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.
+}