvar"
     /// error, not an "reassignment" error.
     ExceptUpvars,
     No,
 }

 #[derive(Copy, Clone, Debug)]
 enum InitializationRequiringAction {
     Borrow,
     MatchOn,
     Use,
     Assignment,
     PartialAssignment,
 }

 struct RootPlace<'tcx> {
     place_local: Local,
     place_projection: &'tcx [PlaceElem<'tcx>],
     is_local_mutation_allowed: LocalMutationIsAllowed,
 }

 impl InitializationRequiringAction {
     fn as_noun(self) -> &'static str {
         match self {
             InitializationRequiringAction::Borrow => "borrow",
             InitializationRequiringAction::MatchOn => "use", // no good noun
             InitializationRequiringAction::Use => "use",
             InitializationRequiringAction::Assignment => "assign",
             InitializationRequiringAction::PartialAssignment => "assign to part",
         }
     }

     fn as_verb_in_past_tense(self) -> &'static str {
         match self {
             InitializationRequiringAction::Borrow => "borrowed",
             InitializationRequiringAction::MatchOn => "matched on",
             InitializationRequiringAction::Use => "used",
             InitializationRequiringAction::Assignment => "assigned",
             InitializationRequiringAction::PartialAssignment => "partially assigned",
         }
     }

     fn as_general_verb_in_past_tense(self) -> &'static str {
         match self {
             InitializationRequiringAction::Borrow
             | InitializationRequiringAction::MatchOn
             | InitializationRequiringAction::Use => "used",
             InitializationRequiringAction::Assignment => "assigned",
             InitializationRequiringAction::PartialAssignment => "partially assigned",
         }
     }
 }

 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     fn body(&self) -> &'cx Body<'tcx> {
         self.body
     }

     /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
     /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
     /// place is initialized and (b) it is not borrowed in some way that would prevent this
     /// access.
     ///
     /// Returns `true` if an error is reported.
     fn access_place(
         &mut self,
         location: Location,
         place_span: (Place<'tcx>, Span),
         kind: (AccessDepth, ReadOrWrite),
         is_local_mutation_allowed: LocalMutationIsAllowed,
         flow_state: &Flows<'cx, 'tcx>,
     ) {
         let (sd, rw) = kind;

         if let Activation(_, borrow_index) = rw {
             if self.reservation_error_reported.contains(&place_span.0) {
                 debug!(
                     "skipping access_place for activation of invalid reservation \
                      place: {:?} borrow_index: {:?}",
                     place_span.0, borrow_index
                 );
                 return;
             }
         }

         // Check is_empty() first because it's the common case, and doing that
         // way we avoid the clone() call.
         if !self.access_place_error_reported.is_empty()
             && self.access_place_error_reported.contains(&(place_span.0, 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 conflict_error || mutability_error {
             debug!("access_place: logging error place_span=`{:?}` kind=`{:?}`", place_span, kind);
             self.access_place_error_reported.insert((place_span.0, place_span.1));
         }
     }

     #[instrument(level = "debug", skip(self, flow_state))]
     fn check_access_for_conflict(
         &mut self,
         location: Location,
         place_span: (Place<'tcx>, Span),
         sd: AccessDepth,
         rw: ReadOrWrite,
         flow_state: &Flows<'cx, 'tcx>,
     ) -> bool {
         let mut error_reported = false;
         let tcx = self.infcx.tcx;
         let body = self.body;
         let borrow_set = self.borrow_set.clone();

         // Use polonius output if it has been enabled.
         let polonius_output = self.polonius_output.clone();
         let borrows_in_scope = if let Some(polonius) = &polonius_output {
             let location = self.location_table.start_index(location);
             Either::Left(polonius.errors_at(location).iter().copied())
         } else {
             Either::Right(flow_state.borrows.iter())
         };

         each_borrow_involving_path(
             self,
             tcx,
             body,
             location,
             (sd, place_span.0),
             &borrow_set,
             borrows_in_scope,
             |this, borrow_index, borrow| match (rw, borrow.kind) {
                 // Obviously an activation is compatible with its own
                 // reservation (or even prior activating uses of same
                 // borrow); so don't check if they interfere.
                 //
                 // NOTE: *reservations* do conflict with themselves;
                 // thus aren't injecting unsoundness w/ this check.)
                 (Activation(_, activating), _) if activating == borrow_index => {
                     debug!(
                         "check_access_for_conflict place_span: {:?} sd: {:?} rw: {:?} \
                          skipping {:?} b/c activation of same borrow_index",
                         place_span,
                         sd,
                         rw,
                         (borrow_index, borrow),
                     );
                     Control::Continue
                 }

                 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
                 | (
                     Read(ReadKind::Borrow(BorrowKind::Shallow)),
                     BorrowKind::Unique | BorrowKind::Mut { .. },
                 ) => Control::Continue,

                 (Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
                     // This used to be a future compatibility warning (to be
                     // disallowed on NLL). See rust-lang/rust#56254
                     Control::Continue
                 }

                 (Write(WriteKind::Move), BorrowKind::Shallow) => {
                     // Handled by initialization checks.
                     Control::Continue
                 }

                 (Read(kind), BorrowKind::Unique | 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 => {
                             let err = this
                                 .report_use_while_mutably_borrowed(location, place_span, borrow);
                             this.buffer_error(err);
                         }
                         ReadKind::Borrow(bk) => {
                             let err =
                                 this.report_conflicting_borrow(location, place_span, bk, borrow);
                             this.buffer_error(err);
                         }
                     }
                     Control::Break
                 }

