Edition notes about ?

[mark-i-m]

cc rust-lang/rust#51934

The new Kleene op is not stable yet, but the removal of ? as a separator is. I can split this up into two PRs if you want.

[Centril]

Please include a note that ? is unstable :)

[mark-i-m]

I wasn't sure if we wanted to wait until ? was stable before merging this or if we want to include notes in the edition guide about planned-but-currently-unstable features. If we are planning to merge this now, I can add a note about unstable-ness...

[Centril]

I would at least like to document the edition breakage soon -- if you want to you can split up the PR to include only the breakage.

[steveklabnik]

I wasn't sure if we wanted to wait until ? was stable before merging this or if we want to include notes in the edition guide about planned-but-currently-unstable features. If we are planning to merge this now, I can add a note about unstable-ness...

Is this planned on being stable before the edition ships, or after?

[mark-i-m]

Likely after.

[mark-i-m]

rust-lang/rust#48075 is going through stabilization, so this will likely be available in 1.32 or so...

[Centril]

@mark-i-m Now that we've stabilized ?, want to fix this PR up so we can merge? :)

[mark-i-m]

@Centril Done 👍

[Centril]

Thanks!