Move `master` branch to `main`

[jennybc]

Cc @schloerke

The master branch of this repository will soon be renamed to main, as part of a coordinated change across several GitHub organizations (including, but not limited to: tidyverse, r-lib, tidymodels, and sol-eng). We anticipate this will happen by the end of September 2021.

That will be preceded by a release of the usethis package, which will gain some functionality around detecting and adapting to a renamed default branch. There will also be a blog post at the time of this master --> main change.

The purpose of this issue is to:

• Help us firm up the list of targetted repositories
• Make sure all maintainers are aware of what's coming
• Give us an issue to close when the job is done
• Give us a place to put advice for collaborators re: how to adapt

message id: entire_lizard

[jennybc]

GitHub's support for default branch renaming means that, in general, pull requests that target the default branch will be correctly re-targetted.

However, there are some edge cases, where this is not true. Some pull requests are automatically closed when the default branch is renamed and they cannot be re-opened. This happens when the PR-making branch, fork, or user no longer exists. (Literally, it appears to boil down to whether HEAD of the PR branch is available for whatever behind-the-scenes magic is happening.)

There are 2 open pull requests in this repo that are at risk of auto-closing:

325 and #217

A way to "rescue" the work on such a PR is described in https://github.com/isaacs/github/issues/168#issuecomment-374201226. Here's the TL;DR:

If there is a PR displaying unknown repository after the fork was deleted, and you want to resurrect that PR, simply type:

git fetch origin refs/pull/123/head:foo

substituting (if necessary) origin for the remote pointing at the target repo, 123 for the PR number, and foo for the name of the local branch you want created to point to the head of the PR.

Then you can simply git checkout foo ... and resubmit a new one ....

message id: hardhearted_newt

[jennybc]

We're ready to rename master to main here (and elsewhere)!

This blog post announces the larger effort and explains how contributors can update their local environments:

Renaming the default branch

Here's the TL;DR:

1. Update usethis (you want usethis v2.1.2 or higher):

   install.packages("usethis")

2. Someone with admin permissions on this repo needs to do the renaming, as I do not have the power:

   usethis::git_default_branch_rename()

   If you wish, you can read the documentation for git_default_branch_rename(). Or do the equivalent from the command line and in the browser (see the blog post).

3. All remaining contributors can adjust to the renamed default branch with:

   usethis::git_default_branch_rediscover()

   If you wish, you can read the documentation for git_default_branch_rediscover(). Or do the command line equivalent (see the blog post).

message id: amused_halibut