mirror of
https://github.com/rust-lang/rust.git
synced 2024-11-23 07:14:28 +00:00
49 lines
1.7 KiB
Rust
49 lines
1.7 KiB
Rust
// This is a reduction of a concrete test illustrating a case that was
|
|
// annoying to Rust developer niconii (see comment thread on #21114).
|
|
//
|
|
// With resolving issue #54556, pnkfelix hopes that the new diagnostic
|
|
// output produced by NLL helps to *explain* the semantic significance
|
|
// of temp drop order, and thus why inserting a semi-colon after the
|
|
// `if let` expression in `main` works.
|
|
|
|
//@ revisions: edition2021 edition2024
|
|
//@ [edition2021] edition: 2021
|
|
//@ [edition2024] edition: 2024
|
|
//@ [edition2024] compile-flags: -Z unstable-options
|
|
//@ [edition2024] check-pass
|
|
|
|
#![cfg_attr(edition2024, feature(if_let_rescope))]
|
|
|
|
struct Mutex;
|
|
struct MutexGuard<'a>(&'a Mutex);
|
|
|
|
impl Drop for Mutex { fn drop(&mut self) { println!("Mutex::drop"); } }
|
|
impl<'a> Drop for MutexGuard<'a> { fn drop(&mut self) { println!("MutexGuard::drop"); } }
|
|
|
|
impl Mutex {
|
|
fn lock(&self) -> Result<MutexGuard, ()> { Ok(MutexGuard(self)) }
|
|
}
|
|
|
|
fn main() {
|
|
let counter = Mutex;
|
|
|
|
if let Ok(_) = counter.lock() { }
|
|
//[edition2021]~^ ERROR: does not live long enough
|
|
|
|
// Up until Edition 2021:
|
|
// With this code as written, the dynamic semantics here implies
|
|
// that `Mutex::drop` for `counter` runs *before*
|
|
// `MutexGuard::drop`, which would be unsound since `MutexGuard`
|
|
// still has a reference to `counter`.
|
|
//
|
|
// The goal of #54556 is to explain that within a compiler
|
|
// diagnostic.
|
|
|
|
// From Edition 2024:
|
|
// Now `MutexGuard::drop` runs *before* `Mutex::drop` because
|
|
// the lifetime of the `MutexGuard` is shortened to cover only
|
|
// from `if let` until the end of the consequent block.
|
|
// Therefore, Niconii's issue is properly solved thanks to the new
|
|
// temporary lifetime rule for `if let`s.
|
|
}
|