* Split ShardedWorkerHandlingConfig
This is so that we have a type level understanding of when it is safe to
call `get_instance(..)` (as opposed to `should_handle(..)`).
* Remove special cases in ShardedWorkerHandlingConfig.
`ShardedWorkerHandlingConfig` tried to handle the various different ways
it was possible to configure federation senders and pushers. This led to
special cases that weren't hit during testing.
To fix this the handling of the different cases is moved from there and
`generic_worker` into the worker config class. This allows us to have
the logic in one place and allows the rest of the code to ignore the
different cases.
The idea is that the parse_config method of extension modules can raise either a ConfigError or a JsonValidationError,
and it will be magically turned into a legible error message. There's a few components to it:
* Separating the "path" and the "message" parts of a ConfigError, so that we can fiddle with the path bit to turn it
into an absolute path.
* Generally improving the way ConfigErrors get printed.
* Passing in the config path to load_module so that it can wrap any exceptions that get caught appropriately.
This is *not* ready for production yet. Caveats:
1. We should write some tests...
2. The stream token that we use for events can get stalled at the minimum position of all writers. This means that new events may not be processed and e.g. sent down sync streams if a writer isn't writing or is slow.
This is *not* ready for production yet. Caveats:
1. We should write some tests...
2. The stream token that we use for events can get stalled at the minimum position of all writers. This means that new events may not be processed and e.g. sent down sync streams if a writer isn't writing or is slow.
