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temporary value dropped while borrowed #132578
Description
Code
I tried this code:
pub const fn concat(_x: &[u8], _y: &[u8]) -> [u8; 1024] {
[0u8; 1024]
}
const _: &[u8] = &concat(
if b"".len() > 0 {
&concat(b"", b"")
} else {
b""
},
b""
);I expected to see this happen: compiles
Instead, this happened: fails to compile with the following error:
error[E0716]: temporary value dropped while borrowed
--> <source>:7:10
|
5 | const _: &[u8] = &concat(
| ------ borrow later used by call
6 | if b"".len() > 0 {
7 | &concat(b"", b"")
| ^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
8 | } else {
| - temporary value is freed at the end of this statement
|
= note: consider using a `let` binding to create a longer lived value
Version it worked on
It most recently worked on: 1.78.0
Version with regression
rustc --version --verbose:
rustc 1.79.0 (129f3b996 2024-06-10)
@rustbot modify labels: +regression-from-stable-to-stable -regression-untriaged
Activity
vickenty commentedon Nov 3, 2024
This error can be worked around by adding the freshly stabilized
const {}block around the second call toconcat, but I think this should not be required, given it worked fine before.saethlin commentedon Nov 3, 2024
This is #121557. In particular, see this comment (that GitHub has hidden so the page load might be weird):
#121557 (comment)
You might be interested in the RFC that motivated this: https://rust-lang.github.io/rfcs/3027-infallible-promotion.html