Rollup merge of #161442 - zakrad:regr-test-59333, r=JonathanBrouwer

Add regression test for dead code on type alias used in impl self type

Closes #59333

Author: jhpratt

tests/ui/lint/dead-code/type-alias-used-in-impl-59333.rs

@@ -0,0 +1,34 @@
+//@ check-pass
+//! Regression test for <https://github.com/rust-lang/rust/issues/59333>.
+//! A type alias used only as (part of) the self type of an impl was
+//! incorrectly flagged as dead code.
+
+#![deny(dead_code)]
+
+struct Runner;
+
+type RuntimeImpl = Runner;
+
+trait Runtime {
+    fn run(&mut self);
+}
+
+impl Runtime for &mut RuntimeImpl {
+    fn run(&mut self) {}
+}
+
+struct Walker;
+
+type WalkerImpl = Walker;
+
+trait Walk {
+    fn walk(&self) {}
+}
+
+impl Walk for WalkerImpl {}
+
+fn main() {
+    let mut runner = Runner;
+    (&mut runner).run();
+    Walker.walk();
+}