                 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
                     match rw {
                         Reservation(..) => {
                             debug!(
                                 "recording invalid reservation of \
                                  place: {:?}",
                                 place_span.0
                             );
                             this.reservation_error_reported.insert(place_span.0);
                         }
                         Activation(_, activating) => {
                             debug!(
                                 "observing check_place for activation of \
                                  borrow_index: {:?}",
                                 activating
                             );
                         }
                         Read(..) | Write(..) => {}
                     }

                     error_reported = true;
                     match kind {
                         WriteKind::MutableBorrow(bk) => {
                             let err =
                                 this.report_conflicting_borrow(location, place_span, bk, borrow);
                             this.buffer_error(err);
                         }
                         WriteKind::StorageDeadOrDrop => this
                             .report_borrowed_value_does_not_live_long_enough(
                                 location,
                                 borrow,
                                 place_span,
                                 Some(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,
         flow_state: &Flows<'cx, 'tcx>,
     ) {
         // Write of P[i] or *P requires P init'd.
         self.check_if_assigned_path_is_moved(location, place_span, flow_state);

         // Special case: you can assign an immutable local variable
         // (e.g., `x = ...`) so long as it has never been initialized
         // before (at this point in the flow).
         if let Some(local) = place_span.0.as_local() {
             if let Mutability::Not = self.body.local_decls[local].mutability {
                 // check for reassignments to immutable local variables
                 self.check_if_reassignment_to_immutable_state(
                     location, local, place_span, flow_state,
                 );
                 return;
             }
         }

         // Otherwise, use the normal access permission rules.
         self.access_place(
             location,
             place_span,
             (kind, Write(WriteKind::Mutate)),
             LocalMutationIsAllowed::No,
             flow_state,
         );
     }

     fn consume_rvalue(
         &mut self,
         location: Location,
         (rvalue, span): (&'cx Rvalue<'tcx>, Span),
         flow_state: &Flows<'cx, 'tcx>,
     ) {
         match *rvalue {
             Rvalue::Ref(_ /*rgn*/, bk, place) => {
                 let access_kind = match bk {
                     BorrowKind::Shallow => {
                         (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
                     }
                     BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
                     BorrowKind::Unique | BorrowKind::Mut { .. } => {
                         let wk = WriteKind::MutableBorrow(bk);
                         if allow_two_phase_borrow(bk) {
                             (Deep, Reservation(wk))
                         } else {
                             (Deep, Write(wk))
                         }
                     }
                 };

                 self.access_place(
                     location,
                     (place, span),
                     access_kind,
                     LocalMutationIsAllowed::No,
                     flow_state,
                 );

                 let action = if bk == BorrowKind::Shallow {
                     InitializationRequiringAction::MatchOn
                 } else {
                     InitializationRequiringAction::Borrow
                 };

                 self.check_if_path_or_subpath_is_moved(
                     location,
                     action,
                     (place.as_ref(), span),
                     flow_state,
                 );
             }

             Rvalue::AddressOf(mutability, place) => {
                 let access_kind = match mutability {
                     Mutability::Mut => (
                         Deep,
                         Write(WriteKind::MutableBorrow(BorrowKind::Mut {
                             allow_two_phase_borrow: false,
                         })),
                     ),
                     Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
                 };

                 self.access_place(
                     location,
                     (place, span),
                     access_kind,
                     LocalMutationIsAllowed::No,
                     flow_state,
                 );

                 self.check_if_path_or_subpath_is_moved(
                     location,
                     InitializationRequiringAction::Borrow,
                     (place.as_ref(), span),
                     flow_state,
                 );
             }

             Rvalue::ThreadLocalRef(_) => {}

             Rvalue::Use(ref operand)
             | Rvalue::Repeat(ref operand, _)
             | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
             | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/)
             | Rvalue::ShallowInitBox(ref operand, _ /*ty*/) => {
                 self.consume_operand(location, (operand, span), flow_state)
             }
             Rvalue::CopyForDeref(place) => {
                 self.access_place(
                     location,
                     (place, span),
                     (Deep, Read(ReadKind::Copy)),
                     LocalMutationIsAllowed::No,
                     flow_state,
                 );

                 // Finally, check if path was already moved.
                 self.check_if_path_or_subpath_is_moved(
                     location,
                     InitializationRequiringAction::Use,
                     (place.as_ref(), span),
                     flow_state,
                 );
             }

             Rvalue::Len(place) | Rvalue::Discriminant(place) => {
                 let af = match *rvalue {
                     Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
                     Rvalue::Discriminant(..) => None,
                     _ => unreachable!(),
                 };
                 self.access_place(
                     location,
                     (place, span),
                     (Shallow(af), Read(ReadKind::Copy)),
                     LocalMutationIsAllowed::No,
                     flow_state,
                 );
                 self.check_if_path_or_subpath_is_moved(
                     location,
                     InitializationRequiringAction::Use,
                     (place.as_ref(), span),
                     flow_state,
                 );
             }

             Rvalue::BinaryOp(_bin_op, box (ref operand1, ref operand2))
             | Rvalue::CheckedBinaryOp(_bin_op, box (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.
             }

             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>| {
             // We have three possibilities here:
             // a. We are modifying something through a mut-ref
             // b. We are modifying something that is local to our parent
             // c. Current body is a nested closure, and we are modifying path starting from
             //    a Place captured by our parent closure.

