Kill borrows from a projection after assignment.
This commit extends previous work to kill borrows from a local after assignment into that local to kill borrows from a projection after assignment into a prefix of that place.
This commit is contained in:
David Wood
parent
1149c58bb8
commit
db635fc566
8 changed files with 132 additions and 88 deletions
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@ -63,7 +63,7 @@ mod move_errors;
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mod mutability_errors;
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mod path_utils;
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crate mod place_ext;
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mod places_conflict;
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crate mod places_conflict;
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mod prefixes;
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mod used_muts;
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@ -1370,7 +1370,8 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
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place,
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borrow.kind,
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root_place,
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sd
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sd,
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places_conflict::PlaceConflictBias::Overlap,
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) {
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debug!("check_for_invalidation_at_exit({:?}): INVALID", place);
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// FIXME: should be talking about the region lifetime instead
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@ -68,6 +68,7 @@ pub(super) fn each_borrow_involving_path<'a, 'tcx, 'gcx: 'tcx, F, I, S> (
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borrowed.kind,
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place,
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access,
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places_conflict::PlaceConflictBias::Overlap,
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) {
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debug!(
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"each_borrow_involving_path: {:?} @ {:?} vs. {:?}/{:?}",
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@ -17,6 +17,43 @@ use rustc::mir::{Projection, ProjectionElem};
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use rustc::ty::{self, TyCtxt};
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use std::cmp::max;
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/// When checking if a place conflicts with another place, this enum is used to influence decisions
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/// where a place might be equal or disjoint with another place, such as if `a[i] == a[j]`.
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/// `PlaceConflictBias::Overlap` would bias toward assuming that `i` might equal `j` and that these
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/// places overlap. `PlaceConflictBias::NoOverlap` assumes that for the purposes of the predicate
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/// being run in the calling context, the conservative choice is to assume the compared indices
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/// are disjoint (and therefore, do not overlap).
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#[derive(Copy, Clone, Debug, Eq, PartialEq)]
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crate enum PlaceConflictBias {
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Overlap,
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NoOverlap,
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}
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/// Helper function for checking if places conflict with a mutable borrow and deep access depth.
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/// This is used to check for places conflicting outside of the borrow checking code (such as in
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/// dataflow).
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crate fn places_conflict<'gcx, 'tcx>(
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tcx: TyCtxt<'_, 'gcx, 'tcx>,
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mir: &Mir<'tcx>,
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borrow_place: &Place<'tcx>,
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access_place: &Place<'tcx>,
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bias: PlaceConflictBias,
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) -> bool {
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borrow_conflicts_with_place(
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tcx,
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mir,
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borrow_place,
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BorrowKind::Mut { allow_two_phase_borrow: true },
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access_place,
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AccessDepth::Deep,
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bias,
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)
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}
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/// Checks whether the `borrow_place` conflicts with the `access_place` given a borrow kind and
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/// access depth. The `bias` parameter is used to determine how the unknowable (comparing runtime
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/// array indices, for example) should be interpreted - this depends on what the caller wants in
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/// order to make the conservative choice and preserve soundness.
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pub(super) fn borrow_conflicts_with_place<'gcx, 'tcx>(
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tcx: TyCtxt<'_, 'gcx, 'tcx>,
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mir: &Mir<'tcx>,
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@ -24,10 +61,11 @@ pub(super) fn borrow_conflicts_with_place<'gcx, 'tcx>(
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borrow_kind: BorrowKind,
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access_place: &Place<'tcx>,
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access: AccessDepth,
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bias: PlaceConflictBias,
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) -> bool {
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debug!(
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"borrow_conflicts_with_place({:?},{:?},{:?})",
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borrow_place, access_place, access
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"borrow_conflicts_with_place({:?}, {:?}, {:?}, {:?})",
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borrow_place, access_place, access, bias,
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);
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// This Local/Local case is handled by the more general code below, but
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@ -46,7 +84,8 @@ pub(super) fn borrow_conflicts_with_place<'gcx, 'tcx>(
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borrow_components,
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borrow_kind,
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access_components,
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access
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access,
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bias,
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)
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})
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})
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@ -59,6 +98,7 @@ fn place_components_conflict<'gcx, 'tcx>(
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borrow_kind: BorrowKind,
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mut access_components: PlaceComponentsIter<'_, 'tcx>,
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access: AccessDepth,
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bias: PlaceConflictBias,
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) -> bool {
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// The borrowck rules for proving disjointness are applied from the "root" of the
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// borrow forwards, iterating over "similar" projections in lockstep until
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@ -121,7 +161,7 @@ fn place_components_conflict<'gcx, 'tcx>(
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// check whether the components being borrowed vs
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// accessed are disjoint (as in the second example,
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// but not the first).
