I feel like I'm having a conversation with myself.

After thinking some more, the [previous version](https://github.com/mozilla/rust/pull/10735#discussion_r8010441) (with the two asserts) isn't so bad, because that's also checking to make sure that `if true { expr }` behaves like `{ expr }` rather than behaving like `expr`, which seems to me to be the correct interpretation. FWIW, that version (again, the one with the two asserts) passes with this patch applied.