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Modified error for loop mut borrow conflicts

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Error message now makes clear that mutable borrow conflicts on a single
value in a loop body is caused by the borrow outlasting a single pass of
the loop.
Loop conflicts are detected by seeing when two borrow locations are the
same - which indicates the same code being run more than once.
This commit is contained in:
Isaac van Bakel 2017-07-25 01:13:18 +01:00
parent 5c126bdee6
commit c802fc7103
1 changed files with 27 additions and 13 deletions
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40
src/librustc_borrowck/borrowck/check_loans.rs
View file

@ -466,19 +466,33 @@ impl<'a, 'tcx> CheckLoanCtxt<'a, 'tcx> {
let mut err = match (new_loan.kind, old_loan.kind) {
(ty::MutBorrow, ty::MutBorrow) => {
let mut err = struct_span_err!(self.bccx, new_loan.span, E0499,
"cannot borrow `{}`{} as mutable \
more than once at a time",
nl, new_loan_msg);
err.span_label(
old_loan.span,
format!("first mutable borrow occurs here{}", old_loan_msg));
err.span_label(
new_loan.span,
format!("second mutable borrow occurs here{}", new_loan_msg));
err.span_label(
previous_end_span,
"first borrow ends here");
err
"cannot borrow `{}`{} as mutable \
more than once at a time",
nl, new_loan_msg);
if new_loan.span == old_loan.span {
// Both borrows are happening in the same place
// Meaning the borrow is occuring in a loop
err.span_label(
new_loan.span,
format!("mutable borrow starts here in previous \
iteration of loop{}", new_loan_msg));
err.span_label(
previous_end_span,
"mutable borrow ends here");
err
} else {
err.span_label(
old_loan.span,
format!("first mutable borrow occurs here{}", old_loan_msg));
err.span_label(
new_loan.span,
format!("second mutable borrow occurs here{}", new_loan_msg));
err.span_label(
previous_end_span,
"first borrow ends here");
err
}
}
(ty::UniqueImmBorrow, ty::UniqueImmBorrow) => {