src/test/ui/issues/issue-20616-9.stderr

error: expected one of `#`, `>`, `const`, identifier, or lifetime, found `,`
  --> $DIR/issue-20616-9.rs:34:15
   |
LL | type Type_9<T,,> = Box<T>;
   |               ^ expected one of `#`, `>`, `const`, identifier, or lifetime

error: aborting due to previous error