From 6bb0f18de2961595cd50990d2624dd18f2f32564 Mon Sep 17 00:00:00 2001
From: mu001999 <mu001999@outlook.com>
Date: Sat, 20 Jul 2024 23:12:03 +0800
Subject: [PATCH] mark the self ty live when check impl item

---
 compiler/rustc_passes/src/dead.rs             |  6 ++++++
 .../alias-type-used-as-generic-arg-in-impl.rs | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 tests/ui/lint/dead-code/alias-type-used-as-generic-arg-in-impl.rs

diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index 55514883cb1f8..5915bb6b8e991 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -525,6 +525,12 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                         _ => {}
                     }
                 }
+
+                // the self_ty may contain alias type, mark it live
+                if let hir::ItemKind::Impl(imp) = self.tcx.hir().expect_item(item).kind {
+                    intravisit::walk_ty(self, imp.self_ty);
+                }
+
                 intravisit::walk_impl_item(self, impl_item);
             }
             Node::ForeignItem(foreign_item) => {
diff --git a/tests/ui/lint/dead-code/alias-type-used-as-generic-arg-in-impl.rs b/tests/ui/lint/dead-code/alias-type-used-as-generic-arg-in-impl.rs
new file mode 100644
index 0000000000000..4857ef6a9b8bf
--- /dev/null
+++ b/tests/ui/lint/dead-code/alias-type-used-as-generic-arg-in-impl.rs
@@ -0,0 +1,19 @@
+//@ check-pass
+
+#![deny(dead_code)]
+
+struct T<X>(X);
+
+type A<X> = T<X>;
+
+trait Tr {
+    fn foo();
+}
+
+impl<X> Tr for T<A<X>> {
+    fn foo() {}
+}
+
+fn main() {
+   T::<T<()>>::foo();
+}