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Overlapping borrows can point to different lvalues.

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There's always a basis for the overlap, so instead of removing the
assert entirely, I instead pass in the prefix that we found and check
that it actually is a prefix of both lvalues.

Fix #44829
This commit is contained in:
Felix S. Klock II 2017-10-03 14:00:38 +02:00
parent 61bad301f1
commit aac64c4756
1 changed files with 38 additions and 10 deletions
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48
src/librustc_mir/borrow_check.rs
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@ -385,7 +385,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
// borrow of immutable ref, moves through non-`Box`-ref)
let (sd, rw) = kind;
self.each_borrow_involving_path(
context, (sd, lvalue_span.0), flow_state, |this, _index, borrow| {
context, (sd, lvalue_span.0), flow_state, |this, _index, borrow, common_prefix| {
match (rw, borrow.kind) {
(Read(_), BorrowKind::Shared) => {
Control::Continue
@ -399,6 +399,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
ReadKind::Borrow(bk) =>
this.report_conflicting_borrow(
context, lvalue_span,
common_prefix,
(lvalue_span.0, bk), (&borrow.lvalue, borrow.kind)),
}
Control::Break
@ -408,6 +409,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
WriteKind::MutableBorrow(bk) =>
this.report_conflicting_borrow(
context, lvalue_span,
common_prefix,
(lvalue_span.0, bk), (&borrow.lvalue, borrow.kind)),
WriteKind::StorageDead |
WriteKind::Mutate =>
@ -704,7 +706,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
access_lvalue: (ShallowOrDeep, &Lvalue<'gcx>),
flow_state: &InProgress<'b, 'gcx>,
mut op: F)
where F: FnMut(&mut Self, BorrowIndex, &BorrowData<'gcx>) -> Control
where F: FnMut(&mut Self, BorrowIndex, &BorrowData<'gcx>, &Lvalue) -> Control
{
let (access, lvalue) = access_lvalue;
@ -726,9 +728,8 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
// to #38899. Will probably need back-compat mode flag.
for accessed_prefix in self.prefixes(lvalue, PrefixSet::All) {
if *accessed_prefix == borrowed.lvalue {
// FIXME: pass in prefix here too? And/or enum
// describing case we are in?
let ctrl = op(self, i, borrowed);
// FIXME: pass in enum describing case we are in?
let ctrl = op(self, i, borrowed, accessed_prefix);
if ctrl == Control::Break { return; }
}
}
@ -753,9 +754,8 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
for borrowed_prefix in self.prefixes(&borrowed.lvalue, prefix_kind) {
if borrowed_prefix == lvalue {
// FIXME: pass in prefix here too? And/or enum
// describing case we are in?
let ctrl = op(self, i, borrowed);
// FIXME: pass in enum describing case we are in?
let ctrl = op(self, i, borrowed, borrowed_prefix);
if ctrl == Control::Break { return; }
}
}
@ -780,6 +780,30 @@ mod prefixes {
use rustc::ty::{self, TyCtxt};
use rustc::mir::{Lvalue, Mir, ProjectionElem};
pub trait IsPrefixOf<'tcx> {
fn is_prefix_of(&self, other: &Lvalue<'tcx>) -> bool;
}
impl<'tcx> IsPrefixOf<'tcx> for Lvalue<'tcx> {
fn is_prefix_of(&self, other: &Lvalue<'tcx>) -> bool {
let mut cursor = other;
loop {
if self == cursor {
return true;
}
match *cursor {
Lvalue::Local(_) |
Lvalue::Static(_) => return false,
Lvalue::Projection(ref proj) => {
cursor = &proj.base;
}
}
}
}
}
pub(super) struct Prefixes<'c, 'tcx: 'c> {
mir: &'c Mir<'tcx>,
tcx: TyCtxt<'c, 'tcx, 'tcx>,
@ -946,12 +970,16 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
fn report_conflicting_borrow(&mut self,
_context: Context,
(lvalue, span): (&Lvalue, Span),
common_prefix: &Lvalue,
loan1: (&Lvalue, BorrowKind),
loan2: (&Lvalue, BorrowKind)) {
use self::prefixes::IsPrefixOf;
let (loan1_lvalue, loan1_kind) = loan1;
let (loan2_lvalue, loan2_kind) = loan2;
// FIXME: obviously falsifiable. Generalize for non-eq lvalues later.
assert_eq!(loan1_lvalue, loan2_lvalue);
assert!(common_prefix.is_prefix_of(loan1_lvalue));
assert!(common_prefix.is_prefix_of(loan2_lvalue));
// FIXME: supply non-"" `opt_via` when appropriate
let mut err = match (loan1_kind, "immutable", "mutable",