Add a dead code test for using anon const in pattern

src/test/ui/lint/dead-code/anon-const-in-pat.rs

@@ -0,0 +1,45 @@
+// check-pass
+#![feature(inline_const)]
+#![allow(incomplete_features)]
+#![deny(dead_code)]
+
+const fn one() -> i32 {
+    1
+}
+
+const fn two() -> i32 {
+    2
+}
+
+const fn three() -> i32 {
+    3
+}
+
+fn inline_const() {
+    // rust-lang/rust#78171: dead_code lint triggers even though function is used in const pattern
+    match 1 {
+        const { one() } => {}
+        _ => {}
+    }
+}
+
+fn inline_const_range() {
+    match 1 {
+        1 ..= const { two() } => {}
+        _ => {}
+    }
+}
+
+struct S<const C: i32>;
+
+fn const_generic_arg() {
+    match S::<3> {
+        S::<{three()}> => {}
+    }
+}
+
+fn main() {
+    inline_const();
+    inline_const_range();
+    const_generic_arg();
+}