Why does our try_opt macro require &&?

[nrc]

If foo wants a &str and bar: Option<String>, I would expect foo(&try_opt!(bar) to work, but we need foo(&&try_opt!(bar). Which is odd looking.

[marcusklaas]

It is odd! I noticed this as well, and I have no explanation for it.

[cassiersg]

This is caused by rust-lang/rust#26978.