Issue rust-lang#50974: Adding issue number in the test

Author: lambtowolf

src/test/ui/struct-duplicate-comma.rs

@@ -10,6 +10,8 @@
 
 // compile-flags: -Z parse-only
 
+// Issue #50974
+
 struct Foo {
     a: u8,
     b: u8

src/test/ui/struct-duplicate-comma.stderr

@@ -1,5 +1,5 @@
 error: expected identifier, found `,`
-  --> $DIR/struct-duplicate-comma.rs:20:14
+  --> $DIR/struct-duplicate-comma.rs:22:14
    |
 LL |     let bar = Foo {
    |               --- while parsing this struct