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Diffstat (limited to 'src/test/ui/nll/issue-54556-niconii.rs')
-rw-r--r-- | src/test/ui/nll/issue-54556-niconii.rs | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/src/test/ui/nll/issue-54556-niconii.rs b/src/test/ui/nll/issue-54556-niconii.rs new file mode 100644 index 000000000..cae389e8c --- /dev/null +++ b/src/test/ui/nll/issue-54556-niconii.rs @@ -0,0 +1,31 @@ +// 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. +} |