             // Handle (c), the path being modified is exactly the path captured by our parent
             if let Some(field) = this.is_upvar_field_projection(place.as_ref()) {
                 this.used_mut_upvars.push(field);
                 return;
             }

             for (place_ref, proj) in place.iter_projections().rev() {
                 // Handle (a)
                 if proj == ProjectionElem::Deref {
                     match place_ref.ty(this.body(), this.infcx.tcx).ty.kind() {
                         // We aren't modifying a variable directly
                         ty::Ref(_, _, hir::Mutability::Mut) => return,

                         _ => {}
                     }
                 }

                 // Handle (c)
                 if let Some(field) = this.is_upvar_field_projection(place_ref) {
                     this.used_mut_upvars.push(field);
                     return;
                 }
             }

             // Handle(b)
             this.used_mut.insert(place.local);
         };

         // This relies on the current way that by-value
         // captures of a closure are copied/moved directly
         // when generating MIR.
         match *operand {
             Operand::Move(place) | Operand::Copy(place) => {
                 match place.as_local() {
                     Some(local) if !self.body.local_decls[local].is_user_variable() => {
                         if self.body.local_decls[local].ty.is_mutable_ptr() {
                             // The variable will be marked as mutable by the borrow.
                             return;
                         }
                         // This is an edge case where we have a `move` closure
                         // inside a non-move closure, and the inner closure
                         // contains a mutation:
                         //
                         // let mut i = 0;
                         // || { move || { i += 1; }; };
                         //
                         // In this case our usual strategy of assuming that the
                         // variable will be captured by mutable reference is
                         // wrong, since `i` can be copied into the inner
                         // closure from a shared reference.
                         //
                         // As such we have to search for the local that this
                         // capture comes from and mark it as being used as mut.

                         let 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 InitLocation::Statement(loc) = init.location else {
                             bug!("temporary initialized in arguments")
                         };

                         let body = self.body;
                         let bbd = &body[loc.block];
                         let stmt = &bbd.statements[loc.statement_index];
                         debug!("temporary assigned in: stmt={:?}", stmt);

                         if let StatementKind::Assign(box (_, Rvalue::Ref(_, _, source))) = stmt.kind
                         {
                             propagate_closure_used_mut_place(self, source);
                         } else {
                             bug!(
                                 "closures should only capture user variables \
                                  or references to user variables"
                             );
                         }
                     }
                     _ => propagate_closure_used_mut_place(self, place),
                 }
             }
             Operand::Constant(..) => {}
         }
     }

     fn consume_operand(
         &mut self,
         location: Location,
         (operand, span): (&'cx Operand<'tcx>, Span),
         flow_state: &Flows<'cx, 'tcx>,
     ) {
         match *operand {
             Operand::Copy(place) => {
                 // copy of place: check if this is "copy of frozen path"
                 // (FIXME: see check_loans.rs)
                 self.access_place(
                     location,
                     (place, span),
                     (Deep, Read(ReadKind::Copy)),
                     LocalMutationIsAllowed::No,
                     flow_state,
                 );

                 // Finally, check if path was already moved.
                 self.check_if_path_or_subpath_is_moved(
                     location,
                     InitializationRequiringAction::Use,
                     (place.as_ref(), span),
                     flow_state,
                 );
             }
             Operand::Move(place) => {
                 // move of place: check if this is move of already borrowed path
                 self.access_place(
                     location,
                     (place, span),
                     (Deep, Write(WriteKind::Move)),
                     LocalMutationIsAllowed::Yes,
                     flow_state,
                 );

                 // Finally, check if path was already moved.
                 self.check_if_path_or_subpath_is_moved(
                     location,
                     InitializationRequiringAction::Use,
                     (place.as_ref(), span),
                     flow_state,
                 );
             }
             Operand::Constant(_) => {}
         }
     }

     /// Checks whether a borrow of this place is invalidated when the function
     /// exits
     #[instrument(level = "debug", skip(self))]
     fn check_for_invalidation_at_exit(
         &mut self,
         location: Location,
         borrow: &BorrowData<'tcx>,
         span: Span,
     ) {
         let place = borrow.borrowed_place;
         let mut root_place = PlaceRef { local: place.local, projection: &[] };

         // FIXME(nll-rfc#40): do more precise destructor tracking here. For now
         // we just know that all locals are dropped at function exit (otherwise
         // we'll have a memory leak) and assume that all statics have a destructor.
         //
         // FIXME: allow thread-locals to borrow other thread locals?

         let (might_be_alive, will_be_dropped) =
             if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
                 // Thread-locals might be dropped after the function exits
                 // We have to dereference the outer reference because
                 // borrows don't conflict behind shared references.
                 root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
                 (true, true)
             } else {
                 (false, self.locals_are_invalidated_at_exit)
             };

         if !will_be_dropped {
             debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
             return;
         }

         let sd = if might_be_alive { Deep } else { Shallow(None) };

         if places_conflict::borrow_conflicts_with_place(
             self.infcx.tcx,
             &self.body,
             place,
             borrow.kind,
             root_place,
             sd,
             places_conflict::PlaceConflictBias::Overlap,
         ) {
             debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
             // FIXME: should be talking about the region lifetime instead
             // of just a span here.
             let span = self.infcx.tcx.sess.source_map().end_point(span);
             self.report_borrowed_value_does_not_live_long_enough(
                 location,
                 borrow,
                 (place, span),
                 None,
             )
         }
     }

