Permit subteams to have subteams

[fmease]

This would allow us to create the team rustdoc-contributors (#1040).

Let me know if I should add a test anywhere.
Should we enforce a depth limit?

Outdated information

According to #1040 (comment), nothing should be negatively affected except for the website. I've built its server locally with a patched rust_team_data package (part of this repo) and a patched rust_team_data static API (that contains the new team) and the only consequence is that rustdoc-contributors doesn't show up anywhere on the website (it doesn't crash the server or anything like that). Therefore, updating the website is not a hard blocker.

I've opened rust-lang/www.rust-lang.org#1854 proposing to add proper website support for subsubteams (etc.). I plan on implementing it (or GuillaumeGomez will).

[fmease]

I'm not super familiar with the intricate details of our infra and don't know 100% which tools and services depend on the team repo. As I've said I've only tested the website (of course, you can check this for yourself in case I've overlooked something). Please let me know if I should double-check anything else.

[fmease]

Alrighty, website support for subsubteams (etc.) has been merged (rust-lang/www.rust-lang.org#1857).
All blockers should now be resolved for this PR to land, right?

I've updated the crate to handle cycles gracefully and to flag them as errors during validation.
On master, it chokes on any sort of cycle and loops indefinitely.
For example, for the complex cycle alpha ↦ beta, beta ↦ gamma, gamma ↦ alpha, we now emit

[ERROR rust_team::validate] validation error: team `alpha` is part of a cycle
[ERROR rust_team::validate] validation error: team `beta` is part of a cycle
[ERROR rust_team::validate] validation error: team `gamma` is part of a cycle

I still disallow non-teams (working groups, project groups, etc.) to be “subteams” of subteams,
mostly since the website can't support them nicely (see the linked PR as to why).

[fmease]

@rylev, do the changes in this PR look good to you?

(Website with the new changes has now been deployed, rust-lang/www.rust-lang.org#1859)

[rylev]

I've got a small concern about an error message, but otherwise I agree this is ready to merge.

[fmease]

alpha ↦ beta, beta ↦ gamma, gamma ↦ alpha now errors with:

[ERROR rust_team::validate] validation error: team `alpha` is a subteam of itself: alpha => beta => gamma => alpha
[ERROR rust_team::validate] validation error: team `beta` is a subteam of itself: beta => gamma => alpha => beta
[ERROR rust_team::validate] validation error: team `gamma` is a subteam of itself: gamma => alpha => beta => gamma

Edit: If you would like me to, I can deduplicate error messages by cycle in order to only show a single message in the case above. Not sure if it's worth it though.

[fmease]

Once this is merged, could you kick off a CI run for #1040 and also merge the latter once it's green (only if you deem the PR sufficiently approved ofc)? Thanks a lot! :)

[rylev]

Thanks a bunch for working on this!