Skip to content

Overlapping borrows can point to different lvalues. #44999

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Oct 4, 2017
Merged

Overlapping borrows can point to different lvalues. #44999

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
48 changes: 38 additions & 10 deletions src/librustc_mir/borrow_check.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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
Expand All @@ -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 =>
Expand Down Expand Up @@ -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;

Expand All @@ -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; }
}
}
Expand All @@ -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; }
}
}
Expand All @@ -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>,
Expand Down Expand Up @@ -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",
Expand Down