Assign a random team member with r+ priviliges on r? @rust-lang/<team>

[Centril]

If someone writes:

r? @rust-lang/docs 

Then we could for example assign steveklabnik since they have r+ rights.

This mistake happens from time to time; what happens now when someone writes the above is to leave the PR without a reviewer...

cc rust-lang/rust#57357 (comment)

[Centril]

I'm not familiar with the code-base but... To do this, it should be sufficient to:

1. update the regex here: https://github.com/rust-lang-nursery/highfive/blob/414fd076a3c67cfa8b0790733c0a734cd5231cb1/highfive/newpr.py#L42
2. add a rewrite on the form @<org>/<team> in this if statement: https://github.com/rust-lang-nursery/highfive/blob/414fd076a3c67cfa8b0790733c0a734cd5231cb1/highfive/newpr.py#L416
   1. when this form is encountered, fetch the available users in that team from GH.
   2. fetch the available users with r+ rights.
   3. intersect users in i. and ii. -- if the intersection is empty, bail and don't assign anyone (possibly comment on GH with a warning).
   4. pick a user in the intersection at random.
   5. set reviewer to whatever user selected in iv.
3. update relevant tests somewhere in this file: https://github.com/rust-lang-nursery/highfive/blob/414fd076a3c67cfa8b0790733c0a734cd5231cb1/highfive/tests/test_newpr.py#L1

cc @pietroalbini to correct mistakes I might have made or clarifications if need be.

[pietroalbini]

I'm not sure if it's that useful to intersect with the list of users with r+ rights though. The list seems correct to me, cc @davidalber

[davidalber]

That should cover the case for new comments. You probably want to have this behavior for messages in new PRs, as well. You'll want to encapsulate all of the logic for converting the team alias to a user inside a function, possibly inside find_reviewer.

[SimonSapin]

Would it be enough to stick to the default directory-based assignment algorithm? #241 could be an alternative if so.

when someone writes the above is to leave the PR without a reviewer

That sounds like a bug in itself, highfive should never unassign without assigning someone else.