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match place_element_conflict(tcx, mir, borrow_c, access_c) {
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match place_element_conflict(tcx, mir, borrow_c, access_c, bias) {
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Overlap::Arbitrary => {
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// We have encountered different fields of potentially
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// the same union - the borrow now partially overlaps.
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@ -193,7 +233,7 @@ fn place_components_conflict<'gcx, 'tcx>(
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bug!("Tracking borrow behind shared reference.");
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}
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(ProjectionElem::Deref, ty::Ref(_, _, hir::MutMutable), AccessDepth::Drop) => {
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// Values behind a mutatble reference are not access either by Dropping a
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// Values behind a mutable reference are not access either by dropping a
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// value, or by StorageDead
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debug!("borrow_conflicts_with_place: drop access behind ptr");
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return false;
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@ -331,6 +371,7 @@ fn place_element_conflict<'a, 'gcx: 'tcx, 'tcx>(
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mir: &Mir<'tcx>,
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elem1: &Place<'tcx>,
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elem2: &Place<'tcx>,
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bias: PlaceConflictBias,
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) -> Overlap {
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match (elem1, elem2) {
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(Place::Local(l1), Place::Local(l2)) => {
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@ -448,11 +489,21 @@ fn place_element_conflict<'a, 'gcx: 'tcx, 'tcx>(
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| (ProjectionElem::ConstantIndex { .. }, ProjectionElem::Index(..))
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| (ProjectionElem::Subslice { .. }, ProjectionElem::Index(..)) => {
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// Array indexes (`a[0]` vs. `a[i]`). These can either be disjoint
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// (if the indexes differ) or equal (if they are the same), so this
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// is the recursive case that gives "equal *or* disjoint" its meaning.
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// (if the indexes differ) or equal (if they are the same).
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match bias {
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PlaceConflictBias::Overlap => {
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// If we are biased towards overlapping, then this is the recursive
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// case that gives "equal *or* disjoint" its meaning.
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debug!("place_element_conflict: DISJOINT-OR-EQ-ARRAY-INDEX");
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Overlap::EqualOrDisjoint
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}
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PlaceConflictBias::NoOverlap => {
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// If we are biased towards no overlapping, then this is disjoint.
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debug!("place_element_conflict: DISJOINT-ARRAY-INDEX");
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Overlap::Disjoint
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}
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}
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}
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(ProjectionElem::ConstantIndex { offset: o1, min_length: _, from_end: false },
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ProjectionElem::ConstantIndex { offset: o2, min_length: _, from_end: false })
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| (ProjectionElem::ConstantIndex { offset: o1, min_length: _, from_end: true },
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@ -11,7 +11,6 @@
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use borrow_check::borrow_set::{BorrowSet, BorrowData};
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use borrow_check::place_ext::PlaceExt;
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use rustc;
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use rustc::mir::{self, Location, Place, Mir};
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use rustc::ty::TyCtxt;
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use rustc::ty::RegionVid;
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@ -24,6 +23,7 @@ use dataflow::{BitDenotation, BlockSets, InitialFlow};
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pub use dataflow::indexes::BorrowIndex;
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use borrow_check::nll::region_infer::RegionInferenceContext;
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use borrow_check::nll::ToRegionVid;
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use borrow_check::places_conflict;
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use std::rc::Rc;
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@ -191,12 +191,54 @@ impl<'a, 'gcx, 'tcx> Borrows<'a, 'gcx, 'tcx> {
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}
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}
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fn kill_borrows_on_local(&self,
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/// Kill any borrows that conflict with `place`.
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fn kill_borrows_on_place(
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&self,
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sets: &mut BlockSets<BorrowIndex>,
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local: &rustc::mir::Local)
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{
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if let Some(borrow_indexes) = self.borrow_set.local_map.get(local) {
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location: Location,
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place: &Place<'tcx>
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) {
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debug!("kill_borrows_on_place: location={:?} place={:?}", location, place);
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// Handle the `Place::Local(..)` case first and exit early.