     /// Reports an error if this is a borrow of local data.
     /// This is called for all Yield expressions on movable generators
     fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
         debug!("check_for_local_borrow({:?})", borrow);

         if borrow_of_local_data(borrow.borrowed_place) {
             let err = self.cannot_borrow_across_generator_yield(
                 self.retrieve_borrow_spans(borrow).var_or_use(),
                 yield_span,
             );

             self.buffer_error(err);
         }
     }

     fn check_activations(&mut self, location: Location, span: Span, flow_state: &Flows<'cx, 'tcx>) {
         // Two-phase borrow support: For each activation that is newly
         // generated at this statement, check if it interferes with
         // another borrow.
         let borrow_set = self.borrow_set.clone();
         for &borrow_index in borrow_set.activations_at_location(location) {
             let borrow = &borrow_set[borrow_index];

             // only mutable borrows should be 2-phase
             assert!(match borrow.kind {
                 BorrowKind::Shared | BorrowKind::Shallow => false,
                 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
             });

             self.access_place(
                 location,
                 (borrow.borrowed_place, span),
                 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
                 LocalMutationIsAllowed::No,
                 flow_state,
             );
             // We do not need to call `check_if_path_or_subpath_is_moved`
             // again, as we already called it when we made the
             // initial reservation.
         }
     }

     fn check_if_reassignment_to_immutable_state(
         &mut self,
         location: Location,
         local: Local,
         place_span: (Place<'tcx>, Span),
         flow_state: &Flows<'cx, 'tcx>,
     ) {
         debug!("check_if_reassignment_to_immutable_state({:?})", local);

         // Check if any of the initializations of `local` have happened yet:
         if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
             // And, if so, report an error.
             let init = &self.move_data.inits[init_index];
             let span = init.span(&self.body);
             self.report_illegal_reassignment(location, place_span, span, place_span.0);
         }
     }

     fn check_if_full_path_is_moved(
         &mut self,
         location: Location,
         desired_action: InitializationRequiringAction,
         place_span: (PlaceRef<'tcx>, Span),
         flow_state: &Flows<'cx, 'tcx>,
     ) {
         let maybe_uninits = &flow_state.uninits;

         // Bad scenarios:
         //
         // 1. Move of `a.b.c`, use of `a.b.c`
         // 2. Move of `a.b.c`, use of `a.b.c.d` (without first reinitializing `a.b.c.d`)
         // 3. Uninitialized `(a.b.c: &_)`, use of `*a.b.c`; note that with
         //    partial initialization support, one might have `a.x`
         //    initialized but not `a.b`.
         //
         // OK scenarios:
         //
         // 4. Move of `a.b.c`, use of `a.b.d`
         // 5. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
         // 6. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
         //    must have been initialized for the use to be sound.
         // 7. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`

         // The dataflow tracks shallow prefixes distinctly (that is,
         // field-accesses on P distinctly from P itself), in order to
         // track substructure initialization separately from the whole
         // structure.
         //
         // E.g., when looking at (*a.b.c).d, if the closest prefix for
         // which we have a MovePath is `a.b`, then that means that the
         // initialization state of `a.b` is all we need to inspect to
         // know if `a.b.c` is valid (and from that we infer that the
         // dereference and `.d` access is also valid, since we assume
         // `a.b.c` is assigned a reference to an initialized and
         // well-formed record structure.)

         // Therefore, if we seek out the *closest* prefix for which we
         // have a MovePath, that should capture the initialization
         // state for the place scenario.
         //
         // This code covers scenarios 1, 2, and 3.

         debug!("check_if_full_path_is_moved place: {:?}", place_span.0);
         let (prefix, mpi) = self.move_path_closest_to(place_span.0);
         if maybe_uninits.contains(mpi) {
             self.report_use_of_moved_or_uninitialized(
                 location,
                 desired_action,
                 (prefix, place_span.0, place_span.1),
                 mpi,
             );
         } // Only query longest prefix with a MovePath, not further
         // ancestors; dataflow recurs on children when parents
         // move (to support partial (re)inits).
         //
         // (I.e., querying parents breaks scenario 7; but may want
         // to do such a query based on partial-init feature-gate.)
     }

     /// Subslices correspond to multiple move paths, so we iterate through the
     /// elements of the base array. For each element we check
     ///
     /// * Does this element overlap with our slice.
     /// * Is any part of it uninitialized.
     fn check_if_subslice_element_is_moved(
         &mut self,
         location: Location,
         desired_action: InitializationRequiringAction,
         place_span: (PlaceRef<'tcx>, Span),
         maybe_uninits: &ChunkedBitSet<MovePathIndex>,
         from: u64,
         to: u64,
     ) {
         if let Some(mpi) = self.move_path_for_place(place_span.0) {
             let move_paths = &self.move_data.move_paths;

             let root_path = &move_paths[mpi];
             for (child_mpi, child_move_path) in root_path.children(move_paths) {
                 let last_proj = child_move_path.place.projection.last().unwrap();
                 if let ProjectionElem::ConstantIndex { offset, from_end, .. } = last_proj {
                     debug_assert!(!from_end, "Array constant indexing shouldn't be `from_end`.");

                     if (from..to).contains(offset) {
                         let uninit_child =
                             self.move_data.find_in_move_path_or_its_descendants(child_mpi, |mpi| {
                                 maybe_uninits.contains(mpi)
                             });

                         if let Some(uninit_child) = uninit_child {
                             self.report_use_of_moved_or_uninitialized(
                                 location,
                                 desired_action,
                                 (place_span.0, place_span.0, place_span.1),
                                 uninit_child,
                             );
                             return; // don't bother finding other problems.
                         }
                     }
                 }
             }
         }
     }

     fn check_if_path_or_subpath_is_moved(
         &mut self,
         location: Location,
         desired_action: InitializationRequiringAction,
         place_span: (PlaceRef<'tcx>, Span),
         flow_state: &Flows<'cx, 'tcx>,
     ) {
         let maybe_uninits = &flow_state.uninits;

