Code
#![warn(tail_expr_drop_order)]
async fn foo() -> bool {
false
}
pub async fn bar() {
while let true = foo().await {}
}Current output
warning: relative drop order changing in Rust 2024
--> src/lib.rs:8:28
|
8 | while let true = foo().await {}
| ------^^^^^ - now the temporary value is dropped here, before the local variables in the block or statement
| | |
| | this value will be stored in a temporary; let us call it `#1`
| | up until Edition 2021 `#1` is dropped last but will be dropped earlier in Edition 2024
| `__awaitee` calls a custom destructor
| `__awaitee` will be dropped later as of Edition 2024
|
= warning: this changes meaning in Rust 2024
= note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/temporary-tail-expr-scope.html>
= note: most of the time, changing drop order is harmless; inspect the `impl Drop`s for side effects like releasing locks or sending messagesDesired output
Something else instead of “__awaitee”.
Rationale and extra context
Note that arguably the lint shouldn’t be firing at all because there are no other local variables, but that is just because the example is minimal; in the real cases, there were other local variables with significant Drops.
Rust Version
rustc 1.86.0-nightly (2f348cb7c 2025-01-27)
binary: rustc
commit-hash: 2f348cb7ce4063fa4eb40038e6ada3c5214717bd
commit-date: 2025-01-27
host: aarch64-apple-darwin
release: 1.86.0-nightly
LLVM version: 19.1.7
Anything else?
@rustbot label A-edition-2024
Code
Current output
Desired output
Something else instead of “
__awaitee”.Rationale and extra context
Note that arguably the lint shouldn’t be firing at all because there are no other local variables, but that is just because the example is minimal; in the real cases, there were other local variables with significant
Drops.Rust Version
Anything else?
@rustbot label A-edition-2024