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if let Place::Local(local) = place {
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if let Some(borrow_indexes) = self.borrow_set.local_map.get(&local) {
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debug!(
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"kill_borrows_on_place: local={:?} borrow_indexes={:?}",
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local, borrow_indexes,
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);
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sets.kill_all(borrow_indexes);
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return;
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}
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}
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// Otherwise, look at all borrows that are live and if they conflict with the assignment
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// into our place then we can kill them.
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let mut borrows = sets.on_entry.clone();
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let _ = borrows.union(sets.gen_set);
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for borrow_index in borrows.iter() {
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let borrow_data = &self.borrows()[borrow_index];
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debug!(
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"kill_borrows_on_place: borrow_index={:?} borrow_data={:?}",
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borrow_index, borrow_data,
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);
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// By passing `PlaceConflictBias::NoOverlap`, we conservatively assume that any given
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// pair of array indices are unequal, so that when `places_conflict` returns true, we
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// will be assured that two places being compared definitely denotes the same sets of
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// locations.
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if places_conflict::places_conflict(
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self.tcx,
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self.mir,
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place,
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&borrow_data.borrowed_place,
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places_conflict::PlaceConflictBias::NoOverlap,
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) {
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debug!(
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"kill_borrows_on_place: (kill) place={:?} borrow_index={:?} borrow_data={:?}",
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place, borrow_index, borrow_data,
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);
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sets.kill(borrow_index);
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}
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}
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}
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}
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@ -222,7 +264,7 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
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}
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fn statement_effect(&self, sets: &mut BlockSets<BorrowIndex>, location: Location) {
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debug!("Borrows::statement_effect sets: {:?} location: {:?}", sets, location);
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debug!("Borrows::statement_effect: sets={:?} location={:?}", sets, location);
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let block = &self.mir.basic_blocks().get(location.block).unwrap_or_else(|| {
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panic!("could not find block at location {:?}", location);
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@ -231,21 +273,17 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
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panic!("could not find statement at location {:?}");
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});
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debug!("Borrows::statement_effect: stmt={:?}", stmt);
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match stmt.kind {
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mir::StatementKind::Assign(ref lhs, ref rhs) => {
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// Make sure there are no remaining borrows for variables
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// that are assigned over.
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if let Place::Local(ref local) = *lhs {
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// FIXME: Handle the case in which we're assigning over
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// a projection (`foo.bar`).
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self.kill_borrows_on_local(sets, local);
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}
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self.kill_borrows_on_place(sets, location, lhs);
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// NOTE: if/when the Assign case is revised to inspect
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// the assigned_place here, make sure to also
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// re-consider the current implementations of the
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// propagate_call_return method.
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if let mir::Rvalue::Ref(_, _, ref place) = **rhs {
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if place.ignore_borrow(
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self.tcx,
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@ -279,19 +317,13 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
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mir::StatementKind::StorageDead(local) => {
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// Make sure there are no remaining borrows for locals that
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// are gone out of scope.
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self.kill_borrows_on_local(sets, &local)
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self.kill_borrows_on_place(sets, location, &Place::Local(local));
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}
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mir::StatementKind::InlineAsm { ref outputs, ref asm, .. } => {
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for (output, kind) in outputs.iter().zip(&asm.outputs) {
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if !kind.is_indirect && !kind.is_rw {
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// Make sure there are no remaining borrows for direct
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// output variables.
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if let Place::Local(ref local) = *output {
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// FIXME: Handle the case in which we're assigning over
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// a projection (`foo.bar`).
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self.kill_borrows_on_local(sets, local);
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}
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self.kill_borrows_on_place(sets, location, output);
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}
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}
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}
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@ -342,4 +374,3 @@ impl<'a, 'gcx, 'tcx> InitialFlow for Borrows<'a, 'gcx, 'tcx> {
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false // bottom = nothing is reserved or activated yet
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}
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}
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@ -31,7 +31,6 @@ impl Foo {
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};
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let c = other;
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//~^ ERROR cannot move out of `other` because it is borrowed [E0505]
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}
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}
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@ -10,19 +10,6 @@ LL | None => (*other).new_self()
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| second mutable borrow occurs here
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| first borrow later used here
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error[E0505]: cannot move out of `other` because it is borrowed
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--> $DIR/issue-46589.rs:33:17
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LL | *other = match (*other).get_self() {
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| -------- borrow of `**other` occurs here
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...