         // Bad scenarios:
         //
         // 1. Move of `a.b.c`, use of `a` or `a.b`
         //    partial initialization support, one might have `a.x`
         //    initialized but not `a.b`.
         // 2. All bad scenarios from `check_if_full_path_is_moved`
         //
         // OK scenarios:
         //
         // 3. Move of `a.b.c`, use of `a.b.d`
         // 4. Uninitialized `a.x`, initialized `a.b`, use of `a.b`
         // 5. Copied `(a.b: &_)`, use of `*(a.b).c`; note that `a.b`
         //    must have been initialized for the use to be sound.
         // 6. Move of `a.b.c` then reinit of `a.b.c.d`, use of `a.b.c.d`

         self.check_if_full_path_is_moved(location, desired_action, place_span, flow_state);

         if let Some((place_base, ProjectionElem::Subslice { from, to, from_end: false })) =
             place_span.0.last_projection()
         {
             let place_ty = place_base.ty(self.body(), self.infcx.tcx);
             if let ty::Array(..) = place_ty.ty.kind() {
                 self.check_if_subslice_element_is_moved(
                     location,
                     desired_action,
                     (place_base, place_span.1),
                     maybe_uninits,
                     from,
                     to,
                 );
                 return;
             }
         }

         // A move of any shallow suffix of `place` also interferes
         // with an attempt to use `place`. This is scenario 3 above.
         //
         // (Distinct from handling of scenarios 1+2+4 above because
         // `place` does not interfere with suffixes of its prefixes,
         // e.g., `a.b.c` does not interfere with `a.b.d`)
         //
         // This code covers scenario 1.

         debug!("check_if_path_or_subpath_is_moved place: {:?}", place_span.0);
         if let Some(mpi) = self.move_path_for_place(place_span.0) {
             let uninit_mpi = self
                 .move_data
                 .find_in_move_path_or_its_descendants(mpi, |mpi| maybe_uninits.contains(mpi));

             if let Some(uninit_mpi) = uninit_mpi {
                 self.report_use_of_moved_or_uninitialized(
                     location,
                     desired_action,
                     (place_span.0, place_span.0, place_span.1),
                     uninit_mpi,
                 );
                 return; // don't bother finding other problems.
             }
         }
     }

     /// Currently MoveData does not store entries for all places in
     /// the input MIR. For example it will currently filter out
     /// places that are Copy; thus we do not track places of shared
     /// reference type. This routine will walk up a place along its
     /// prefixes, searching for a foundational place that *is*
     /// tracked in the MoveData.
     ///
     /// An Err result includes a tag indicated why the search failed.
     /// Currently this can only occur if the place is built off of a
     /// static variable, as we do not track those in the MoveData.
     fn move_path_closest_to(&mut self, place: PlaceRef<'tcx>) -> (PlaceRef<'tcx>, MovePathIndex) {
         match self.move_data.rev_lookup.find(place) {
             LookupResult::Parent(Some(mpi)) | LookupResult::Exact(mpi) => {
                 (self.move_data.move_paths[mpi].place.as_ref(), mpi)
             }
             LookupResult::Parent(None) => panic!("should have move path for every Local"),
         }
     }

     fn move_path_for_place(&mut self, place: PlaceRef<'tcx>) -> Option<MovePathIndex> {
         // If returns None, then there is no move path corresponding
         // to a direct owner of `place` (which means there is nothing
         // that borrowck tracks for its analysis).

         match self.move_data.rev_lookup.find(place) {
             LookupResult::Parent(_) => None,
             LookupResult::Exact(mpi) => Some(mpi),
         }
     }

     fn check_if_assigned_path_is_moved(
         &mut self,
         location: Location,
         (place, span): (Place<'tcx>, Span),
         flow_state: &Flows<'cx, 'tcx>,
     ) {
         debug!("check_if_assigned_path_is_moved place: {:?}", place);

         // None case => assigning to `x` does not require `x` be initialized.
         for (place_base, elem) in place.iter_projections().rev() {
             match elem {
                 ProjectionElem::Index(_/*operand*/) |
                 ProjectionElem::OpaqueCast(_) |
                 ProjectionElem::ConstantIndex { .. } |
                 // assigning to P[i] requires P to be valid.
                 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
                 // assigning to (P->variant) is okay if assigning to `P` is okay
                 //
                 // FIXME: is this true even if P is an adt with a dtor?
                 { }

                 // assigning to (*P) requires P to be initialized
                 ProjectionElem::Deref => {
                     self.check_if_full_path_is_moved(
                         location, InitializationRequiringAction::Use,
                         (place_base, span), flow_state);
                     // (base initialized; no need to
                     // recur further)
                     break;
                 }

                 ProjectionElem::Subslice { .. } => {
                     panic!("we don't allow assignments to subslices, location: {:?}",
                            location);
                 }

                 ProjectionElem::Field(..) => {
                     // if type of `P` has a dtor, then
                     // assigning to `P.f` requires `P` itself
                     // be already initialized
                     let tcx = self.infcx.tcx;
                     let base_ty = place_base.ty(self.body(), tcx).ty;
                     match base_ty.kind() {
                         ty::Adt(def, _) if def.has_dtor(tcx) => {
                             self.check_if_path_or_subpath_is_moved(
                                 location, InitializationRequiringAction::Assignment,
                                 (place_base, span), 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, place_base, span, flow_state);

                             // 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(place.local);
                         }

