Synchronizing a git mirror with hg-git

Posting this since it might save someone else the time it took me to figure out.

There are several tutorials for creating a git repo from an hg one using hg-git. But none of them go much into how to keep the git repo up to date when the hg one changes (assuming work is done in the hg repo). And, just doing a push with hg-git to github fails... silently :( (But it succeeded the first time, to create the repo.) Even adding -v --debug in hopes of getting some useful information is no help.

The solution is to push to a local git repo first, then push from there to github. But even pushing to a local git repo won't just work - you will get

error: refusing to update checked out branch: refs/heads/master
error: By default, updating the current branch in a non-bare repository
error: is denied, because it will make the index and work tree inconsistent
error: with what you pushed,

To get around that, create another branch in the local git repo (git branch side), switch to it (git checkout side), then push to it using hg-git. Then switch back to master (git checkout master) and finally push that to github.

I think it might also work to make the local git repo into a bare repo, but the above worked for me so I stopped there.