Support for default branch names other than master

[mattmccutchen]

We are about to start seeing a lot more git repositories being created with default branch names other than master or renaming their default branch away from master. At a minimum, braid add with no branch, tag, or revision specified should use the default branch of the upstream repository (as given by its HEAD symref) rather than hard-coding master.

If, in the future, there is a standard way for the upstream repository of an existing mirror to indicate that the branch used by the mirror has been renamed (currently under discussion), Braid could offer to update its configuration. This would mainly be for cleanliness, as it sounds like the plan is that the old name would continue to work. There is probably no need for Braid to have a new mirror mode that automatically follows the upstream default branch as given by the HEAD symref; it doesn't sound like other tools are planning to take that approach.

[olfway]

Just ran into this bug:

/home/user/chadburn > braid add 'https://github.com/PremoWeb/chadburn.git' chadburn -v
Braid: Executing `git --version` in /home/user/chadburn
Braid: Executing `git rev-parse --is-inside-work-tree` in /home/user/chadburn
Braid: Executing `git rev-parse --show-prefix` in /home/user/chadburn
Braid: Executing `git status` in /home/user/chadburn
Braid: Executing `git rev-parse HEAD` in /home/user/chadburn
Braid: Executing `git add .braids.json` in /home/user/chadburn
Braid: Adding mirror of 'https://github.com/PremoWeb/chadburn.git'.
Braid: Executing `git --version` in /home/user/chadburn
Braid: Executing `git rev-parse --is-inside-work-tree` in /home/user/chadburn
Braid: Executing `git rev-parse --show-prefix` in /home/user/chadburn
Braid: Executing `git config remote.master/braid/chadburn.url` in /home/user/chadburn
Braid: Setup: Mirror 'chadburn' already has a remote. Replacing it (force)
Braid: Executing `git remote rm master/braid/chadburn` in /home/user/chadburn
Braid: Setup: Creating remote for 'chadburn'.
Braid: Executing `git remote add master/braid/chadburn /Users/unlimint/.braid/cache/https___github.com_PremoWeb_chadburn.git` in /home/user/chadburn
Braid: Executing `git config remote.master/braid/chadburn.url` in /home/user/chadburn
Braid: Executing `git fetch` in /home/user/.braid/cache/https___github.com_PremoWeb_chadburn.git
Braid: Executing `git fetch -n master/braid/chadburn` in /home/user/chadburn
Braid: Executing `git rev-parse master/braid/chadburn/master^{commit}` in /home/user/chadburn
Braid: Resetting to '2d5945f'.
Braid: Executing `git reset --hard 2d5945f4109faee2e82dcf2ec3e802b6dd15ca53` in /home/user/chadburn
Braid: Error: unknown revision: master/braid/chadburn/master^{commit}

It wasn't obvious that the problem were with remote branch name

[mattmccutchen]

I have a fix for the basic case (braid add should use the default branch of the upstream repository) mostly done and will submit a PR soon; it turned out not to be too messy.

AFAIK, the proposal for a standard way for a repository to signal that a branch has been renamed never went anywhere, and in any case, supporting that in Braid would be a low priority for me, so I'll declare it out of scope of this issue.

[mattmccutchen]

Released in Braid 1.1.8. After so much work on infrastructure for future maintainability, it's fun to deliver a small feature for a change.