There have been too many flaky tests as a result of leaking state in
Redis so it is easier to resolve them by ensuring we flush Redis'
database.
Locally on my machine, calling `Discourse.redis.flushdb` takes around
0.1ms which means this change will have very little impact on test
runtimes.
This method is a huge footgun in production, since it calls
the Redis KEYS command. From the Redis documentation at
https://redis.io/commands/keys/:
> Warning: consider KEYS as a command that should only be used in
production environments with extreme care. It may ruin performance when
it is executed against large databases. This command is intended for
debugging and special operations, such as changing your keyspace layout.
Don't use KEYS in your regular application code.
Since we were only using `delete_prefixed` in specs (now that we
removed the usage in production in 24ec06ff85)
we can remove this and instead rely on `use_redis_snapshotting` on the
particular tests that need this kind of clearing functionality.
This commit allows us to set the channel slug when creating new chat
channels. As well as this, it introduces a new `SlugsController` which can
generate a slug using `Slug.for` and a name string for input. We call this
after the user finishes typing the channel name (debounced) and fill in
the autogenerated slug in the background, and update the slug input
placeholder.
This autogenerated slug is used by default, but if the user writes anything
else in the input it will be used instead.
