Add test

Author: Jarcho

tests/ui/only_used_in_recursion.rs

@@ -169,4 +169,15 @@ impl E<()> for () {
     }
 }
 
+fn overwritten_param(flag: u32, mut a: usize) -> usize {
+    if flag == 0 {
+        return 0;
+    } else if flag > 5 {
+        a += flag as usize;
+    } else {
+        a = 5;
+    }
+    overwritten_param(flag, a)
+}
+
 fn main() {}

tests/ui/only_used_in_recursion.stderr

@@ -227,5 +227,17 @@ note: parameter used here
 LL |         _with_closure(Some(x), b, f)
    |                                ^
 
-error: aborting due to 19 previous errors
+error: parameter is only used in recursion
+  --> $DIR/only_used_in_recursion.rs:172:37
+   |
+LL | fn overwritten_param(flag: u32, mut a: usize) -> usize {
+   |                                     ^ help: if this is intentional, prefix it with an underscore: `_a`
+   |
+note: parameter used here
+  --> $DIR/only_used_in_recursion.rs:180:29
+   |
+LL |     overwritten_param(flag, a)
+   |                             ^
+
+error: aborting due to 20 previous errors