                         _ => {}
                     }
                 }
             }
         }

         fn check_parent_of_field<'cx, 'tcx>(
             this: &mut MirBorrowckCtxt<'cx, 'tcx>,
             location: Location,
             base: PlaceRef<'tcx>,
             span: Span,
             flow_state: &Flows<'cx, 'tcx>,
         ) {
             // rust-lang/rust#21232: Until Rust allows reads from the
             // initialized parts of partially initialized structs, we
             // will, starting with the 2018 edition, reject attempts
             // to write to structs that are not fully initialized.
             //
             // In other words, *until* we allow this:
             //
             // 1. `let mut s; s.x = Val; read(s.x);`
             //
             // we will for now disallow this:
             //
             // 2. `let mut s; s.x = Val;`
             //
             // and also this:
             //
             // 3. `let mut s = ...; drop(s); s.x=Val;`
             //
             // This does not use check_if_path_or_subpath_is_moved,
             // because we want to *allow* reinitializations of fields:
             // e.g., want to allow
             //
             // `let mut s = ...; drop(s.x); s.x=Val;`
             //
             // This does not use check_if_full_path_is_moved on
             // `base`, because that would report an error about the
             // `base` as a whole, but in this scenario we *really*
             // want to report an error about the actual thing that was
             // moved, which may be some prefix of `base`.

             // Shallow so that we'll stop at any dereference; we'll
             // report errors about issues with such bases elsewhere.
             let maybe_uninits = &flow_state.uninits;

             // Find the shortest uninitialized prefix you can reach
             // without going over a Deref.
             let mut shortest_uninit_seen = None;
             for prefix in this.prefixes(base, PrefixSet::Shallow) {
                 let Some(mpi) = this.move_path_for_place(prefix) else { continue };

                 if maybe_uninits.contains(mpi) {
                     debug!(
                         "check_parent_of_field updating shortest_uninit_seen from {:?} to {:?}",
                         shortest_uninit_seen,
                         Some((prefix, mpi))
                     );
                     shortest_uninit_seen = Some((prefix, mpi));
                 } else {
                     debug!("check_parent_of_field {:?} is definitely initialized", (prefix, mpi));
                 }
             }

             if let Some((prefix, mpi)) = shortest_uninit_seen {
                 // Check for a reassignment into an uninitialized field of a union (for example,
                 // after a move out). In this case, do not report an error here. There is an
                 // exception, if this is the first assignment into the union (that is, there is
                 // no move out from an earlier location) then this is an attempt at initialization
                 // of the union - we should error in that case.
                 let tcx = this.infcx.tcx;
                 if base.ty(this.body(), tcx).ty.is_union() {
                     if this.move_data.path_map[mpi].iter().any(|moi| {
                         this.move_data.moves[*moi].source.is_predecessor_of(location, this.body)
                     }) {
                         return;
                     }
                 }

                 this.report_use_of_moved_or_uninitialized(
                     location,
                     InitializationRequiringAction::PartialAssignment,
                     (prefix, base, span),
                     mpi,
                 );
             }
         }
     }

     /// Checks the permissions for the given place and read or write kind
     ///
     /// Returns `true` if an error is reported.
     fn check_access_permissions(
         &mut self,
         (place, span): (Place<'tcx>, Span),
         kind: ReadOrWrite,
         is_local_mutation_allowed: LocalMutationIsAllowed,
         flow_state: &Flows<'cx, 'tcx>,
         location: Location,
     ) -> bool {
         debug!(
             "check_access_permissions({:?}, {:?}, is_local_mutation_allowed: {:?})",
             place, kind, is_local_mutation_allowed
         );

         let error_access;
         let the_place_err;

         match kind {
             Reservation(WriteKind::MutableBorrow(
                 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
             ))
             | Write(WriteKind::MutableBorrow(
                 borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
             )) => {
                 let is_local_mutation_allowed = match borrow_kind {
                     BorrowKind::Unique => LocalMutationIsAllowed::Yes,
                     BorrowKind::Mut { .. } => is_local_mutation_allowed,
                     BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
                 };
                 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
                     Ok(root_place) => {
                         self.add_used_mut(root_place, flow_state);
                         return false;
                     }
                     Err(place_err) => {
                         error_access = AccessKind::MutableBorrow;
                         the_place_err = place_err;
                     }
                 }
             }
             Reservation(WriteKind::Mutate) | Write(WriteKind::Mutate) => {
                 match self.is_mutable(place.as_ref(), is_local_mutation_allowed) {
                     Ok(root_place) => {
                         self.add_used_mut(root_place, flow_state);
                         return false;
                     }
                     Err(place_err) => {
                         error_access = AccessKind::Mutate;
                         the_place_err = place_err;
                     }
                 }
             }

             Reservation(
                 WriteKind::Move
                 | WriteKind::StorageDeadOrDrop
                 | WriteKind::MutableBorrow(BorrowKind::Shared)
                 | WriteKind::MutableBorrow(BorrowKind::Shallow),
             )
             | Write(
                 WriteKind::Move
                 | WriteKind::StorageDeadOrDrop
                 | WriteKind::MutableBorrow(BorrowKind::Shared)
                 | WriteKind::MutableBorrow(BorrowKind::Shallow),
             ) => {
                 if self.is_mutable(place.as_ref(), is_local_mutation_allowed).is_err()
                     && !self.has_buffered_errors()
                 {
                     // rust-lang/rust#46908: In pure NLL mode this code path should be
                     // unreachable, but we use `delay_span_bug` because we can hit this when
                     // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
                     // enabled. We don't want to ICE for that case, as other errors will have
                     // been emitted (#52262).
                     self.infcx.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
                     | BorrowKind::Mut { .. }
                     | BorrowKind::Shared
                     | BorrowKind::Shallow,
                 )
                 | ReadKind::Copy,
             ) => {
                 // Access authorized
                 return false;
             }
         }

