Fenix: Rename master branch to main

[ekager]

See: https://www.hanselman.com/blog/EasilyRenameYourGitDefaultBranchFromMasterToMain.aspx

While this is not something that needs to happen tomorrow, we'd like to start the discussions and see if this is possible in the near future. Glean recently has done this as well. Fenix is slightly more complicated because of our TaskCluster release setup/hooks (for Nightly etc) which Glean does not have yet. This will need more investigation and verification by rel-eng before the Fenix team can proceed with our (mostly small) tasks here.

• [ ] Investigate releng impact and complexity
• [ ] Update scripts in Fenix repo
• [ ] Update any other documentation (ie readme, release checklist etc)
• [ ] Document changes in repo and send team email about changes needed locally
• [ ] Edit current PRs against new branch
• [ ] Move master into new main branch and set new default

[ekager]

The "master" reference on git can be traced back etymologically to a master/slave reference https://mail.gnome.org/archives/desktop-devel-list/2019-May/msg00066.html

We will also be making sure we stop using "blacklist/whitelist". Words matter.

[JohanLorenzo]

The "master" reference on git can be traced back etymologically to a master/slave reference https://mail.gnome.org/archives/desktop-devel-list/2019-May/msg00066.html

TIL!

There is some work needed for Releng, but I don't think this has a high complexity. Here's what has to be done:

• The hook in charge of watching to .cron.yml has to watch another branch than master. This can be done by making this logic smarter.
  
  
  
  • Then we have to handle what we call "action tasks". These are the tasks that enable reruns and retriggers, for instance. As of now, we monitor the master branch. We need to make this piece smarter too.
  
  
• Then, we need to rename master-specific scopes to refer to main instead. That said, that shouldn't be necessary once bug 1631839 is done. I sent an email out about a month ago and sent a reminder earlier today. If I don't hear any concerns, I'll handle it by the end of this month.

Apart from that, I don't see anything else. One quick note: I only looked into Fenix, there may be some differences if we want to make the change on other mobile projects. @tomprince, do you see anything I might have missed?