Rollup merge of rust-lang#55469 - pnkfelix:issue-54477-regression-tes…

…ts, r=nikomatsakis

Regression tests for issue rust-lang#54477.

At some point someone may want to revisit PR rust-lang#53564

it would be really good to have regression tests for rust-lang#54477 before that happens. :)

src/test/run-pass/issues/issue-54477-reduced-2.rs

@@ -0,0 +1,25 @@
+// rust-lang/rust#54477: runtime bug in the VecDeque library that was
+// exposed by this test case, derived from test suite of crates.io
+// `collection` crate.
+
+use std::collections::VecDeque;
+
+fn main() {
+    let mut vecdeque_13 = VecDeque::from(vec![ ]);
+    let mut vecdeque_29 = VecDeque::from(vec![ 0 ]);
+    vecdeque_29.insert(0,  30 );
+    vecdeque_29.insert(1,  31 );
+    vecdeque_29.insert(2,  32 );
+    vecdeque_29.insert(3,  33 );
+    vecdeque_29.insert(4,  34 );
+    vecdeque_29.insert(5,  35 );
+    // println!("vecdeque_13: {:?}", vecdeque_13);
+    // println!("vecdeque_29: {:?}", vecdeque_29);
+
+    // println!("Invoking: `vecdeque_13.append(&mut vecdeque_29)`");
+    vecdeque_13.append(&mut vecdeque_29);
+
+    // println!("vecdeque_13: {:?}", vecdeque_13);
+
+    assert_eq!(vecdeque_13, VecDeque::from(vec![30, 31, 32, 33, 34, 35, 0]));
+}