prevent potential promotion in const_discriminant

Author: lcnr

src/test/ui/consts/const_discriminant.rs

@@ -3,6 +3,8 @@
 
 use std::mem::{discriminant, Discriminant};
 
+fn identity<T>(x: T) -> T { x }
+
 enum Test {
     A(u8),
     B,
@@ -15,8 +17,8 @@ const TEST_B: Discriminant<Test> = discriminant(&Test::B);
 
 fn main() {
     assert_eq!(TEST_A, TEST_A_OTHER);
-    assert_eq!(TEST_A, discriminant(&Test::A(17)));
-    assert_eq!(TEST_B, discriminant(&Test::B));
+    assert_eq!(TEST_A, discriminant(identity(&Test::A(17))));
+    assert_eq!(TEST_B, discriminant(identity(&Test::B)));
     assert_ne!(TEST_A, TEST_B);
-    assert_ne!(TEST_B, discriminant(&Test::C { a: 42, b: 7 }));
+    assert_ne!(TEST_B, discriminant(identity(&Test::C { a: 42, b: 7 })));
 }