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// 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.
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() { } //~ ERROR does not live long enough
// 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.
}
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