         // rust-lang/rust#21232, #54986: during period where we reject
         // partial initialization, do not complain about mutability
         // errors except for actual mutation (as opposed to an attempt
         // to do a partial initialization).
         let previously_initialized =
             self.is_local_ever_initialized(place.local, flow_state).is_some();

         // at this point, we have set up the error reporting state.
         if previously_initialized {
             self.report_mutability_error(place, span, the_place_err, error_access, location);
             true
         } else {
             false
         }
     }

     fn is_local_ever_initialized(
         &self,
         local: Local,
         flow_state: &Flows<'cx, 'tcx>,
     ) -> Option<InitIndex> {
         let mpi = self.move_data.rev_lookup.find_local(local);
         let ii = &self.move_data.init_path_map[mpi];
         for &index in ii {
             if flow_state.ever_inits.contains(index) {
                 return Some(index);
             }
         }
         None
     }

     /// Adds the place into the used mutable variables set
     fn add_used_mut(&mut self, root_place: RootPlace<'tcx>, flow_state: &Flows<'cx, 'tcx>) {
         match root_place {
             RootPlace { place_local: local, place_projection: [], is_local_mutation_allowed } => {
                 // If the local may have been initialized, and it is now currently being
                 // mutated, then it is justified to be annotated with the `mut`
                 // keyword, since the mutation may be a possible reassignment.
                 if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
                     && self.is_local_ever_initialized(local, flow_state).is_some()
                 {
                     self.used_mut.insert(local);
                 }
             }
             RootPlace {
                 place_local: _,
                 place_projection: _,
                 is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
             } => {}
             RootPlace {
                 place_local,
                 place_projection: place_projection @ [.., _],
                 is_local_mutation_allowed: _,
             } => {
                 if let Some(field) = self.is_upvar_field_projection(PlaceRef {
                     local: place_local,
                     projection: place_projection,
                 }) {
                     self.used_mut_upvars.push(field);
                 }
             }
         }
     }

     /// Whether this value can be written or borrowed mutably.
     /// Returns the root place if the place passed in is a projection.
     fn is_mutable(
         &self,
         place: PlaceRef<'tcx>,
         is_local_mutation_allowed: LocalMutationIsAllowed,
     ) -> Result<RootPlace<'tcx>, PlaceRef<'tcx>> {
         debug!("is_mutable: place={:?}, is_local...={:?}", place, is_local_mutation_allowed);
         match place.last_projection() {
             None => {
                 let local = &self.body.local_decls[place.local];
                 match local.mutability {
                     Mutability::Not => match is_local_mutation_allowed {
                         LocalMutationIsAllowed::Yes => Ok(RootPlace {
                             place_local: place.local,
                             place_projection: place.projection,
                             is_local_mutation_allowed: LocalMutationIsAllowed::Yes,
                         }),
                         LocalMutationIsAllowed::ExceptUpvars => Ok(RootPlace {
                             place_local: place.local,
                             place_projection: place.projection,
                             is_local_mutation_allowed: LocalMutationIsAllowed::ExceptUpvars,
                         }),
                         LocalMutationIsAllowed::No => Err(place),
                     },
                     Mutability::Mut => Ok(RootPlace {
                         place_local: place.local,
                         place_projection: place.projection,
                         is_local_mutation_allowed,
                     }),
                 }
             }
             Some((place_base, elem)) => {
                 match elem {
                     ProjectionElem::Deref => {
                         let base_ty = place_base.ty(self.body(), self.infcx.tcx).ty;

                         // Check the kind of deref to decide
                         match base_ty.kind() {
                             ty::Ref(_, _, mutbl) => {
                                 match mutbl {
                                     // Shared borrowed data is never mutable
                                     hir::Mutability::Not => Err(place),
                                     // Mutably borrowed data is mutable, but only if we have a
                                     // unique path to the `&mut`
                                     hir::Mutability::Mut => {
                                         let mode = match self.is_upvar_field_projection(place) {
                                             Some(field) if self.upvars[field.index()].by_ref => {
                                                 is_local_mutation_allowed
                                             }
                                             _ => LocalMutationIsAllowed::Yes,
                                         };

