Unit test from #57866.

src/test/ui/issues/issue-57866.rs

@@ -0,0 +1,26 @@
+// compile-pass
+
+#![feature(type_alias_enum_variants)]
+
+enum Outer<T> {
+    A(T)
+}
+
+enum Inner {
+    A(i32)
+}
+
+type OuterAlias = Outer<Inner>;
+
+fn ice(x: OuterAlias) {
+    // Fine
+    match x {
+        OuterAlias::A(Inner::A(_)) => (),
+    }
+    // Not fine
+    match x {
+        OuterAlias::A(Inner::A(y)) => (),
+    }
+}
+
+fn main() {}