batches: support renaming a batch change

[courier-new]

It's common for a batch change to evolve over time. With that, its title should be as flexible. Users don't realize they're committing to a more-or-less permanent title when they first start their batch change, and it's painful to have to create a new one and copy all your work over just to rename it, which is the only way to achieve this today.

Feedback from Olaf Geirsson when running server-side for the first time:

Small feature request: it would be nice if I could rename a batch change. I first used the name "Openrewrite" but on a second thought I wish I had used the name "openrewrite-maven" or something like that

There's a couple complications to doing this.

The first is that we currently match batch specs to batch changes based on their name. We'd need to make sure when updating the batch change name in the database, we also update the name in all batch specs that are associated with it.

The second is that we'd be breaking the link back to the parent batch change that appears in pull request descriptions:

There's a couple ways we could get around this:

• Dynamically create a redirect for the URL with the original batch change name when renaming it
  • This gets kinda messy though because we'd need to prevent anyone else from reusing that old name for new batch changes, too, or else it'd conflict with the redirect URL
• Prompt the user to re-run the batch spec to update their changesets after they change the name
  • This might feel way overcomplicated/heavy to the end user, but it should be pretty quick to run the spec again because most if not all of the workspace execution results would still be cached.
  • There'd technically be a brief window of time between changing the name + pushing the updated changeset descriptions where the links would be broken
• Create a random ID for batch changes like we already do for changesets and batch specs and support looking up the batch change at URLs like: sourcegraph.com/<namespace>/batch-changes/<random ID>, then use that URL for the batch changes link that is added to changeset descriptions
  • This feels like the cheapest solution and the best UX, but existing changeset descriptions wouldn't be updated automatically, so we'd still need to communicate that you need to re-run the spec if renaming a batch change that was created on an earlier version of SG

[github-actions[bot]]

Hey, @sourcegraph/batchers (@eseliger @courier-new @adeola-ak @BolajiOlajide @Piszmog @malomarrec @chrispine @danielmarquespt) - we have been mentioned. Let's take a look.

[courier-new]

As with all of the server-side UX enhancement issues, I think these are best saved for another day soon when we can prioritize a whole slew of UX improvements. I'd vote backlog on this for now.