                                         self.is_mutable(place_base, mode)
                                     }
                                 }
                             }
                             ty::RawPtr(tnm) => {
                                 match tnm.mutbl {
                                     // `*const` raw pointers are not mutable
                                     hir::Mutability::Not => Err(place),
                                     // `*mut` raw pointers are always mutable, regardless of
                                     // context. The users have to check by themselves.
                                     hir::Mutability::Mut => Ok(RootPlace {
                                         place_local: place.local,
                                         place_projection: place.projection,
                                         is_local_mutation_allowed,
                                     }),
                                 }
                             }
                             // `Box<T>` owns its content, so mutable if its location is mutable
                             _ if base_ty.is_box() => {
                                 self.is_mutable(place_base, is_local_mutation_allowed)
                             }
                             // Deref should only be for reference, pointers or boxes
                             _ => bug!("Deref of unexpected type: {:?}", base_ty),
                         }
                     }
                     // All other projections are owned by their base path, so mutable if
                     // base path is mutable
                     ProjectionElem::Field(..)
                     | ProjectionElem::Index(..)
                     | ProjectionElem::ConstantIndex { .. }
                     | ProjectionElem::Subslice { .. }
                     | ProjectionElem::OpaqueCast { .. }
                     | ProjectionElem::Downcast(..) => {
                         let upvar_field_projection = self.is_upvar_field_projection(place);
                         if let Some(field) = upvar_field_projection {
                             let upvar = &self.upvars[field.index()];
                             debug!(
                                 "is_mutable: upvar.mutability={:?} local_mutation_is_allowed={:?} \
                                  place={:?}, place_base={:?}",
                                 upvar, is_local_mutation_allowed, place, place_base
                             );
                             match (upvar.place.mutability, is_local_mutation_allowed) {
                                 (
                                     Mutability::Not,
                                     LocalMutationIsAllowed::No
                                     | LocalMutationIsAllowed::ExceptUpvars,
                                 ) => Err(place),
                                 (Mutability::Not, LocalMutationIsAllowed::Yes)
                                 | (Mutability::Mut, _) => {
                                     // Subtle: this is an upvar
                                     // reference, so it looks like
                                     // `self.foo` -- we want to double
                                     // check that the location `*self`
                                     // is mutable (i.e., this is not a
                                     // `Fn` closure).  But if that
                                     // check succeeds, we want to
                                     // *blame* the mutability on
                                     // `place` (that is,
                                     // `self.foo`). This is used to
                                     // propagate the info about
                                     // whether mutability declarations
                                     // are used outwards, so that we register
                                     // the outer variable as mutable. Otherwise a
                                     // test like this fails to record the `mut`
                                     // as needed:
                                     //
                                     // ```
                                     // fn foo<F: FnOnce()>(_f: F) { }
                                     // fn main() {
                                     //     let var = Vec::new();
                                     //     foo(move || {
                                     //         var.push(1);
                                     //     });
                                     // }
                                     // ```
                                     let _ =
                                         self.is_mutable(place_base, is_local_mutation_allowed)?;
                                     Ok(RootPlace {
                                         place_local: place.local,
                                         place_projection: place.projection,
                                         is_local_mutation_allowed,
                                     })
                                 }
                             }
                         } else {
                             self.is_mutable(place_base, is_local_mutation_allowed)
                         }
                     }
                 }
             }
         }
     }

     /// If `place` is a field projection, and the field is being projected from a closure type,
     /// then returns the index of the field being projected. Note that this closure will always
     /// be `self` in the current MIR, because that is the only time we directly access the fields
     /// of a closure type.
     fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
         path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
     }
 }

 mod error {
     use rustc_errors::ErrorGuaranteed;

     use super::*;

     pub struct BorrowckErrors<'tcx> {
         /// This field keeps track of move errors that are to be reported for given move indices.
         ///
         /// 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.
         buffered_move_errors:
             BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>)>,
         /// Diagnostics to be reported buffer.
         buffered: Vec<Diagnostic>,
         /// Set to Some if we emit an error during borrowck
         tainted_by_errors: Option<ErrorGuaranteed>,
     }

     impl BorrowckErrors<'_> {
         pub fn new() -> Self {
             BorrowckErrors {
                 buffered_move_errors: BTreeMap::new(),
                 buffered: Default::default(),
                 tainted_by_errors: None,
             }
         }

         // FIXME(eddyb) this is a suboptimal API because `tainted_by_errors` is
         // set before any emission actually happens (weakening the guarantee).
         pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
             self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
             t.buffer(&mut self.buffered);
         }

         pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
             t.buffer(&mut self.buffered);
         }

         pub fn set_tainted_by_errors(&mut self) {
             self.tainted_by_errors = Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
         }
     }

     impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         pub fn buffer_error(&mut self, t: DiagnosticBuilder<'_, ErrorGuaranteed>) {
             self.errors.buffer_error(t);
         }

         pub fn buffer_non_error_diag(&mut self, t: DiagnosticBuilder<'_, ()>) {
             self.errors.buffer_non_error_diag(t);
         }

         pub fn buffer_move_error(
             &mut self,
             move_out_indices: Vec<MoveOutIndex>,
             place_and_err: (PlaceRef<'tcx>, DiagnosticBuilder<'tcx, ErrorGuaranteed>),
         ) -> bool {
             if let Some((_, diag)) =
                 self.errors.buffered_move_errors.insert(move_out_indices, place_and_err)
             {
                 // Cancel the old diagnostic so we don't ICE
                 diag.cancel();
                 false
             } else {
                 true
             }
         }

         pub fn emit_errors(&mut self) -> Option<ErrorGuaranteed> {
             // Buffer any move errors that we collected and de-duplicated.
             for (_, (_, diag)) in std::mem::take(&mut self.errors.buffered_move_errors) {
                 // We have already set tainted for this error, so just buffer it.
                 diag.buffer(&mut self.errors.buffered);
             }

             if !self.errors.buffered.is_empty() {
                 self.errors.buffered.sort_by_key(|diag| diag.sort_span);

                 for mut diag in self.errors.buffered.drain(..) {
                     self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
                 }
             }

             self.errors.tainted_by_errors
         }

         pub fn has_buffered_errors(&self) -> bool {
             self.errors.buffered.is_empty()
         }

         pub fn has_move_error(
             &self,
             move_out_indices: &[MoveOutIndex],
         ) -> Option<&(PlaceRef<'tcx>, DiagnosticBuilder<'cx, ErrorGuaranteed>)> {
             self.errors.buffered_move_errors.get(move_out_indices)
         }
     }
 }

 /// 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,
 }