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LL | let c = other;
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| ^^^^^
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| |
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| move out of `other` occurs here
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| borrow later used here
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error: aborting due to previous error
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error: aborting due to 2 previous errors
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Some errors occurred: E0499, E0505.
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For more information about an error, try `rustc --explain E0499`.
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For more information about this error, try `rustc --explain E0499`.
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@ -27,10 +27,8 @@ fn nll_fail() {
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//~| ERROR (Mir) [E0506]
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data.0 = 'f';
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//~^ ERROR (Ast) [E0506]
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//~| ERROR (Mir) [E0506]
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data.0 = 'g';
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//~^ ERROR (Ast) [E0506]
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//~| ERROR (Mir) [E0506]
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capitalize(c);
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}
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@ -17,7 +17,7 @@ LL | data.0 = 'f';
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| ^^^^^^^^^^^^ assignment to borrowed `data.0` occurs here
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error[E0506]: cannot assign to `data.0` because it is borrowed (Ast)
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--> $DIR/loan_ends_mid_block_pair.rs:31:5
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--> $DIR/loan_ends_mid_block_pair.rs:30:5
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LL | let c = &mut data.0;
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| ------ borrow of `data.0` occurs here
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@ -26,7 +26,7 @@ LL | data.0 = 'g';
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| ^^^^^^^^^^^^ assignment to borrowed `data.0` occurs here
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error[E0506]: cannot assign to `data.0` because it is borrowed (Ast)
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--> $DIR/loan_ends_mid_block_pair.rs:41:5
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--> $DIR/loan_ends_mid_block_pair.rs:39:5
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LL | let c = &mut data.0;
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| ------ borrow of `data.0` occurs here
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@ -34,21 +34,21 @@ LL | capitalize(c);
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LL | data.0 = 'e';
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| ^^^^^^^^^^^^ assignment to borrowed `data.0` occurs here
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error[E0506]: cannot assign to `data.0` because it is borrowed (Ast)
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--> $DIR/loan_ends_mid_block_pair.rs:41:5
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|
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LL | let c = &mut data.0;
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| ------ borrow of `data.0` occurs here
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...
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LL | data.0 = 'f';
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| ^^^^^^^^^^^^ assignment to borrowed `data.0` occurs here
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error[E0506]: cannot assign to `data.0` because it is borrowed (Ast)
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--> $DIR/loan_ends_mid_block_pair.rs:43:5
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|
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LL | let c = &mut data.0;
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| ------ borrow of `data.0` occurs here
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...
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LL | data.0 = 'f';
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| ^^^^^^^^^^^^ assignment to borrowed `data.0` occurs here
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error[E0506]: cannot assign to `data.0` because it is borrowed (Ast)
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--> $DIR/loan_ends_mid_block_pair.rs:45:5
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|
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LL | let c = &mut data.0;
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| ------ borrow of `data.0` occurs here
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...
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LL | data.0 = 'g';
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| ^^^^^^^^^^^^ assignment to borrowed `data.0` occurs here
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@ -64,30 +64,6 @@ LL | data.0 = 'e';
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LL | capitalize(c);
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| - borrow later used here
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error[E0506]: cannot assign to `data.0` because it is borrowed (Mir)
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--> $DIR/loan_ends_mid_block_pair.rs:28:5
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|
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LL | let c = &mut data.0;
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| ----------- borrow of `data.0` occurs here
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...
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LL | data.0 = 'f';
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| ^^^^^^^^^^^^ assignment to borrowed `data.0` occurs here
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...
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LL | capitalize(c);
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| - borrow later used here
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error[E0506]: cannot assign to `data.0` because it is borrowed (Mir)
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--> $DIR/loan_ends_mid_block_pair.rs:31:5
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|
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LL | let c = &mut data.0;
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| ----------- borrow of `data.0` occurs here
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...
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LL | data.0 = 'g';
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| ^^^^^^^^^^^^ assignment to borrowed `data.0` occurs here
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...
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LL | capitalize(c);
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| - borrow later used here
|
||||
|
||||
error: aborting due to 9 previous errors
|
||||
error: aborting due to 7 previous errors
|
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|
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For more information about this error, try `rustc --explain E0506`.
|
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|
|
|
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Loading…
Reference in a new issue